- Two-stroke engine has no valves instead they have ports.
- They are inlet port, transfer port (transfer fuel from the crankcase to the cylinder) and an exhaust port.
- Since the one cycle is completed in one revolution of the crank, the sequence of operation of the ports can be represented in a circle (360°).
- This representation is known as a port timing diagram.
- The port timing diagram gives an idea about when a phase of the two-stroke cycle takes place.
The
diagram shown in above illustrates the sequence of various events such as
opening and closing of ports. Here,
TDC - Top Dead Center
BDC - Bottom Dead Center
IPO - Inlet port open
IPC - Inlet port close
TPO - Transfer port open
TPC - Transfer port close
EPO - Exhaust port open
EPC - Exhaust port close
- When the piston move from BDC to TDC - Transfer port close, Exhaust port close, Inlet port open.
- Ignition starts about 20° before TDC When the piston moves from TDC to BDC - Inlet port close, Exhaust port open, Transfer port open.
EPO- 70 ° before BDC
TPO - 60° before BDC
TPC - 60° after BDC
EPC - 70° after BDC
IPO - 50° before TDC
Ignition- 20° before TDC
IPC - 50° after TDC
The
angle slightly varies with engine design and specifications.