Engine knock remains one of the major barriers to further improve the thermal efficiency of spark-ignition (SI) engines. SI engine is usually operated at knock-limited spark advance (KLSA) to achieve possibly maximum efficiency with given engine hardware and fuel properties. Co-optimization of fuels and engines is promising to improve engine efficiency, and predictive computational fluid dynamics (CFD) models can be used to facilitate this process. However, cyclic variability of SI engine demands that multicycle results are required to capture the extreme conditions. In addition, Mach Courant–Friedrichs–Lewy (CFL) number of 1 is desired to accurately predict the knock intensity (KI), resulting in unaffordable computational cost. In this study, a new approach to numerically predict KLSA using large Mach CFL of 50 with ten consecutive cycle simulation is proposed. This approach is validated against the experimental data for a boosted SI engine at multiple loads and spark timings with good agreements in terms of cylinder pressure, combustion phasing, and cyclic variation. Engine knock is predicted with early spark timing, indicated by significant pressure oscillation and end-gas heat release. Maximum amplitude of pressure oscillation analysis is performed to quantify the KI, and the slope change point in KI extrema is used to indicate the KLSA accurately. Using a smaller Mach CFL number of 5 also results in the same conclusions, thus demonstrating that this approach is insensitive to the Mach CFL number. The use of large Mach CFL number allows us to achieve fast turn-around time for multicycle engine CFD simulations.
Prediction of Cyclic Variability and Knock-Limited Spark Advance in a Spark-Ignition Engine
Contributed by the Internal Combustion Engine Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received March 20, 2019; final manuscript received March 29, 2019; published online April 18, 2019. Assoc. Editor: Hameed Metghalchi. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.
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Yue, Z., Edwards, K. D., Sluders, C. S., and Som, S. (April 18, 2019). "Prediction of Cyclic Variability and Knock-Limited Spark Advance in a Spark-Ignition Engine." ASME. J. Energy Resour. Technol. October 2019; 141(10): 102201. https://doi.org/10.1115/1.4043393
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