Run your car on water? No, seriously.....

[SecondMonkey]

I know there's a ton of "run your car on water" posts here and even more scams to back them up. My idea, however, is completely different.

Let's say I'm burning gasohol in my Jeep. (call it E20 for arguements sake) That means in a 20 gallon tank, I have a full 4 gallons of ethanol.

Now, knowing ethanol absorbs water, what if I actually added some water into my tank ON PURPOSE?!

Wouldn't that increase the fuel volume and provide further mileage? Obviously water doesn't burn, but it would flash to steam. If nothing else I think the engine would be really clean inside, no?

 

[Shannow]

If you add water, you will separate out the ethanol and the petrol, and it will run like a busted ahole.

If you ran straight alcohol, your plan sort of works in racing applications.

There was a system being trialled during the 70s of forming a stable emulsion of petrol and water that appeared somewhat promising.

 

[SecondMonkey]

Hmmm...what about a small water injection at the fuel line right before the injectors? Or maybe a continuous light mist to the throttle body and let it mix in mid air?

 

[chevrofreak]

Originally Posted By: SecondMonkey
Or maybe a continuous light mist to the throttle body and let it mix in mid air?


That's pretty common on high performance turbocharged cars. The mist of water cools the charge down and lets them get by with a bit more boost before detonation occurs.

 

[kd5byb]

Here are my thoughts:

Yes, the water in the cylinder will flash to steam. But, the energy to flash it to steam has to come from somewhere. The energy that is required to flash the water to steam is not available to push down on the piston. So you're getting more expanding gasses, but it's requiring more energy to do so...

later,
b

 

[SecondMonkey]

Originally Posted By: kd5byb
But, the energy to flash it to steam has to come from somewhere.


Hmmmm...how about pre-heated water? My engine has plenty of heat to throw away....

 

[severach]

You could preheat it to 211*F and not gain a thing. It takes more energy to go from 211*F to 212*F than it does to go from 33*F to 211*F. You would need to preheat it above 212*F under pressure and have the pressure release after the valve is closed. I don't see any way to do that.

 

[oilyriser]

I wonder what the octane number blending formula is for water plus gasoline.

A high compression engine can extract more energy out of gasoline, getting better MPG. Water injection would make it able to use 87 octane gas. But you have to maintain a supply, and keep it warm in winter. High levels of EGR can be used to increase equivalent octane effect, but the exhaust gas is dead space and will lower the power of the engine unless you turbo. I think Smokey Yunick must have been using this trick, along with vaporization of the fuel, to build his super efficient engine back in the 70's.

 

[SecondMonkey]

Hmmmm.....ok....how 'bout this?

Install a 12 gallon fuel cell in the back of my Jeep. Design the fuel cell to have a built in paddle to keep the gas/alky/water in suspension with a small motor on top of the tank to spin the paddle.

Just thinking outloud here...

 

[oilyriser]

That might work. The fuel pump constantly circulates gas while the motor runs. If the emulsion partially layers out overnight, you could set something up to run a second pump to mix things up before you start. An ultrasound mixer in line with the pump could keep the droplets small. This would lower the amount of expensive surfactant needed to keep the water emulsified.

 

[lame_penguin]

A little detergent will keep the water in the fuel. I came across a youtube video where someone had the same idea, he was running it through a small generator- the generator gave him the ability to vary the load quite accurately to compare different mixes. I thought that was a slick way to do it.

There's a problem with water injection though, and to understand it you have to be up on phase changes. Above, severach came close: water will exist at 32F, as will ice. The difference between the two is the latent heat of fusion: you have to add heat to ice at 32F to turn it into water at 32F. The same case with water and steam: you have to add the latent heat of vaporization to turn water at 212F to steam at 212F. This latent heat is the difference between the different phases of the same water. (It's also the reason why a steam burn is such a vicious injury- the steam condenses and releases its latent heat, raising the skin temperature far above the boiling point of water).

What this means is that all the latent heat that the water has absorbed in turning into steam is lost from the cylinder, because the water can't condense before the exhaust valve opens.

This is also one of the reasons why a heavier fuel offers the potential for greater economy: CO2, being exhausted into typical ambient temperatures and pressures will give up no more heat in going through a phase change. Burned in the same engine, alcohol cannot offer equal mileage with gasoline because alcohol has a higher proportion of hydrogen to carbon, the same with gasoline compared to a fuel oil.

As a side note, steam engines use a device called an economizer to condense the steam and pull the exhaust pressure down below atmospheric pressure- which, when you think about it, works out equal to raising the boiler pressure by the amount the economizer lowered the exhaust pressure.

http://en.wikipedia.org/wiki/Latent_heat



lp

 

[Shannow]

um..no..

 

[lame_penguin]

No?

 

[Shannow]

Economisers are heat recovery devices in the flue gasses exiting the boiler. They heat the feedwater entering the boiler drum.

Alcohol is already oxygenated, meaning that you need more mass of it to combust with the air that's flowing through an engine

 

[Kestas]

Back in the late 70s, the University of Michigan chemical engineering department was working on a way to make water miscible with gasoline as a way to extend gasoline. This was along the same lines as what secondmonkey suggested... having water in the combustion chamber to take advantage of the waste heat and convert water to steam, aiding the volume expansion from combustion and saving on gasoline. I never learned what came from the study.

 

[Shannow]

Kestas, I remember that in a 1976 (?) Pop science magazine. The emulsification was a coconut based detergent/surfactant.

IIRC, the biggest gain was in having the water improve the octane rating (sans expensive hydrocarbons), allowing a significant hike in compression ratio, and chasing efficiency that way.

Doesn't one of the cam gurus (Crower??) have a "6 cycle" engine ?

Exhaust doesn't open at BDC (or thereabouts), but recompresses it, and adds a squirt of water to extend the power stroke ?

 

[Kestas]

I've always wondered why all engines don't have a water injection system, considering all the benefits. I would like to install one on my car, but the winter season would either freeze the water or force me to dig into my pocket and pay for alcohol antifreeze. I'll bet it's the cold weather the fact that people don't want to be bothered with another maintenance item on their vehicles that is keeping this technology from becoming popular.

I believe water injection is one of the modifications one can make to their engine for real benefits of economy, and not be referred to as "snake oil". Correct me if I'm wrong.

 

[lame_penguin]

Re; economizer- Wikipedia says you're correct. Thanks, I appreciate it. What the heck do they call a condenser that's specifically intended to lower exhaust pressure on a steam engine? Gotta dig out my Audel's book on it and see..

Re; alcohol fuel. Hydrogen and carbon will each release a particular amount of heat when burned, it doesn't matter where the oxygen comes from.

Here's a Wikipedia page that makes the point about latent heat of vaporization carried by steam into IC exhaust:

http://en.wikipedia.org/wiki/Lower_heating_value

Note HHV/LHV. CO is best, because no latent heat is released by the combustion product at ambient temperature/pressure. Hydrogen is worst.

 

[Shannow]

Kestas,
given that you fill the tank with the octane rating that you only need a couple of percent of the time, water injection across the board would be a great idea.

Optimise compression ratio and timing for efficiency, drop octane rating, and use water injection when needed.

Olds tried it with their turboed 215 V-8, but messed it up somewhat by specifying that thei own "rocket fuel" was waht went in the tank rather than water/metho.

People didn't fill the tank, and the concept suffered.

 

[Shannow]

lame_penguin, the condenser is simply called a condenser, whether operating at atmospheric, or below atmospheric.

Big thermal stations usually run 6-7kPa absolute in the condenser.

Heat exchange surface is huge (17,000 to 30,000 1"diameter tubes 30 to 50 feet long). A 100(ish) hp liquid ring pump to keep the small amount of air in leakage out.