exhaust size vs. temp Options

[ShadowFX]

lol yeah okay.. it sounds dumb but its for a physics assignment, would a bigger diameter exhaust have a difference on the exhaust gas temperature? if so, minor or major?

[orvillescelica]

so assuming the flow is isentropic (reversible and no heat addition), steady, quasi 1-D, and all of the same species (or not massivly different), we can model this as flow moving through an increasing area duct (from smaller area of the engine into larger area of exhaust piping)

Assume you know the incoming gas velocity, density and areas (v1, rho1, A1, A2), use a simple area velocity relation of conservation of mass flow: rho1*v1*A1=rho2*v2*A2

Now that you have the gas velocity in A2. Now you need pressure. You can get this from bernoulli's eqn: 1/2 rho*v^2+P=const

now that you have the pressure, its simply P=rho*R*T to get temp.

Do this for A2 for the two differnet size exhaust pipe sizes you are looking at and compare the temps.

**edit: i am ignoring an viscous (friction) effects and any heat loss that may occur and defining the control volume as the flow that is leaving the engine and entering the exhaust pipes, nothing upstream or downstream of that.

This post has been edited by orvillescelica: Apr 28, 2004 - 1:17 AM