Comment by cookiengineer | Hacker News Reader

Comment by cookiengineer | Hacker News Reader

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Technically, the Wankel rotary engine design allows much higher power output than an I-4 or even a V-6 engine design due to no strains on the rods, and much less strains on the piston(s) as those literally blow up all the time in I4 engine designs in similar power output ranges.

I've seen many very reliable 3 or 4 rotary wankel swaps in RX7 FD3S that output far beyond anything imaginable any V8/V12 could produce. 2000hp is not a joke here, when being run on pure ethanol as fuel input. Apart from fuel injectors, clutch and gearbox, these engines run very stable and reliable.

There was an RX-8 Blue model being sold in Japan which was burning hydrogen directly, effectively producing water as output, which, in the prototype was being converted back to hydrogen via a fuel cell. And this was in 2004.

I wish there were more Wankel engines being used as "pocket generators", because they can reliably run on synthesized alcohol and hydrogen and be a potential generator replacement for all that Diesel based crap that's being used in rural areas.

Imagine a solar roof on your house that produces hydrogen with some fuel cells (which also produce heat for your home). This could be the optimum cycle for use in a decentralized home, as chemical energy storage has no loss compared to li-ion batteries that have a limited lifetime. The multiple use of hydrogen (e.g. a stove just needs to burn the gas) also makes it very low tech, and possibly much more reliable than a circuit based system where transformers might fail over time.

But of course, can't sell decentralized approaches via gas stations, so it will never take off...

While I also share in your love of Wankel engines I think you are grossly skipping over their unreliability (mostly around the seals).

There's an extremely good reason "rural" applications are reliant on diesels. It's not uncommon for a diesel engine to hit 300k+ miles and still operate reliably. And not to mention simply. They are relatively easier to maintain than a standard gasoline engine.

Diesels also greatly benefit from being on a fixed power band. It's why they work so dang well on large ships.

Where as rotary engines(rx-7's at least) need a rebuild every 80-100k miles. So I think without really knowing what you're doing mechanically or having access to a mechanic that can repair those kinds of engines you aren't going to be super reliable with a rotary.

Green hydrogen approaches via rotary engines does seem quite interesting. I think if the reliability of the rotary could be improved that could have some serious merit. Or at least making small enough generators that you can easily ship them out to be replaced/repaired could have serious merit.

My guess is this: Mazda believes its battery-only range is enough for most driving situations. If they're right, the rotary engine's more limited lifespan would be a moot point since it will still last the vehicle's entire lifetime. One can only hope.

The maintenance thing is concerning, though. Nobody knows how to work on these things. As an RX-7 or RX-8 owner, you're either doing most of your engine work by yourself, or you're driving very long distances to go to a specialty shop. We can pray that it's reliable enough for this to not be a problem, but if these engines start failing, it's going to be a huge mess.

Side note - the geometry of a Wankel rotary engine makes a diesel version impossible - you can't get enough compression. Diesel rotaries do exist though. An American company called Liquid Piston is making them for the Army. The intent is to use them in diesel generators, since the resulting generator is much smaller and lighter than more traditional diesel generators.

"The multiple use of hydrogen (e.g. a stove just needs to burn the gas)"

Oh, no. You don't want to be cooking over a flame capasble of melting platinum. You will utterly destroy your pots and pans temper. I do jewelry work, hydrogen gas is one of the hardest gases to properly work with. I'd rather let a newbie play with oxy-acetylene than a hydrogen torch.

Could you elaborate on why this is? Naively, the temperature of a simple hydrogen flame is not too much hotter than a methane flame. And in torch form, it seems like MAPP is several hundred degrees (C) hotter? And oxy-acetylene a few hundred more on top of that. Any torch seems to have way more than enough heat to melt platinum (1700C)?

A hydrogen-oxygen flame (this is what happens naturally since you're burning hydrogen in open atmosphere) burns closer to 2800C, and also has the fun property of causing embrittlement (which is especially worsened at higher temperatures where metal expands and becomes more porous.) Your steel pots and pans are essentially toast under a hydrogen flame.

People think "Fire is fire" and no, no it is not.

When I was doing a bit of research, I was coming up with 2050C or so for hydrogen open flame (in air; with pure oxygen it was 2600C), and about 1950C for methane in air. Natural gas is mostly methane and has a pretty similar flame temperature, but it does not melt our pots and pans. Why would hydrogen? It is hotter, sure, but not dramatically so.

Hydrogen really likes to strip out all the carbon in your steel, leaving you with pure iron (given enough time). It's a well known phenomenon called hydrogen embrittlement.

Where are you seeing all these magically rotaries? Yeah the guys in NZ and maybe some Americans(Rob Dahm) have some high horsepower rotaries but let's not pretend it's the norm and that they are more reliable than an equivalent piston engine.

Built Nissan VR38DETT V6 produces 2000hp. A full billet block will produce 3000hp+. Nissan GT-R guys(T1, ETS,AMS) Let's not even get into the big block V8's because these things will run all day at that hp and be a whole lot more reliable than anything mentioned here.

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