Ronald Raygun wrote in
. uk:

Many engines are fitted with electric glow-plug preheaters. I don't
think they heat the injectors, but part of the combustion chamber.

Glow plugs are situated in the path of the spray pattern of the injector,
usually in a pre-combustion chamber which not only makes the engine much
easier to start, but much quieter to run.

http://www.kenrockwell.com/190d/images/lvp.gif
Here's the precombustion chamber of a Mercedes Benz 190D diesel. The
glowplug is the gold pin right under the spray head. It heats red hot
just before the engine starts, causing the fuel to explode reliably as
soon as it is injected, by the injector directly above it. It continues
to glow, as does the grey resonator under it while the engine is running,
not by the electrical current, but by the last time the fuel exploded.

The explosion happens in the precombustion chamber and an immense
pressure pushes the explosion into the air charge down in the cylinder
through those tiny holes, maybe 1/8" diameter, in a radial pattern on top
of the piston to balance the pressure on the piston top. After 25 years
of constant use, my '73 220D sedan's little 57hp diesel piston had 5
little tracks across the top of the piston showing where the explosion
went by it at TDC on ever other stroke. I couldn't get over how small
these holes are and how clean they stayed all those years when we
overhauled it at about 250,000 miles. It really only needed new rings.

Notice in MB cars, the whole chamber screws out so it can be easily
replaced if it cracks under the pressure. Smart, very smart.

All this is done to reduce the compression necessary to start it cold and
run it QUIETLY in a nice car. It ran fine on vegetable oil going to
breakfast with my old friends, this very morning...(c;


Larry
--
Have a little fun in the checkout line....
Ask the nearest American, "Did you see the ICE
agents chasing those Mexicans out the back door?"
....Shortens that checkout line right up...(c;