Superheated steam driven turbo

[obanion]

The CO2 idea I thought was bad, thanks to everyone here for comfirming it. Now I can inquire about something that may actually work.

Turbo will NOT be connected to exhaust. Turbine will have it's own dedicated "on demand" system.

As follows:

Combustion chamber, still unsure of size (thinking 4" tubing by 12" long, necking down to 2.5" at the end to enter turbo).

Four things will go into the chamber:

1. Propane (already being used as main fuel, others would use gasoline)
2. Pure oxygen gas
3. Water (probably pre-heated by engine coolant to save fuel)
4. Powerful ignition source. Seen some things used by back yard turbo-> jet makers, probably get something similar.

The ratio of propanexygen will be 1:3.62 (stoich), maybe a little richer if I get more heat by doing so. Ratio of waterropane I calculate at 13.76:1. My initial math tells me this should give me a result of 1500F superheated steam, with some other 1500F products of combustion.

Since at 1500F, steam has about 1.57x the volume of air, and that there are no serious drawbacks to running elevated amounts of backpressure if it aids things, I think I could power a compressor to move 60-70lb/min of air with as little as 1.6GPM water, and 3.5lb/min oxygen. Certainly a reasonable usage cost.

Feel free to point out anything I'm missing.

 

[obanion]

I should also note that the lower I can push the water:fuel ratio, I will get better efficiency. A lower ratio means a higher total steam temperature, which increases volume flow and energy, while using less fuel, oxygen, and water. It's just the thermal limitation of the turbo to be worried about. If a Inconel turbine could allow me to run 2000F steam temps, that would boost things considerably.

 

[SBBlue]

A few calculations. . . . .

I'm assuming that when you talk about 60-70 lbs air/min you are working with a boost pressure of one or two atmospheres. For discussion sake, let's assume a 20 psi boost pressure, and 60 lb/min air flow. We'll also assume that the compressor efficiency is 80%

Such a setup will require 2700 BTU/min of energy to run the compressor. If we have a steam cycle engine that is working at 30% efficiency (it will probably be lower than that), the amount of thermal energy required per hour will equal about 540,000 BTU. Assuming a BTU content of fuel of 20,000 BTU per pound (it will vary), we can see that about 27 pounds of fuel will be required per hour to power the compressor. If we are using gasoline, we are looking at about four and one half gallons of gasoline per hour to run the supercharger. The water requirements will be a little less than a gallon a minute, or 60 gallons an hour.

 

[obanion]

Well it that's the case, that's better than I thought!

BTU content of propane is ~21800 BTU/hr. You are suggesting I'll only need less than .5 lb/min propane, which would need about 1.5 lb/min oxygen, and less than a gallon a minute? Hot damn, that will work JUST fine.

Will the propane/oxygen gas mixture burn well with all that water around? I'd think so, as the resulting output temperature (1500F+) is well past the autoignition temperature of propane (975F). Ignition should be ok, as the water will mostly be liquid before ignition, and won't do much to keep the propane and the oxygen apart. I could conversely, ignite the propane/oxygen, and within .1sec start adding the water.

I am also pondering using a mix of methanol/water, so as to only have to meter in two things instead of three. The fuel:water ratio would be higher, more like a 25-30% mix of methanol. This would present more difficult ignition, although I think after that it should self propagate, again because the generated temps are well over the autoignition point of the fuel.

 

[obanion]

BTW, you give me the equation you used for that estimation?

 

[SBBlue]

1) The calculations were done with the standard air tables and the superheated steam tables. The steam information I did from memory, but it should be reasonably close. It takes about 1000 BTU to vaporize a pound of water, and raising the temperature of steam from 212 deg F to 1500 deg F will take somewhere around 600-700 BTU/lb.

2) The propane/oxygen mixture probably won't burn at all in the presence of that amount of water -- after all, water is used to put out fire. There is a work around to that -- combine the oxygen and propane and burn it first, and then add the water a bit further down your combustion chamber.

3) I'd have to go through the calculations, but you might be better off setting up a turbocharger as a jet turbine to provide the power for your supercharger.

 

[GregLocock]

Point 3 is the issue, effectively you /are/ building a gas turbine, albeit with water injection as well.

Cheers

Greg Locock

 

[obanion]

1. Yes your math agrees with mine. I was speaking of calculating the amount of power required to make a compressor move X air at Y pressure ratio.

2. You sure? Yes water puts out fires, but only once it is applied in sufficent quantity to kill the heat of the reaction. In my hopeful combustion chamber, there is only enough water present to keep the temps down to 1500F, where combustion will still occur. No matter, if I'm right, it will work. If you are right, I'll just move the water injection point to just in front of the main ignition point of the propane/oxygen.

3. I like the idea of using a small turbo as a jet turbine to then power the main turbo. That way I wouldn't need compressed oxygen. However, I want a system that can be "on demand," and it wouldn't work that way. Too much delay in getting the jet turbine to power the main turbo. I'd also need to keep it idling. Neat idea though. Would work pretty well for drag cars.

 

[obanion]

Well I got a great calculator program:

http://www.processacesoftware.com/ProcessAceSoftwarePage4.html

It's for a Palm Pilot, so I had to also get a Palm simulator program. I found direct PC programs, but none of them would take steam temps above about 900F. The palm one above goes to 1472F.

Anyway, you input the input pressure, input temperature, output pressure, turbine efficiency, and it tells you how much steam flow you need per hp per hour.

The results seem to agree with the above posted info.

Increased pressure shows increased efficiency, but it's not linear. Double pressure is more like a 50% increase in efficiency. I should size the turbine such that I develop about 50-60psi of pressure in the steam generation chamber. This is a happy medium.

Increased steam temp also increased efficiency, confirming that the hotter I run it, the less of the combustion products I'll need to use. It's simply a matter of how hot can it handle. I need to find out what kind of turbines I can get in inconel or titanium, and what their safe temperature limits are.

At my calculations for 1472F outlet temps, with heated 180F water in, I get a ratio of waterropanexygen of 15:1:3.62. About 70% of the input density is water. So I figure, whatever I get with the above steam calculation, to multiply by .7, as I'll get more steam from the propane/oxygen combustion, and a little superheated CO2, which is pretty close to the steam.

Looks like it should work. On to building a steam generator chamber. I'll test that, then add a turbo on the end. I'll also build a test chamber at the compressor outlet, that I can use to simulate the resistance of the motor. That will be a large chamber, with a small tube exiting to atmosphere, which will be sized to simulate the restriction of the motor at various RPM points.

 

[obanion]

Another good idea, I should get a water cooled turbo, and run the water supply through the turbo on it's way to the steam chamber. Reuse the lost heat that goes into the turbine housing.

 

[anonabcd]

GregLocock (Automotive) Jan 18, 2004
Point 3 is the issue, effectively you /are/ building a gas turbine, albeit with water injection as well.

obanion (Automotive) Jan 19, 2004
...
3. I like the idea of using a small turbo as a jet turbine to then power the main turbo...

I think his point was that even without adding a "small turbo", you're already building a gas turbine. In this case, you're using the output of your "gas turbine" to drive a compressor feeding air to an engine instead of using the output to drive a mechanical load such as a propeller "directly".

I confess my ignorance on this subject but IMHO, it sure sounds like he's correct.

 

[turbododge]

A lot of folks were messing with "fired" turbos about 20 years ago. The would inject combusted gas/air mix into the exhaust manifold ahead of the turbine to help power it. Don't remember any great success with it, as you needed compressed air to overcome the exhaust pressure, and the turbine temps got very high, but some of the dyno numbers with and with it on the same engine were very, very impressive, especially at low rpm and spoolup.

 

[JayMaechtlen]

For use in a vehicle (car? pickup?) you'll need to tote the Oxygen around, as well as the fuel. That won't be very light, will it? (compressed, or liquid in a dewar?)
At least, you are hauling the fuel anyway- the Oxy and water are extra: in tankage, plumbing, and metering.
jay


Jay Maechtlen

 

[Andy330hp]

I don't think I'd be too hot on the idea of stapping my oxy-acetylene (or oxy-propane in this case) torch in the trunk of my car and trying to drive off of it, but to each his own.

I think you still run into a problem, much as you did with the CO2, of maintaining the flow rate of oxygen. If you had a 80 ft^3 tank of oxygen at 3000 psi, you'll only get around 2 min of fun, and that's IF you had a specially made tank with a spring/piston that maintained that 3000 psi, otherwise you'd have far less.

Not to mention the oddity of having to contantly light and extinguish the combustion chamber for this "on-demand" system.

Get a nitrous kit if you want an on/off boost, and a turbo if you want it always vailable.

 

[obanion]

Any way to break up Hydrogen Peroxide rapidly? My oxygen and water would be in one place.

 

[kiwinjuneer]

If you want to check out the impact water injection has on a gas turbine, do a google search on "cheng cycle". This process has been around for a long time and has been well proven as a means of reducing NOx while also improving the efficiency of a simple cycle GT generator.