A study on homogeneous charge compression ignition HCCI combustion of diesel fuel with external mixture formation

Abstract

Conventional diesel engines operate at higher compression ratios than SI engines. In this type of engine, the air-fuel mixture auto-ignites because of piston compression instead of ignition by spark plug. These processes effectively limit the rate of combustion. The in-cylinder temperature in a conventional diesel engine is about 2700 K, which leads to a significant production of Oxides of Nitrogen (NOx) emissions. For diesel engines, a trade-off made between NOx and soot. After treatment systems are used in the modern day engines which are expensive. Consequently, the obvious ideal combination would be to find an engine type with high efficiency as that of diesel engines and very low emissions as that of gasoline engines with catalytic converters. One such technology is homogeneous charge compression ignition (HCCI). In the present work, homogeneous mixture was prepared outside the combustion chamber (External mixture formation) by using Ultrasonic fuel injection (USFI) system and Diesel fuel vapouriser system. The key to the external mixture formation method with diesel is proper fuel preparation. In the first approach, the Ultra sonic atomiser receives diesel fuel in liquid state and by means of ultrasonic vibration energy, performs work on the fuel, transforming it to a highly atomised state and then effectively mixing with air to form a more uniform fuel- air mixture. Similarly, in the second approach, the Diesel fuel vapouriser receives fuel in liquid state and it converts into vapour form by means of an external power source, and effectively mixes with the incoming air to form a uniform fuel-air mixture. The experimental results show that, NOx and smoke reduces by about 80 % and 92 % respectively with USFI system. Whereas, in Diesel fuel vapouriser (DFV) system, the NOx and smoke reduction is about 95 % and 83 % respectively. The engine operated from no load to 75 % load without any problem in the case of diesel fuel vaporiser system, whereas in USFI system the engine operated between 25% to 75% load on