Experimental Investigation of Combustion Characteristics of Homogenous Charge Compression Ignition Engine

Abstract

In diesel compression ignition engine, simultaneous reduction of NOx and PM is extremely challenging task. The most favorable solution for this is HCCI. It is an impulsive auto ignition of very lean air fuel mixture at multiple sites. It has advantages of both CI and SI engines. It also gives higher thermal efficiency like CI engines, higher ROHR, minimum DOC and has no flame propagation and mainly it has simultaneous control over NOx as well as PM. The combustion of homogeneous mixture in HCCI combustion helps in reducing DOC because of higher ROHR. The present experiment is conducted on engine having two cylinders; they are made to operate on HCCI and conventional CI mode respectively. Both DI and PI systems were used simultaneously to investigate the performance characteristics. The toughest part is to prepare homogeneous mixture for combustion. As the diesel is a low volatile fuel, the preparation of homogeneous mixture is difficult therefore diesel vaporizer comes into picture. EGR is used to control the ROHR. To investigate the combustion characteristics experiment was performed at different relative air fuel ratios (λ). The DOC and ROHR is increases with increasing λ. EGR dilutes the homogeneous mixture and leads to minimum NOx emission by keeping maximum temperature in cylinder low. The increased boost pressure is responsible for short DOC and high rate of combustion. Also the indicated mean effective pressure is improved by 3% by DI method as compared to PI in HCCI.