Conventional and Alternative Jet Fuels for Diesel Combustion: Surrogate Development and Insights into the Effect of Fuel Properties on Ignition.

Abstract

The use of kerosene-based jet fuels for all military applications has been mandated by U.S. military’s single fuel forward concept. Recently, interest in non-petroleum-derived alternative jet fuels has also been increasing as a way to diversify the source of jet fuels. Computational Fluid Dynamics (CFD) simulations with detailed kinetic modeling can be used to model the combustion behavior of real fuel and predict their performance. This thesis revolves around the development of a surrogate mixture for real jet fuels, kinetic models for the surrogate components, and CFD simulations of diesel engines to assess the effects of surrogate’s chemical and physical properties on fundamental combustion processes. Fuel surrogates are mixtures of one or more simple fuels that are designed to emulate key properties of a more complex fuel. For the first time we report on a comprehensive jet fuel surrogates that successfully emulate physical and chemical properties of conventional and alternative jet fuels. To identify the target properties that need to be used to reproduce the diesel combustion, in the first part of this dissertation, a sensitivity analysis was conducted with CFD simulations of pure n-dodecane spray in a constant volume chamber to identify temperature dependent liquid physical properties that are of significance to the diesel ignition process. Out of six physical properties that were tested, density, viscosity, volatility, and specific heat showed major impact on liquid penetration length and ignition delay time. Using a six-component surrogate palette (n-dodecane, n-decane, iso-cetane, iso-octane, decalin, and toluene), the surrogate optimizer generated surrogate mixtures for Jet-A POSF-4658, a petroleum-derived conventional jet fuel, IPK POSF-5642, a coal-derived synthetic jet fuel, and S-8 POSF-4734, a natural-gas-derived synthetic jet fuel. Kinetic modeling of the surrogate fuels were enabled by a detailed chemical mechanism. Numerical experiments were conducted using CFD simulations to evaluate the importance of physical and chemical properties of surrogates on the ignition process of the fuel spray for two fuels. This study indicates that the chemical properties of fuel are much more important to the duration of the ignition delay period than the physical properties, which emphasizes the chemical aspect of the diesel ignition phenomena.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120818/1/gogum_1.pd