Off-design operation of super critical CO2 cycle integrated with reciprocating engine.

This paper presents the results of simulations of a supercritical CO2 system integrated with a 180 kW nominal power piston engine. The sCO2 system consists of a compressor, expander, and four heat exchangers. The analysis delivered the optimum operating point of the system, where the sCO2 system generates an extra 18.03 kW. The main research was oriented into generation of off-design characteristics of the system, where sCO2 system were subjected to varying engine load and the system response was analyzed. The results of the calculations refer to the nominal point of the system and are given as maps of parameter changes normalized to the nominal point. The supercritical CO2 system itself is not controlled (only the speed of the turbomachinery is kept constant), while the power of this system depends on the current state of the reciprocating engine and directly influences the amount and temperature of the exhaust gases fed to the heater. The study revealed that the sCO2-biogas piston engine hybrid system would benefit from extra power generated by sCO2 when the engine operates with at least 60 % of its nominal power.