In order to validate the potential advantage of low friction loss for free-piston engine generators
a hybrid lubrication model of the piston ring was established. The thickness of oil film
friction force and friction loss power in both crankshaft engines and free-piston engine generators with the same cylinder diameter were obtained through the numerical simulation. The comparison analysis indicates that their oil film thickness is close with the similar average power of friction losses. The peak friction force of the free-piston ring is greater than that in crankshaft but its duration is shorter. In terms of the total friction loss
the free-piston engine generator will have a significant advantage if the losses of other components such as the cam and crankshaft in crankshaft engines are considered.
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