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

TL;DR

This study investigates how adding water affects ethanol/air flames at high temperatures and pressures, and proposes a new correlation for burning velocity.

Contribution

A novel correlation for laminar burning velocity of hydrous ethanol/air mixtures is proposed and validated.

Findings

Water addition reduces laminar burning velocity, especially in fuel-rich mixtures.

The new correlation performs well under elevated temperatures and pressures.

Dilution effect is the main factor in reducing burning velocity.

Abstract

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.

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