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Many combustion researchers use peak pressure rise rate or ringing intensity to indicate combustion noise in lieu of microphone data or using a combustion noise meter that simulates the attenuation characteristics of the engine structure. In this paper, peak pressure rise rate and ringing intensity are compared to combustion noise using a fully documented algorithm similar to the ones used by combustion noise meters. Data from multiple engines operating under several low-temperature combustion strategies were analyzed. The results suggest that neither peak pressure rise rate nor ringing intensity provides a direct correlation to engine noise over a wide range of operating conditions. Moreover, the estimation of both metrics is often accompanied by the filtering of the pressure data, which changes the absolute value of the results.

The paper reports the application of a look-up table approach within a LES combustion modelling framework for the prediction of knock limit in a highly downsized turbocharged DISI engine. During experimental investigations at the engine test bed, high cycle-to-cycle variability was detected even for relatively stable peak power / full load operations of the engine, where knock onset severely limited the overall engine performance. In order to overcome the excessive computational cost of a direct chemical solution within a LES framework, the use of look-up tables for auto-ignition modelling perfectly fits with the strict mesh requirements of a LES simulation, with an acceptable approximation of the actual chemical kinetics. The model here presented is a totally stand-alone tool for autoignition analysis integrated with look-up table reading from detailed chemical kinetic schemes for gasoline.

Improved wall models for LES are presented in this paper. The classical Werner-Wengle (WW) wall shear stress model was used along with the eddy viscosity near walls. A sub-grid scale turbulent kinetic energy was employed in a model for the eddy viscosity. To provide heat flux results, a modified classical variable-density wall heat transfer model, which includes the variation of the turbulent Prandtl number in the boundary layer, was also employed. The fully turbulent developed flow in a square duct with constant wall temperature was used to validate the model and the friction factor and Nusselt number predictions are in good agreement with experimental results. The resulting time and spatially averaged velocity and temperature wall functions from the new wall models match well with the law-of-the-wall experimental data. Additionally, the model was validated using experimental data from a Caterpillar engine operated with conventional diesel combustion.

In this work non-reacting spray simulations are performed using two Computational Fluid Dynamic (CFD) codes, KIVA and OpenFoam. The metric used is the liquid tip penetration which is compared with experimental data from the Engine Combustion Network at Sandia National Laboratories. Some important spray sub-models, available in KIVA, are implemented in OpenFOAM so that the two codes have more common models. In addition, model coefficients and computations cells used in the simulations are the same in both codes. The differences in spray source terms formulations and other spray sub models between the codes and their effect on liquid penetration are discussed.