Injecting prior to turbo comp' impellers

[hotrod]

I think the answer to your question can only be answered in context of a specific engine turbo setup, and your specific performance goals.

If the turbo is of adequate size, so it can feed the engine without straining at max rpm, and your going for max power, then post intercooler would likely be the best in my opinion.

If the turbo is a bit undersized and your pushing its air delivery capability, then I think either pre-compressor or a bit of both would be best.

There is also the consideration about ease of implementation. If its nearly impossible to squeeze a spray nozzle inbetween the intercooler and the throttle body (which is almost the case for the WRX) then the simplicity of pre-compressor injection has to be considered as well.

There may also be an advantage to over injection pre-compressor or pre-intercooler and then cooling to super saturation. It would be hard to beat a true fog of microscopic water dropplets for detonation protection I suspect. Only testing will tell for sure.

It's obvious that the WWII military aircraft did quite well with pre-compressor injection, so it may be that the only thing that really counts is the suspended water fraction and it may not matter much how it gets there once its in the cylinder.

I guess the question is, which of several problems is the most urgent for you to resolve on YOUR setup. Detonation (not an issue for a diesel), might depend on the degree of evaporation vs suspended dropplets in the combustion chamber, high EGT's (probably only dependent on the total water fraction, max power ( depends on highest VE so pre-intake valve cooling would dominate).

I think we sometimes forget that WI can be used to resolve several different problems and the setup that most effectively solves one, may be less effective for another.

Larry

[masterp2]

Well put. Evaporation would seem to me important also from the combustibility aspect. Using a meth solution, meth drops (liquid) are worthless to cylinder power enhancement (correct me if I'm wrong). Only once it is a vapor, is it explosive. Dry air (desert SW) would seem to be a real advantage, as so much water AND meth can be vaporized. (thinking out loud)

A friend on-line claims he has reached 127HP using WW fluid, in dry Colorado, 6000 ft altitude, won't share much of the details, but he claims to have unusual nozzles and very high pressure.

[hotrod]

There are several WI diesels up here that are very quick for their size. A couple of them run in the 13 second range. It's kind of funny to see a heavy duty diesel pickup beat a supposedly fast car in the quarter mile. We also have a turbocharged diesel dragster up here that runs in the low 10's high 9's. It's so much quieter than the AA fuelers that you can litterally hear its slicks chirping the full length of the strip.

As you know from where you live, ultra-low humidities are pretty common up here, and in the desert sw. During our forest fire summer a couple years ago, the fire fighters were absolutely stunned when they got morning fire weather reports that they had temps of 80+ deg F and RH humidities of 6%.

That is one of the reasons I have such good luck in the summer with the pre-compressor injection.

Your correct that only the vapors are flamable, but dropplet size is also important. Very small dropplets of fuel vaporize very quickly during combustion due to their very large surface area to volume ratio. It's only an issue if the fuel dropplets are too big to evaporate during the combustion time. This becomes a problem with fuels that have high 90% evaporation temperatures, (like xylene spiked pump gas) that can end up blowing still burning fuel drops out the exhaust valve, giving very high EGT's.

Larry

[masterp2]

Originally Posted by hotrod

I guess the question is, which of several problems is the most urgent for you to resolve on YOUR setup. ... max power ( depends on highest VE so pre-intake valve cooling would dominate).

Larry

Could you elaborate on this part? You are talking air charge density I think. Drops vaporizing in great quantity at the 1000 F valve opening to do what, lower temps and condense more air into the cylinder before detonation? The liquid is important then. Does the meth enter in?

[hotrod]

There are some differences between diesels and gasoline engines so that needs to be considered. As far as VE increase is concerned, it is clear that charge air cooling due to evaporation helps inprove VE all else being equal.

In one of the NACA studies they tried injecting the WI mix both well before the intake valves and immediately before the intake valve. The postion that was "pre-vaporization tank" was several feet from the intake valve and the other injection point was only inches from the intake valve.

Study E5E18 page 5.

"For vaporization-tank injection, the mixture temperature decreased as more internal coolant was injected until the fuel-air mixture became saturated (fig 12) and then the mixture temperature remained relatively constant. In a corresponding manner, the power at peak-power spark advance increased because of the increased charge weight inducted into the cylinder until the internal coolant-fuel ratio for saturation was reached ( fig 13), at which point the power leveled off. After complete saturation of the incoming mixture with the internal coolants, any additional cooling of the mixture must occur after the intake valve closes, which makes it impossible to increase engine power through an effect on air flow. From this point, the power obtainable at peak-power spark advance dropped slightly as the internal coolant-fuel ratio was increased because some heat of vaporization was extracted from the air during the compression stroke, resulting in a decrease in cycle efficiency. When the internal coolant was injected at the manifold elbow, the power increase at peak-power spark advance was relatively small (fig 13) because there was insufficient time for charge cooling before the intake valve closed."


As you can see on a gasoline engine the intake charge cooling due to evaporation of the WI mixture can have an effect on maximum cylinder filling and hence power up to the point you reach 100% humidity (saturation) of the intake charge, AND if there is suffecient time for the evaporation to take place. Spraying beyond, that will increase the cooling effect on the engine due to reduction in combustion chamber temperatures, but at a slight cost in power. You might be able to recover that loss in power by upping the boost more to levels that couldn't be reached at lower injection rates, so you need to consider the fact that you are not only changing cylinder filling but also how much boost, and spark advance you can get away with. This interaction of multiple variables means you have a very complex system to optimize.

Now in your case, your dealing with a diesel, which has too much air to begin with, so the power limit is mostly determined by the amount of fuel available to burn and maximum EGT numbers, and how much cylinder pressure you can tolerate before you start blowing head gaskets or lifting the heads.

If you went with a WI mix that was pure water or low in alcohol content you would maximize cooling at the cost of some reduction in the power gain possible. If you upped the alcohol content you would be increasing the fuel load, and power.

If you increased the alcohol content injected by overspraying a lower alcohol mix, you should be able to get both a power increase and a strong cooling effect on the combustion temps. Only some experimentation would tell you the ideal balance of the variables. For testing purposes you may want to experiment with a 2 nozzle system where you inject water alcohol from one and straight water from the other. That would allow you to sort out the ideal total injection weight of water and alcohol for your goals.


My guess is that on diesels you will need to spend more time sorting out how much extra fuel you can accept (ie alcohol ) to reach your power goals without blowing head gaskets and then control cooling by increasing or decreasing the total WI spray mix and increasing or decreasing the alcohol fraction so you don't exceed your max additional fuel level.



As far as engine cooling due to WI, this paragraph is worth noting.

NACA report 756 ( page 71 , Conclusions item 3.)

Water injection had a marked cooling effect on the engine head and cylinder. The exhaust-valve guide was the only point on the head at which the temperature showed a tendency to increase with indicated mean effective pressure. The temperature was less, however, than that obtained with a straight fuel permitting equivalent power.

Larry

[masterp2]

This some very dynamic conversation. I do appreciate someone who understands the science behind result. I am going to read those reports, they (indirectly) seem to make a case for SOME pre-turbo injection for it's contibution to evaporation. Heres one for ya:

Meth, as a more volatile liquid than water, evaporates at greater rate than water. Given a droplet of mix, won't a greater fraction of meth evaporate per unit of water? Seems as though water will still be liquid when the meth is mostly vapor. Hypothetically, a WW fluid mix, 70/30, might be 90/10 by the time the remaining liquid hits the cylinder.

BTW, I don't plan on playing with proportions. Will use water or WW fluid.
Study E5E18-where can I see this?

[hotrod]

Your correct, the various chemicals will evaporate independently of each other. The methanol does not know or care what the water vapor content of the air is, and likewise the water does not know about the methanol.

(okay there is a very slight impact because methanol is so hygroscopic but not enough for us to worry about).

Due to this you are correct that as the air cools and water evaporation falls to near zero, methanol will still see an environment it can evporate into. That is one of the reasons your temperature drops in the pre-compressor intake tract, exceed the expected 30 deg F you would get with water only before it gets to 100% RH.

For any of the NACA studies you can usually find them with a google search of the form: +NACA +(study number)


A google on:
+NACA +E5E18

Returns the link in the first hit.

If the NASA server does not work -- they are in the process of "improving" the site. You can try the UK mirror. I personally think the recent changes in the report server are a step backwards but what do I know.

http://naca.central.cranfield.ac.uk/

It still has the old interface and lets you search on key words.

Larry

[masterp2]

Thank you. I thought I would mention, I used to fly B-52G models, which had WI for takeoff high GW.

10,000 lbs of water in 90 seconds (8 engines). I'll have to break out the manuals and look at where the rings were placed.

Funny looking at typewriter print. Now on to the patent office website to scout out other ideas.

[doctorfrag]

This thread really has been one of the most impressive threads I have read, thanks to all for a read, that has led me to getting littel work done this afternoon! :wink:

However, apart from a couple of subjective reports, there does seem to be little objective evidence for the use pre-impellar in cars, such as rolling road printouts etc.

I currently am running a Fiat coupe 20vt with a T28 hybrid 60 trim comp wheel, EVO6 uprated IC and aqumaist 1s system with DDS2.

I can run 340bhp with some mild detonation, 320bhp without, and have trimmed the base ignition map back to 303 bhp for safety.
However, although I get excellent spool up, just over 3000rpm, my current turbo simply runs off the edge of its comp map at 1.3bar and 6000rpm, and as you see torque drops off post 5500rpm quite dramatically.



The Top line

I've been thinking of increasing my jet size from 0.4 mm to beyond 1mm to get on top of the detonation, but this thread got me thinking as well. I could inject pre-impellar, and as well as cooling the charge, I will increase my relatively (still small) turbo efficiency, and keep the same sppol-up, sounds all too good to be true!!

I would activatee it on boost says over 1 bar like I have at the moment and I can place it about 15" pre impellar.


Main concern will be as my IC entrance and exit are lower than the turbo ,will I run a risk of my IC simply filling up with condensed water?, and then running a risk of hydrolastic lock?

If I do this, if I have the money for experimentation, then I will run RR power graphs before/after so we can some objective results

Joe

[Richard L]

Near the bottom of this page, it shown power increase and temperature reduction also.

http://www.aquamist.co.uk/phpBB2/viewtopic.php?t=645