The exhaust nitric oxide (NO) emission from a divided-chamber diesel engine was correlated with a function which included the effects of temperature, mixing time, and phasing between the temperature and fuel-burning histories. The correlation was evaluated for variations in combustion timing, overall air-fuel ratio, engine speed, intake-manifold pressure and intake-air temperature.The correlation had two forms. The variable-and constant-temperature correlations used the temperature history and the peak temperature during combustion, respectively, as one of the input data. These temperatures were measured along a single line of sight by a two-color optical method. The other input data were the engine speed and the fuel-burning rate derived from the measured cylinder pressure.These two techniques could correlate both the exhaust emission index of NO and the normalized mass of NO during combustion. However, comparison of the latter with experimental data suggested that the variable-temperature correlation was superior.The correlation was investigated for various activation temperatures and for two mixing time scales. The activation temperature used to correlate the data suggested that most of the NO was formed in the vicinity of the flame zone. Equally good correlations were obtained when the mixing time scale was assumed to be proportional to either the Kolmogorov or the Corrsin time Scale.The constant-temperature correlation could be used to predict the exhaust NO emission when it was evaluated with the flame temperature estimated from the cylinder pressure.