22. Experimental Investigation of a Diesel Engine Run on Simulated Gaseous Fuels Under Varying Compression Ratio

This research work attempts to explore the combined effect of engine load and compression ratio (CR) on the performance, combustion, and emission characteristics of a 3.5 kW diesel engine utilizing simulated biogas (SBG), simulated producer gas (SPG), and SPG-SBG mixture under dual fuel (DF) mode. The compositions of the gaseous fuels are prepared based on the volumetric percentage of the individual gas components and are inducted into the engine cylinder using a novel venturi-type air-gas mixer. For the preparation of SBG, methane (CH₄) and carbon dioxide (CO₂) are mixed at a 70:30 ratio. Similarly, hydrogen (H₂) and carbon monoxide (CO) are also mixed at a 70:30 ratio for the preparation of SPG. Again, H₂ and CO at a 50:50 ratio are mixed with a 70:30 ratio of CH₄ and CO₂ to simulate the SPG-SBG mixture. Engine experiments are executed at five different loads, viz. 20%, 40%, 60%, 80%, and 100%, and four different CRs, viz. 16, 17, 17.5, and 18, at a standard injection timing (IT) of 23° BTDC. Maximum brake thermal efficiency (BTE) and pilot fuel replacement (PFR) are obtained at 100% load and CR of 18. At this operating condition, SBG, SPG, and SPG-SBG mixture showed a BTE of 20.66%, 20.94%, and 22.11% respectively, and PFR of 89.76%, 81.44%, and 84.36% respectively. The combustion data indicated a decrement in ignition delay (ID) with an increase in CR. It has also been observed that SBG, SPG, and SPG-SBG mixture showed an average decrease of 10.51%, 9.93%, and 11.16%, respectively, of unburned carbon monoxide (CO) emission when the CR is raised from 16 to 18. Similarly, an average unburned hydrocarbon (HC) emission reduction is obtained to be 16.13%, 13.01%, and 20.07% for SBG, SPG, and SPG-SBG mixture, respectively.