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Mazda’s rotary engine in the age of the electric car

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Re: Mazda’s rotary engine in the age of the electric car

#51

Post by calfuris »

deelowe wrote: post #25
mattmaroon wrote: post #15

I have never understood why the Volt Series Hybrid idea never took off. It is more efficient to turn gasoline into electricity and then drive the car with that than to directly connect the engine to the wheels. Is it perhaps that the cost involved is just too much more than a plugin hybrid to make the small extra fuel savings worth it?

That seems unlikely. A mechanical coupling should be close to near perfect efficiency where as using the engine to drive electric motors requires several conversion steps.

The trick is having a large buffer, so that typically the engine can operate at the point with the best specific fuel consumption or shut down entirely. Getting energy from the engine to the wheels is less efficient than a mechanical transmission, but the increased average efficiency of the engine can more than offset that.

Re: Mazda’s rotary engine in the age of the electric car

#52

Post by porphyra »

kjkjadksj wrote: post #48
porphyra wrote: post #36

Earlier quoted context omitted.

Sports cars, in general, are much loved but seldom bought.

You’d think its a different time now that the kids who grew up lusting over these cars now have money for one, enough money to create a new car market where even a pickup truck can be almost six figures optioned out

Yeah but by the time you're able to afford one you will be married with kids and therefore prioritize practicality over drifting.

Re: Mazda’s rotary engine in the age of the electric car

#53

Post by aidenn0 »

dragontamer wrote: post #47

A good article. It barely addresses the elephant in the room however: The Toyota Prius and its Atkinson engine. The Atkinson engine is 99% the same as a regular engine (aka: Otto cycle), except the timing is different. Instead of closing the valves when the piston+cylinder is full of gasoline+air mix... the Atkinson engine waits a bit and "leaks" some gasoline+air back out before closing the intake valve, effectively…

I am mildly annoyed that Toyota calls late intake valve closing (LIVC) an "Atkinson-cycle" Atkinson made 3 engines none of which are anything like a 4-stroke with LIVC. The closest is perhaps his two-stroke engine, which kept the exhaust valve closed during the power stroke and open for part of the compression stroke.

The Miller-cycle is much closer to what the Prius uses than anything Atkinson made; it was a traditional 4-stroke with LIVC, but required a super-charger to generate power at low RPMs.

The Prius has a CVT and electric motor, overcoming any issues at low RPMs. Also now that VVT is more common, many engines run with LIVC under certain conditions.

Re: Mazda’s rotary engine in the age of the electric car

#54

Post by aidenn0 »

shanusmagnus wrote: post #32

What was the purpose of using the rotary engine in the first place, for ICE cars? From the comments it seems it's maybe lighter for a given power output. Is that it, other than just the novelty of it?

Power density is indeed the main advantage. It's also much easier to balance; hunks of metal changing direction many times per second (6000 RPM is 100Hz) is somewhat mechanically exciting.

Re: Mazda’s rotary engine in the age of the electric car

#55

Post by rootusrootus »

tokai wrote: post #12
rootusrootus wrote: post #4

Almost feel bad for GM, the article did not mention the Volt when talking about series hybrids. But I guess it is a Japan-focused news source.

The point is the wankle engine. No sense in mentioning the Volt.

They did mention a couple other series hybrids, however, neither of which has a Wankel.

Re: Mazda’s rotary engine in the age of the electric car

#56

Post by coryrc »

WalterBright wrote: post #38
coryrc wrote: post #28

Earlier quoted context omitted.

Then you may as well use a gas turbine, which is pretty much better in every way that matters for generating purposes.

Gas turbine cars have been built, but they tend to set anyone on fire if they walk behind the car. https://bandimere.com/previewing-the-brakes-plus-jet-car-nat...

You're probably being silly, but for anyone else, gas turbines as used for generators don't have jet exhausts on them, i.e. https://www.youtube.com/watch?v=yR5oVn-Fvvg

Re: Mazda’s rotary engine in the age of the electric car

#57

Post by rootusrootus »

dragontamer wrote: post #29
HPsquared wrote: post #19

Earlier quoted context omitted.

Surely the "generator -> charger -> battery -> inverter -> motor" chain is less efficient than a driveshaft. Perhaps the only benefit is the engine can run at an optimal speed, but an appropriate gear ratio should handle that.

> but an appropriate gear ratio should handle that. See Prius's "Powersplit Device". I'd describe the Powersplit device to be a combination of generator/alternator, starter/electric motor, reversed-differential (2x power inputs -> 1x driveshaft), and effective gear-ratio. All in one planetary gearset. EV motor2 determines the speed of the car. The ICE motor can spin at any speed that the computer determines to be use…

The Volt was a great idea, but I couldn't make it work for me. I need a four door car which regularly holds four people, and the Volt (especially the newer one, which was when I was shopping) has a low roofline. Only time I've hit my head harder on a car roof was when I tried to sit in a new Supra. So I ended up finding something where the physics of getting in and out were more agreeable. Still a sedan, just with fewer headaches.

I wish they had offered that same powertrain design in something other than a Cruze.

Re: Mazda’s rotary engine in the age of the electric car

#58

Post by deelowe »

calfuris wrote: post #51
deelowe wrote: post #25

Earlier quoted context omitted.

That seems unlikely. A mechanical coupling should be close to near perfect efficiency where as using the engine to drive electric motors requires several conversion steps.

The trick is having a large buffer, so that typically the engine can operate at the point with the best specific fuel consumption or shut down entirely. Getting energy from the engine to the wheels is less efficient than a mechanical transmission, but the increased average efficiency of the engine can more than offset that.

Still seems like a traditional hybrid would be more efficient. I'm not sure what's gained by removing the mechanical coupling altogether (other than cost/reliability).

Re: Mazda’s rotary engine in the age of the electric car

#59

Post by rootusrootus »

themerone wrote: post #24
mattmaroon wrote: post #15

I have never understood why the Volt Series Hybrid idea never took off. It is more efficient to turn gasoline into electricity and then drive the car with that than to directly connect the engine to the wheels. Is it perhaps that the cost involved is just too much more than a plugin hybrid to make the small extra fuel savings worth it?

Aside from your suggestion violating the laws of physics, that's actually not how the Volt worked. The original concept for the volt was that the engine would only generated electricity, but in production models, the engine was connected to the drivetrain.

That remains true for more recent "series hybrids" as well, such as the Honda mentioned in the article. The efficiency gain from engaging the ICE when cruising on the highway is just too good to pass up.

Re: Mazda’s rotary engine in the age of the electric car

#60

Post by ggreer »

skellera wrote: post #8
486sx33 wrote: post #2

Does it produce more low end torque verses a traditional gasoline combustion engine? If not then why is it better suited for electrical generation? Is it more efficient with less load? The article mostly makes it sound like Mazda just loves the wankle and wants to find any possibly way to bring it back - even though it has “high” emissions… so coupling it with a hybrid electric motor makes it happen.. That can’t be t…

I don’t understand why Mazda doesn’t just make a drift-tuned electric car. You could do amazing stuff with software focused on that driving style. A true electric successor to the RX-7 would capture so much attention.

Several reasons.

First, like most of the Japanese manufacturers, Mazda bet against electric vehicles. They focused R&D on improving engine efficiency and getting their engines to run on hydrogen. If Mazda wants to make electric vehicles now, they have to play catch-up, or license key technologies from other manufacturers.

Second, batteries are heavy. For sedans and mid-size crossovers, this isn't much of a problem. EVs of that class are about the same weight as combustion vehicles. But for a lightweight sports car with decent range, batteries would be a big chunk of the total weight. Tesla's 85kWh battery weighs around 1,200lbs. If your desired weight is 2,500lbs, that only leaves 1,300lbs for the actual car. Yes you can save some weight by making the battery part of the structure, and you don't need an exhaust system, engine block, alternator, intake, etc, but it's still a tough set of constraints to work within.

Why do customers want sports cars to be light? Well all else equal, a lighter vehicle will have better performance. But even when all else isn't equal, vehicle weight can drastically affect driving enjoyment. I have a 4,048lb Model 3 Performance and a 2,182lb Mazda Miata. In terms of specs, the Model 3 is better in every way. It can accelerate, brake, and turn better than the Miata. It even has more range than the Miata. But the Model 3 feels like it's using brute force to beat inertia into submission. (Don't get me wrong, that can be fun.) The Miata is the opposite. Its light weight means that there's very little inertia to overcome, and something about that is extremely satisfying. It's almost like having a street legal go-kart. Until battery technology improves, an electric version just won't have the same appeal.

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