Why do some cars spew so much water from tail pipe?

[Sig]

I have always wondered why it is that some cars flow so much water from their mufflers. I notice it most often at initial acceleration after sitting at a stoplight. Some of these cars could fill up a small glass with the water that shoots out.
Common offenders:
1)V8 Mustangs
2)All Lincolns
3)Mitsu SUV's

Anyone know?

 

[dlongo]

hmmmm. I never really noticed one type of car having more water coming out the exhaust than others, except when my GF blew the head gasket on her cavalier, then it was like a steam bath back there. Now I'm going to have to start paying attention to V8 mustang ehausts...

Well, I'll take a stab at answering and say a big displacement engine with a long large diameter exhaust and large cats is going to have the most potential for exhaust vapor condensation in the exhaust. All cars will condense some water out of the vapor on startup. It continues until the wall temperatuere of the exhaust path is sufficiently raised to keep the water vaporized. There is more mass to heat up in the exhausts of these big displacement cars, and there is more surface area on the exhaust pipe walls for condensation to occur, hence more water. I can go pull out my multiphase flow textbook if you want the more scientific version.



Dave

 

[Soichiro]

Dave I think the multiphase flow textbook answer is mandatory for this thread. Does it cover aftermarket HID beam patterns too :--) ?

 

[Meeyatch1]

Well, especially for the Lincolns that do it....the owners rarely ever step on the gas and clean out the exhaust system so that moisture just stays in the exhaust. That is why when you floor it and the water and carbon deposits shoot out you will notice that after that there is far less in there for subsequent rapid accelerations.

 

[dlongo]

Dave I think the multiphase flow textbook answer is mandatory for this thread. Does it cover aftermarket HID beam patterns too :--) ?

haha, I actually considered quoting something insanely over- detailed from the textbook as a joke. The HID beam thread, well I'm not even reading that one anymore, it makes my brain hurt.

Oh, what the heck, here's a sample of whay you're missing

From "Convective Boiling and Condensation, 3rd Ed., Collier& Thome"

Condensation is defined as the removal of heat from a system in such a manner that vapour is converted into a liquid. This may happen when vapour is cooled sufficiently below the saturation temperature to induce the nucleation of droplets. Such nucleation may occur homogeneously withing the vapour or heterogeneously on entrained particulate matter [in this case, carbon particles in the exhaust gas]. Heterogeneous nucleation may also occur on the walls of the system, particularly if these are cooled as in the case of a surface condenser [in this case, a long exhaust tube subjected to ambient air temperature], In this case there are two forms of heterogeneous condensation, drop-wise and film-wise, corresponding to the analogous cases in evaporation, of nucleate boiling and film boiling. Film-wise condensation occurs on surface which is easily wetted. On non-wetted surfaces the vapoutr condenses in drops which grow by further condensation and coalescenceand then roll over the surface. New drops then form to take their place.

The liquid may form in one of three ways corresponding to the departure from a stable, metastable, or unstable equilibrium state. The formation of liquid at a planar interface occcurs when the vapour temperature is decreased fractionally below the corresponding saturation temperature.

zzzzzz.... I have 600 pages of this stuff.