Sunz
Member
Registered: 12th Jan 07
Location: SE England
User status: Offline
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Astra van 1900Tdi
Matt asked me a question to work out, anyone know the formula.
He said " atmosphere pressure of 2-3psi works out to be 200psi on my engine and my engine boosts @ 6psi (turning it upto 10) work out my totall dry (without fuel) compression"
No idea what his on about, I understand how Diesel engines work with the compressed air but this totally baffeled me  
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Robin
Premium Member
Registered: 7th Jan 04
Location: Northants Drives: Clio 182 Cup
User status: Offline
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Basically, what he's saying is -
- The outside air is at atmospheric pressure.
- When it goes in to the engine, and is compressed by the piston, the pressure is increased.
- BUT, with a turbo engine, the air is already compressed when it enters the cylinder (in this case, at 6psi now, or 10psi soon)
His figures are a bit wrong though.
Atmospheric pressure at sea level is 14.6psi.
The compression ratio of his engine is 18:1 (if it's a 120 model)
So, you need to times 14.6 by 18 to get the cylinder pressure.
14.6 x 18 = 262.8psi
262.8 is the pressure in PSI, in the cylinder without a turbo, in a 1.9 cdti 120 engine.
at 6 psi, the air is at 20.6psi (the 6psi is on top of atmospheric pressure)
That means with 6psi, the cylinder pressures are 370.8psi.
Increase the boost pressure to 10psi and you get 14.6 + 10 (24.6) times that by the compression ratio (18) and you end up with 442.8psi.
So, at 10psi, the cylinder pressures peak at 442.8psi, dry.
Make sense? 
[Edited on 08-08-2007 by Robin]
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