The Effects of Reingested Particles on Emissions from a Heavy-Duty Direct Injection of Natural Gas Engine

The use of exhaust gas recirculation (EGR) to control NO_x emissions from direct-injection engines results in the reintroduction of exhaust particulate matter (PM) into the intake manifold. The influence of this recirculated PM on emissions from a pilot-ignited direct injection of natural gas engine was studied by installing a filter in the EGR system. Comparison tests at fixed engine conditions were conducted to identify differences between filtered and unfiltered EGR. No significant variations in gaseous or PM mass emissions were detected. This indicates that the recirculated PM is not contributing substantially to the increases in PM mass emissions commonly observed with EGR. Reductions in black carbon and ultra-fine particle exhaust concentrations in the exhaust were observed at the highest EGR fractions with the filter installed. This reduction suggests that with unfiltered EGR a fraction of the recirculated carbonaceous particles may be passing unreacted through the combustion chamber.