Numerical study of CNG engine combustion using CFD with detailed chemical kinetics

A three dimensional model which considers the effects of turbulence and detailed chemi cal kinetics is built to simulate the combustion process of engine fueled by compressed nature gas （CNG）. The model is accomplished by integrating CFD software KIVA3V and chemical kinetic soft- ware CHEMKINII. Meanwhile, a turbulence combustion model which is suitable for describing the reaction rate under the coupled simulation is developed to balance the effects of turbulence and de tailed chemical kinetics. To reduce the computation time, subsequent development of the simulation code is realized, which enables the simulation code to have the function of parallel computing and run on parallel computing facility based on message passing interface （MPI）. The coupled software is used to simulate the combustion process of spark ignition CNG engine. The results show that sim ulation data have a good consistency with experimental results and parallel computing has good effi ciency and accelerate ratio.

Influences of Catalytic Combustion on the Ignition Timing and Emissions of HCCI Engines

The combustion processes of homogeneous charge compression ignition （HCCI） engines whose piston surfaces have been coated with catalyst （rhodium or platinum） were numerically investigated. A singlezone model and a multi-zone model were developed. The effects of catalytic combustion on the ignition timing of the HCCI engine were analyzed through the single-zone model. The results showed that the ignition timing of the HCCI engine was advanced by the catalysis. The effects of catalytic combustion on HC, CO and NOx emissions of the HCCI engine were analyzed through the multi-zone model. The results showed that the emissions of HC and CO （using platinum （Pt） as catalyst） were decreased, while the emissions of NOx were elevated by catalytic combustion. Compared with catalyst Pt, the HC emissions were lower with catalyst rhodium （Rh） on the piston surface, but the emissions of NOx and CO were higher.

On the Necessary Grid Resolution for Verified Calculation of Premixed Laminar Flames

We consider the grid resolution necessary to resolve combustion in a mixture of calorically imperfect ideal gases described by detailed kinetics and multicomponent transport.Using the steady premixed laminar flame as a paradigm,the required spatial discretization to capture all detailed physics in the reaction zone is found via 1)determination of the finest grid used in a standard software tool which employs adaptive mesh refinement,2)examination of peak values of intermediate species mass fractions in the flame zone as a function of grid size,3)a formal grid resolution study,and 4)a robust new eigenvalue analysis developed to estimate the finest length scale.Application to laminar premixed flames in hydrogen-air flames reveals that the finest length scale is on the order of 10^(−4) cm for combustion at atmospheric pressure.Resolution at this scale is shown to be necessary to capture detailed species mass fraction profiles;other features such as steady flame speeds and equilibrium thermochemical properties do not have such a stringent length scale requirement.