Recent trash-talking about all-electric range by GM’s Bob Lutz highlights a crucial benefit of the Volt’s Extended Range Electric Vehicle (EREV- nee “serial hybrid”) concept. Though an EREV may be less cost-effective than a plug-in parallel hybrid over the long haul (or not), its initial EV-only range is better. Which means EREV marketers can claim “zero fuel use” for many standard commutes. Autocar reports that Mazda has fallen under the EREV spell; they’re hard at work on their own system using a rotary engine as a battery generator. According to “senior sources,” testing is “sufficiently advanced that Mazda has a working prototype in a Mazda 5 MPV bodyshell.” Unlike GM though, Mazda isn’t relying on its EREV to fly it to the moon by late 2010. Start-stop is the first step on Mazda’s voyage of eco-discovery, set to deploy in Japan next year and around the world thereafter. There are currently no plans to bring an EREV to market. Still, using a small rotary engine as an electricity generator has lots of potential upside. It eliminates the engine’s thirstiness by running constantly at lower rpms, and could actually be more efficient at battery-charging than a standard ICE. Hopefully the system won’t be entirely dependent on rotary engines though, as Mazda’s sister company Ford will doubtless be interested in appropriating the technology.
Find Reviews by Make:
Read all comments
I’ve been intrigued lately about the use of small turbine engines as generators in EREV’s; can be very efficient, and run on a variety of fuels (even vodka in a pinch).
Seems a rotary would be pretty much “married” to gasoline; something we’re trying to use less of.
Seems a rotary would be pretty much “married” to gasoline; something we’re trying to use less of.
Fuel is fuel. It’s not free to extract or refine, so where you get it from and what it is doesn’t really matter that much, especially if the net energy used to make it exceeds the energy it produces.
Ethanol is the prime example of this.
The trick is to use energy more efficiently, not to play a shell game with fuels.
I’ve been intrigued lately about the use of small turbine engines as generators in EREV’s; can be very efficient, and run on a variety of fuels (even vodka in a pinch).
A lot of alternative fuels are filthy when they burn, and turbines aren’t necessarily well-suited to pairing with a catalytic converter. That will be tricky. Heck, clean exhaust is a problem for rotary engines, too.
To borrow a phrase from Mr. Farago…
“Uh… No.”
The extra complexity involved with any hybrid engine does combined with the reliablility issues of a rotary do not bode well.
I owned a RX-7, although it was a blast to drive, it had an appitite for fuel and oil. Adding a hybrid to a rotary would be simply a zero-sum equation. Whatever eco-friendliness you got from the hybrid would be counteracted by the gas, oil, and apex seal guzzling rotary.
I thought they fixed the apex seal in the new genesis rotary. Still drinks oil but that could be minimized by keeping it low revving and constant. Plus there isn’t a huge hybrid complexity problem here, its just like hooking an alternator up to the fly wheel. If well engineered this could be a viable approach, the weight savings and compactness have real advantages in an electric car.
I can’t remember what is the compression on the new rotary engines? I wonder if running E100 with a relatively high compression could give good results.
I haven’t paid close attention to the Volt et al., so maybe I’m misinterpreting things. But I have the idea that they’re promoting these as having some dinky little fuel sipper of an engine that just trickles a little electric juice to the battery sometimes. In fact these cars have to have gas engines that, in a fully discharge situation, are fully capable of getting the car up to interstate speeds going up a short up hill on ramp with whatever load is legal. So other than the normal hybrid start-stop, brake regen and short trip electric only goodies, where are the savings? Granted, for some people, like me, who can do a large part of their driving with battery only, it might have advantages. But ALL of these cars will have to have a gas engine capable of the on ramp scenario. Am I missing something?
Still drinks oil but that could be minimized by keeping it low revving and constant.
I think the issue was that, even with the Renesis, the rate of oil burn is bad enough that emissions are still problematic. What a hybrid powertrain allows is, I think, a fighting chance for the rotary to meet tier 2 bin 4 or higher.
But yes, you’re right in all other respects: a hybrid-electric powertrain complements a rotary perfectly. The rotary is very space efficient, but doesn’t make much torque, especially at the low end of it’s rev range; a hybrid motor-generator can help address that, while the extra space it takes is easier to work around given the rotary’s physical size.
A sub-1.0L rotary/parallel hybrid would probably fit in vehicles that couldn’t otherwise accomodate the traditional piston engine + hybrid motot/generator. The RX-8 makes ~230hp from a 1.3L two-rotor the size of a football; the ~120hp figure of the Prius could be achieved with something even smaller.
I don’t get it. The rotary is a gas guzzler. There are several reasons why. The biggest is high surface to volume ratio of the combustion chamber. It loses heat, reducing efficiency. There’s no way to avoid that. What’s the point of a hybrid if the gasoline part is a guzzler? (anyone who wants a copy of my article on why the rotary’s guzzling can’t be mitigated email me at motorlegends@aol.com.)
“The extra complexity involved with any hybrid engine does combined with the reliablility issues of a rotary do not bode well.”
I think you’re confusing a Wankel engine with something else regarding reliability. They are extremely reliable and they fail-safe (ie do not seize) which is why so many light aircraft use them.
Furthermore they do use oil but like a two-stroke this is by design and should be considered part of the consumables.
psarhjinian :
Let’s see – Gas turbine: Continuous combustion with no vibration, the ability to run on a variety of fuel sources, no worrisome seals (and lubrication-related emissions), compact size/power ratio, efficient when run in a relatively narrow RPM/load range (which a generator would supply).
Rotary: All the problems mentioned above.
I would still work with the turbine myself.
The rotary is a perfect hydrogen engine. Yes it does run well on hydrogen. So it doesn’t surprise me. It also runs on many other fuels and can run a long time at steady state, with few emission related issues. It starts to lose efficiency with varying loads. Imagine on on 85% ethanol.
Many here have no experience with Rotaries to be speaking.
Oh wait. It’s the INTERNET…
“Oh wait. It’s the INTERNET…”
Bill Kurtis? ;-)
Blunozer:
the RX8’s RENESIS engine fixed the issues of the RX7’s DEI and REW Variants – the focus of that development was better fuel economy and exhaust emissions. Apex seals are also no longer an issue.
The “RENESIS2” that Debuted with Mazda’s Taiki car moves even further in this direction but adds direct injection, further increasing fuel economy.