A mathematical model of a spray combustion in direct-injection diesel engines has been developed to predict engine performance, thermal efficiency and pollutant emissions. Injected fuel spray was divided into many small packages. Gas and fuel droplet temperatures and evaporated mass of fuel in each package were computed. In considering the complete air-fuel jet mixing process and temperature in each package, the model also enabled subsequent spatial and temporal history of burning rate, local temperature and air-fuel ratio to be calculated.