Effect of direct water injection at different crank angles on diesel engine emission and performance

Abstract

It is well known that in DI diesel engines the formation of NOx is chiefly due to the prevailing high pressure and temperature in the combustion chamber. The methods used for lowering NOx is by induction of water which is blended with diesel oil, which leads to longer delay period, improper combustion and lowered release of thermal energy of fuel thus lowering the efficiency of the engine. In overcoming above problems, a novel approach is proposed in this work in which water is directly injected into the combustion chamber just when the temperature and pressure of gases inside the combustion is about to rise to a peak value. This lowers the formation of NOx very effectively. Adding to this aspect, the water sprayed absorbs heat from the hot gases as well as from the hot metallic surfaces of the combustion chamber and becomes super-heated steam, which augments the pressure built up at a lower temperature. This will help in increasing the power output of the engine. Experiments have been conducted spraying water at different injection timings such as; at 0 degree and at 8 degrees before and after TDC. The quantity of water injected is varied in the ratio of diesel to water from 1:1 to 1:4. The study shows that injection of water before TDC has yielded better results. NOx has reduced by 85 % at 1:4 diesel to water ratio and also injection at 24 degree BTDC. Drop in brake thermal efficiency by 10% to 20% is observed when water ratio is increased from 1:1 to 1:4.