Micropyretic synthesis is a technique whereby a material is synthesized by the propagation of a combustion front across a powder. Composition variations in reactants and diluent are common during micropyretic synthesis when powders are mixed and the conventional modeling treatments thus far have only considered uniform systems. Composition variations are thought to result in the local variations of such thermophysical/chemical parameters for the reactant as density, heat capacity, and thermal conductivity; the result is changes in the combustion temperature, propagation velocity, and propagation pattern of a combustion front. This study investigates the impact of composition variations during micropyretic synthesis with Ni + Al. Correlations of variations in the reactants and diluent with the propagation velocity and combustion temperature are both studied by a numerical simulation.