Fig. 10 Detail of Heat Exchangers
2.2 1kW Low Temperature Difference Stirling Engine
1) Structure of the Engine
The 1kW low temperature difference Stirling engine is shown in figure 7. The specifications are shown at table 3.
This engine is an α type engine which has expansion side piston and compression side piston. Heat exchangers are placed between both pistons. Working gas reciprocates in the space of both pistons on the straight route. Therefore, it is possible to minimize the pressure losses which may occur due to the flow of the gas. Both pistons are bore: 400mm, stroke: 160mm. One-way type piston rings [3] are fitted in the gloves of the pistons. It works to reduce the working gas leakage minimum. Consequently, the lowest pressure in the cylinder is raised against the buffer pressure. Heat exchange performance of heater and cooler increases by means of the plate fin and tube type heat exchangers. It works to increase the heat quantity from the hot water to working gas. Regenerator is laminated with the wire gauze made of the brass. Casing of the engine works as a buffer tank, and it can be pressurized up to the maximum pressure of IMPa.
The crank mechanism is shown in figures 8. This mechanism ( We called X-yoke mechanism) is using linear motion bearings to minimize friction losses. Both pistons have slant rails which are arranged to have certain angles each other. From this configuration, it is a variation of the scotch yoke mechanism, we can get proper motion of pistons which have phase angle. Engine size is also minimized by using this mechanism.
The movement principle of the X-yoke mechanism is shown in figure 9. When crank disk 2] rotates, slider 3] on crank pin 1] reciprocates on rail 4], and rail 4] itself reciprocates to the vertical direction with each piston. This figure shows a case for the rail angle to be 15deg and the phase angle of both pistons to be 150deg. At figure 9(a), right side yoke mechanism operates the expansion side piston and left side yoke mechanism operates the compression side piston.
The top dead center of the compression side piston is θ =0deg. The behavior of the cycle from θ =0deg (figure 9 (a)) to θ =30 deg (figure 9 (b)) works mainly for expansion stroke, from θ =30deg (figure 9 (b)) to θ =180 deg (figure 9(c)) works mainly for cooling stroke, from θ =180deg (figure 9 (c)) to θ =210 deg (figure 9 (d)) works mainly for compression stroke, from θ =210deg (figure 9 (b)) to θ =0deg (figure 9 (a)) works mainly for heating stroke. High phase angle gives large amount of heating and cooling gas flow. This is a very important feature for a type low temperature difference Stirling engine.
