The Wankel Engine – PART III – Problems and Disadvantages

The Wankel Engine is a widely used term for rotary engine, being another type of internal combustion engines. Engine main parts, assembly process and work cycle have been described in the article "The Wankel Engine – Part I". In "Wankel Engine – Part II – Advantages" we have seen the numerous unique engine advantages. In this article we deal with engine problems and flaws which should explain why the Wankel rotary engine is a rare guest in everyday technology.

The main disadvantage of the Wankel engine is problematic sealing. The rotor has to be sealed against the chamber ends. That means the 3 chambers, formed throughout the cycle of the rotor have to be completely separated. Piston rings are used to achieve that. Unfortunately, due to different expansion coefficient of the materials, the sealing is far from perfect. This leads to decrease in overall engine efficiency. Engine life is also influenced form this factor, and though a "sudden death" scenario is unlikely (as said in "Wankel Engine – Advantages" article), those engines generally have shorter life that ordinary piston engines.

Another factor is a relatively problematic combustion. Although the air-fuel are better mixed, the combustion chamber is big and, more important "moving". This causes the "squeeze stream", which prevents the flame from reaching chamber trailing side – especially at high rotor speeds. The exhaust stream is therefore, enriched with unburned mixture and carbon monoxide.

The above represents yet another factor – the Wankel Engine is not "green" at all. In fact, it's level of pollution are so high that it is very hard to meet, for instance, US emissions regulations. Also, in general, Wankel engines consume more fuel than regular piston engines. However, in some models special measures were taken to reduce fuel consumption – for instance in Mazda 26B a 3-spark plug ignition system is used.

Overall, all this problems cause limited usage of the Wankel Engines – leading to yet another aspect – price. Since the manufacturing volumes of engine parts are relatively low, they tend to be more expensive. However, there are some industries that are using Wankel rotary engines. Those will be covered in the next article.