Investigation of a cold starting system for an indirect injection diesel engine: Using railplugs as an ignition source.

摘要

Diesel cold start difficulties can be attributed to: loss of battery capacity under cold weather; increase of lubricating oil viscosity, thus the increase of friction loss; cold inlet air temperature; high rate of energy loss through heat transfer to the cold combustion chamber wall; and fuel waxing at temperatures below {dollar}-30spcirc{dollar}C, resulting in either the inability to achieve autoignition or the incapability to attain self-sustained combustion. For conventional diesel engines, the dominating factor of cold start is the pre-ignition chemical delay. Therefore, the most energy effective way to aid diesel cold start is using a forced ignition source to reduce the chemical delay to its least. However, the conventional spark ignition system can hardly produce successful ignition and self-sustained combustion under borderline cold start conditions for diesel engines, especially the IDI diesel engines which have very strong turbulence but poor fuel injection characteristics, due to the different nature of igniting diesel fuel sprays compared to igniting premixed gasoline mixtures. In this dissertation work, a railplug system, a concept transferred from railgun technology, is developed and has been proved the ability of improving cold startability of the IDI diesel engines. A railplug was installed in the fourth cylinder of a VW IDI 1.6 liter engine and the cold startability of this engine was investigated through systematically designed experiments. The major advantages of the railplugs are the very high rate of energy deposit and the high speed plume of plasma which can penetrate into the gas deeply. Thus, it is capable of igniting the diesel fuel spray and enhancing the flame development at cold temperatures as proved by comparison of engine cold starting tests using glow plugs and railplugs respectively. Effects of various factors affecting diesel cold start and railplug performance were investigated through various experiments designed by Taguchi methods. An "optimum" strategy of arranging railplug ignition for this VW diesel engine has been established through engineering tests and analysis, and confirmed by confirmation tests. The investigation also showed that Taguchi method is a powerful tool to study complicated phenomena especially those with highly randomized nature.