"We found the solution."

It's a short statement followed by a firm, confident smile from the senior engineer. This casual conversation over dinner resulted in a two year journey where Bobby slowly pieced together what might just be the keys‍‍‍ to the Pandora's box that sealed the fate of Mazda's rotary engine.

words Bobby Ang

As the only car maker that never gave up on Dr Felix Wankel's creation, Mazda was once thought to have abandoned their rotary engines when the final RX-8 rolled off its assembly lines in 2011. Ever since, the philosophical approach of 'SkyActiv' not only helped Mazda stepped out of the rotary engine's shadows, but also led many to fear its impending demise.

Little was known however that Mazda actually never stopped trying to see how they can solve the inherent problems of Wankel's creation, of burnt apex seals and unburnt fuel, of a theoretically efficient engine that in practical was anything but. the lingering question has always been "Is it even possible to salvage this 'horrible' engine?"

For years we've heard rumours of Mazda's attempt in the revival of rotary engines. While it may sound brilliant for aspirational enthusiasts all over the world, it spells more questions than answers for those in the know, and especially those who have burnt a fair amount of apex seals off their wallets in their quest for the art of #braapp. 

Before we start, let's begin by explaining how rotary engines work, and what were the promises that led to it once being hailed as a wonder-engine to its demise as nothing more than half a century of engineering cock block for the automotive world.

The Wankel engine came with the promise of a lighter engine, fewer components, lesser vibration, higher horsepower output and all kinds of explicit feel-good euphoria only a good porn movie can produce. A rotary engine works by rotating a medium within a confined chamber, and the only way to do this, is to have a triangle rotating offset within what seems to be a peanut shaped chamber. With the triangle rotating offset, there will be areas that shrink and expand, creating the needed volumetric expansion and contraction of chambers crucial for combustion and compression to happen. The turning of the triangle piston serves the job of intake valves, camshafts, pistons, con rods and crankshaft all at once.

The logic behind is the pursuit of a combustion process with the linearity that does not need the reciprocating process of a piston going up and down, or to be more precise, going forwards upon combustion, and then wasting energy to go backwards in order to move forward again in the next cycle. It worked well in the era where 6.0 litre V8s were making 150hp while returning the fuel consumption equivalent to that of a fighter jet. But as the advancement of piston engines continued to forged ahead, the inherent problems of the rotary engine became more and more glaring, and almost impossible to fix.‍‍

Intake phase - The inlet port 'opens' when the rotor isn't 'covering' it. There are no opening of valves. As the rotor swings by, it literally sucks in air with the expansion of the chamber, of course, fuel too.

Compression phase - The apex seal at the edge of the rotor turns and compresses the air and fuel mixt‍‍‍ure it 'sucked' in and received earlier on

Combustion phase - As the air-fuel mixture passes by the narrowest poi‍‍‍nt in the housing, the spark plugs ignit‍‍‍e the air-fuel mixture and combustion process begins

Exhaust phase - This is where the expansion of the exploding air-fuel mixture pushes the rotor to spin. As it continues, the bottom apex seal will push all exhaust gas out via the exhaust port on top. Readying for the next cycle.


How rotary engines wo‍‍‍rk?

Temperature - ‍‍‍The part‍‍‍ as indicated here is always cooler than the bottom part as this is just the intake. What this also means is that within one cycle, the apex seals are travelling through multiple heat cycles of expansion and contraction, destabilising and deteriorating the metal seals.

Burning Oil - To be able to effectively seal off the chambers while the rotor is turning, the engine was designed to burn engine oil by injecting them into the combustion chamber, thus it is important to check engine oil levels periodically.

Low Efficiency‍‍‍‍‍‍ - Rotary engine's combustion chamber 'runs' away as the spark plugs are trying to ignite it. Because of the way it's designed, the combustion always needs to play catch up to the rapidly expanding chamber, most often than not, the fuel isn't fully burnt.

Bad Emission - ‍‍‍When you can't fully burn your fuel, you emit them out of the exhausts. Which also means that you waste more ‍‍‍fuel than you should, and also means you don't pass emission tests, but you do get real back fires from the exhausts when the fuel ignites down the pipes.


When I heard Mazda engineers had 'found the solution', I was scratching my head thinking hard; Is this a solution in the form of a breakthrough in reliability, or efficiency? As in a more hard wearing apex seal? No, it can't be, as the 13B's problem isn't just the fact that it might blow itself up. Is it in the form of efficiency? No, it can't be either because it has to spew engine oil into the combustion chamber, and then spew fuel out of the exhaust manifold. Basically burning things it shouldn't be burning at the first place, and also, in the wrong place.

How about making them lighter? Let's say Titanium here and Tungsten there, or maybe Carbon here and then Graphene there? Unlikely, because Mazda always tries to build their cars cheaper. The current Mazda 2 is 100kg lighter, has a higher quality interior and exterior, yet costing 1/3 lesser to build. All of the above that went through my mind never come close to the development of even a starting line for me to progress further in my research. But that single phrase uttered during dinner kept haunting me. "Pre-combustion". Pre - combustion. Pre-com-bus-tion.

It was during the global media drive of the current second generation Mazda CX-5, along with the MX-5 RF and the super secretive G-Vectoring back in 2016. I go‍‍‍t to meet the entire team from the Jinba Ittai division - I'm not joking, that's a real division. And I met so many senior Mazda engineers that I couldn't even recall who uttered that to me during our casual talks. I can remember he wouldn't divulge further, but he uttered "Pre-combustion" when I asked what is the single biggest breakthrough that resulted in Mazda willing to invest further to solve the Wankel Engine's inherent problems, short of being seen as the engineering department wanking themselves into the oblivion realms of research and development, I set out on a quest to study, and attempt to find what Mazda discovered, and here's the story, and the findings.

Top: You can clearly see combustion only happens in one chamber, meaning there's a great disparity in the temperature across chambers. This also means the Apex Seals mounted on the edges of the triangle rotor have the impossible task to stay in place firmly because of the heat expansion cycles when travelling through different chambers. Not only making the seals less reliable, but requires injecting engine oil into the chambers to further seal and lubricate against the wall. This inadvertedly resulted in bad emissions. Also, noticed how the combustion was chasing the expansion of the chamber caused by the spinning rotor, which means unburnt fuel and horrible emissions.

"It's mathematics"

Let's start with the geometry of a Wankel engine. There's actually a relationship between the 'outer shell' that looks like a fat peanut and the inner triangular rotor. The 'fat peanut' is what we call an Epitrochoid, a shape derived from a rotating circle around the circumference of a fixed circle with double the radius. There are many types of Epitrochoids that can be generated when the dimension between the rotating circle and the fixed circle changes. Basically, this is the fundamentals of the relationship between a rotational lever going round and round without the need of reciprocation.

For a Wankel engine, the ratio of the radius of the fixed rotor to the radius of the rotating rotor is 2:3. The centre of the rotating rotor follows a circle as well, which as mentioned above, are the fundamentals of an Epitrochoid. The distance between the centre of the fixed rotor and the centre of the rotating rotor is called eccentricity. The ratio of the radius of the rotor divided by the eccentricity of the engine is called the K factor. And the K factor for a Wankel engine is mostly between 6-10.

So now that I've understood the fundamentals of a rotary engine and the delightful news that Epitrochoids can be had in a multitude shapes as long as it revolves around the relationship of two spinning circles, I began seeking solutions beyond that of the current rotary engine. Basically I thought out of the trochoid instead of the box. This is of course mainly due to the fact that no matter how I look at current rotary engines, I just couldn't fit these narratives into the equation:

  • - A manageable temperature range to protect the apex seals, or apex seals that doesn't move at all so that it's easier to manage its temperature range.
  • - A combustion chamber that doesn't expand as the burning was ongoing, so that the combustion can be complete and the compression ratio maintains.
  • - A pre-combustion chamber as mentioned by the Mazda engineer. Which means a high compression ratio can be achieved.

Rotary Engine: 1‍‍‍0‍‍‍ Parts

Piston Engine: 85 P‍‍‍arts

"Nothing more than half a century
of engineering cock block for the automotive world."

Now there are many types of 'rotary engine' possibilities out there. Some are downright stupid and unnecessarily complicated like the one above. Too many parts, too many hinges and at the end of the day just doesn't achieve the targeted goal of why the Wankel engine was created at the first place. Which is to be lightweight, few parts and high RPM. In fact the one above is actually a reciprocating engine just that the reverse motion was 'masked' with another pair of pistons.

As I looked through various shapes and form of Epitrochoids, I realised the relationship between the "fat peanut" and the triangular rotor can be inverted. Meaning the triangle shape forms the block and the "fat peanut" becomes the rotating piston itself. This arrangement also means we now have three chambers on each end of the triangular block, and the chamber itself can be shaped to house the most needed components for a pre-combustion chamber - the injectors and spark plugs! What this means is that we can now have three combustion chambers instead of one! What this also means is that we will have equal temperatures across the block. Best of all, the apex seals can be mounted on the inner walls of the block, not moving, but merely interacting with the spinning "fat peanut"!‍‍‍

Discovering this is groundbreaking, not only because it fits every single criteria that solves the inherent flaws of the rotary engine, but it also fits the tip given to me by that Mazda engineer of a pre-combustion chamber. Best of all, it is in the shape of a triangle, the global symbol of rotary engines that Mazda had marketed for the past 50 years. This gives Mazda no reason to not employ this solution as it achieves the following:

  • - Three pre-combustion chambers
  • - Equal temperatures across the block
  • - Apex seals are fixed on a static location
  • - Lightweight, few components
  • - U‍‍‍ltra high compression is now possible
  • - With three combustion chambers, extremely high speeds can be achieved even with a very small engine block.

Arriving at this, I decided to focus on researching more about this format of rotary engine. One with a pre-combustion chamber, one with the external block in the shape that Mazda would most desire it to be from a marketing stand point, and one that is able to solve the problems that are inherent with the old rotary engines. And as I studied every single self proclaimed engineering firm out there who claims to have designed a better rotary engine, I was tipped by an American friend about this company called Liquid Piston. Studying through their papers, I am thrilled beyond comprehension. Because they have arrived at the same conclusion as I do - albeit I'm not an engineer by any means, and they are. In fact, they're geniuses to be able to complete the prototype, test cycles, and created the exact thing that fits the tip of the Mazda engineer. Every single feature of their little rotary engine fits the salvation for rotary engines like a glove. EUREKA! In fact, EU-fucking-REKA!

Top: Compared to the Wankel engine, the biggest difference is of course the inverted block and rotor. But as you can see, their biggest breakthrough is utilising the rotor itself for the breathing of the engine. Meaning the intake and exhaust was done by scooping up of the chamber with the rotor itself and then expelling or delivering air through the spinning motion. As illustrated earlier on, the Apex seals that are not visible here can then be fixed on the side walls, achieving the objective of a controlled materia‍‍‍l to anticipate the temperature cycles that are not too vastly different between each combustion cycles.

This I strongly believe, is the same solution that Mazda had arrived at. It can't be too far from this I reckon. No, I'm pretty sure about this! A small rotary engine with the power to weight ratio of 3.3kw per kg, low vibration, low noise, and super lightweight as well as small and compact. With an extremely small pre-combustion chamber for spark ignition or a diesel-like compression ignition. This solution that Liquid Piston has achieved, I believe, is the same solution that Mazda came across after all these years of studying how to improve the rotary engine. And this application is also perfect for as a range extender for a hybrid powertrain, because as a range extender or as a charger, the RPM of the engine is more important than how much torque that engine generates. So with three combustion chambers, it can spin at extremely high speeds, and with extreme high speeds, it doesn't need to be a big engine to serve its purpose as a range extender. In fact, it can be as small as a palm even!

For now, I do not have any idea on how Mazda's SkyActiv Rotary engine will be as Mazda has yet to divulge any information, but I believe it wouldn't be too far away from this solely because the current architecture of the existing rotary engine has too many flaws, and this new concept fits the bill. Moreover, this company has already proved the viability of these engines. And best of all, they've recently won a DARPA contract to mount these small engines to UAVs for noise reduction. Anyhow, I believe we are witnessing yet another round of ground breaking invention from Mazda soon regarding the SkyActiv R powertrain that will be fitted to their next generation Rotary Hybrid flagship GT car. A car that runs on electricity most of the time yet without range anxiety made possible with these palm sized combustion ignited diesel or spark ignited petrol rotary engines that serves as a range extender. With these sort of power density, imagine a couple of these working together? Will this be a revolutionary engine that deserves a place in the historical books of the evolution of internal combustion engines? Or are these my pipe dreams only that will never be fulfilled? I remain hopeful though, because this is Mazda we're talking about, a different kind of car company. A company that challenges boundaries, always have, always will. ‍‍‍


The problem with rotary engines