Search Results

A software “Automatic Scheme Reduction Tool (ASRT)” [1], which was developed by the authors to reduce the number of detailed elementary reactions automatically with CHEMKIN-II code [2], was applied to the reduction of the elementary reaction scheme for gas oil, ethanol and dimethyl ether (DME). It was found that the reduced scheme obtained for a fuel-rich mixture has the capability to predict heat release histories and ignition delay characteristics not only for fuel-rich mixtures, but also for stoichiometric and lean mixtures. As a result, the reduction scheme for DME, which was obtained by the ASRT combined with optimization method, was applied to three-dimensional engine combustion analysis.

In order to numerically simulate the mixture formation and combustion processes in a direct-injection gasoline engine, the validity of the submodels for fuel spray and combustion was investigated. The physical model proposed by the authors was employed for hollow-cone sprays injected from a swirl injector along with the authors' original submodels. This hollow-cone spray model was validated by comparing the calculated and measured results of the behavior of hollow-cone free spray. As a combustion model, Reitz's model was employed. These submodels were incorporated into the authors' GTT code, and the mixture formation and combustion processes in a direct-injection gasoline engine were numerically analyzed using this code. The validity of the submodels was confirmed by comparing the calculated results of the temporal variation of fuel vapor concentration and gas pressure in the cylinder with the experimental ones under various operating conditions of stratified charge combustion.

A practical method has been developed for numerically predicting pressure losses and acoustic characteristics in silencers simultaneously under the quasi-operating conditions of internal combustion engines. In the present method, three-dimensional gas flow and pressure dynamics in silencers have been numerically simulated by means of a new three-dimensional non-linear fluid-dynamic model, where the gas exchange process in entire intake and exhaust systems has been calculated by a one-dimensional non-linear fluid-dynamic model for saying the computing time. In this three-dimensional fluid-dynamic model, an accurate numerical scheme with less numerical diffusion has been applied to the Reynolds average Navier-Stokes equations using an eddy-viscosity hypothesis. Pressure losses and insertion losses in silencers have been examined using the three-dimensional model. It has been shown that the present method can predict the pressure losses and acoustic characteristics simultaneously.

To find more effective lean mixture preparation methods for smokeless and low NOx combustion, a numerical study of the effects of in-cylinder flow field before injection on mixture formation in a premixed compression ignition engine was conducted. Premixed compression ignition combustion is a very attractive method to reduce both NOx and soot emissions, but it still has some problems, such as high HC and CO emissions. In case of early direct injection, it is important to avoid wall wetting by spray impingement, which can cause higher HC and CO emissions. Since it is not easy to examine the effects of initial flow and injection parameters on mixture formation over the wide range by practical engine tests, a computer program named “GTT (Generalized Tank and Tube)” code was used to simulate the in-cylinder phenomena before autoignition.