The Wankel Engine is a widely used term for rotary engine, being another type of internal combustion engine. Engine main parts, assembly process and work cycle have been described in the previous article ("The Wankel Engine – Part I"). In this article we deal with engine common – yet unique – advantages.
The greatest advantage of the rotary engine is the number of parts – especially moving parts. No valves or valve-trains, no connecting rods, no crankshaft and crankshaft balance weights, no timing belt, no rockers, etc. Generally, only 2 parts are in motion – the Rotor and the Eccentric Shaft. If there are 2 rotors (a mainly-used configuration for standard rotary engine) the number of parts will increase by 50%… from 2 to 3. But compared to about 40 moving parts in even the simplest piston engine – it is a huge advantage. Also, because of engine geometry, the rotor(s) are moving at only 1/3 of a speed of the eccentric shaft. Less moving parts, relatively low movement speed – this means less chances of failure, i.e. better reliability and easier maintenance.
No “Sudden Death”
Talking of reliability, it has to be noted that since the rotor is made of cast iron and the rotor housing material is usually aluminium (which has a greater thermal extension) – even severely overheated Wankel engine would not seize. In general, Wankel is almost immune to sudden shut-downs, as it will continue to produce power during its "failure stages" (as a result compression loss, oil pressure drop or poor cooling and overheat) – in complete contrast to piston engine which is likely just "break".
Smoothness and good combustion
Smoothness is yet another advantage of the rotary engines. The methodical rotation of the rotor on the eccentric shaft is very smooth when compared to constant and sharp direction changes of the moving parts in piston engines
The last advantage that should be mentioned is a good combustion. Since the combustion duration is almost 3/4 of the stroke time, the air-fuel mixture is usually better, making it very suitable for direct injection.
Summary and more
Well, with all those advantages, it seems we should have Wankle engines all over the world. So why isn’t it so popular? Well, rotary engines have several serious problems, which will be discussed in the next article.
This post is part of the series: The Wankel engine – Ultimate guide to rotary motors
Does rotay engine have advantages over piston engine? This series is your complete guide to the rotary engines world.