Re: [DMCForum] Martin's class on basic diesel theory

[Martin Gutkowski <martin@xxxxxxxxxxxxxx>]

cruznmd wrote:

> Martin,
>
> Thanks for explaining all of that. I definitely did not know that the
> amount of air metered into the engine was constant at all throttle
> positions.

That's not what I said. Diesels have no throttles and therefore air flow 
is unrestricted. The manifold air pressure is near enough constant at 
one atmosphere (in an ideal world) whatever engine load/speed is. And 
because air pressure is constant, so too is fuel delivery with respect 
to throttle position and engine speed. Engine speed sorts itself out 
because the pump is driven off the cam belt, and throttle position is a 
valve on the fuel pump controlled by the throttle cable.

Simplicity itself, see?

Full pelt in a diesel is putting enough fuel in to use up all the 
oxygen. Running part throttle basically means running very lean - a 
condition in a petrol which results in preignition, or "dieseling". I 
think that explains it pretty well!

Diesels suit turbocharging for the same reason, and there's a very 
simple mechanical link from manifold air pressure to the fuel pump to 
enrich under boost

http://www.johns306.com/guides/turbo_diesel_tuning.php

We all know what the warm up reg on a DeLorean does. On the XUD diesel 
engine as in the above article, and in my BX, the warm up enrichment is 
achieved with a piece of thermo-something wire (can't remember the name) 
but it's wire that contracts when cold, pulling a little lever on the 
pump. It's worth £12.

Martin

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