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nikhilrreddy

cars powered by air turbines

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i need more info on about the above title so please help me with info

 

please provide info about the feasibility

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It is certainly feasible but not very practical. I am sure somebody, somewhere has probably built one just to show it can be done but unless you have a very large tank or one that can be pressurized to many thousands of psi your range until refilling the tank would pretty limited.

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There was an article in popular science a while back that talked about using an air compressor type device to decelerate a car, and the use that stored energy to re-accelerate after a stop.

 

They mentioned a 30,000 psi tank, wrapped in carbon fiber, as the energy storage medium. The negative that they listed was that it sounded like an air wrench.

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I am not sure that this is what you meant but it is certainly related to all of the keywords: wind powered cars than go straight against the wind:

 

Links (mostly in dutch, I couldn't find anything completely in English - but it's with pictures and videos!)

 

http://www.ecn.nl/wind/extra/aeolus/

 

http://www.energieportal.nl/Nieuws/Windenergie/-ECN-in-de-prijzen-op-Racing-Aeolus-3771.html

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I am not sure that this is what you meant but it is certainly related to all of the keywords: wind powered cars than go straight against the wind:

 

Links (mostly in dutch, I couldn't find anything completely in English - but it's with pictures and videos!)

 

http://www.ecn.nl/wind/extra/aeolus/

 

http://www.energieportal.nl/Nieuws/Windenergie/-ECN-in-de-prijzen-op-Racing-Aeolus-3771.html

 

Interesting, airboats for land use. I am so stuck in the engineering paradigm of using turbines to generate the power I never even considered one of those cars.:doh:

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He may be interested in a car powered by a gas turbine....

 

Notably, Chrysler researched the idea, their concept even made it past the prototype stage, with limited test productions.

 

The idea was solid; A turbine engine that could run on almost any combustible liquid, with 1/3rd the moving parts of a standard gasoline-piston engine - a simplified jet-engine.

 

Here's a good site:

 

http://www.allpar.com/mopar/turbine.html

 

Ultimately, this concept went down the lanes of the more famous GM electric car (EV1).

 

It's quite possible that the auto/oil-industry top-wigs of the day saw this concept as a possible threat; Why build something that costs less to maintain, with fuel less easily controlled? some say, oil and auto industries at that time shared the same bed.

 

Anyway, the idea was snuffed out by a paper-work technicality.

 

True? You decide. In my mind, it is a solid concept, worth having a second look at....

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The problem challenge with most, if not all, turbines is the startup. As described in the article (which is interesting), the cars all had an "acceleration lag", because the compressor needs to build up speed (and pressure) before you can actually accelerate. In the newest versions of GM, this was 1 second.

 

I also question the fuel efficiency, although I have no reason for that other than that US manufactured cars of the 60ies, 70ies and 80ies aren't famous for fuel efficiency.

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The problem challenge with most, if not all, turbines is the startup. As described in the article (which is interesting), the cars all had an "acceleration lag", because the compressor needs to build up speed (and pressure) before you can actually accelerate. In the newest versions of GM, this was 1 second.

 

I also question the fuel efficiency, although I have no reason for that other than that US manufactured cars of the 60ies, 70ies and 80ies aren't famous for fuel efficiency.

 

I agree with you, there are some hurdles. However they are workable problems - its what we (as engineers) do best.

 

Lets brainstorm a little (throwing todays technology into the equations):

 

Acceleration lag: One possible way to overcome this would be via a hybrid electric design; Have the turbine kick in only after a set compressor ratio is reached. Or, just have the thing running purely on DC, using the turbine as your DC generator eliminating the need for a mechanical transmission (similar to an aircraft APU).

 

Fuel efficiency Lets look at some numbers: 22mpg [9.35 Km/L] tested on the fith generation turbine engine referenced in that article is roughly

 

10.7 L per 100 km.

 

Lets compare:

 

7.1 liters/100km (city/highway combined) - my 2007 1.8L civic [link]

15.7 liters/100km(city/highway combined) - 2007 Hummer H3 [link]

 

That's roughly:

-50% efficiency compared to the little civic.

+68% efficiency compared to an H3.

 

Not bad for an engine built in the 80's, that could run on a wide range of different fuels.

 

Think what you could do with that number when you add todays lighter/more temperature resistant alloys. Computer controlled fuel injectors, composite fans (see the technology pumped into the GE-90 turbines [link])

 

It all boils down to R&D, the talent in said department, and its allocated capital.

Edited by spirytus

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The acceleration lag can also be solved by adding a small flywheel to the vehicle. You'd only have the lag once, at the initial ignition moment. But many cars need a couple of seconds to come to life.

 

Indeed, I totally agree that there are solutions...

 

I'm curious if the turbines would be able to run on sustainable (and nasty) fuels such as pyrolysis oil which, if I'm allowed to exaggerate (a lot), contains all the chemicals that you can find in the organic chemistry section of the Handbook of Chem.&Phys.

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I'm curious if the turbines would be able to run on sustainable (and nasty) fuels such as pyrolysis oil which, if I'm allowed to exaggerate (a lot), contains all the chemicals that you can find in the organic chemistry section of the Handbook of Chem.&Phys.

 

Apparently you could:

 

Orenda Aerospace Corporation of Canada (http://www.orenda.com) has built more than 5,000 gas turbines. Over recent years it has developed equipment to use pyrolysis oil in specially modified gas turbines, with the oil first being conditioned in a treatment module.

[link - news article] + [link vendor website]

 

So sure, its a possibility....

 

However, from what little I've read about it in the past hour, I wouldn't consider it a good alternative to petrol. Doubt it would pass emission standards, than again I'm not a chemical engineer - so who knows?

 

This actually brings us to another issue. Emissions...

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Reaching emission standards are just a matter of:

1. Good combustion

2. Cleaning up the mess after you're done with step 1.

 

And with pyrolysis oil, I also think that the combustion will generate quite a lot of particulate matter (aerosols, soot and such). The presence of water will mean that the combustion temperature is lower. This in turn can possibly mean that the combustion forms more soot. The soot can be cleaned with the same technology that is applied to modern diesel cars (a filter).

 

A nice advantage however is the fact that plants (and therefore pyrolysis oil) contain very little sulfur.

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Soot happens due to insufficient oxygen. Nitrous Oxides happen due to high combustion temperatures. Water injection metered properly should not cause soot, in fact it's a well known "fix" for cleaning out a carboned up engine. It can however reduce NOx. It's possible that a well tuned engine with water injection could meet tailpipe emissions standards without a catalytic convertor, and due to the change in thermodynamic properties occasioned by putting something other than gasoline and air into a motor, can enhance efficiency. However, catalytic convertors are mandatory, so no auto manufacturer is going to do it. There are rumbles that due to enhanced technological opportunities, and the quest for efficiency, that the auto manufacturers are fighting against mandatory equipment such as catalytic convertors, because there are ways to get the same result more efficiently without them. Consider that a motor has to allow enough unburned HC through to keep the cat hot and provide regeneration for the NOx catalytic component, and also has to put out enough NOx to regenerate the HC catalyst.

 

Pyrolysis oil should be usable cleanly in motors that allow enough time for it's full combustion. Faster higher revving diesel motors would probably not be a good candidate, but slower, longer stroke, constant load motors would. In industrial turbine plants, steam injection along with the pyrolysis oil would probably enhance combustion efficiency, due to steam cracking the heavier chains during the combustion process.

 

 

Anyway, back to the topic, I know there is some significant work being done right now on a similar system with a hydraulic accumulator and hydraulic motors. The hydraulic motors provide all the drive, the internal combustion motor is only run at peak efficiency. The hydraulic system is supposedly far less lossy than any electrical hybrid system. Equivalent I'm told to the normal losses in an automatic transmission and not requiring a conventional transmission, because the motors provide adequate torque across a very large speed range. Even before regeneration this means that this system should be nearly twice as fuel efficient as a conventional motor of the same displacement in a vehicle. That is qualified as such because vehicles do not use IC motors efficiently, the maximum efficiency of an IC motor comes only at full load at the top of the torque peak. Since most cars are specced with a motor that has 4 to 8 times the power needed to maintain highway speed, they barely ever see peak efficiency, because they are running very lightly loaded with the throttle nearly closed. This means that overall efficiency in use is only 15 to 20 percent. Since the vehicle is driven from pressure stored in the accumulator, the power of the IC motor is irrelevant to acceleration performance, so a much smaller motor than generally specified for a certain size of car can be used. There's probably a sweet spot, between running the motor all the time and it just keeping up, and oversizing it such that it cools off too much between cycles. Add into that the regeneration potential, where 80% of the energy stored in momentum is recaptured in the accumulator, and you get a vehicle that is approaching 4x the efficiency in use of similar sized vehicle. 100mpg is in sight for a family sized car with a system like that. The engineer that's working on this also has a somewhat novel form of IC engine that can be used with this system, that has greater efficiency than a conventional 4 stroke carnot cycle motor. If he gets it all together in an "all out" efficiency vehicle similar in concept to a Honda Insight, then 200mpg may be on the cards.

 

By the way, going back to the idea that motors are 4 to 8 times too big, you will perhaps realise that a way of trimming them down to size is to reduce the volume of the combustion chamber, or the volume of chamber available for combustion. This is one of the benefits of water or steam injection. The volume taken by the steam reduces the pumping loss, effectively meaning that the motor is higher on the load curve, which is a more efficient range. There are of course limits on how much you can put in and still get the fuel/air mixture to go bang of course.

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What about the concept behind a rail gun, could you power a turbine instantly using that technology to some extent, say the turbine was built into some rechargeable electric engine, could driving it add to the turbines ability to do work at all? It just seems to me you could get the turbine to be a bit more responsive maybe, do you have to make just it solely responsible for powering a car, what about if it just shared the burden along with the engine.

 

I have often thought if you could make some car that really is some overall porous composite if you could do that, or what that would offer, but I think it would still be open to some form of hydrogen embrittlement unless you had some super paint. I just think another avenue to look at is lightweight but strong materials replacing heavy ones.

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Soot happens due to insufficient oxygen. Nitrous Oxides happen due to high combustion temperatures.

 

Hmm. I thought that the soot particles simply wouldn't burn unless the temperature is high enough because they have a close to zero vapor pressure and are also not decomposing, and that this problem also occurs when sufficient oxygen is present. Pyrolysis oil burns at a much lower temperature due to the presence of lots of water. (Pyrolysis oil is really wet, with up to 40% water). Your explanation sounds pretty good, and I assume you're more an expert on the matter than me :)

 

Thanks also for the additional explanation of the combustion (on the combustion time or residence time and presence of water). Sorry for not talking too much about the turbines in this post.

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Soot burns at a temperature of about 1100*C, peak flame temperature of gasoline and diesel is in the 1800-2000*C range, but Nitrogen oxides start forming around 1600*C. Soot could form if the temperature is damped enough, but is more usually the result of incomplete combustion due to insufficient oxygen.

 

So if you can keep peak flame temperatures in the 1500*C range, you can burn the soot and avoid the NOx. I think that at high temperatures, the nitrogen will grab up the oxygen faster than any stray carbon can. It might be something to do with the flame front speed of carbon. Though it's fast enough that large, low RPM industrial diesels can be made to run on coal dust.

 

Getting water/steam involved gets complicated, various cracking reactions can occur at temperatures of 850*C on any unburned hydrocarbons, free carbon can be converted to "water gas" http://en.wikipedia.org/wiki/Water_gas ... However everything is very short lived and will re-react in milliseconds.

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I am not sure that a pyrolysis oil flame can reach even 1100 deg C. It should be able to, I hope :D It really depends on the amount of water in the fuel. But you can probably imagine that if you have 40% water, and that all has to be heated, evaporated and heated even more... without it adding any heat (water obviously will not burn). It reduces the combustion temperature a lot.

 

I have no time to really dig into it, unfortunately, because the topic is interesting. It would really be cool if you can have a car running on liquid wood :D Pyrolysis is simple, and the feedstock is very abundant.

I had a quick look around on google and in literature that I have available close to me, but I couldn't find anything specific about combustion temperature of pyrolysis oil.

 

Those turbines seem the right type of equipment though. It seems to me to be more robust than a normal combustion engine.

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My favorite prospect for "liquid wood" gasoline replacement is a blend of methanol and turpentines. Though you can probably further process pyrolysis oil into lighter fractions by cracking it. Sometime I'm going to look into making a wood fueled gas convertor that works as a turpene and methanol distiller at the same time. So what happens is, you can start the car at the same time as you fire the converter on stored liquid fuel, drive 15 mins, then switch to converter gas output, drive on convertor gas output, and meanwhile it's distilling off methanol and turpenes for the next start. It would be nice if you could implement electronic control and fuel handling such that it's pretty much transparent in use. You can theoretically get this working on any organic materials, grass clippings, rags, old tires, etc.

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What process are you thinking of?

Do you want to place wood pellets into a heating to distill the methanol and turpentines straight out of the wood? I know that these components are present (well, methanol isn't too abundant in wood, but if you distill at high enough temperature, it will form from wood).

 

But if you plan on doing a pyrolysis step, then I fear that the selectivity towards methanol and the turpentines (a mixture) is rather poor. I'm curious to hear your opinion about it.

 

Btw, processing pyrolysis oil further by cracking is is called gasification :D (It's the next step. Pyrolysis is from 400-600 deg C, gasifiers can run at 750 and up). One of the challenges with pyrolysis oil is its high reactivity (and low stability).

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I don't really have a good plan yet, it's likely that it will be a dual or multiple stream process with more than one reaction vessel. Might even need some funky engineering like a centrifugal vortex gas separator to get H2 rich gas out of the output stream to use in a thermal depolymerisation reaction to break up tars, which might also be able to provide a methane rich stream for conversion to methanol.

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Yes, it is likely you will need a gas separation, because almost all gasifiers and pyrolysis equipment that I've heard of will produce some kind of solids (char). In addition, sand or other solids can be used as a way to bring the necessary heat into the reaction chamber. This sand is heated in a combustion section where for example the char is combusted for heating.

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...centrifugal vortex gas separator...

 

 

you mean a gas centrifuge?

 

i suspect a membrane separator would be better for this as hydrogen leaks through pretty much everything. also, cheaper.

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You don't want to separate gases I think, unless you can do it by condensation. Any other process is too bulky for applications in a car. Well, it might work, but I am skeptical about large surface area processes (membranes) that need to be shock-proof and preferably light-weight in a moving vehicle.

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membrane seperators do not need to be fragile. for instance, you can even make a hollow fibre seperator flexible enough to tie into knots(assuming its long enough) and still have it function fine. its perfectly shock proof(okay, not totally, but if its going to damage it then it will probably do the car in anyway.)

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i suspect a membrane separator would be better for this as hydrogen leaks through pretty much everything. also, cheaper.

Slightly off topic, and not likely to be cheaper, but I read this article the other day discussing new ways to contain and wrap liquids and gases.

 

 

 

http://www.aip.org/press_release/nanoballoon.html

Airtight containers are not always so airtight. As any child will discover the day after a birthday party, even a tightly tied helium balloon will leak its gas out over the course of many hours. Now scientists have come up with a supremely efficient barrier that lets nothing in or out.

 

As described in a recent issue of the journal Applied Physics Letters, this new wrapping material is made of graphene, a natural carbon fabric that is only a single-atomic-layer thick.

 

 

The actual journal article:

 

http://link.aip.org/link/?APPLAB/93/193107/1

We have performed a first-principles density functional theory investigation of the penetration of helium atoms through a graphene monolayer with defects. The relaxation of the graphene layer caused by the incoming helium atoms does not have a strong influence on the height of the energy barriers for penetration. For defective graphene layers, the penetration barriers decrease exponentially with the size of the defects but they are still sufficiently high that very large defects are needed to make the graphene sheet permeable for small atoms and molecules. This makes graphene a very promising material for the construction of nanocages and nanomembranes.

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