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For further improvement of diesel combustion performance, in-cylinder air injection was applied to enhancing air entrainment in an attempt to shorten the combustion duration. A modified commercially available gasoline injector was used for air injection. The original six-hole nozzle was removed, and a three-hole nozzle (ϕ0.43 mm × 1 hole, ϕ0.5 mm × 2 holes) was used. The air injector was installed near the fuel injection nozzle on a single-cylinder diesel engine, and a performance test was conducted to investigate the effects of the air injection duration, timing, and pressure under the operating conditions of an engine speed of 1200 rpm, fuel injection pressure of 120 MPa, natural aspiration, and without exhaust gas recirculation. In addition, the effects of supplying different gases were considered.

In-cylinder total sampling technique utilizing a single-cylinder diesel engine equipped with hydraulic valve actuation system has been developed. In this study, particulate matter (PM) included in the in-cylinder sample gas was collected on a quartz filter, and the polycyclic-aromatic hydrocarbons (PAHs) component and soot were subsequently quantified by thermal desorption-gas chromatograph mass spectrometry (TD-GCMS) and a carbon analyzer, respectively. Cylinder-averaged histories of PAHs and soot were obtained by changing the sampling timing. It was found that decreasing intake oxygen concentration suppresses in-cylinder soot oxidation, and the fuel with higher aromatic and naphthenic contents accelerates soot production.

A reduced chemical kinetic model of diesel fuel, which can be applied to computational fluid dynamics (CFD) simulation coupled with detailed chemistry using the CONVERGE software, is developed to simulate the particulate matter (PM) formation process. We analyzed the influence of varying intake oxygen concentrations and fuel composition on the polycyclic aromatic hydrocarbons (PAHs) and soot formation processes. When the intake oxygen concentration was decreased, no significant difference was observed in PAH formation associated with soot formation, and the soot mass generated after the peak was high. When the fuel contained high levels of aromatics and naphthene, the PAH and soot formation mass increased. These tendencies were in good agreement with experimental results [1].

To improve the impinging spray's computational fluid dynamics (CFD) calculations under evaporating conditions, a detailed large eddy simulation (LES) code was constructed and examined for modeling the near-wall-velocity behavior of the impinging jet. The near-wall-velocity profile within the impinging jet was found to be different from that obtained using the steady wall functions. On the basis of this knowledge, a simple model of the wall boundary conditions was proposed for the impinging jet. The tests covered two different turbulence models. Comparing with the conventional wall functions, the proposed model improved the accuracy of the impinging spray simulations.

The cause of unburnt hydrocarbon emission (HC) in small DI Diesel engines at light load was studied both by engine emission tests and combustion process visualizing with a common rail injection system. An optically accessible engine, which was enabled to visualize both combustion chamber and squish area, was used to investigate the behavior of spray, mixture distribution and so on. Factors supposed to be the major cause of forming HC in small DI Diesel engines, such as the direct impingement of liquid-phase fuel spray on the combustion chamber wall, the uneven formation of fuel sprays from hole to hole and the spread of the fuel droplets, mixture and flame to the squish area were investigated. Meanwhile, measures for further reducing HC were discussed.

Spray model of KIVA-II code was modified by comparing with experimentally measured spray liquid phase penetration and spray image in a transparent engine. The KIVA-II code with modified spray model was applied to a HSDI engine with different combustion chamber shapes, nozzle specifications and injection pressures. The results were compared with experimental emissions and it was found that the modified KIVA-II code was relatively able to predict the effects of engine design factors such as combustion chamber shape and injector on NOx and soot emissions.

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.

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.