The effects of post injection on the combustion efficiency, exhaust emissions, and in-cylinder hydrogen generation were experimentally investigated in a modern heavy duty diesel engine. As the post injection was moved away from top dead center (TDC), the test results generally showed increasing carbon monoxide (CO) and total hydrocarbons (THC), fairly constant nitrogen oxide (NOx) emissions while the smoke emissions were more sensitive to the post injection timing. Hydrogen production was observed to be higher at later post injection timings. In a majority of instances, hydrogen production and carbon monoxide formation were very well correlated. Additional tests explored the effects of the overall air-to-fuel ratio on the in-cylinder hydrogen production and the experimental results indicated that a lower air-to-fuel ratio seemed to promote the in-cylinder generation of hydrogen. However, the increased hydrogen production was offset by less efficient power production from the post injection combustion. A Fourier transform infrared (FTIR) spectroscopy analysis of hydrocarbon emissions was carried out in an attempt to determine the effects of diesel post injection timing on individual light hydrocarbon species.

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