Effects of charge preheating on the performance of a biogas-diesel dual fuel CI engine

This study explores the viability of preheating the intake charge as a means to enhance the performance of a compression ignition (CI) engine operated on biogas and diesel in dual fuel mode. Biogas is the primary fuel, which is mixed with air in the intake, preheated and inducted into the engine. This mixture is compressed and subsequently ignited by means of pilot diesel injection within the cylinder. The influence of charge temperature and biogas flow rate on brake thermal efficiency, volumetric efficiency, diesel fuel consumption, diesel equivalent brake specific fuel consumption, exhaust gas temperature and overall equivalence ratio are investigated under two speeds and various loads. Charge preheating, low biogas flow rates and high speed operation are observed to enhance brake thermal efficiency. Methane enrichment is effective in improving thermal efficiency at low biogas flow rates. While charge preheating and increasing the biogas flow rate reduce diesel fuel consumption, volumetric efficiency is lowered. Displacement of air by biogas increases the overall equivalence ratio and exhaust gas temperature. Low speed mode is characterised by reduced diesel fuel consumption and high volumetric efficiency. Under low speed operation, biogas can provide more than 90% of the total energy release.