RE: Mazda EVs might hold the secret for RX-8 successor
Discussion
nicfaz said:
if I were ever to manufacture an EV then it would be silent at low throttle and then make increasingly loud "Tie Fighter" noises as the throttle was depressed 
I think I've said this before, but I think the future will be in different types of sound from EVs as it is with ICE, either programmable generated noise under the guise of "pedestrian warning", or simply a strong motor-ey whine to give that feeling of power in acceleration.I can definitely see hacks being sold for new programmed sounds though (business opportunity right there).
NJ72 said:
Hard to believe, but a rotary engine used as a generator is actually much more efficient than a reciprocating engine.
Mainly hard to believe because it has no basis in fact!Rotaries have the benefit of high specific power (power per unit mass or volume) and good NVH (because there are no significant out of balance forces) but everything else is a deficit compared to a reciprocating engine.
The last RX8 made a (slightly flakey) 230 bhp odd, and there's no more tricks really to be had in terms of making a higher specific output, and since then, emissions requirements have got a lot stricter, and customers have also got used to high torque turbo engines, so either the "new" rotary sportscar, should it ever actually happen (which i doubt) will have to have a bigger engine capacity, or be turbo charged, neither of which will do it's ultimate efficiency any good (and so it'll be even more fuel in-efficient than the RX-8, which i'd rate as mildly catastrophic in that regard....
Nerdherder said:
A rotary sports car with an electric motor sitting somewhere on the driveline 'augmenting' performance seems like a great recipe to me.
P.s; Iirc Rotax (or is it another company?) has been offering rotaries that act as range extender/aggregate engines for quite a while now.
AVL and Audi both spring to mind. Rotax make a rotary-vale two-stroker, which might also do the job!P.s; Iirc Rotax (or is it another company?) has been offering rotaries that act as range extender/aggregate engines for quite a while now.
Max_Torque said:
Mainly hard to believe because it has no basis in fact!
Rotaries have the benefit of high specific power (power per unit mass or volume) and good NVH (because there are no significant out of balance forces) but everything else is a deficit compared to a reciprocating engine.
The last RX8 made a (slightly flakey) 230 bhp odd, and there's no more tricks really to be had in terms of making a higher specific output, and since then, emissions requirements have got a lot stricter, and customers have also got used to high torque turbo engines, so either the "new" rotary sportscar, should it ever actually happen (which i doubt) will have to have a bigger engine capacity, or be turbo charged, neither of which will do it's ultimate efficiency any good (and so it'll be even more fuel in-efficient than the RX-8, which i'd rate as mildly catastrophic in that regard....
A rotary engine tuned for and run at a constant rpm (2000 rpm is optimal) runs much more efficiently than a piston engine. Efficiencies of 60% are achieved.Rotaries have the benefit of high specific power (power per unit mass or volume) and good NVH (because there are no significant out of balance forces) but everything else is a deficit compared to a reciprocating engine.
The last RX8 made a (slightly flakey) 230 bhp odd, and there's no more tricks really to be had in terms of making a higher specific output, and since then, emissions requirements have got a lot stricter, and customers have also got used to high torque turbo engines, so either the "new" rotary sportscar, should it ever actually happen (which i doubt) will have to have a bigger engine capacity, or be turbo charged, neither of which will do it's ultimate efficiency any good (and so it'll be even more fuel in-efficient than the RX-8, which i'd rate as mildly catastrophic in that regard....
For the size and weight of the engine the RX8 made a lot of power (more than all but the JDM version of the FD turbo rotaries). It did suffer from poor fuel consumption of course. Times have moved on and we already have helicopters and aircraft using these engines and recently a motorbike. The motorbike particularly has pushed things on as it uses coatings to avoid the need to inject oil. Rotary engines have a lot opportunities to be developed. Piston engines have come a long way, rotaries will too.
Edited by delta0 on Wednesday 29th August 22:16
bodhi said:
Tryke3 said:
Mazda should be ashamed of the rx8, you cant expect people to spend 30k on coupe that is worth 500 quid in 5 years
Considering 2009 models are currently priced at £4k + I suspect some, if not all of this post is complete nonsense. Would have to tread very carefully to not get one that is totally fudged mind. But there seem to be a few honest ones about for that kind of money with proof of rebuilds and compression results.
Otispunkmeyer said:
bodhi said:
Tryke3 said:
Mazda should be ashamed of the rx8, you cant expect people to spend 30k on coupe that is worth 500 quid in 5 years
Considering 2009 models are currently priced at £4k + I suspect some, if not all of this post is complete nonsense. Would have to tread very carefully to not get one that is totally fudged mind. But there seem to be a few honest ones about for that kind of money with proof of rebuilds and compression results.
I've always had a soft spot for the RX-8, and would definitely look into one for the usage you suggest. I gave them serious consideration when I bought the 125i, but the BMW was faster, more economical and less likely to grenade itself. A friend's partner had one though, and it was great fun. Sounded great too.
I'm not a rotary fanboi - never owned one and never will.....
Now that's cleared up - some thoughts and opinions on the arguments..
MPG - People say it's bad for a "1.3"
It's not a 1.3 though. How many non turbo charged cars were making 230hp without MASSIVE engines in 2003?
The BMW M54 3.0 made 230bhp - 3.0 straight 6 24v. Mine did around 25mpg generally and used a liter of oil every 1k or so miles.
Is that SO different from the RX Rotary?
The reliability doesn't seem to be in question however, it seems rare any of them survive regardless of how well you maintain them. Guess that's a big big thing for Mazda to think about .
Now that's cleared up - some thoughts and opinions on the arguments..
MPG - People say it's bad for a "1.3"
It's not a 1.3 though. How many non turbo charged cars were making 230hp without MASSIVE engines in 2003?
The BMW M54 3.0 made 230bhp - 3.0 straight 6 24v. Mine did around 25mpg generally and used a liter of oil every 1k or so miles.
Is that SO different from the RX Rotary?
The reliability doesn't seem to be in question however, it seems rare any of them survive regardless of how well you maintain them. Guess that's a big big thing for Mazda to think about .
PHMatt said:
The reliability doesn't seem to be in question however, it seems rare any of them survive regardless of how well you maintain them. Guess that's a big big thing for Mazda to think about .
Within the community the issues ARE known about:-- Treat coil-packs as service items. A coil-pack failure = overfuelling = washing the oil away from the engine = rebuild time. Bit more serious than in a 4-stroke petrol...
- Treat the engine as a quasi 2-stroke, i.e. add a little oil with every other tank of fuel (or something like that). Not officially sanctioned due to the emissions issues that causes, but it helps no end...
- Try not to turn the car off soon after starting it (i.e. you can't pop to the corner shop for milk in it, or get petrol just after starting your journey). This is arguably the biggest weakness of the car (economy aside).
Follow those 3 rules and apparently reliability is just fine...it's just that (a) Mazda didn't communicate any of this; and (b) most buyers expected it to be 'white goods plug and play' just like the competition...which leads to the reliability problems that (a) and (b) address.
Max_Torque said:
Please post a link to actual data to prove your statement.
Not being funny, but just read up about the 787B and its efficiency compared to the piston engines it raced against for a start.Secondly, the usefulness of a generator is to run at a high rpm constantly. Because of the way a rotary engine works (at least the Felix wankel rotary engine) it thrives on high rpm and will happily sit at ~9,000rpm all day long without breaking a sweat - unlike its piston counterparts.
You are also looking at it the wrong way, because efficiency of an individual engine, sat on a workbench is not the point. power to weight of said engine is what's important, and rotary engines can be easily made in much smaller packages without compromising so much on rpm and output.
http://www.rotaryeng.net/RX8-TC-eng3.html This web page explains the principle behind why a rotary engine is a much better generator for a range extender than a piston engine. Not because its finite "fuel per horsepower" figure, but because it could generate the same volume of electricity as a piston engine, whilst lugging around MUCH less weight and take up much less space than it's reciprocating bretheren.
Alter the design of the rotary engine away from the wankel design and you end up with the 'LiquidPiston' concept engine as detailed here: http://liquidpiston.com/technology/how-it-works/ even more efficiency in a power-to-weight setting which is more important than power-per-litre-consumed.
So yes, the information is out there on the internet, but basic logic also backs it up.
If you're trying to hoof a large capacity rotary engine about in a car that weighs 1.4 tonnes along the road at 65mph, yes a reciprocating engine is more efficient. If you're running at peak power for any length of time, the comparative lack of engine weight is a better bet and, by extension, a more efficient use of space, fuel and engineering.
NJ72 said:
Not being funny, but just read up about the 787B and its efficiency compared to the piston engines it raced against for a start.
So you can't post any data or links then? The old rotary race cars were hugely in-efficient, it's just that the old non rotary race cars were even more in-efficient! (Assuming you believe what you assert, which tbh, i don't) Fundamentally, which every way you cut it, a rotary is not as fuel efficient (in terms of BSFC) as a reciprocating engine, due to several important fundamental factors, such as higher surface area to volume ratio, sliding seal friction, and not to mention the difficult of changing something like inlet/exhaust timing (less critical for a fixed load/speed generator, but something that made the old RX8 a bit, er peaky to drive (despite it having a complex variable intake manifold to try to even out the torque curve)
NJ72 said:
Secondly, the usefulness of a generator is to run at a high rpm constantly.
Sorry, but also false. You can wind a generator to produce power at what ever rpm you want. Grid based gensets used to be fixed at 3000rpm simply to get a nice easy 50 Hz AC output, but a range extender puts out DC, and so the speed at which it spins can be optimised to suit the engine driving it. Here, where higher rpm = higher losses, you want to downspeed as much as possible, ie make high torque at low rpm, precisely the opposite of what a rotary is good at!NJ72 said:
Because of the way a rotary engine works (at least the Felix wankel rotary engine) it thrives on high rpm and will happily sit at ~9,000rpm all day long without breaking a sweat - unlike its piston counterparts.
Should you be crazy enough to design a genset that runs at 9krpm (for reasons mentioned) then there are plenty of modern reciprocating piston engines that can sit at that speed continuously, without any problem at all.NJ72 said:
You are also looking at it the wrong way, because efficiency of an individual engine, sat on a workbench is not the point. power to weight of said engine is what's important, and rotary engines can be easily made in much smaller packages without compromising so much on rpm and output.
As someone who is actively involved with the design, test, calibration and certification of passenger cars, i can assure you i am not "looking at it the wrong way"!! ;-) Specific power is of importance, but is irrelevant if you can't ever sell the product due to emissions non compliance, or the fact it wears out after 5 years (or less)NJ72 said:
http://www.rotaryeng.net/RX8-TC-eng3.html This web page explains the principle behind why a rotary engine is a much better generator for a range extender than a piston engine. Not because its finite "fuel per horsepower" figure, but because it could generate the same volume of electricity as a piston engine, whilst lugging around MUCH less weight and take up much less space than it's reciprocating bretheren.
that web site doesn't "explain" anything. It simply shows that a rotary engine has both a high minimum BSFC, and that this operating condition is only available in a very narrow window of load/speed (as to be expected for an engine with fixed gas exchange etc)NJ72 said:
Alter the design of the rotary engine away from the wankel design and you end up with the 'LiquidPiston' concept engine as detailed here: http://liquidpiston.com/technology/how-it-works/ even more efficiency in a power-to-weight setting which is more important than power-per-litre-consumed.
So yes, the information is out there on the internet, but basic logic also backs it up.
irrelevant. The world is littered by "this engine will rewrite the rules and take over the world" engines of increasingly mad layout and design. This means nothing to an OEM who actually has to get a car into production and meet all the necessary targets for emissions, power, durability, servicing, NVH, Productionisation, even re-cycling etc!So yes, the information is out there on the internet, but basic logic also backs it up.
NJ72 said:
If you're trying to hoof a large capacity rotary engine about in a car that weighs 1.4 tonnes along the road at 65mph, yes a reciprocating engine is more efficient. If you're running at peak power for any length of time, the comparative lack of engine weight is a better bet and, by extension, a more efficient use of space, fuel and engineering.
Right now, you can go to a company like MAHLE, and buy a reciprocating range extender, that meets all worldwide emissions, produces sufficient power, and critically is already fully validated and has a supply chain that uses all the existing suppliers and parts the OEs already use. You could turn up at the door and offer them an engine that was twice as good and they'd still tell you to do one.........
I really like rotary engines but I don’t agree with how they are measured.
Due to the nature of the piston movement you can’t eaisly define the same swept piston size like you can with a conventional engine.
The reason the 737b won me mans is mainly due to it being rated at a specific engine capacity forumla that was simply wrong.
To me the rx8 has similar output, fuel economy and other features that would be reasonable for a 2.6 engine of its time. Ilthe whole ‘it Has great output for its cylinder capacity’ just reaffirms that it is being measured poorly. Esp when you consider the losses and the issues with sealing over piston engines.
Now yes the engine is compact which is an advantage. But I would like to see a kw/fuel burn rate and compare with other engines. 60% efficiency is up there with the (frankly stunning) hybrid f1 cars.
Due to the nature of the piston movement you can’t eaisly define the same swept piston size like you can with a conventional engine.
The reason the 737b won me mans is mainly due to it being rated at a specific engine capacity forumla that was simply wrong.
To me the rx8 has similar output, fuel economy and other features that would be reasonable for a 2.6 engine of its time. Ilthe whole ‘it Has great output for its cylinder capacity’ just reaffirms that it is being measured poorly. Esp when you consider the losses and the issues with sealing over piston engines.
Now yes the engine is compact which is an advantage. But I would like to see a kw/fuel burn rate and compare with other engines. 60% efficiency is up there with the (frankly stunning) hybrid f1 cars.
Max_Torque said:
again, irrelevant, all that matters for any new car, and for any range extended hybrid, is getting to a decent BSFC at an achievable cost and risk.
Right now, you can go to a company like MAHLE, and buy a reciprocating range extender, that meets all worldwide emissions, produces sufficient power, and critically is already fully validated and has a supply chain that uses all the existing suppliers and parts the OEs already use. You could turn up at the door and offer them an engine that was twice as good and they'd still tell you to do one.........
Actually if you read the LiquidPiston (which was obviously not done) you can see they are achieved 60% efficiency with their rotary. You will also know as a petrol head that the 787B was the most efficient car at the Le Mans event.Right now, you can go to a company like MAHLE, and buy a reciprocating range extender, that meets all worldwide emissions, produces sufficient power, and critically is already fully validated and has a supply chain that uses all the existing suppliers and parts the OEs already use. You could turn up at the door and offer them an engine that was twice as good and they'd still tell you to do one.........
Toyota have just bought rotary engines as range extenders for their future EVs.
Edited by delta0 on Thursday 30th August 22:08
Gassing Station | General Gassing | Top of Page | What's New | My Stuff