Cold-to-electricity conversion using a piston based engine in cold energy storage (CES) system, part two: An experimental study

This study concerns the practical power tests in a piston based engine with a new valve scheme. By developing the controlling method, the injection of expansion gas into the engine cylinder can be flexibly controlled in terms of requirements under different conditions. The effects of motor speed, p-crank angle, gas pressure and temperature and the category of the expansion gas were all investigated. With increasing of the motor speed, gas pressure or temperature, power generation by the piston-based engine increases. However, the power generation was restrained due to the limited volume flow rate caused by the minimum internal diameter of the valves. The optimal p-crank angle was found in the range of 55°-76° for obtaining the maximum power generation under certain conditions. In practical engine system, the p-crank angle was normally set below 60° for diminishing the gas resistance in the engine cylinder. The experimental results shows that the net electricity consumption is induced due to the block of the exhaust gas in the cylinder. However, by improving the limit value of flow rate at the engine inlet, the engine performance was significantly improved, leading to an overall electricity output by the engine system. This shows the value of the piston-based engine in the CES system.