Not turbo related, but exhaust design!
Turbo Mini Forums

Chaps,

I am stuck on an assignment for exhaust design. I am doing it on the a series engine but have come across one bone of contention. When working out the tuned lengths for the exhaust primaries i am stuck when it comes to the centre port, the siamesed one. For the pulse tuning does it matter that it is like this, the firing order 1-3-4-2 does not have the two cylinders firing one after each other so not too sure!!!

Anyone who can help cos i can't think of it being any different but the Long centre branch exhuast must be like that for a reason!!!

Have you read Vizzard's book?

Alex

AlexF

Just got it sitting next to me, kinda answers my question, but curiously the LCB is designed so that the pulse from the 1st cylinder helps pull the gas from cylinder 4, and the central one works just for that one.

Kinda answers it, just gotta work out how it goes with the equation!!

Don't know how far you have got with your assignment but I would choose an easier engine to do it on e.g. something with four exhaust ports for four cylinders!!!

Why is it confusing?

Firing order 1-3-4-2 (or an easier to use when considering ports: 3-4-2-1)


Let's call the port nearest the waterpump 'A' the middle one 'B' and the clutch end 'C'

Hence the pulses are: A-B-C-B-A-B-C-B-A etc...

To begin with, consider the pulses start and end at every 180 crank degrees. Also, assume the pulses continue to flow at the same velocity down the pipes as a solid 'slug' of fixed volume.

Now you can start expanding the theory, starting firstly with the exact timing of the exhaust cycle from camshaft data.

Other things to consider: Different CC engines with identical camshaft/valve sizes will make a 'slug' of exhaust gas with a larger volume than a smaller CC engine.
Next, diameters of the primary and secondary pipes on the outer and inner branches will affect the velocity of the exhaust gas 'slug'.
Also, the further the exhaust gas from the exhaust valve, the cooler it will be - hence less dense, and occupying less volume. Also consider that hotter exhaust gas will drop by greater temp than a cooler gas over a same time period.

etc, etc, etc...

That is pretty interesting stuff actually! Never really thought about it before! It's almost certain that an LCB designed for a mild 1275 is far from that needed for a supercharged 1380!

How about posting your findings here? Or at least blat us a copy of it. I'd be interested!

To be completely honest the assignment is very criteria based. We have to cover fuel systems, exhaust systems and pressure charging systems in the one assignment.

Basically its quite low level stuff, but i am trying to relate it to my turbo mini project hence asking for the compressor maps!!

Also take into account that exhaust pulses travel at the speed of sound and the speed of sound changes with the exhaust gas temperature. A critical but often over looked part of the calculations.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Yeah i took that into account, i found out the temperatures on a website at various rpms and worked it out that way. Assignment went well i got a Distinction 90%!!!! So cheers chaps for ur guidance.

90%, Cool!

Only stuff I got 90% or above in on my degree was a project on designing an automotive transmission... Luckilly I knew a little about the subject!

The course i am on is a bit weird really. Its meant to be a motorsport course, but to take an example we did all about On Board Diagnostics on Tuesday! I am doing quite well overall, the worst mark was 75% for maths which is far too much like hard work. But at the end of the day, its costing me a fortune to do the course so i gotta have something to prove for it. I do my three days in Surrey, then travel back Thursday nite to Norwich, do four days work then back to Surrey monday nite!!! Is it any wonder I haven't found an engine yet!!! But on the upside i'm off to Hockenheim with work on Wednesday!!! Happy days :)