Alternative Fuels for Spark-Ignition Engines: Mixing Rules for the Laminar Burning Velocity of Gasoline–Alcohol Blends

Abstract

Experimental measurements of the laminar burning velocity are mostly limited in pressure and temperature and can be compromised by the effects of flame stretch and instabilities. Computationally, these effects can be avoided by calculating one-dimensional, planar adiabatic flames using chemical oxidation mechanisms. Chemical kinetic models are often large, complex and take a lot of computation time, and few models exist for multi-component fuels. The aim of the present study is to investigate if simple mixing rules are able to predict the laminar burning velocity of fuel blends with a good accuracy. An overview of different mixing rules to predict the laminar burning is given and these mixing rules are tested for blends of hydrocarbons and ethanol. Experimental data of ethanol/n-heptane and ethanol/n-heptane/iso-octane mixtures and modeling data of an ethanol/nheptane blend and blends of ethanol and a toluene reference fuel are used to test the different mixing rules. Effects of higher temperature and pressure on the performance of the mixing rules are investigated. It was found that simple mixing rules that consider only the change in composition are accurate enough to predict the laminar burning velocity of ethanol/hydrocarbon blends. For the blends used in this study, a Le Chatelier's rule based on energy fractions is preferable because of the similar accuracy in comparison to other mixing rules while being more simple to use.

Laminar burning velocity of gasoline and the gasoline surrogate components iso-octane, n-heptane and toluene

“…Sileghem et al [16,17] investigated the laminar burning velocity of alcohol-hydrocarbon blends. Methanol has the highest laminar burning velocity followed by ethanol and gasoline.…”

A quasi-dimensional model for SI engines fueled with gasoline–alcohol blends: Knock modeling

“…Similar to the mixing rules for laminar burning velocity of methanol-gasoline blends, the energy fraction mixing rule has the best agreement [26,27].…”

Gasoline-ethanol blend formulation to mimic laminar flame speed and auto-ignition quality in automotive engines

“…In [46], Sileghem et al demonstrated that a mixing rule applied to the components of a TRF surrogate can be used to predict the LFS of a commercial gasoline over a given temperature range. In [48], the same authors investigated the capability of simple mixing rules, applied to ETRF components, to predict LFS of gasoline-ethanol blends. The results proved that simple mixing rules taking into account only the ethanol-hydrocarbon blend composition are sufficiently accurate to predict s L .…”

“…where n is the number of the blend components. As stated earlier, many other mixing rules (even more complex) are available in literature [48,49,50]. All can be used in the methodology proposed in the present work, if analytical equations are based on the pure component concentrations, as Eq.…”