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We visualized behavior of crevice flows in a spark ignition gas engine by laser-induced fluorescence (LIF) of acetone and OH. The fuel used in this work was methane with 10 vol. % acetone vapor. Acetone acts as a LIF tracer for unburned fuel, and OH radical which exists naturally in hydrocarbon flames is used as a marker species of high temperature zones. This technique enables simultaneous tomographic observations of high temperature zones and unburned zones in engine cylinders, and the technique gives abundant information on oxidation process of fuel. A transparent engine whose cylinder wall was made of fused silica for observations and laser access was used for experiments. A crevice flow released from a crevice between a piston and a cylinder wall was visualized. In this work, we investigated effects of valve timing, back-pressure, and ignition timing. We found that behavior of the crevice flow changes suddenly at moment of exhaust valve opening.

Although Homogeneous Charge Compression Ignition (HCCI) engines are expected to attain higher thermal efficiency while reducing NOx emission, the operation performance suffers under high load conditions. In a previous report, we have showed the basic operating characteristics of a natural gas-fired HCCI engine. The present study focuses on the characteristics of HCCI combustion using cooled EGR. It was found that with EGR the load increased by over 20% compared with the previous baseline case. Furthermore, effects of inhomogeneity are investigated by varying EGR supply methods. Inhomogeneous EGR narrows a suitable operation range for EGR and modifies the heat release pattern, indicative of the inhomogeneity to possibly regulate HCCI combustion.

The lean burn gas engine ignited by pilot oil is a promising alternative combustion system [1]. First, pilot flame is auto-ignited, then ignition source propagate toward lean gas mixture. Despite much research work conducted experimentally [2] [3], little phenomenological understanding has been made on ignition characteristics of this combustion system. This makes improvement of engine performance a difficult task. The main objective of the present study is to reveal the combustion phenomena and ignition characteristics by visualizing the combustion chamber while the engine is operated under the dual-combustion mode and the pure diesel mode at the same amount of light diesel-oil. An open-chamber type single cylinder research engine is employed, together with an endoscope suitable for observing a small space. Endoscope was inserted into the combustion chamber to allow continuous observation of the very fast combustion phenomenon that was photographed using a high-speed video camera.

Lean burn gas engines are expected to reduce NOx emission while improving engine performances such as output and thermal efficiency. Recently, an ignition method using a small quantity of diesel fuel (pilot fuel) as an ignition source for lean-burn gas engines has introduced further improvement of their performance. Generally, this method has been used for pre-chamber engines because it could not successfully lead to reduce NOx and Particulate emissions when adopted for open-chamber engines. However, the possibility of improvement of performances of open-chamber engines with this ignition method has also been expected(1). An experimental study was conducted to investigate the performance of an open-chamber gas engine with pilot fuel for ignition source. Experiments were conducted by using a single cylinder gas engine equipped with a common-rail injection system.

Research and development of a low NOx lean burn combustion for open chamber gas engines have been carried out. The target NOx level has been set below 200 ppm with superior thermal efficiency to the engines with three-way-catalyst. A number of open combustion chambers were tested. Swirl combustion chambers NEBULA and TG (the latter was newly developed by the authors) and a squish chamber REENTRANT have satisfied the target while maintaining sufficient stability of combustion. It has been demonstrated that open chamber gas engines are potentially capable of achieving low NOx emission while maintaining high thermal efficiency.