Anders posted a link to this excellent paper a while back:
"Boosting Gas Turbines" -
jetandturbineowners.proboards.com/thread/889/boosting-gas-turbines-bill-gunstonIt is well established that water meth is an excellent coolant that can be used to increase the air density before the inducer to provide a significant increase in power. But it can also be injected behind the compressor wheel for additional cooling of the charge air, reducing the compressor work, providing additional power gain from the cooling effect AND the increase in mass flow. People do it on their turbocharged cars all day, every day.
If you spray it before the compressor inducer and get good evaporation, it can increase thrust on a large axial turbine engine by about 5-15 %.
However, there can be technical challenges to injecting it into a turbine engine.
For example, Anders did exactly this at his last event. Some kind of an instability was experienced. Possibly surge or what I think "may" have been ignition of the water methanol mix before it went into the flame can.
Cool combustion or not, if it ignites before making its way into the flame can it will definitely be a problem. So we can't let anything like that happen. It will have to be formulated and/or injected in such a way that it doesn't ignite before entering the flame can. This can be dealt with and its not a big problem to over come. Just a little testing and development time to get it dialed in.
I've been doing my own research and testing on ways to inject "reactive coolants" into an air stream and found it can be done without a pump.
By using a small pressure vessel (like a stainless steel paintball tank) and a 12V solenoid valve that's all you need. No pump. I did comparative comparative air flow testing of water/meth spray through a leaf blower and onto a wire thermocouple (with and without dissolved CO2 in the meth). It works and no pumps are needed.
I filled a small stainless steel pressure vessel 1/2 full of a water/methanol mix and then saturated it with CO2. I transferred gaseous CO2 from a CO2 cylinder and into the top of the water meth tank through a series of valves and AN lines. The water/meth was allowed saturate at full pressure 720 PSI for about 1 hour. Then the water/meth were gently swirled at pressure for about 5 minutes to promote additional dissolution.
Then the water/meth was violently shooken, at pressure, for about a minute. This was to insure maximum gaseous saturation of the solution.
Then the meth tank was set into a rack to hold it in place while I held up the CO2 cylinder over the water/meth tank and held the CO2 tank upside down. This was to fill in any remaining meth tank ullage with liquid CO2. Now it is 100% saturated. Probably even 2 phase.
Once it was completely filled I closed all the valves and disconnected the CO2 tank lines. The first thing to do was to vent a small amount of CO2 from the top of the water/meth tank. This was to create a safety ullage to allow for thermal expansion and contraction of the liquid.
The resulting solution is like extremely effervescent soda water. A self pressurized tank with the necessary fittings ready to supply saturated CO2/water/meth @ 500-700 PSI. The contents, while in the tank, are completely non-reactive and indefinitely stable. Impervious to adiabatic compression. The hazzards are the moderated flammability & toxicity of the methanol and being under pressure. It has about the same pressure hazard level as a paint ball tank but probably even less due to all the water.
Water meth is a good coolant because 1) it has a very high heat capacity and 2) when it is sprayed as a mist, the evaporation process is highly endothermic. It gets cold.
Water/meth will be very finely atomized at 500+ PSI. But by dissolving the water/meth mix in liquid CO2 it increases the mixture vapor pressure so high that the mist droplets explode when sprayed out of a misting nozzle. Enhancing the atomization and cooling even more. Instead of spraying as a cold mist, it expands out more like a cold fog for faster and more efficient evaporation. Stick that upstream of your compressor inducer.
Because the coolant has methanol in it, it can be reacted with the air,
at the right place and time, to provide additional heat release and steam/CO2. Its combustion efficiency will be low because there is so much water in it, but that can be turned to your advantage if we are talking about spraying it into the inter-stage just before a power wheel.
Think of it like an after burner in the interstage.
If you inject pure fuel into an after burner it burns super hot. Lots of energy released but way too hot for any kind of turbine free power wheel. Insuring rapid destruction of the nozzle and turbine in seconds.
If you were to inject pure water into an after burner it could make a little more thrust and power but only if you inject a small amount. The gas temperature will drop very rapidly when water is injected.
Then extend the same process to a water/methanol mix. Inject it into an after burner. Some of the methanol will burn and much of it wont. There is too much water for complete combustion. The combustion efficiency will be low... but you want this. You will have extracted more combustion energy from all the free oxygen and increased the mass flow. In a controlled manner. Extra heat, extra steam, extra power... but not too hot. Now you can flow it through a free power wheel at a reasonable working temperature.
By experimenting with the water/methanol percentage, more concentrated or less concentrated, you can tailor the interstage combustion temperature to anything you want it to be. Colder, hotter or you can even regulate it to the same temperature as your gas producer... but... now you have a higher mass flow rate.
You will want to test spraying before the compressor inducer. How much is optimum?
Into the combustor inducer. How much is optimum?
Into the inter-stage. How much is optimum?
Do lots and lots of testing so you can map out the optimums. I can help with test mapping if needed. Just let me know.
Inject the meth like it were a small bottle of nitrous. A limited resource that will be used up fast. Plan how and where you want to use it for the best effect. And make sure the bottle is depleted before crossing the finish line.
Here is how I would do it.
1) Define how big of a bottle can you install? Lets say 2 liters as an example. That's not much so load it up with as much energy as you can.
2) Test. Do lots of testing to see where everything stands and what the limits are.
The first thing you want to do is maximize the energy content but you dont want to melt or blow up any part of the drive train either. Do lots of pre-race testing to verify how high of a concentration of methanol you can put into the mix and stay within reasonable temperature limits. 85%, 65%, 50%? Go with the highest flame temperature the system can tolerate.
How much is sprayed into the compressor?
How much is sprayed into the combustor?
How much is sprayed into the inter-stage?
At what mixture ratio(s)?
If you want to be at your best, do lots of test!
3) What mass flow rate can you spray into the system without putting it into surge?
You may not experience surge but lets say the hypothetical test results indicate you can safely spray 0.25 liters per second. With a 2 liter bottle that means you have 8 seconds worth of spray to boost with. Or roughly 220 grams per second for 8 seconds.
4) How much extra heat can the system tolerate for 8 seconds?
Probably a lot more than steady state temperature. Let testing define this value for you.
5) How long is the duration of the race?
Lets say, hypothetically, 20 seconds for a 1 mile race. (Its just a number).
OK, so you have 2 liters or 8 seconds of spray to be used in under 20 seconds.
6) What is the objective of the race? Do you want the highest trap speed and/or the lowest elapsed time ET?
If you simply want the highest trap speed, save the bottle for the last 8 seconds of the race and deplete it just as you cross the finish line. That will give you the highest speed. However, if you want shortest elapsed time, spray the bottle early in the race so you pick up speed quickly... and you carry the added velocity with you for the remainder of the race. This wont give you the highest speed but it will give you the shortest elapsed time.
A little extra testing, analysis and time will define everything. If you can extract an additional ~5-10% power from the inducer, 5% from the combustor and roughly another 5-10% from the interstage injection. That would be well worth the added weight of a tank and solenoid.
With meth as a limited resource you will want to place priority at the compressor inducer first. Cool the air to cram as much of it as you can into the compressor. That alone will increase the mass flow. In Anders case there will be a limit here because the atmospheric temperature will probably be around freezing anyways. In Azwoods case, it can produce a good gain on a hot day.
In either case, spray as much as can into the combustor. Spray it in somewhere between zone 2 and zone 3. Maximize your Kerosene fuel flow rate in the combustor while the coolant is spraying into the combustor at the same time. While the increased kerosene flow will increase combustion temperature, the meth will bring it back down to a more reasonable temperature... but in the process, it will generate more turbine power for the compressor. Assuming its not over speed, choked or surged, more power for the compressor means more pressure and more air mass flow through the system.
Then with all the additional air coming into the system you now have more Mdot and more oxygen. By injecting meth into the interstage you can burn more of the oxygen and still maintain a reasonable temperature. The final result is more pressure and mass flow through your free power wheel. Inject as much as you can at every station where you can shove it in.
PS - Map out everything in test to clearly define the limits!
