latent heat - ? for engineer

[brett_celicacoupe]

im still looking through notes etc....

but a novel way to implement WI is to connect a boost line to your WI tank and then inject upstream of your compressor (turbo or SC). this given proportional injection of water to boost

ie WI tank pressurises and pushes water out. only issue to atomisation may not occur so well at low boost levels

[JustenGT8]

Yeah but have you seen what WI does to a comp wheel...water jets are pretty effective

My existing setup is well proven with the TT, just a matter of optimising for an SC.

[brett_celicacoupe]

take ideal, no real world stuff...
big horsepower car say 30kg/min of air? (garret turbo map for GT45 in the sweet spot) = 0.5kg/sec air
specific heat of air - approx 1 kj/kg.K
say 90 degrees sc outlet down to 40 degrees?
q=m.Cp.deltaT = 0.5 x 1 x 50 = 25kJ/s = 25kW

Vaporisation heat - 0.5kg/s sec of air @ 9:1 AFR = approx 0.06kg/sec fuel.
Assume 100% vaporisation with ethanol value from wiki...
latent heat = 920kJ/kg
q=m.latent heat = 0.06X920=51kJ/sec=51kW

Compare the two and add real world factors as well as revising your air flow and cooling needs. It looks though like E85 should take a fair bit of heat out.

Equivalent petrol vaporisation heat...
0.5kg/s air @14.7 AFR = approx 0.035kg/s fuel
latent heat (wiki) = 430kJ/kg
q=m.latent = 0.035 x 430 = 14.6kW, which is 3.49 times less than the ethanol example

Anyone need to correct my math?

0.5kg/sec is prob a little extreme.

So, an engine with a target peak horsepower of 400 Hp will require 36-44 lb/min of airflow to achieve that target

convert this to SI..... approx 0.0757kg/sec per 100hp

rest of your math looks about right

[brett_celicacoupe]

remember for a supercharger, since its displaces a fixed volume of air its desirable to increase the density as much as possible. ie drop the temp as much as possible

[oldcorollas]

before da pump you mean?

[JustenGT8]

remember for a supercharger, since its displaces a fixed volume of air its desirable to increase the density as much as possible. ie drop the temp as much as possible

That's a good point, lends weight to going both pre and post SC. I hope to have a plenum to test fit today so will suss out mounting points for the nozzles next

[oldcorollas]

what about injecting E85 pre-SC? potentially explosive, but its higher vapour pressure may be more effective in cooling than the water spray. As it would only be used "on throttle" might be ok as long as there are no backfires
would be good to have a second injector table with maybe a single injector pre-SC, so you could phase it into the main map with throttle

[JustenGT8]

The WI is actually 50:50 water/meth spirit ie E50 without the petrol No way would you run E85 pre SC...turn the car into a bloody big bomb!!

[o_man_ra23]

Query here... What effect will the water mist have on the SC rotors with respect to corrosion?? If you have steel based rotors, and the water is allowed to settle on the rotors at the end of your drive, and then due to whatever circumstances the vehicle sits for a month before starting, will you not then have the opportunity for pitting??

Of course, if you kill the WI and allow enough run on time to clear any water mist leftover, you should be fine, but still something that perhaps should be considered if you are going to run the WI pre-SC...

[oldcorollas]

the rotors and the casings are almost always aluminium alloys, sometimes with resin coatings..
is a good point.. you don't really want pooled water in there for long.

[JustenGT8]

Any half decent rotor is coated so no worries there....plus WI is well off by the time you shut the engine off.

[oldcorollas]

but the casing isn't, nor are the end plates? but yeah, common sense driving should prevail

[trdee]

but some people like accelerating at full throttle into their driveways!!

and hence the turbo timer was born

back to my previous question; what sort of temperature rise are we expecting to see across the supercharger brosef?

[JustenGT8]

Lots...it's a more eff model than an old skool SC14 or M112 but it's not a twin-screw

Could easily be 150 deg C with no WI

[boxh34d]

Thread dig:

Justin, what sort of pre SC water flow figures are you looking at, in comparison to post?