Design and Simulation of Two Stroke Engines

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Chapter 5 - Computer Modeling of Engines
DELIVERY RATIO
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CC END INLET DUCT X ^ ^ ^ ^
AIR BOX END
OF INLET DUCT CRANKCASE
100
1 • 1 •
200 300
CRANKSHAFT ANGLE, deg. atdc
400
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Fig. 5.24 Pressure related to airflow in a chainsaw at 9600 rpm.
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100 -
80 -
60 -
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CRANKCASE
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CRANKCASE END N
OF INTAKE
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1 1 • 1 1-
100 200 300
CRANKSHAFT ANGLE, deg. atdc
AIR BOX END
OF INTAKE
Fig. 5.25 Temperatures in the intake system of a chainsaw at 9600 rpm.
The crankcase pressure has already dropped to 0.8 atm by the time the inlet port opens,
sending a sharp, i.e., noisy, pulsation as an intake wave into the inlet duct, which peaks at
about the tdc position. The ensuing crankcase pumping action raises its pressure to about 1.5
atm, aided at that juncture by the higher pressure cylinder backflow into the scavenge ducts,
as discussed above.
The temperatures throughout the intake process are shown in Fig. 5.25 for the crankcase
air and at both ends of the intake duct. Heat transfer in the crankcase and inlet tract is responsible
for the dichotomy which exists. The air in the crankcase never drops below 60°C, whereas
most of the air in the inlet duct oscillates around 40°C. During induction into the crankcase,
391
400