Piston Vs Turbine Vs Jet - For ground transportation

John Creighton · 2004-11-24 15:53:00

What is the advantage of a piston over a turbine and vice versa. I know there is something called
an autocycle, I forget is there something called a diesel cycle? What is the difference?

GraemeSkinner · 2004-11-26 23:00:40

For one the power to weight ratio is better for turbines than piston engines for one. I've been told that a basic turbine engine is so simple that it can't go wrong (I don't however believe that claim). So for a lighter engine with good power capabilities the turbine seems like a good choice, but perhaps piston engines are more workable, a simple diesel engine really are easy to work on (if the worst happens and you break down on a journey).

Graeme

John Creighton · 2004-11-26 23:02:57

For one the power to weight ratio is better for turbines than piston engines for one.

What about fuel efficiency. Maybe that is the tradeoff. I think the auto cycle is fairly efficient with a long stroke length.

John Creighton · 2004-11-26 23:03:47

but perhaps piston engines are more workable, a simple diesel engine really are easy to work on (if the worst happens and you break down on a journey).

Really then why does it cost so much when your engine goes on your car?

Austin Stanley · 2004-11-26 23:51:25

First off the topic of this post is realy messed up for me, symbouls numbers, whats up with all that? Anyone else seeing something similar?

Obviously there are serious diffrences in the method of opertaion of a ICE or a Gas Turbine engine.

Performance wise there are alot of diffrences. Turbines tend to have both much higher power to weight ratios and tend to be generaly more efficent. Turbines also generaly have fewer moving pecies than ICE engines. Also, nearly all the motion is rotary as opposed to the reciprocating motion in a ICE engine. All this generaly translates to more reliability.

The problem with turbines is that they are generaly very big. We have little expirence with building them to smaller scales. So it is uncertian if the benifits associated with them will scale down to the 2-10kW size that a mars rover would need. I am not aware of any turbine engines currently produced in this size. Progress is being made on these issues however, and turbines probably hold the potential to beat both ICE and Fuel Cells in terms of efficency and power-weight ratios.

Another point to consider, why did air-liners change over to turbine engines. Simple they had vastly higher power to weight ratios than piston engines of the time and were far more reliable than the piston engines as well. When first introduced that were less efficent, but modern turbines do considerably better than ICE.

John Creighton · 2004-11-26 23:57:14

First off the topic of this post is realy messed up for me, symbouls numbers, whats up with all that? Anyone else seeing something similar?

That is what I get for copying and pasting from word perfect. I think the numbers could be unicode for tab maybe.

MarsDog · 2004-11-27 02:48:31

Ultimate Engine ?

http://www.futureenergies.com/print.php … asiturbine;
requires no timing mechanism and always operates at 100% component use factor.

John Creighton · 2004-11-27 10:58:42

Ultimate Engine ?

The hole in the middle looks to big. To take full advantage of a preassure difference you would need to stack several in series. Each one getting smaller.

Trebuchet · 2004-11-27 12:06:24

Actually, we do have turbines small enough to power light vehicles. Jay Leno has a turbine-powered motorcycle, for instance. There's some motorsports guy who modifies very small turbine engines to fit into vehicles, because of the higher power-weight of the turbines. NASA would be looking at things differently, minimizing weight instead of maximizing power, but it's doable, and we already have some fairly small turbines, such as the one on a Tomahawk cruise missile. It's merely a matter of fitting them to a rover.

Oh, a problem does exist with turbines in ground vehicles, from Leno's experiences with the turbine motorcycle, which the world's worst case of turbo lag. With a piston car, when you stomp on the gas, the car accelerates more or less immediately. Small turbines take a while to kick in. This isn't a problem for, say, the pressurized rover on long trips, but for the base 'donkey' rover, it might be very annoying in regards to trying to move stuff.

John Creighton · 2004-11-27 12:33:16

Oh, a problem does exist with turbines in ground vehicles, from Leno's experiences with the turbine motorcycle, which the world's worst case of turbo lag. With a piston car, when you stomp on the gas, the car accelerates more or less immediately. Small turbines take a while to kick in. This isn't a problem for, say, the pressurized rover on long trips, but for the base 'donkey' rover, it might be very annoying in regards to trying to move stuff.

How about a hybrid? Keep the turbine running and whatever load you are not using dump it back into a battery. When the battery is fully charged reduce the speed of the turbine.

GraemeSkinner · 2004-11-27 13:22:38

but perhaps piston engines are more workable, a simple diesel engine really are easy to work on (if the worst happens and you break down on a journey).
Really then why does it cost so much when your engine goes on your car?

Depends on what engine you have in your car, of the four cars we own, I can easily strip and rebuild two of them - the other two are modern engines that I have not got a clue where to start on them. The other reason it costs so much to have an engine change is the usual greedy commercial reasons that we don't need to go into.

Graeme

C M Edwards · 2004-11-27 13:35:40

The main difference between motors using the Otto cycle, Diesel cycle, and the various turbine types is operating torque, which affects everything else about the motor design.

The efficiency of any heat engine cycle varies according to what pressure you run it at, and pressure determines the minimum torque needed to run a rotary motor using that cycle. Since each cycle works most efficiently at a different range of pressure, each engine type works best in a different range of torques.

For example, a diesel motor needs huge pressures and consequently huge torques, but an Otto motor can work at lower pressure and a turbine motor can operate at near zero pressure. Consequently, you will never see a model airplane using a diesel - those tiny little motors would burst apart before developing enough pressure to run a diesel cycle. But you can run them with a turbine or otto cycle motor. A turbine engine can't quite reach the same overpressure as an Otto cycle engine, so it's range of torques is smaller, but can run at even lower pressures. A turbine engine could even conceivably run on the surface of Mars without extensive vacuum modifications, though you wouldn't get much work out of it.

There is a theoretical smallest optimum size for a turbine engine using pressure differentials alone to drive the engine. Below that, a simple fan turbine can't reach a very high efficiency. However, fluid adhesion can drive a turbine as well, allowing turbines to reach sizes smaller than the smiley at the end of this sentence.

GraemeSkinner · 2004-11-27 13:44:09

I know its not practical for a rover, but the least parts the engine has, the less there is to go wrong, so with that in mind a rover with a pulsejet engine would be fun - not sure how economical they are on fuel though

Graeme

GraemeSkinner · 2004-11-27 14:08:01

What about a Hydrogen fueled Wankel Rotary Combustion Engine for a Mars Rover? They have clean exhausts, and are fairly efficient on fuel.

Graeme

MarsDog · 2004-11-27 14:44:14

The hole in the middle looks to big. To take full advantage of a preassure difference you would need to stack several in series. Each one getting smaller.

Not the whole in the middle, combustion takes place in the side chambers.

http://quasiturbine.promci.qc.ca/EQTDis … 0.htm]Even impressed Discover Magazine.

John Creighton · 2004-11-27 15:13:30

Here is a better link.
http://quasiturbine.promci.qc.ca/QTpasWankel.html]Why is the Quasiturbine not a Wankel type engine ?

The thing is weird. But since it is so compact I bet it can deliver allot of power per weight. I am surprised it is also efficient.

MarsDog · 2004-11-27 16:52:54

But still more important, is the fact that much higher pressure ratio (up to diesel) can be obtained while keeping all engine parameters unchanged (Compression ratio difficult to reach without sacrificing intake volume)

Ready to take on the diesel ?

http://www.visionengineer.com/mech/quas … ml]Compete, as a hybrid, against fuel cell vehicles ?

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#1 2004-11-24 15:53:00

Re: Piston Vs Turbine Vs Jet - For ground transportation

#2 2004-11-26 23:00:40

Re: Piston Vs Turbine Vs Jet - For ground transportation

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Re: Piston Vs Turbine Vs Jet - For ground transportation

#4 2004-11-26 23:03:47

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#5 2004-11-26 23:51:25

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