Abstract
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.
Highlights
From the viewpoints of CO2 emission reductions and energy security, natural gas could be a promising alternative fuel for internal combustion engines
As the injection fuel, the experiments here used JIS No 2 diesel fuel as a reference, neat PLME, PLiP30 (70% PLME and 30% iso-pentanol blend), and PLiB30 (70% PLME and 30% iso-butanol blend); the supercharger power input was not considered in the thermal efficiency calculations
A diesel dual fuel engine with compressed natural gas (CNG) introduced from the intake pipe was operated by combining cooled EGR and supercharging with ignition fuels with generation bio-alcohol blended fatty acid methyl esters (FAMEs) fuels
Summary
From the viewpoints of CO2 emission reductions and energy security, natural gas could be a promising alternative fuel for internal combustion engines. A number of studies of diesel dual fuel operation (DDF) which introduce compressed natural gas (CNG) from the intake pipe and ignite it by a liquid fuel injected into the combustion chamber and have used conventional diesel engines. Paul et al (2014) have conducted a study to apply pongamia pinnata methyl ester (PPME) as an ignition fuel to a diesel dual fuel engine in which CNG, as the primary fuel, is injected into the intake pipe. In the PPME-CNG mode, the brake thermal efficiency increased, as well as the smoke opacity, CO emissions, and unburned hydrocarbon emissions significantly reduced, in total showing this as more effective in improving engine performance and emission characteristics than DieselCNG dual fuel mode. The results showed that compared with conventional diesel fuel, the biodiesel blends improved SPL, vibration acceleration, and CO emissions over those of ordinary diesel operation. The above features of DDF engines would suit cogeneration systems well, but substantial reductions in NOx emissions will be needed for this to be adopted
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