Effects of CO2 ratio in Biogas on Performance, Combustion and Emissions of a Dual-Fuel Diesel Engine

In this study, biogas was generated by anaerobic co-digestion process of pig manure and corn straw. The biogas was used as an alternative gaseous fuel in a DI (direct injection) turbocharged diesel engine, in the dual fuel mode with diesel as pilot fuel. Three compositions of biogas generated from pig manure and corn straw: 45BG55CO 2 , 50BG50CO 2 and 60BGCO 2 (containing 45%, 50% and 60% of methane (CH 4 ) by volume respectively) and two compositions of enriched biogas: 75BG25CO2 and 85BG15CO 2 (containing 75% and 85% of CH 4 by volume) were used. The effects of carbon dioxide (CO 2 ) ratio in biogas on combustion, performance and emission characteristics of the engine in the dual fuel operation were numerically analyzed at four various engine loads (0.425, 0.85, 1.275 and 1.7MPa ), and compared with that of diesel fuel operation. The numerical simulations were carried out using GT-Power commercial package. The results showed that the BTE values for biogas-diesel fuel operations were found to be higher compared to that of diesel fuel operation. The BTE was not considerably impacted by CO 2 ratio. The highest BTE value of 38.22% was recorded for 45BG55CO 2 (45% methane and 55% CO 2 ). The exhaust gas temperatures (EGT) of the biogas-diesel fuels were found to be 8.5-20.3% lower than that of the diesel fuel operation at higher load condition. With respect to emissions, The NO X (Nitrogen oxides) and carbon monoxide (CO) emissions in the dual fuel operation were found to be lower by about 55.3-83.3% and 73.1-97.4%, compared to that of diesel operation. However, the unburned hydrocarbons (HC) and carbon dioxide (CO 2 ) discharges of dual-fuel operation were found to be higher by average of 349.7% and 39.8% respectively. The utilization of biogas with diesel by all accounts is attractive to cut down discharges and improve performance of the engine. The engine performance did not deteriorate with up to 45% CO 2 content biogas.