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.

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.

Andy

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

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.

http://www.rotaryengineillustrated.com/renesis.php

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.

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.

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.

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!

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.

Mike

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.

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.

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.