Performance study of automotive heat pump system with different refrigerants and leakage combustion characteristics of R290.

R290 (propane) has emerged as a viable natural alternative to R134a (1,1,1,2-tetrafluoroethane) in automotive heat pump air conditioning (HPAC) systems, owing to its similar thermodynamic properties and compatibility with conventional cooling and heating cycles. However, the flammable and explosive nature of R290 introduces significant safety concerns, particularly in vehicular environments. To mitigate these risks, this study employed a secondary circuit HPAC system. The system performance of cabin cooling and heating modes was investigated under different ambient temperatures and compressor speeds, with a fixed refrigerant charge of 275 g and an electronic expansion valve (EXV) set at 30 % opening. And through the method of theoretical calculation, the threshold range of critical leakage volume flow of 1 mm diameter leakage hole is determined to be 0.5 to 1.5 L/ min (low pressure domain) and 1.75 to 2.3 L/min (high pressure domain). A central innovation of this work lies in its comprehensive analysis of R290 combustion behavior under varying leakage conditions. The findings indicate that while increased flow rates promote combustion, excessive turbulence leads to flame instability, bifurcation, and localized extinction. Moreover, higher initial gas temperatures significantly lower the ignition threshold. In addition, automotive HPAC system with secondary circuits, in which the coolant circuit can block some of the radiant heat transfer and reduce the risk of secondary ignition. This research provides critical insights into the safe application of R290 in automotive HPAC systems, demonstrating that effective control of refrigerant flow rate and ambient thermal conditions can substantially reduce combustion risks. The results offer valuable design and operational guidelines for the development of high-efficiency, environmentally friendly, and intrinsically safer R290-based thermal management systems for electric vehicles.