Why not use turbine engines in cars?

[dvsk000]

Thank you for reading.

Turbine engines have been used earlier by Chrysler. If throttle response is a reason they aren't prevalent there are many ways to reduce it. If I am not wrong, the compressor can have variable geometry vanes(similar to VGTs) and thereby reduce lag.

I learned that it is less fuel efficient..but it also said that any fuel can be used to combust the mixture and pass it on to the turbine. (not just petrol or diesel) There could be another a less expensive option to counter this inefficiency.

Apart from this, can there be other reasons as well?

 

[Kozy]

Turbines are not suited to use in cars by using the shaft torque for a number of reasons, throttle response is one but another major one is the speeds at which they turn are not suited to gearing down to the wide range of road speeds a car sees.

Using the turbine to generate electricity for use in motors does work and can be very fuel efficient.

 

[dvsk000]

Turbines are not suited to use in cars by using the shaft torque for a number of reasons, throttle response is one but another major one is the speeds at which they turn are not suited to gearing down to the wide range of road speeds a car sees.

Using the turbine to generate electricity for use in motors does work and can be very fuel efficient.

Thanks Mr. Kozy,

I just went through wiki in search of operating range.
http://en.wikipedia.org/wiki/Gas_turbine

Its been quoted that the operating range of jet engines is around 10,000 rpm and micro gas turbines is around 500,000 rpm. I can understand that it is a bit high to gear down but the rev limit of Formula 1 cars 18,000 rpm and it has 7 gears.

I also read that smaller the turbine larger the revs are to keep the pressure up. So yeah, it sounds like it won't suit the purpose and IC engines will turn out to be better. :)

 

[Aero_UoP]

Besides, if you drive in front of a bike let's say, the poor biker will probably turn to roast beef :p

 

[dvsk000]

Besides, if you drive in front of a bike let's say, the poor biker will probably turn to roast beef :p

Yeah but it is possible to make it street legal with the right design I believe :)

http://en.wikipedia.org/wiki/MTT_Turbine_Superbike

 

[Aero_UoP]

Interesting!

Funny too. I thought we were talking about reaction engines and not shaft engines :p lol

 

[siddharth23]

A very high reduction would be required. But like cozy said, usind turbines to produce electricity which inturn will run the car sounds interesting..

 

[rcgldr]

I learn that it is less fuel efficient ...

Turbines are especially fuel inefficient at low throttle (low rpm) settings.

 

[geoff033]

Its been quoted that the operating range of jet engines is around 10,000 rpm and micro gas turbines is around 500,000 rpm. I can understand that it is a bit high to gear down but the rev limit of Formula 1 cars 18,000 rpm and it has 7 gears.

F1 cars have no torque at low revs, as do most racecars. Try driving a RB9 to the shops or worse...in a traffic jam.

 

[HowlerMonkey]

Turbines are especially fuel inefficient at low throttle (low rpm) settings.

RCgldr has hit the nail on the head.

 

[geoff033]

Discovery channel had a show on concept cars tonight and the Chrysler was featured. They claimed drivers were uncomfortable that the 'Bronze Blowtorch' didn't decelerate when the throttle was closed.

 

[Meizirkki]

I think the main reason is the high cost of efficient microturbines. The most exciting project lately in this area, the Jaguar C-X75 hybrid car was canceled "due to the ongoing global economic crisis" (Wikipedia).

I'm wondering whether low-cost solutions such as bladeless turbines are being developed further to fix the issue. Hybrid solutions with gas turbines seems to me like the next step towards cleaner driving.

 

[xxChrisxx]

I think the main reason is the high cost of efficient microturbines. The most exciting project lately in this area, the Jaguar C-X75 hybrid car was canceled "due to the ongoing global economic crisis" (Wikipedia).

I'm wondering whether low-cost solutions such as bladeless turbines are being developed further to fix the issue. Hybrid solutions with gas turbines seems to me like the next step towards cleaner driving.

Turbine was binned long, long ago. Last incarnation of the C-X75 was a twincharged 4 pot.
We can only speculate as to the real reason it was canned.

 

[psycho rich]

Turbines are much lighter and therefore would not require a heavy chassis. Weight reduction is one main key to fuel efficiency. The Chrysler was a stock car (fairly heavy) and didn't take advantage of the turbines low weight.
A turbine can run on biodiesel. Hemp can be grown on marginal land not displacing other crops. It's oil and other by products are in demand. With falling oil prices I don't think my dream will come true.

 

[psycho rich]

Two stroke engines are 30% lighter than 4 strokes. A 2 stroke out fitted car might actualize a 50% weight reduction. Chrysler was working on a four valve design that used a compressor to help evacuate the exhaust cycle, therefore reducing emissions. Unfortunately the oil company's set fuel economy standards in this country and only rising fuel costs will lead to more efficient vehicles. I for see a day in the not too distant future when we (our children) look back and consider this a very dark age.

 

[JonathanGl]

Thank you for reading.

Turbine engines have been used earlier by Chrysler. If throttle response is a reason they aren't prevalent there are many ways to reduce it. If I am not wrong, the compressor can have variable geometry vanes(similar to VGTs) and thereby reduce lag.

I learned that it is less fuel efficient..but it also said that any fuel can be used to combust the mixture and pass it on to the turbine. (not just petrol or diesel) There could be another a less expensive option to counter this inefficiency.

Apart from this, can there be other reasons as well?

A vane pump compressing air for a turbine , if done properly will most likely be more efficient than a piston engine. The turbine would not need to be of an axial type but tangential and if the pressure from the compressor was powered by an electric motor it could be stored and the turbine could start and be running at it's nominal constant velocity in only a few seconds. this would then be able to drive a generator without the need for large batteries and could run on any fuel including gases.

 

[Meizirkki]

I'm curious about Tesla's (the inventor, not the car company) idea for a car engine. In his patent "Valvular Conduit", he describes a bladeless turbine powered by a small combustion chamber directly above it (Fig 4). The fuel gas and air would enter the chamber through special conduits that allow flow in one direction, but stop the exhaust gases from going back. Instead the exhaust gases are guided between the disks of the turbine through a de laval nozzle. Cyclic combustion in a small chamber allows for higher pressures and temperatures. There's also no need for forced ventilation.

I've been pondering for a while whether I should build one. Blades could easily be made out of tungsten sheet, which would make it sustain crazy temperatures (which would yield higher efficiency). Materials for a small prototype would likely cost no more than few thousand €.

 

[cjl]

Turbine engines aren't used for a number of reasons.

1) Their idle and low-load fuel efficiency is appalling. Most car engines spend the majority of their lives far from peak power output, so turbines' high efficiency at high load wouldn't really help them here.
2) Throttle response. Sure, this could be improved with all kinds of variable geometry stuff, but we already have something with perfectly good throttle response.
3) Cost. Turbines rely on high temperature and tight clearances to get efficiency and high power output. Components that can maintain tight clearances at high temperature are expensive.
4) They really don't have any major benefits. Why fix what isn't broken?

 

[Meizirkki]

Turbine engines aren't used for a number of reasons.

1) Their idle and low-load fuel efficiency is appalling. Most car engines spend the majority of their lives far from peak power output, so turbines' high efficiency at high load wouldn't really help them here.
2) Throttle response. Sure, this could be improved with all kinds of variable geometry stuff, but we already have something with perfectly good throttle response.
3) Cost. Turbines rely on high temperature and tight clearances to get efficiency and high power output. Components that can maintain tight clearances at high temperature are expensive.
4) They really don't have any major benefits. Why fix what isn't broken?

When turbines were first put into cars, these were very probably the very reasons why the technology never took off. It's 2015 now, and hybrid cars are all over the streets. As discussed in the thread, 1 and 2 are no longer actual problems since the drivetrain can be electric. Materials for gas turbine are expensive, but you need less of them. Turbines only have "one moving part" so things that wear out and need to be exchanged are few.

Two major benefits are lower weight and simplicity, turbines aren't so picky about the fuel either so that's third.

 

[cjl]

When turbines were first put into cars, these were very probably the very reasons why the technology never took off. It's 2015 now, and hybrid cars are all over the streets. As discussed in the thread, 1 and 2 are no longer actual problems since the drivetrain can be electric. Materials for gas turbine are expensive, but you need less of them. Turbines only have "one moving part" so things that wear out and need to be exchanged are few.

Two major benefits are lower weight and simplicity, turbines aren't so picky about the fuel either so that's third.

You're right that point 2 could be solved with an appropriate hybrid, but 1 is still a problem, since cars need much higher peak (and even sustained) power outputs available than they use most of the time. Turbines are really good in applications like power plants, where they can be run at peak efficiency all the time, or like aircraft, where they'll pretty much always be used at a fixed throttle setting for 80+% of the journey. In cars though, the average power output in city driving is going to be tiny, but for something like highway or mountain driving, you need to be able to sustain a much higher power level. As a result, you need a turbine large enough to allow for that high power output when necessary, but that means that in slower driving (a huge proportion of the time), you'll be at low load, and the efficiency will suck. You could run the turbine only part of the time, but then you're heat cycling the parts a lot, which isn't great for longevity.

Realistically, if you want a super high efficiency hybrid, you don't want to look at a turbine anyways. Turbodiesels get you similar (or even better, in some cases) efficiency, while not having the issues with tolerances, costs, exotic materials, or terrible part-load efficiency.

As for your point about reliability, modern piston engines are spectacularly reliable as well, so that's not really an issue for modern vehicles. Nearly any modern piston engine will go 150k miles or more with minimal maintenance, and engines built for reliability (e.g. diesel engines for trucks) go a million miles or more. Turbines have their own set of reliability issues too, since they tend to run several of the metal components at extremely high temperatures, necessitating fairly elaborate cooling systems and exotic alloys. True, they only have one moving part, but that does not make them simple.

 

[Meizirkki]

Turbines are really good in applications like power plants, where they can be run at peak efficiency all the time, or like aircraft, where they'll pretty much always be used at a fixed throttle setting for 80+% of the journey. In cars though, ... in slower driving (a huge proportion of the time), you'll be at low load, and the efficiency will suck.

Turbines in power plants and aircrafts are designed for those specific applications. Ergo, to reach their peak efficiency over a narrow set of conditions. The efficiency of a Formula One engine would suck too, if you were going around 20mph.

Turbines might very well be able to compete with piston engines in cars, if someone made the effort to design one that suits the purpose. Modern piston engines, especially turbocharged ones, are not free of the issues you attributed to turbines. Reaching high efficiency means higher temperatures regardless of the engine type.

 

[Nidum]

A viable gas turbine for a car would not be a simple single shaft design . Two shaft gas generator and a power turbine stage would be needed to give good efficiency over most of the power range and a give a relatively low output shaft speed to avoid drive train problems . It would be an expensive option right now but rapid developments in gas turbine manufacturing technology are likely to bring cost down a lot in next few years .

 

[cjl]

Turbines in power plants and aircrafts are designed for those specific applications. Ergo, to reach their peak efficiency over a narrow set of conditions. The efficiency of a Formula One engine would suck too, if you were going around 20mph.

Turbines might very well be able to compete with piston engines in cars, if someone made the effort to design one that suits the purpose. Modern piston engines, especially turbocharged ones, are not free of the issues you attributed to turbines. Reaching high efficiency means higher temperatures regardless of the engine type.

Turbines are used in power plants and aircraft because they are well-suited to those applications. Low efficiency at part throttle isn't something that you can easily design around though, since it is related to the continuous burn of a turbine (rather than discrete explosions in a piston engine) and the fact that a turbine engine's pressure ratio varies with RPM. In addition, turbine efficiency is strongly related to turbine tip clearances, and those get worse (proportionally) as an engine is scaled down. Large engines have significant inherent efficiency advantages that cars could not take advantage of.

As for the temperatures, you're correct that high efficiency implies a high peak temperature. In the case of a piston engine, however, the high peak temperature is hit once per two revolutions in each cylinder, and then the cylinder has an opportunity to cool down between power strokes. This means that the peak temperature can be near the melting point of the materials used to make the engine and it will still survive. In addition, no component is completely surrounded by peak temperature flow in a piston engine, which allows for simple, easy cooling. The piston can be cooled from below via oil, and the block is cooled around each piston bore with the coolant. Turbochargers do somewhat negate this point, since a turbocharger turbine is exposed to fairly high levels of continuous heat, but the temperature of the exhaust flowing into a turbocharger is still far below the temperature of the combustion itself, since the gas has been expanded by a factor of 8 or 10 to 1 and then has flowed through a significant amount of piping before reaching the turbo.

In a turbine engine however, the first stage turbine blades are surrounded continuously by peak temperature flow immediately post-combustor, and as a result, either efficiency must be sacrificed to make the flow cool enough to not melt or overheat the turbine, or a complicated cooling system must be utilized such as the internal passages used in most modern jet aircraft engines that must be constantly supplied with high pressure air.

A viable gas turbine for a car would not be a simple single shaft design . Two shaft gas generator and a power turbine stage would be needed to give good efficiency over most of the power range and a give a relatively low output shaft speed to avoid drive train problems . It would be an expensive option right now but rapid developments in gas turbine manufacturing technology are likely to bring cost down a lot in next few years .

Out of curiosity, what makes you think that there are likely to be rapid developments in gas turbine manufacturing that will bring down the cost in the next few years? Gas turbines are well understood, and have been manufactured en masse for well over half a century now. If anything, the trend recently has been towards higher initial cost to improve efficiency, not towards low-cost turbines, and I'd be very curious to know why you think that will change.

That having been said, I absolutely agree with you that a multi-shaft design would be much better for a car. Single shaft, while a nice concept, introduces a lot of difficulties that could be nicely sidestepped through an intelligent multi-shaft design.

 

[Nidum]

It is already happening . The arrival of additive manufacturing and in particular precision 3D laser metal deposition has changed everything . Experimental high performance engines are now being developed costing 10% of what they would have done with traditional manufacture . It is now possible to make complex components out of previously very difficult to work metals quickly , cheaply and reliably . RR is testing some large components made this way in actual engines . GE have made a complete small demonstrator engine which worked to specification first try .



http://www.theengineer.co.uk/news/news-analysis/rolls-royce-breaks-additive-record-with-printed-trent-xwb-bearing/1020596.article

Additive manufacture can also be used to make components out of some types of ceramic materials and that could lead to a whole new generation of low cost high temperature engine designs .

 

[Meizirkki]

Low efficiency at part throttle isn't something that you can easily design around though, since it is related to the continuous burn of a turbine

In a conventional gas turbine, yes. How about an external combustion turbine? One with discrete explosions? Have a look at the patent I linked few posts back. Designs for external, cyclic combustion gas turbines existed a hundred years ago. Sure they fell into oblivion, but that doesn't necessarily mean they suck. External combustion turbines fell into oblivion, but not necessarily because they sucked. I think, with todays material technology and simulation software such designs can be made to achieve outstanding efficiency as well as reliability.

Think about it, cyclic combustion in a small external chamber, exhaust gases fed into a centripetal flow turbine. Make the small parts, chamber and the nozzle out of extreme materials, and you can safely achieve combustion temperatures far beyond those practical for conventional turbine designs or piston engines. With high combustion temperature we have a strong basis for efficient operation. We can expect to achieve this high efficiency during most of driving situations, since centripetal flow turbine's efficiency is at it's best at low and medium power output.

 

[cjl]

It is already happening . The arrival of additive manufacturing and in particular precision 3D laser metal deposition has changed everything . Experimental high performance engines are now being developed costing 10% of what they would have done with traditional manufacture . It is now possible to make complex components out of previously very difficult to work metals quickly , cheaply and reliably . RR is testing some large components made this way in actual engines . GE have made a complete small demonstrator engine which worked to specification first try .



http://www.theengineer.co.uk/news/news-analysis/rolls-royce-breaks-additive-record-with-printed-trent-xwb-bearing/1020596.article

Additive manufacture can also be used to make components out of some types of ceramic materials and that could lead to a whole new generation of low cost high temperature engine designs .

Additive manufacturing does not magically enable extremely close tolerances and exotic materials to be used cheaply. It does have some very interesting possibilities, but the cost of jet engines isn't about to plummet any time soon. I am very excited about the new range of turbine inlet temperatures enabled by ceramics, but I don't expect high efficiency gas turbines to get into the sub-6 figure range of pricing anytime soon.

In fact, just look at that article - to make one component, they're talking about 120+ hours of manufacturing time, and 10 hours of cooling time in a vacuum, using a 3d printer that only has a lifetime of 600-800 hours, so it must be replaced every 5 parts or so. After that's done, the surface finish is rough enough that it still must be machined to the final shape to finish it off. That's not mass-production friendly at a cost that automotive manufacturing could bear. In the aerospace industry, where weight and efficiency are all that matter, almost regardless of cost, additive manufacturing enables a lot of interesting new things. However, this isn't going to revolutionize the auto industry with turbine-powered cars anytime soon.

 

[cjl]

In a conventional gas turbine, yes. How about an external combustion turbine? One with discrete explosions? Have a look at the patent I linked few posts back. Designs for external, cyclic combustion gas turbines existed a hundred years ago. Sure they fell into oblivion, but that doesn't necessarily mean they suck. External combustion turbines fell into oblivion, but not necessarily because they sucked. I think, with todays material technology and simulation software such designs can be made to achieve outstanding efficiency as well as reliability.

Think about it, cyclic combustion in a small external chamber, exhaust gases fed into a centripetal flow turbine. Make the small parts, chamber and the nozzle out of extreme materials, and you can safely achieve combustion temperatures far beyond those practical for conventional turbine designs or piston engines. With high combustion temperature we have a strong basis for efficient operation. We can expect to achieve this high efficiency during most of driving situations, since centripetal flow turbine's efficiency is at it's best at low and medium power output.

It's an interesting concept, but I'd be worried about much higher pressure losses in the flow than you get in a traditional turbine, and you still need some way of feeding the combustion chamber with high pressure air (so you have to have some kind of compressor). I'd be interested to see an implementation, but there are probably good reasons they haven't been explored much for any practical application. In general, when peak efficiency is desired (including at partial load), turbodiesels are preferred, not turbines, and this is for a very good reason.

 

[Meizirkki]

It's an interesting concept, but I'd be worried about much higher pressure losses in the flow than you get in a traditional turbine, and you still need some way of feeding the combustion chamber with high pressure air (so you have to have some kind of compressor).

Instead of compressing the input air, an equivalent of a "suction stroke" can be created by maintaining vacuum at the exhaust. For the most efficient operation of a centripetal flow turbine, you'll want this anyway, as the input fluid should never enter the turbine at higher pressure than that within the turbine. In his later designs, Tesla employed an axial turbine for creation of this vacuum, connected to the same shaft with his turbine (GB patent 174,544).

I'd be interested to see an implementation, but there are probably good reasons they haven't been explored much for any practical application.

We can only speculate as to what these reasons are. There is nothing wrong with it in principle, so I too, am interested in seeing an implementation, and very curious to see what unexplored possibilities may lie in it.

 

[cjl]

Instead of compressing the input air, an equivalent of a "suction stroke" can be created by maintaining vacuum at the exhaust. For the most efficient operation of a centripetal flow turbine, you'll want this anyway, as the input fluid should never enter the turbine at higher pressure than that within the turbine. In his later designs, Tesla employed an axial turbine for creation of this vacuum, connected to the same shaft with his turbine (GB patent 174,544).

You're sacrificing a lot of efficiency if you do that though, since compression ratio is highly correlated to efficiency for combustion engines.

 

[Nidum]

http://www.imeche.org/news/engineering/british-firm-wins-funding-for-micro-gas-turbine-car-engines
http://fortune.com/2015/03/05/ge-engine-3d-printing/
http://www.geglobalresearch.com/innovation/3d-printing-creates-new-parts-aircraft-engines

http://www.ttengines.com/DCGT.html

 

[Meizirkki]

You're sacrificing a lot of efficiency if you do that though, since compression ratio is highly correlated to efficiency for combustion engines.

A good point.

Also, my last contained BS. Sorry. Tesla did use axial turbine in combination with his turbine, but not in the way I described. In the referenced patent he describes an engine where the two are used in combination for achieving high efficiency. His turbine is "the first stage" subject to high temperatures and violently expanding gases and an axial turbine is a "second stage" extracting energy from the remaining high pressure.

 

[cjl]

His turbine is "the first stage" subject to high temperatures and violently expanding gases and an axial turbine is a "second stage" extracting energy from the remaining high pressure.

That makes sense. Two stage turbines with different rotational speeds and other design parameters between the stages are quite common, since you can improve efficiency with a lower pressure ratio across each stage.

 

[Nidum]

(1) A gas turbine powered car would really have to be designed specially to make best use of engine characteristics . Coupling a gas turbine to a conventional piston engine clutch , gearbox , drive shaft and differential to get power to the wheels is definitely not best way to do things .

Many studies have been done regarding drive systems . Modified conventional , hydrostatic , hydrodynamic and electric drives have had most attention .

For most purposes electric drive seems to be best all round and with part hydrodynamic + part conventional a good runner up .

Electric drive is relatively easy to implement .

Electric drive also fits in well with hybrid technology vehicle designs .

(2) One of the arguments against use of gas turbines has always been that they could not be maintained and repaired in old style vehicle repair shops . I don't think this has ever been a real problem . Some repair shops would install new facilities and train staff . Otherwise the actual gas turbines could be dealt with as change out components and any defective ones returned to manufacturer in exchange for a refurbished one .

Bit of nostalgia : Morris cars had a change out scheme many years ago for their tiny Morris 1000 piston engines (and gear boxes) . These were simple enough to repair but there was the option to send back to manufacturer and get a refurbished one back . Replacement came with a little embossed Gold Seal on it and a signed test certificate .

 

[mheslep]

When nothing matters (cost, efficiency) besides power density, turbines are sometimes the way to go. Honeywell AGT1500, 1500 HP, 2750 lb-ft torque.

 

[mheslep]

https://www.physicsforums.com/threads/why-are-gas-turbine-engines-not-used-in-automobiles.712881/

https://en.wikipedia.org/wiki/Jaguar_C-X75