Modeling of the turbulent burning velocity considering the effect of fuel composition in EGR condition

Abstract

To reduce CO2 emissions, it is essential to enhance the thermal efficiency of internal combustion engines and utilize carbon-neutral fuels. Recent studies have shown that blending fuels with oxygenated components can extend the lean operating limit. This extension is partly attributed to the increased turbulent burning velocity, as indicated by the shorter combustion duration observed with such fuels. Similarly, an increase in turbulent burning velocity may also help expand the Exhaust Gas Recirculation (EGR) limit. Therefore, identifying fuel compositions that can expand the lean or EGR limits by increasing turbulent burning velocity is crucial. Given the ongoing research into various carbon-neutral fuel candidates, internal combustion engines must achieve high thermal efficiency with any fuel type. It is also important to quickly understand the requirements for achieving high thermal efficiency with different fuels. The purpose of this study is to clarify the effect of fuel composition on turbulent burning velocity under lean or EGR dilution conditions and to develop a model that accounts for these effects. The Markstein number, a dimensionless parameter indicating changes in burning velocity due to flame stretch, varies with fuel composition and is an important indicator under EGR conditions. Therefore, a modified model based on Peters’ model, which focuses on flame stretch and the Markstein number, was considered. To investigate the effect of fuel composition and verify the modified model, experiments were conducted using a Rapid Compression Machine (RCM) to measure the turbulent burning velocities of various fuels under EGR conditions. Ethanol-blended fuel and ETBE-blended fuel were used to clarify the impact of potential carbon-neutral fuel candidates on combustion and to assess the influence of the Markstein number. The comparison between the turbulent burning velocities obtained from the models and experiments confirmed that the modified model more accurately reproduced the experimental results than the base model. Using the modified model, the effect of fuel composition on turbulent burning velocity was further investigated. It was found that blending ethanol decreased the Lewis number, which in turn increased the turbulent burning velocity.

Keywords

SI combustion model turbulent burning velocity flame stretch fuel composition EGR dilution

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