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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

#71

Post by xattt »

mrighele wrote: post #64
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.

If all you need is power generation, use a nuclear reactor. Time to bring back the Ford Nucleon ! [1] Comes with daily free health checkup (in form of an X-Ray). [1] https://en.wikipedia.org/wiki/Ford_Nucleon

Aaahktually, the radiation given off the reactor would be too “hard” and useless in soft-tissue imaging.

Maybe neutrino imaging?

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

#72

Post by akira2501 »

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…

> All in one planetary gearset.

In the first version. In later versions they added a second separate gear set. Then even later they merged the two gear sets back into one but with two separate planetary arrangements.

I'm not a particular fan of EVs in general, but I do very much like the Prius and the careful engineering that went into this drive train. This video[0] does a great job of explaining the overall system in the context of an operating vehicle.

[0]: https://www.youtube.com/watch?v=PIYNAroYEk0

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

#73

Post by user_7832 »

coryrc wrote: post #28
sethhochberg wrote: post #16

Earlier quoted context omitted.

They have a pretty narrow power band (produce efficient max power at a small range of RPMs) which always somewhat limited their use for normal ICE cars, but is a pretty workable constraint for an electrical generator. So you have compact size, good power to weight ratio, and power limitations that don't really matter for range extender purposes. Lots of potential. I can't find the article right now, but I'd swear I r…

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

Apparently they really don't scale well. I found this reddit post explaining it better:

> Gas turbines scale extremely poorly. They rely on small clearance between the rotating blades and the housings for efficiency. The smaller the turbine, the greater the relative clearance and the more energy is lost. Gas turbines, at least with established technology, make very little sense below 300ish HP. As a real life comparison: A Robinson R44 piston helicopter and an R66 turbine Helicopter have almost identical design, dimensions, and weights. Power is around 250 / 300hp. The former burns between 50-60L of gas per hour at cruise, the latter around 90-110L of Jet fuel.

1 - https://old.reddit.com/r/cars/comments/s8vkv8/are_wankel_eng...

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

#74

Post by lostlogin »

ggreer wrote: post #60
skellera wrote: post #8

Earlier quoted context omitted.

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. E…

Going with this theme, the idea of a battery car with longer range is appealing to me. However a smaller battery but quick charging would mostly remove the need.

I’m not sure I want to drive around with a capacitor in the boot, but a huge battery isn’t ideal either.

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

#75

Post by samdunham »

jdblair wrote: post #46
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?

Lighter and mechanically simpler were the selling points. Poor fuel efficiency and trouble with the seals were the downsides. My uncle had an RX-7 back in the 80s when I was a kid. I remember when it was idling I could see the exhaust puffing, in pulses. It only had a single combustion chamber after all.

I've had three RX-7s. A first generation and two second generations. I drove the first until the wheels literally fell off (I was a young, stupid kid that ignored the crunching sounds of the rear wheel bearings falling apart. The rear wheel(s) seized while I was driving down a bridge causing the axel to snap in half. That was an interesting "drive" down the rest of the bridge). The second was a base model second gen that I gave up when I suddenly had two cars because of getting married, then divorced. The third was my favorite. A late model second gen fully loaded. That one eventually caught on fire due to negligence at a tire place. I loved that car.

The third generation never got cheap enough for me to consider one, but oh, I wanted one badly. The RX-8 never really caught me. Plus they had some early issues. That Iconic concept definitely has my attention, though.

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

#76

Post by user_7832 »

ggreer wrote: post #60
skellera wrote: post #8

Earlier quoted context omitted.

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. E…

It would be theoretically possible to have a small battery ("just a 60 mile/100km range, or even smaller) combined with a generator, but I don't know if markets would appreciate that.

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

#77

Post by lostlogin »

_ea1k wrote: post #7
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…

Low end torque tends to be the rotary's Achilles heel. I think the claim being made is that efficiency is better at high, steady RPMs, but tbh, I've always found that claim a bit dubious. If you love the rotary engine, this does have some nice perks as the electric motor basically fixes the rotary engine's main weakness. Having said that, I'd have been much more excited about this 10-15 years ago.

It fixes the terrible efficiency by having an entirely different power source?

As others have pointed out, the article doesn’t do a great job of explaining how the rotary helps.

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

#78

Post by callalex »

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?

“It is more efficient to turn gas into electricity”

I don’t think that’s correct. It may be true for highly variable/low loads where the pumping losses in the pistons dominates. However the majority of fuel consumption in a car happens at traveling speed (highway miles). That is the area that needs to be optimized for.

My 2015 Honda Accord Hybrid takes this approach. At below-freeway speeds the gas motor runs in series to drive an electric motor. At highway speeds, it engages a clutch and directly connects the engine to a low-loss 1-speed transmission.

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

#79

Post by nradov »

Tagbert wrote: post #33
jmspring wrote: post #9

Earlier quoted context omitted.

The funning thing is, people I know who have a Volt love their cars. Haven't tried one myself. My family has a couple of paid of Toyota gas vehicles that are 8+ years old and will probably live longer than we will.

I drive a 2017 Volt gen 2 and love it. I drive about 90+% of miles in EV mode and mostly use the gas engine for road trips. It is fun to drive and (other than a couple of common, and easily fixed issues) has been reliable. I do plan to replace it in the next year because it sits very low and has a very low roofline. My spouse is uncomfortable getting into it so we almost never drive it when together.

I don't understand why GM never put the Voltec drivetrain into a compact SUV. It would have sold much better than an odd looking hatchback with little interior space.

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

#80

Post by callalex »

idontwantthis wrote: post #43
ch_sm wrote: post #20

Earlier quoted context omitted.

> 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 I thought so too, but my research suggested that the efficiency is pretty much the same if not worse and power delivery is worse. Do you have some links? I‘d like to be wrong on this one.

I thought the idea is that the battery acts as a buffer and the engine is always either off or at constant rpms in its ideal power band.

You also have to keep in mind that the average consumer is…quite stupid, or more charitably quite sensitive. There are lots of cars on the market today with CVTs (continuously variable transmissions) that enable the motor to always be driven in the most optimal RPM. However in software, the engines are intentionally driven at less efficient rpm’s so that the driver can feel steps and lurches as the car accelerates which is somehow more “correct” to the average car buyer.
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