Why so smooth in the rain ?

[Claude]

I've notice that mainy time with different cars they seem to run more smootly when in high humidity condition (when it's raining for exemple).

Is it just an illusion ? If not is there a technical explanation ?

Claude

[neil_004]

I would think it is an illusion. The only technical things I can think of might be lower intake temp or that moisture might provides lower combustion temp allowing a more agressive ignition map (like the EGR system).

[632 Regal]

definetly not your imagination. Not positive of why but the water does somehow help combustion.

[BillionPa]

2 reasons why.

the humidity slows down the combustion rate while simultaneously increasing the amount of fully combusted exhaust.

also it does help lower the pre compression intake temp, which lets more air into the cylinder.

there are probably other reasons, but those 2 are big.

[duby55]

the air is much more dense when humid or raining, thus giving the engine more air. The same guy told me he soaked his air filter in water before he went for an emissions test on his troublesome car and it passed the test , I don't know about that one, it sounded a little wet for me.

[guinness]

Harrier jets use water injection into the combustion chamber to boost power.

[mamilapon]

Harrier jets use water injection into the combustion chamber to boost power.
Higher humidity=higher mass air flow. Water injection into a jet engine will provide a higher thrust output, this is used at take off from high altitude airports particularly if the outside temp is high.

[Zeuk in Oz]

Harrier jets use water injection into the combustion chamber to boost power.
Water injection in cars was all the rage in the 80s in Oz to reduce fuel consumption.

[ThoreauHD]

Interesting. I learned something new today. Yay for me.

[guinness]

Higher humidity=higher mass air flow. Water injection into a jet engine will provide a higher thrust output, this is used at take off from high altitude airports particularly if the outside temp is high.
True about the thrust output, if I remember right they use it for vertical take-offs or landing. They only carry enough water for about 90 sec.

[Dash01]

When I flew C-135 aircraft for USAF, we had water-injected J-57 engines. Water injection increased takeoff thrust by ~25%, til the water ran out.

Generally, wet weather is cooler weather, so the air would be denser on that account, helping engine performance (more air/fuel in the cylinders).

However, at a given air temperature, moist air is less dense, so the wings generate a bit less lift and the engines would have a bit less air to breathe.

Moisture in the air/fuel mix slows the combustion process, making a reciprocating (piston) engine run smoother.

In WWII, various piston-powered fighter planes had water injection systems, to augment thrust for combat. The added weight of the water, however, compromised manouevability of the plane.

[borderchris]

Absolutely agree. Here is San Diego, it's typically pretty dry. The last few days have been quite humid and rainy, and I've noticed a smoother, more velvety tone from the old M30, almost like a better gasoline.

[shogun]

some interesting stuff from the net
http://www.dawesdevices.com/water.html
http://website.lineone.net/~da.cushman/misc/mannject.html
http://www.rallycars.com/Cars/WaterInjection.html
http://www.turbomirage.com/water.html
http://www.motherearthnews.com/library/1979_September_October/Water_Injection_Wizardry

[Paul in NZ]

also you will notice your car runs better at night for similar reasons,cooler air more dense etc etc

[Morgenster]

I had the exact same idea but never dared to ask. It goes to show how I should not assume my questions can be stupid.
That is very new info for me and I'm no stranger to airplanes.

[632 Regal]

I used to run water injection to ported vacume on a couple cars, made the cam sound like a dragster and got a few more MPG.


2 reasons why.

the humidity slows down the combustion rate while simultaneously increasing the amount of fully combusted exhaust.

also it does help lower the pre compression intake temp, which lets more air into the cylinder.

there are probably other reasons, but those 2 are big.

[kick7ca]

I'm going to disagree with some statements made here,

This effect is something I've noticed on all my cars.

For one thing, I don't see how humidity can improve combustion. I think that is BS. I've always noticed a notable decrease in performance on hot, humid days.

It's the dry days (low humidity) where I notice more power, smoother too.

Also when it's raining I notice more power and smoother, this is because the water is no longer vaporized in the air, but is falling as drops to the ground, so again the motor is getting less humid air when it's raining.


The other variable is air temp, cooler air is more dense and is therefore better for performance.

[BillionPa]

what kind of effect do you see on a high humidity low temp day?

[guinness]

I'm going to disagree with some statements made here,

This effect is something I've noticed on all my cars.

For one thing, I don't see how humidity can improve combustion. I think that is BS. I've always noticed a notable decrease in performance on hot, humid days.

It's the dry days (low humidity) where I notice more power, smoother too.

Also when it's raining I notice more power and smoother, this is because the water is no longer vaporized in the air, but is falling as drops to the ground, so again the motor is getting less humid air when it's raining.


The other variable is air temp, cooler air is more dense and is therefore better for performance.

kick7ca,
check out this site, it should explain what water does.
http://www.rallycars.com/Cars/WaterInjection.html

[Claude]

Mainly two:
1) motor seems to run like a turbine (no sens of roughness at all)
2) a bit more peppy / quicker to react

That's subjective effects the second more than the first one, that's mines, but based on the above presented technical explanations they make sens.

[Paul in NZ]

Also when it's raining I notice more power and smoother, this is because the water is no longer vaporized in the air, but is falling as drops to the ground, so again the motor is getting less humid air when it's raining.


The other variable is air temp, cooler air is more dense and is therefore better for performance.


isnt that what we have been saying throughout this thread?

[kick7ca]

but I'm proposing it happens for a different reason.

[Ausmpower]

When I flew C-135 aircraft for USAF, we had water-injected J-57 engines. Water injection increased takeoff thrust by ~25%, til the water ran out.

Generally, wet weather is cooler weather, so the air would be denser on that account, helping engine performance (more air/fuel in the cylinders).

However, at a given air temperature, moist air is less dense, so the wings generate a bit less lift and the engines would have a bit less air to breathe.

Moisture in the air/fuel mix slows the combustion process, making a reciprocating (piston) engine run smoother.

In WWII, various piston-powered fighter planes had water injection systems, to augment thrust for combat. The added weight of the water, however, compromised manouevability of the plane.

Those WWII aircraft actually used water/ methanol injection since they lacked intercooling in any form and they were all super charged (Spitfire, hurricane, p51 Mustang, p38 lightning etc) the power increase was due to the air density increasing from the evaporation of the water/ alcohol mix(which also eliminated detonation).

[Traian]

Hmm, does anyone know why everyone isn't doing this, if it burns less fuel AND makes more power AND emits less pollutants according to the sites? I was also wondering about water being incompressible and all, but I guess the vapour produced by the combustion IS compressible and there is a very small amount of it. Is that the explanation?

[VentoGT]

Also when it's raining I notice more power and smoother, this is because the water is no longer vaporized in the air, but is falling as drops to the ground, so again the motor is getting less humid air when it's raining.

When it is raining, the ambient air is at 100% relative humidity, so the air is most humid when rain is falling. As for the other statements in the thread, I don't know enough about them to comment, but the colder air=more dense=more power is correct.

[BillionPa]

why isnt everyone doing it? because a properly calibrated water injection system with 3D mapping control costs about $1000

[nizmainiac]

the air is denser , alot better for engines , turbo or n/a