Multidimensional laser diagnostic and numerical analysis of NO formation in a gasoline engine

Laser diagnostic imaging techniques were used to obtain detailed in-cylinder data from a commercial gasoline engine. Mean flowfields and turbulence intensities were acquired using particle imaging velocimetry (PIV). Instantaneous quantitative NO-concentration fields were measured using planar laser-induced fluorescence (LIF). From experimental images of NO, also the flame propagation could be deduced. Combustion and NO formation were simulated with a 3-D computer code SPEEDSTAR. The overall agreement between experimental data and computational results is encouraging in general, with remaining issues to be solved. The mean flow is well predicted, whereas the prediction of turbulence quantities is less satisfactory. Calculated results for flame propagation are in good agreement with measurements. NO concentrations resulting from calculations are close to those measured, both in respect to their spatial distribution and absolute number densities. As could be expected, the highest NO concentrations are found in regions where combustion started earliest. Local concentrations of NO are found be up to 4 times higher than those in the exhaust. The comparison of experimental results with calculations clearly shows that, although the 3-D computer model can predict major features of the in-cylinder processes in agreement with measurements, details such as the exact flow pattern and flame development are difficult to capture and depend critically on some of the models parameters used.