Speciation Analysis of Light Hydrocarbons and Hydrogen Production During Diesel Low Temperature Combustion

The simultaneous reduction in engine-out NOx and soot emissions with diesel low temperature combustion (LTC) is generally accompanied by high levels of hydrocarbon (THC) and carbon monoxide (CO) emissions in the exhaust. To achieve clean diesel combustion in terms of low regulated emissions (NOx, soot, THC, and CO), the exhaust combustibles must be dealt with the exhaust aftertreatment (typically a diesel oxidation catalyst). In this work, engine tests were performed to realize LTC on a single-cylinder common-rail diesel engine up to 12 bar IMEP. A single-shot fuel injection strategy was employed to push the diesel cycles into LTC with exhaust gas recirculation (EGR). The combustibles in the exhaust were generally found to increase with the LTC load and were observed to be a function of the overall equivalence ratio. A Fourier transform infrared (FTIR) spectroscopy analysis of light hydrocarbon emissions found methane to constitute a significant component of the hydrocarbon emissions under the tested LTC conditions. The relative fraction of individual species in the hydrocarbons also changed, indicating a richer combustion zone and a reduction in engine-out THC reactivity. The hydrogen production was found to correlate consistently with the CO emissions, largely independent of the boost pressure or engine load under the tested LTC conditions. This research intends to identify the major constituents of the THC emissions and highlight the possible impact on exhaust aftertreatment.