Wave Disk Engine Could Be 3.5 Times More Efficient Than Combustion Engines
nextbigfuture.com
nextbigfuture.com
Either way thanks for improving my understanding of the system.
I do feel like we've seen this movie before. The problem with rotary engines, usually, is that their round shape and operation, though efficient, can make sealing difficult. So they can be plagued by emissions issues when it comes to the wear-and-tear of everyday use.
But it would be sweet if this engine licked all of that.
Unless the weight of the competing engine is 20% of the weight of the car plus payload, reducing the weight of the engine can't get you to 20% less weight.
Also, cost and reliability don't necessarily go up as weight goes down.
http://en.wikipedia.org/wiki/Rotary_combustion_engine
The Wankel engine is by far the most mature of those, and it's a lot more complicated in 3d than in a 2d cross-section. Sealing and such are an issue. Mazda has really done a lot of good things with them, and their power-weight is way better than your average 4-stroke, but it is still a niche product.
I'm not saying the Wave Disk engine isn't going to be great, I'm saying you're not going to see one of these in your car in the next 20 years, and 20 years from now, who knows what the "average car engine" is going to be and how well the wave disk engine will compare to it.
So, I think it is feasible that we'll see some movement away from the 4 stroke otto cycle that is standard today, and some ideas that didnt work out in the past might work out better now.
How efficient are current wave disk engines? Any claim about a future, non-existent engine is just hot air. (In fact, the current wave disk engines probably generate way too much hot air already, or their current efficiency would be featured more prominently in the article.)
A novel cycle and construction may leave more headroom for improvement, even if first implementation aren't particularly efficient.
IIRC turbines are usually highly efficient, but only in a narrow band, near maximum output; at low RPM they literally suck. Perhaps a novel construction could widen the gap considerably.
A "typical" car with a piston engine directly mechanically connected to the wheels needs an engine with a wide rpm and power output range.
A hybrid electric drivetrain doesn't necessarily need that - if a motor that could run at 60% efficiency but only at 8725 +- 15 rpm existed, it'd be useless for a traditional car, but it'd be easy to integrate that into a hybrid electric vehicle...
Basically: This is only appropriate for use in hybrid engines, as the range of efficiency is very narrow.
That said, if it works, this would be terrific for further upping the efficiency of hybrids.
http://blogs.insideline.com/straightline/2010/09/jaguar-c-x7...
This does look like nothing more than a new turbine design, I agree, but frankly a turbine driving a generator and a battery is by far the most energy efficient means of running a vehicle from a combustion fuel source anyway; that's been the case for years, and if this tech helps get us to that point then all the better.
But they're expensive and the efficiency advantage largely disappears as they're scaled down to a size appropriate to power a car.
Probably the fundamental reason we don't see production gas turbine cars is that there are cheaper and less technically risky ways to remove weight from a car, and weight savings often isn't even the cheapest way to improve efficiency.
http://en.wikipedia.org/wiki/DesignLine_Corporation
Sadly, they don't seem to have taken the market by storm even though they claim to double to fuel efficiency of a 40 ft bus. Unless fuel prices go up significantly, factors other than fuel efficiency will probably stand in their way (questions of reliability and supply chain are mentioned).
It seems to me that such an engine could work well for direct propulsion with a good CVT. Perhaps someone more educated on the issue can comment.
Google helped me find it again, the pictures and animations are at the bottom http://quasiturbine.promci.qc.ca/ETheoryQTConcept.htm
>The resulting sudden build-up of pressure in the chamber generates a shock wave
that makes me doubtful about longevity of the engine if the shock wave touches the metal.
A shock contacting the metal isn't a big deal. A typical jetliner will have a standing shock on the upper surface of its wing during cruise flight, visible if the lighting is just right. With this I doubt there will be significant stresses caused by the pressure gradient because the thing is pretty much a compact and flat disk (short moment arms).
Sure. But what about the common reciprocating engine style. There's a lot of mechanical strain with the pistons being yanked back-and-forth 1000s of times/second not to mention the energy lost in counteracting momentum.
60k is 3x the RPM of an F1 motor.
3.5 * .30 = ???
T_high is limited by chemistry and materials to abt 1400 K, T_low depends on a whole pile of stuff, but in practice cannot be lower than 700 K or so for a simple (as opposed to compound) cycle that this engine uses. So the absolute maximum theoretical efficiency, using perfect insulators, frictionless bearings and ideal gases is about 50%.
Modern car turbo-diesel engines get abt 40% efficiency, stationary diesels reach 50% efficiency. Note these are compound cycles.
tldr: 3.5x efficiency improvement claim is bullshit.
An efficient car may run at about 18% on average (hence the 15% after external losses), but quite possibly have a peak efficiency of 30%
Also, they compare to a gasoline Otto cycle engine. The diesel cycle is more efficient than the Otto cycle. A cars turbocharged diesel may run nearly 30% average efficiency, and peak efficiency in the 40s. (The ratio of peak/average eefficiency in diesel engines tends to be closer to unity than in gasoline engines).
There are actual operating now diesel engines operating at over 50% efficiency, but they are not the sort of thing you would put in your car (more the sort of thing where your car would fit inside the engine).
[edit]I wanted to find info on the prius before posting this, but was unable to. I finally did, and the complexity of the drivetrain is to (among other things) maximize the amount of the time that the engine is in it's peak efficiency area of 230g/kWh which is roughly an efficiency of 33%. Since the article specifically talks about running the engine in a hybrid comparison, this is apples-to-apples, and it is less than a 2x improvement, not 3.5x
[edit2]The Prius is not a vanilla Otto cycle, but it's pretty close. I really think of it as more of a Miller cycle than an Atkinson, but in any event it's a 4-stroke spark-ignited reciprocating piston engine.
To all of you voting up articles like this: you suck.