A Rotary engine has a radial configuration and the cylinders are arranged around the crankshaft. In a radial engine, the pistons are connected to the crankshaft with a master-and-articulating-rod assembly. One piston attaches with the crankshaft using a master rod. The remaining pistons attach themselves to rings around the edge of the master rod. The number of the cylinders is always odd, to maintain uniformity in firing order which is important for smoothness.
Advantages
In rotary engines, smoothness is achieved easily than in other engines. Since rotary engines are air-cooled, they are less heavy and thus can be used in battle vehicles. A rotary engine has a comparatively shorter crankshaft, which means less vibration and thus higher durability.
Disadvantages
Since the engine is air cooled, cooling isn’t achieved perfectly. Since all the cylinders are exposed to airflow, it results in drag. Due to it’s bulk size, it also makes difficult pilot looking outside. They also cost a lot to maintain which is undesirable.
Usage
The usage of Rotary engines were limited until the World War II, when it was used in air crafts and tanks. The main reason behind its usage in tanks was that it had a good weight-power ratio and was considered better than the inline engines at the time.
Types
1) Multi-row rotary engine: As the size and requirements of the engine increased, it became necessary to increase the number of rows of the engine. The rows of cylinders are placed next to each other on different planes. However, they are joined to the same stationary crankshaft.
2) Diesel engine: Most rotary engines are built as gasoline engines. Diesel engines were made in 1920s and 1930s due to two advantages. Diesel engines consume less amount of fuel and they have a reduced fire risk.
3) Compressed-air engine: In compressed air rotary engines, air is used in the cylinders instead of fuel. It’s used mostly in model airplanes and gas compressors.
4) The Wankel engine: An engine that works with a similar principle as that of a rotary engine is the Wankel engine. It was developed by Felix Wankel in 1957. Like a piston engine, the Wankel engine also uses the pressure from combustion.
In a rotary engine, the pressure of combustion is held in the space created by a housing and a triangular rotor fixed inside it. Fuel is pumped into one of these chambers and is moved towards the ignition location. It also gets compressed because the housing surrounding it gets narrower. When it gets ignited, the rotor is pushed with force and the next chamber automatically draws in fuel towards compression and ignition. A Wankel engine has the advantage of fewer moving parts but the parts are expensive if they are to be replaced with.