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Author Topic: For and against water injection  (Read 19650 times)
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NathanStewart
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« Reply #15 on: June 11, 2010, 02:01:12 PM »

I've asked in another thread if water injection is helpful for a normally aspirated engine, but got no response.  Anybody care to chime in, and if so, what would be a target ratio of air/fuel : water?

Definitely helpful if you're trying to run a high(er) compression motor on a fuel with a lower anti-knock index (pump gas for instance).  Typical water:fuel ratio for n/a applications is 10-15%. 

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I've read where water injection can cost power because the cylinder volume has less air/fuel mixture.

If this were really true I probably wouldn't have a job.  grin

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« Reply #16 on: June 12, 2010, 01:58:38 AM »

I've asked in another thread if water injection is helpful for a normally aspirated engine, but got no response.  Anybody care to chime in, and if so, what would be a target ratio of air/fuel : water?

I've read where water injection can cost power because the cylinder volume has less air/fuel mixture.

  I've got to learn how to take fotos and post, my chemistry book [ typical effect of temperature on gas volume at 1 atmosphere] two of the 5 examples 

  300 deg kelvin =-----570 ml volume
                                                                V2=VI X T2 DIVIDED T1
  610 deg kelvin ==== 1180 ml volume

  This shows that as air is heated [supercharged in our case] the volume increases but its just expanded air with no extra oxygen molecules and when it is cooled it shrinks, again no extra molecules but it is denser. the shrunk air from cooling [water injection--intercooler--alcohol] allows more air and molecules to be packed into the same space.
  This is why roots style blowers [they heat air more than turbos or centrifugals] are so much better when ran on alcohol than gas.

                         JL222
« Last Edit: June 12, 2010, 02:04:09 AM by jl222 » Logged
hotrod
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« Reply #17 on: June 13, 2010, 12:58:01 AM »

This is a subject that has many twists and turns.

The usual rule of thumb for NA engines is to start at water injection rates of about 10%-20% of fuel flow. As mentioned above, ADI used in WWII aircraft like the Pratt and Whitney R2800 engine used about 50% of fuel flow, with a mixture of 50% methanol and 50% water, and in extreme cold conditions they also had a mixture of ethanol, methanol and water, if I recall correctly it was about 60% alcohol by volume.

http://www.enginehistory.org/Frank%20WalkerWeb1.pdf

Water vapor actually assists in the combustion process, as it facilitates conversion of carbon monoxide to CO2. In lab tests you can take a mixture of dry carbon monoxide gas and oxygen and it is nearly impossible to ignite, but add just a bit of water vapor and it ignites easily. This is one of the pathways that water injection uses to help make more power.

It cools the fuel air mixture by evaporation and due to the high specific heat of water (how much energy it takes to raise a water droplet one degree compared to a similar weight of gasoline). It also takes considerably more energy to evaporate the water droplet, to gas (steam) than it does to evaporate the gasoline droplet.

This means that during the compression stroke the fuel air mixture does not heat up as much due to compression, so the work that used to be spent fighting rising pressure due to heat in the cylinder is spent evaporating the water alcohol mist. This gains engine power by reducing compression losses.

The water does slightly retard the effective ignition due to its cooling effect but in many engines that moves the time of peak cylinder pressure slightly later in the combustion stroke closer to its ideal 12-14 degrees after top dead center for maximum power recovery. Also during the burn phase the water gives back the energy that was invested to evaporate it. It lowers peak cylinder pressure (cooling effect during compression and higher heat capacity), but the steam generated during combustion stretches out the pressure peak so although the peak cylinder pressure is slightly lower the total effective pressure goes up because the pressure does not fall as fast as the piston descends down the cylinder due to waters high specific heat (it has to expand more to cool off the same amount as a normal fuel air charge).

The slightly lower peak cylinder temperature, lowers heat stress, and heat losses to the cooling system, and helps keep valves alive at power levels that would melt them without the water injection.

The evaporative cooling as the fuel air water mist enters the cylinder also increase volumetric efficiency of the engine as the fuel air charge heats up less as it passes the hot head of the intake valve, and cools off hot spots like spark plug electrodes and any other possible sources of pre-ignition.

All these effects allow you to produce more useful work out of the same or even more fuel than you could burn before without killing the engine due to high heat loads.

Larry
« Last Edit: June 13, 2010, 12:59:36 AM by hotrod » Logged

jl222
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« Reply #18 on: June 13, 2010, 02:11:07 AM »

 Hotrod...that reference article about Frank Walker and his work on water injection is one of the best I've ever read.
  It's a must read for anyone interested in water injection and clears up alot of myths.
  150 in [60 lbs boost] and 3800 hp wow!! Also testing for 100 hrs at full military power shocked
  Hey guys if somebody says water injection doesn't make any power, just say how much you wana bet grin

                                       JL222

 P.S.  Wish I knew all about the hydraulic drive for the superchargers on that E model.
« Last Edit: June 13, 2010, 02:17:38 AM by jl222 » Logged
hotrod
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« Reply #19 on: June 13, 2010, 01:56:49 PM »

Yes and that is on an engine that started out rated at 2000 hp, which gives good field validation to test results by NACA that water injection was capable of increasing MEP and power up to 160-180% of gasoline only power on supercharged aircraft engines of the day.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093187_1993093187.pdf

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091074_1993091074.pdf


The primary limit to engine power for most internal combustion spark ignition engines is knock limits imposed by fuel octane and heat limits posed by combustion temperatures. If you don't melt it you break it due to detonation. Water injection attacks both of those problems at the same time, by internal cooling and raising the effective fuel octane very substantially. That is where most of the power gain is. By increasing the effective fuel octane you can stuff more fuel and air into the engine than is physically possible on gasoline only.

Larry
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« Reply #20 on: August 25, 2010, 05:29:03 PM »

For anyone worried about water/meth affecting engine durability, I ran a Snow Performance kit on a TRD  Supercharged Tacoma 3.4L V6  for 140,000 miles. It still ran great when I traded it for my Dodge Ram. In the North in the winter, WalMart sells -30F windshield washer fluid. I would stock up on it, because it worked great and was cheap. I ran an overdrive pulley and the 4x4 Extra Cab truck would run mid 14's, though the suspension was not up to handle the power. I also have installed water meth on a turbocharged Sisu 8.4 L diesel in a working 38' Lobster Boat. This is one of the Northern Bay 38's that I build. It draws 4 feet of water, weighs 18,000 lbs and is 13' 8" beam. With the stock 410 hp diesel we were able to get 35 mph. By adding water meth and some careful tuning we got 41.5 mph and were able to beat smaller boats with 750 hp diesels. I'd say if you are running a boosted motor, water meth is your friend. If the economy was better, I'd trade my hemi Ram in on a Cummins and talk to Matt Snow about a water meth kit.
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« Reply #21 on: August 28, 2010, 05:35:16 PM »

You can still read this - just page down to the bit of rudeness posted by some troll.
« Last Edit: August 30, 2010, 11:03:05 AM by panic » Logged
sabat
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« Reply #22 on: August 28, 2010, 10:25:01 PM »

Roots blowers accept the charge radial to the rotor OD, separate it into two streams, which are conveyed in the concave (female) lobe spaces around the inner wall of the case on both sides, to discharge 180 away. The convex/concave inter-lobe volume is not a factor, but only permits both sealing the rotors to prevent backflow, and prevents interference. All compression (if any) is induced by resistance in the manifold.
Screw blowers (Opcon AB, Sprintex, Autorotor) appear similar, but the principle and flow path are very different. The intake is axial (not radial) to the rotors, with the charge volume contained entirely between the male and female rotors (which is zero at tangency in a Roots). As the charge is passed lengthwise down the case by the helix angle (like Archimede's screw pump), the inter-lobe volume shrinks causing internal compression. Finally, at the "blind" end the lobes rotate apart and expose the charge to the exhaust port.

Spambot?
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« Reply #23 on: August 28, 2010, 10:31:40 PM »

Panic has been on this forum for along time.

Tom G.
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Asking questions is one's only way of getting answers. As a young boy I was always taught that there is no such thing as a stupid question. It suggests that the quest for knowledge includes failure, and that just because one person may know less than others they should not be afraid to ask rather than pretend they already know. In many cases multiple people may not know but are too afraid to ask the "stupid question"; the one who asks the question may in fact be doing a service to those around them.
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« Reply #24 on: August 29, 2010, 01:28:31 AM »

A spambot always has a live link to another website in the signature area.

Pete
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« Reply #25 on: August 29, 2010, 02:25:18 AM »

my experience is the water injection only works in lower boost application..... now if your talking aircraft stuff yeah it would probably work in higher boost especially at altitude where their is no oxygen ... i feel it is a band aid... if your using it to slow burn race then your head squish and piston dome isn't right... if your using it to keep valves from stretching get a bigger stem size or a different supplier.... if your using it to fix a problem then fix the problem right... W I can have too many variables.... man up for the expensive stitches not the band aid.... let me add this, so yer only gonna get so much stuff past an intake port... so if you displace some of that air fuel area with 2 parts hydrogen than that's good right? humm.... don't you 4 stroke guys wanna run in the 12 to 13 AF range?  I mean fuel and oxygen makes the heat and heat is power so.... yeah yeah we can beat this dead horse around for a while..... black/white, Ford/Chevy, Yankees and Raiders still suck..... tonic water with my Gin please!
Kent
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Stan Back
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« Reply #26 on: August 29, 2010, 12:40:16 PM »

"expose the charge to the exhaust port"  -- the exhaust port?
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« Reply #27 on: August 29, 2010, 01:23:48 PM »

Stan,

My advice to you is to ignore the subject of exhaust ports - as we know your problem is on your INTAKE side.
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« Reply #28 on: August 29, 2010, 01:47:27 PM »

"expose the charge to the exhaust port"  -- the exhaust port?

Blower Stan Blower. LOL.

Tom G.
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Asking questions is one's only way of getting answers. As a young boy I was always taught that there is no such thing as a stupid question. It suggests that the quest for knowledge includes failure, and that just because one person may know less than others they should not be afraid to ask rather than pretend they already know. In many cases multiple people may not know but are too afraid to ask the "stupid question"; the one who asks the question may in fact be doing a service to those around them.
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« Reply #29 on: August 29, 2010, 07:59:48 PM »

if you were to inject water into the ex port or ex pipe on a turbo setup, the instant steam would spool up the turbo quickly and possibly out of the boost operating range
kent
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