Birotary Engine – Diference and Advantages to The Wankel Engine

The bi-rotary engine concept solves the shortfalls of the Wankel engine and other rotary engine designs. The major difference is superior sealing the combustion chamber.

Seals of rotary engines are commonly located in their rotating parts and inertia forces from rotor movements are applied on them. These forces limit the maximum engine speed and cause shocks, which cause frequent breakdowns and leaks.

The bi-rotary engine has a patented seal, which is static. Inertia forces of the rotor do not affect the seals and the applied force on the seals is therefore independent of the engine speed.

Wankel engine apex seals have a line contact with the surface of housing, and the angle between the seal and the housing varies during the cycle. Sealing under these conditions is difficult and inefficient.

Our patented sealing solution achieves performs significantly better. The side seals have surface contact with the cylinder block. The transverse seal has tangential contact with the cylinder block with a constant contact angle. Both seals form a surface seal that are effective and durable.

Unlike the Wankel engine, the bi-rotary engine has two combustion areas. The heat stress on the engine housing is therefore divided into two places. This reduces the requirements for cooling and design.

The two combustion areas increase the power-to-weight ratio, because the engine performs double the number of cycles of the Wankel engine in a single rotation of the cylinder block. This design feature also reduces the friction speeds on seals. When comparing the bi-rotary and Wankel engines with similar parameters, the maximal rotor operating circumferential speeds and hence the frictional velocities on the sealing elements of the bi-rotary engine will be lower by approximately one third.

The bi-rotary engine utilizes several rows in both axial and tangential directions. A multiple seal approach has clearly a greater sealing efficiency. The location of sealing elements in the stationary part of the engine ensures no inertial forces act on the seals. The seal location also facilitates efficient cooling, which reduces the formation of hard carbon and guarantees optimal operation over long time.

A key disadvantage of the Wankel engine is the shape of its combustion chamber, which is long and narrow, and at the same time has a limited compression ratio. A long flame path leads to a large amount of unburned fuel and weak anti-knocking characteristics of the engine. Its large surface area to volume ratio leads to low thermal efficiency. These features result in high fuel consumption, high CO and CO2 emissions and excessive HC emission from unburnt fuel.

The bi-rotary engine uses standard pistons so the shape of its combustion chamber is similar to conventional four-stroke engines. Its compression ratio is not geometrically limited. A combustion space of any shape could be provided in the piston. Thus, the bi-rotary engine promises better combustion efficiency than the Wankel engine.

The hard, smooth surface for sliding of the sealing elements is inevitable for the rotary engine. In the case of the Wankel engine, this surface is on the inside of its housing and it has the shape of an epitrochoid. The machining of such a surface is a demanding task and the surface is virtually irreparable. In addition, the inner surface of the side lids must also have these demanding properties. At the same time, the casing is thermally loaded and deforms, which in connection with one sealing blade in the corner of the piston causes significant issues with sealing and durability of the casing. The other components are also very demanding for manufacturing precision and wear resistance.

The bi-rotary engine has a hard and polished outer surface of the rotating cylinder block. This surface is cylindrical, so it can be made without any special working processes, this surface could be relatively easily repaired in case of need. Most parts of the engine are similar to conventional engines. Easy repairs lead to lower costs.