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Originally Posted by JohnA
...Or more accurately, which one has the highest latent heat of evaporation?
I'm talking to a NOS guru and he insists that nitrous would far outdo WI as far as charge cooling is concerned. (gas is cooled down to -128F blah blah...)
But is this true, if we also take in-cylinder cooling into account?
Cheers
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One other thing you have to take into account when comparing the two:
The nitrous oxide will only absorb heat during the expansion phase - ie at the point of evaporation. Any further cooling effect will only be in gasous state (no latent heat of evaporation), it will be very similar to blowing cold air into a cluster of hot gas, the effect will be proporational to the ratio of the two gases.
Water on the other hand, is injected in liquid form. Cooling is taking place during the entire journey into the engine until it comes out of the exhaust.
In my opinion, without any mathematical proof, just a hunch - water will cool more than nitrous per unit mass - can't wait for the next post to tell me the contrary.
There are a great deal of mis-information out there when pushing a product for the innocent Joe public. As JohnA mentioned...
charge cooling is concerned. (gas is cooled down to -128F blah blah...) ...
The fact the figure of -128F is mention, the human brain will aurtomatically conclude that nitrous is a better intercooling coolant than water.
There are two types of nitrous injection system on the market:
1) The traditional (USA) type delivers and meters the gas at the point of injection, ie the restrictor is placed at the inlet runners - an eight cylinder engine has eight jets with inbuild restrictor. This type will give good cooling effect as the liquid nitrous enters the inlet tract is still partially liquid, evaporation is taking place there - the rule of latent heat of evaporation applies.
2) The second type (I am not qualify to judge which is better), has only one restrictor, the quantity of nitrous is metered there and then split into eight un-restricted delivery tubes and fed into the individual runners of each cylinder. This is the very point of my concern about the cooling effect this type of nitrous system. Need to calculate before comparing WI and NI.
Conclusion: since the state change of the second system is remote from the runners, there are no cooling effect by evaporation (excellent cooling properties), only by mixing (not so good, in fact it is pretty poor). So IMO, if the phase change (expansion) is remote from the point of delivery, the cooling is worse than water injection.
I hope there will be more inputs from others and hope that we can leave no stone un-turned on this site - just the bare truth and not just taken for granted that -128F is better.
Thank hodrod for giving some basic properties of the two liquids.