REFLECTOR: Water injection

Geoff Gerhardt geoff.gerhardt at gmail.com
Fri Apr 4 09:03:05 CDT 2014


Guys,

Attached is a NACA report on water injection.  It was used in WWII by the
air force to provide short bursts of increased power for use in dog fights,
short take offs and the like.  Old, but it contains lots of good,
fundamental info where they talk about optimal water/fuel ratios for
increased power, best fuel economy (through use of advanced timing).

I am going to order a water injection kit meant for automotive use.  Drag
racers use water injection quite a lot.  It has a controller that has a MAP
input and it will vary the injection flow based on MAP.  I'll do some
experimenting and let you know how it works.

Again, I'm new to this - anyone with experience or knowledge in water
injection, please weigh in.

Thanks.

Geoff



On Fri, Apr 4, 2014 at 9:52 AM, Geoff Gerhardt <geoff.gerhardt at gmail.com>wrote:

> Richard,
>
> I run LOP for every phase of flight except take off and climb.  I have a
> Dynon Skyview panel that gives me all the engine data, plus I've installed
> an air-fuel monitoring system that tells me the exact air/fuel ratio I'm
> running at.  Rather than using EGT to find LOP, I just pull back the
> mixture and watch the AFR - very slick.
>
> Running LOP in cruise significantly lowers CHT's, but in climb, it doesn't
> lower temps.  I'll easily go over 400F if I use LOP on climb.  I think the
> climb attitude/speed does not produce enough cooling air flow in my
> configuration.  That cooling that comes from evaporating excess fuel seems
> to be very effective.  I think I will be able to get that same cooling with
> water injection, but with much less water flow.  Back of the envelope
> calculations - on full-rich climb, I'm burning ~12-13gal/hr where as in LOP
> I'd be burning ~8-9gal/hr.  So, I'm using ~4gal/hr for cooling.  Water
> should provide better cooling than fuel, so I'm guessing that I'll be able
> to get away with half that flow, say 2gal/hr water to provide equivalent
> cylinder cooling.  So, a 15min climb would require less than a gallon of
> water, so a 5gal tank would last for several flights (could probably get
> away with a 2gal tank).
>
> Geoff
>
>
> On Thu, Apr 3, 2014 at 11:59 PM, Richard J. Gentil <
> richard at naples-air-center.com> wrote:
>
>> Hi Geoff,
>>
>> You can achieve better cooling by climbing using lean of peak mixture
>> setting if you have an engine analyzer especially with a turbo charged
>> engine. If you are still a little too warm you can pull back the prop a
>> little. The less explosions per minute, the cooler the engine will run.
>>
>> Richard
>>
>> Sent from my iPhone 5 Classic
>>
>> > On Apr 3, 2014, at 10:41 PM, Geoff Gerhardt <geoff.gerhardt at gmail.com>
>> wrote:
>> >
>> > Guys,
>> >
>> > I've been considering using water injection to keep cylinder temps down
>> on climb.  Seems like a better idea than running full rich all the way up.
>>  It looks pretty straightforward, but I'm wondering if there's a reason why
>> others don't use it more.  For those who are not familiar with water
>> injection, essentially, you spray water (or a water/methanol mix) into the
>> intake (typically before the fuel servo).  The large heat of vaporization
>> of water pulls a lot of heat out.  Plus, you get a bit of a performance
>> boost both by lowering the inlet charge temperature as well as the steam
>> expansion during the power stroke.  Another nice benefit is that your
>> pistons get a nice steam cleaning with every stroke.
>> >
>> >
>> > I figure a 5gal tank would do more than enough for a few trips if only
>> used on climb.  I have had some high temps when cruising at high altitudes
>> as well, which it might help with.
>> >
>> > I'd welcome any
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