Studying the Roles of Kinetics and Turbulence in the Simulation of Diesel Combustion by Means of an Extended Characteristic-Time-Model

A study was performed that takes into account both turbulence and chemical kinetic effects in the numerical simulation of diesel engine combustion in order to better understand the importance of their respective roles at changing operating conditions.

An approach was developed which combines the simplicity and low computational and storage requests of the laminar-and-turbulent characteristic-time model with a detailed combustion chemistry model based on well-known simplified mechanisms. Assuming appropriate simplifications such as steady state or equilibrium for most of the radicals and intermediate species, the kinetics of hydrocarbons can be described by means of three overall steps. This approach was integrated in the KIVA-II code. The concept was validated and applied to a single-cylinder, heavy-duty engine. The simulation covers a wide range of operating conditions.

The turbulence seems to play a significant role in the predictions of the early stages of combustion and on the soot-NO_x trade-off versus injection timing. The traces of calculated pressure and heat release for different operating conditions are in good agreement with the measured values. However, the model does not allow accurate prediction of some minor pollutant species as CO and unburned hydrocarbons, especially at light loads.