The Rotary Engine is not dead yet!

Mazda — The Automotive Hipsters

Mazda unveiled its new Rotary engine this year and it is insanely engineered to perfection. This may be the comeback for the Rotary engine after 10 years.

Photo by Wassim Chouak on Unsplash

This is not the first time Mazda has tried to create innovative rotary engines.

The relationship between Mazda and Rotary engines is far longer and stronger than you think.

Mazda released its first rotary engine-based cars famously known as “ Cosmos”, Rx, Rx-2, and Rx-3 during the 1960s. Among these, Rx-2 and Rx-3 were long-running cars. By the end of 1991, Mazda’s Cosmo race car 787B was celebrated as the Winner of Le Mans throughout the World.

Not only did Mazda register its first win based on a rotary engine, but it was also the first time that Japan won the championship as a country after a decade of trying.

Car enthusiasts would often term rotary engines as the least efficient and the less common engines in the industry. But the car nerds won’t give up on the rotary engines. Especially Mazda after this Special historical moment.

My interest in this rotary engine grew when I learned about the performance of the 3380cc Twin Rotor GM Rotary engine and 5030 cc V8 engine (GM 307).

For new learners: Based on the CC, which engine do you think has a better HP output?

The V8 engine is an 8-piston-cylinder arrangement that is configured in a V shape manner for balancing purposes. While the twin-rotor engine has 2 rotors moving in an engine.

The V8 reciprocating engines create work (Horsepower) by moving the piston through the cylinder to burn fuel through Intake, compression, expansion, and exhaust strokes. On the contrary end, the rotary engine has a Dorita-shaped rotor spinning around the engine to deliver power by following the same intake, compression, expansion, and exhaust cycles for burning fuel.

Rotary Vs Reciprocating Engine

In my example, you would assume that the work done by 8 reciprocating engines is higher than the 2-rotor engines. You need more parts to get more power and more sturdy designs to achieve that. That was my assumption too, years back.

Or in other simple words, would you agree if the turtle won the race in 2 laps although the hare raced for 8 laps?

Unbelievably, you are using over 1108 parts to fabricate this V8 GM 307 Engine to produce a Horsepower of 130, while on the other end, you are using just 698 parts to manufacture a twin-rotor engine to produce a Horsepower of 150.

Not only that, if you have noticed, it requires a smaller engine capacity (3380cc) as compared to the IC engine (5030cc).

Thus, It would occupy less space than the IC engines and increase the power-to-weight ratio of the car.

What are the chances of a V8 Engine being beaten by a Twin Rotor Engine?

Always!

This is because the work done by the rotary engine is more consistent than IC engines which have more heat loss and energy losses based on the different bores and strokes.

For example, a reciprocating engine with a longer stroke length is more efficient but the very same engine with a larger bore has more power. Because of the large bore size, the fuel it can take is huge.

But a rotary engine always has more power because it has a consistent and large engine capacity that is dependent on the rotor design and engine itself. Just like the bore size example in a reciprocating engine, except it doesn’t have the torque (reciprocating) element to it.

This means that by the time a piston goes back and forth to complete a cycle (4 back and forth) of intake, compression, expansion, and exhaust, the rotor would simply rotate to complete 4 cycles of intake, compression, expansion, and exhaust in a shorter time.

In simple words, I gave you the assumption that Hare was the reciprocating engine. When in practice, the hare is the rotary engine that gets more work done than the turtle (Reciprocating engine). It is indeed deceiving in the automotive world that Reciprocating engines are always assumed to have done more work but in reality, it’s not.

Here’s an animation from my simple CAD design

Now that the basics have been established, what insane innovation did Mazda deliver in the latest Rotary engine design?

Unarguably, Mazda admitted that when fuel is injected into a conventional rotary engine, a lot of fuel ends up at the back of the combustion chamber not fully combusting.

This is true for many reasons,

1. The Rotary engine has no inlet valve timing
2. The Rotary engine has a small hole for the inlet that is always consistent, meaning if the engine speed increases, the intake cycle won’t be timed properly. And hence this would lead to an uneven air-fuel mixture.
3. As the work done is more, it would consume more fuel than an IC engine. That would go unused.

So how did Mazda solve this glitch in the discovery of the Rotary engine?

With the need of eliminating the use of fossil fuels, also came the need for hybrid and electric cars.

The rotary engines are known for their high HP, which could play a prominent role in Hybrid cars. Could you imagine the range it could deliver in this electric vehicle era?

From the layout below, we can understand that the rotary engine is disconnected from the drivetrains. Instead, it is the electric motors that are doing the work for you. But the Rotary engine would be powering the battery through a generator and inverter.

By introducing an additional electric motor to the same shaft as the Rotary Internal combustion engine, the rotor is adjusted for better fuel efficiency.

Electric Motor 2 to control the Speed of the Engine

This is achieved in all 3 conditions::

1. Lower RPM:

During lower RPM, we need a short intake time to get the rich mixture. This Electric motor would create a negative torque to fasten the movement of the rotor in the intake stroke.

2. Normal — RPM — that we mostly use:

The engine is designed to handle the air-fuel mixture in an ideal state throughout this state. Thus the electric motor is disengaged.

3. Higher RPM:

During higher RPM, we need a longer intake time to get the rich mixture. Thus the electric motor would create a positive torque to slow the movement of the rotor in the intake stroke.

For understanding this perspective imagine a Dorito-shaped rotor running at a normal rpm and then the positive and negative influence causes the Dorito-shaped rotor to slow down at an angle of 270 deg for Higher RPM and to run fastly only at 270 deg for Lower RPM.

We are controlling the rotor itself instead of the valve.

I believe this comes as a surprise, but at the same time, this reflects the time when VVT (Variable Valve Timing) was introduced in IC engines for controlling the same problem (problem of unburnt fuel) the Rotary engine is facing now.

It is a shame that we did not have many players in the rotary engine development, although it had the same problem of Fuel efficiency as the IC engines years ago.

But these little efforts made by Mazda are keeping our minds open that anything is possible in this engineering world.

Any Design concept could be brought back. The Rotary Engine is not dead yet!