Studying the cyclic variability (CCV) of performance and NO and CO emissions in a methane-run high-speed SI engine via quasi-dimensional turbulent combustion modeling and two CCV influencing mechanisms

This work studies the cyclic variability otherwise cycle-by-cycle variations (CCV) of performance, combustion, and nitric oxide (NO) and carbon monoxide (CO) emissions in an experimental, high-speed, spark-ignition (SI) engine run on methane, for which relevant experimental data exist. For this purpose, use is made of an in-house, two-zone, quasi-dimensional turbulent combustion model that follows closely the flame-front movement, which has been previously validated performance-, emissions- and exergy-wise in spark-ignition engines. The model is extended here to investigate the CCV of performance, combustion, and main emissions of NO and CO. To this end, the influence on cyclic variability of two mechanisms of small-scale turbulence with its associated flame propagation and the inlet (fuel) equivalence ratio (EQR) fluctuations is considered assessing their effects. The numerical results are compared with the measured data of maximum cylinder pressure and indicated mean effective pressure (IMEP) for validation purposes, using the related coefficients of variation (COV), frequency distributions, and illustrative diagrams for their cycle to cycle variations. This methodology extends also the corresponding information onto the NO and CO emissions, over a wide range of EQRs, affording insight into the influence of the CCV mechanisms on this technologically significant phenomenon affecting adversely engines operation.