Sealing characteristics of piston ring in a free-piston diesel engine for linear alternator

In order to study the sealing characteristics of piston ring in free-piston engine, a mathematic model of piston ring sealing in cylinder was established based on thermodynamics equations and one dimensional isentropic flow equation. The effectiveness of the sealing model was verified with the experimental data of static sealing in engine. The difference of piston rings sealing in crankshaft-piston engine and free-piston engine with the same cylinder diameters was obtained and analyzed with the mathematic sealing model and an existing engine performance model. The results show that the piston ring of free-piston engine possesses a longer sealing time than the piston ring of crankshaft-piston engine with less gas leak in one working circle. In compression stroke, gas leak in the combustion chamber of free-piston engine are more than that in crankshaft-piston engine, but less in combustion and expansion strokes. Selection of appropriate compression ratio, rings spacing and electromagnetic load is helpful for reducing leakage loss.