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Three dimensional computational model has been developed to predict the macroscopic behavior of the fuel spray in D. I. diesel engines. The model was based on the KIVA-II code with modification of some submodels that it can deal with the observed phenomena such as liquid column near the nozzle tip and spray impingement on a wall. Firstly, this model was verified by comparing the prediction with the experimental results in a constant volume vessel. Secondly with application to a D.I. diesel engine, the detailed behavior of the spray in a combustion chamber was revealed. Moreover, the engine performance under different spray angles were discussed with the prediction of this model.

This paper introduced a very simple method to measure the liquid phase of spray in an optically accessible DI diesel engine. Particular attention was paid to easy usage and maintaining the compression ratio of the real engine. As a result, a less-expensive 4 W argon laser was used as the beam source and an E-10 high-speed camera was used for continuously observing the elastic-scatter liquid phase image. Meanwhile, the compression ratio can be kept as the real engines by this method. Through this method, the effects such as injection pressure, nozzle specification, intake air boost and temperature on liquid phase penetration before ignition were investigated. Reducing nozzle hole diameter decreased the length of the liquid phase. Increasing injection pressure hastened the evolution of liquid phase, while the liquid phase length varied complexly. Increasing intake air boost considerably shortened the liquid phase penetration and ignition delay.

Fuel injection rate pattern represents an important factor for emissions reduction. In this study, fuel spray photography, combustion photography and experimental data analysis indicate. 1) effect of pilot injection 2) effect of a gradual shaped injection profile using nozzle needle lift control 3) effect of a boot shaped injection profile using pressure control Common rail type fuel injection equipment was used in these experiments, and the engine was single cylinder naturally aspirated D.I. diesel engine. As a result, we found out that it is important to control the pre-mixed combustion for NOx reduction and to activate the diffusion combustion for smoke, and various fuel injection rate patterns we studied have similar effect on combustion and emissions at the most suitable condition respectively.

Supercharging as the method of increasing the output of diesel engines has a long history. Recently, because the potential for lower exhaust emissions for a given power output, supercharging has been considered as a method to reach increasingly strict emissions standards. Some research investigating the effects of supercharging has shown favorable results in terms of emissions(e.g.[1][2][3] *). Also some fundamental studies have examined the effect of ambient pressures on the characteristics of spray and ignition in constant volume combustion borb[4][5][6][7]. However, for further improvement of combustion when utilizing supercharging, more detailed information inside of the combustion chamber is needed about the effects of supercharging on fuel spray and combustion. In order to gather this information, it is necessary to observe the processes within the combustion chamber of a supercharged engine.

To analyze the combustion phenomena of DI diesel engines in detail, the “cross-correlation method” and the “two-color method” have been applied to measure the combustion flame motion and the flame temperature, respectively by processing the high speed photographs. The purpose of this investigation is to study the effects of engine parameters such as pumping rate, injector nozzle hole size, and injection timing on combustion processes; particularly on flame motion and flame temperature. The results showed that the flame motion was more active during the injection period; and after the end of injection, the motion of flame was largely governed by the air swirl. Increasing fuel pumping rate and using a small hole area injector nozzle, caused the flame motion to become more active, especially during the injection period. The flame temperature was higher with both increased pumping rate and advanced injection timing.

An experimental study aiming to investigate the effects of combustion chamber geometry on combustion process has been carried out in an optically accessible DI diesel engine. The combustion processes of three different chamber geometries, included the production type, were revealed and the flame movement behaviors such as the distribution of flame velocity vectors and the averaged flame velocity inside and outside the combustion chamber were measured by means of a cross-correlation method. Meanwhile, an endoscope system was used to acquire information about the distribution of flames inside and outside the chamber. BY comparing the flame movement and distribution between different chambers and nozzle protrusions, the results showed that; The chamber geometry has significant effect on the flame velocity, the flame velocities of the reentrant chamber were larger than that of the dish chamber during expansion period.

It is well known that a high-pressure fuel injection is effective for the reduction in particulates and smoke emissions. Exhaust gas recirculation (EGR) is effective for the reduction in NOX emission. In this study an experiment aiming to understand more comprehensive combustion under the condition of EGR and high-pressure fuel injection was carried out by using gas sampling method for the purpose of understanding what occurred inside the spray before and after combustion. The number of combustion cycles in this engine can be controlled in order to change EGR conditions by adjusting the residual gas concentration in the cylinder. Main results were: (1) Close to the nozzle tip, the sampling gas data showed little reaction which implies that combustion never occurs in this area during the injection period. (2) In the case of high-pressure fuel injection O2 concentration decreased faster and air dilution was more active and earlier.