The Insulated Pulse Engine

IPCengine2011fig50c.jpg
Fig10 - The Insulated Pulse Engine concept of 2010 (on left) is intended to function throughout a wide range of operating environments.  The concept of 2011 (on right) is cost-reduced for use in more specialized environments.  The Insulated Pulse Engine runs cool without a cooling system, functions quietly without a muffler, combusts cleanly without a catalytic converter, and exhaust gasses are sufficiently cool that exhaust ducting can be made of plastic. [enlarge.jpg].
    
     
The Insulated Pulse Engine: A cold adiabatic engine concept
By Dave Schouweiler, updated 11May2016
    
This personal study presents a thermally efficient concept for combusting fuel in an internal combustion engine.  This is a conceptual paper, not a technical paper, as it contains intuitive approximations and primitive constructions which require refinement.  I am not an engine designer, but I have been wishing car manufacturers would someday build a vehicle which contains an engine like this so I could buy one.  Since there are no signs it will happen, the time came to share the idea on this web page in the hope of finding answers.  I appreciate the support and guidance that has come in.
     
I will keep this web page updated with my latest findings. This engine concept can be fabricated using century-old technology.  I'm learning that similar concepts were popular in the decades leading up to the jet-age, but almost no information from these experiments can be found in print or on the internet. Technical critique regarding this concept, and any information on similar experiments, is welcome.
             
IPCengine2011fig51c.jpg
Fig11 – The Insulated Pulse Engine is an evolving concept modeled as a 3.2 liter inline 4-cylinder with a bore of 100mm and a stroke of 100mm. The 2011 revision (on left) and the 2010 revision (on right) are 2-stroke engines, each producing 65 horsepower.  The 2009 revision, formerly presented on this webpage, is a 4-stroke engine which produces 50 horsepower and explores various application of twin crankshafts to minimize piston sliding friction. [enlarge.jpg].
     
     
Background
 
There is an ongoing effort to improve fuel mileage in motor vehicles. In the last half century, fuel mileage improvements from internal combustion engines have most often resulted from volumetric efficiency improvements (i.e.: increased peak horsepower per unit volume of cylinder displacement) rather than thermal efficiency improvements. Fuel mileage gains have come by way of increased strength and horsepower of engines, allowing smaller displacement engines to be installed into larger vehicles where the engines are tasked to operate within a more thermally efficient segment of their operating range. Fuel mileage improvements can become tougher to achieve as small displacement engines more routinely populate large vehicles.
  
Atkinson engines, which are found in some of today’s most fuel efficient cars, achieve improved thermal efficiency through an expansion process which reduces volumetric efficiency and which expels less heat energy to the exhaust duct than equivalently powered Otto engines. HCCI engine development programs, now popular in laboratories around the world, achieve improved thermal efficiency through a combustion process which reduces volumetric efficiency and which expels less heat energy to the exhaust duct than equivalently powered Otto and Diesel engines. Atkinson and HCCI engines suggest some thermodynamic processes with reduced volumetric efficiency and cooler exhaust gas temperature can provide a pathway toward improved engine thermal efficiency and vehicle fuel economy.  Ernest E. Chatterton's "Simplic" engine prototype (documentation posted at the bottom of this webpage) steps significantly deeper into this realm, as does my "Insulated Pulse-Combustion" engine concept.  Entirely new "split-cycle" engine prototypes are beginning to emerge from laboratories which similarly step deeper into this realm.
        
Exhaust emissions aftertreatment devices in motor vehicles often require a high exhaust gas temperature to scrub pollutants from the exhaust stream. Some engines which combine high thermal efficiency with low volumetric efficiency will have unconventionally cool exhaust temperatures, rendering many conventional emissions aftertreatment devices inoperative.  A method to prevent the formation of pollutants during the combustion process is applied in the Insulated Pulse-Combustion engine, reducing the need for exhaust emissions aftertreatment.
    
       
A Brief Introduction to the Insulated Pulse Engine
  
The "insulated pulse-combustion engine", sometimes abbreviated "insulated pulse engine" or "IPC engine", is a reciprocating piston engine concept which explores five pathways of non-productive energy export from internal combustion engines (thermal conduction, exhaust heat, exhaust pressure, exhaust pollution, and mechanical losses), with the goal of providing fuel economy that is improved over commercially available engines.  The IPC engine concept applies principle attributes of the Diesel engine (unthrottled induction and high compression ratio), of ceramic adiabatic engine prototypes of the early 1980s (thermal insulation), of current HCCI engine prototypes (isochoric heat addition), and of Ernest E. Chatterton’s “Simplic” 2-stroke engine prototype (isobaric heat rejection).
  
Several key philosophies of the Chatterton Simplic engine prototype, as published by The Institution of Mechanical Engineers in the 1975 book entitled, "Some Unusual Engines", are reprised in the IPC engine concept, including what the book's author, L.J.K. Setright, termed a "hyper-expansion" cycle, induction preceding exhaustion, uniflow gas transfer, an aversion to supercharging, the absence of a cooling system, and high fuel economy.  Documentation describing the Chatterton Simplic engine is posted at the bottom of this webpage.
      
The thermodynamic sequence of both the Chatterton Simplic engine and the IPC engine, known as the Humphrey cycle, provides opportunity for high thermal efficiency, however it also carries the penalty of comparatively low volumetric efficiency, which adds the requirement that mechanical friction be commensurately managed.
  
Compared with naturally-aspirated 4-stroke Diesel engines at full-throttle, a similarly displaced 2-stroke IPC engine at full-throttle can consume only a twelfth of the fuel each combustion event. This is based on the observation that HCCI prototype engines consume 1/4 of the full-throttle fuel that similarly displaced Diesel engines consume each combustion event, and that only 1/3 of a piston stroke in the 2-stroke IPC engine applies to the compression cycle.
      
The 2-stroke IPC engine’s compression cycle begins when the piston reaches 1/3 of a crankshaft stroke before TDC.  The combustion chamber then transitions to become fuel-stratified when the piston reaches 1/8 of a stroke before TDC, whereupon fuel is direct-injected into a central region of the chamber.  Fuel is constrained to, and becomes mixed within, the central region using tumble-turbulence generated by inducted air surging inward from a fuel-devoid perimeter region of the chamber.  Fuel stratification, in conjunction with spark ignition or other precision ignition method, permits throttling a locally-homogenous fuel-air equivalence ratio within the highly reactive range of 0.40-0.80 to assure a rapid, complete combustion reaction with practical torque band.  A fuel-air equivalence ratio below 1.00 represents the deviation of a stoichiometric ratio toward fuel-lean.
   
Combustion initiates at the center of the combustion chamber near TDC, propagates radially outward a short distance on a controlled supersonic wavefront, whereupon the reaction efficiently concludes near TDC, assuring the entire fuel budget performs work on the piston through the full expansion cycle. Expansion occurs from TDC until the piston travels 1/3 of the stroke past TDC.  Expansion then extends beyond convention (hyper-expansion) until the piston reaches 2/3 of the stroke past TDC, with the combustion chamber reaching 1 bar to extract all available combustion energy and eliminate the need for a cooling system.  The chamber volume then develops a vacuum while the inlet ports open, drawing fresh inducted air into the bottom 1/3 of the chamber.  At BDC, induction ends, exhaustion begins, and the piston begins quietly exhausting oxygen-rich combusted gasses residing in the upper 2/3 of the chamber, leaving mostly fresh inducted air within the combustion chamber when the piston reaches 1/3 of the stroke before TDC.  The cycle then repeats.
    
Conventional exhaust emissions aftertreatment devices are not effective at scrubbing pollutants from the comparatively cool, pressureless exhaust gasses that the piston pushes out of the combustion chamber.  The IPC engine prevents the formation of pollutants by constraining fuel to a tumble-turbulent, thermally-insulated, crevice-free region of the combustion chamber specifically shaped (only at TDC) to support clean combustion.  Rather than using brittle ceramic thermal insulators, as was the practice in the ceramic adiabatic engine experiments of the early 1980s, the IPC engine contains two thermally-insulating Fe60Ni40 alloy iron disks, one integrally cast into the piston, the other into the cylinder head, to prevent the formation of quench-sourced pollutants.   These thermally-insulating disks also promote rapid warm-up of the combustion chamber which minimizes cold-start forms of pollution emissions, and they help retain combustion heat in the chamber to improve performance and fuel economy.
     
Volumetric Efficiency and Fuel Efficiency
    
  
Modern Otto and Diesel engines operate at high volumetric efficiency.  To this extent they introduce fuel energy into the engine at a high rate.  They transfer this fuel energy at high rate productively to the flywheel, and at high rate to five nonproductive energy exporting pathways.
   
The IPC engine concept operates at low volumetric efficiency, such that it introduces fuel energy into the engine at a low rate.  It transfers this fuel energy at low rate productively to the flywheel, and at low rate to five nonproductive energy exporting pathways.
    
Whether it is more fuel efficient in a given application to transfer fuel energy at a high rate using a small displacement Otto or Diesel engine or at a low rate using a large displacement IPC engine is dependent on construction detail and operating conditions.  What is easy to see are the energy equations differ between these two approaches, and one will likely prove more fuel efficient than the other.  It is the goal of the IPC engine concept to determine which approach is more fuel efficient, and under which conditions.  Commercially available engine simulation software, such as AVL Fire, GT Suite, and Ricardo Wave, can provide answers, though access to this specialized software currently exceeds the budget of this study.
      
IPCengine2011fig11c.jpg
Fig12 – Cutaway image of the 2-stroke Insulated Pulse Engine concept of 2011. [enlarge.jpg], [animate.gif], [video.mpg], If the "video.mpg" link is selected, a low-res sample video is quickly presented in a new window, along with an option to download the full-resolution (uncompressed) video file of a single engine cycle.
     
   
Elements of Energy Efficiency
     
Energy efficiency in an internal combustion engine is determined by the ratio between the rate at which heat energy is kinetically transferred to the flywheel and the rate at which fuel energy is introduced into the engine, with the arithmetic difference representing fuel energy lost to five nonproductive energy-exporting pathways.  A yardstick used for measuring energy efficiency in an internal combustion engine is called "brake specific fuel consumption", abbreviated BSFC, and is often dimensioned in terms of grams of fuel consumed per kilowatt hour (g/(kW*h)) of work performed.  The lower the BSFC number, the more energy efficient the engine is.
   
Energy loss in an internal combustion engine can be managed by tending five efficiencies:
1. High "insulation efficiency" minimizes loss of combustion energy to a cooling system in the form of heat, and is driven by the thermal conductivity of the combustion chamber. If maximizing fuel efficiency is the primary goal, and if excessive heat is lost to a cooling system, the insulation efficiency must be improved. If improved insulation efficiency causes the combustion chamber material to overheat and fail, the average temperature of combustion chamber gasses through a full engine cycle must be reduced.
2. High "combustion efficiency" minimizes loss of combustion energy to the exhaust duct in the form of elevated exhaust temperature, and is driven by compression ratio, ignition timing, and combustion duration. If maximizing fuel efficiency is the primary goal, and if the temperature of combusted gasses is excessive at the end of the expansion cycle, the combustion efficiency must be improved.
3. High "expansion efficiency" minimizes loss of combustion energy to the exhaust duct in the form of elevated exhaust pressure, and is driven by the expansion ratio. If maximizing fuel efficiency is the primary goal, and if the pressure of combusted gasses is excessive at the end of the expansion cycle, the expansion efficiency must be improved.
4. High “emissions efficiency” minimizes loss of fuel energy to the exhaust duct in the forms of either insufficiently combusted fuel or excessively combusted fuel.  Insufficiently combusted fuel refers to incomplete oxygenation, excessive combustion refers to the overheating of combustion chamber gasses such that compounds of nitrogen form.  If maximizing fuel efficiency is a primary goal, combustion must be constrained to promote only the desired chemical reactions.
5. High "mechanism efficiency" minimizes loss of combustion energy to mechanical component friction, to fluid pumping losses, and to vibration within the engine.  Mechanism efficiency is a lesser consideration in Otto and Diesel engines that exhibit high cooling and exhaust system energy losses, but mechanism efficiency plays a dominant role in determining the fuel efficiency of the IPC engine. Mechanical component friction can include piston skirt sliding friction, compression ring sliding friction, friction bearing losses, fluid seal friction, and elastic spring losses.  Fluid pumping losses can include blower pumping, compressor pumping, fuel pumping, lubricant pumping, crankcase windage, induction throttling, induction blowdown, induction flow resistance, exhaustion blowdown, and exhaustion flow resistance.  Vibration losses can include external engine vibration resulting from rotating and reciprocating components within the engine, and crankshaft resonance damping.
Some forms of mechanical friction correlate more closely with generated horsepower than to cylinder displacement.  A larger-displacement engine need not always indicate greater friction than a smaller-displacement engine.  Included in this realm is piston skirt sliding friction, since sliding friction is low when average combustion chamber pressure is low.  Skirt friction can be additionally reduced through application of a high connecting rod ratio or crosshead.  Since the average combustion chamber pressure of the IPC engine is unconventionally low, piston sliding friction can be further reduced by combining low tension compression sealing rings with gas ported pistons.  Gas ported pistons tend to be impractical in production engines due to the issue of fuel clogging the ports and crevice-sourced pollution emissions, however, due to fuel stratification in the IPC engine, fuel can neither clog piston gas ports nor can it generate crevice-type pollutants.
    

Cooling System Efficiency Losses
     
Insulation efficiency is low in Otto and Diesel engines because a cooling system is incorporated to quickly remove heat energy absorbed by combustion chamber metals after each combustion event.  This removal is necessary, since chamber metals would otherwise attain the average temperature of the combustion chamber gasses, a temperature too hot for sustainable engine operation.  Heat energy conducted through thermally conductive combustion chamber metal into the cooling system represents a significant loss of fuel energy which would otherwise be available to drive the crankshaft.
   
Following the oil crisis of 1979, internal combustion engine manufacturers around the world began developing “ceramic adiabatic engine” prototypes which contained thermally insulated ceramic combustion chambers in an attempt to improve engine thermal efficiency without sacrificing volumetric efficiency. Thermally insulating the combustion chamber reduced, and sometimes eliminated, the need for a cooling system, thus retaining a larger fraction of combustion heat energy for mechanical work output.  Unfortunately, to retain volumetric efficiency while simultaneously minimizing mechanical shock loading of the brittle ceramic insulators, these adiabatic engines were designed to combust with a conventional low heat release rate. The portion of fuel combusting later in the expansion cycle expands at a lower effective compression ratio than the fuel which combusts near TDC.  The latter combusting fuel, in combination with thermal insulation, resulted in the superheating of combustion chamber gasses before expulsion into the exhaust duct.  Ceramic adiabatic engines evolved to emphasize exhaust energy recovery through turbocompounding and other post-processing methods, but only a fraction of the exhaust energy could be recovered.
  
Experimental results on three published ceramic adiabatic engine projects can be reviewed in S.A.E. Technical Papers 810070 (1981), 820431 (1982), and 840428 (1984), with abstracts viewable at the SAE.org website and where the papers may be downloaded. Ceramic adiabatic engines provided slightly improved fuel efficiency over Otto and Diesel engines, but they operated under the most brutal conditions and could not be made practical for commercial application.
   
The use of ceramic thermal insulators, or the use of any thermally insulating material, in the combustion chamber of internal combustion engines for the primary purpose of improving fuel economy in vehicles, has found minimal interest in the industry since the conclusion of these experiments
.
    

Exhaust System Efficiency Losses
    
Exhaust efficiency in the IPC engine comprises two components: Combustion efficiency and expansion efficiency.
     
Combustion efficiency is low in Otto, Diesel, and ceramic adiabatic engines because combustion is engineered to progress gradually, beginning near TDC and continuing well into the expansion cycle. This low heat release rate allows a lot of fuel to gradually burn without exceeding the pressure limits of the combustion chamber. Volumetric efficiency is high because the piston experiences high levels of combustion pressure through a significant portion of the expansion cycle. Thermal efficiency is low because the late burning fuel effectively combusts at a low compression ratio, causing large amounts of fuel energy to be expelled into the exhaust duct in the form of heat.  As a contrast, HCCI engine prototypes and the IPC engine concept combust all fuel near TDC and none during the expansion cycle, allowing combusted gasses to adiabatically cool through the entire expansion cycle.
   
Expansion efficiency is low in Otto, Diesel, and ceramic adiabatic engines because the compression process and expansion process are conveniently of equal stroke length, a length optimized only for compression, resulting in significant combustion pressure energy being released to the exhaust duct in the form of blowdown, before it can perform work on the piston. It should be noted that the compression cycle and the expansion cycle are independent functions and will seldom be of equal length in an engine optimized for high fuel economy.  As a contrast, Atkinson engines, which are found in some of today’s most fuel efficient vehicles, extend the expansion cycle slightly beyond that of the compression cycle to utilize a greater share of available combustion pressure.  Both the Chatterton Simplic engine and the IPC engine concept extend the expansion cycle significantly beyond that of the compression cycle to utilize all available combustion pressure.
   
HCCI and Atkinson engines both release less heat and pressure energy to the exhaust than do equivalently powered Otto, Diesel, and ceramic adiabatic engines.  Taken to the next level, the Chatterton Simplic engine and the IPC engine concept both release less heat energy and less pressure energy to the exhaust stream than do any of the five aforementioned engines.  Entirely new "split-cycle" engine prototypes are beginning to emerge from laboratories (Doyle, General Motors, Motiv, Scuderi, Tour) which similarly release less heat energy and less pressure energy to the exhaust stream than do Otto, Diesel, ceramic adiabatic, Atkinson, or HCCI engines.  Split-cycle engines fundamentally differ in construction from the IPC engine concept, but are similar philosophically to the IPC engine in many unconventional ways.
         
     
The Chatterton Simplic Engine, Revisited
    

The "Simplic" engine is a descendant of the Napier "Deltic" (1950) and Napier Nomad Mk II (1952) 2-stroke Diesel engines, both designed by Mr. Ernest E. Chatterton, B.Sc.(Eng.), M.I.Mech.E., F.R.Ae.S., who was Chief Engineer of the piston engine division at D. Napier & Son, Ltd.   With a BSFC of 210 g/(kW*h) and an energy efficiency of 39.8%, the Nomad Mk II is recognized as the most fuel efficient engine ever to have flown.  The Simplic engine may have been developed independently by Mr. Chatterton around 1961 when D. Napier & Son, Ltd sold its aero engine division to
Rolls-Royce.
      
L.J.K. Setright, author of the book, "Some Unusual Engines", writes that the Chatterton Simplic engine was "apparently successful, on a pilot scale".  It is not presently known why the Chatterton Simplic engine prototype did not succeed commercially.  While I consider it a challenge to employ exhaust scavenging in an engine with so little excess exhaust energy on which to draw, it does not appear scavenging was a limiting issue.  Exhaust pollution would also not likely have been a driving consideration at the time.  What may have been a more immediate issue is the Simplic was tuned to optimize fuel efficiency only at full-throttle, as it did not employ features which would extend high fuel efficiency to reduced throttle levels.
       
A more complicated cousin to the Simplic engine prototype can be reviewed in the 1962 British Patent GB988,378 of Mr. Chatterton.  This related 2-stroke engine applies the Simplic’s hyper-expansion cycle, but employs Mr. Chatterton’s “Nomad Mk II” gas train in place of the Simplic’s exhaust scavenging system.  This patent consists of the following pages: [1of6.jpg], [2of6.jpg], [3of6.jpg], [4of6.jpg], [5of6.jpg], [6of6.jpg].
    
It is apparent that Mr. Chatterton was developing his fuel efficient hyper-expansion engine prototypes to extend the flying range of aircraft.  Ongoing breakthroughs in jet engine technology at the time resolved flight range limitations, with turbine engines able to operate in the thinner air of much higher altitudes to make up for reduced fuel efficiency.  As jet engines took over, commercial and military interest in large fuel-efficient piston engines for aircraft virtually ceased, shelving further development of the Napier Nomad engine, and perhaps defunding the Chatterton Simplic project before it could find application in ground transportation.  At the time of the Simplic, turbine engines looked poised to take to the highways in cars and trucks, possibly distracting automotive design teams toward turbine engine development and away from hyper-expansion engine development.
     
Regardless of what ultimately caused the Chatterton Simplic project to be shelved, the IPC engine concept circumvents the need for exhaust scavenging by employing a different construction.  The IPC engine also focuses on low pollution emissions and provides a substantial throttle range in which the engine operates at high fuel efficiency.  The IPC engine concept effectively revisits the Chatterton Simplic experiment, while addressing anticipatable shortcomings.  I very much wish to learn more about any of the "numerous" hyper-expansion experiments which L.J.K. Setright glancingly mentions had existed.  Documentation describing the Chatterton Simplic engine is posted at the bottom of this webpage.
     
IPCengine2011fig12c.jpg
Fig13 – This is a cutaway image containing only the rotating, reciprocating, and counterbalance components of the 2-stroke IPC engine of 2011, and represents essentially all moving components within the engine, outside of ordinary fuel and oiling functions. The energy of mechanical vibration neutralized by this counterweight scheme is redirected into productive crankshaft output. [enlarge.jpg], [animate.gif], [video.mpg].
   
    
Exhaust Emissions
     
Gasoline, propane, ethanol, methanol, ammonia, or other fuels can be applicable to the IPC engine.  Exhaust emissions resulting from the combustion of fuel comprise both desirable (non-toxic) and undesirable (toxic) components.
    
Desirable components of exhaust emissions comprise carbon dioxide (CO2) and water (H2O), and result when fuel is fully combusted under ideal conditions.
     
Undesirable components of exhaust emissions traditionally associated with internal combustion engines fall into four simplified categories:
1. Unburned hydrocarbon (UHC) exhaust emissions can form when fuel is in proximity of combustion chamber crevices such as are found near the head gasket, upper piston ring, piston ring gas ports, and intake valve seat.
   
2. Soot emissions, also known as particulate matter (PM) exhaust emissions, which represent fuel that is 1/3 combusted, can form when fuel is direct injected into the dense flame kernel of a compression ignition engine which has already consumed all adjacent oxygen.
    
3. Carbon monoxide (CO) exhaust emissions, which represent fuel that is 2/3 combusted, can form when fuel is combusted near chilled surfaces within the combustion chamber, or when oxygen has been depleted due to an excessive level of exhaust gas recirculating into the inducted air stream.
    
4. Oxides of nitrogen (NOx) exhaust emissions, which represent fuel that is overcombusted, can form when heat energy becomes unproductively high in the combustion chamber and the very stable 3-bond nitrogen molecule in air breaks apart.
In the unique case of green ammonia (green NH3) fuel, the desirable components of exhaust emissions comprise nitrogen (N2) and water (H2O) under ideal conditions.  Green ammonia, which has about half the volumetric energy density of gasoline, is manufactured by combining water and air using renewable electricity.  This conceptual paper does not attempt to determine applicability of ammonia as a practical fuel, but recognizes it is a carbon-free liquid fuel with high energy density.  Use of ammonia in the IPC engine would likely require the engine be started using ethanol, switched over to ammonia when the engine reached a clean-burning operating temperature, and switched back to ethanol on shut-down to purge ammonia from the fuel injectors.
    
The cause of exhaust pollution in internal combustion engines is complex but well understood, as are exhaust processing methods which remove pollutants, and as are clean combustion methods which prevent the formation of pollutants.
            
IPCengine2011fig17c.jpg
Fig14 – Two different cutaways of cylinder 4 shown in three views at TDC. [enlarge123a.jpg], [animate3z.gif], [video1a.mpg], [video3a.mpg], [video3z.mpg].
     
   
Basic Description of the Insulated Pulse Engine
      
The IPC engine is a reciprocating piston internal combustion engine which applies unthrottled air induction, precision spark ignition, direct fuel injection, high compression ratio, and the following four unconventional functions, to achieve high thermal efficiency:
Unconventional Function #1 - Rapid "pulse" combustion (like an HCCI engine).
Unconventional Function #2 - Thermally insulated combustion chamber (like a ceramic adiabatic engine).
Unconventional Function #3 - Hyper-extended expansion cycle (like a Chatterton Simplic engine).
Unconventional Function #4 - Fuel-stratified combustion chamber.
The resulting engine can run cool without a cooling system, can function quietly without a muffler, can combust cleanly without a catalytic converter, and exhaust gasses can be sufficiently cool and pressureless that exhaust ducting can be made of plastic.
    
Unconventional Function #1 - Rapid “Pulse” Combustion
 
In the IPC engine, combustion initiates near TDC and is rapidly consumed near TDC, providing a combustion reaction with low volumetric efficiency and high thermal efficiency. The volumetric efficiency is low because a comparatively small amount of fuel will generate sufficient temperature and pressure near TDC to reach the limits which do not form NOx exhaust pollutants. Thermal efficiency is high because the entire fuel budget combusts at TDC and presses upon the piston through the entire expansion cycle, greatly reducing the percentage of heat energy available to the exhaust and lowering the average temperature of the combustion chamber. The ordinary methods used to achieve a high heat release rate are:
1. High compression ratio sufficient to promote a supersonic combustion wavefront
2. Stratified combustion chamber locally shaped to fully support efficient combustion
3. Stratified fuel-lean equivalence ratio calibrated for rapid, complete reaction
4. Fuel-air charge turbulently mixed prior to ignition
5. Combustion chamber turbulence present at time of ignition
6. Spark ignition precisely controls the combustion envelope
7. Thermally insulated combustion chamber reduces quenching of reaction
8. Additional turbulence generated during combustion assists complete reaction
While the rate of pressure rise (dP/dt) during combustion is unconventionally high (>50 bar rise per crank angle degree vs. <10 bar/CAD in an Otto or Diesel engine), the IPC engine does not generate unusually high cylinder pressure, as there is an insufficient quantity of fuel in the combustion chamber during each combustion event to generate excessive pressure. Pressure and temperature limits in the IPC engine’s combustion chamber are not driven by structural limits, but are driven by the need to prevent the formation of NOx pollutants during combustion. If temperature and pressure in the combustion chamber climb sufficiently high that the very stable 3-bond nitrogen molecule breaks apart and forms NOx pollution emissions, then injected fuel volume must be readjusted below NOx-producing levels.
      
The rapid rate of pressure rise in the combustion chamber of the IPC engine is the result of a controlled supersonic combustion wavefront which generates significantly more shockwave noise energy than the subsonic combustion wavefront in an Otto or Diesel engine.  The predictable combustion wavefront in the IPC engine will generate significantly less structural excitation noise than the unpredictable detonation reaction in HCCI engine prototypes.  Detonation reaction noise is a recognized problem in HCCI engines, but due to the predictable nature of the IPC engine’s combustion wavefront, due to the predictable centralized location of the iron-shrouded reaction, and due to the fact that only 1/3 of the fuel is present in the IPC engine’s full-throttle combustion reaction, when compared to a full-throttle HCCI reaction, combustion noise generation can be managed.
   
Should piston noise be an issue, a variation of U.S. Patent 2659351, applied either to the piston or reciprocating cylinder or both, is one method to reduce piston skirt side-load (side-thrust) friction, reducing piston side-load noise while managing side-load distortion of the reciprocating cylinder.  As an incidental benefit, if lever axis (62) in U.S. Patent 2659351 is made repositionable, the deck height of the piston can be varied, and the compression ratio made dynamically adjustable, which can make the engine assembly less susceptible to barometric variables and thermal expansion differentials.  If combustion noise is not an issue, actuating the reciprocating cylinder using a small neighboring crankshaft, variably phased with the piston crankshaft, can provide a dynamically adjustable compression ratio without varying the deck height.
     
Engine misfire may occasionally cause an anomalous stoichiometric fuel-air mixture to combust at excessive detonation pressures in the chamber. The IPC engine, like conventional engines, is constructed to occasionally handle this type of misfire condition without damage.
 

Unconventional Function #2 - Thermally Insulated Combustion Chamber
     
The IPC engine thermally insulates the combustion chamber fully when the piston is at TDC. It continues to partially insulate the combustion chamber as the piston drops away from TDC. Three reasons for insulating are: 1) to burn cleanly at TDC by assuring critical combustion chamber surfaces quickly flash to higher temperatures during compression and combustion to prevent the formation of quench-type exhaust emissions, 2) to bring combustion chamber surfaces up to operating temperature quickly at cold engine start-up to minimize exhaust pollutants commonly associated with Fig15.jpgcold engine starts, and 3) to increase thermal efficiency by minimizing heat energy loss to a cooling system during the hottest portion of the compression and expansion cycles.
     
The combustion chamber is not fully insulated when the piston drops from TDC in order that lubricated cylinder bore surfaces can quickly dissipate friction heat generated by direct contact with compression sealing rings.
     
The full extent of thermal insulation in the IPC engine is the piston contains a 3mm thick nickel-iron insulating cap and the cylinder head contains a 3mm thick nickel-iron insulating dish. One of these cast iron insulators is pre-inserted into the die cast mold of an aluminum piston, the other is pre-inserted into the mold of a cast aluminum cylinder head.
     
The preferred thermal insulating material in the IPC engine's combustion chamber is an iron alloy containing 40% nickel, with thermal conductivity of 10 W/m K at 200 degrees C. As a comparison, the thermal conductivity of cast A356-T6 aluminum is 130 W/m K at 200 degrees C with conventional Fig17.jpgthermal gradient distance of 10mm between combustion chamber and cooling system, and compacted graphite iron is 40 W/m K with conventional gradient distance of 5mm.
    
A ceramic popular in the adiabatic engine prototypes of the 1980s, with thermal conductivity of 2 W/m K and known as “partially stabilized zirconia” (PSZ), can be a thermal insulator in a future embodiment of the IPC engine concept.  PSZ ceramic was not sufficiently durable in the adiabatic engine experiments to become commercially applicable, though it performed remarkably well considering the severity of the application.  S.A.E. Technical Papers 820429 (1982) and 830318 (1983), with abstracts available at the SAE.org website, discuss internal combustion engine uses for PSZ ceramic components.
     
Other combustion resistant thermally insulating materials can be used in the IPC engine.  As a lowest-cost limit for practical insulation, compacted graphite iron can be effective as a thermal insulator.
            
Fig16.jpg
Fig17 - The investment cast nickel-iron thermal insulators shown here are used in the 2009 and 2010 IPC engines which incorporate poppet valves in the cylinder head.  The 2011 IPC engine uses no poppet valves and employs simplified versions of these castings.
  
    
Unconventional Function #3 - Hyper-Extended Expansion Cycle

The IPC engine incorporates a hyper-extended expansion cycle, which resembles an Atkinson engine and which matches a Chatterton Simplic engine, to let combustion energy perform additional motive work before being discharged to the exhaust. The extended expansion cycle further reduces average combustion chamber temperature and pressure, bringing the average combustion chamber temperature down to the level where a cooling system is not required at all.  The Chatterton Simplic engine claims a 60:1 static expansion ratio (which includes the induction cycle) while the IPC engine claims a 36:1 dynamic expansion ratio (which excludes the induction cycle), effectively describing the same specification in two different ways.
  
Otto and Diesel engines have, perhaps unfortunately, evolved such that the compression and expansion cycles are matched in stroke length. The compression cycle and the expansion cycle are each driven by significantly different processes and mathematical equations, and their stroke lengths will seldom coincide if maximized fuel economy is the primary goal. The 2-stroke IPC engine's compression cycle is one third of a piston stroke and the expansion cycle is two-thirds of a piston stroke. The 4-stroke IPC engine's compression cycle is half of a piston stroke and the expansion cycle is a full piston stroke.
  
Regardless of which fuel is selected, the hyper-expansion ratio in the IPC engine will tend toward 36:1 to minimize heat energy loss to the exhaust duct, in the same way the Chatterton Simplic engine minimized exhaust energy loss. The selection of 36:1 for the expansion ratio is based on the assumption that an arbitrary (a.k.a.: currently unknown) peak combustion chamber pressure of 150 bar at TDC is at the threshold which will not form oxides of nitrogen pollutants, and on the prevalence of predominantly diatomic gasses of the fuel-lean combusted charge obeying, to a first order approximation, the 150 bar / (36 ^ 1.4) = 1.0 bar equation, where 1.4 represents the isentropic expansion factor of a diatomic gas.  The IPC engine inducts unthrottled air, much like a Diesel engine, and it adiabatically pre-warms the inducted charge during compression to a temperature level below the auto-ignition temperature of the fuel-air mixture, but to a temperature level which is sufficient to promote rapid, controlled combustion when precision spark ignition is introduced near TDC.  With a 36:1 expansion ratio and an 18:1 compression ratio of the presently described construction, ammonia would be a preferred fuel.  With the nominal compression ratio adjusted to 16:1, propane would become a preferred fuel, and would be an easier fuel to employ during IPC engine development.  Other fuels will have lower compression ratios, such as 14:1 for ethanol, and 10:1 for gasoline.
    

IPCengine2011fig20c.jpg
Fig18 – Close-up cutaway of cylinder 4. [enlarge.jpg], [animate(small).gif], [animate(large).gif], [video.mpg].
     
   
Unconventional Function #4 - Fuel-Stratified Combustion Chamber
     
Two issues exist with the combustion process described above in the basic description of the IPC engine:
1) Complete full-throttle combustion which combines a thermally efficient compression ratio with a non-stratified stoichiometric mix of fuel and air generates destructive pressure levels if all fuel is combusted at TDC.  As demonstrated in HCCI prototype engines which use gasoline as the fuel, a fuel-lean equivalence ratio of no more than 0.25 prevents excessive combustion chamber pressure when all fuel combusts at TDC. Full-throttle equivalence ratios in this low range approach "lean flammability limits" and combust incompletely, generating significant exhaust pollutants. Partial-throttle equivalence ratios in HCCI engines drop below 0.15 and can become too lean to combust.
    
2) With homogenously mixed combustion reactions, there exist stagnant "quench" locations in the combustion chamber which don’t support efficient combustion, yet which contain fuel and air. Examples of these locations include the tiny crevice volume between the O.D. of the piston and I.D. of the cylinder bore above the compression sealing rings, and also at the segment of the head gasket exposed to the combustion chamber. Significant UHC pollution is created in these tiny locations of a homogenously inducted combustion chamber, but because the IPC engine has unconventionally cool exhaust gas temperatures the IPC engine is unable to use exhaust emissions aftertreatment devices which would otherwise scrub away this pollution.
The IPC engine resolves both the "lean flammability" problem and the "quench location" problem by stratifying the combustion chamber into two regions just prior to direct fuel injection.
   
With a 100mm piston stroke, the combustion chamber of the IPC engine is stratified only when the piston is located within 12mm, or 30 crankshaft degrees, of TDC. When the piston is more than 12mm from TDC there is only a single region in the chamber. The stratified combustion chamber forms when the piston is at 12mm BTC, segregating into two regions, one is named a "perimeter region" which contains air and actively rejects fuel, and the other is named a "central region" which also contains only air when the chamber forms, but which is optimized beginning at 8mm BTC to turbulently mix this air with direct-injected fuel in order to combust cleanly.
  
A "transfer passageway", which can be annular, also forms at 12mm BTC to communicate between the two regions, transferring air toward the central region as the piston travels from 12mm BTC to TDC, and transferring fully combusted gasses to the perimeter region as the piston travels from TDC to 12mm ATC. The transfer passageway additionally acts as a buffer to support and contain the expanding combustion reaction when the piston is within 0.5mm of TDC
.
    
Fig25.jpg
Fig19 - Similar in shape to the 2011 combustion chamber, the 4-stroke IPC engine of 2009 shows the combustion chamber at the transition position between stratified and unstratified, 12mm from TDC.  The 4-stroke head assembly includes four small induction valves and four small exhaust valves within each cylinder.  The valves are positioned such that fuel never contacts them, and therefore pollution emissions cannot form within the crevices surrounding them.  The 2-stroke IPC engine of 2010 employs the same head, with all eight poppet valves used for exhaustion.  The central combustion chamber is now called the central region, the crevice chamber is now called the perimeter region, and the annular passage is now called the transfer passageway.
   
     
The stratified combustion chamber becomes optimally shaped for clean, fast combustion only when the piston is within 0.5mm of TDC. A precisely timed and located source of ignition, as a spark ignition can provide, is used to assure combustion initiates and concludes precisely within this positional constraint.
   
As the combusting reaction heats up within 0.5mm of TDC, the gasses expand beyond the central region. The combusting gasses efficiently spill into the thermally insulated transfer passageway, which fully supports combustion just like the central region, while pure air already residing within the transfer passageway is pushed, in laminar fashion, into the perimeter region which does not support efficient combustion. Only when the piston falls to 0.5mm ATC can expanding combusted gasses reach the perimeter region. By this time the combustion reaction has concluded and there is no concern for pollution development in creviced chamber locations.
   
The perimeter region actively keeps fuel away from combustion chamber features which do not efficiently support combustion. The volume of the perimeter region effectively approaches zero as TDC approaches, whereas the volume of the central region effectively approaches a finite value as TDC approaches, effectively creating an air surge directed from the perimeter region toward the central region during the last 12mm BTC.  The perimeter region actively pumps this air toward the central region to reinforce stratification and to turbulently mix injected fuel with air prior to ignition. Direct fuel injection begins when the piston is 8mm BTC and ends by 6mm BTC, and is aimed to inject fuel only into the central region. The air pumping action constrains fuel to the central region, permitting selection of an optimal fuel-air equivalence ratio in the range of 0.40 to 0.80 which combusts rapidly and cleanly, rather than the pollution-prone equivalence ratio range of 0.15 to 0.25 commonly found in HCCI engine prototypes.
     
Fig26.jpg
Fig20 - This image of the 4-stroke IPC engine of 2009 at TDC presents durable nickel-iron thermal insulators in combination with an obsoleted overpressure-bypass valve originally intended to protect obsoleted ceramic insulators from stoichiometric misfire conditions.  The induction and exhaustion ducts are designed to emphasize low flow resistance rather than tuned flow.  The central combustion chamber is now called the central region, the crevice chamber is now called the perimeter region, and the backfill passage is now called the transfer passageway.
  
   
The central region and transfer passageway are both shaped to fully support combustion, in that the surface areas are comparatively low to minimize quenching of the combustion reaction. The thermally insulated chamber surface heats up quickly during compression and combustion to assure fuel in close proximity to the insulated material combusts fully. During compression, the central region is shaped to generate within itself a tumbling vortex as air surges inward from the perimeter region, assuring all fuel is in motion to uniformly combust, the turbulence mixing fuel and air uniformly while minimizing both hot and cold spots throughout the central region, minimizing both pre-ignition and pollution issues.
    
The rate of the combustion reaction is driven, in part, by the selected fuel, the compression ratio, the fuel-air equivalence ratio, chamber turbulence, and engine RPM, and requires sufficient time to burn completely and cleanly. The reaction rate defines an engine RPM maximum which, if exceeded, will result in incomplete combustion and pollution emissions. Any residual fuel that is not completely combusted when the piston falls to 0.5mm ATC is subject to exit the combustion chamber as a pollutant.  Due to the lean-flammability limits of fuel, there is not a second opportunity to combust fuel that does not initially combust near TDC. If pollutant generation is to be low, quench features, such as conventional spark plug insulation recesses, should be avoided in the central region or transfer passageway.
   
The fuel-stratified combustion chamber uniquely allows pollution-free application of gas-ported piston rings which can minimize sliding friction during the low-pressure segment of the engine cycle. This improves fuel economy and minimizes port window interface wear
.
     
IPCengine2011fig10c.jpg
Fig21 - The 2-stroke Insulated Pulse Engine of 2011. [enlarge.jpg].
    
     
Construction Summary of the 2-Stroke Insulated Pulse Engine

The 2-stroke IPC engine concept is a reciprocating piston engine developed around a 3.2 liter inline 4-cylinder platform with 100mm bore and 100mm stroke and 90-degree firing interval.  Each piston is installed within a ported reciprocating cylinder, the piston and reciprocating cylinder each joined to the crankshaft using connecting rods.  The piston and reciprocating cylinder coordinate to provide induction and exhaustion functions for the combustion chamber.  The reciprocating assembly is installed into a cylinder block containing a ported fixed cylinder, an integral induction plenum, and an integral exhaustion plenum.  A high connecting rod ratio combines with a crankshaft counterbalance scheme that compensates for both rotating and reciprocating mass to assure smooth engine operation
.
     

Piston Assembly
The piston assembly of the IPC engine is comprised of a thermally insulated piston, a connecting rod, and conventionally associated components
   
The piston contains an investment-cast combustion-resistant thermally insulating nickel-iron cap which is cast integrally with the aluminum piston. The visible portion of the nickel-iron cap comprises the piston deck, with the function of minimizing the formation of quench-sourced pollution emissions, minimizing cold-start forms of pollution emissions, and minimizing combustion chamber heat lost during compression and combustion.  The aluminum body of the piston provides a lightweight thermally conductive pathway for the small amount of combustion heat which escapes through the thermal insulator to quickly dissipate into the engine assembly, where the dissipated heat is eventually carried away by induction air and unconventionally cool exhaust gasses.
    
The piston assembly contains a set of rings near the piston deck which manage combustion pressure sealing and ring lubrication, and a set of rings near the crankcase end which manage crankcase vacuum sealing and ring lubrication. The crankcase end ring set is lubricated, in part, by immersion in oil thrown from the rotating crankshaft. Since the crankcase end ring set is shrouded from much of the thrown oil by the reciprocating cylinder assembly, ring oiling is supplemented through a metered passageway within the piston which transfers pressurized crankshaft oil via the connecting rod. Lubricating oil is metered from the crankcase end ring set to the piston deck ring set via positional overlap within the bore during the course of a full engine cycle. Oiling requirements for the piston deck ring set is reduced from convention because the cylinder bore never contacts combustion flame. To reduce pumping losses created by crankcase windage, particularly windage between the piston and reciprocating cylinder, the crankcase is kept at a significant level of vacuum using a crankcase vacuum pump.
    
The sealing rings near the piston deck travel across a band of twelve induction ports in the reciprocating cylinder. To prevent wear caused by introduction of the ends of the rings to the unsupported space of a port window, the rings can be pinned in the piston grooves, allowing them to float in position within the groove without being allowed to rotate in the bore, keeping ring ends away from port windows.
    
The piston can incorporate a gas-ported type of sealing ring, since fuel does not approach the perimeter region of the combustion chamber occupied by sealing rings or gas ports, and therefore fuel cannot clog the ports and pollution emissions cannot form within the gas ports. Gas ports permit the use of low-tension compression sealing rings which reduce sliding friction when combustion chamber pressure is low, improving fuel economy and minimizing port window interface wear.
     

Reciprocating Cylinder Assembly
The reciprocating cylinder assembly, sometimes called a sleeve valve assembly, is comprised of a reciprocating cylinder, two connecting rods, plus components conventionally associated with a piston assembly.  The reciprocating cylinder assembly is connected to the crankshaft through two connecting rods, and the crankshaft journals are located such that the stroke and phase angle of the cylinder is not matched with piston motion. The reciprocating cylinder, with a bore of 100mm and an O.D. of 114mm, has a 60mm stroke, with the journal’s phase angle retarded 35 crankshaft degrees from the piston.
   
The reciprocating cylinder assembly contains two circumferential bands of twelve ports, the band nearer the cylinder head assembly provides exhaustion, the band nearer the crankcase end provides induction.
   
The reciprocating cylinder is preferably made of cast iron, as cast iron is durable, low in cost, high in lubricity, and absorbs less heat energy from combusted gasses than would a hypereutectic aluminum reciprocating cylinder.  Since a cast iron reciprocating cylinder is heavy, a composite reciprocating cylinder can contain a cast iron bore surrounded by a lightweight aluminum sheath. An aluminum sheath provides a second benefit, in that it can quickly carry heat away from the portion of cast iron which absorbs compression and combustion heat.
   
The reciprocating cylinder is constrained at the crankcase end by the OD, and at the cylinder head by the ID.  The crankcase end OD measures 114mm to provide positional constraint within the 114mm fixed bore of the cylinder block, the remainder of the reciprocating cylinder is stepped down to 113mm at the OD to provide a clearance to the fixed bore of the cylinder block. This clearance is large enough to prevent scuffing of the reciprocating cylinder against the cylinder block, and small enough to prevent significant port leakage.
   
The reciprocating cylinder contains a set of rings at the crankcase end which manage crankcase vacuum sealing while assuring the reciprocating cylinder OD will have a lubricating film of oil near the crankcase end to prevent wear of the cylinder block bore.  The set of rings at the crankcase end can be calibrated for low friction through the full engine cycle.
   
The reciprocating cylinder additionally slides against a set of sealing rings contained by the piston, and against another set of sealing rings contained by the head. Both of these latter ring sets seal against high combustion pressures, and therefore will generate notable friction when sealing combustion pressure. The reciprocating piston has a 100mm stroke, the reciprocating cylinder a 60mm stroke which is phase-angle shifted from the piston. The result is the piston rings actually slide only 60mm within the reciprocating cylinder, and the head rings slide 60mm within the reciprocating cylinder, generating 120mm of total compression ring travel per half engine cycle.
   

Crankshaft Assembly
The crankshaft assembly consists of a nodular iron crankshaft containing five main bearings and a counterbalance assembly. The central main bearing also comprises a thrust bearing function. Each cylinder position on the crankshaft contains three bearing journals, a central journal to attach the piston assembly flanked by a pair of journals to attach the reciprocating cylinder assembly. The crankshaft is fully drilled for pressure-oiling twelve connecting rods.
  
Balance compensation for both rotating mass and reciprocating mass is included with the crankshaft assembly using an abstraction of the Detroit Diesel 453 engine balance compensation scheme. The rotating mass is compensated by a portion of conventional counterweights at each end of the crankshaft, and reciprocating mass is compensated by the remainder of counterweight mass combined with a concentric reverse-spinning counterweight at each end of the crankshaft.  The piston assemblies and the reciprocating cylinder assemblies employ unconventionally high connecting rod ratios, permitting a closer approximation to sinusoidal reciprocating motion than found in many Otto and Diesel engines.  The energy of mechanical vibration neutralized by the counterweight scheme is redirected into productive crankshaft output.  The helix angle is reversed between the front set of counterweight gears and rear set to prevent loading the crankshaft thrust bearing as engine RPM changes. Gear tooth loading is low, permitting the use of low-cost counterweight gears
.
   

Cylinder Block Assembly
The cylinder block assembly is comprised of a cylinder block, a maincap block, a front panel, a rear panel, and conventional components associated with a cylinder block assembly.  The volume of the cylinder block assembly below the cylinder block, above the maincap block, and between the front panel and rear panel, is called the crankcase volume, or crankcase.
   
The cylinder block casting contains four fixed cylinder block bores, each having two circumferential bands of twelve ports each, and an additional band of eight ports. The band of eight ports is nearest the deck (top) surface and is included for incidental venting. The band of twelve ports nearest the crankcase is for induction, and the middle band of twelve ports is for exhaustion.
   
The cylinder block is designed to contain four reciprocating cylinders within its four fixed cylinder bores. These reciprocating cylinders each have sealing/oil control rings contacting the fixed bore nearest the crankcase end, with the reciprocating cylinders only contacting the fixed bores nearest the crankcase end. The fixed bores are constructed to handle the associated sliding friction of the reciprocating cylinders. The cylinder block can be constructed entirely of a hypereutectic aluminum alloy to support the reciprocating cylinders, but a lower cost method can be to cast cylinder liners into a non-hypereutectic aluminum block, the integrally-cast inserts permitting specific wear-resistant cylinder sleeves at appropriate positions within the block.
   
The cylinder block has four enclosed levels positioned above the crankcase volume
:
1) The uppermost enclosed chamber is the incidental venting plenum which provides incidental mechanism venting specific to this embodiment. This level also provides two entryway ports at the top which enable filtered ambient air to be drawn into the cylinder block.
  
2) The second enclosed chamber from the top is an exhaust plenum which collects combusted gasses ejected by each chamber volume as the exhaust ports open, and which directs exhaust gasses at low-restriction toward an exhaust flange exiting the cylinder block.
  
3) The third enclosed chamber from the top is an induction plenum which draws fresh filtered air entering the incidental venting plenum of the cylinder block, air which traverses the exhaust plenum at four corner passageways, providing low-restriction filtered ambient air as the induction ports open and draw filtered air into the chamber volume.
  
4) The fourth enclosed chamber from the top is the recirculating oil reservoir for the engine.

Cylinder Head Assembly
The IPC engine runs a separate cylinder head assembly for each combustion chamber.  The cylinder head assembly contains an investment-cast combustion-resistant thermally insulating nickel-iron dish which is cast integrally with the aluminum head.  The nickel-iron dish comprises the combustion chamber surface of the cylinder head, with the function of minimizing the formation of quench-sourced pollution emissions, minimizing cold-start forms of pollution emissions, and minimizing combustion chamber heat lost during compression and combustion. The aluminum body of the cylinder head provides a lightweight thermally conductive pathway for the small amount of heat which escapes through the thermal insulator to quickly dissipate into the engine assembly, where the dissipated heat is eventually carried away by induction air and unconventionally cool exhaust gasses.
  
The cylinder head assembly is affixed to the cylinder block using six head bolts which are positioned to maximize the support of thrust forces applied to the reciprocating cylinder by the piston assembly.
  
The cylinder head assembly contains a primary set of rings positioned near the combustion chamber surface of the head casting which manage combustion pressure sealing, and a secondary set of rings positioned further from the combustion chamber surface which manage pressurized oil to prevent scuffing as the reciprocating cylinder’s bore slides against the head. The travel path of the secondary set of rings overlaps the travel path of the primary set of rings, providing a controlled volume of lubricating oil to the reciprocating cylinder.  The cylinder head connects to a crankcase vacuum passageway which is present to continually draw oil from the cylinder head and return it to the sump.
     
Since oil pressure drops to zero instantly as the engine stops, and since crankcase vacuum is retained for a controlled period of time after the engine is turned off, crankcase vacuum is used to withdraw the small amount of oil remaining in cylinder head passages when the engine is turned off, to prevent overnight migration of oil past the oil control rings and into the combustion
chamber.
   

Spark Plug and Coil
The IPC engine uses a precision timed and precision positioned source of ignition to manage combustion and minimize creation of pollution emissions.  The ignition source is a spark plug with two insulated electrodes which permit reduced electrode voltage, with ignition coil integrated into the assembly.  This construction is presented to enable discussion, and is not intended to suggest a best-design practice.
         
The spark plug in the IPC engine is constructed in a manner which minimizes crevice-type volumes, since crevices trap fuel in locations which do not support efficient combustion. The ceramic and electrode of the spark plug are constructed to resist stresses induced by a supersonic combustion shockwave.

Oiling System
The oil reservoir is integral to the cylinder block, just above the crankshaft.
     
The helical intermediate gears associated with crankshaft counterweights are each machined to allow fitment of a small auxiliary gear which drives the oil pump and sump/vacuum pump systems at the front and rear of the crankcase.  The pumps and auxiliary gears are omitted from the presented model, but all oiling circuitry is present. The IPC engine contains a single oil pump, as well as a front sump/vacuum pump and a rear sump/vacuum pump.  The two sump/vacuum pumps make passive contact with a pressurized oil passage in the cylinder block to assure they remain lubricated when the engine assembly is operated at a severe tilt angle.
   
Atop the engine assembly, directly centered on the air cleaner cover, is the dip stick.  Forward of the dip stick and rearward of the dipstick are two oil filler caps, which also act as oil reservoir vents.  The vents receive crankcase air delivered to the oil reservoir by the sump/vacuum pumps and contain condensers which catch and condense aerosol oil droplets.  Two vents exist instead of one vent, assuring proper lubrication when the engine assembly is significantly tilted during operation and one vent becomes occluded with reservoir oil
.
     

Air Cleaner Assembly
The air cleaner assembly sits atop the engine block, providing filtered ambient air at low restriction for induction.  The air cleaner lid is held in place by three plastic nuts which occupy a perimeter region surrounding the central dip stick and two oil filler/vent caps.  The three nuts do not interfere with operation of the dip stick and filler caps, but rather attach and thread outboard of three supports attached to the top of the engine block, while the dipstick and fillers attach and thread inboard on the same three supports and operate independently of the three air cleaner nuts
.
    
     
Practical Application of the Insulated Pulse Engine Concept
    
The IPC engine stratifies fuel within the central region of the combustion chamber to enable clean combustion at high fuel efficiency. The IPC engine combusts cleanly when the stratified fuel-air equivalence ratio is nominally between 0.40 and 0.80, the actual range determined by the selected fuel. A stratified 0.80 equivalence ratio represents the full-throttle value and 0.40 represents the half-throttle value, with throttle position independent of crankshaft RPM. The IPC engine differs from Otto and Diesel engines in that Otto and Diesel engines handle low-throttle combustion operations without issue whereas the IPC engine does not permit throttle activity below half-throttle due to pollution susceptibility. When the equivalence ratio rises significantly above 0.80 in the IPC engine, the combustion reaction begins to slow and pollutants of the type which suggest oxygen deprivation begin to form. When the equivalence ratio drops significantly below 0.40 pollutants of the type which suggest an excessively cool reaction begin to form.
   
In the 3.2 liter 2-stroke IPC engine, an equivalence ratio of 0.80 arbitrarily translates to generating 65 horsepower at 4000 RPM (the arbitrary redline determined by combustion velocity and pollution constraints) and 0.40 arbitrarily translates to 32 horsepower at 4000 RPM. Anticipating the IPC engine will operate reliably as low as 1000 RPM, 0.40 generates as little as 8 horsepower. In order to achieve a 1000 RPM idle with no crankshaft load, an alternator or pump is tasked with dissipating the generated 8 horsepower as heat.
  
A method to more efficiently reduce power output at idle involves deselecting individual cylinders by halting direct fuel injection to them. If a pair of cylinders are deselected, a 4 horsepower minimum output at 1000 RPM can be achieved, tasking the alternator or pump with only 4 horsepower of heat
dissipation.
     
Operating Sequence of the 2-Stroke Insulated Pulse Engine
The operating sequence of a 2-stroke IPC combustion chamber will now be presented, first in summary form and then in detailed form.
        
The 2-stroke IPC engine incorporates an operating sequence summarized as follows:
1) Compression - 33mm BTC to 0.5mm BTC
2) Ignition – 0.5mm BTC
3) Combustion – 0.5mm BTC to 0.5mm ATC
4) Conventional expansion – 0.5mm ATC to 33mm ATC
5) Hyper-expansion – 33mm ATC to 67mm ATC
6) Induction - 67mm ATC to 90mm BTC
7) Exhaustion - 95mm ATC to 33mm BTC
The 2-stroke IPC engine's cylinder block includes intake ports on a lower segment of the cylinder block bore and exhaust ports on a middle segment of the cylinder block bore. The detailed operating sequence comprises:
33mm BTC: Exhaust ports close, compression of fresh air and traces of exhaust begins.
32mm BTC: Fresh air begins adiabatically heating.
12mm BTC: Combustion chamber transitions to become stratified.
08mm BTC: Fuel is direct injected into the central region.
07mm BTC: Perimeter region pumps fresh air toward central region, constraining fuel.
06mm BTC: Direct fuel injection ends.
05mm BTC: Air sourced from perimeter region generates turbulence in central region.
01mm BTC: Fuel and air homogenously mixed in turbulent central region.
0.5mm BTC: Spark ignites fuel and air mixture, combustion progresses rapidly.
0.2mm BTC: Combustion reaction expands into transfer passageway.
0.2mm ATC: Transfer passageway forces pure air back into perimeter region.
0.5mm ATC: Combustion reaction completes and extinguishes in perimeter region.
05mm ATC: Combusted gasses are adiabatically cooling in combustion chamber.
12mm ATC: Stratified combustion chamber transitions to become single chamber.
33mm ATC: Conventional expansion cycle ends, hyper-expansion cycle begins.
50mm ATC: Chamber pressure at half-throttle reaches 1 bar, vacuum forms in chamber.
67mm ATC: Hyper-expansion ends.  Chamber pressure at full-throttle reaches 1 bar.
67mm ATC: Intake ports in lower cylinder open.
67mm ATC: Vacuum forms and draws fresh air into lower third of combustion chamber.
67mm ATC: Upper 67mm of chamber contains gasses with 1/8 to 1/4 oxygen consumed.
95mm ATC: Exhaust ports in upper cylinder begin to open.  Intake ports are fully open.
100mm BDC: Intake ports begin to close.
99mm BTC: Lower 1/3 of combustion chamber contains air, upper 2/3 contains exhaust gasses.
95mm BTC: Exhaust ports in upper cylinder fully open.
90mm BTC: Intake ports in lower cylinder close.
89mm BTC: Piston pushes oxygen-rich exhaust gasses in upper 2/3 chamber out exhaust ports.
33mm BTC: Exhaust ports close, compression of fresh air begins.
IPCengine2012Fig85a.jpg
Fig30 - Revision 2012 of the IPC engine concept introduces efficient low throttle constructions.  It introduces an optional idling port and associated idling plunger (light yellow), the function being either active (fully retracted) or inactive (fully inserted).  Detail of an actuating linkage for the plunger is omitted from this introduction. [video.mpg].
     
     
Optimizing Idling Efficiency in the Insulated Pulse Engine Concept 
                   
The 4-stroke IPC engine of 2009 applies variable exhaust port timing to optimize the hyper-expansion cycle through the full range of engine operation from half-throttle to full-throttle. Due to limitations in variable induction port and exhaust port timing in the 2-stroke IPC engine of 2011, the hyper-expansion cycle of the 2-stroke IPC engine of 2011 is tuned to operate most efficiently only at full-throttle. As the throttle position drops from full-throttle toward half-throttle, a level of vacuum forms in the combustion chamber toward the end of the hyper-expansion cycle. The presence of vacuum at the end of the hyper-expansion cycle results in blowdown-type pumping losses each time the induction ports open, negatively affecting part-throttle fuel economy to a small degree. The level of vacuum reaches a maximum when cylinders are deselected, as can be done to a pair of cylinders when the engine is idling, resulting in maximum blowdown energy losses at idle. The intrinsically low rate of fuel consumption at idle means the fuel cost of this inefficiency is comparatively low.
   
With the IPC engine designed to minimize all forms of friction in order to overcome low volumetric efficiency, blowdown energy loss can comprise a significant portion of "mechanism efficiency" at idle.  At idle, when two cylinders are tasked to operate at half-throttle and two cylinders are deselected, chamber vacuum begins to form in the pair of half-throttle cylinders near 50mm ATC and chamber vacuum begins to form in the pair of deselected cylinders at 33mm ATC. Vacuum peaks in all four cylinders near 67mm ATC, with the blowdown energy loss occurring when the induction cycle begins. Since there can be applications in which the IPC engine spends an inordinate amount of time operating with a pair of cylinders deselected, such as idling with an air conditioning pump operating, fuel savings can quickly accumulate if this induction blowdown inefficiency is resolved.
    
One resolution to induction blowdown losses at idle in the 2-stroke IPC engine of 2011 is to add a circumferential band of ports in the cylinder block bore which deactivates the hyper-expansion function when the cylinder is idling and which activates the hyper-expansion function when the cylinder is operating. This band of optional ports are named IPCengine2012Fig81c.gif"idling ports".  These ports are positioned in the 2012 revision of the IPC engine's cylinder block between the induction ports and exhaust ports such that, when open, they provide an additional low-restriction connection between the combustion chamber and the exhaust plenum for the purpose of preventing the formation of combustion chamber vacuum between 33mm ATC and 67mm ATC, effectively turning the hyper-expansion cycle completely off.  An idling plunger (light yellow, animated at right) can then be installed into each of the idling ports such that, when the idling port becomes blocked by the "inserted" plunger the hyper-expansion function is restored for optimal efficiency at full-throttle. The idling plunger can be applied in the form of a two-position plunger which is inserted flush to the cylinder bore to apply the hyper-expansion cycle, or is withdrawn from the cylinder block bore to efficiently disable the hyper-expansion cycle, replacing hyper-expansion function with an exhaust reversion function. Detail of an actuating linkage for the idling plunger is omitted.
     
Idling ports are not applicable to the 4-stroke IPC engine, since variable exhaust port timing in the 4-stroke IPC engine fully resolves this issue.
      
Idling Sequence of the 2-Stroke Insulated Pulse Engine
The idling sequence of a 2-stroke IPC combustion chamber will now be presented, first in summary form and then in detailed form.
        
The 2-stroke IPC engine incorporates an idling sequence summarized as follows:
1) Compression - 33mm BTC to 0.5mm BTC
2) Ignition – 0.5mm BTC
3) Combustion – 0.5mm BTC to 0.5mm ATC
4) Conventional expansion – 0.5mm ATC to 33mm ATC
5) Exhaust reversion – 33mm ATC to 67mm ATC
6) Induction - 67mm ATC to 90mm BTC
7) Exhaustion - 95mm ATC to 33mm BTC
The 2-stroke IPC engine's cylinder block includes intake ports on a lower segment of the cylinder block bore, exhaust ports on a middle segment of the cylinder block bore, and idling ports on a lower-middle segment of the cylinder block bore which adjoin to the exhaust plenum. The detailed idling sequence comprises:
33mm BTC: Exhaust ports close, compression of fresh air and traces of exhaust begins.
32mm BTC: Fresh air begins adiabatically heating.
12mm BTC: Combustion chamber transitions to become stratified.
07mm BTC: Perimeter region pumps fresh air toward central region.  No fuel is injected.
0.2mm ATC: Transfer passageway begins drawing pure air back into perimeter region.
12mm ATC: Stratified combustion chamber transitions to become single chamber.
33mm ATC: Chamber pressure reaches 1 bar.
33mm ATC: Idling ports connected to exhaust plenum open and draw exhaust into cylinder.
67mm ATC: Chamber pressure remains 1 bar.  Idling ports connected to exhaust plenum close.
67mm ATC: Exhaust-reversion cycle endsIntake ports in lower cylinder open.
67mm ATC: Vacuum forms and draws fresh air into lower third of combustion chamber.
95mm ATC: Exhaust ports in upper cylinder begin to open.  Intake ports are fully open.
100mm BDC: Intake ports begin to close.
95mm BTC: Exhaust ports in upper cylinder fully open.
90mm BTC: Intake ports in lower cylinder close.
89mm BTC: Piston begins pushing gasses in upper 2/3 of chamber out exhaust ports.
33mm BTC: Exhaust ports close, compression of fresh air begins.
       
Expansion Buffering 
       
IPCengine2012Fig80b.jpgExpansion buffering is an optional function which broadens the throttle range in which the hyper-expansion cycle operates near peak fuel efficiency in the 2-stroke IPC engine. Expansion buffering can function in association with the idling ports, though it is independent of them. If idling ports are omitted from an engine, expansion buffering uses only a circumferential band of small ports (not shown) cut into the cylinder block bore which are positioned just above the induction ports and which adjoin to the exhaust plenum. When expansion buffering is applied in conjunction with idling ports (as shown), an optional expansion buffering aperture is added to the lowest segment of the idling plunger (as shown in the lower plunger pair at left). In the animated gif image immediately above, the expansion buffering aperture is shown in both the operating position (idling plunger inserted) and in the inactive position (idling plunger withdrawn).
     
The expansion buffering aperture can recalibrate the hyper-expansion cycle away from a single-point optimum, nominally set at full-throttle, to a broader optimum range, nominally centered at 7/8-throttle (0.70 equivalence ratio in various embodiments), such that blowdown pumping losses can be minimized from 3/4-throttle (0.60 equivalence ratio) through full-throttle and blowdown pumping losses can additionally be improved below 3/4 throttle. The expansion buffering aperture allows 3/4-throttle cylinder operation to become more fuel efficient by venting some cylinder vacuum which accumulates near the end of the hyper-expansion cycle, while full-throttle operation vents some excess combustion chamber pressure just prior to induction, assuring induction can proceed nominally.
      
Expansion buffering is not applicable to the 4-stroke IPC engine, since variable exhaust port timing in the 4-stroke IPC engine fully resolves this issue.
      
Expansion Buffering Sequence of the 2-Stroke Insulated Pulse Engine
The expansion buffering sequence of a 2-stroke IPC combustion chamber will now be presented, first in summary form and then in detailed form.
        
The 2-stroke IPC engine incorporates an expansion buffer sequence summarized as follows:
1) Compression - 33mm BTC to 0.5mm BTC
2) Ignition – 0.5mm BTC
3) Combustion – 0.5mm BTC to 0.5mm ATC
4) Conventional expansion – 0.5mm ATC to 33mm ATC
5) Hyper-expansion – 33mm ATC to 58mm ATC
6) Expansion buffering - 58mm ATC to 67mm ATC
7) Induction - 67mm ATC to 90mm BTC
8) Exhaustion - 95mm ATC to 33mm BTC
The 2-stroke IPC engine's cylinder block includes intake ports on a lower segment of the cylinder block bore, exhaust ports on a middle segment of the cylinder block bore, and expansion buffer ports (not shown) in a lower-middle segment of the cylinder block bore which adjoin to the exhaust plenum. In an embodiment, the detailed expansion buffer sequence comprises:
33mm BTC: Exhaust ports close, compression of fresh air and traces of exhaust begins.
32mm BTC: Fresh air begins adiabatically heating.
12mm BTC: Combustion chamber transitions to become stratified.
08mm BTC: Fuel is direct injected into the central region.
07mm BTC: Perimeter region pumps fresh air toward central region, constraining fuel.
06mm BTC: Direct fuel injection ends.
05mm BTC: Air sourced from perimeter region generates turbulence in central region.
01mm BTC: Fuel and air homogenously mixed in turbulent central region.
0.5mm BTC: Spark ignites fuel and air mixture, combustion progresses rapidly.
0.2mm BTC: Combustion reaction expands into transfer passageway.
0.2mm ATC: Transfer passageway forces pure air back into perimeter region.
0.5mm ATC: Combustion reaction completes and extinguishes in perimeter region.
05mm ATC: Combusted gasses are adiabatically cooling in combustion chamber.
12mm ATC: Stratified combustion chamber transitions to become single chamber.
33mm ATC: Conventional expansion cycle ends, Hyper-expansion cycle begins.
50mm ATC: Expansion buffer ports begin to open.  Half-throttle hyper-expansion ends.
58mm ATC: Expansion buffer ports open.  3/4 throttle hyper-expansion ends.
58mm ATC: Chamber pressure 1.0 bar at 3/4 throttle, 1.3 bar at full-throttle.
62mm ATC: Below 3/4 throttle, chamber vacuum draws from exhaust plenum.
62mm ATC: At 7/8 throttle, gas exchange through expansion buffer is minimal.
62mm ATC: At full-throttle, slight chamber pressure is vented into exhaust plenum.
67mm ATC: From 3/4 to full-throttle, expansion buffer maintains chamber pressure near 1 bar.
67mm ATC: Expansion buffer closes, intake ports in lower cylinder open.
67mm ATC: Vacuum forms and draws fresh air into lower third of combustion chamber.
67mm ATC: Upper 67mm of chamber contains oxygen-rich combusted gasses.
95mm ATC: Exhaust ports in upper cylinder begin to open.  Intake ports are fully open.
100mm BDC: Intake ports begin to close.
99mm BTC: Lower 1/3 of combustion chamber contains air, upper 2/3 contains exhaust.
95mm BTC: Exhaust ports in upper cylinder fully open.
90mm BTC: Intake ports in lower cylinder close.
89mm BTC: Piston pushes combusted gasses in upper chamber out exhaust ports.
33mm BTC: Exhaust ports close, compression of fresh air begins.
       
Operating Sequence of the 4-Stroke Insulated Pulse Engine
    
The 2009 revision of the IPC engine, formerly presented on this webpage, has a 4-stroke construction based on an in-line 4-cylinder construction with 100mm bore and 100mm stroke.  An updated 4-Stroke IPC engine will be presented on this page as time permits.  The 4-stroke IPC engine does not require idling ports or expansion buffering to broaden the throttle range in which the hyper-expansion cycle operates near peak fuel efficiency.  The 4-stroke IPC engine instead applies camshafts, poppet valves, and variable port timing to optimize fuel efficiency at every throttle position.  Variable port timing in a 4-stroke IPC engine applies, to each cylinder pair, two fixed phase camshaft events controlling IVO and EVC and two variable phase camshaft events independently controlling IVC and EVO.
     
The 4-stroke IPC engine comprises a sequence of cyclic events starting with a compression cycle and ending with an induction reversion cycle.  The compression cycle can be described as beginning the instant the induction port closes at 50mm BTC and ending the instant spark ignition is triggered at 0.5mm BTC.  A combustion cycle then begins, and combustion ends quickly when the reaction is consumed and concluded on or before 0.5mm ATC.  A conventional expansion cycle then begins, and it ends at 50mm ATC when the piston reaches the same distance from TDC that the piston was positioned when the compression cycle began.
    
A hyper-expansion cycle then begins at 50mm ATC, and it continues until the piston reaches 100mm BDC.  The hyper-expansion cycle in the 4-stroke IPC engine
 is comprised of two sequential stages, the hyper-expansion stage followed by the exhaust reversion stage, each of which vary in duration from 0% to 100% of the hyper-expansion cycle, dependent on throttle position.  The hyper-expansion stage is characterized by combustion chamber pressure remaining above 1 bar.  The exhaust reversion stage opens the exhaust port when combustion chamber pressure drops below 1 bar to prevent throttling-type losses at the start of the exhaust cycle.  At full-throttle, the hyper-expansion cycle initially comprises a hyper-expansion stage for 100% of the duration, followed by an exhaust reversion stage for 0% of the duration, wherein the hyper-expansion stage is characterized by combustion chamber pressure remaining above 1 bar and the exhaust reversion stage is characterized by combustion chamber pressure dropping below 1 bar.  At 3/4-throttle, the hyper-expansion cycle initially comprises a hyper-expansion stage for 75% of the duration, followed by an exhaust reversion stage for 25% of the duration, the exhaust reversion stage opening the exhaust port when combustion chamber pressure drops below 1 bar to prevent throttling-type losses at the start of the exhaust cycle.  At half-throttle, the hyper-expansion cycle initially comprises a hyper-expansion stage for 50% of the duration, followed by an exhaust reversion stage for 50% of the duration.  At idle, the hyper-expansion cycle initially comprises a hyper-expansion stage for 0% of the duration, followed by an exhaust reversion stage for 100% of the duration.
    
An exhaust cycle then begins at 100mm BDC and ends at 15mm BTC when the exhaust port closes.  An incidental compression cycle then begins, and it elastically rebounds and concludes when the induction port opens at 15mm ATC.  An induction cycle then begins, and it ends at 100mm BDC.  An induction reversion cycle begins at 100mm BDC, and it concludes at 50mm BTC when the compression cycle begins, completing the 4-stroke IPC engine cycle.
      
Compared with naturally-aspirated 4-stroke Diesel engines at full-throttle, a similarly displaced 4-stroke IPC engine at full-throttle can consume only an eighth of the fuel each combustion event. This is based on the observation that HCCI prototype engines consume 1/4 of the full-throttle fuel that similarly displaced Diesel engines consume each combustion event, and that only 1/2 of a piston stroke in the 4-stroke IPC engine applies to the compression cycle.  With this fuel consumption constraint, a 4-stroke IPC engine can be expected to produce 75% of the horsepower that a 2-stroke IPC engine can produce.  Pollution emissions characteristics of equivalently powered 2-stroke and 4-stroke IPC engines are comparable.  Variable valve timing in the 4-stroke IPC engine provides opportunity for a variable compression ratio, allowing operation throughout an extended range of operating environments which can include high altitude and flex-fuel.
     
      
Cold Weather Icing in the Insulated Pulse Engine
          
Operating with a deselected cylinder pair in cold ambient conditions can mix within the exhaust plenum the combination of warm humid exhaust and cold uncombusted air, potentially resulting in frost build-up which can restrict exhaust flow.  Providing separate exhaust circuits would permit the deselected cylinder pair to exhaust cold dry air to the atmosphere while the active cylinder pair exhausts warm humid exhaust gases to the atmosphere.  The presented 2-stroke 90-degree crankshaft construction pairs cylinders 1 with 4 and 2 with 3 in a conventional manner, but an alternate 90-degree crankshaft construction might pair cylinders 1 with 2 and 3 with 4 to assist with frost-prevention measures, such as to streamline re-induction of exhausted air from deselected cylinder pairs to help retain heat within the engine.
    
Due to unconventionally cool operating temperatures, water condensation and the resulting corrosion may be a more significant issue in the IPC engine than in conventional engines.  A heating function within the engine block may be required during cold weather operation to quickly bring the IPC engine's oil up to an operating temperature which prevents the accumulation of water condensation.
       
      
"Some Unusual Engines", a book authored by L.J.K. Setright
     
There have been "numerous" hyper-expansion engine experiments according to author L.J.K. Setright in his 1975 book entitled, "Some Unusual Engines", but finding information on any of them has proven to be a challenge.  Fortunately, Ernest E. Chatterton's Simplic engine prototype is reviewed on pages 43 to 46 of this book.  This record is reproduced here, and provides historic context on which the IPC engine concept can draw:
        

         
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