Numerical study of [formula omitted]-fuelled micro-free piston CHP system, coupled with thermophotovoltaic (TPV) and battolyser units

Abstract

Hydrogen (H2) fuelled internal combustion engines (ICEs) can play an important role in small-scale applications despite low efficiency, short reactant residence time and pre-combustion issues. In this study, a hybrid green H2 production and utilisation system covering renewable-powered H2O electrolysis, micro-CHP (combined heat and power) and thermoelectric units was developed. The solar or wind powered battolyser system stores electricity and utilises it to produce H2. The produced green H2 combusts with air in the cylinder to drive the turbine and the electric generator. While the thermophotovoltaic (TPV) unit converts the heat radiation into electrical energy to maximise the power efficiency of the developed hybrid system. The result showed a better temperature distribution, higher pressure discharge on both pistons’ walls and increased energy efficiency by replacing a single-piston with the opposed piston cylinder combustor and using cylinder exit gas to generate more electricity. Steam coolant reduced the thermal stress on the cylinder wall. The mounted TPV unit on the cylinder wall converted the absorbed heat flux to 3.9 kW. The maximum power output of the solar PV and wind turbine systems was reached at an irradiance of 1200 W/m2 under ambient temperature conditions and a wind speed of 17 m/s. By using the exhaust gas from the cylinder to drive the gas turbine, 8.8 kW power output and an electrical efficiency of 31.9 % were recorded. NOx emissions <6 ppm and a CHP efficiency of 93.5 % were achieved for the developed hybrid system. The proposed system can substitute the current domestic gas boiler which is in the phase-out state.