Ingemar Magnusson

MODELING DIESEL SPRAY IGNITION USING DETAILED CHEMISTRY WITH A PROGRESS VARIABLE APPROACH

In this work, a progress variable approach is used to model diesel spray ignition with detailed chemistry. The flow field and the detailed chemistry are coupled using the flamelet assumption. A flamelet progress variable is transported by the computational fluid dynamics (CFD) code. The progress variable source term is obtained from an unsteady flamelet library that is evaluated in each grid cell. The progress variable chosen is based on sensible enthalpy. By using an unsteady flamelet library for the progress variable, the impact of local effects, for example variations in the turbulence field, effects of wall heat transfer etc. on the autoignition chemistry can be considered on a cell level. The coupling between the unsteady flamelet library and the transport equation for total enthalpy follows the ideas of the representative interactive flamelet (RIF) approach. The method can be compared to having an interactive flamelet in each computational cell in the CFD grid. The results obtained using the proposed model are compared to results obtained using the RIF model. Differences are exhibited during the autoignition process. After ignition, the results obtained using the proposed model and RIF are virtually identical. The model was used to study lift-off lengths in sprays as function of nozzle diameter and injection pressure. A good agreement between model predictions and experimental trends was found.

Modeling Diesel Engine Combustion With Detailed Chemistry Using a Progress Variable Approach

In this work, we present an unsteady flamelet progress variable approach for diesel engine CFD combustion modelling. The progress variable is based on sensible enthalpy integrated over the flamelet and describes the transient flamelet ignition process. By using an unsteady flamelet library for the progress variable, the impact of local effects, for example variations in the turbulence field, effects of wall heat transfer, etc., on the autoignition chemistry can be considered on a cell level. The coupling between the unsteady flamelet library and the transport equation for total enthalpy follows the ideas of the representative interactive flamelet approach. Since the progress variable gives a direct description of the state in the flamelet, the method can be compared to having a flamelet in each computational cell in the CFD grid. The progress variable approach is applied to high-EGR, late injection operating conditions, and we demonstrate that the model can be applied for 3D engine simulations. (Less)

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 veloci-metry (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.

Laser spectroscopic investigation of flow fields and NO-formation in a realistic si engine

This paper presents results from a quantitative characterization of the NO distribution in a SI engine fueled with a stoichiometric iso-octane/air mixture. Different engine operating conditions were investigated and accurate results on NO concentrations were obtained from essentially the whole cylinder for crank angle ranges from ignition to the mid expansion stroke. The technique used to measure the two-dimensional NO concentration distributions was laser induced fluorescence utilizing a KrF excimer laser to excite the NO A-X (0,2) bandhead. Results were achieved with high temporal and spatial resolution. The accuracy of the measurements was estimated to be 30% for absolute concentration values and 20% for relative values. Images of NO distributions could also be used to evaluate the flame development. Both the mean and the variance of a combustion progress variable could be deduced. The engine used in the investigation was a one cylinder version of a Volvo N1P engine equipped with good optical access. Using the same engine and the same operating conditions, data on the in-cylinder flow field was also obtained using particle imaging velocimetry. The comprehensive and detailed data base generated in the present work is currently being used for detailed validation and improvements of models for numerical simulation of engine combustion and emission formation.