Investigation of the effects of biogas composition on the performance of a biogas-diesel dual fuel CI engine

In this study, biogas is used in a CI engine in dual fuel mode with diesel as pilot fuel. Biogas has been replicated using a mixture of methane (CH4) and carbon dioxide (CO2), whose flow rates can be independently varied. This helps in evaluating the effect of biogas composition on engine performance. Apart from the conventional diesel-only mode, the engine is operated in dual fuel mode with induction of (a) pure CH4 and (b) CH4 + CO2 mixtures with variable CH4: CO2 ratios, representing biogas. Dual fuel operation is observed to have better brake thermal efficiencies compared to diesel-only mode at high loads. Though volumetric efficiency is almost identical in diesel-only and diesel -CH4 dual modes, induction of biogas causes it to drop. Exhaust gas temperatures were higher in diesel-biogas mode, followed by diesel-methane and diesel-only modes. Dual fuel mode, especially with biogas, results in higher overall equivalence ratios. Compared to diesel-only mode, dual fuel mode has relatively high unaccounted losses at low loads, while exhaust and coolant losses are greater at high loads. Biogas composition does not significantly affect any of the above parameters except the exhaust gas temperature and air-fuel ratio, which show a slight increase with methane enrichment.