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

Experimental studies have been augmented by computer modelling and simulations for the development and optimization of future fuels and automotive engines. Traditional reliance on the simplified global reactions for combustion simulations reduces the credibility of the prediction of combustion and engine performance parameters, such as in-cylinder pressure, heat release and pollutant formation. The study of engine performance parameters helps in improving the performance as well as the reduction of emissions in the engines. The present study has used detailed chemistry by augmenting the combustion model of a three-dimensional unsteady compressible turbulent Navier-Stokes solver with liquid spray injection by coupling its fluid mechanics solution with detailed kinetic reactions solved by a commercial chemistry solver. A skeletal reaction mechanism was reduced to study the in-cylinder pressure in a direct injection spark ignition (DISI) engine. Sensitivity analysis was performed to reduce the reaction mechanism for the compression and power strokes utilizing computational singular perturbation (CSP) method. An interface was developed between fluid dynamics and chemical kinetics codes to study iso-octane that is a well-established surrogate fuel for gasoline. Gasoline is a complex mixture of various compounds and hydrocarbons. The study used 90% iso-octane and 10% n-heptane as surrogate fuel because this combination best modelled the results. A mesh independent study was performed at stoichiometric conditions that validated and showed a good agreement of peak in-cylinder pressure against the experimental data for a direct injection spark ignition (DISI) engine. This study has been comprehensive as it includes a detailed study performed for premixed case at ϕ = 0.98 and 1.3 as well as stoichiometric condition in a direct injection spark ignition (DISI) engine, that resulted in the development of a reduced mechanism that has the capability to validate in-cylinder pressure and heat release rate from stoichiometric to rich mixtures for premixed cases in a spark ignition engine. The study concludes that it is imperative to establish a library of reduced mechanisms for various spark ignition engines as well as other combustion systems.

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Use of detailed chemistry augments the combustion model of a three-dimensional unsteady compressible turbulent Navier–Stokes solver with liquid spray injection when coupled with fluid mechanics solution with detailed kinetic reactions. Reduced chemical reaction mechanisms help in the reducing the simulations time to study of the engine performance parameters, such as, in-cylinder pressure in spark ignition engines. Sensitivity analysis must be performed to reduce the reaction mechanism for the compression and power strokes utilizing computational singular perturbation (CSP) method. To study a suitable well-established surrogate fuel, an interface between fluid dynamics and chemical kinetics codes must be used. A mesh independent study must be followed to validate results obtained from numerical simulations against the experimental data. To obtain comprehensive results, a detailed study should be performed for all ranges of equivalence ratios as well as stoichiometric condition. This gives rise to the development of a reduced mechanism that has the capability to validate engine performance parameters from stoichiometric to rich mixtures in a spark ignition engine. The above-mentioned detailed methodology was developed and implemented in the present study for premixed and direct injection spark ignition engines which resulted in a single reduced reaction mechanism that validated the engine performance parameters for both engine configurations.

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