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Influence of Trapped Residual Gasses in Air-Diluted Spark Ignited Combustion
ISSN: 1946-3936, e-ISSN: 1946-3944
To be published on November 18, 2022 by SAE International in United States
Citation: Clasén, K. and Koopmans, L., "Influence of Trapped Residual Gasses in Air-Diluted Spark Ignited Combustion," SAE Int. J. Engines 15(6):2022.
Homogeneous air-diluted spark ignition (SI) is one advanced combustion concept that is recognized for its potential of efficiency improvement, which can be utilized in the next-generation, affordable, light-duty propulsion systems. However, cyclic dispersion and high-load end-gas autoignition of diluted combustion remain a challenge, preventing necessary nitric oxide (NO) emission suppression, which, in turn, obstructs market penetration. It is well known that trapped residual gasses (RG) in the cylinder influence the cyclic dispersion of combustion by contributing to the total amount of charge dilution which influences the total mean flame speed and thereby the combustion sensitivity to cyclic perturbations. However, the amount of trapped RG in the cylinder is difficult to measure, and therefore, its influence is complicated to assess. In lean combustion research, the presence of RG is often acknowledged, but few studies have investigated the influence of a combined dilution of RG and air. This article aims at assessing the influence of trapped RG on lean combustion through combining engine experiments with one-dimensional (1D) computer simulations using a three-pressure analysis (TPA). A TPA utilizes experimentally acquired data such as crank angle-resolved port and cylinder pressures to minimize the scope of discretization and predictability of the model to improve accuracy. The experimental results were replicated in the simulation and quantities, such as residual gas fraction (RGF) and total trapped in-cylinder mass, were estimated.
From the performed engine experiments and corresponding simulations, it has been concluded that RG have a substantial influence on combustion. The total dilution, the blend of residuals and air, is highly correlated to nitrogen oxides (NOx) emissions at all investigated operating conditions. Additionally, at low loads, the total dilution correlates with the dilution stability limit, rather than air-dilution solely. At high loads, residuals contribute little to the total dilution, but have been linked to the increased propensity of knock.