In this work, a multidimensional model that the authors have previously developed for computing radiant heat loss in an internal combustion engine is applied to study radiant heat loss characteristics in a Diesel engine. The model is applied to study the effects of load and speed on radiant heat transfer in the engine. It is shown that as load is increased the radiant heat loss increases and the fraction of radiant to total heat loss increases from about 12% at an overall equivalence ratio of 0.3 to 16% at an overall equivalence ratio of 0.5. As speed is increased, the radiant and total heat loss again increase but the ratio of radiant to total heat loss remains about the same for the cases considered. It is shown that there is a strong correlation between the radiant heat loss characteristics and soot concentration and temperature in the chamber.