PREMIER Combustion of Natural Gas Ignited with Diesel Fuel in a Dual Fuel Engine -Effects of EGR and Supercharging on End-gas Auto Ignition and Thermal Efficiency

To control the auto ignition in end-gas region and to achieve higher thermal efficiency in a natural gas dual fuel engine operated under PREMIER combustion mode where the end-gas auto ignition occurs without knocking-like oscillation, the EGR (exhaust gas recirculation) and supercharging were applied. The EGR rate and the intake air pressure as well as the pilot injection timing of diesel fuel were varied, and the profiles of the in-cylinder pressure, the exhaust emissions and the heat balance were examined at the indicated mean effective pressure around 680 kPa. The experimental results showed that higher thermal efficiency can be achieved with the combination of the PREMIER combustion and the EGR rate of 30% due to the improvements in the combustion efficiency and the degree of constant volume heat release while reducing the cooling loss. It was elucidated that the PREMIER combustion with the optimum level of the supercharging maintains the higher combustion efficiency, higher degree of constant volume heat release, and lower COV of IMEP, and it is possible to achieve the higher thermal efficiency with the optimized combination of supercharging and pilot injection timing.