In low-emission combustion systems, especially, conditions are frequently encountered in which the chemistry must not be infinitely fast. This can apply to heat release as well as to pollutant formation (e.g. NOx, soot). In such cases, modelling combustion is particularly difficult. In combustion models that integrate chemical reaction mechanisms, it is necessary to solve transport equations for all the relevant components. It is possible with ‘presumed’ or PDF transport equation methods to take turbulence-chemistry interaction into account when modelling combustion processes. Both these approaches are pursued at the Institute. There are no known simulation models that are capable of simulating soot formation in combustion chambers to any satisfactory extent. When developing such models, especially for 3D simulation, a compromise must be found between complex chemical approaches and the amount of computing time required. The Computer Simulation department, in close cooperation with the Chemical Kinetics department, is developing techniques for detailed modelling of soot formation using CFD code and testing these techniques by comparing with measurements.