A modified EPISO, or Engine Pressure Implicit with Splitting of Operators, algorithm called EPISOC, is presented that specifically caters to combustion calculation in internal combustion engines. For the EPISOC algorithm, the bulk adjustment, one of the key elements in the EPISO, is dispensed with and a correction step is provided for sealant, EPISOC is incorporated with a discrete droplet model for diesel spray and a hybrid of Arrhenius kinetics and the eddy breakup model for simulation of diesel engine combustion processes. An application case is examined by comparing the present calculations with those obtained using the KIVA code and with experiments.