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.

[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.

[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.

[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.

[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.

[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.