Design and Simulation of Two Stroke Engines

Scavenging (continued)
scavenging efficiency (SE) (continued)
volumetric scavenging efficiency (tested),
226
vs. AFR (low emissions engine), 487-489
vs. SR and TE (Benson-Brandham model),
216-219
vs. SR (QUB loop-scavenged test, Yamaha
DT250 cylinders), 229-230, 232-233
vs. SR (QUB single-cycle test, Yamaha
DT250 cylinders), 227, 228-229
see also scavenging flow, experimental assessment
of (below)
scavenging flow, experimental assessment of
introduction, 219
chainsaw engine simulation, 386-389
comparison with wind-tunnel testing, 223
dynamic similarity, importance of, 224-225,
226-227
laminar vs. turbulent flow, accuracy of,
223-224
liquid-filled single-cycle apparatus, 224
loop, cross, uniflow scavenging compared
(QUB apparatus), 227, 229-233
piston motion, importance of, 223-224
QUB apparatus and Benson-Brandham models
compared, 233-236
QUB single-cycle gas scavenging apparatus,
224-227
Sammons' proposal for single-cycle apparatus,
224
scavenging coefficients, experimental values
for, 236
visualization of (wet-dry methods), 219
see also Jante test method (above); Computer
modeling (engine)
theoretical model with experimental correlation
introduction and discussion, 237
chainsaw engine simulation, 386-389
description and equations of flow, 237-238
exhaust port purity, calculation of, 238-239
exhaust port purity, typical curves (eight test
cylinders), 239-240
Sher interpretation of profile linearity, 239
final cautionary note, 240-241
uniflow scavenging
introduction, 11
advantages vs. complexity of, 12
617
Index
bore-stroke ratio, optimum, 253
in diesel engines, 11-12
engine configurations for, typical, 13
influence on SE-SR and TE-SR characteristics,
218-219
port design for. See Port design, scavenging
suitability to long-stroke engines, 253
tendency to vortex formation, 253
volumetric scavenging model (in engine simulation)
introduction, 241
exit charge temperature, determination of,
241-242
temperature, trapped air/trapped exhaust gas,
242-243
temperature differential factor, 241-242
Yamaha DT250 cylinders scavenging test results
compared with Benson-Brandham models,
234-235
exhaust port purity (correlated theoretical
model), 239-240
full-throttle QUB tests, 227, 228-229
loop-scavenged QUB tests, 229-230, 232,
233
see also specific valves; Port design; Port timing;
Trapping
Scott, Alfred
and deflector piston design, 10
Flying Squirrel machines, 1
Sher, E.
interpretation of scavenging profile linearity,
239
Shock waves, moving (in unsteady gas flow)
introduction, 201
First Law of Thermodynamics, application of,
202
flow diagram, 201
gas particle velocity, 202
momentum equation, 201-202
pressure/density relationships, 201, 204
temperature/density relationships, 203
see also Gases, properties of
Short circuiting
basic two-stroke engine, 8
Silencers/silencing
silencer design, fundamentals of
introduction, 548