Combustion and Emissions Performance of Simulated Syngas/Diesel Dual Fuels in a CI Engine

Small diesel engines are a common primer for micro and mini-grid systems, which can supply affordable electricity to rural and remote areas, especially in developing countries. These diesel generators have no exhaust after-treatment system thus exhaust emissions are high. This paper investigates the potential of introducing simulated synthetic gas (syngas) to diesel in a small diesel engine to explore the opportunities of widening fuel choices and reducing emissions using a 5.7kW single cylinder direct injection diesel generator engine. Three different simulated syngas blends (with varying hydrogen content) were prepared to represent the typical syngas compositions produced from downdraft gasification and were injected into the air inlet. In-cylinder pressure, ignition delay, premixed combustion, combustion stability, specific energy consumption (SEC), and gaseous and particle emissions were measured at various power settings and mixing ratios. Particle size distributions (PSD) were measured by DMS500, and gaseous emissions were measured by the HORIBA MEXA7100 series. The correlations between combustion and emission performance and mixing ratios and substitution ratios were investigated. Dual fuel operation led to a decrease in diesel consumption, thermal efficiency, NO_x, and NO emissions and an increase in THC and CO emissions. For all dual fuel tests, a reduction in the total particle number concentration (TPNC) was noted while the particle size distribution curves remained unchanged relative to diesel baseline data at all engine loads except for 30%. At 30% engine load, the change in the particle size distribution curves was dependent on the syngas blend used. The syngas with the highest hydrogen content showed superior combustion performance relative to the other syngas blends evaluated due to shorter ignition delay times and higher maximum in-cylinder pressure values, thus producing lower THC and CO emissions, but higher NO_x emissions.