Pre-turbocharger methanol injection
Pre-turbocharger methanol injection
(OP)
Hello,
I am trying to understand what the limits are of pre-compressor methanol injection on turbocharged cars.
From my understanding, erosion occurs when you have the wrong combination of compressor speed and droplet size.
I have a turbocharger and I calculated the tip speed of the compressor to be at about 1158 ft/s at maximum boost.
My question is if the inlet tubing to the compressor is 3 feet long and I am flowing 100 ml/min of pure methanol (tiny amounts) will I see erosion if my ambient inlet temps are 80 degrees F?
I did a quick hand calc and the speed the air is moving through the inlet tube is about 160 ft/s so it will take about 20 ms for the air to reach the compressor.
I dont know how to compute the content of liquid left in this mixture, the methanol is injected via a super atomizing nozzle. So inlet droplet size can be assumed some value. I just dont know droplet size at the end of the tube feeding the compressor.
Thank you,
- D
I am trying to understand what the limits are of pre-compressor methanol injection on turbocharged cars.
From my understanding, erosion occurs when you have the wrong combination of compressor speed and droplet size.
I have a turbocharger and I calculated the tip speed of the compressor to be at about 1158 ft/s at maximum boost.
My question is if the inlet tubing to the compressor is 3 feet long and I am flowing 100 ml/min of pure methanol (tiny amounts) will I see erosion if my ambient inlet temps are 80 degrees F?
I did a quick hand calc and the speed the air is moving through the inlet tube is about 160 ft/s so it will take about 20 ms for the air to reach the compressor.
I dont know how to compute the content of liquid left in this mixture, the methanol is injected via a super atomizing nozzle. So inlet droplet size can be assumed some value. I just dont know droplet size at the end of the tube feeding the compressor.
Thank you,
- D





RE: Pre-turbocharger methanol injection
http://www.aquamist.co.uk/vbulletin/ is a very good resource
RE: Pre-turbocharger methanol injection
Methanol has a high latent heat value, so it would provide a nice reduction in charge air temps.
The droplet size would not likely be an issue, since the small amounts of methanol you propose to use would readily vaporize before contacting the compressor wheel. But methanol is also very corrosive to some metals/materials. So you would need to check for compatibility.
You would also need to make sure that your turbo's compressor shaft seals are capable of keeping the methanol out of your lube oil.
Good luck.
Terry
RE: Pre-turbocharger methanol injection
In general, methanol is injected either directly into the cylinders or into the inlet ports of the engine, when used as "regular" fuel. This does prevent most effects of long term corrosion. When risking the chance of condensation of your methanol onto the compressor wheel, intercooler and inlet tract, you will probably expose your aluminium much more than when injecting further towards the inlet valves.
I don't think that experimenting with the size and concentration of the droplets will make a fundamental difference. Maybe a practical, but you're still exposing aluminium to (heated) methanol. It will corrode in the end. I don't know if cavitation plays a part in this process, but purely chemical, concentration and temperature are your main factors. If cavitation plays a part, you'd want the stuff evaporated before it hits your compressor wheel. If not, you'd want large droplets so only a small portion of the alcohol is directly exposed to the aluminium and most will just fly past and evaporate further down. Maybe the high impact speed at the tips of your compressor wheel would cause cavitation in larger droplets?
Remember that the evaporation of the methanol is what cools the mixture, once it's gaseous, it's just another gas that you are heating. It makes sense to evaporate it at the point where temperatures are highest. That would be either just before the intercooler, or during the compression stroke inside the cylinder.
RE: Pre-turbocharger methanol injection
If you inject after the inter cooler you get the coolest charge as the inter cooler is dependant on delta T.
Erosion of the compressor wheel is always a risk but depends on a number of variable including droplet size, wheel speed, number of droplets, material used for wheel temperature of the methanol and wheel and construction of wheel.
Regards
Pat
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RE: Pre-turbocharger methanol injection
Your argument to maximize the temperature drop in the intercooler and thus to put the methanol injection after that, is what I was looking for in my original reply. Thanks for making it clear.
RE: Pre-turbocharger methanol injection
Simplicity - no high pressure pumps required. If you use a boost-pressurized tank, a pump isn't even required.
Uneven water distribution becomes more of a problem, admittedly.
RE: Pre-turbocharger methanol injection
RE: Pre-turbocharger methanol injection
Liquid methanol is corrosive to aluminum (don't store it in an aluminum tank) but you are not very likely to see actual corrosion with vapor.
There is a lot of information in the forum I linked to earlier.
You will want a pump and a check valve, low pressure is not the way to go. Will siphon or drip without a check valve.
RE: Pre-turbocharger methanol injection
I am injecting pre turbo because the turbos sized for this vehicle are small and loose a lot of top end power. The turbos come from the factory running at about 8 psi boost, I am running about 17 psi boost with methanol injection.
about 900 ml/min at the throttle body and the other 100 ml/min are split to each turbo (there are two) 50 ml/min each, a very small amount.
I am trying to create a cooler inlet air charge to the compressor to shift the efficiency up towards topend engine speed where these turbos are poor. Cooling the air before the turbos lets them create target boost at a reduced compressor RPM.
I am just worried about erosion, right now I am using a super atomizing nozzle to do this. The nozzle is over 3 feet from the compressor with ample time to vaporize. Methanol vaporizes very fast, if anyone has any other suggestions please let me know.
Thanks for your time
RE: Pre-turbocharger methanol injection
I think that if you reduce the pressure behind the turbo, the total amount of air flowed will still be the same. The turbo has to create a pressure difference between pre and post turbine. If you lower the pressure of the compressed air with methanol injection, that should give the same effect as injecting pre turbine? Is there a flaw in my reasoning here?
RE: Pre-turbocharger methanol injection
I am not injecting methanol before the turbine I am injecting it before the compressor.
Reducing the inlet temperature to the compressor will allow me to hit target boost at a lower compressor speed and greater efficiency, that is my goal.
I am just worried about erosion over long term.
RE: Pre-turbocharger methanol injection
Here's a picture of the compressor inlet from a Cosworth XB turbocharged, methanol fueled Champ Car engine (This engine uses a very small PR and no intercooling):
http:
Note the location of the (4) injectors......
Regards,
Terry
RE: Pre-turbocharger methanol injection
Thanks for the pic, I have seen that pic many times and admittedly I studied that setup. It turns out they dont care about long term erosion (im talking 50k miles not a 24 hour race).
So they can essentially dump fuel into the compressor like that and it will live, but long term I have seen compressors get torn up because of droplet impact.
I am just looking for a way to quantify erosion vs. droplet size and speed or even rules of thumb for this application. I have checked out aquamist website many times and there isnt any theoretical data on the subject. Just that "it's good to use".
The whole purpose of this injection method is to reduce the inlet temperature of the compressor and that will greatly aid in compressor efficiency, because as I mentioned earlier the turbos are undersized units from the factory and I don't intend to replace them with anything bigger.
RE: Pre-turbocharger methanol injection
They have a coating called turbo coat. It's primarilly for the turbine side but can also be used on the intake side. I coated my intake mani runners with it. They claim it flows better than an uncoated surface. Since the greater majority of the car world agrees a slightly rough intake flows best I emailed them and asked them if they did flow comparisons of their coating vs different surface finishes and that totally threw them. Whatever the case though it's good stuff and should be very resistant to alcohol. It also goes on very thin. If you apply it right it shouldn't throw off the balance of your turbines or cause interference between the turbine and housing. Recommended application is 1 mil.
RE: Pre-turbocharger methanol injection
Engineering is the art of creating things you need, from things you can get.
RE: Pre-turbocharger methanol injection