Design and Simulation of Two Stroke Engines

FUEL
INJECTOR
ROOTS BLOWER JL
Chapter 1 - Introduction to the Two-Stroke Engine
K £ ^^^~^^^~ fezzzzz—=L|_iJ=l__w
'flZZZZZZ.
5P
TURBOCHARGER
Fj'g. 7.6 .A supercharged and turbocharged fuel-injected two-stroke engine.
1.3 Valving and porting control of the exhaust, scavenge and inlet processes
The simplest method of allowing fresh charge access into, and exhaust gas discharge
from, the two-stroke engine is by the movement of the piston exposing ports in the cylinder
wall. In the case of the simple engine illustrated in Fig. 1.1 and Plate 1.5, this means that all
port timing events are symmetrical with respect to top dead center (tdc) and bdc. It is possible
to change this behavior slightly by offsetting the crankshaft centerline to the cylinder centerline,
but this is rarely carried out in practice as the resulting improvement is hardly worth the
manufacturing complication involved. It is possible to produce asymmetrical inlet and exhaust
timing events by the use of disc valves, reed valves and poppet valves. This permits the
phasing of the porting to correspond more precisely with the pressure events in the cylinder or
the crankcase, and so gives the designer more control over the optimization of the exhaust or
intake system. The use of poppet valves for both inlet and exhaust timing control is sketched,
in the case of uniflow scavenging, in Fig. 1.5. Fig. 1.7 illustrates the use of disc and reed
valves for the asymmetrical timing control of the inlet process into the engine crankcase. It is
15