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Multidimensional computations were carried out on a spark-ignition natural gas engine with a bowl-in-piston combustion chamber. The engine in-cylinder flow distributions and their effects on combustion are examined. The fact that the engine swirl would speed up the combustion process is confirmed due to the enhancement of turbulent diffusion process. The engine squish increases both the mean velocity and the turbulence intensity of the gas flow and, therefore, quickens the combustion process. The computations indicate further that the engine swirl impacts the engine in-cylinder flow fields more profoundly than the engine squish does. When the piston bowl is offset, the in-cylinder gas motion can be enhanced considerably. Computations were also made to study the sensitivity of the computed cylinder pressure history to initial values of the selected thermodynamic parameters and chosen initial turbulence conditions.

Multidimensional computations were made of combustion of natural gas engine via the KIVA-II code to evaluate the combustion and emission characteristics. In the combustion submodel, a two-step kinetic reaction mechanism is employed to account for oxidation of methane. The first of the two global rate equations controls the disappearance of methane, and the second, the oxidation of carbon monoxide. Four types of combustion chamber and a two-spark-plug geometry are considered to achieve quick flame propagation of the lean air-methane mixture. The effect of spark plug locations on the combustion processes is discussed. The calculated results show that the more effective burning process with lower NOx emission could be achieved by proper design of the geometry of the piston bowl and the arrangement of the spark plug by matching of the flame front development with the in-cylinder gas flow.

The emission characteristics of a fleet of five dual fueled trucks are reported. Detailed emission data of CO, THC and NOx are presented at various modes of operation. In most cases, the CO and NOx concentrations are lower for engines using compressed natural gas. The THC emission is lower for engines fueled with gasoline. The concentration of all emitted species increases with truck mileage driven. The catalytic converter is less effective for natural gas operation.

Three types, namely the open type chamber, the twin type chamber and the squash type chamber were investigated for their suitability and adaptability in high speed and high output diesel engine applications. Six different chamber configurations were considered and possible variations such as the change of compression ratio and the utilization of unit and regular injectors were examined for fuel and air interactions. Effect of the temperature of the fuel, droplet size in terms of Sauter mean diameter, the inlet pressure (supercharging), the initial engine swirl, the inclination angle of fuel spray and the opening lip size were discussed. The squash chamber seems to possess a unique potential for uniform fuel distribution throughout the entire chamber volume when the factors of the fuel temperature, the supercharging, the engine swirl ratio and the inclination angle of the spray plume are maximized for the D2 chamber.

The developed k-ε-R model for computing the mean in-cylinder gas motions is being applied to a spark-ignited L-head engine of three different chamber designs. The theoretically calculated burned gas fraction is significantly affected by the flame front radius, the spark location and the squish area of the engines. The basic concept of the spherical flame kernel was employed in the early stage of flame development and later super-imposed with the in-cylinder gas motion to define the flame front radius. The calculated pressure rise was then compared with the measured pressure for its practicality in engine design.

The k - ε turbulent model in conjunction with a discrete fuel droplet model is used to evaluate the flow velocity field and fuel spray relationship in bowl combustion chambers of a directly injected diesel engine. Effects of flow field and fuel mixing are greatly influenced by the engine chamber geometry, the clearance volume and the engine speed. Fuel spray penetration and dispersion are primarily controlled by the injector hole size and fuel exit velocity, and that only at the tip of fuel spray near the end of injection, the structure of the spray is found to be most influential by the in-cylinder flow velocities. Computations were carried out through the newly published KIVA-II program.

Performance comparisons of gasoline-water and gasoline-methanol emulsions as spark ignition engine fuels are presented. The gasoline-water mixture as a fuel contains 5%, 10% and 15% of water by volume versus 30% of methanol by volume in gasohol. Engine output, peak pressure, fuel consumption, and mass burning rate of all fuel emulsions were recorded and analyzed with the pressure-time data. The experiments were carried out on a commercial single cylinder, air cooled spark ignition engine at 2000 RPM and MBT operating conditions. Satisfactory running results were obtained and no abnormal or sluggish movement of the engine was observed during the tests. Preliminary results indicate that the gasoline-water emulsion can be adopted and burned efficiently in an existing SI engine power plant.