Analysis of thermal and pressure stresses in y exhaust

[mpaige1]

Hey, i just have a couple questions that need answers. Below I have a list of notes I have taken whilst researching how to analyze thermal and pressure stresses in a y bar exhaust. Things I need to design include the valve and the exhaust pipe itself. Am I missing anything to analyze? About how many hours do you think it will take to accomplish all of this (there are two people working on this)?

- Laminar flow at exit
Use Reynolds number to find maximum velocity before transitional
Turbulent flow decreases exit velocity
Large pipe slows velocity
Determine area of pipe (optimized using maximum velocity)
fluid mechanics
- Operating RPM range
needed for determining back pressure
use maximum RPM to find pressure
find increase in temperature due to pressure
determine thermal and pressure stress
fluid mechanics
- find energy loss from engine
Thermodynamics
- take into account different atmospheric pressures at different altitudes
research race track altitudes
use highest and lowest values found to make calculations
fluid mechanics
- quick cooling is bad
generate cracks in material
find maximum temperature in pipe at maximum rpm
use temperature to find pressure
material science
- Rapid expansion
creates more stress due to increase in pressure and temperature
determine gas expansion in exhaust
determine thermal and pressure stress due to rapid expansion
analyze different materials
determine best treatment and material
material science/thermodynamics
- dependent on race/street car and whether or not car is mostly idle, full or part throttle
assume full throttle
- engine displacement
volume swept by all pistons inside cylinders
determine volume of gas displaced by piston
determine pushing and pulling force
find maximum stress due to forces
solid mechanics

Designed for:
- Racing engine
- 24V VR6
- Toyota 2ZZ

All of it put together:
- Sum pressure and thermal stresses
- Determine best material to use
- Analyze using CAD software (Pro/E)
- Finalize project

Deliverables:
- hand calculations
- working exhaust design
- CAD work

Let me know if you have any questions or comments about any of the notes above. All the topics listed need some sort of review and the only topic I need to completely learn is thermal stress. I'll be checking this daily in addition to researching more in order to get a better understanding of what I need to accomplish and how to do it. This is a pretty big project and I just need some elaboration and feedback on these ideas.

 

[mpaige1]

Ok, I've done some more research on what to do, reviewed thermodynamics and fluid mechanics a little bit. I've come up with a way to find the back pressure and temperature for the pipe. I have some more focused questions;

1) How would I go about finding a way to use turbulent flow through the pipe that would benefit the output?

Ideas:
a) I'm thinking about using some type of boring technique that would create a smoother flow through the pipe. I know it won't be cost effective but I'm not really worried about that.

b) Another idea I have is tapering the pipe but I don't know what that would do for the overall power of the car. I think it will hinder it more than help it because the added pressure in the pipe will just slow down the velocity more. I really think boring would be the way to go out of these ideas.

2) How would I find the pressure in an angled pipe?

Ideas:
a) Find pressure force of gas at valve in y exhaust and use law of sines to find pressure, temperature and flow velocity through the angled pipe. I think that sounds about right but I'm not too sure.

Elaboration or more ideas are helpful. I'm in the brainstorming part of this project. The only factor I am currently optimizing is power. Any and all ideas are helpful.

 

[mpaige1]

Alright, I'm on to doing the thermodynamics portion of the project, starting with the cylinder head. I know I have to find the amount of gas injected into the cylinder. What should I learn to be able to find the force that combustion of the gas will give me? I'm just not really sure what subject I should be studying. A little help please?

 

[jack action]

My best advice: read http://books.sae.org/book-r-186" .

 

[mpaige1]

ok thanks for the help, that's pretty much all I need to get this project going :-)