Effects of Water Addition on Laminar Premixed Ethanol/Air Flame at Elevated Temperature and Pressure

In this study, the effects of water addition on ethanol/air flames with high water content at elevated temperature and pressure are numerically investigated, and a novel correlation for their laminar burning velocity (LBV) is proposed based on experimental results. The dependence of the temperature and pressure exponents on thermodynamic parameters is numerically analyzed and considered in the new correlation to optimize the existing correlation. The fitting results of LBV correlations based on experimental measurements using a constant-volume method demonstrate that incorporating high-order and cross terms into the correlation enhances the overall performance, particularly under fuel-rich conditions where existing correlations exhibit significant discrepancies. The new LBV correlation of hydrous ethanol/air mixtures performs well over a wide range of elevated temperatures and pressures and agrees well with experimental data in the literature at high temperatures and pressures. The calculated LBV using the new correlation is also in good agreement with simulations using various mechanisms, except for fuel-rich mixtures with high water content, where the LBV is underpredicted by all mechanisms considered, suggesting further development of chemical mechanisms is needed. A sensitivity analysis suggests that under high water content, the dominant reactions of fuel-rich flames are different from those in stoichiometric and fuel-lean mixtures, highlighting that fuel-rich hydrous ethanol/air flames are very sensitive to water addition. The results also suggest that water addition leads to a reduction in the LBV. Both the burnt gas temperature and the peak heat release rate decrease with the water content, with a stronger influence on fuel-rich ethanol/air mixtures. Furthermore, the dilution effect of water addition constitutes the single largest effect in reducing the LBV, while chemical and thermophysical effects are found to be comparatively minor. The findings are helpful in understanding the fundamental combustion properties of hydrous ethanol and optimizing the LBV correlation under engine-relevant conditions.