CorvAircraft> Re: water injection

[Dave Morris "BigD"]

Will you guys have to mix ethylene glycol into your water supply 
while carrying it aloft, so it doesn't freeze?
Has anybody here ever actually engineered a water injection system in 
an airplane, or is this all theoretical?

Dave Morris

At 12:11 AM 8/23/2006, you wrote:
>Dan, Mark, and Clare,
>
>I appreciate your responses to my steam injection post.  It seems my science
>was a little off the mark, so now if you don't mind I'd like to back peddle
>and ask some relevant science related questions.
>
>Yes it is true, water vapor displaces incoming air/oxygen, but is it
>possible that since true that fuel vapors burn more readily than raw liquid
>fuel (fuel "gas" vapors burn, but liquid "solid" fuel do not), wouldn't the
>heat from the high pressure steam cause the partially vaporized fuel coming
>from the carburetor to become more vaporized, thus promoting more complete
>combusion of the fuel/air/water vapor mixture? --And thus somewhat
>increasing (not decreasing) performance and fuel efficency and somewhat
>negating the effect of the "intruding" water vapor in the fuel/air (oxygen)
>mixture?
>
>Good point about the lack of vacuum at wide open throttle Mark.  Installing
>a vacuum switch that activates at low manifold like the one you had on your
>Karmann Ghia is a very good idea.  I guess the main reason I am shying away
>from a direct water injection-type system is because I read on the website
>that I mentioned before (http://www.better-mileage.com/water4.html ) and
>other water injection websites that unless a very high pressure pump and
>very fine water injection nozzle (read expensive) are used, spraying a
>straight jet of raw water into a carb or manifold doesn't do a great deal of
>good in a full-time water injection system in a normally aspirated engine.
>Supposedly most of the water puddles in the bottom of the manifold until it
>boils off.  Don't get me wrong, I realize the (full time?) water injection
>system you had on your Ghia worked very well for your purposes.  However, my
>guess is that a steam injection-type system might be a slight improvement
>over a windshield washer injection-type system.  --Understand I am not
>trying to step on your or anyone's toes here.  I'm just tryng to find
>balanced and educated answers to my questions.
>
>Related stuff to chew on from the steam injection website:
>
>      Admitting liquid water into a vacuum line doesn't work. The resulting
>droplets are way too large and rough running will result. The exception to
>this is in a turbo vehicle with the water admitted before the inlet turbine.
>The high speed turbine blades chop the water into a fine mist. This is not
>recommended though because the turbine blades can be rapidly eroded.
>
>        Steam injection is what we have had the most success with. You can
>inject useful amounts of water as steam, without the problems associated
>with large water droplets. Exhaust manifold heat is used to boil water which
>is then admitted to the inlet manifold. The key principle here is that the
>steam, upon mixing with the cooler air and fuel mixture, will condense into
>a dense fine cloud prior to entering the cylinders. Being so fine it can mix
>and distribute evenly. Another benefit is the condensing steam liberates
>heat which helps to vaporize the liquid fuel droplets.
>
>       Since we are boiling the water under quite high vacuum, the
>temperature doesn't have to reach 212 degrees F / 100 C to begin boiling.
>
>
>Thanks,
>
>Doug
>
>
>Doug Naylor
>Arkansas
>Wittman Buttercup
>
>
>
> >From: "Dan Benson" <DBenson at oceaneering.com>
>
> >Water vapor in the incoming air displaces oxygen (Boyles Law?) and
> >reduces the available power.  To make up for the loss of oxygen the WWII
> >pilots increase the manifold pressure.  The methanol increased the
> >octane of the fuel.  That throttle wire in the Corsair was for a reason.
> >
> >
> >In a normally aspirated Corvair engine, water injection will reduce
> >power.  In a detonation situation, it might help maintain power....that
> >is you dont have to back off the timing etc.  Trade-off type of thing.
>
> >From: "Clare Snyder" <claresnyder at rogers.com>
>
> >main advantage of steam injection verses water injection systems is that
> >steam supposedly mixes with the fuel/air charge more readily than straight
> >water injection.  Apparently the heat from the steam makes for a more dense
> >fuel/air mixture.
>
>You've got your physics mixed up. Heat makes a LESS dense mixture.
>
>Best to inject it just before the intake devides into two unless you can
>meter and inject just before the intake ports (then best if timed injection,
>but not necessary) and have the water ONLY inject at high power settings
>(high manifold pressures) You want it evenly distributed, finely atomized,
>and injected into high velocity air where it is unlikely to "puddle out".
>
>
> >From: "Mark Langford" <n56ml at hiwaay.net>
>
> >I assume you meant that a low vacuum signal will be used to activate a pump
> >to inject the water?  Because I'm sure you know that at wide open throttle
> >the vacuum is pretty low and wouldn't suck any water when you needed it
> >most.  You'd be sucking a bunch of water at idle, which would not be good.
> >I used injected water in  my Karmann Ghia when I lived in Las Vegas due to
> >the 9.9:1 compression ratio that I first built the engine with.  I was
> >using
> >the wiper washer method and a vacuum switch that activated at low manifold
> >vacuum.  It worked great, and as has been mentioned, when I tore it down to
> >upgrade to larger valves, the heads and piston crowns had no deposits of
> >any
> >kind on them.  I love the stuff....
>
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