engine Operating with almost no vibration Not prone to engine-knock Cheaper to mass-produce, because the engine contains fewer parts Supplying torque for about two-thirds of the combustion cycle rather than one-quarter for a piston engine Easily adapted and highly suitable to use hydrogen fuel. Wankel engines are considerably lighter and simpler, containing far fewer moving parts than piston engines of equivalent power output. Valves or complex valve trains are eliminated by using simple ports cut into the walls of the rotor housing. Since the rotor rides directly on a large bearing on the output shaft, there are no connecting rods and no crankshaft. The elimination of reciprocating mass gives Wankel engines a low non-uniformity coefficient, meaning that they operate much smoother than comparable reciprocating piston engines. For instance, a two-rotor Wankel engine is more than twice as smooth in its operation as a four-cylinder reciprocating piston engine. A four-stroke cylinder produces a power stroke only every other rotation of the crankshaft, with three strokes being pumping losses. The Wankel engine also has higher volumetric efficiency than a reciprocating piston engine. Because of the quasi-overlap of the power strokes, the Wankel engine is very quick to react to power increases, giving a quick delivery of power when the demand arises, especially at higher engine speeds. This difference is more pronounced when compared to four-cylinder reciprocating engines and less pronounced when compared to higher cylinder counts. Due to the absence of hot exhaust valves, the fuel octane requirements of Wankel engines are lower than in reciprocating piston engines. As a rule of thumb, it may be assumed that a Wankel engine with a working chamber volume Vk of 500 cm³ and a compression of ε=9 runs well on mediocre-quality petrol with an octane rating of just 91 RON. If in a reciprocating piston engine the compression must be reduced by one unit of compression to avoid knock, then, in a comparable Wankel engine, a reduction in compression may not be required. Because of the fewer injector count, fuel injection systems in Wankel engines are cheaper than in reciprocating piston engines. An injection system that allows stratified charge operation may help reduce rich mixture areas in undesireable parts of the engine, which improves fuel efficiency. Disadvantages Thermodynamic disadvantages Wankel rotary engines mainly suffer from poor thermodynamics caused by the Wankel engine's design with its huge surface area and poor combustion chamber shape. As