What is a rotary engine?

There have been many famed engine configurations and types over the years – not least the flat-six boxer – but none have achieved such cult status as the Rotary Engine.

Made (in)famous by Mazda, the rotary engine is a unit which offers several quirky characteristics – while some will supply a car with a few desirable traits, a rotary engine also carries with it a few drawbacks.

How does a rotary engine work?

The first combustion rotary engine was invented back in the 1950s by German engineer Felix Wankel, who at the time was at the German firm NSU Motorenwerke, and had been developing rotary technology for around 30 years up to that point.

Contrary to a typical combustion unit, the rotary engine removes the need for pistons and instead creates a reciprocating motion within a single chamber, with a three-sided rotor as the centrepiece.

A rotary engine does have similarities with a more common engine, in so much that it goes through the four phases of intake, compression, ignition, and exhaust – however, the rotary engine manages this in a continuous, circular motion.

Firstly, the air-fuel mixture is drawn into the chamber before this is then compressed and subsequently ignited, which results in the rotor being pushed by the expanding gas (and creating power), before the exhaust gases are then vented.

What’s great about the rotary system is that one rotation equals three separate power strokes – a four-stroke piston engine, meanwhile, will only make power on one movement out of four.

Given that a rotary engine can make do with a single chamber and no pistons, you’ll likely not be too surprised to hear that a rotary engine has much fewer moving parts, and as such is notably smaller and lighter than a typical combustion engine.

A rotary engine also makes no use of valvetrains, crankshafts, or connecting rods, as the rotor covers all bases.

Rotary engine pros & cons

There are several reasons as to why you might want to get involved with rotary engines, but the drawbacks can be equally as compelling – for hypermiling fans the rotary engine is not.

Pros:

Noise – It’s fair to say that a rotary engine offers a very defined aural experience, one that many get quite excited about; if you’ve ever seen videos of the Mazda 787B fly down the Mulsanne Straight, you’ll know what is possible with a rotary engine.

High RPM – A key player in how a rotary engine manages to sound so wonderful is its ability to hit high revs, and do so with a smooth and responsive delivery thanks to less vibration.

Lightweight – For anyone wanting to lessen the load in the engine bay, a rotary engine could be an option to consider. The compact nature of a rotary engine enables it to keep off the pounds.

Fewer Moving Parts – Also key to its lightness is the rotary engine’s reduced number of components compared to that of a conventional power unit. This also helps reduce the chance of mechanical failure, and maintenance is simplified to a degree.

Cons:

Terrible Fuel Efficiency – While not quite Ford GT levels of fuel economy, don’t expect to get out of the 20s when it comes to MPG. This is down to the rotary engine just not being particularly efficient in general, with its design lending itself to high levels of heat loss.

No Low-End Torque – While the top end of the rev counter is easy to come into action, things lower down in the range aren’t quite as keen to get things moving due to a lack of low-end torque.

Oil Consumption – If multiple visits to the gas pump are annoying enough, you may be upset to learn that a rotary engine also has an insatiable need for oil.

Apex Seal Wear – One of the most common jobs on a rotary engine is to replace apex seals; this is seen as a pretty big undertaking, and could happen more often than you’d like.

High Emissions – For those concerned about the level of emissions being created by their vehicle, a rotary engine might not be for them, which produces an above average amount of pollutants.

Mazda & the rotary engine

Japanese manufacturer Mazda is the only firm to take the rotary engine mainstream, and the powerplant has featured in many of the marque’s most iconic models, both on the road and the track.

In the 1970s half of Mazda’s car production was powered by the rotary engine, as it looked to push for being a bit different to its rival manufacturers.

Notable cars for the road have included the Cosmo 110S, the RX-7, and its successor the RX-8 – but Mazda has utlised the rotary engine in everything from pickups to minivans.

On track, the most famous instance is the 787B winning at the 24 Hours of Le Mans in 1991 –  however, there have been additional instances of rotary engine success, including the TWR RX-7 winning the 1981 edition of the Spa 24 Hour, and an RX-3 taking a class win at Bathurst in 1975 after duking it out with the V8s.

Will Mazda ever make use of the rotary engine again? Technically it has done with the MX-30 R-EV’s range extender, but in this context it’s not really worth the mention, unfortunately.

Mazda itself continues to give passing mention to its famed engine from time to time, but it’s anyone’s guess as to whether we’ll see the Hiroshima firm take the plunge once more.