Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

nippon.com

Post reply on HN
Print view View original

191–200 of 295 posts

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

#191

Post by bruce511 »

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…

Weeelll, "freeway driving" depends on the freeway and time of day.

For too many freeways, for too much of the day, I can ride a bicycle at speeds greater than the surrounding traffic.

And in those conditions hybrids, and electric cars are perfect.

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

#192

Post by Retric »

willis936 wrote: post #189
Retric wrote: post #178

Earlier quoted context omitted.

That rate isn’t a deal killer for a plug in hybrid. The engine might see ~1/4th the ware per mile spending the vast majority of its time off. Meanwhile hybrids really want a small and lightweight engine because of all the extra equipment.

Right but then why not use a more efficient and reliable engine? The motors will last hundreds of thousands of miles. The power circuitry should have a similar run if kept cool. Why have an ICE that's more likely to fail with lower thermal efficiency? The engine used in Toyota's most popular cars runs in Atkinson most of the time with a 40% thermal efficiency. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7425626/

Because the engine isn’t the only thing being optimized. Suppose your options are 50 miles of effective plug in range and a 40% efficient engine or a 35% efficient engine and a 100 miles of plug in range. The second option might use a lot less gas.

It’s not just the cost of batteries that’s a concern resulting in short plug in hybrid ranges. Weight is a real limiting factor when you also need a gas engine and large fuel tank.

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

#194

Post by willis936 »

AYBABTME wrote: post #161
mikewarot wrote: post #160

Instead of a Wankel, why not use a small custom turbogenerator, like the APU in aircraft?

They're efficient at higher power levels but really not at small-power-generator level. An 8kw jet powered generator I saw recently used 0.5kw-hr per kg, which is 5x more than an equivalent one based on a traditional diesel engine. Their main advantage is high power for low mass of generator, but consume massive amount of fuels.

Seems unreasonable for a powertrain, but pretty reasonable for a series hybrid generator.

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

#195

Post by willis936 »

Retric wrote: post #192
willis936 wrote: post #189

Earlier quoted context omitted.

Right but then why not use a more efficient and reliable engine? The motors will last hundreds of thousands of miles. The power circuitry should have a similar run if kept cool. Why have an ICE that's more likely to fail with lower thermal efficiency? The engine used in Toyota's most popular cars runs in Atkinson most of the time with a 40% thermal efficiency. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7425626/

Because the engine isn’t the only thing being optimized. Suppose your options are 50 miles of effective plug in range and a 40% efficient engine or a 35% efficient engine and a 100 miles of plug in range. The second option might use a lot less gas. It’s not just the cost of batteries that’s a concern resulting in short plug in hybrid ranges. Weight is a real limiting factor when you also need a gas engine and large f…

That would be a worthy trade, but that is vastly overstating the weight of aluminum block engines compared to Li+ and not at all realistic.

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

#196

Post by AYBABTME »

willis936 wrote: post #194
AYBABTME wrote: post #161

Earlier quoted context omitted.

They're efficient at higher power levels but really not at small-power-generator level. An 8kw jet powered generator I saw recently used 0.5kw-hr per kg, which is 5x more than an equivalent one based on a traditional diesel engine. Their main advantage is high power for low mass of generator, but consume massive amount of fuels.

Seems unreasonable for a powertrain, but pretty reasonable for a series hybrid generator.

Not really because the power rating at which they start to make sense is in the multiple hundreds of kW. Cars don't need that much average continuous power while driving, on the order of 15-30kW depending on speed and grade. So a "more efficient than piston" turbine engine would be way too big and powerful and would cycle about once per hour. Overall excess mass and bad reliability due to frequent cycling. It's better to have a smaller engine that's sized for slightly over 15-30kW continuous duty. Realistically this will be a piston engine, or a fuel cell. I would love to use a turbine engine for my own application but the math doesn't work, unfortunately.

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

#198

Post by kcrwfrd_ »

nogridbag wrote: post #183
Supermancho wrote: post #181

Earlier quoted context omitted.

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…

Wait you paid 25k for a used/salvage RX-8 in 2009? That sounds crazy. I think I bought one new for around 26k in 2008.

That does sound crazy. The sticker price for the brand new Subaru BRZ limited manual transmission I got in 2012 was $28k.

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

#199

Post by cookiengineer »

ryukoposting wrote: post #141
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…

It has nothing to do with sentimentality. Wankels have tremendous power-to-weight and power-to-size ratios. Their main problem is reliability. The generally accepted solution to improve rotary engine reliability (oil injection) results in poor emissions. The wide, flat-ish combustion chamber doesn't help the emissions problem, either. The Wankel is at its most efficient and its most reliable when operating at a const…

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...

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

#200

Post by Merad »

_yb2s wrote: post #104
user_7832 wrote: post #73

Earlier quoted context omitted.

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 compari…

Thank you, I've wondered for years why we didn't have tiny gas turbine engines...

They definitely exist for small RC aircraft, but they're very expensive.
Post reply on HN