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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.

For better understanding, model development and its validation of in-cylinder soot formation processes of Gasoline Direct Injection (GDI) engines, visualization of piston surface fuel wetting, vaporization and soot formation processes of in-cylinder pool fire via high-speed UV (266nm) and visible (445nm) laser shadowgraphy was attempted in an optically accessible Rapid Compression and Expansion Machine (RCEM). A direct-injection, spark-ignition and single-shot combustion event was achieved in the RCEM under engine-equivalent, simplified and well-defined conditions operated with engine speed 600 rpm, compression ratio 9.0, equivalence ratio 0.9 and natural aspiration. The tested fuel was composed of 70% iso-octane and 30% toluene by volume and the UV absorption by toluene enabled visualization of the in-cylinder fuel distribution.

For better understanding of in-cylinder soot formation processes and governing factors of the number of emitted soot particles of Gasoline Direct Injection (GDI) engines, Transmission Electron Microscope (TEM) analysis of morphology and nanostructure of the soot particles sampled in the exhaust should provide useful information. However, the number concentration of the soot particles emitted from GDI engines is relatively low, which was impeding reliable morphological analysis of the soot particles based on a sufficient number of sampled particles. Therefore, in the present study, a water-cooled thermophoretic sampler for simple and direct sampling of exhaust soot particles was developed and employed, which enabled to obtain a sufficient number of particle samples from the exhaust with Particulate Number (PN) 105 #/cc level for quantitative morphology analysis.

Recently, mechanically driven superchargers are being manufactured and applied to engines in order to increase the torque in low speed range and improve acceleration response. In our study, four types of positive displacement superchargers were picked up and the engine performance tests were carried out with each of them. The results were compared to each other, and finally, the advantage of a screw type supercharger was confirmed. At the same time in this paper, three types of high technology turbochargers are introduced, which are superior to the conventional ones from the viewpoint of low speed characteristics, transient response, and so on. Effectiveness of high technology turbochargers were described here with the test results.

Turbochargers have become very popular on passenger cars since the first mass-produced turbocharged passenger cars were put on market in Japan in 1979. Turbo lag is one of the most serious problem since the first mass-production started. Several new technologies such as a variable geometry turbocharger, ceramic turbocharger, etc. have been introduced to improve acceleration performance. A variable geometry turbocharger changes the area of gas flow passage and increases exhaust gas speed at low engine speed. A ceramic turbocharger reduces inertia moment of a turbine wheel and shaft. Turbocharger mechanical efficiency has equal importance as compressor efficiency and turbine efficiency. This paper describes the test results of ball bearing turbochargers developed at our company.