Alternative Diesel Fuel Combustion Acceptance Criteria for New Fuels in Legacy Diesel Engines

Alternative diesel fuels from various renewable sources have recently been achieving high volume production status. These fuels are generally paraffinic in nature, and are notably absent of aromatic and cyclo-paraffinic hydrocarbon compounds. Combustion differences exist with these new fuels. Ignition delay and combustion duration are often different than conventional fuels leading to changes in combustion phasing and thus differences in engine brake metrics. How much of an indicated combustion change is acceptable? Currently no alternative fuel combustion acceptance criteria or metrics exist for new alternative fuels in diesel engines. In this paper a proposed set of indicated combustion acceptance criteria is presented with companion data from two new hydro-treated renewable fuels in a legacy military diesel engine. The three combustion criteria are: 1. relative change in ignition delay, 2. Angle of Peak pressure (AOP location) and 3. relative maximum rate of heat release. The relative change criteria are compared to experimental base engine-fuel data. The "green" acceptable range for ignition delay variation is ±20% relative change, AOP must stay in the range of 4° to 18° ATC, and the acceptable relative maximum heat release change is ±15% as compared to the base fuel performance. Combustion changes in the "green" range typically represent ±10% changes in brake metrics (BMEP and BSFC). Additionally, metric ranges for "yellow" and "red" are presented with minimal discussion, as they don't directly apply to the new fuels presented.