Design And Performance Of Active Free Piston Stirling Engine

The situation of energy and environment in the world is becoming more and more severe.With its unique advantages,Stirling engine is becoming a hot spot in the research and development of new energy.However,research work at home and abroad is mostly concentrated on passive Stirling engine?PSE?.The problem of poor adaptability to variable working conditions and the inability to start quickly at any time has been difficult to solve.The active Stirling engine?ASE?can employ an adjustable actuator to achieve better performance while solving above problems.A3D model of active free piston Stirling engine?AFPSE?was built by Pro/Engineer software.The physical prototype was manufactured,and the whole test bench was built.The relevant experimental research was carried out on AFPSE by using indicator diagram method and the DC motor reverse drag method.The main research contents and conclusions are as follows.?1?From the analysis of the motion law of the power piston and displacer piston,it was found that the test was carried out in a non-resonant state,and the engine performance was not optimal.The stroke of the power piston increased with the increase of speed.Under low speed condition,the stroke of the power piston increased with the increase of heating temperature,and vice versa at higher speeds.The smaller the spring stiffness,the larger the power piston stroke and the greater the increase with the increase in speed was.As the speed and heating temperature increased,the upshift of power piston bottom dead center?PPBDC?was far smaller than power piston top dead center?PPTDC?and the increase in power piston stroke was mainly determined by the upshift of PPTDC.The displacer piston stroke fluctuated within a certain range.The stroke of displacer piston at low speed condition was larger than that of high speed.Within the range of 1000¹300r/min,the stroke of the displacer piston decreased with the increase of speed.The power piston and the displacer piston moved up or down at the same time.There was less phase difference,and the motion law of the power piston did not conform to the sinusoidal curve.?2?The temperature of hot cylinder decreased with the increase of speed,and higher heating temperature dropped more.The unprofitable volume of the cylinder increased with the increase of speed.?which is the ratio of increased unprofitable volume due to PPBDC moves up to the unprofitable volume of the cylinder up to 34.8%.The compression ratio became smaller as the speed and spring stiffness increased,and became larger as the heating temperature increased.The compression ratios at different temperatures gradually became the same as the speed increased.?3?The ratio of P₁,P_d and P_h?loss power of DC motor,drive mechanism and piston ring respectively?to P₃?mechanical loss power?was from P₁,P_h,P_d in descending order.Both P₁ and P_h become larger as the speed increased.The increasing slope of the P₁ power curve increased with the increase of speed and vice versa of the increasing slope of the P_h power curve.The value of P_d was small,and it did not change significantly with the speed.P₃ became larger as the rotation speed increased.The variation of P₃ was quite different under different heating temperatures.Under the condition of low heating temperature,the value of P₃ was larger,and the slope of the curve became larger with the increase of speed,and vice versa under higher heating temperature condition.At the same speed,the higher the heating temperature,the smaller the mechanical loss power was,so the higher heating temperature was beneficial to reduce the mechanical loss power.?4?The order of P_h of the four piston rings from small to large is 3#,1#,2#,4#.The open piston ring with the diameter of 65.04mm consumed the least power,which indicated that this open piston ring was the best match with the engine cylinder.It was also proved that the innovatively designed split-type piston ring had the effect of reducing friction loss between the piston ring and the cylinder wall.In addition,the friction loss power of the innovatively designed split-type open piston ring was sensitive to the diameter of the large piston ring,so when designing the piston ring,special attention should be paid to the size of the piston ring diameter.?5?The distribution power,indicated power,and net power increased as the speed and heating temperature rose.Under higher speed conditions,the distribution power tended to be flat as the speed increased,but the net power was reversed.The indicated power was almost proportional to the speed.When the speed exceeded 1300r/min,the net power of the engine changes from negative to positive and began to increase rapidly.The net power decreased as the temperature of cooling water rose,so reducing the temperature of cooling water was beneficial to increase the net power.The greater the spring stiffness,the greater the net power of the engine was.The area of the indicator diagram increased with the increase of speed.Compared with low speed,the indicator diagram of higher speed was fuller.Under test conditions,the maximum cycle thermal efficiency of AFPSE was 7.2%which was lower than other Stirling engines.It was mainly because the engine is not in resonance state and the performance is not optimal.