Intercooling turbo compressor directly to boost flow
Intercooling turbo compressor directly to boost flow
(OP)
A compressor moves a certain VOLUME of air. Even though most compressor maps list airflow by mass (lbs/min), it's actually a matter of VOLUME (CFM), that has been translated to mass by assuming a certain temperature and pressure (~25C and 1 atmosphere).
So, what this means is that a compressor that maxes out at say 55lb/min airflow on it's compressor map, should be able to flow about 10% more (60 lb/min) if the inlet temperature was 0C (0C air is about 10% denser than 25C air).
Right?
I imagine another big part of the limitation of the compressor is the amount of force of stacking up the air and compressing it. Although the ENGINE benefits from a intercooler, the compressor really doesn't care. It's still working hard, and making hot temps. These hot temperatures which result naturally from compression, work to expand the air, while the compressor works to contract it.
So, what if you could "intercool" the compressor itself? Add a mist of methanol/water to the inlet, which would vaporize and cool the air as it passes through the compressor? I'm still unsure on this, but wouldn't that mean a even bigger jump in the efficiency and upper limit of a given compressor, seeing as how it has to work against the air far less?
My guess here is that a compressor works on relative volume in vs out. When you see a compressor map, and one section says say 75% efficient at 60lb/min and a 3 pressure ratio. What REALLY matters, is how much volume is going in, vs going out. You get a 3x reduction in volume through compression, and gain 30% volume through heat expansion (25C in, 150C out). That's a mass boost of 2.1:1.
Now, IF the out temp of the compression process was reduced to say 40C through methanol vaporization, look what happens:
Pressure ratio of 3:1 remains
Temperature gain now only expands the air by 5%.
3*.95=2.85
So, if I'm not missing anything, the same compressor, operating at the same 3:1 pressure ratio, will be able to flow 2.85/2.1=35% more air if the air only heats up to 40C during the process instead of 150C.
Combine the gains of pre-compressor cooling to freezing temps, and the integrated cooling (actually heat gain reduction) during compression, and a compressor rated to only flow 55lb/min could flow: 55*1.1*1.35=81.675lb/min.
So, what this means is that a compressor that maxes out at say 55lb/min airflow on it's compressor map, should be able to flow about 10% more (60 lb/min) if the inlet temperature was 0C (0C air is about 10% denser than 25C air).
Right?
I imagine another big part of the limitation of the compressor is the amount of force of stacking up the air and compressing it. Although the ENGINE benefits from a intercooler, the compressor really doesn't care. It's still working hard, and making hot temps. These hot temperatures which result naturally from compression, work to expand the air, while the compressor works to contract it.
So, what if you could "intercool" the compressor itself? Add a mist of methanol/water to the inlet, which would vaporize and cool the air as it passes through the compressor? I'm still unsure on this, but wouldn't that mean a even bigger jump in the efficiency and upper limit of a given compressor, seeing as how it has to work against the air far less?
My guess here is that a compressor works on relative volume in vs out. When you see a compressor map, and one section says say 75% efficient at 60lb/min and a 3 pressure ratio. What REALLY matters, is how much volume is going in, vs going out. You get a 3x reduction in volume through compression, and gain 30% volume through heat expansion (25C in, 150C out). That's a mass boost of 2.1:1.
Now, IF the out temp of the compression process was reduced to say 40C through methanol vaporization, look what happens:
Pressure ratio of 3:1 remains
Temperature gain now only expands the air by 5%.
3*.95=2.85
So, if I'm not missing anything, the same compressor, operating at the same 3:1 pressure ratio, will be able to flow 2.85/2.1=35% more air if the air only heats up to 40C during the process instead of 150C.
Combine the gains of pre-compressor cooling to freezing temps, and the integrated cooling (actually heat gain reduction) during compression, and a compressor rated to only flow 55lb/min could flow: 55*1.1*1.35=81.675lb/min.





RE: Intercooling turbo compressor directly to boost flow
RE: Intercooling turbo compressor directly to boost flow
And it does work pretty much as you suggest, although I didn't go through your numbers to see how they add up.
RE: Intercooling turbo compressor directly to boost flow
It's kind of a deal with the devil isn't it? Increased compressor wear, but superb usage results. I guess I wouldn't mind changing compressor wheels every 10k miles too much, considering I'll do that about every 5 years with this car, and a standard GT37 compressoor is only about $75 anyway.
RE: Intercooling turbo compressor directly to boost flow
RE: Intercooling turbo compressor directly to boost flow
It is common practice in Champ Car racing to inject methanol into the compressor inlet. Intercooling is not permitted by the rules, so injecting methanol fuel (with its high latent heat value) into the compressor inlet provides a significant reduction in inlet manifold air temperatures.
Terry
RE: Intercooling turbo compressor directly to boost flow
RE: Intercooling turbo compressor directly to boost flow
I can run with or without the water very easily, and if I am holding a boost level and turn on the water, you feel a very positive increase in accelleration. I am also running an intercooler, so this is beyond the intercooling affects.
If you do a good job of setting up the system, I would not be afraid to inject ahead of the turbo, as I have seen very good results that way.
RE: Intercooling turbo compressor directly to boost flow
Couple things, you say you inject into the turbine, you mean the compressor right?
Secondly, I'm not sure methanol would make a difference. Any wear on the compressor occurs due to mechanical corrosion, ie the collosion of the liquid droplets with the fast moving compressor blades. There is no time or contact for chemical corrosion to occur, which IMO takes hours to days of contact to cause issues. If anything methanols lower viscosity would reduce compressor wear slightly vs water or isopropyl.
RE: Intercooling turbo compressor directly to boost flow
I am not up on the viscosity/vapor pressure etc with methanol vs isopropyl, but I know I have seen methanol systems corrode the compressor wheel, but never an isopropyl setup do the same. Downstream corrosion is even more of a problem with with methanol, and I have even seen corroded throttle shafts stick in the carb base. Intercoolers will also sometimes condense out a small amount of water or alcohol in cold weather and the methanol will also go work on the intercooler. I would guess that the compressor gets wet enough with the methanol someplace along the line, either at cold start, cold idle or such. The corrosion I have seen covered more of the depth of the blade than impingement damage which tended to be very close to the entrance edges of the blades.
The other thing that goes with this is that all the other systems that had problems with corrosion also were on/off, non variable, systems, which can heavily overload the compressor at low rpms, cool air conditions. I have literally seen liquid drip from the compressor housing hose connections after a run.
I am sure there are lots of folks that have successfully run methanol in their setups, but for me the isopropyl makes it much easier and more reliable, with very little downside.
RE: Intercooling turbo compressor directly to boost flow
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Intercooling turbo compressor directly to boost flow
Assume "x" miles under boost with injection. For x = 1 or 2, if you calculate the heat of vaporization versus air intake mass, this has virtually no effect. A better cold air intake system would do more IMHO.
overrev
Dave at USI
RE: Intercooling turbo compressor directly to boost flow
Although I did not mention it earlier, as the question I was addressing was the feasibility of injecting into the compressor, is that my system is not primarily used for inlet charge cooling, as I have an intercooler for that. My system is to allow me to run decent boost, without detonating, on 92 octane pump gas. Without the water I will get detonation at 10 to 12 psi, depending on the gas and weather conditions. It takes much less water to reduce detonation (as long as you have an intercooler to cool the air) than it does to cool the air enough to make power. That said, if I run up to 10 psi with the water turned off, and then turn it on, you can feel the car pull harder, so I am either gaining from cooling of the air further, or because of a better combustion process in the cyliders. I don't know what it is, but you sure can tell if the water is on or off.
The car also has a very good cold air system on it that takes air in through the boxed wheelwells that a fed from spoiler ducts, with only 6" of ducting before the turbos, after the large K & N filters.
RE: Intercooling turbo compressor directly to boost flow
1. Only operate under boost, no spray during starting, idle, cruise, etc.
2. Be fully progressive. More than a straight ratio of methanol:air, the ratio will start lean, then get richer at higher boost, to counteract the higher charge air temperature increasing at higher pressure ratios. I'd calculate a perhaps 20:1 air:methanol ratio at activation, going to 10:1 at full boost. I have the delivery and fuel computer to do this. The idea is to add only enough methanol to achieve a static turbo out temperature, and not leave extra methanol to stream along as liquid. Since the primary fuel I will be using is propane, I'd like to preserve a totally vapor fuel charge.
RE: Intercooling turbo compressor directly to boost flow
Also, on several occassions I have seen turbo housings GLOWING ORANGE from heat after a high end run. I'm not sure I'd feel comfortable injecting a flamable liquid with air, into something that hot, mind you, before the engine air inlet, < HEH. You'd be ingesting pre-ignited mixture into the engine, resulting in SUPER HOT chamber temps, severe detonation, and No doubt engine damage.
Water injection does help, but it is no replacement for an intercooler/aftercooler. It depends how hot your induction is running in the first place, as to how effective water will really be. On an eaton roots blower, at about 8psi it only buys you about 2 degree's of timing, heh.
Having said that, if you do actually raise the efficiency of the compressor by cooling down air for/and aft, your going to be running more air into the engine at given shaft speeds, so depending on what induction systems your running adjustmens maybe be needed with your tune, unless you left a lage enough margin in your A/f ratio's. I don't know if your running EFI, if so, best solution is a blow through MAF (or other method) between the turbo and the engine, measuring actuall air flow regardless of compressor efficiency.
Good Luck!
RE: Intercooling turbo compressor directly to boost flow
If I were to build another, it would be Tu, have a larger intercooler, and no water injection. Anything you inject that is not air or fuel reduces the charge density.
Back in the late 70's we ran a 327 with dual turbos with a carb; fuel air mix thru the turbos. Ran high 10's. Bad mixture distribution problems and kept cracking heads at the siamesed ports. Much better with today's LS1 type heads where ports are equally spaced and tempting to brew up another.
Dave at USI