This paper presents a quasi-dimensional emission model for calculating the transient nitric oxide emissions of a diesel engine. Using conventional and high-speed measurement technology, steady-state and transient emissions of a V6 diesel engine were examined. Based on measured load steps and steady-state measurements a direct influence of the combustion chamber wall temperature on the nitric oxide emissions was found. Load steps to and from, as well as steady-state measurements down to almost stoichiometric global combustion air ratios were used to examine the behavior of nitric oxide formation under these operating conditions.An existing emission model was expanded in order to represent the direct influence of the combustion chamber wall temperature on the nitric oxide emissions as well as enabling the forecasting of nitric oxide emissions at low global combustion air ratios: Both particularly important aspects for the simulation of transient emissions. This also improves forecasting at steady-state operating points and enables forecasting for low global combustion air ratios in the first place.The improved model was validated for both steady-state and transient cases using measurements. In the area of the measured engine characteristics, an enhanced forecasting quality of the improved model was demonstrated for steady-state operating points. The simulated transient load steps delivered significantly better forecasts with the improved model. Overall, the improved model thus enables not only the prediction of nitric oxide emissions in a wider operating range, but rather also delivers more precise forecasts within the complete performance map, as well as in the case of transient operation.