Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
gas velocities is well known, and the theory or practice can be found in any textbook on fluid
mechanics [3.14]. The comb of pitot tubes shown in Fig. 3.4 can be connected to a variety of
recording devices, ranging from the simplest, which would be an inclined water manometer
bank, to some automatic data logging system through a switching valve from a pressure transducer.
Irrespective of the recording method, the velocity of gas, c, in line with the pitot tube is
given by:
4,/Ap~ water m/s (3.2.1)
where Apwater is the pitot-static pressure difference in units of mm of water. The engine can
be motored at a variety of speeds and the throttle set at various opening levels to vary the
value of scavenge ratio, SR. The most important aspect of the resulting test is the shape of the
velocity contour map recorded at the open cylinder bore. Jante [3.5] describes various significant
types of patterns, and these are shown in Fig. 3.5. There are four velocity contour patterns,
(a)-(d), shown as if they were recorded from various loop-scavenged engines with two
side transfer ports and one exhaust port. The numerical values on the velocity contours are in
m/s units.
Jante describes pattern (a) as the only one to produce good scavenging, where the flow is
ordered symmetrically in the cylinder about what is often referred to as the "plane of symme-
PITOT TUBES CONNECTED
TO THE RECORDING
INSTRUMENTATION
COMB OF PITOT TUBES
ENGINE VITH TEST CYLINDER J
BEING MOTORED—•*
mmt
Fig. 3.4 Experimental configuration for Jante test.
220
EXHAUST
PORT
INLET
PORT