This paper describes a modeling study on the effects of the mixing ratio of biodiesel derived from rice on combustion and emission characteristics. In order to model ignition and combustion processes, a combined mechanism of methyl butanoate and n-heptane was used after modifying some reaction constants. The oxygen content of rice oil was maintained at the measured value (11 vol.%) by assuming that one mole of rice oil was composed of one mole of methyl butanoate and two moles of n-heptane. The fuel property library of the KIVA code was expanded to include physical properties such as density and surface tension of rice oil (i.e., biodiesel). In addition, a discrete multi-component fuel evaporation model was employed to model the fuel injection, atomization, and evaporation. Calculated pressure histories and carbon monoxide (CO) and hydrocarbon (HC) emissions of the present study agreed reasonably with experiments at a 100 MPa injection pressure and a 10 degrees BTDC injection timing for D100, BD20, and BD40. However some discrepancies were observed in predicting nitrogen oxide (NO(x)) emissions. The effect of the start of injection timing on fuel consumption and CO emissions were also studied. (C) 2009 Elsevier Ltd. All rights reserved.