The reciprocating Joule-cycle engine operates on A recuperated gas--turbine cycle and is intended, to provide high thermal efficiency in small sizes (1-10 kW). It is designed to achieve a higher efficiency than a comparable gas-turbine by using a reciprocating compressor and expander to provide very high compression and expansion efficiencies, Possible power plants for small combined heat-and-power systems currently include Stirling engines, internal-combustion engines, gas-iurbines and fuel cells. The reciprocating Joule-cycle engine. appears to have considerable advantages compared with-other prime movers in terms I of efficiency, emissions and multi-fuel capability. The present study estimates, the performance of such an engine and is the first stage in a larger project that will in due course produce a demonstration engine. (C) 2004 Elsevier Ltd. All rights reserved.