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UBC Theses and Dissertations

Characterization of fuel injection and premixing in direct-injected dual-fuel natural gas engines using in-cylinder infrared absorption and high speed Schlieren imaging Knight, Matthew Rockwell


Anthropogenic climate change has become an increasingly dire challenge in recent decades motivating research on alternative fuel sources for heavy-duty engines. Compared with traditional diesel, natural gas (NG) offers an abundant, inexpensive alternative with potential for lower CO₂ emissions [1]. The main objectives of this work are to develop techniques to characterize gaseous fuel injection and premixing processes for pilot-ignited direct-injection NG (PIDING) engines, describe how these processes are affected by injection parameters and combustion chamber geometry and how they affect engine performance metrics such as emissions and efficiency. While the research presented here is focused on NG, the results are applicable to other lower carbon gaseous fuel sources such as H₂, biomethane, etc. with some adaptation. Gas premixing was investigated through local infrared absorption measurements of fuel concentration (using the LaVision internal combustion optical sensor (ICOS)) in an optically accessible research engine using high-pressure direct injection (HPDI) of NG and diesel. Engine measurements were performed with varying relative injection timing (RIT) across several previously identified combustion regimes [2]. High speed imaging techniques (Schlieren and background-oriented Schlieren (BOS)) were developed to describe the effects of combustion chamber geometry on gas injection and mixing. Techniques were developed using ICOS measurements to characterize the level of NG premixing at varying RIT. When NG jets impinged within the piston bowl, increasing NG premixing was shown to correlate with increasing gross indicated efficiency (ηi,g), increasing NOᵪ emissions and decreasing CO emissions while having a comparatively small impact on CH₄ emissions. The piston bowl shape was found to affect gas mixing, including whether jets are directed into the topland region above the piston bowl. When jets enter the topland, much of the jet was shown to become entrapped with large residence times leading to incomplete fuel oxidation. This in turn leads to higher emissions of CH₄ and reduced ηi,g relative to when jets impinge within the piston bowl. The experimental systems developed throughout this report offer a framework for further study of novel piston bowl designs and the effects of combustion chamber geometry on gas injection and mixing.

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