Influence of Boost Pressure on the Combustion Characteristics of a Dual Fuel Diesel Engine Ignited by Biofuels with Natural Gas

抄録

This paper describes the results of supercharging applied to dual fuel diesel combustion using natural gas (CNG) introduced from an intake-pipe. To ignite the CNG-air premixed-mixture formed in the cylinder, the experiments used coconut oil methyl ester (CME), a blended fuel with 60 mass% CME and 40 mass%1-butanol (termed CMEB), and standard JIS No. 2 diesel fuel as the ignition fuel. The boost pressures were varied from 100 kPa (naturally aspirated condition) to 130 kPa with a Roots blower type supercharger driven by a motor. The influence of the kind of ignition fuel and boost pressure on the engine performance, combustion characteristics, and emissions were investigated at different CNG supply rates. The results showed that at the naturally aspirated condition, the brake thermal efficiency with the CME and diesel fuel is maintained at a high value even when the CNG supply is increased up to 80%. Regardless of the kind of ignition fuel, however, the brake thermal efficiency under supercharged operation decreased linearly with increasing CNG supply due to significant increases in HC and CO emissions. The ignition delay with CMEB at naturally aspirated operation was much longer than with CME and diesel fuel, and this tendency was enhanced with increasing CNG supply. When supercharging was employed, the ignition delay with CMEB shortened remarkably and the combustion characteristics improved markedly.