Source Apportionment of Particulate Matter from a Diesel Pilot-Ignited Natural Gas Fuelled Heavy Duty DI Engine 2005-01-2149

In recent years there has been a growing awareness that particulate matter, especially fine diesel particulate, is a health concern. This has stimulated research to develop new technologies to reduce particulate emissions without increasing nitrogen oxide (NO_x) emissions or fuel consumption.

Westport Innovations has developed a technology involving high pressure direct injection and combustion of natural gas for medium and heavy-duty engine platforms. At practical compression ratios, the natural gas will not auto-ignite, so a diesel pilot injection is used for ignition. Thus, the soot emissions can have contributions from the combustion of natural gas, diesel pilot, or lubricating oil. While the soot emissions with natural gas as the main fuel are significantly lower than in a conventional diesel engine, it remains important to determine where the soot is coming from to aid in emission reduction strategies. In this study, the contribution of the pilot fuel (a biodiesel blend with higher ¹⁴C content than diesel fuel) was determined using accelerator mass spectrometry (AMS) measurements of ¹⁴C in the exhaust particulate.

Results indicate that the pilot fuel contribution to soot ranges from 4-40% over the tested operating conditions; correspondingly, the contribution by natural gas and lubricating oil combined ranges from 60-96%. The highest fraction of soot from the pilot source is at low load without exhaust gas recirculation. The lowest fraction of soot from the pilot source is at high load with exhaust gas recirculation, i.e. the conditions contributing most to mode-averaged emissions.