Multibody analysis of the opposed-piston aircraft engine vibrations

Abstract

Abstract One of the characteristic features of piston engines are vibrations caused by the pistons moving in the cylinders. During the engine design process, it is necessary to determine the level of vibration that can occur in the engine. This is especially important for aircraft engines. Due to the minimization of the weight of the aircraft, it is necessary to limit the factors that may cause damage to the structure. One of these factors is engine vibration, which can cause resonance and, consequently, a dangerous stress concentration. Long-term action of variable loads may also lead to the formation of fatigue cracks. The article presents the results of a multibody analysis of an opposed-piston diesel engine. It is a two-stroke three-cylinder aircraft engine. The engine has two crankshafts and six pistons that run opposite each other, but the rotation of the shafts is shifted in phase 14°. Engine vibration will also be caused by crankshafts which, to reduce weight, are not equipped with counterweights. The calculation results are presented in the form of time courses of forces and displacements on the engine supports and FFT analysis of the vibration velocity. The results show that the maximum vibration velocity is 7 mm/s and occurs at a frequency of 140 Hz, which corresponds to twice the rotational speed of the crankshafts. The results obtained from the tests allow for the selection of the flexible elements used in the real prototype engine supports.