Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
combustion process. Appendix A4.1 showed how hydrocarbon emissions due to scavenge
losses may also be included with those emanating from combustion. Both types of gaseous
emission creation are incorporated into the GPB simulation system. However, the use of
simulation for design purposes is possible only if the computer model can be shown to provide
similar trends to the measurements for the computed emissions, so calculations are presented
to reinforce this point.
7.2.1.1 Measured performance data from a QUB 400 research engine
The first set of data to be presented is from the QUB 400 single-cylinder research engine
[1.20]. This engine is water cooled with very good scavenging characteristics approaching
that of the SCRE cylinder shown in Figs. 3.12. 3.13 and 3.18. The bore and stroke are 85 and
70 mm, respectively, and the exhaust, transfer and inlet ports are all piston-controlled with
timings of 96° atdc, 118° and 60°, respectively.
The engine speed selected for discussion is 3000 rpm and the measured performance
characteristics at that engine speed are given here as Figs. 7.3-7.8. Figs. 7.3-7.5 are at full
throttle and Figs. 7.6-7.8 are at 10% throttle opening area ratio. In each set are data, as a
function of air-fuel ratio, for bmep, bsfc, unburned hydrocarbon emissions as both ppm and
bsHC values, and carbon monoxide and oxygen exhaust emission levels. It is worth noting
that this engine employs a simple exhaust muffler and so has no exhaust pressure wave tuning
to aid the trapping efficiency characteristic. Therefore, the performance characteristics attained
are due solely to the design of the porting, scavenging, and combustion chamber. The
engine does not have a high trapped compression ratio as the CRt value is somewhat low at
6.7. Even without exhaust pressure wave tuning, that this is not a low specific power output
engine is evident from the peak bmep level of 6.2 bar at 3000 rpm.
6.4
6.2 -
,_ 6.0
ra
& 5.8
E
5.6
5.4
5.2
QUB 400 ENGINE
WOT 3000 rpm
DR=0.85
10 12
i
14
AIR-FUEL RATIO
16 18
r 0.6
-0.5
o
C/3
h 0.4 -O
Fig. 7.3 Air-fuel ratio effect on bmep and bsfc at full throttle.
All
0.3