Humid Weather Effect ?

marc hildebrant

marc hildebrant

Well-known member
Group,

I had the 31 Tudor out for a ride today. I live in Minnesota and drove on highway 13 near the Mississippi River.

I noticed that I was able to drive at 50-55 MPH with very little vibration. The air was really heavy due to a pending storm.

The car seemed "smoother" than normal....humis air a factor ? I know that water injection was used at times.

Marc
 
I thought the main purpose of water injection was to cool combustion temperatures much like nitrous oxide so you could run higher compression and or boost?

Though I can see humid air causing it to run richer due to less oxygen.
 
Actually, when air is cooler it becomes more dense and more can be brought into the engine on the intake stroke. This would make the engine run leaner. The increased water vapor content on humid days decreases the precombustion tendency found in lower grade gasoline. In small amounts, water has the same effect as a higher octane gasoline. When A models and gasoline tractors were state of the art machines eighty years ago, octane ratings for gasoline were questionable at best. Water injection was an accepted method for overcoming lower grade fuel precombustion or "spark knock". Many tractors such as a John Deere D had valves that allowed water to be introduced into the combustion chamber right out of the cooling system. On a Rumely Oil Pull tractor, the Secor-Higgins carburetor contained two chambers. One was for fuel and the other was for water that was carried in a separate container above the fuel tank. Both chambers used needle valves for adjusting fuel and water ratios to attain the optimal mixture to produce power with no knock.
John W
 
So.....I didn't change the GAV setting and I didn't change my normal position on the spark advance. Why then did the motor run smoother ?

Marc
 
Chris Pelikan, who rebuilt my Zenith a few years back, said that with the humidity in South Georgia, I'd rarely have to run more than a 1/8th turn on the GAV.
 
marc hildebrant said:
So.....I didn't change the GAV setting and I didn't change my normal position on the spark advance. Why then did the motor run smoother ?

Marc
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When I was a teenager I was told that the water vapor turns to steam during combustion and the steam would give the cylinder more pressure, which means more power.
 
I stand corrected.

I still wouldn't think there is enough expansion in such a small amount to matter though.
 
MrTube said:
I stand corrected.

I still wouldn't think there is enough expansion in such a small amount to matter though.
Click to expand...

I think the expansion ratio is one cc of water turns into 1600 cc's of steam. So, a little mist can have a big effect.
 
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But that water mist absorbs a lot of heat as it turns to steam ("latent heat of vaporization" as I recall?) so with less combustion heat there will be less pressure on the piston, so likely no gain. Now for some speculation, no science: Which idles smoother, an engine with high compression or an engine with stock low compression? If it's the low compression one, it's because of the lower cylinder pressure when firing; combustion is 'lazier', if you will. Maybe it's the same effect on a humid day; the humid air is 'calming' things down. Question: On a cool, humid day air is denser, as noted in a previous post, so more oxygen is available in the cylinder. BUT, the water vapor is displacing (or replacing) some of the oxygen in that cool air, so do we have a net total of more oxygen in the mixture, or less? Are we running richer, or leaner? I don't have the answer but imagine there are charts that spell it all out somewhere.
 
Didn't WWII fighter aircraft have a water injection system that the pilot could use now and then to get a horsepower boost? Seems like I read that somewhere.
 
40 Deluxe said:
But that water mist absorbs a lot of heat as it turns to steam ("latent heat of vaporization" as I recall?) so with less combustion heat there will be less pressure on the piston, so likely no gain. Now for some speculation, no science: Which idles smoother, an engine with high compression or an engine with stock low compression? If it's the low compression one, it's because of the lower cylinder pressure when firing; combustion is 'lazier', if you will. Maybe it's the same effect on a humid day; the humid air is 'calming' things down. Question: On a cool, humid day air is denser, as noted in a previous post, so more oxygen is available in the cylinder. BUT, the water vapor is displacing (or replacing) some of the oxygen in that cool air, so do we have a net total of more oxygen in the mixture, or less? Are we running richer, or leaner? I don't have the answer but imagine there are charts that spell it all out somewhere.
Click to expand...

From the weather side, rain=low pressure area (counter clockwise rotation Low). If the water vapor in humid air displaced the OH-TWO, would that be the same as a lower pressure as you climb a mountain from sea level to X-thousand feet? I don't think you can "replace" OH-TWO, but you would certainly see it spread out more.

The heat would make all molecules more active than at a lower temperature, although H-TWO-OH does some funny things at freezing.

Perhaps it is anti-matter, anti-OH-TWO??
 
Michael in Sedona said:
Didn't WWII fighter aircraft have a water injection system that the pilot could use now and then to get a horsepower boost? Seems like I read that somewhere.
Click to expand...

I believe the water injection was always on and it was to cool combustion temperatures the same way nitrous oxide is commonly used these days. They were running high compression and quite a bit of boost trying to get every ounce of power out of those engines and the gas octane which if I recall was well over 100 just wasn't enough.

I'm not 100% sure on this but its what I can remember. :(
 
It's a physical chemical kinetics thing. Combustion consists of several so-called elementary step reactions. A small amount of water vapor in the air-fuel mix catalyzes some of these combustion reactions, resulting in a smoother burn.

I've noticed what you're talking about many times. On the real damp days (assuming car starts), it just seems to quietly purr along.

Steve
 
On unrestored (or older restoration) vehicles, humid, rainy days make for a much quieter car due to the wood swelling slightly and getting rid of a lot of rattles. My 29 CCPU always felt better on wet days; don't think it was running any better, but it was always a lot quieter and felt smoother.
 
Group,

So.......if the car engine runs smooth on humid days (Mine sure Does), does that mean that I could make the car run smooth on dry day's by having the engine ?

Balanced ?

Different Carb Mixture ?

Different Spark ?

I would like to have this smooth operation all the times, as it was great to cruise at 50-55 MPH.

Marc
 
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