Water/meth injection (was: new to ms)

[Kurt A]

Water injection will be more efficient after the intercooler. The intercooler will get rid of more heat in the air with the highest temperature difference between the compressed air and the ambient air. That's basic physics: higher temperature difference means higher heat transfer. If you inject water before, you will cool down the compressed air which will reduce the intercooler heat transfer.

Jean

That makes sense to me Jean. So thinking that the solution gets injected after the intercooler which option would be the better choice. In plenum or in runner.
Kurt

[racingmini_mtl]

That one is not so clear cut, at least to me. I guess it depends on how it's injected (how fine the water droplets are) and it also depends if you want water vapor or droplets to go into the cylinders. Thinking about it, it would probably ideal if it was possible to inject both in the plenum and in the runners and be able to change how much is injected in either place depending on the air temperature and engine RPM.

So with high temperature and/or low RPM you'd want to inject mostly in the runners while at high RPM and/or low temperature, you'd want to inject mostly in the plenum. And a mix of both in between. That would do something similar to race engine which have one set of injector at the port and one set at the runner entrance which give time for the fuel (or water in this instance) to vaporize (and mix) completely before going into the cylinder.

But I doubt that such a complexity is necessary but it might be interesting to think about it and experiment.

Jean

[Tjabo]

Jean,

I'm not 100% sure I'm with you on this one. . . Yes, the intercooler with cause the greatest amount of heat transfer that it can with the highest incoming air temperature (I think that is basically what your saying), HOWEVER the water/methanol injectant also does its best work when injected into the highest temperature environment.

Most people choose not to inject water/methanol pre-intercooler, due to the potential for puddling in the intercooler. There are some people though, who have gotten good results by using a small nozzle prior to the intercooler to keep the intercooler from heat-soaking, and then use a bigger nozzle after the intercooler to inject the bulk of the injectant. In this thread, Richard Lamb of Aquamist documented the benefits of a small nozzle before the intercooler (or more precisely, what can happen if you don't have it):

http://www.aquamist.co.uk/phpBB2/viewtopic.php?t=12

It seems that while the phase change of water, with its high latent heat, from liquid to gas does hold the potential to take a lot of heat out of the induction stream, this effect is much more pronounced in the combustion chamber. This is what makes it such a great knock suppressor.

Conversely, the methanol seems to do a better job of cooling the induction stream, and also is a high octane fuel that carries its own oxygen, so you can inject a ton of it, which also does a lot of cooling. Obviously there are merits to injecting both, but the location of the nozzles doesn't necessarily follow the simple logic you've laid out here. . . It seems that there is a lot of needed testing to be done, and the datalogging potential of MS3 makes it the perfect vehicle for so doing! (as with so many other reasons to be excited about it!)

Anyway. food for thought,

Thad

[racingmini_mtl]

The thread mentions a dyno run with an inefficient fan to cool the intercooler. That's a very bad setup to evaluate the efficiency of an intercooler. In my view, this is a crutch for a non-optimal setup where the intercooler is not getting cooled enough for the job it needs to do.

Having said that, the crutch might well be needed in a lot of cases due to the physical constraints of an engine bay. There are always some compromises that need to be done when confronted with the real world issues compared to what the theory says.

Anyways, you might want to have a look at this nice calculator and play with the different WI-related parameters. Again this is theory but shows how much efficiency can be gained by optimizing different things.

Jean

[Tjabo]

Thanks for the site reference Jean! I've been enjoying that calculator for years now, and have undoubtedly spent dozens of hours on there messing around with different parameters of my engines. Unfortunately though, due to some of the assumptions that are made in the calculations where reality diverges from theory, I have learned to regard the outputs from that site as nothing more than "something to think about." It IS interesting stuff though.

Back on the topic of the WRX and the dual water injection nozzles, I agree with your assessment that the intercooler setup in question is quite inefficient, and that the setup left even more to be desired in the sited instance than a normal dyno run does (which is quite a lot in my opinion). Still though, Richard Lamb probably has more experience with water injection systems for performance applications than almost anyone else, from his involvement with World Rally Championship teams. Therefore, I wouldn't disregard his knowledge gained through his experiences any more than I would disregard your thoughts on designing add-on PCBs for MegaSquirt applications!

Thanks again for your contributions to the discussion in this thread! (and to the MS project in general!)

Thad

[Kurt A]

Great posts guy`s,
I have been using Eric's site for years now as well. Interesting to note that there is people seeing positive results with spraying before the inter-cooler. I can certainly see that there is no best way to do this and really relies upon application specific circumstances. Logging before and after results will be the only true way of confirming if your application benefited from your install specifics. It certainly makes sense to me that with a less than perfect inter-cooler being wet, damp, as the air travels past that a change of state will occur causing an improvement of efficiency. Maybe we should be looking at incorporating an inter-cooler temp sensor that MS could control a WMI nozzle and in effect help control inter-cooler efficiency. Nothing in this world is perfect and I am sure that there is many that could benefit from such a set up.
Kurt

[Kurt A]

Ok so I have managed to digest the first 3 pages of this thread.
http://www.aquamist.co.uk/phpBB2/viewtopic.php?t=267
These guy's really seem to know what they are talking about when it comes to water injection. A ton of good info here.
Thanks
Kurt

[Tjabo]

Yeah, that is a great thread. I read the whole thing a few years ago. At the time I was planning to use an SRT-4 turbo, which is rather severely undersize, so I was excited by the prospect of using WI pre-impeller to assist with the flow potential of it. Then I went to the other extreme and got a turbo that's a bit big for what I'm using it for, so it's kind of a non-issue for me. Still, that is one of the better threads on that board if you asked me.

Thad