Design and Simulation of Two Stroke Engines

Chapter 7 • Reduction of Fuel Consumption and Exhaust Emissions
mixing with the trapped charge of cylinder air and retained exhaust gas would permit a homogeneous
combustion process.
The test results for the engine, shown in Figs. 7.32 and 7.33 as fuel consumption and
bmep levels at several throttle openings, reveal significantly low levels of fuel consumption.
Most of the bmep range from 2 bar to 5.4 bar over a speed range of 1500 to 5500 rpm, but the
bsfc levels are in the band from 360 to 260 g/kWh. These are particularly good fuel consumption
characteristics, at least as good if not superior to an equivalent four-stroke cycle engine,
and although the hydrocarbon emission levels are not recorded, they must be significantly
low with such good trapping of the fuel within the cylinder. The power performance characteristics
are unaffected by this stratified charging process, for the peak bmep of this engine at
5.4 bar is quite conventional for a single-cylinder engine operating without a tuned exhaust
system.
The mechanical nature of the engine design is relatively straightforward, and it is one
eminently suitable for the conversion of a simple two-stroke cycle engine. The disadvantages
are the extra complication caused by the twin throttle linkages and the accurate carburetion of
a very rich mixture by a carburetor. The use of a low-pressure fuel injection system to replace
the carburetor [7.51] would simplify that element of the design at the further disadvantage of
increasing the manufacturing costs.
0-45
0-40
0 35
0'30
0-25
Full Throttle
• Half Throttle
• Quarter Throttle
J 1 U J I 1_
a.
It
ir0-7
300-
250-
200
1000 2000 3000 4000 5000 6000
Engine Speed (rev/mm)
Fig. 7.32 Optimized fuel consumption levels for the QUB stratified charging engine.
499
0-6
0-5
0-4