Tully has my teddy bear hostage in his basement and won’t release him until I make a post on Wankel engines.

Background

It is commonly thought that the Wankel engine was first conceived the moment Tully first sneezed. However, this is incorrect.

The Wankel engine was actually first patented in 1929 by a gentleman known as Felix Wankel (some say Eternal Darkness spawned into the server this year). Felix spent most of his working life as a mechanical engineer. To give you an idea as to the kind of man Mr Wankel was, he told his friends at the age of 17 he was going to invent a new kind of engine and then 5 years later he did. You know… As you do. Meanwhile I’m 23 years old and have only just worked out that you should put the milk in first before hot water in a cup of coffee. Squirrel’s all about that un-burned coffee granules life.

A Wankel Engine

If you aren't familiar with the basics of how an engine works, I highly advise reading my first Engine Types post.

Wankel Engine Operation

Unlike the other engines I’ve talked about thus far, the Wankel is both different from the reciprocating/piston engine and the jet engine. However, I personally find it easier to think of it as a close relative to the piston engine due to their use of spark plugs and everything happening in the same chamber. As with all the engines talked about so far, the same operational principles apply. Suck air in, compression, ignition and blow the air out as demonstrated by the image below:

Wankel Engine Operation

The Wankel engine is made up of 4 main components:

• Stator Housing – houses the main components and contains the reaction.
• Rotor – has the job of drawing the air in, compressing it and expelling it, in turn driving the drive shaft.

• Drive/Eccentric Shaft – driven by the rotor, the drive shaft turns its irregular motion into a useful and consistent output.

• At this point all you need to do is slap on a gearbox and you can basically emulate a piston engine.

For even more Wankelness, Rolls Royce engineers sometimes add an extra Wankel on top of the Wankel. Then the world ends and everyone goes to Wankel heaven. Or so they thought. Putting a Wankel on top of another Wankel is actually done to improve the engine’s compression ratio to allow for compression-ignition with the use of diesel as a fuel. This is known as a two stage design:

Rolls Royce R1C Design. Two-rotor Design

The rotor on the bottom (LP rotor) takes in the air through the inlet and transfers it to the HP rotor (top). Here, fuel is introduced (fuel injector depicted in red) and then the mixture combusts before being transferred to and expelled via the LP rotor and exhaust.

Other than that, there really isn’t a whole lot more to cover on operation of the Wankel engine.

Advantages

So, this is all very well and good making a new engine type while simultaneously sending every 17-year-old into a midlife crisis, but what does it bring to the table?

Well for a start these bad boys throw out a lot of power. We’re talking 1/3 of the size of a piston engine with the same output. Thus, the power to weight ratio is pretty damn good. It’s the equivalent of busting out a Duracell to replace your “smart price” AA batteries.

They also use a lot less parts due to their simplicity, so they’re cheaper to make and because of their rotary motion, they vibrate a lot less, while simultaneously being able to operate at higher RPMs.

If that somehow doesn’t satisfy you, then its worth noting that they are also able to operate with a wider variety of fuels and are easily adapted to accept hydrogen to power them. Still not good enough? Well Wankel’s got you covered, because some can operate on both petrol AND hydrogen.

So, what could possibly go wrong? As it turns out quite a few things.

Disadvantages

There’s a reason Wankel engines haven’t caught on all that well in the world of engineering. The first issue is that everything is occurring in different sections all within the same area. Unlike a piston engine where everything happens in the same chamber at different times, or a jet engine where everything happens at the same time in different chambers, the Wankle has the unfortunate compromise of having everything happen within the same chamber. Meaning the cold air is being taken in as the hot air is being expelled in roughly the same area. This leads to wildly different temperatures in different areas within the chamber. This coupled with different materials being used, all with different expansion rates and centrifugal forces means reliably sealing the engine is a very difficult task to achieve.

To add insult to injury, while the Wankel engine can use a wide variety of fuels, it isn’t very efficient and subsequently has higher emissions due to unburnt fuel, mainly where petrol is concerned.

Conclusion

These issues and the ever-increasing demand for better fuel economy mean the Wankel engine is a difficult engine to implement. In this regard, the Wankel is very much the Stoat of the engine world; fast and powerful for its size, but produces a lot of waste and doesn’t live for very long.

However, hope is not lost. Mazda recently filed for two patents in 2019 and is pushing for a new Wankel equipped car in 2020 and there is still a significant market for the engine. This coupled with continuous improvements to materials and new materials means the Wankel’s shortcomings could be a thing of the past in the future, perhaps even surpassing that of the typical reciprocating engine.

In conclusion, please set Mr Snuffles free, Tully.

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