Josh:
The problem is that an ultrasonic device does not boil the water, it makes it into a mist. This in itself does not transfer heat. The mist evaporating in the air does, however that removes heat from the air, which goes counter to my end goal. It's great for small droplet size for water injection, but not so much for steam injection.
The latent heat of vaporization of water is 2260 kj/kg
The specific heat capacity of water is 2kj/kg kelvin (or substitute celcius for kelvin.) So preheating with engine coolant is pretty pointless.
Don't mean to sound like an ass, but I've already been down similar roads on pen and paper myself.
Not saying that an ultrasonic mister isn't good for water injection. But if you are going down that road, a jar with a bubble stone routed as a throttle bypass would be much simpler and more reliable in the long run.
Quote:
Originally Posted by drmiller100
if you do the math, it takes a LOT of energy to evaporate or boil water to vapor. Way more energy then exists in the air.
I think the secret to this is to look at what happens on the compression stroke - absolute pressure goes from 10psi to 100 psi or something, and all the vapor turns back to liquid, sucking some of the heat up and slowing detonation.
Then, ignition and everything starts burning. As the fuel and air burn, they give off heat. LOTS of heat.
I think if you had SMALL droplets, this heat would turn the liquid water to steam, giving more thrust on the piston, as well as a LOT more controlled pressure.
Further, this would limit the absolute temperature of the burn event, lowering emissions due to the reduction of NOX.
An absolute win win win for lean burn.
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When the compression stroke happens the water does boil, or more to the point it evaporates due to partial pressures (a fancy way of looking at dew-point or saturation point). Pressure increases, temperature also increases, this causes the saturation point of the air to get higher. The water the seeks a new equilibrium with the air removing heat in the process. The actual pressure changes very little (from the effect of the water that is), but the compression is much more efficient. Any remaining water, and the goal is to have remaining water, is then boiled as the temperature increases as the pressure DECREASES. Leading to lower combustion temperatures. This could all happen with simple water injection if you could insure ultra small water droplets in the combustion chamber, but the intake track is unintentionally a mechanical moisture separator on most cars making for huge amounts of wasted water. Also injecting steam allows you to recoup exhausted heat and preheat your intake at the same time.
The idea is that steam condensing in an airstream produces very small droplets. The smaller the droplet the better the heat transfer and the harder it is to mechanically separate. Add to that the air preheat as the water condenses, and you should have an efficiency booster with it's own anti detonation agent. I'll show my math, but the short story is that you should gain a couple kw of power out of the increased efficiency with a 1gph injection rate.
Quote:
Originally Posted by drmiller100
When done, I think the secret is to inject a bunch of very small droplet liquid water into the intake tract.
Hmmmm.... What do we have which can do this????
A fuel injector. So, we run 50 psi of water to a fuel injector located in the runner right next to the existing fuel injector. Then we piggy back the water injector to the fuel injector.
The more fuel, the more water.
I think twice as much water as fuel is a good place to start, once the engine gets up to speed of course.
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Tried it. NACA tried it as well. It does help when lean burning in the hot zone while increasing fuel economy, but at stoic it does next to nothing, also in the lean burn zone that production cars use it would be pointless as well since the excess air is already taking the excess heat. Also I have inadvertently found out a few times twice as much water to fuel is way too much, both because you will start to have ignition problems and because you won't be able to reasonably carry that much water.
Here is the NACA study on water injection. It took me a whole night to decipher what it meant as the units are both foreign to me and some of them are not in common usage, so let me know if you have any trouble understanding it. It pretty much lays out what water injection can and can't do.
world wide web (dot) turbotuning (dot) net/Artikel/naca-wr-e-264.pdf
I'm sorry if I seem argumentative, but I have been researching this for a while. I've already found a lot of things that either don't work or don't work well. All I need to do is find one that works.
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