Mazda’s rotary engine in the age of the electric car • Hacker News Board

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

#201

Post by adrianN » Sat, Mar 30, 2024, 4:20 AM UTC

m463 wrote: post #188

It's worth mentioning that serial hybrids, like the BMW i3 rx, might not be able to drive on the freeway on the output of their generator. That's why it's a "range extender" - at some point you have to pull over and charge. EDIT: this is a big secret that none of the marketing materials (want to) make clear. I'm uncertain the output of the wankel, but maybe with its power-to-weight it might get closer to being able t…

Does that matter in practice? What's the effective range for highway driving in these cars?

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

#202

Post by adrianN » Sat, Mar 30, 2024, 4:41 AM UTC

wkat4242 wrote: post #179

One of the cool things about this engine is that it can run on hydrogen with minimal modifications. Not sure if the article mentions this, I don't have time to read it now. But that could make it more interesting when renewable hydrogen becomes common (right now it's not)

Why would you burn hydrogen in a car? It's more efficient to burn it in a power plant and run the car on electricity.

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

#203

Post by amatecha » Sat, Mar 30, 2024, 4:43 AM UTC

Supermancho wrote: post #181

14 wrote: post #175

Earlier quoted context omitted.

Except in Mazdas case the data was there to characterize it. They were notorious for failing very early and suffered bad seals around the rotary shaft. This has been well known for a long time. Many Rx owners knew ride it for 100k miles then sell it before it is too late.

I had an RX-8 for years. It was made in 2007. Someone defaulted on the loan or lost it in a divorce and drove it into a lake, marking it salvage. I bought it for 25k and was the owner from 2009 to 2019, from 60k to over 150k mi. The maintenance was a bit pricey, due to the fuel injection problems and the electronics would fail in extreme heat of sustained 110+ outside temp (southern california heat) or cold (seattle…

$25k USD? That does sound really high for a salvage RX-8 in 2009. My 2005 RX-8 was about $12k CAD in 2011 and was not salvage status. Though I guess yours was just a couple years old, mine was older, but still.

In regards to reliability, not long into owning it I had to get the engine rebuilt due to low compression (luckily JUST within the extended warranty period which Mazda offered due to the very issue everyone in here is mentioning, loss of compression due to failing seals).

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

#204

Post by npunt » Sat, Mar 30, 2024, 4:49 AM UTC

I've always seen rotary engines as one of the best examples of a particular approach to design that solves something very elegantly but relies too much on one critical component where all the pressure of the design is applied. In the case of a rotary engine, it's the apex seals.

They're a great warning for designers/architects/engineers to not get too enamored with the elegance of a system if parts of it are not yet completely solved. It's so easy when designing to try to shove aside some complex problem and say you'll solve it later, or play some shell game where every time you hit some hard to solve problem you wind up shuffling it around to someplace else [1], but that kind of instinct ultimately leads to unworkable things in practice.

[1]: 'we'll solve the seals problem later.. maybe materials has an answer' or 'just add oil in the mix to protect the seals there, we'll solve emissions later'

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

#205

Post by danans » Sat, Mar 30, 2024, 5:10 AM UTC

m463 wrote: post #188

It's worth mentioning that serial hybrids, like the BMW i3 rx, might not be able to drive on the freeway on the output of their generator. That's why it's a "range extender" - at some point you have to pull over and charge. EDIT: this is a big secret that none of the marketing materials (want to) make clear. I'm uncertain the output of the wankel, but maybe with its power-to-weight it might get closer to being able t…

The Mitsubishi Outlander plug-in hybrid can do up to 60mph on a flat road in serial hybrid mode.

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

#206

Post by idontwantthis » Sat, Mar 30, 2024, 5:13 AM UTC

callalex wrote: post #80

idontwantthis wrote: post #43

Earlier quoted context omitted.

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 wh…

I just bought a car with a CVT and now I’m upset.

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

#207

Post by hatsunearu » Sat, Mar 30, 2024, 5:17 AM UTC

npunt wrote: post #204

I've always seen rotary engines as one of the best examples of a particular approach to design that solves something very elegantly but relies too much on one critical component where all the pressure of the design is applied. In the case of a rotary engine, it's the apex seals. They're a great warning for designers/architects/engineers to not get too enamored with the elegance of a system if parts of it are not yet…

No, rotary engines are terrible. For one, the equivalent of variable valve timing doesn't exist/cannot exist for rotary engines, unless Mazda creates a miracle. VVT and VVL lets you do some insane things in terms of efficiency and good engine behavior, so the rotary falls behind a lot.

The rotor is pretty much unable to be cooled too.

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

#208

Post by [deleted] » Sat, Mar 30, 2024, 5:24 AM UTC

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.

[deleted]

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

#209

Post by seabrookmx » Sat, Mar 30, 2024, 6:00 AM UTC

hatsunearu wrote: post #207

npunt wrote: post #204

I've always seen rotary engines as one of the best examples of a particular approach to design that solves something very elegantly but relies too much on one critical component where all the pressure of the design is applied. In the case of a rotary engine, it's the apex seals. They're a great warning for designers/architects/engineers to not get too enamored with the elegance of a system if parts of it are not yet…

No, rotary engines are terrible. For one, the equivalent of variable valve timing doesn't exist/cannot exist for rotary engines, unless Mazda creates a miracle. VVT and VVL lets you do some insane things in terms of efficiency and good engine behavior, so the rotary falls behind a lot. The rotor is pretty much unable to be cooled too.

I'm not saying rotaries are great, but two stroke piston engines can have variable port timing (typically called a "power valve"). I don't see why the same method couldn't be applied to a rotary.

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

#210

Post by seabrookmx » Sat, Mar 30, 2024, 6:05 AM UTC

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.

Exactly. The Volt uses the same planetary gear set style transmission that the Prius does.

Everyone bemoaning the death of the Volt can now just buy a Prius Prime (the PHEV variant). It's the same thing just newer/better. It even looks sporty-ish now.