Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
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Fig.
CHAINSAW ENGINE, 9600 rpm, SE=0.75
TDC
320 340 360 380 400
CRANKSHAFT ANGLE, degrees
b B =64 a
4.7(d) Mass fraction burned characteristics of a chainsaw engine.
It can be observed that the data from Reid [4.31] are fitted with a common "a" coefficient
of 6.0 and the "m" coefficient is 0.765, 1.25 and 0.95, with burn durations of 49°, 43° and 45°,
in Figs. 4.7(a) to (c), respectively.
More information on combustion characteristics in two-stroke engines is in Fig. 4.7(d) for
a chainsaw engine running at 9600 rpm. The data are for full throttle operation, but in such a
unit the scavenging efficiency is modest at 0.75, for the delivery ratio is low so that the bmep
produced approaches 4 bar at a high trapping efficiency, giving good fuel consumption and
low hydrocarbon exhaust emissions. It should not be thought that the scavenging of this engine
is inferior; indeed the very opposite is the case as this is the actual engine defined as
"loopsaw" in Figs. 3.12, 3.13 and 3.19. The mass fraction burned characteristics are for three
fueling levels, with X ranging from near stoichiometric to 0.85. This has little effect on the
measured B characteristic. The measured curves are seen to be modeled by Vibe coefficients,
a and m, of 5 and 1.05, respectively. The burn period, b°, at the high engine speed of 9600
rpm, and a scavenging efficiency of 0.75, is long at 64°. The 50% burn position is at 10° atdc;
the periods of 0-20%, 0-50%, and 0-80% burn are recorded as 15°, 24° and 36°, respectively.
Further information on combustion characteristics in two-stroke engines is in Fig. 4.7(e)
for a Grand Prix racing motorcycle engine running at 10,350 rpm where the bmep is 9 bar.
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