Particulate matter emission characterization from a natural-gas high-pressure direct-injection engine

• Main Author: Patychuk, Bronson David
• Language: English
• Published: University of British Columbia 2013
• Online Access: http://hdl.handle.net/2429/44341

Stringent regulations have been enacted to reduce particulate matter (PM) emissions from heavy-duty compression-ignition (CI) engines. New regulations (Euro VI) restrict PM mass and particle number concentration. To help meet these regulations, a greater understanding of the physical and chemical characteristics of the PM is desired. This thesis is concerned with the mobility, morphology (by electron microscopy), mass (filter sampling), light scattering and semivolatile content of the particles. Natural gas has become an increasingly attractive transportation fuel for both environmental and economic reasons. One technology to utilize gaseous fuels in heavy-duty engines is Westport Innovations Inc.’s High Pressure Direct Injection (HPDI™) system. This is a system where the natural gas is directly injected late in the compression stroke and ignition of the natural gas is provided by a diesel pilot. PM emissions were characterized from a heavy-duty Cummins ISX engine converted to single cylinder operation and operating under HPDI™ fueling. Tests were performed to observe the effects of speed and load combinations, the effects of operating parameter variations (Injection timing, equivalence ratio, gas supply pressure, EGR % and diesel injection mass) and the effects of fuel premixing on the PM emissions. Engine load was more important than speed for qualitatively grouping the PM emission characteristics (mass, number, semi-volatile fraction). The exception is at low engine speeds where low mass and number concentrations were observed, along with nearly constant particle sizes, across different loads. The effects of the input parameter variations were analyzed with response surface methods. The PM emissions were more sensitive to changes in the input parameters than the gaseous emissions. Equivalence ratio, engine power and injection pressure were the most important parameters for PM mass emissions. Overall, the PM emissions varied monotonically with the input parameters and no local PM emission minima were observed. Partially premixing some of the natural gas before ignition can reduce PM emissions by over 80% at some conditions at the expense of cycle-to-cycle variability and pressure rise rates. Some optimized equivalence ratios and EGR percentages were developed to improve the stability of combustion.