【作者】

Guenter Elsbett，Zongying Gao，Zhong Wang

【摘要】

论文已在中国上海举行的2013年CIMAC大会上发表，论文的版权归CIMAC所有。Opposed Piston Engines (OPE's) are looking back to more than 100 years history and have been produced as Otto and Diesel engines, offering a promising challenge in specific output and thermal efficiency. Diesel-OPE's have been used regularly for commercial aircraft due to excellent power/weight ratio, but powering also merchant ships with big engines of several thousands of kW. Already 75 years ago a brake efficiency of more than 40% could be achieved. In recent decades these engines seems for-gotten while the research and development engineers put their main focus on emission improvement. Conventional OPE-technology is known for emission problems, especially caused by scraping lubrication oil into in-and outlet ports, as common OPE's scavenging is limited for use in 2-stroke engines only. Now some new developments in OPE-technology show their relevance to future power-train challenges. Better thermal efficiency is attracting the development engineers, as two pistons share only one combustion chamber, thus leading to beneficial volume/surface ratio of the combustion chamber. Nevertheless, also in most today's opposed-piston-engines the scavenging is con-trolled by pistons. Whereas the OPE presented is operated as 4-stroke-engine by arrangement of hydraulically shifted liners undisrupted by scavenging holes or gaps so that the pistons with their rings are shielded against crossing any in-or outlet-ports. Therefore all the modern engine-technology to increase mileage, reduce oil consumption, wear and emission can be implemented in this OPE-Technology presented. So this design combines the advantages of an opposed-piston-principle with the benefits of the classic engine technology for technical and economic progress. A first prototype has been tested successfully, demonstrating also the mechanical function of shift-liners without problems and showing very low friction losses for the shift liners. The wall thickness of these liners can be kept low-like conventional dry liners-as they are supported by the surrounding cylinder, leading to low oscillating liner masses during shifting. The in-and outlet ports are located near the pistons top dead center area and are opened and closed by the upper end of the shift liners like valves, which are closed by spring forces and opened by hydraulic actuation. Different to conventional OPE's there are no distinct exhaust or intake pistons and thermal load is nearly equally distributed on both pistons. The hydraulic system shares the lubrication oil with the engine, avoiding leakage problems and providing a simple oil circuit. The presented design offers also two different modes of combustion technologies: Injection from the outer combustion chamber edge towards the chamber center(from cold to hot), or injection from above the combustion chamber center towards the chamber walls(from hot to cold). For the first mode one or more injectors are positioned around the cylinder, providing the chance for multi-nozzle injection in different time and quantities. For the second mode the cylinder inner wall must be considered as a virtual cylinder head with all same geometric dimensions as for a classic combustion chamber, but including injection completely rotated by 90. It is providing state-of-the-art conditions like well developed common engines today in production, but requiring only one injector for 2 pistons. As no piston rings are crossing the in-and outlet ports, the presented engine is aiming for very big gas flow sections-not interrupted by window lands or port ribs so far much bigger than conventional multi-valve technique could allow for-with the result of better cylinder filling and less dynamic gas flow losses. As the shift liners are hydraulically actuated a variable valve timing can be easily achieved, as well as a complete cylinder cut-off in multi-cylinder engines.

【会议名称】

第27届CIMAC会议

【会议地点】

上海

【下载次数】

1

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