The stress analysis of high loaded diesel engine piston

Modern diesel engines reach high power out put per volume unit. This is the main reason, why modern passenger cars and other medium size vehicles are powered by those engines. It is very important to keep reliability, characteristic for past generations of diesel engines. It is a difficult task, because of higher thermal loading of engine parts, especially pistons. Typical fuel injection systems are now, almost all, high pressure, common-rail systems. Modern common-rail injectors are situated centrally between valves, and are manufactured as minimum six nozzle injectors. Combustion chamber is made in piston crown. This is the highest thermal loaded part of whole engine. Injected fuel starts to burn when piston is near to TDC position. Flame acts piston surfaces, what can be proven by inspection of piston with help of endoscope, or after removing engine head. The thermal load of piston crown is not uniform, due to not uniform conditions of heat transfer at piston crown surface. Part of piston crown reaches higher temperature due to direct flame acting. Authors present results of numerical simulations, which were done to check how stresses in piston depend on injector position and temperature distribution in piston materiał. The results of calculations indicate, that injector should not to be situated randomly. If nozzles of injector are situated in such way, that burningfuel sprays acts piston in the piston pin plane, stresses in hub of piston pin and piston crown increase significantly. That can decrease reliability of engine due to piston failure. Authors indicate, that thermal load is the most dangerous for piston of modern, common-rail diesel engines. Load caused by mass forces and pressure are less important when temperature of some regions of piston is above 320°C.