performance and humidity

Hoofer B · Dec 10, 2019

Just a question for discussion on a cold night. Does the amount of humidity in the air effect how a gas or diesel engine performs. I thought of this yesterday as the temps were in the mid 30's and half foggy and half rainy ( Very damp ). What about in the dry heat of the desert? Thanks, Bill

Richard G. · Dec 10, 2019

Years ago, I always heard engines performed better wih high humidity or rain.
Richard

Adirondack case guy · Dec 10, 2019

Cold damp air expands much more in an engine increasing output more than hot dry air.-------------------------Loren

r.w.b. · Dec 10, 2019

Nite air is much heavier,run a tractor of a nite n watch the flame come out the exhaust pipe unless its turbocharged

Janicholson · Dec 10, 2019

Water injection changes the flame travel and thus anti-knock properties. Water injection was used on kero and distillate engines and gasoline aircraft engines. The water droplets in fog also expand when super heated to steam in the combustion process. Wet condensing air is also probably colder and more dense as well.

Moonlite37 · Dec 10, 2019

To prove it, at least good enough for me, is to look at the exhaust temperature gauge on a diesel. Exhaust temperature increases an a damp night.

wd9garymn · Dec 10, 2019

Many years ago when running dad's M-M pull type combine with wisconsin motor in soybeans in the late evening and getting damp, it seemed that old wisconsin had more power. Gary.

fixerupper · Dec 10, 2019

Back in the days of the 105 Deere combine with the barely adequate 4020 gas engine I could combine corn a twitch faster at night with the cool damp heavy air.

Steve@Advance · Dec 10, 2019

Cold damp air is denser, denser air needs more fuel to satisfy the optimal fuel air ratio, 14.7 to 1.

More fuel/air mix in the cylinder means more power output.

MarkB_MI · Dec 10, 2019

Humidity lowers the density of air. Increased temperature also lowers air density. So hot, humid air is less dense than cool, dry air. That's why internal combustion engines generate more power in cold ambient temperatures.

gab · Dec 10, 2019

I always liked plowing or disking at night. Those old Farmall Ms seemed like they had a little more guts.

4play · Dec 10, 2019

I don't know how anyone can believe humid air is denser or provides better power in a gas or diesel engine vs dry air, that is simply false. Humidity hurts an engines performance regardless of air temps. The engine wants oxygen for combustion , anything else in the air is waste.

kencombs · Dec 10, 2019

IMHO, cooler air is denser, thus contains more oxygen by volume. Humidity decreases O2 content by volume. cool air more potential , wet air less. But when you combine the two, cool and damp air it likely is a net increase.

And, it is confusing as cool night air always feels damp to human skin. But, that may not be really true. Think of it this way, there is usually no weather change effecting humidity coincident with sundown. Just feels that way.

water injection works because it is introduced after the air and fuel is mixed. It work in different ways in different engines. It allows more timing advance on supercharged or turbocharged engines. It was used on early jets to lower power turbine temps and increase thrust through the increased mass of exhaust gases. Anybody remember early b47/b52 or even b707s on takeoff and that huge plume of black?

MarkB_MI · Dec 11, 2019

Regarding humidity: The humidity we perceive is RELATIVE humidity. But what affects an engine's performance is ABSOLUTE humidity. If the dew point equals the current temperature, we have 100 percent relative humidity. Then, as the temperature rises, the relative humidity decreases, but the absolute humidity remains constant or even increases. So even though on a cool morning there's dew on the ground, the air is still fairly dry in absolute terms. Engines like cool, dry air.

showcrop · Dec 11, 2019

(quoted from post at 16:40:14 12/10/19) Nite air is much heavier,run a tractor of a nite n watch the flame come out the exhaust pipe unless its turbocharged

At the night tractor pulls you always see some, including plenty that are turboed, shooting flame, but very few in daylight. I see flame from my Ford's stack only at night.

Geo-TH,In · Dec 11, 2019

The efficiency of an engine has something to do with the difference between the thigh and low temps.

I WW 2 water injection was a short term post in hp.

Not scientific, I feel I get better mpg when it's raining or foggy.

dr sportster · Dec 11, 2019

Tell it to a million drag racers with sling psychrometers. Humidity matters.

Super H Mike · Dec 11, 2019

I certainly notice a difference on my high performance vehicles, always feel a bit soggy or lazy on hot humid days. Nice cool dry nights and they feel very crisp. 1970 Chevelle SS big block, and an S10 PU with a hi revving 327.

dr sportster · Dec 11, 2019

Sling psychrometer
Untitled URL Link

Brian G. NY · Dec 11, 2019

(quoted from post at 18:47:04 12/11/19) I certainly notice a difference on my high performance vehicles,

Interesting, I noticed it most back when I had a '51 Ford convertible with a stock flathead V-8.
That engine was just marginal for that heavy car.
Because I live in the hills, it is easy to notice differences in performance when climbing the same hills day after day.
Absolutely more power with high humidity and especially rain.

performance and humidity

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