Abstract
Concerning the issues regarding driving mileage reduction for electric vehicles (EVs) in cold climates, a heat pump system with low global warming potential refrigerant R290/R1234yf is employed as one of the promising solutions. Different from the widely used mobile refrigerant R134a, R290 and R1234yf are both flammable or explosive. The application of R290/R1234yf in the mobile heat pump system is hindered by unexpected refrigerant leakage with the existence of fire and explosion risk. In this study, the combustion characteristics of R290/R1234yf in a potential leakage process from an air-conditioning heat pump system for EVs were investigated. Firstly, thermodynamic behaviours of R290/R1234yf used in a typical heat pump system were analysed based on a special experimental facility designed for EVs. Then the leakage and combustion characteristics of R290/R1234yf including flame shape, temperature, radiation etc. were obtained by the experimental method under different initial temperature and mass flow rate conditions. It was found that R290/R1234yf leaked is difficult to ignite at low temperatures, while the blow-off phenomenon of the jet flame would occur at high temperature with high leakage mass flow rate. In addition, the results showed that combustion intensity would be enhanced by the leakage mass flow rate between 30 and 60°C. These results could provide guidance for fire detection and rescue system design for new energy vehicles.
Highlights
Electric vehicles (EVs) have drawn increasing worldwide attention as an alternative to internal combustion engine vehicles (ICEVs), owing to their lower energy consumption and almost zero carbon emission
Heat utilization from air source by an airconditioning heat pump (ACHP) system is proposed and proved to increase by 20% driving mileage compared with positive temperature coefficient (PTC) [3,4]
To figure out the risk of the R290 use for an automobile ACHP system, a three heat exchanger–ACHP system with functions of cooling and heating was designed, as shown in figure 1. This is a calculated model of an R290 vapour compression system, which includes components of two electronic valves, two thermal expansion valves (TXV), two indoor heat exchangers (IHEX), two mass flow meters, outdoor heat exchanger (OHEX), compressor, gas–liquid separator, PTC, etc
Summary
Electric vehicles (EVs) have drawn increasing worldwide attention as an alternative to internal combustion engine vehicles (ICEVs), owing to their lower energy consumption and almost zero carbon emission. Heat utilization from air source by an airconditioning heat pump (ACHP) system is proposed and proved to increase by 20% driving mileage compared with PTC [3,4]. High global warming potential (GWP) refrigerant will be phased down gradually after January 2019 due to the Kigali Amendment, which more than 170 counties agreed and signed in 2016 [9,10]. It indicated that R134a would be replaced by low GWP refrigerants in the near decades in EVs with great probability (table 1)
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