Optimizing the Compression Ratio of a CNG Converted Diesel Engine

Abstract

An experimental investigation on optimizing the compression ratio (CR) of diesel to retrofitted complete CNG converted engine was conducted. The investigation was done by experimental setup buildup. In the present experimental study a CNG converted diesel engine (HINO WO4D, 4.009 liter) was used for investigation. The modified diesel engine was fitted with a 3-stage diaphragm type pressure regulator CNG fuel system, a mixing chamber with throttle and a spark ignition system. The converted engine was run only CNG. The existing diesel engine compression ratio of 19.2 would be reduced to a range between 11 to 13. The clearance volume in the cylinder was increased by removing the material from the piston top surface, while keeping the stroke lengths the same. During change of each piston set the gaskets, piston rings and lubricating oil was changed to keep the physical parameters to be identical. Engine performance measurements were taken for each set of compression ratios using a hydraulic dynamometer setup with necessary instrumentation. The wide open throttle conditions were used for evaluation of engine performance. A theoretical study of the comparative analysis of the stresses on the piston top was done for different piston top thicknesses and all was found within safe range. The investigation was carried out in wide open throttle (WOT ) and 1450 to 2300 rpm as better running condition and data obtained was compared within three CRs and the better or optimum performance CR setup was selected. Basing on the peak pressure, volumetric efficiency , brake specific fuel consumption (Bsfc) and temperature distribution for CR=12 was considered as an optimized performance setup for a diesel bus engine converted to CNG.