A modern common-rail diesel engine was used to investigate hydrocarbon emissions under low temperature diesel combustion conditions. In this work, various EGR ratios and fuel mixing strategies were applied under a series of fixed-load conditions to progressively lower the flame temperature, which is verified by progressively reduced NOx emission. During the tests, the concentrations of total hydrocarbons, representative light hydrocarbon species (methane, acetylene, and ethylene), and hydrogen gas were measured with a set of emission analyzers, FTIR, and H2 mass-spectrometer. The trend for light hydrocarbon emissions was identified to be a function of both load and EGR ratio. Hydrogen gas can be emitted in significant quantities with the application of very high EGR. Under ultra-low NOx production conditions for medium and high load conditions, the light hydrocarbon species can account for the majority of hydrocarbon emissions.

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