MRT - Intercooler water spray, how and why

I have been pondering the real benefits of ICE on its own, Ice in the water or JUST water (grin) for water spray kits, and after Tony's comment on this, I had several people ask of the benefits..

It took me some time to detail and technically prove what's worth it and what's not, my own experience tells me what does and does NOT work, but to build confidence in readers here is what I have found......

Whilst we used ice on the "IC" (Intercooler) at events like the Dutton rally, this should NOT be confused with the use of water on "normal road / track use" water with ICE or water with say, methylated spirit like some do.

If you have a front mount IC read JUST the way a IC works only (lucky you!)

Here is the details

Use ICE....

When you have a short run and the car has no time to flow enough air to take advantage of the evaporative benefits of water, (IE a motorkhana)

Or you have high soak down of engine bay heat, (IE a drag) in this case you would benefit from the ice THEN the water spray towards the end of the run.(if you don't get disqualified for dropping water!)

Also ICE can be a good alternative if you are on a Dyno for short run, BUT use water if its a long run and you have GOOD air flow (see notes)

Be careful when using the ice as you can EASILY bend the fins on the IC, best is crushed ice and literally throw it into the bonnet scoop to get it to the very back of the IC (see how an IC works) then all the way to the front so the WHOLE 'hole' is FULL, DON'T open the bonnet!

If you are doing a motorkhana and the first "test" has heavy braking use race tape over the bonnet scoop or the ice will slide out forwards!!!!!

USE Water

When you are on the track as the ice wont last

When you have problems with dropping water initially (some drag events)

Use water spray 'initiation' TEMP dependant (if you can) not BOOST dependant as often boost does NOT relate to IC heat!

We will have some (very) technical data from a friend at MoTeC soon who is logging IC temps via a MRT water spray kit and a MoTeC ADL (dash!)

MRT Water Spray Kits - a customers comment

NOTES

Dyno's.....ice is ONLY good for about 1 minute and it has little soak down thru the IC [see IC how it works] (if its still in the plastic bag) [common]

Water is best esp. if you have manual control of the spray kit and have GOOD air flow, (IE on the MRT Dyno we fit a HUGE "pre" scoop to the bonnet to 'ram' more air into the top mount (MRT) Intercooler. With water spray on all the time and high load conditions (20 psi boost and 7000 rpm) the IC and water spray will comfortably hold a REAL inlet temp of around 70 deg.

If you have a std IC and or no water, you will be lucky to get one power run at this level before the IC is so hot you would get 3rd degree burns off it. [ and the engine starts to pre detonate]

Surface area of the IC is often forgotten, the REAR underside (or entry point) of the IC is where all the hot inlet turbo (heated) air comes in, so this is where you SHOULD direct most effort (IE water spray) the TOP 20% of the IC does approx %80 of the work due to the fact that when the [scooped inlet] air passes THRU the core the lower portion of the IC has an increasing level of heated air to try and soak up the heat INSIDE the IC.

SUMMARY the back TOP of the IC is where you get most cooling, the front bottom is least, and somewhere in between is a complicated graph that a tech head could create if they had all the whiz bang temp probes to check it! <GRIN>

WHY adding ice is not worth the effort

The specific heat of water is 1 calorie or 4.184 joules absorbed to HEAT 1gram of water by 1degC

The latent heat of water is 540 calories or 2260 joules absorbed to EVAPORATE 1gram of water.

In other words the heat absorbed by water is negligible (in massive volume sense NO evaporation) BUT when it is evaporated the benefits are huge.

around 5 to 10 times greater

Misting of water is important but not at the expense of reduced volume!

Being GENEROUS, the use of ice water in an I/c spray reduces spray temperature from PERHAPS 34degC to 4degC. This gives an absorption benefit of 30 calories or 125 joules per gram of water. Sounds impressive? Not REALLY.

This is a gain of less than 5% on the 606 calories (540 + 66) absorbed by 1gram of water at 34degC.

Brett Middleton
MRT performance

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