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Old 08-04-2017, 08:13 PM   #1 (permalink)
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Water injection improves MPG?

I understand the basic idea of how water injection works: Water mist gets sprayed into the intake, intake cools off, combustion temp drops, the chance of knock decreases. But would that actually mean better MPG with no other changes? I know that water injection would allow for more ignition timing advance, which would improve MPG. But would water injection improve MPG with no other changes? Thanks

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Old 08-04-2017, 08:27 PM   #2 (permalink)
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Water vapor is LIGHTER than AIR, but it does take of space nevertheless, so the amount of oxygen-containing AIR being drawn into the cylinders will go down, the equivalence of running a rich AF-ratio.
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Old 08-04-2017, 08:46 PM   #3 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
Water vapor is LIGHTER than AIR, but it does take of space nevertheless, so the amount of oxygen-containing AIR being drawn into the cylinders will go down, the equivalence of running a rich AF-ratio.
Water is definitely heavier than air. I just know this because there was a huge different in weight when my 20-litre water-tanks were filled with water compared to when they were empty or filled with air. 20kg of difference thereabouts.

Water-Injection works by the water absorbing heat and turning to steam. When water vaporises it expands x1800 times and will give additional driving force to the pistons. That is more power, so you get a lighter throttle pedal and don't need much pedal force to drive around.

I got up to using 50%-water/50% fuel. So for 20 litres of water I used 20 litres of fuel.

The EPA for the vehicle was around 17mpg and I consistently got 21 mpg and the best was 26mpg.

This was on an old Mitsubishi L300 with a 4G63 SOHC Carburator engine. yes, it can work.

Best thing was the improvement in Torque. When the water was on, the engine felt like it gained 2-cylinders because it drove like a 6. You'd turn the water off after getting used to it, and you'd be wondering if the engine was broke because it felt gutless - haha.

However, with EFI vehicles it's harder. The computer will try to thwart all your good idea's. So when I tried on my next EFI car, it didn't work anywhere near as well.
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Old 08-04-2017, 08:51 PM   #4 (permalink)
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Typical water injection systems spray a mist of water droplets into the intake. This mist, consisting mostly of fine droplets of liquid water, doesn't do a whole lot by itself, because typically you'd spray at most a 1:4 ratio of water to fuel. The water mist that does vaporize will cool off the intake charge, but not by a lot. Most of the cooling occurs within the combustion chambers themselves, as the water mist absorbs heat from the charge being compressed, and then vaporizes. If you could optimize the spark and fuel maps to take advantage of this cooling effect, then you could get some modest fuel economy gain there.

Now, you could set it up so that you would inject very hot water into the intake. Although it is counterintuitive, this may also give some fuel economy gain because the hot water mist will more completely vaporize than with traditional water injection. This will displace the air in the intake such that less oxygen is being drawn in than before, and your throttle plate would have to open a bit more to compensate. This would lower intake manifold vacuum, and since the engine would not longer have to work as hard to make that intake vacuum, it would use less fuel than before.

I use a variant of the second type, but I use fuel instead. The 12-hole fuel injectors spay a very fine mist into heated intake air, which causes the fuel to mostly evaporate. This lowers the amount of work each piston has to perform to suck in the intake charge, and has the added benefit of more uniformly mixing the fuel air mixture. I saw a 11% improvement in fuel economy by switching to these injectors, and am going to press on with an auxiliary hot water injection system to verify this idea will work.
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Old 08-05-2017, 12:54 AM   #5 (permalink)
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On diesel engines yes.
On gasoline engines, usually not unless the engine is specially tuned and designed around using water injection because it runs unusually high compression or something else.
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Old 08-05-2017, 06:26 AM   #6 (permalink)
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In a gasser, it's all about how you fool the ECU to adjust the injection to go leaner when water injection is on.
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Old 08-05-2017, 08:02 AM   #7 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
In a gasser, it's all about how you fool the ECU to adjust the injection to go leaner when water injection is on.
Well, I opened the bonnet today on my V6 to inspect if I could find space for Water-Injection and it seems that I was in-luck.

Since it's a sucky V6 (a powerful one), 270hp or so it would be interesting to attempt a Water-Injection build on this car. The car was bought as a muck-around toy rather for any practical transportation use.



It's a 20mpg around town, 30mpg freeway. It would be good to get more.

On such a car it's worth doing. I'm pretty sure that hacking the IAT sensor is the way to temporarily go leaner. But the o2-sensors eventually reset during the calibration phase which I'm led to believe is running at constant speed 80kmh+. I've used o2-sensor extenders in the past, they did achieve a change in economy.

To come will be photo's of it having a Water-Injection system.
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Old 08-05-2017, 09:23 AM   #8 (permalink)
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Quote:
Originally Posted by ar5boosted View Post
I might have been born in the wrong country, because I do love the Holden Commodore.

Quote:
It's a 20mpg around town, 30mpg freeway. It would be good to get more.
Is it manual or automatic? Those mileage figures are quite good for an engine which has around 80% more displacement than the Subaru Impreza that my dad used to have, which got similar mileage figures (only slightly better in city, even though it could get close to 35 MPG while not going faster than 80km/h).
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Old 08-05-2017, 06:48 PM   #9 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Is it manual or automatic? Those mileage figures are quite good for an engine which has around 80% more displacement than the Subaru Impreza that my dad used to have, which got similar mileage figures (only slightly better in city, even though it could get close to 35 MPG while not going faster than 80km/h).
It's a five-speed Automatic that also has like flappy-paddle select like race-car. Gearchange is steering-wheel mounted if you want to use it so not really separate paddles but close.

It also has LSD because trying to be race-car with 190kW. Feels like a Sports car and drives nicely. I just bought it to try to improve the fuel economy tbh and add turbo. It's booked in for Track days in August and September.

Before I do the Turbocharging I'll run some tests with simple Water-Injection. I checked out it's Sensors yesterday which include an AirFlow sensor which would be all I would need to calculate water-flow. I then just need to find the IAT sensor and hook into that.
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Old 08-07-2017, 02:41 AM   #10 (permalink)
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Quote:
Originally Posted by ar5boosted View Post
Before I do the Turbocharging I'll run some tests with simple Water-Injection. I checked out it's Sensors yesterday which include an AirFlow sensor which would be all I would need to calculate water-flow. I then just need to find the IAT sensor and hook into that.
Even with water injection, I hope you don't disconsider getting an intercooler.

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