VEB BERLIN SR59, Руководство по эксплуатации

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2 Description
2.1 Engine
2.11 Mode of operation
The aircooled supercharged single cylinder two-stroke engine of the SR59 Cityscooter operates as
a loop-scavenging-triple-port-Engine. This engine is an advanced version of the reliable and
successful 125cc two-stroke motor of the MZ-125-2 Motorbike. The following section describes the
mode of operation of the RM150 engine:
As the piston moves upward (from bottom dead center (BDC) to top dead center(TDC)), a vacuum
is created beneath the piston in the enclosed volume of the crankcase. The piston uncovers a little
air inlet just before reaching the top dead center. This little air inlet is the end of the intake port,
through which fresh air enters the crank case due to the vacuum created before. Because this very
same air had to pass through the carburetor prior to entering the crank case, it is mixed with just the
right amount of fuel and oil (the oil being necessary for the lubrication of the engine) When the
piston is on a downward move after passing TDC it relocks the intake port and thus compresses the
air/fuel mix. By now, the oil has dropped out of the mix and attached itself to bearings and other
parts within the engine. Just before reaching BDC two openings called transfer ports are uncovered
in the cylind
e
r.
The scavenging phase has begun. Meaning that the unburned mixture gasses are flowing out of the
transfers and merging together to form a loop. The gasses travel up the backside of the cylinder
and loops around in the cylinder head to
scavenge out the burnt mixture gasses from the previous
power stroke. It is critical that the burnt gasses are scavenged from the combustion chamber, to
make room for as much unburned gasses as possible. Now the loop of unburned mixture gasses
have traveled into the exhaust pipe's header section. Most of the gasses aren't lost because a
compression pressure wave has reflected from the baffle cone of the exhaust pipe, to pack the
unburned gasses back into the cylinder before the piston closes off the exhaust port. Now the
crankshaft has rotated past bottom dead center (BDC 180 degrees) and the piston is on the
upstroke. The compression wave reflected from the exhaust pipe is packing the unburned gasses
back in through the exhaust port as the piston closes off the port to start the compression phase.
Image 3. Explosion drawing of engine