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Improved Reaction Models for Petroleum and Alternative JP-5/8 Fuels


OBJECTIVE: Develop and employ accurate combustion reaction mechanisms for logistic hydrocarbon fuels with vitiation and/or exhaust gas recirculation (EGR). DESCRIPTION: The Department of Defense has two goals for future use of fuels in the battle space. The first is to operate with a single fuel in the battle space to simplify logistics and supply concerns. Currently that fuel is JP-8/JP-5. The second is to develop alternative fuels for the battle space that are derived from more secure sources. These alternative fuels, while meeting the JP-8 specification, can have properties that vary widely. Recent research at Air Force Research Laboratory indicate that variations in Cetane Number and aromatic content of JP fuels, while meeting the JP-8 specifications, significantly impact combustion in gas turbine engines. Cetane number of the fuel also dictates weather the fuel will be acceptable for use in diesel engines. Vitiation, or EGR, is the combustion of fuel with a reactant stream that has previously undergone the combustion process but still has sufficient oxygen to sustain further reaction. In a gas turbine engines the inter-turbine burner and/or augmentor is a secondary combustor downstream from the main combustor and either between or behind the turbine respectively. These combustion systems increase the enthalpy of the core stream further through the reaction of available oxygen. For highly supercharged diesel engines with low compression ratios, EGR is sometimes used to improve the performance of the engine. In all of these cases the air in the reactant stream has undergone reaction with fuel once resulting in reduced oxygen and increased CO2, H2O, and NOx. The effects of vitiation or EGR on secondary combustion are significant [Fuller et al, Risberg et al., Kalghatgi]. The CO2, H2O, and NOx in the EGR/vitiation reactant stream influence both the progress of the chemical reactions and the laminar flame speed of the combustion. The influence of these species on combustion and flame speed varies widely with pressure. These effects are non-monotonic in pressure. Very little work on the interaction of EGR, especially NO, and JP-8 at typical diesel engines conditions has been reported in the literature. In order to fully understand and properly implement EGR in the diesel cycle and maintain stable combustion in gas turbine engines, it is necessary to have accurate, validated models for the chemical kinetics of the ignition, combustion process, and flame speed under vitiated conditions at various pressures. Specifically, the chemical kinetic implications of exhaust gas interaction with paraffinic and aromatic components on the overall ignition of JP-8 must be examined. In addition, most combustion kinetic mechanisms that are intended for use with jet fuels have been primarily developed for reactions with clean air, and have not been validated for vitiated oxidizer conditions, especially at the conditions encountered in diesel engines and interturbine burners. Desired is an improved chemical kinetics model that accounts for vitiation over the pressure and temperature range of diesel engine, interturbine burner, and afterburner operation. The model should also be validated using ignition delay, flame speed, and species time history data for the best possible accuracy for use in combustion simulations. Improved models should be easily implemented into commercial combustion codes. It is desired that the software and associated documentation be delivered at the end of the Phase II effort for additional evaluation by U.S. Government personnel. PHASE I: Demonstrate feasibility for improvement of current chemical kinetics models for the inclusion of exhaust gas/vitiation over a wide range of pressures and temperatures. Model shall have the ability to predict major species, laminar flame speed, and ignition delay time measurements over the range of conditions of interest for diesel engines, interturbine burners and gas turbine augmentors. PHASE II: Further develop the kinetics model to predict flame speed, ignition time and major species in a vitiated environment over a range of pressure and temperatures and pressures relevant to diesel and gas turbine engines and augmentors. Validate the model to simultaneously match flame speed, ignition delay time and major species. It is desired that the software and associated documentation be delivered at the end of the Phase II effort for additional evaluation by U.S. Government personnel. PHASE III: Potential applications include numerous commercial codes used for reactive flow modeling. Potential markets include commercial diesel engine manufacturers as well as furnace and boiler manufacturers. REFERENCES: 1."Large-scale computations,"AIAA 2008-969, AIAA Aerospace Sciences Meeting and Exhibit, 7-10 January 2008, Reno, Nevada. 2. C. Fuller, P. Gokulakrishnan, M. S. Klassen, R.J. Roby, and B.V. Kiel,"Investigation of the Effect of Nitric Oxide on the Autoignition of JP-8 at Low Pressure, Vitiated Conditions,"45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Vol. AIAA 2009-4295, August 2009. 3. Risberg, P., Kalghatgi, G., and Angstrom, H.E.,"The Influence of EGR on auto-ignition quality of gasoline-like fuels in HCCI engines,"SAE 2004-01-2952, 2004. 4. Kalghatgi, G.,"Auto-Ignition Quality of Practical Fuels and Implications for Fuel Requirements of Future SI and HCCI Engines,"SAE 2005-01-0239, 2005.
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