The Effects of Varying EGR Test Conditions on a Direct Injection of Natural Gas Heavy-Duty Engine with High EGR Levels

Determining what exhaust gas recirculation (EGR) control parameters have the largest impact on engine performance and emissions is of critical importance when developing an EGR-equipped engine. These tests studied the effects of varying the net charge mass, the fresh air charge mass, the indicated power, and the oxygen equivalence ratio at various EGR fractions. The research was carried out on a direct-injection, natural gas fuelled, pilot-ignited four-stroke heavy-duty engine using Westport Innovations Inc.'s pilot-ignited, direct injection of natural gas technology. The testing was carried out using a prototype injector and the standard diesel-fuelled engine's combustion chamber. The results indicate that fuel efficiency, as well as emissions of Nitrogen Oxides (NO_x) and Carbon Monoxide (CO) depend primarily on the EGR level, and not on the values of the EGR control parameters. Total Hydrocarbon (tHC) and particulate matter (PM) emissions were more dependant on the parameter combination, due primarily to changes in the combustion heat release rate and in the ignition delay time.