Analysis of Reduced Order Chemical Mechanisms for Oxygen-enriched Combustion of Methane and n-decane

Abstract

Micro-combustors operating with oxygen-enriched combustion of hydrocarbon fuels promise exceptionally high energy densities. However, to effectively design and analyze novel micro-combustor concepts using computational fluid dynamics (CFD) models, the CFD tools must employ accurate and efficient chemical mechanisms to represent the combustion process, especially with oxygen-enrichment. Accurate modeling of the laminar flame speed is a critical aspect to micro-combustor performance and must be accurately predicted using reduced order chemical mechanisms. The flame speeds of premixed oxygen-enriched combustion of methane and n-decane fuels were analyzed using new reduced order mechanisms in CHEMKIN which are suitable for use in numerical models of micro-combustor performance. Methane has been taken as a preliminary test case. Numerical simulations were run in CHEMKIN to predict flame properties of methane. The numerical and experimental data were in good agreement. In addition to the rate of production analysis and identification of rate-limiting reaction techniques, this study also considers flame speed sensitive reactions to determine the accuracy of the reduced model based upon the flame speed. Simulations are run to perform analysis of three reduced order methane and n-decane mechanisms at = 0.8, 1.0 and 1.2 and at oxygen concentrations of 21%, 25% and 30%. These simulations showed the percent error or deviation in flame speeds from the actual mechanism. Nomenclature Ф = equivalence ratio S L = flame speed V u = unburnt velocity ρ u = unburnt density Q = heat transfer from the flame to the burner A = area of burner sccm = standard cubic centimeters per minute MFC = mass flow controller GC = gas chromatograph

Numerical Simulations and Validation of Engine Performance Parameters Using Chemical Kinetics

“…The redundant reactions identified by this method are non-rate limiting slow reactions. As the redundant reactions are eliminated, the species taking part in those reactions gets automatically eliminated, hence, a reduced mechanism is obtained [1][2][3]. Sensitivity analysis is discussed further in detail in the next section with detailed references.…”

“…Surrogate fuel mechanisms that contain limited number of hydrocarbons from all the abovementioned hydrocarbon types are important in this regard. There is a necessity to use reduction techniques to produce reduced order mechanisms that can replicate the predictions of detailed mechanisms [3]. The reduction techniques decrease the number of species and reactions.…”