Experimental study of a pneumatic engine with heat supply to improve the overall performance

As an environmental friendly technology, hybrid pneumatic concept regenerating the engine braking energy to boost the engine performance for better fuel economy and lower engine emissions attracts ever increasingly attentions in automotive industry. However, the pneumatic operational mode of the engine suffers from low energy efficiency, which requires more research efforts. This study presents an optimisation method for the pneumatic mode of hybrid pneumatic engine by supplying heat during the expansion process of compressed air. A pneumatic prototype engine has been designed, constructed and used to simulate the working process of the engine during pneumatic mode. Hot water has been used as the heat source to heat up the engine cylinder wall in order to study the effects of using heat supply on the performance of the pneumatic engine. The results show that the power and torque of the pneumatic prototype engine under the heat source temperate at 90 °C and 1 MPa intake pressure are both increased. The maximum power output of the HPE obtained is around 1.5 kW, which is 22% higher than that of the HPE without heat supply. Under the engine rotational speed at 400 r/min, the torque produced from the HPE is about 29 N·m, which is 7% improvement than that without heating supply. The maximum energy efficiency of the HPE can be improved from 27% to 35%, when the cylinder wall is heated by 90 °C water and the intake pressure is set at 1 MPa. Moreover, the effects of hot water temperature have also been investigated and in total twenty-one testing points have been conducted under the engine intake pressure set at 1 MPa. The maximum power output from the HPE under water temperature at 70 °C and 90 °C can respectively be as high as 1.4 kW and 1.5 kW, which is about 14% and 22% improvement compared with the HPE without heat supply.