Heat Soak?

[Craig.]

  PHANTMXR6 said:

Why do people us water injection?

Got another lame reason for that?

I thought you would never ask!

Water injection works in three ways.

Firstly, when the water is injected into the intake system prior to the cylinder head, the small droplets absorb heat from the intake air. Water has a very high specific heat rating (it can absorb lots of energy while only slowly increasing in temperature) and so the intake air is initially cooled.

Next, the small drops of water start to evaporate. Water has a very high latent heat of evaporation (its change of state absorbs a lot of heat) and so the intake air charge is cooled still further.

Finally, when the remaining water droplets and water vapour reach the combustion chamber, steam is produced. This acts as an anti-detonant and also keeps the interior of the engine very clean, so preventing the build-up of carbon "hot spots".

Water injection was first experimented with in the 1930s. At the time it was discovered that detonation could initially be prevented by enriching the air/fuel ratio. As cylinder pressures rose still further and that approach ceased being effective, the injection of water into the intake air stream was found to prevent detonation. Interestingly, the detonation remained suppressed, even if the air/fuel ratio was then leaned-out. This occurred because the excess fuel was being used to cool the combustion process. When water replaced fuel in performing this function, less fuel was then required.

Anything else you would like to know? What about methanol injection? Research carried out during World War II indicated that pure water is best at suppressing detonation, while a 50/50 mixture of water and methanol permits the greatest power output before detonation occurs. One reason for this may be that the alcohol burns more slowly than petrol, so causing peak cylinder pressures to occur at a later crankshaft rotation, increasing torque.

The question of whether a water injection system can increase engine power is a contentious one. While the intake air will be lower in temperature (and so denser) when a water injection system is operating, the presence of an increased amount of water vapour in the air means that there is less room for oxygen. It is for this reason that dry air (that is, air with a low relative humidity) can allow an engine to develop more power. So when the air is cooler but its water vapour content is higher, will more power be developed? If no changes are made to air/fuel mixtures, theoretically the two factors almost exactly cancel each other out.

This means that if water injection is used without any changes made to the tuning of the engine, improvements in power are possible but not probable. However, if the engine air/fuel ratio is leaned out, or boost is increased, or the ignition timing is advanced, more power is very likely. Supercharged aircraft engines using water injection had mechanisms that leaned out the air/fuel ratio simultaneously with the operation of the water injection. However it is very important to note that making random changes to the air/fuel ratio and ignition timing at high engine loads can be very dangerous for the health of the engine. Such changes should be made with care - it is very easy to blow up a forced induction engine with random leaning of the mixtures and/or ignition timing changes!

Google is your friend!

Edited 06/03/09 12:00 PM by craiginmackay

[Racerx]

Has anyone used or tried a water spray set up on their I/c?

[PHANTMXR6]

Now that's a bit more useful.

Thanks for that.

[bjc]

Blueboost has used the snow performance kits with very good results up in mackay and further north.

In dec 04 I first had my XR6T tuned in brisbane and then was moved to townsville, same tune, same brisbane fuel 4days later I litterally could not drive the car as it would ping its head off once on boost where as flogging it in brisbane had no such side effects.

Even with the townsville fuel it didn't do sh!t all difference.

[RSK]

Comeback of the year.

Ownage.

[jared87]

So can an octane booster or even better fuel compensate for the heat?? With the more octane can it run at a higher inlet temp with more humidity and not retard???