Insulated pulse engine

Last Updated on July 22, 2024 by Mutiara

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The Insulated Pulse Engine: A cold adiabatic engine concept

by Dave Schouweiler, Minneapolis, MN USA, http://insulatedpulseengine.com

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 have been wishing car manufacturers might 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 in the hope of finding answers. I appreciate the support and guidance that has come in.

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.

The Insulated Pulse Engine runs cool without a cooling system, function quietly without a muffler, combusts cleanly without a catalytic converter, and exhaust gasses are sufficiently cool that exhaust ducting can be made of plastic:

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 they 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 steps significantly deeper into this realm, as does my “Insulated Pulse-Combustion” engine concept.

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 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 documented in the 1975 book published by The Institution of Mechanical Engineers 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.

A 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, indicating the engine was being developed to extend the flying range of aircraft.

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 centrally 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 is hyper-extended to 2/3 of the piston stroke, extracting all available combustion energy and eliminating the need for a cooling system. The chamber volume then develops a vacuum which draws fresh inducted air into the bottom 1/3 of the chamber. At BDC, induction ends and the piston begins quietly exhausting oxygen-rich combusted gasses residing in the upper 2/3 of the chamber.

Conventional 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 must prevent 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 steel 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.

Cutaway image represents essentially all moving components within the 2-stroke IPC engine, outside of ordinary fuel and oiling functions. The energy of mechanical vibration neutralized by the counterweight scheme is redirected into productive crankshaft output:

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 details 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.

This project is evolving. The full study can be found at http://insulatedpulseengine.com

Insulated pulse engine

The Insulated Pulse Engine: A cold adiabatic engine concept

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A Brief Introduction to the Insulated Pulse Engine

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The Insulated Pulse Engine: A cold adiabatic engine concept

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