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Particulate matter emissions from a Cummins ISX 400 engine operating on high-pressure direct injection of natural gas with diesel pilot Baribeau, Anne-Marie

Abstract

High-pressure direct injection (HPDI) of natural gas coupled with diesel pilot injection is a promising method by which emissions of particulate matter (PM) and nitrogen oxides (NOx) can be reduced. In light of increasingly stringent U.S. EPA emissions regulations on heavy-duty diesel engines, there is great need to develop combustion strategies that reduce targeted pollutants; for heavy-duty engines these are namely PM and NOx. A gravimetric technique has been used in this investigation to measure the PM emissions from a Cummins ISX 400 engine converted to HPDI of natural gas with diesel pilot. The engine experiments have been run using the AVL 8-mode steady-state test protocol, which simulates the U.S. EPA heavy-duty transient test procedure. The repeatability of particulate matter emissions measurements from HPDI fuelling has been established, as well as the effect of varying injection pressure, timing and pilot diesel fuel quantity on PM emissions. In addition, the composition of the HPDI exhaust PM was analysed for fuel-like and oil-like volatile organic fraction (VOF) components using a direct capillary injection of filter-borne PM into a gas chromatograph/flame ionization detector (GC/FID) technique. The effect of retarding injection timing on PM emissions was not consistent across the range of engine operating conditions characterized by modes 1,4,5, and 8 of the AVL test. It was suspected that high cylinder pressures resulting from advanced fuel injection timing or unwanted fuel interaction with cylinder wall and piston surfaces was impeding good mixing between injected natural gas and air for the current engine geometry. Results also showed that increased injection pressure was a potential strategy for reducing PM emissions, but for high load test points and the current engine geometry, a suspected air/fuel mixing problem may have produced higher PM emissions than expected. The difference in the PM emissions for these three injected pilot fuel quantities was not statistically significant, so no conclusions were drawn regarding the effect of increasing the pilot fuel quantity on PM emissions. Finally, the VOF of total PM mass emissions from HPDI combustion was between 34-58% based on analyses using modes 1,4,5,8 of the AVL 8-mode test.

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