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A database of information concerning the spray development and pollutant formation in common-rail, direct-injection Diesel engine is constructed using a transparent model Diesel engine. Spray development is investigated using optical diagnostics: Mie scattering and Laser Induced Exciplex Fluorescence (LIEF) make possible qualitative visualization of liquid and vapor phases. The injection pressure/nozzle hole diameter is found to be the most important parameter (in the parameter range used for the study): it reduces the liquid penetration length and improves the mixing of vapor fuel. Direct imaging of combustion development shows the influence of different engine parameters on flame location. Comparison with measured vapor distributions shows the effect of thermal expansion on the vapor plume before any light from combustion is visible. Soot formation is investigated using Laser Induced Incandescence imaging.

Using a combination of imaging techniques, we have produced a database of the macroscopic properties of sprays produced by a common-rail injection system in a diesel simulation cell. The parameters of the data base include injection pressure (40, 80 and 150 MPa), gas-side temperature (387, 800 and 1100 K), gas density (12, 25 and 30 kg/m3), injector nozzle hole size (0.17 and 0.20 mm) and injection programs (with and without pilot injection). Single component fuels (heptane and dodecane) were used in order to simplify data interpretation and modeling. The spray characteristics which were measured include the initial “dispersion” angle of the nozzle, initial spray tip speeds, and spray tip penetration vs. time for both the liquid and vapor parts of the spray. The sites of initial self ignition and combustion propagation within the sprays were visualized, and a luminous delay was measured for several of the operating conditions.

Using a technique based on holographic interferometry, the total energy transferred from a spark to the surrounding gases was measured for a number of spark plug electrode geometries, flow velocities, gas pressures and coil charge times. A standard automotive ignition coil was used. For the combinations of parameter values studied, we observed “spark efficiencies” (ratio of the energy in the gas heated by the spark to the electrical energy supplied to the spark plug) of from 20 to 60 percent. For realistic engine conditions we estimate the quantity of energy transferred to the gas by our ignition system to be roughly 30 mJ. We show how these measurements of total energy transferred to the gas can be used to estimate the spark power vs. time characteristic of a standard inductive ignition system.