Combustion System - Robin America DY30 Service Manual

4-15 COMBUSTION SYSTEM
For lower fuel consumption and easy starting of the engine,
the direct injection system is adopted in the combusition
chamber.
4-15-1 FORMING of COMBUSTION GAS and COMBUS-
TION
/INTAKE V A L V E
INTAKE PORT
SWIRL
CYLINDER
PISTON
Fig. 13
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 pro-
motes 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 spiral form; and while the inspired
air is passing through this part,
swirl is generated
around the intake valve. Thus, intake port plays an im-
portant role in generating swirl. (See Fig. 13.)
SQUISH (Squished air flow)
In the piston, combustion chamber (dish type com-
bustion 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. 14.)
FORMING
of COMBUSTION
GAS
and COMBUSTION
For igniting quickly the fuel injected from the nozzle, it is essential to atomize very fine oil particles for distributing
evenly in the combustion chamber. For t h s purpose, fuel should be injected through hole type nozzle by very high
pressure, i. e. 195 kg/cm2. The fue!, 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.
Fig. 14
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