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Old 03-17-2017, 12:23 PM   #1 (permalink)
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I May Be Wrong About Water Injection WRT Improving Fuel Economy

From the recent vapor carb thread, I got the idea that the fuel economy gain from warm air intakes is possibly due to:
  • Increased vaporization of injected fuel as it hits the warmed-up air, causing more of the fuel to become a gas with its own partial pressure,
  • Causing an increase in the total pressure of the fuel-air mix going into each cylinder on its intake stroke (due to Dalton's Law of Partial Pressures),
  • Thereby reducing the amount of work required to pull the fuel-air mix into said cylinder.

Since then, I've been toying around with this idea, first trying to figure out how to further heat up the intake air without adding too much more complexity, and then last week it hit me - what if did water injection, but with the water (50/50 ethanol/water mix, if you will) already near its boiling point?

I am thinking of using a water injection system, heating the water to near its boiling point using engine coolant and a heat exchanger, and injecting this warmed water into the intake manifold near the intake ports of the cylinders.

The idea is that the heated water will be injected into the intake, near the intake valve, as a fine mist. As it does so, the fine mist will be encouraged to vaporize into a gas because it is already heated and the intake pressure will already be low due to part-throttle conditions.

That will increase the partial pressure of the already-present water vapor, and add the partial pressure of ethanol. Again, due to Dalton's Law, that should increase the total pressure of the gas mixture being drawn into each cylinder, thereby reducing the amount of work the piston has to do WRT drawing in this gas mixture, which will then reduce the amount of fuel consumed.

And it seems that, 35 years ago, the US EPA has already published a paper that shows that this effect does in fact happen. However, they chose to focus on the the drop in volumetric efficiency caused by their methanol injection setup, so they did not evaluate whether this method would increase part-throttle fuel economy.

Methanol Vaporization: Effects on Volumetric Efficiency and on Determination of Optimum Fuel Delivery System

A benefit of this system I am thinking about doing, is that it can be shut off at will, say at wide open throttle, for when full engine power is needed.

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Old 03-17-2017, 03:54 PM   #2 (permalink)
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I thought it was due to fewer oxygen molecules in the thinner air, so that the engine needed to inject less fuel for any given scenario, with the downside of less available horsepower at full throttle.
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Old 03-17-2017, 04:21 PM   #3 (permalink)
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A gasoline engine seeing a benifet from water injection could work it's just not easy and usually doesn't work.
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Old 03-17-2017, 04:30 PM   #4 (permalink)
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Warm air = higher load / less pumping losses
Hot air + freezing weather = quicker warm up

Hot air + water = ????

Normally waters needs to be DI to improve economy a lot.
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Old 03-17-2017, 05:55 PM   #5 (permalink)
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Why not just more EGR?
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Old 03-17-2017, 08:02 PM   #6 (permalink)
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Quote:
Originally Posted by jakobnev View Post
Why not just more EGR?
That only works to a point (before you foul ignition)
but yes, hot EGR heats the intake also
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Old 03-17-2017, 09:25 PM   #7 (permalink)
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I believe water injection has good possibilities for economy and power, but it depends how you inject it!! I'm looking at testing out bubbling the egr through water to cool it down will also evaporating the water to go into the engine!! I believe on multipoint fuel injection it evaporates the fuel by injecting it on the hot valves to better atomize the fuel!?!
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Old 03-17-2017, 10:19 PM   #8 (permalink)
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Not sure if adding steam to the intake flow would be so effective at all to ease the vaporizing of gasoline, even though water has a higher thermal conductibility than air. I'd still remain quite concerned about knocks.
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Old 03-17-2017, 10:38 PM   #9 (permalink)
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Never say never.
I'm going to try to use water injection on my 489 cubic inch big block Chevy with 11:1 compression.
Hopefully it will allow me to run regular gasoline on 11:1 compression and no water injection when I'm just cruising along maintaining high way speed.
When I need a few hundred horsepower then the water kicks on.
Or I buy premium gasoline all the time which is 40 to 60 cents a gallon more then RUG.
So I have pretty good motivation to figure out how to use water injection to make 11:1 compression run on RUG.
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Old 03-17-2017, 11:00 PM   #10 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Not sure if adding steam to the intake flow would be so effective at all to ease the vaporizing of gasoline, even though water has a higher thermal conductibility than air. I'd still remain quite concerned about knocks.
I'm hoping it gives me the 20% water injection will seconding as a egr cooler!! What I'd really like to see is greater power with increased fuel economy and cooler combustion temps all around!! But I think I might have to compromise on one or two of those!! 😋😋

From what I've read you gain no benefit from going over 20% water injection to fuel, or going over 20% egr to intake volume!?!

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