Biodiesel-fueled engine simulations were performed using the KIVA3v-Release 2 code coupled with Chemkin-II for detailed chemistry. The model incorporates a reduced mechanism that was created from a methyl decanoate/methyl-9-decenoate mechanism developed at the Lawrence Livermore National Laboratory. A combination of Directed Relation Graph, chemical lumping, and limited reaction rate tuning was used to reduce the detailed mechanism from 3299 species and 10806 reactions to 77 species and 209 reactions. The mechanism was validated against its detailed counterpart and predicted accurate ignition delay times over a range of relevant operating conditions. The mechanism was then combined with the ERC PRF mechanism to include n-heptane as an additional fuel component.The biodiesel mechanism was applied in KIVA using a discrete multi-component model with accurate physical properties for the five common components of real biodiesel fuel. A mixture of methyl decanoate and methyl-9-decenoate was used as the biodiesel surrogate to account for both the saturated and unsaturated components found in real biodiesel fuels. Non-reacting biodiesel spray experiments were reproduced using the KIVA model, and the KH-RT spray model constants were adjusted to improve the liquid penetration trend under varying density and temperature conditions. The complete biodiesel engine model was shown to adequately reproduce the pressure and heat release rate predictions of diesel engine combustion experiments fueled with a soy methyl ester biodiesel. These results show that the model gives accurate predictions of biofuel spray vaporization and combustion for these conditions. The current biodiesel model was also compared to a previous model and found to improve the magnitude of the NOx prediction, as well as the trend of decreasing NOx with increasing load.