Project overview

The Insulated Pulse Engine: A cold adiabatic engine concept by Dave Schouweiler, http://insulatedpulseengine.com

This personal study describes a thermally efficient concept for combusting fuel in an internal combustion engine. It explores adiabatic “ceramic” engines, a usually dormant science that was last active for several years after the 1979 oil crisis. This concept is not like published adiabatic engines which expel superheated combusted gasses into an exhaust duct for the post-processing of energy. Instead, this "cold adiabatic engine” concept applies the principle attribute of the adiabatic engine (thermal insulation), along with principle attributes of the Diesel engine (unthrottled induction), the HCCI engine (isochoric heat addition), and the Atkinson engine (isobaric heat rejection), such that combusted gasses are adiabatically cooled before exiting the combustion chamber.

This is a conceptual paper, not a technical paper, as it contains intuitive approximations and primitive constructions which require refinement. I’m not an engine designer and I don't claim this concept works. I’ve been pondering this idea for a while now and have been wishing car manufacturers would someday build a vehicle which contains an engine like this. Since there are no signs it will happen, and unable to find a technical forum that will sustain a discussion on this topic, the time came to model the idea up on a computer and evolve some answers.

The computer model presented here provides the basis for creating the energy equations needed to eventually prove or disprove this concept on paper. If the computational results look promising, advanced analysis using industry-recognized engine simulation software can next be sought. I will keep this webpage updated with my latest findings. This engine concept can be fabricated using century-old technology, and similar concepts have certainly been studied and dismissed, but the findings are not readily available. Technical critique and information on similar experiments is welcome.

A Brief Introduction to the Insulated Pulse Engine

The "insulated pulse-combustion engine", abbreviated "insulated pulse engine" or "IPC engine", is an engine concept which studies the four sources of heat export from internal combustion engines in an effort to improve fuel economy. This concept applies thermal insulation, rapid combustion, and an extended expansion cycle as the means to achieve this goal. This engine also applies a unique stratified combustion chamber to minimize the creation of pollution emissions, since conventional emissions controls are not effective at scrubbing pollutants from cool exhaust gasses.

The IPC engine’s thermodynamic sequence applies rather pure forms of: 1) isentropic (adiabatic) compression, 2) isochoric (pulsed) heat addition, 3) isentropic (adiabatic) expansion, and 4) isobaric heat rejection. This sequence provides opportunity for comparatively high thermal efficiency, however it also brings with it the penalty of a comparatively low average cylinder pressure (technically dimensioned as low “indicated mean effective pressure” or low IMEP) which, when accounting for friction, delivers comparatively low volumetric efficiency (dimensioned as low “brake mean effective pressure” or low BMEP).

The P-V diagram of an ideal Otto cycle (not shown, but readily searchable) indicates the early Otto engine had a purely isochoric heat addition process, however it is well recognized the modern Otto engine (modern gasoline engine) has evolved to incorporate a two-stage heat addition process which starts out isochoric and transitions to isobaric, with the isobaric segment significantly increasing volumetric efficiency while significantly increasing energy loss to the exhaust stream. Similarly, the P-V diagram of an ideal (early) Diesel engine presents a purely isobaric heat addition process, but, like the Otto engine, the Diesel engine has also evolved toward a two-stage (sometimes called "dual-cycle") heat addition process which starts out isochoric and transitions to isobaric to improve volumetric efficiency.

The IPC engine concept principally differs from a modern gasoline engine in that it:

1. Optimizes isentropic compression through the use of unthrottled induction (much the way a Diesel engine does),

2. Eliminates the isobaric component of heat addition (much the way HCCI engine prototypes do),

3. Extends isentropic expansion beyond convention, enabling isobaric heat rejection (much the way an Atkinson engine does), and in doing so,

4. Enables practical thermal insulation of the combustion chamber (much the way adiabatic engine prototypes did, except the IPC engine is able to use cheap durable insulators).

The combustion chamber of the IPC engine is selectively insulated using economical Fe60Ni40 alloy steel inserts to minimize heat rejection to a cooling system. Combustion initiates, and is consumed rapidly, near top dead center (TDC), assuring the entire fuel budget performs work on the piston through the full expansion cycle. The expansion cycle is extended beyond convention to extract additional energy from the pressurized gasses, further reducing average combustion chamber temperature to minimize stress on the thermal insulators, eliminating the need for a cooling system and resulting in an exhaust stream that is comparatively cool and pressureless.

This project is evolving. Current information can be found at http://insulatedpulseengine.com