Rotary engine with its passive piston running at variable speed

A rotary engine comprising:

• a doughnut-shaped cylinder;
• wherein the doughnut-shaped cylinder has at least one air inlet port and at least one exhaust gas outlet port;
• at least one pair of pistons with one power piston and one passive piston;
• wherein the at least one pair of pistons are disposed inside the doughnut-shaped cylinder, and rotate along the doughnut-shaped cylinder;
• wherein a space between the one power piston in front and the one passive piston at back forms a working chamber surrounded by inner wall of the doughnut-shaped cylinder;
• wherein the working chamber receives fuel from the at least one air inlet port and emits exhaust gas from the at least one exhaust gas outlet port;
• a passive disk, wherein the one passive piston is fixed at edge of the passive disk;
• a passive disk bushing being fixed perpendicularly at center of the passive disk;
• a power disk, wherein the one power piston is fixed at its edge of the power disk;
• a power-output shaft, wherein the power-output shaft is fixed perpendicularly at center of the power disk;
• wherein the power-output shaft is inserted through the passive disk bushing and placed at the center of doughnut-shaped cylinder;
• and wherein an axis of the power-output shaft is coaxial with an axis of doughnut-shaped cylinder and an axis of the passive disk bushing;
• and
• an intermittent driving system, wherein the one power piston drives the one passive piston through the intermittent driving system, and wherein the intermittent driving system is configured so as to enable the one power piston to drive the one passive piston in a way that, within one revolution of the power-output shaft's rotation, the one passive piston is driven by the one power piston in some periods but not in other periods, so that the one passive piston rotates at a speed in an intermittent pattern;
• wherein the one power piston and the one passive piston rotate around the axis of the power output shaft;
• wherein within one revolution of the power-output shaft's rotation, the one power piston rotate continuously at a substantially constant speed and the one passive piston rotates at a speed in an intermittent pattern;
• thereby volume of the working chamber varies in an intermittent pattern.