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The use of pilot-ignited, direct-injected natural gas in a heavy-duty compression-ignition engine has been shown to reduce emissions while maintaining performance and efficiency. Adding recirculated exhaust gas (EGR) has been shown to further reduce emissions of nitric oxides (NOx), albeit at the cost of increased hydrocarbons (tHC), carbon monoxide (CO), and particulate matter (PM) emissions at high EGR fractions. Previous tests have suggested that reducing the delay between the diesel and natural gas injections, increasing the injection pressure, or adjusting the combustion timing have individually achieved substantial emissions benefits. To investigate the effectiveness of combining these techniques, and of using them over a wide range of operating conditions, a series of tests were carried out. The first set of tests investigated the interactions between these effects and the EGR fraction.

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 (NOx) and Carbon Monoxide (CO) depend primarily on the EGR level, and not on the values of the EGR control parameters.