The Simulation Study Of The Working Process Of An Opposed-piston Hydraulic Free Piston Engine

The opposite cylinder dual piston hydraulic free piston engine, whose cylinderand piston were arranged in OPOC style. There was less vibration as two pistonsmove symmetrically, and since the crank was replaced with hydraulic pump as thedriving device, there was no lateral force of the piston, no rigid connection betweenthe piston and power output devices, and variable compression ratio can be easilyachieved. The power generated during combustion is stored in the form of hydraulicoil, which can be directly used by other hydraulic devices, and easily stored inaccumulators.The piston motion of hydraulic free piston engine is governed by the interactionof forces that act on the piston simultaneously, including pressure from cylinder,pressure from hydraulic oil. Earlier studies indicate that compared with conventionalengine working at same frequency, compression stroke in free piston engine spendslonger while expansion stroke spends shorter.The free piston engine studied in this study is still in development, to get preparedfor continuously running, the scavenging process should be studied and optimized.Parameters of the engine breathing system studied in this thesis including the radialangel and the height of the intake ports, and the time spent at bottom dead center.In this thesis, CAD model and CFD model was build using Pro/Engineer andAVL Fire. Simulation study was performed on combustion process and scavengingprocess. The simulation results indicated that:The free piston engine is more sensitive to working frequency than conventionalengine working at same equivalent ratio and compression ratio. Combustion processtrends to breakdown when the working frequency is too high; causing a rather lowindicated thermal efficiency. Such situation won’t be seen on conventional engineworking at the very same condition.The combustion process can be effectively controlled through adjusting theworking frequency of the engine. The peak pressure and peak pressure increase ratecan be reduced through increasing the working frequency before the indicate thermalefficiency begin to drop dramatically. The phase of combustion, peak heat release rate increase rate increased and theheat release duration decreased while the equivalent increased.The highest scavenging efficiency0.907is achieved when the radial angle is5degree, intake port height is11.52mm and the time piston spent at bottom dead centeris0.0092s, trapping efficiency at this point is0.693.The tumble and the squish is not considered during the designing of the enginebreathing system, as the result the fresh charge and the exhaust left in cylinder can’tbe sufficiently mixed...