Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
500
400
E
X>
300
200
o Full Throttle
• Half Throttle
a Quarter Throttle
1000 2000 3000 4000 5000 6000
Engine Speed (rev/min)
Fig. 7.33 BMEP levels at the optimized fuel consumption levels
for the QUB stratified charging engine.
The Piaggio stratified charging engine
The fundamental principle of operation of this power unit is shown in Fig. 7.34 and is
described in much greater detail in the paper by Batoni [7.1] of Piaggio. This engine takes the
stratified charging approach to a logical conclusion by attaching two engines at the cylinder
head level. The crankshafts of the two engines are coupled together in the Piaggio example by
a toothed rubber belt. In Batoni's paper, one of the engines, the "upper" engine of the sketch
in Fig. 7.34, has 50 cm 3 swept volume, and the "lower" engine has 200 cm 3 swept volume.
The crankcase of both engines ingest air and the upper one inhales all of the required fuel for
combustion of an appropriate air-fuel mixture in a homogeneous process. The crankcase of
the upper engine supplies a rich mixture in a rotating, swirling scavenge process giving the
fuel as little forward momentum as possible toward the exhaust port. The lower cylinder
conducts a conventional loop-scavenge process with air only. Toward the end of compression
the mixing of the rich air-fuel mixture and the remaining trapped cylinder charge takes place,
leading to a homogeneous combustion process.
The results of the experimental testing of this 250 cm 3 Piaggio engine are to be found in
the paper by Batoni [7.1], but are reproduced here as Figs. 7.35-7.37. A direct comparison can
be made between this stratified charging engine and the performance characteristics of the
200 cm 3 engine that forms the base of this new power unit. Figs. 7.9-7.11, already discussed
fully in Sec. 7.2.1.2, are for the 200 cm 3 base engine. Fig. 7.9 gives the fuel consumption
behavior of the 200 cm 3 base engine, Fig. 7.10 the CO emission levels, and Fig. 7.11 the HC
emission characteristics.
500
Ft
Q.
a,
£
-75
.65
.55
.45
.35