The overall objective of this contract is to assist in the development of fuel-flexible combustion systems for gas turbines as well as Rankine and Stirling cycle engines. The primary emphasis of the program is on liquid hydrocarbons produced from non-petroleum resources. Fuel-flexible combustion systems will provide for more rapid transition of these alternative fuels into important future energy utilization centers (especially utility power generation with the combined cycle gas turbine). The specific technical objectives of the program are: (a) develop an improved understanding of relationships between alternative fuel properties and continuous combustion system effects, and (b) provide analytical modeling/correlation capabilities to be used as design aids for development of fuel-tolerant combustion systems. This is the second major report of the program. Key experimental findings during this reporting period concern stirred combustor soot production during operation at controlled temperature conditions, soot production as a function of combustor residence time, an improved measurement technique for total hydrocarbons and initial stirred combustor results of fuel nitrogen conversion. While the results to be presented concern a stirred combustor which utilizes premixed fuel vapor/oxidant mixtures, a new combustor which combusts liquid fuel injected into the reactor as a spray has been developed and will be described. Analytical program progress includes the development of new quasiglobal models of soot formation and assessment of needs for other submodel development.

Recent efforts under this contract have involved (1) investigations of soot production phenomena in gas phase jet-stirred combustors, (2) preliminary experiments concerning the effects of liquid spray fuel injection on soot production in jet-stirred combustors, (3) development and shakedown of ER and E's new Variable Pressure Jet-Stirred Combustor, and (4) continued development of SAI's quasi-global chemical kinetic model of hydrocarbon combustion/soot production processes. Progress in each of these subject areas, including experimental results from the first two areas, detailed descriptions of the Variable Pressure Jet-Stirred Combustor and the present quasi-global model, and brief outlooks on future experimental and modeling efforts are discussed. Results from the gas phase jet-stirred combustor studies provide information regarding a possible soot formation mechanism change at 1800°K, the appropriateness of a separate sooting category for 1-methylnaphthalene and other multiring aromatics, the identification of unburned hydrocarbons in the exhaust gases, and the dependencies of soot properties on combustor operating conditions. The liquid fuel spray experiments provide data which relate liquid spray soot yields to fuel type, overall equivalence ratio, atomizing air flow rate, and combustor temperature. Of particular significance is the temperature dependence of the soot yield, which was found to be exactly opposite previous trends obtained in gas phase jet-stirred combustors. The description of the Variable Pressure Jet-Stirred Combustor includes the actual combustor, its versatile air and fuel supply systems, and associated instrumentation and diagnostics. The quasi-global model description contains tentative reaction mechanisms and rate constants and comparisons of model calculations with experimental data.

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