pigeondave
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| posted on 18/5/22 at 06:46 AM |
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You'd have to check.
Get some smoke pellets from screw fix, they use them for chimneys. I put one in a little copper pipe so I could direct the smoke.
I found some interesting flows when the car was stationary and the fan cut in.
It's very difficult to guess these things, and they don't always go as you'd expect.
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coyoteboy
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| posted on 20/5/22 at 12:06 PM |
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quote:
Originally posted by Slater
Hello
Let make some assumptions:
1) 2.0 litre engine
2) Car is cruising at 2,000 rpm
3) Volume of air intake manifold 2 litre (same as big coke bottle)
So for every revolution of the engine, each cylinder goes up and down once, so 2 litres of air pass through every rev.
2,000 rpm x 2 litres = 4,000 litres of air per minute. or 66 litres per second.
[Edited on 15-5-22 by Slater]
4 stroke engine, only 1/4 strokes are intake. On a 2 litre 4 cyl cruising at 2000rpm you're sucking in 2 litres every 4 intake strokes, which
occurs in 2 revs. So you're sucking in 2 litres every 60/1000ths of a sec (0.06s), or vol flow rate of 0.033m3 per sec.
In an intake pipe diam of 60mm, you have a x-sectional area of 0.002m2.
To flow your 0.033m3 per sec through 0.002m2 area, your air is flowing at 16.6m per second.
Assuming your hot area is 200mm long, and the hot surface is 60C, with an average heat transfer coefficient you'd be looking at about 300W max
heating effect.
300W (300 J/sec) into 0.033m3/sec of air (with a heat capacity of 1 J/g-1/k-1) - that's about 43g of air per sec. Assuming averages and even
heating, you'd be looking at about a 7 degree temp rise. Worse when idling, better at high RPM/WOT.
If my maths is not squiffy somewhere.
You need to think about the system as a whole.
The pipe is just an interface between hot bay temp air and intake air. You need to decrease conduction through the pipe wall (make it plastic, not
metal), decrease radiation to the pipe (shielding from hot surfaces with multi-layer metal shields), decrease the wall thickness (to reduce heat
capacity) and specific heat capacity of the pipe (again, move from metal to plastic) and decrease external heat input (lag whatever was hot).
Make sure you feed the intake from outside the bay.
Make sure you keep the heat in hot things
Keep surface areas low (don't go for a massive intake pipe diam if it's not needed and keep heat away from airboxes as they have slow moving
air and large surface areas.
[Edited on 20/5/22 by coyoteboy]
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bikecarbfred
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| posted on 20/5/22 at 10:04 PM |
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epic post.
time to spend some more money
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bikecarbfred
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| posted on 22/5/22 at 08:47 PM |
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The pipe was around 60C hot at the top and under pipe was around 70C;between 20 and 30cm where the pipe is exposed to alot of heat from manifold. so i
decided to build a shield
well the manifold heat shield build is going okay but the space is very tight. and a certain points the aluminum rubs on the manifold/steel tie
wrap.
Just need to close a hole (fill the gap) in the manifold , neaten up around the edges and should be ready to bolt on.
MIght stick some GOLD reflective wrap lol on the underside of the pipe.
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Gaz7612
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| posted on 21/7/22 at 09:24 AM |
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One thing to remember is that the hot the exhaust gasses the quicker they will travel.
Heat shields, exhaust wrapping etc not only minimise radiating heat but also help keep the heat in the exhaust.
The colder the intake air the better for combustion engines, cold air is denser than hot air. Allowing for more fuel to be burnt per cycle.
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