PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 1
chamber goes through three stages when producing power.
They are as
(1) Formation of Nucleus of the Flame. As soon as a spark jumps the
gap of the spark plug electrode, a small ball of blue flame develops in the
gap. This ball is the first stage, or nucleus, of the flame. It enlarges
with relative slowness and, during its growth, there is no measurable
pressure created by heat.
(2) Hatching Out.
As the nucleus enlarges, it develops into the
hatching out stage. The nucleus is torn apart so that it sends fingers of
heat to give a slight rise in the temperature and pressure in the entire
air-fuel mixture. Consequently, a lag still exists in the attempt to raise
pressure in the entire cylinder.
(3) Propagation. It is during the third, or propagation stage that
effective burning occurs. The flame now burns in a front that sweeps across
the combustion chamber, burning rapidly and causing great heat with an
accompanying rise in pressure.
This pressure causes the piston to move
Burning during normal combustion is progressive.
gradually during the first two stages, but during the third stage, the flame
is extremely strong as it sweeps through the combustion chamber.
If detonation takes place, it will happen during the
third stage of combustion.
The first two stages are normal, but in the
propagation stage, the flame sweeps from the area around the spark plug
flame has passed contain inert gases, but the section not yet touched by the
flame contains highly compressed, heated combustible gases.
As the flame
races through the combustion chamber, the unburned gases ahead of it are
further compressed and are heated to higher temperatures.
conditions, the extreme heating of the unburned part of the mixture may
cause it to ignite spontaneously and explode.
This rapid, uncontrolled burning in the final stage of combustion is called
detonation. It is caused by the rapidly burning flame front compressing the