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Old 06-25-2010, 08:59 PM   #11 (permalink)
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Smile impressive maths..

Ok... you trumped me on the maths.. lol

If I ever get my car running on vapour (which I am putting
a lot of time into) then I will be quite happy to use the 60L
fuel tank for water and have a 1.5 gallon fuel tank for the
400 mile range.

Also, I've worked out that there is extra space under the
front wings over the wheels for extra water tanks that
won't be seen.

Thanks for helping out with some equations... :-)

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Old 06-25-2010, 10:21 PM   #12 (permalink)
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Originally Posted by Daox View Post
I don't think you'd ever want nearly that much water injected into the engine. In fact, I don't think you want to inject much at all. If the point is to create steam from the water so the expansion of the steam aids in powering the engine, you want to inject already hot water (easy enough, just use coolant to heat). But, you don't want to inject a ton because the phase change takes quite a bit of heat energy to complete. You might end up just cooling down the combustion, not turning much water to steam, and thus loosing power and decreasing efficiency.
I agree, and with what you said earlier. Water vapor isn't combustible and so acts as a buffer in the chamber, which slows the burn speed, or flame propagation as some call it. This is generally bad, especially during times of loading when power is needed. The system would have to be programmable to coincide water delivery with the proper conditions.

Liquid water would necessarily need to be introduced into the intake manifold in the presence of low pressure to ensure that it is vaporized. You would need a pressure switch to cut delivery at a certain pressure level in the manifold so water would not pool there. A sink at the bottom of the intake manifold would also be a good idea to protect the engine.

The main advantage of water injection is that it allows you to take advantage of much higher than normal cylinder pressures. You see it used in boosted applications, but you could also use it with high static compression ratios as an anti-detonate. Using water injection in combination with a high static compression, and low octane fuel is a winning combination for FE. This has been proven by the work of David Vizard in the 1970's, (book: "Performance with Economy").

As was stated, injecting liquid water into the chamber will absorb a significant amount of combustion heat, which will reduce power as well as slow the flame travel. Ideally you'd want vaporization to take place by the front side of the intake manifold (throttle area), in order to ensure good distribution, and to take advantage of increased mass in the intake ports/runners.

I have done very little with water/steam injection myself.
I have noted differences in power, FE, and detonation/knock (or misfire) threshold with changes in relative humidity.

As for FE, the higher humidity is bad at times when you need the power, but can be good when little power is needed (driving condition dependent).
A car running stoich (closed-loop), but with the maximum possible spark advance can see a gain in FE due to increased humidity. That's not to say that you couldn't get the same FE gain or more by improving the tune without the humidity.

I've also noted that it's common to see a FE improvement while doing test loops in the rain. I'm pretty positive that the gain comes from reduced rolling resistance rather than the increased water in the air. The rain usually cools the air, and actually reduces the relative humidity in a lot of cases.

If you make a water system and test it thoroughly I'd love to see the results.
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Old 06-26-2010, 01:13 PM   #13 (permalink)
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Originally Posted by mpgx2 View Post
Ok... you trumped me on the maths.. lol

Thanks for helping out with some equations... :-)
...ironically, I found MORE useful information about evaporative coolers (aka: swamp coolers) from the Aussie websites than from USA websites!

...it gets hot here in Tucson (117°F record) and Phoenix (122°F record), AZ, but Australia is definitely HOTTER...at least according to "Crocodile Dundee" (ha,ha)!

...back during the OPEC oil embargo, I tried water-vapor injection (ala' "bong" for the engine) using both plain water as well as water-alcohol, but never achieved ANY true success...and, eventually, finally ended up with burnt exhaust valves for my multitude of 'testing' efforts.

...at that time, I was working for the USArmy Automotive-Tank Command in Yuma, AZ, at their Yuma Proving Ground...and was able to "try" LOT's of different things...with access and usage of ALL the appropriate equipment, including thermocouples (temperature), manometers (manifold pressure), prony-brake chassis dynamometer (rear wheel HP), and 5th-wheels (speed) on the 2.2 mile test track (during lunchtime).

...needless to say, I attracted LOTs of curious "lookie-louie" people, from electrical engineers thru nuclear engineers, but it was the mechnical engineers who shook their heads and said, "...no way son..."--and, sadly, they were right. Two burnt valves (on a four cylinder Pinto 1.6L FOB engine) ultimately convinced me they were correct.

...I finally, ended up, "...doing it..." (achieving MPG) the old-fashioned way, by doing things mechanically: front chin spoiler, lower gears (3.55 down to 3.18), electronic ignition (vs. breaker points), and headers (long, long, 4-tubes) and free-flow muffler. Got her from 24 mpg up to 36 mpg.

Last edited by gone-ot; 06-29-2010 at 09:48 AM..
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Old 07-07-2010, 05:53 AM   #14 (permalink)
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so are you saying on a NA engine, leave water injection alone? or would i be wasting my time?

untill now i've been concentration on the wai,

here's a picture of the new setup

the airbox has a vacuum opperated valve that toggles between wai and cai intake, but only at startup, so i think there's a thermostat somewhere in the throttle body where the vacuum hooks up.

i initially used a pvc tube to hold open the WAI valve but it melted and got distorted so the valve closed again. this new version is made from aluminium, but it's also makes for more opening than before, wich hurts acceleration, so prehaps i have to scale it down a bit. ideally i'd like to retain the throttle link trough the engine vacuum the the wai would close gradually under increased throttle pressure.

on the other hand this setup opens both intakes so should reduce intake restriction also.
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Old 07-07-2010, 09:44 AM   #15 (permalink)
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Cool Arduino (ie scanegauge) Water Injection Template

I've been hacking together a basic water-injection system for Arduino.

The latest project source is kept at:

djlyon / mpgx2 Vapour workbench / source — bitbucket.org

Here's the original code. It's a template for a PDE. It will go into a code generator later.

Basically, dependent on rpm and injector-pulse-length, you will want to change
up and down the value going to your electric water pump with a misting nozzle.

// mpgx2 Water Injection Template
// based upon the script located at:
// Arduino playground - ReadingRPM

volatile byte rpmcount;

unsigned int rpm;

unsigned long timeold;

unsigned int WI_PWM_PIN = 3 // The PIN that our Injector pump is on

void setup()
attachInterrupt(0, rpm_fun, RISING);

rpmcount = 0;
rpm = 0;
timeold = 0;

void loop()

if (rpmcount >= 20) {
// Update RPM every 20 counts, increase this for better
// RPM resolution, decrease for faster update
rpm = 30*1000/(millis() - timeold)*rpmcount;
timeold = millis();
rpmcount = 0;

// Update the Water-Injection pump
pwm_level = calc_wi_pumpspeed(rpm,fuel_flow);

// Write that value to the water pump pwm
analogWrite(WI_PWM_PIN, val);


void rpm_fun()
// Each rotation, this interrupt function is run twice

int calc_wi_pumpspeed(int rpm) {

// Customise the water level to the rpm (and later the injector
// pulse length
val = map(val, 0, 1023, 0, 25);

return val

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