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Multiple-Event Fuel Injection Investigations in a Highly-Dilute Diesel Low Temperature Combustion Regime
Abstract:
The objective of this research is a detailed investigation of multiple injections in a highly-dilute diesel low temperature combustion (LTC) regime. This research concentrates on understanding the performance and emissions benefits of multiple injections via experiments and simulations in a 0.48L signal cylinder light-duty engine operating at 2000 r/min and 5.5 bar IMEP. Controlled experiments in the single-cylinder engine are then combined with three computational tools, namely heat release analysis of measured cylinder pressure, a phenomenological spray model using in-cylinder thermodynamics [1], and KIVA-3V Chemkin CFD computations recently tested at LTC conditions [2]. This study examines the effects of fuel split distribution, injection event timing, rail pressure, and boost pressure which are each explored within a defined operation range in LTC. This research compliments simultaneous detailed unburned hydrocarbon research which concentrates on the mechanisms that control the formation of UHC during LTC engine operation [3].
Engine operating conditions for low UHC/CO from previous single injection experiments are observed using split (i.e., multiple-event) injections. Fuel split is defined by the fractional percentage of total fuel injected in the first event. For the split fuel injection experiments it is shown that both the timing and proportion of the fuel split largely impacts emissions and combustion; this is due to the change in injection penetration and momentum flux influencing the fuel distribution in the cylinder. Phenomenological engine spray model and CFD results show how fuel distribution and reactant mixing also strongly influence PM emissions. Non-negligible PM emissions occur when the split-injection fuel distribution produces locally richer regions very close to the start of combustion (SOC). Boost and injection pressure variation also impact the split-injection fuel distribution significantly. There are emissions tradeoffs over the entire split-injection timing range, but lower combustion noise trade-offs are only achieved with later (closer to TDC) fuel injection timings.