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Mazda Developing Next Generation RENESIS Rotary Engine

Next Generation RENESIS (Rotary Engine 16X). Click to enlarge.

Forty years after the introduction of the rotary engine Cosmo Sport in 1967, Mazda is at work on its next-generation rotary powerplant: the direct injection 16X, a 1,600 cc (800 cc x 2) engine with a new trochoid chamber shape aimed at further improving thermal efficiency and boosting torque at all engine speeds.

With the next-generation RENESIS, Mazda has changed the cocoon shape of the trochoid rotor housing. This marks a further evolution of the basic structure of the engine which began with an early period of over seven years spent researching the optimum trochoid shape, from the introduction of the first 10A (491cc x 2) in 1967, followed by the 13A (655cc x 2), 12A (573cc x 2) and the current 13B (654cc x 2).

Shape changes in the new RENESIS. Note the change in shape from the current 13B rotary. Click to enlarge.

This shape change is brought about by reducing the rotor housing width and housing thickness while increasing the trochoid outline, resulting in a displacement increase to 800 cc x 2. But despite this dimensional increase, Mazda was able to keep the engine itself essentially as compact and lightweight as the current RENESIS.

As for its specific shape, increasing the trochoid radius and eccentricity and reducing rotor housing width achieved a longer stroke, thereby shrinking the combustion chamber aspect ratio. Due to this modification, the surface area-to-volume ratio of the combustion chamber decreases, enabling a reduction in cooling losses.

Also, since the very tight space in the combustion chamber is reduced, flame growth is promoted and the engine exhibits faster combustion and better fuel economy. As well as improving fuel economy, Mazda is simultaneously pursuing higher torque at all engine speeds.

The next-generation RENESIS is the first gasoline rotary engine developed to use direct fuel injection. The system inherits the basic design concept of the hydrogen rotary engine, injecting gasoline in a high-pressure spray during the intake cycle, promoting atomization and vaporization of fuel and the formation of a stable air-fuel mixture.

The latent heat of fuel vaporization lowers the temperature of the air-fuel mixture, thus raising the engine’s charging efficiency. At the same time, it reduces fuel adhesion to the chamber wall, which has been a problem of the conventional port injection system, while promoting a more homogeneous air-fuel mixture. This in turn leads to substantially improved thermal efficiency and increased torque, and Mazda is actively researching further improvements in efficiency.

The concept Taiki uses the new rotary engine. Click to enlarge.

In developing the new engine, Mazda engineers have dramatically improved both power output and environmental efficiency. They have also contributed to further increases in fuel-economy and driving performance by lightening the vehicle weight.

Mazda Taiki concept. Mazda applied a version of the new RENESIS combined with a dry twin clutch 7-speed power shift in its Taiki concept car, unveiled at the Tokyo Motor Show.



Can it meet 120 grams of CO2 per kilometre? Can it run for 100,000 km without a major overhaul? Word was a V8 had less problems for the same fuel consumption. I drove a Mazda RX7 once and wasn't overwhelmed.


I've always found these engines to be pretty cool, but the advantages they offered now seem past their prime, and poorly applied when in the unreliable RX-7. To keep pushing it now, without specifying some real alternative fuel, revolutionary efficiency or hybridization is just so much mental masturbation. If you don't believe me look at the picture of the Taiki concept.


By the way, the last RX-7 was one of the most beautiful and awesome Japanese cars ever brought to the US, and didn't look like something influenced by Victoria's Secret and Minority Report.


This engine will never meet 120g/km in its lifetime. Not unless it runs on hydrogen which they've already engineered in various demonstrators.

This will always be Mazda's halo engine. And as such they'll still sell it in limited volumes countered by selling hugh volumes of their dross little cars which will average below 120g/km.

Also with the stricter limitations being put on manufacturers I'm beginning to wonder when car co's will start deliberatley selling underpowered sports cars with the customer having the option to have it "re-engined" at a local dealership using either a factory crate engine or a recon engine from elsewhere.

If I wanted a V8 BMW 3 series its almost financially worth my while buying a new 318d and having the engine/gearbox swopped out along with the fueling gear.

It would save a fortune in vehicle exice tax in the UK and in the future may be the only way I'd be able to purchase a high performance car.


Roger Pham

Ah ha, so direct injection is how Mazda is able to boost power from the Hydrogen Renesis by 40%. Impressive development, but Hydrogen is still the best fuel for the Wankel rotary engine.

Direct injection gets rid of a lot of the major problems of the rotary engine when powered by a liquid fuel. There is so much fuel lost to combustion by being dragged all the way around the engine before it is actually burnt and this is what causes a lot of the rotor tip and oil consumption problems.

If compared with a poppet valved piston engine, the fuel path between port injection and final combustion location has a much greater amount of wetted wall area. DI will help this. However, it will not yield the same volumetric efficiency benefits as it does on a piston engine as the fuel injection and induction process cannot occur contemporaneously.

The fuel economy isn't bad on these engines if you actually state the engine size as it actually is rather than simply stating the volume of one chamber. The current engine is quoted as a 1.3 (which makes it look bad) but if you work through the thermodynamics, the 1.3 running to 9000rpm is thermodynamically the same as a 3.9l V6 running to 5500rpm. At that point you realise that the fuel econ seems appropriate, just that the specific output is not all that great for a 3.9l engine.

What you have to realise is that the rotor speed and the output shaft speed are not the same and that the engine by design has a primary drive reduction gear built in. By the same token, you wouldn't quote the engine speed of a motorbike by counting the revolutions of the clutch basket. Once this is adjusted for, the firing all makes sense


Apols for blank post


This pretty confusing since the RX-8 has been using the RENESIS rotary for several years now and the 13B rotary engine used in the 3 generations of the RX-7 hasn't been manufactured for a very long time.


What is confusing about the article? It states next generation RENESIS and makes little mention of the 13B other than in the historical perspective. [unless you mean confusion caused by the commentors who are talking about vehicles which have not been sold in the US for more than a decade (RX-7 stopped selling on US shores in 1995...]

Rafael Seidl

Note that 7-gear dual dry clutch transmission - well suited to high-revving engines and better for fuel economy plus noise than a full CVT. The high number of gears means the engine can be kept near to its optimum SFC curve at all power levels.

Mazda has been soldiering on with Wankel technology for decades, addressing emissions, seal reliability and oil consumption issues. Now, they are addressing heat loss and switching to homogenous DI to eliminate wall film losses.

The reason for all this work is that Wankels run very, very smoothly, rev very high and deliver very high power-to-weight and power-to-volume ratios, just what you want in a sports car. Plus, the high revs generate the sound that sports car drivers crave.

Unfortunately, Wankels will never deliver higher fuel economy than comparable high-revving piston engines. The trochoid geometry and seals limit the compression ratio to ~10, which explains why diesel is not an option. However, a CI of 10 is anyhow about as high as you can go in an intercooled turbocharged concept running on gasoline. Improved specific fuel consumption and low-end torque are therefore still possible in a Wankel, especially if sequential turbos are used. Alternatively, lean-boost combustion systems based on 20-30% externally cooled low-pressure EGR (cp. Ricardo LBDI) should be feasible in a Wankel as well, permitting the use of a single variable geometry turbo (VGT) based on affordable materials.

For applications that need only moderate power levels, a single-rotor design with an inertial compensation mechanism should be cheaper than scaling down a traditional two-rotor design. Smoothness would suffer, but still far exceed that of an inline three piston engine.

The diminutive size of a small Wankel could make it interesting for PHEV concepts. In addition to offering up more space for batteries, the block would heat up faster if and when ICE operation is required after all.

As far as alternative fuels go, adsorbed hythane would be preferable to pue hydrogen in terms of cost, availability and environmental impact. The small amount (~5% by volume) of hydrogen in hythane assists ignition and increases the burn rate, issues that are particularly problematic in Wankels due to elongated shape of the combustion chamber.


Seems like the Wankel would be perfect for light aircraft (high power/weight, low vibration, simplicity & reliability). Apparently many ex-Mazda auto engines have found their way into experimental aircraft.


The real world fuel economy of all Wankel engines is absolutely horrific. I'm surprised Mazda is still throwing good money after bad on this insanely inefficient engine design. Check out the HP, acceleration and EPA MPG ratings for the RX-8 vs. its competition, they are all laughable.

Roger Pham

yeah, but the H2-Renesis with direct injection and hybrid drive gets an equivalent of 60 mpg, according to jack's calculation.

Rafael made an excellent point regarding using 5% mixture of H2 and methane (hythane). A gasoline direct injection version with a separate H2 injector from a small compressed H2 bottle can achieve the same efficiency level as a pure H2 version, yet offer dual fuel versatility.

I suspect that we have not, til now, seen the best that the Wankel rotary can offer. The great deal of weight saving will further help improve fuel efficiency.


Ah yes, trash the rotary. The mileage is terrible you say... If you are driving a sportscar, you shouldn't really be too worried about it. If you wanted a low rpm torque monster, buy something else. There's more than enough torque to get yourself in trouble if you have half a clue how to keep the revs up. So if you want to powershift at 9K rpm, hold on and have a hell of a good time, buy a rotary.

Aussie: If you can't get a rotary to survive 100000kms, you're really doing something wrong. The most beat 7 I ever saw was still running at 120k miles.

Chin Bong

Is the same reason why Subaru and Porsche continues with boxer engine. It is also the same reason why the 911 is always a rear engine-real wheel drive. I really want to see what the Mazda can cook up this time.


Building a 3 cilindre 1,2 litre turbocharged engine following the fuel efficient 'downsizing' trend does not make you special.

Praise Mazda for building on their own heretage and especially, doing something different!


I read somewhere that poor reputation of Wankel engine with regard to fuel consumption is mostly due to it poor performance in this area at partial loads, and especially in low load range. However, I was unable to find any SFC curves for Wankels plotted against engine load. Still, that would explain to some degree why Mazda sports cars suffer from somewhat poor fuel efficiency, especially in city driving cycles - their powerful Wankels can't give good fuel consumption figures when loaded to 10-20%. OTOH, the same thing could make small Wankel engines an excellent choice for serial PHEV onboard range-extender generators, as in this application they would only either run loaded to 100%, or wait. Moreover, single cylinder from any Mazda engine seems to be quite well sized for such an application. And there's one more thing: see Paul's Lamar, and his insights into a potential fuel efficiency breakthrough that turbo compounding could give to Wankel engines, as they in his opinion should benefit much more from turbo compounding than piston engines. There may still be hope for efficient Wankels, especially in aviation (Paul's area) and serial PHEVs, as in both these applications low loads do not contribute much to the overall fuel consumption picture.


Finally direct injection!

I tried to convince most of Orbital Corps management at the time (over ten years ago) to do a proto. We had guys messing around with them (my self included) on a hobby basis. For some reason I couldn't get them to go for it!

As stated I too would love to see some some BSFC number on the new engine to see were they are at!

I like tother comments like a one rotor series hybrid generator. These engines are remarkably compact and a pancake generator on the end would produce a very neat package.


Roger Pham

Paul Lamar in fact did propose a two-engine car with Wankel rotaries, one small engine for continous cruise power and one larger engine for acceleration only. Since the Wankel engine can allow a hollow shaft for a crankshaft, the small engine's shaft will go through the hollow shaft of the larger engine to feed into one transmission unit. The small engine is adjacent to the large engine whereby the heat from the small engine will keep the larger engine warmed up in order to be ready for a quick spurt of power on demand. Of course the small engine will be sized to be most efficient when producing cruise power. A hydraulic transmission with torque-lockup mechanism at cruise will provide a means for recuperative braking and additional accelerational power. This will allow the Wankel rotaries to exceed the overall efficiency of a piston engine, even more so now with direct injection and hydrogen-assisted combustion. The two Wankel rotaries are still very compact and light weight in comparison to an equivalent piston engine.


I don't think that sports cars have to be fuel hungry if by fuel you mean gasoline. They'll always want more energy, they put more down, but I'd prefer that energy be stored in batteries, and come from hydro or the sun or some clean, renewable source.

I don't mind being guilty of speeding, but I don't want to be guilty of buying petroleum-based fuel anymore.


I have personally seen a junk-yard rotary used for racing last through two 24hr races and years of hard racing seasons, without ever being rebuilt. In fact, it out lasted two of the cars it was in. Rarely do you see a rotary engined racecar have an engine failure. The 1st Mazda production rotary raced in an 84 hr race to prove reliability. One broke an axle @ 82 hrs the other finished 4 out of 58 cars. The Wankel has had a bad stigma around it due to reliability problems 1) from the early days and 2) from people who don’t treat it properly. 1) It was brought to market early and did not have time spent to properly test wear, etc. 2) Lubrication is critical in a rotary. If you don’t change the oil like you’re supposed to don’t expect it to last long. This is even truer in a turbocharged rotary.

Big Point. The Wankel has been around for little more than 50 years. The Otto cycle has been around for 160 years and the reciprocating piston for over 200 years. What would the piston engine be like if it was created less than 60 years ago? What would the rotary engine be like if it had been invented 200 years ago?


Well, for those of you knocking the rotary, go take a test drive in an RX 8.

I drove a 350Z, AudiTT, Honda S2k, and an RX 8.

I bought the RX for the rotary, when these guys say 9k, that is 9k and still SMOOTH, and the small size of the renesis allows it to be placed behind the front axle, distributing the weight evenly. This is a serious sports car with a base price of 27k to boot. Oh, and you can get a 3500 cash back on 2007.

Just drive an RX and you too will root for the renesis, and if each generation gets better, WOW.


Its been long coming, but finally Mazda has given us rotary fans an engine with a little more displacement where we can make up for low torque issues with the previous engines. If we cant get a three rotor here in the states then at least let us have this new engine. Its only going to add to the number of angry Mustang and Viper owners that just cant seem to keep up with this tiny engine that just wont go away!Dont worry Ford and Dodge you can always add a few more litters to your engines, oh hold on you already did! haha!

i drive an RX8. i don't race owners of 350z or S2k. i just tell them that they can always find spares for their engine from a Renault MPV or Type-Rs. The Renesis is unqiue for the RX8.

i drive an RX8. i don't race owners of 350z or S2k. i just tell them that they can always find spares for their engine from a Renault MPV or Type-Rs. The Renesis is unqiue for the RX8.

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