Fuel-Induced System Response Issues: The Role Unconventional Fuels May Play in Altering Exhaust Conditions from Conventional and Low Temperature Modes of Combustion

Timothy  Jacobs, Texas A&M University

Unconventional fuels, such as biodiesel but including any “non-commercial diesel” fuel, may impose system-responses in an engine that unwittingly may change exhaust characteristics. For example, direct replacement of biodiesel in a diesel engine might cause the engine control module to alter injection timing, injection pressure, exhaust gas recirculation level, and / or variable geometry turbocharger vane position. Adjustments to any of these parameters will influence combustion characteristics and ultimately affect exhaust temperatures and potentially species. The issue becomes further complicated when novel modes of combustion, such as low temperature combustion, are developed for use in diesel engines and then coupled with unconventional fuels. For example, a low-NOx / low-soot (i.e., low temperature) combustion mode operating with petroleum diesel has a different exhaust temperature characteristic than that of biodiesel, mostly due to biodiesel’s different low temperature combustion characteristics (in spite of having similar NOx and soot levels). Further, biodiesel in general (regardless of mode of combustion) has different hydrocarbon and carbon monoxide concentrations.

This presentation will highlight the fuel properties that are largely responsible for manifesting such changes in engine system and combustion behaviors. Major results will highlight exhaust temperature, hydrocarbon, carbon monoxide, and oxides of nitrogen characteristics for conventional and low temperature modes with both petroleum diesel and biodiesel fuels. Analysis of heat release, along with study of the engine control parameters, are used to explain the exhaust characteristics.

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