Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
Scavenging (continued)
exit properties, determining by mass
introduction, 242
exhaust gas temperature, 242-243
exit charge purity (by mass), 243
incorporation into engine simulation, 244
instantaneous SE, SR (conversion from mass
to volumetric value), 243
four-stroking (from inadequate scavenging),
218,285
Hopkinson, B.
perfect displacement/perfect mixing scavenging,
213-215
seminal paper on scavenging flow, 211, 276
isothermal (ideal) scavenge model
charging efficiency, 213
mixing zone/displacement zone, 212
physical representation of, 212
scavenging efficiency, 212-213
trapping efficiency, 213
Jante test method
introduction, 219
advantages/disadvantages of, 223
pi tot tube comb (motorcycle engine test), 221
QUB employment of, 222-223
test configuration, 219-220
"tongue" velocity patterns, 221-222
velocity contours, typical, 220-222
loop scavenging
influence on SE-SR and TE-SR characteristics,
218-219
invention of, 8-9
litigation about, 10
manufacturing disadvantages of, 10
piston for (typical), 10
port plan design for. See Port design
scavenging efficiency of, 10
SR vs. SE (QUB loop-scavenged test,
Yamaha DT250 cylinders), 229-230,
232-233
loopsaw scavenging (in chainsaw engine simulation),
380,388
perfect displacement, 213-214
perfect mixing, 214-215
perfect displacement/perfect mixing (combined),
215-216
port designs (all types)
See Port design
616
positive-displacement scavenging
engine configuration, typical, 15
functional description, 13-14
scavenge ratio (SR)
defined, 27, 212
chainsaw engine simulation, 386-389
in GPB engine simulation model, 168
instantaneous SR (conversion from mass to
volumetric value), 243
in isothermal scavenging (tested), 212
in perfect mixing scavenging, 214-215
in perfect displacement scavenging, 213-214
in mixing/displacement scavenging combined,
215
from QUB single-cycle test apparatus,
225-226
QUB single-cycle testv5\ Benson-Brandham
model, 233-236
with short-circuited air flow, 216
SR plots (CFD vs. experimental values),
248-250
vs. SE and TE (Benson-Brandham model),
216-219
vs. SE (QUB loop-scavenged test, Yamaha
DT250 cylinders), 229-230, 232-233
vs. SE (QUB single-cycle test, Yamaha
DT250 cylinders), 227, 228-229
scavenging efficiency (SE)
chainsaw engine simulation, 386-389
defined, 28, 212-213
effect on flammability (SI engines), 285
evaluation of test results (discussion),
232-233
instantaneous SE (conversion from mass to
volumetric value), 243
isothermal scavenging characteristics (tested,
Yamaha DT250 cylinders), 227, 228-229
in perfect displacement scavenging, 213-214
in perfect mixing scavenging, 214-215
in mixing/displacement scavenging combined,
215
in QUB single-cycle gas scavenging tests,
226,233-236
racing motorcycle engine simulation,
395-396
SE plots (CFD vs. experimental values),
248-250
with short-circuited air flow, 216