Combustion System - Robin DY23-2D Service Manual

4- 21 COMBUSTION SYSTEM
For lower fuel consumption
and easy
starting of the .engine, the direct injection
system is adopted in the combustion
chamber.
4 - 2 1 - 4 FORMING OF COMBUSTION GAS
AND COMBUSTION
( 1
1
SWIRL
(Inspiring swirl)
In order to promote mixing injected
fuel and air under the direct injection
system, swirl flow is utilized for good
combustion. Swirl is spiral flow of air
generated in the cylinder during
inspiring stroke, and it decreases
during compressing stroke but it still
remains and promotes mixing of fuel
and air toward ignition timing.
Spiral flow of air (swirl) is generated
by the shape of intake port, which is
called helical port
or
spiral port.
Tail end of intake port, i. e. upper part
of intake valve seat, is made in the
/INTAKE V A L V E
INTAKE PORT
SWIRL
CY LlNDER
PISTON
FIG. 19
/c
SQUISH
FIG. 20
spiral forrn : and while the inspired air
is passing through this part, swirl is
generated around the intake valve.
Thus, intake port plays an important
role in generating swirl.
(See Fig. 19.)
SQUISH (Squished
air flow)
In the piston, combustion chamber (dish
type combustion chamber) is formed.
When the piston comes up to
TDC
(top
dead center), air in the gaps is squished
in the combustion chamber and air flow
is generated, which is called "squish."
(See Fig. 20.)
FORMING OF COMBUSTION GAS AND COMBUSTION
For igniting quickly the fuel injected from the nozzle, it is essential to atomize very
fine fuel particles for distributing evenly in the combustion chamber.
For this purpose, fuel should
be injected through hole type nozzle by very high
pressure, i. e. 195 kg/c m'. The fuel, thus injected, is 'mixed with air by the flow of
swirl and squish while piston is coming up. Accompanying crimb of the piston,
combustion gas compressed further and finally it automatically begins igniting and
while piston is going down,"squish" functions and promotes combustion.
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