Dynamic Analysis of the Single Piston Hydraulic Free Piston Engine

Abstract

The connection of the engine body and the base was simplified as a spring and a damper to analyze the body vibration of the single piston hydraulic free piston engine. It was demonstrated that the increasing of the connection spring rate can reduce the amplitude of the body vibration. But the reduced vibration amplitude was trivial after the spring rate was increased above 300KN/m. The damp ratio of the connection had little influence on the body vibration. The introduction of a pump chamber into the structure in the compression stroke can shorten the rebounding displacement of the free piston assembly (FPA) while it was settled at the right dead center working in pulse pause modulation (PPM) mode. Furthermore it can keep the FPA have an enough stroke to achieve a predetermined compression ratio and reduce the fluctuation of the pump flow. The compression ratio can be improved through increasing the pressure of the compression accumulator and decreasing the pressure of the high pressure accumulator. Also the compression ratio and the operation frequency of the engine can be improved by shortening the switch time of the control valve and prolonging the open time.

Coupled effect of injection position variation on gas exchange stability of a free-piston engine

“…(5) The scavenging CFD model is re-established and then calculated using the updated piston motion and combustion results. (6) Rebuild the combustion CFD model and then calculate it based on the updated piston motion and gas exchange results. (7) Steps ( 4), (5), and (6) will be repeated until they satisfy the iterative convergence condition.…”

“…5 As a result of the lack of crankshaft, FPE features many performance advantages such as free movement, variable compression ratio and flexible combustion drive. 6,7 As a key part of the cycle operation of FPE, the gas exchange process has a significant impact on the combustion performance of the engine. Thus, there are many researches focusing on the gas exchange process.…”

“…5 As a result of the lack of crankshaft, FPE features many performance advantages such as free movement, variable compression ratio and flexible combustion drive. 6,7…”

On–off motion of a hydraulic free-piston engine

“…Many simulation models have been proposed for FPE simulation. [12][13][14][15] A full-cycle model of the SPHFPE has been presented by Hu et al 12 The simulation model used in the present research was developed from the full-cycle model. To forecast the piston on-off motion more accurately, some changes in the full-cycle model were made.…”