[Vwdiesel] Engine state

[Val Christian]

> 
> If I go for a short run in my car say 1 mile and stop do
> some shopping for 20 25 minutes; I can start my car without
> glowplugs. Outside temps between 3 and 8 deg C.

	This is common, even in marginal compression
	VW diesel engines.

	Face it, there are real advantages of being in warm
	WX when you have a diesel engine.  Including no
	vapor lock.  

> Does this tell me anything about my engine? I felt blowby a
> little high but reduces under increased revs.

	Uncertain whether you're seeing blow-by, or just
	the results of turbulence.  As the RPMs increase
	the turbulence increases in frequency, and 
	the capacity of the crankcase smooths out the pulses.

> I've spent the last few days trying t owork out temps
> created by compression. Looks like it could reach 800 deg C
> assuming no heat losses to bores/head.

	If I recall my thermodynamics and chemistry right, 
	it isn't just the temperature, it has allot to do with
	the compression.  Think of the compression pushing 
	that carbon and hydrogen closer to the oxygen.

	Also, the major heat loss will not be the bore, but
	the head, and secondarily, the piston.

> How much glow does a plug need to help ignite the diesel?

	Again, it will be temperature and pressure.  If you
	increase the temp, ignition will occur at lower
	pressures.  The same thing in turbine engines,
	which are essentially continuous compression 
	ignition cycles..

	Unfortunately, when a VW diesel IDI engine starts having
	other problems, like leaky injectors, or suffers from 
	"runaway" oil ingestion, the glow plugs can get damaged.
	Usually this happens in older engines, where the compression
	might also be down.

	Other ways that some diesels are started, include flame
	heating of the intake chamber.  Consider that you're cranking
	your diesel, on a cold morning, and while cranking, the
	"ring of fire" adds several hundred degrees to the intake air.
	Yep, that works.  I suppose a piezo lighter, controlled
	from inside the car would help make that a single-man 
	operation.  (Oh, don't stop cranking, until the flame 
	is off.)  Also, preheating the engine block (well,
	really the cylinder head) helps raise the temperature.
	Some engines have a compression release, which unreleases
	while the engine is turning.  Since the engine is turning 
	faster, there's more stored mechanical (kinetic) energy to
	invest in the next compression stroke (or two), and 
	the engine has more pressure to light up easier.




> If the bores were insulated maybe we wouldnt need GPs at
> all...
>  Ceramics?

	Could be a good choice.  There's less shock in CI vs SI
	cycles.  But diesel engines have less wear than gassers,
	so there's less reason for modifying the bore material.
	Besides. the cylinder head is the big heat sink.  A cast
	iron cylinder head will sink less heat per unit time.

	BTW, B&S made a ceramic engine, which was marketed in 
	natural gas powered heat pumps several years ago.  It 
	was supposed to be a long life engine.  The story goes
	that the demand was low, and that HVAC contractors had
	problems servicing the engines (staff training and expertise).
	So the line of York heat pumps were dropped.  Good thing
	I waited, and didn't buy one right away.  Has anyone 
	heard anything about these engines?


	Val


> Miser
>