The reciprocating joule cycle engine for micro combined heat and power applications

Abstract

Micro CHP has been identified as a means of reducing the carbon dioxide emissions from household energy consumption. Large scale field trials undertaken in the UK, with systems internal to a single dwelling and based on Stirling engines, were disappointing because of the low thermal efficiencies of such engines. Alternative engines/devices with higher thermal efficiencies are currently being evaluated in Japan but such systems are external to the dwelling. The reciprocating Joule cycle engine is proposed as an engine for a micro CHP system because of its potential to be more thermally efficient than a Stirling engine and at least as thermally efficient as an internal combustion engine. Such an engine has not previously been analysed in detail nor is there any information that such an engine has been built and operated, particularly at power output levels below 5 kW. Mathematical modelling of the RJC engine is used to determine power outputs and efficiencies taking into account frictional, thermal and pressure losses. Such modelling indicated an engine with a maximum thermal efficiency of 33% making it suitable for micro CHP applications. When the individual models are combined to model a CHP system, and using the engine exhaust heat to preheat the combustion air, an overall maximum system efficiency of 79% was indicated.