No x. reduction from a heavy-duty diesel engine with direct injection of natural gas and cooled exhaust gas recirculation

Abstract

Abstract

A heavy-duty ISX diesel engine has been commissioned for single-cylinder operation fuelled with pilot diesel ignited natural gas injected directly into the cylinder. The stock ISX engine was modified by replacing the diesel fuelling system with a high-pressure natural gas system, replacing the turbocharger with an independently controlled supercharger and installing a variable-flow exhaust gas recirculation (EGR) system. A study of the impact of cooled EGR on engine performance and gaseous emissions was carried out. Various engine speeds, loads and injection timings were tested over a range of EGR fractions. A preliminary study of the effect of EGR ‘type’—supplemental or replacement—was also carried out. The results indicate that the NO_x emissions varied linearly with the intake oxygen mass fraction (representative of the EGR fraction) until NO_x emissions reached 20 per cent of their non-EGR levels. Further NO_x reductions were achieved with higher EGR fractions, but the rate of reduction was significantly reduced. The NO_x reductions were found to be independent of engine speed and load. An overall activation energy for NO_x formation was determined by correlating the NO_x reductions with a representative flame temperature. The emissions of combustion by-products, including carbon monoxide (CO) and unburned total hydrocarbons (THC) increased significantly at higher EGR fractions. The engine performance and efficiency were not significantly affected except at very high EGR fractions.