Experimental approaches to investigating liquefied LPG spray characteristics

Abstract

Liquefied petroleum gas (LPG) has been used as an automotive fuel due to its advantages of low cost and low emissions. Vaporizer-type LPG engines were prevalent in the past, but new injection systems directly injecting liquid-phase fuel into the intake port are being pursued to improve engine performance, charging efficiency, and cold start capability. Because liquid-phase LPG behaves somewhat differently from conventional liquid fuels, it is necessary to understand the spray characteristics and evaporating processes of the LPG for developing more efficient and lower emission LPG engines. With this goal in mind, an analysis of LPG spray injecting from a single injector was carried out. First, the LPG injection quantity was measured for four different injection pressures. Spray visualization experiments were then performed under atmospheric pressure to investigate how varying injection pressures affect the spray characteristics. The spray images show that LPG spray penetration length decreases with higher injection pressure. In addition, the higher injection pressure promotes fuel atomization, resulting in enhanced vaporization of the fuel. The results were validated using an optical line patternator, providing measured data in terms of a surface area per unit volume along the stream of the LPG spray, and they were in excellent agreement with the results obtained from the patternator. Elastic light-scattering technique was used to measure the spray droplet size as well. These results are surely expected to provide valuable information on macroscopic spray structure and design factors for developing liquid-phase LPG injectors and engines.