## 1 Introduction  
Energy conservation and recyclability are among the greatest concerns of modern research studies in automotive industry. Regarding all the energy consumed within a vehicle, the air-conditioning system typically takes up a larger part. With major breakthroughs in refrigeration system technologies in the usage of low-grade energy, steam ejector refrigeration systems have become one of the potential devices for effective energy conversion, which can be driven by industrial and automobile exhaust heat waste [1]. The applications of steam ejectors range from transportation systems, fire safety [2], petroleum, chemical industry and seawater desalination [3]. Throughout the last century, the automobile has accounted for the majority of transport worldwide. However, the fuel consumption against energy converting ratio is relatively low. The effective thermal efficiency of the engine is generally about 30%. The remaining 65% of the fuel combustion heat includes 10% lost for radiation, 30% lost to the exhaust and 30% lost by the cooling system. That is, the waste heat accounts for 30% [4]. The engine combustion waste heat has the characteristics of high temperature, fast flow rate and strong pressure. Its temperature can range from 200 \({}^{\circ}\)C to 600 \({}^{\circ}\)C [1]. This part of the heat not only exacerbates the air pollution but also causes the overheating of the water tank to affect the dynamic performance of the automobiles. To reduce waste heat or to improve the waste heat utilisation rate is an effective way to decline the air pollution and enhance the operating stability of the automobile. As an independent running individual, the recovery and utilisation of the waste heat are partly limited. In 1980, [PERSON] firstly proposed to apply the combustion waste heat of automobile engine to power a steam ejector refrigeration system [5]. From an application perspective, using the recycled waste heat as a power source for driving the automotive air conditioning system is a promising way to save energy [6]. Comparing the compression cooling system of the automobile, the steam ejector refrigeration system has the potential to be used in automobiles, due to it has no moving parts, simple structure, small equipment area, durable operation and low cost [2]. The steam ejector refrigeration system consists of four major parts: the generator, the steam ejector, the evaporator and the condenser. The water vapour generated from the generator enters the nozzle at a higher temperature. After it flowed through the nozzle, the water vapour was reduced to a low pressure fluid at the entrance of the ejector. Then the water vapor in the evaporator was sucked into the ejector by the pressure difference. Though a series of flow changes, the two streams of fluid are mixed into a mixed fluid and together discharged into the condenser to continue the next refrigeration cycle [7; 8]. There is a direct relationship between the performance of the refrigeration system and ejector working characteristics [9] and the efficiency of the steam ejector refrigeration system largely depends on the characteristics of the steam ejector [10; 11]. Therefore, a comprehensive understanding of the factors affecting the performance of the steam ejector is essential to improve the performance of the whole refrigeration system. The disadvantage of the steam ejector is that its efficiency is relatively low [12]. As early as 1910, [PERSON] proposed the ejector refrigeration cycle system [13]. The researchers have conducted extensive experimental studies and numerical simulations of the steam ejector [14; 15]. Though the main research of the ejector was still focused on the thermodynamic analysis of the ejector [16; 17], the numerical simulation of the steam ejector developed rapidly. For example, the research on the spontaneous condensation inside the ejector has made some progress in the past five years. The wet steam model applied in the optimization of the ejector efficiency was studied by [PERSON] [18].