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A Spray-Guided (SG) Direct-Injection (DI) Spark-Ignition (SI) engine is widely recognized to be a promising technology capable for substantially reducing fuel consumption and carbon dioxide emissions. Accordingly, there is a strong need for developing models of some effects specific to stratified turbulent burning under conditions of elevated and rapidly varying pressure. Two such effects were addressed in the present work by performing unsteady three-dimensional URANS simulations of stratified turbulent combustion in a SG DISI engine. First, a simple method of evaluation equilibrium combustion temperature, implemented into the CFD code OpenFOAM®, was improved in order to take into account the dissociation of the combustion products. Second, stratified turbulent combustion is affected by fluctuations in mixture composition. A widely used approach to modeling this effect consists of invoking a presumed Probability Density Function (PDF) for mixture fraction f.