LPG Spray Flames in Constant Volume Combustion Chamber Having Impinging Plate

The need for more fuel efficient and lower emission vehicles has driven the technical development of alternative fuels such as Liquefied Petroleum Gas which is able to meet the limits of better emission levels without many modifications to current engine design. This study addresses the LPG spray and diffusion flame in a constant volume combustion chamber which has an impinging plate. The spray and flame images are visualized and compared with diesel and gasoline images in the condition of wide ambient gas pressure range. The high speed digital camera is used to take the flame images. The injection pressure is generated by Haskel air driven pump, and the trap pressure is adjusted by pumping air into a constant volume chamber. The LPG spray and flame photographs are compared with those of gasoline and diesel fuel at the same conditions, then the spray and flame development behavior is analyzed.

The LPG spray photos show that the dispersion characteristics depend very sensuously on the ambient pressure soon after injection. In a low trap pressure LPG fuel in liquid phase evaporates quickly and does not reach down easily to the impinging plate having a hot coil for ignition. The quick evaporation makes the temperature low and the low spray penetration makes the equivalence ratio very low near the ignition coil and then makes the ignition hard. On the other side, in a high trap pressure the spray leaving the nozzle is remaining as liquid phase like a diesel fuel spray. The LPG gathers around the ignition site on the plate, which makes an intensive flame near the plate.

It is considered that the behavior of LPG spray might be more dependent on the gas flow motion than the spray injection velocity in the cylinder with low trap pressure. That phenomenon will be found easily on the early injection of a direct injection LPG engine. Therefore, the chamber and intake port shape might be careful to get a suitable flow motion for designing direct injection LPG engines.