Experimental Study Of Intake And Exhaust Schemes Of Free Piston Expander-linear Generator

In recent years,the free-piston expander-linear generator（FPE-LG）has been widely used to recover waste heat energy of engines due to its compact structure and high power output.However,the performance of FPE-LG is substantially affected by intake and exhaust.A FPE-LG device used for waste heat energy of engine is built to analyze the influence of different intake and exhaust schemes on the performance of FPE-LG.Four intake and exhaust schemes used for FPE-LG device are proposed: the scheme based on the displacement control strategy and the intake and exhaust pipes with inner diameter of 8 mm（d = 8 mm）,the scheme based on the displacement control strategy and the intake and exhaust pipes with inner diameter of 12 mm（d = 12 mm）,the scheme based on the time control strategy and the intake and exhaust pipes with inner diameter of 8 mm（d = 8 mm）,the scheme based on the time control strategy and the intake and exhaust pipes with inner diameter of 12 mm（d = 12 mm）.The FPE-LG device with working fluid of compressed air is used to study and analyze four intake and exhaust schemes,the optimal intake and exhaust scheme is selected to maximize the performance output of the FPE-LG device by analyizing the varation of the operation frequency,peak voltage output and peak power output under the four intake and exhaust schemes.Based on the displacement control strategy,the performance ouput of the FPE-LG device with intake and exhaust scheme of d = 8 mm and d = 12 mm is compared and analyzed.Results show that sine wave of displacement,velocity and acceleration of free piston assembly（FPA）with scheme of d = 12 mm is better than that with scheme of d = 8 mm.Operation frequency,actual stroke,peak voltage output,peak current output and peak power output gradually increase with intake pressure,the maximum value with scheme of d = 12 mm is significantly higher than that with scheme of d = 8mm,the maximum peak power output can reach 57.4 W.Based on the time control strategy,the performance ouput of the FPE-LG device with intake and exhaust scheme of d = 8 mm and d = 12 mm is compared and analyzed.Results show that operation frequency,actual stroke,peak voltage output,peak current output and peak power output gradually increase with the increase of intake pressure,the maximum value with scheme of d = 12 mm is significantly higher than that with scheme of d = 8 mm,the maximum peak power output can reach 9.88 W.Based on the displacement control strategy,the influence of intake process on the intake pressure loss,volumetric efficiency and air resistance of FPE-LG with intake and exhaust scheme of d = 8 mm and d = 12 mm is compared and analyzed.Results show that intake pressure loss can be reduced by inincreasing the flow area of the intake and exhaust pipes.The volumetric efficiency increases with fixed position point.The air resistance increases with intake pressure.The performance of FPA with time control strategy and displacement control strategy is compared and analyzed.Results show that FPA with displacement control strategy operate stably under high intake pressure.FPA with time control strategy require strict the symmetry of forth and back due to the disturbance in the intake and exhaust pipes.Therefore,the displacement control strategy is more helpful for stable operation of the FPE-LG,compared with time control strategy.Analyzing the performance of FPE-LG device with four intake and exhaust schemes,it can be seen that the intake and exhaust scheme with displacement control strategy and d = 12 mm is better than others.With this scheme,the maximum operation frequency can reach 4.55 Hz,the maximum peak AC current output can reach 2.361 A,the maximum peak DC current output can reach 2.036 A,the maximum peak AC voltage output can reach 63.28 V,the maximum peak DC voltage output can reach87.58 V,the maximum peak power output can reach 57.4 W.