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Old 09-03-2009, 01:46 AM
Greenv8s Greenv8s is offline
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Default charge temperature drop due to WI - any measurements?

I've been doing some estimates of the expected temperature drop due to evaporative cooling from WI. I'm sure this is well known, but I couldn't spot the numbers anywhere so I looked up the specific heat capacity and latent heat figures and tried to work it out from there.

My calculations suggest that with air:fuel:water at 14.7:1:0.1 by mass, the evaporative cooling from the fuel will drop the charge temperature by around 20C and the evaporative cooling from water will drop it by a further 15C or so. (Obviously increasing the fuel or water would increase the temperature drop.)

The fuel cooling figures stack up with well known effects of carb icing, and when I'm running on the upstream fuelling I routinely see frost forming on the intake. I don't have any practical experience to back up the WI figures though, and with the cooling only occuring under boost it's very hard to get accurate figures on the road.

Has anyone tried to measure the temperature drop - is it anywhere close to the figures above?

Not really relevant to the question, but for the curious the engine is a RV8 4.6 with an Eaton M112 producing 8 psi of boost, upstream injection plus port injection managed by MegaSquirt MS1/Extra, WI upstream currently just supplied by 1S but planned to upgrade to a mapped system later. I'm estimating charge temperatures of around about 110C on boost - not good.
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Old 09-03-2009, 02:24 AM
Richard L Richard L is offline
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Calculated values can only be used as an estimate. Rate of evaporation of water is affect by flow of air mass, pressure, humidity and saturated humidity of water/air mix..

Here is a link of a very simple estimation by calculation:
http://www.aquamist.co.uk/website/re...s.html#results
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Old 09-03-2009, 02:27 AM
Greenv8s Greenv8s is offline
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I did look for it in the Aquamist FAQs but couldn't see it anywhere.

My estimates were based on total evaporation in which case the only thing that matters is the relative mass of air/fuel/water.

(In my setup with this mixture, complete evaporation is pretty much certain. Others with lower charge temps and richer mixtures might not be able to assume that.)
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Old 09-03-2009, 02:33 AM
Richard L Richard L is offline
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Try here:
http://www.aquamist.co.uk/website/re...s.html#results


You will not get total evaporation due to the fact that once full saturation has taken place, no more cooling is expected.

It is same as hanging out a wet towel to dry in a 100% Relative humidity environment.
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Old 09-03-2009, 09:54 AM
Greenv8s Greenv8s is offline
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Quote:
Originally Posted by Richard L
Try here:
http://www.aquamist.co.uk/website/re...s.html#results

You will not get total evaporation due to the fact that once full saturation has taken place, no more cooling is expected.

It is same as hanging out a wet towel to dry in a 100% Relative humidity environment.
I understand what you mean, but I would think in this case with air at 100C and relatively small amounts of water being injected that it's safe to assume it will all evaporate.
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Old 24-03-2009, 03:36 PM
stevenlee2223 stevenlee2223 is offline
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hi Richard,

how can i get a HFS-1 kit from aquamist?
i'm in CHina right now.
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  #7  
Old 07-12-2012, 11:14 AM
Richard L Richard L is offline
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Default Re: charge temperature drop due to WI - any measurements?

Quote:
Originally Posted by Greenv8s View Post
I understand what you mean, but I would think in this case with air at 100C and relatively small amounts of water being injected that it's safe to assume it will all evaporate.
Better be late than never.

You may notice the calculation is not based on 100% evaporation but the saturated vapour pressure at a given pressure and temperature. The enthalpy data is taken by a steam table.
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Old 08-01-2017, 12:27 AM
Richard L Richard L is offline
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Default Re: charge temperature drop due to WI - any measurements?

Corrected the link. Post #2,. it now works.
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