Heating and Evaporation of Gasoline and Gasoline Biofuel Blends

Mengying Su and C. P. Chen
Department of Chemical and Materials Engineering The University of Alabama in Huntsville Huntsville, USA
chenc@uah.edu
Abstract
In new generation Gasoline Direct Injection (GDI) engines, a fuel spray is injected directly into the cylinder during the compression stroke, creating a fuel-air mixture with an ignitable composition at the spark gap at the time of ignition. Spraying droplet breakup, heating and evaporation is essential for the mixture preparation and the ignition/combustion. In this study, we investigate gasoline and gasoline-biofuel multicomponent fuel droplet heating and evaporation in a hot gas flow. For numerical modeling of spray evaporation and combustion, it is not feasible to include all real components (typically in hundreds). To this end, we have recently developed a new 6-component surrogate fuel, composed of i-pentane/n-heptane/toluene/iso-octane/n- propylcyclohexane /iso-undecane with molar fraction of 0.238/0.251/0.117/0.019/0.167/0.208, to match the targeted gasoline fuel in terms of thermo-physical properties. This surrogate fuel is developed based on the inversed batch distillation formulation and closely matches NISTâ??s experimental distillation curve. This new surrogate fuel is then implemented into a new modeling methodology which simultaneously accounts for finite conductivity, finite mass diffusivity and turbulence effects within atomizing multicomponent liquid fuel sprays. This new model incorporated the liquid turbulence effect in modeling the boundary layer heat and mass resistance during multi-component droplet evaporation. The atomization/spray model used is the T-blob/T- TAB model developed by the authors. This model supplies relevant turbulence characteristics within the atomizing droplets from the injector. The finite conductivity and mass diffusivity models are based on two-layer film theory, where the turbulence characteristics of the droplet are used to estimate the effective thermal conductivity and mass transfer diffusivities. The main purpose of this study is to perform analyses of heating and evaporation of the surrogate gasoline and various gasoline-ethanol and other biofuel blends. Validations against available experimental data will be presented and discussed.