Visualization Of Fuel Spray For Multi-port Liquid Phase LPG Injection Engine

Liquefied petroleum gas (LPG) has been considered one of the excellent alternative vehicle fuels for its lower fuel cost and emissions compared with the traditional petroleum fuels. Comparing to the original gasoline engine, a main problem of the most common being used LPG engines which are converted from the gasoline engine with a mixer or a gaseous phase injection fuel supply system, is the power loss. In contrast, multi-port liquid phase LPG injection (MPLI) seems to be a better choice of the fuel supply system since it will not bring such a problem. However, the flashing of the liquid phase LPG makes the spray characteristics widely different from the gasoline's. Spray process has significant effect on combustion and emissions of the engine, so it is very necessary and important to understand the LPG's spray characteristics to control the fuel injection, optimize the combustion, improve the emissions and then exerts the fuel's potential. Therefore, the spray characteristics of LPG are investigated in this thesis using visualization method.With the flashing of liquid phase LPG, a gaseous LPG layer will be formed around the LPG spray body. To observe this layer as well as the spray behavior, the schlieren photography, a method that is very sensitive to refraction index gradient caused by density gradient in a transparent medium, is employed to set up a visualization test apparatus to capture spray images. A control device is designed to trigger the injector and the CCD camera according to a certain time sequence to obtain the spray image at a certain instant. The error analysis is also done to improve the reliability of the experimental results. Based on these, the spray image sequences, with a time interval of 0.1ms, are obtained for two injectors, a single-hole one and a double-hole one, under three injection pressures, 0.5Mpa, 1.0Mpa and 2.0Mpa, respectively.In addition to spray tip penetration and spray angle, another two parameters, projected spray area and spray volume, are also presented to describe the spray. The definitions and calculation algorithms of the two new parameters are given, too. Besides, according to the actual configuration of the spray, the spray angle for LPG spray is redefined.To calculate the four parameters in terms of the given calculation algorithms, the spray outline is obtained and then coordinatized using digital image processing techniques. Comparing the calculation results to manual measurement results, the maximum difference between the two methods is 5.01%, and the most of the differences are within±3%. This proves the accuracy of the calculation algorithms and the creditability of the obtained spray outline. In addition, the comparison also shows that the digital calculation method has efficiency that at least 25 times more than the manual method.By analyzing the calculation results, the following conclusions are made. (1) With the injection pressure increasing, the spray tip penetration, the projected spray area and the spray volume are all increased while the spray angle is decreased. (2) Double-hole injector has better atomization effect than single-hole injector on the fuel spray because the impingement of spray with flow split head of double-hole injector has promoted the atomization and evaporation of liquid phase LPG. Therefore, it will produce a more homogeneous air-fuel mixture. (3) For the same reason of impingement, under the observation with schlieren technique, the spray tip penetration of double-hole injector is longer than that of single-hole injector in a period at the early injection stage.