Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
try." The velocity contours increase in strength from zero at the center of the cylinder to a
maximum at that side of the cylinder opposite to the exhaust port; in the "trade" this side is
usually referred to as the "back of the cylinder." (As with most professional specializations,
the use of jargon is universal!) The other patterns, (b)-(d), all produce bad scavenging characteristics.
The so-called "tongue" pattern, (b), would give a rapid and high-speed flow over the
cylinder head face and proceed directly to, and presumably out of, the exhaust port. The
pattern in (c), dubbed the "wall" pattern, would ultimately enfold large quantities of exhaust
gas and become a classic mixing process. So, too, would the asymmetrical flow shown in (d).
I, at one time, took a considerable interest in the use of the Jante test method as a practical
tool for the improvement of the scavenging characteristics of engines. At QUB there is a
considerable experimental and theoretical effort in the development of actual engines for
industry. Consequently, up to 1980, this method was employed as an everyday development
tool. At the same time, a research program was instituted at QUB to determine the level of its
effectiveness, and the results of those investigations are published in technical papers [1.23,
3.13]. In an earlier paper [3.6] I had published the methodology adopted experimentally at
QUB for the recording of these velocity contours, and had introduced several analytical parameters
to quantify the order of improvement observed from test to test and from engine to
engine. It was shown in Refs. [1.23] and [3.13] that the criterion of "mean velocity," as measured
across the open cylinder bore, did determine the ranking order of scavenging efficiency
in a series of cylinders for a 250cc Yamaha motorcycle engine. In that work the researchers at
QUB also correlated the results of the Jante testing technique with scavenging efficiency
measurements acquired under firing conditions with the apparatus shown in Plate 3.2. The
work of Nuti and Martorano [3.33] confirmed that cylinders tested using the Jante simulation
Plate 3.2 QUB apparatus for the measurement of scavenging efficiency under firing conditions.
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