Trade-off Improvements by Combining EGR and Supercharging Ignited by Next Generation Bio-alcohol Blended FAME Fuels in Diesel Dual Fuel Operation Using Natural Gas

Studies in diesel dual fuel (DDF) operation which introduce compressed natural gas (CNG) from the intake pipe and ignite it by a diesel fuel injection in the combustion chamber have been conducted using conventional diesel engines. The present study investigated the effects of trade-off improvements between NOx and smoke emissions with next generation bio-alcohol blended FAME fuels ignition in DDF operation with a combination of EGR and supercharging. The CNG supply rates were set at 0% (ordinary diesel operation) and at 41-44% (DDF operation) on a heat energy basis, the boost pressures were set to two conditions with supercharger operation: 100 kPa (naturally aspirated operation, N/A) or 120 kPa (supercharged operation, S/C), and the EGR rates were varied from 0 to 25%. Blended fuels with a base fuel vs. alcohol ratio of 7: 3 were prepared using what in the following is termed PLME containing equal proportions of methyl palmitate (PME) and methyl laurate (LME) as the base fuel. The next-generation bio-alcohols used here were iso-pentanol (C5) and iso-butanol (C4), and the engine performance, combustion characteristics, and exhaust emissions were investigated with iso-pentanol blended PLME (termed PLiP30), iso-butanol blended PLME (PLiB30), and neat PLME, as the ignition fuel. The results showed that regardless of ignition fuel, the DDF operation combining cooled EGR and supercharging improved the trade-off relation between NOx and smoke emissions significantly while maintaining relatively high brake thermal efficiencies.