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.