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In a boat two-stroke two-cylinder engine, SC-port fuel injection of CNG was applied at running condition in comparison with the fuelling with a gas-mixer. Three methods of tests were employed; operation at a test-bench, at an anchored condition and on a running boat. In a lower engine speed, the beneficial effect of higher thermal efficiency was obtained, while in higher engine speed range especially at the running condition, it has the inverse effect of lower thermal efficiency. It is based on the limited range of lower injection rate of the fuel injectors, and thus the fuel injection rate of this type of fuel injectors has a key role of developing the technology of the SC-port injection.

This paper presents the effect of application of scavenging-port injection to a two-stroke two-cylinder boat engine fueled with a compressed natural gas (CNG). Experiments were carried out at a constant speed of 3000 rpm and WOT condition with varying excess air ratio in lean region. A CNG injector for a production automobile engine was utilized and installed into the scavenging ports. Comparison was made with homogeneous charge operation using a gas mixer. By applying the scavenging-port injection, unburned-fuel in the exhaust gas was reduced close to half which must be due to the reduction of fuel short-cutting during the gas exchange process. The lean-burn limit was extended from the excess air ratio of 1.21 to 1.57. The maximum decrease of BSFC reached to 25 %. This suggests that stratified-combustion could be realized in its lean-burn region.

This paper presents two factors for improving the performance and emissions characteristics in HCCI diesel combustion, one is reducing compression ratio and another is changing the injector position. In a previous study, it was shown that HCCI diesel combustion could be realized by utilizing a hollow-cone spray with normal injection pressure. However there remained two major problems of engine instability and increase in BSFC (decrease in brake thermal efficiency). By reducing the compression ratio from 18.8 to 16.8, the engine stability was much improved to the level of conventional diesel combustion and the increase in BSFC became almost half, which was mainly due to the change of combustion phasing. In addition to this, application of 5 mm inside position of the injector realized almost no penalty of BSFC at higher load condition.

By using an inside visible carburettor, effects of high voltage application to the injected fuel on its behaviour and engine performances are investigated. At first five electrode arrangements around the venturi are examined to clearify the charging mechanism on the injected fuel and its effect on the fuel atomization. The experimental results show that when induced charging, corona charging and electrostatic force are effectively applied to the injected fuel, its atomization is remarkably improved. The diameter of fuel droplets monotonously decreases with increase of applied voltage and the effect is more distinct when the induced air velocity is low. Firing engine test is also carried out and it is revealed that when the throttle valve opening is large, the application of voltage considerably spreads the combustible range toward leaner side. Cyclic variation is reduced and startability is improved by the charge under the severe operating condition.

This paper presents the fuel atomization effect of a fuel supply system on the lean burn characteristics of a spark-ignition engine and its mechanism. The fuel supply system can realize extremely different two state of atomization, i.e., wall-film of fuel flow and ultra-fine spray (less than 7 um S.M.D. by Malvern measurement). For the first step of the study, the atomization effect is examined under steady operation; several operating parameters including cyclic variability are expressed against the A/F over the wide range of operating condition. Within the operation limits, the fuel atomization does not affect any parameters, while it gives pretty much influence on the lean operation limit. Furthermore, this influencing behavior strongly depends on the throttle valve position and its opening.