Study On Dynamic Characteristics Of Piston Group Of High Pressure Common Rail Diesel Engine

In recent years, with the development of engine technology, the engine has been strengthened in all respects, meanwhile, the emission performance and fuel economy of engine are put forward higher request. As the core components of engine, the piston component is under the more demanding work environment, which is brought by the high enhence, its performance directly affects the engine’s power, economy and emission. Study on the dynamics of piston component can provide theoretical guidance for optimizing engine structure.The piston assembly of a four-cylinder common rail diesel engine was chosen as the research object.Obtained the temperature field of the piston and cylinder by experiment as boundary condition for simulation model. In order to test the validity of the simulation model, compared the simulation results with experiment one, that provided the basis for the subsequent simulation. The impacts of the structure of piston skirt, pin hole position and displacement of cylinder and piston on the piston secondary motion, lubrication characteristics and friction loss were researched. Finally, the influence of different piston ring structure and performance on the engine oil consumption, friction loss and the influence of blow-by in the cylinder is studied.The results indicate that:1) When the diesel engine at rated operation test, the highest temperature of the piston is 360.2℃, which located in the throat of piston,the minimum temperature is 156.3℃, mean temperature is 258.3℃.The highest temperature of the cylinder is 178.3℃, the minimum temperature is 91.3℃.2) The piston structure greatly affects the movement of the piston.Maximum piston tilting angle reduced 48.1%, and friction loss power reduced 84.2% when the convex position of piston skirt rised from 10mm to 15mm. It does contribute to reduce knocking kinetic energy when reduce the ellipticity of piston skir, but too large contact area will make the friction loss increase, friction loss power increase 26.6% when piston ellipticity decreased from 0.4mm to 0.2mm. Regardless of the position of pin hole is biased toward the main thrust or anti-thrust can reduce the noise, but the friction loss can be increase when biased toward anti-thrust. Increasing the clearance between the cylinder and piston can lead to the increase of the secondary motion amplitude and the knocking kinetic energy, but it can reduce the friction loss, friction loss power reduced 25.8% when the displacement of cylinder and piston up to 0.065mm from original clearance.3) The piston ring structure greatly affects the blow-by and oil consumption.The second land clearance of piston from 0.15mm increased to 0.95mm, The quantity of blow-by gas has increased rapidly by growth of 62.9%。The top ring and second ring held clearance has the greatest impact on the blow-by gas quantity in the all ring held clearances,.And the clearance increased from 0.45mm to 0.65mm, the quantity of blow-by gas is increased by 35.2%, meanwhile, the quantity of oil blow has increased. It has less effect on quantity of blow-by gas by ring groove depth and width. Increasing the radial elastic force of the piston ring is beneficial to reduce the gas flow, but it will increase the friction loss of the ring.