Development Of G300 Diesel Engine Composite Piston Used For Power-increased Marine Applicatiion

Based on the increasingly improvement on performance and durability of key parts,a continuous development of internal combustion engine has been acquired. As one of the most stringent components in diesel engine, piston transfers the driving force during its high-speed reciprocating motion and withstands high mechanical load and thermal load. Reliability testings showed that the performance of diesel engine is greatly depended on piston and its relatively weak service life, a poor piston might hinder the development of technology of diesel engine power-increasing. The design and machining of the piston would directly affect the economy,reliability, maintenance interval and life cycle of the diesel engine.As one of four-stroke medium-speed diesel engines, G300 series diesel engine was developed in 1976 for the first time ,which is widely used in marine propulsion and generator sets with the development of power-increasing, fuel consumption reducing, running with heavy fuel oil and a greater than 20,000 h service lifetime. The G300 series diesel engine manufactured by Wuxi Diesel Engine Works and Ningbo Diesel Engine Works accounted for 80% of the domestic marine propulsion and 40% of domestic generator sets market share.To be in line with the requirement of pistons for the sake of G300 diesel engine enhancement, this article aimed at diesel engine output power increasing, combustion performance improving, piston weight reducing, fuel consumption decreasing and heavy fuel oil operation,research on piston structural design, material selection, process assurance has been done to implement theoretical calculation,experimental analysis and fatigue reliability evaluation for the newly developed G300 diesel engine composite piston, detailed as followed:1) The piston structure has been redesigned. Piston structure changed from one-piece nodular casting iron piston to two-piece composite piston , forged steel crown bolted with nodular casting iron skirt.The newly developed piston with 4 ring grooves showed a 6.9% weight-decreasing characteristic compared with its former version,which is a 5-ring grooved piston.A reasonable wall thickness of key structural elements has been established for the sake of piston strength optimizing and piston failure avoiding based on engineering experience and norms.2) By UG modeling and MSC MARC finite element analysing, obtained heat stress and mechanical stress of the new-designed piston with consideration of contact condition. A result showed that piston temperature distribution, piston deformation and dynamic safety factor under its various working conditions are all meeting with the design requirements.3) In order to investigate the movement performance of new-designed piston, piston motion analysis and contact analysis are carried out by using of AVL GLIDE, results showed a satisfied operating performance and contact condition.4) Strain method with resistance is used to test the static strength under various simulated operating conditions, results showed that the static strength safety factor met with the design requirements .5) Hardness plug method is used for piston temperature field testing,a conclusion showed that test results are basically consistent with the results determined by finite element method,which verified the accuracy of theoretical calculation.6) According to the result of calculation,reliability assessment was carried out towards the high-stress part of piston skirt by using stress - strength interference model, a conclusion called out that the reliability of the new-designed piston could reach a more than 0.99999 value with a 20,000 h operating interval.The development of piston used for power-increased G300 diesel engine proved to be successful. Updating and upgrading of piston products are being required more and more frequently due to innovation of design and manufacturing technology, piston with high reliability and high performance is expected to satisfy the development of diesel engine for highly power-increasing, high fuel economy and low fuel consumption as well as low emissions .