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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.

The mixture formation process in a premixed compression ignition engine was numerically analyzed. This study aimed to find out effective injection conditions for lean mixture formation with high homogeneity, since the NOx and soot emissions in the engine are closely related to the mixture homogeneity. To calculate fuel spray behavior, a practical computer code GTT (Generalized Tank and Tube) was employed. In a model for the premixed compression ignition engine, the effects of injection parameters, such as injection timing, initial droplet size, spray angle, injection velocity, nozzle type (pintle and hole) and injection position / direction, on the mixture homogeneity near ignition timing (or TDC) were investigated. To evaluate the homogeneity of the mixture, an index was defined based on the spatial distribution of fuel mass fraction. The fuel vapor mass fractions as well as the homogeneity indices, obtained as a function of time, were compared under various boundary conditions.

The main purpose of this study is to reveal the mechanism of stratified- mixture formation in gasoline direct-injection engines. So far the authors have developed a computer code "GTT" for numerically simulating the fuel spray behavior in fuel injection engines, and have proposed the physical models for droplet breakup, spray impingement and liquid film formation on a wall, and evaporation of a droplet and liquid film, which have been applied mainly to the sprays injected from hole nozzles for diesel engines. In this study, in order to numerically simulate the hollow-cone sprays injected from a swirl injector for gasoline direct-injection engines, a physical model for hollow-cone sprays has been proposed. The injection boundary condition and the model coefficients for the droplet breakup model (improved wave breakup model) have been determined appropriately.

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.

The hollow-cone sprays generated by a high-pressure swirl injector are numerically analyzed using the author's Generalized Tank and Tube (GTT) code with spray models. The effects of the prescription of fuel injection conditions on the spray behavior are investigated and discussed in detail. The calculated results are compared with the results of measurement by Phase Doppler Anemometer (PDA), etc. A reasonable method to numerically reproduce the structure of a hollow-cone spray including the coarse droplet phenomenon is presented. As a result, the structure of a hollow-cone spray and the temporal transition of the structure are clarified in terms of fluid dynamics.

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.