Port-Timing Diagram of Two-Stroke Engine

Read: Working of the Two-Stroke engine with P-V diagram

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. The sequence of operation of the ports is controlled by reciprocating movement of the piston in the engine cylinder.

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 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.

Importance of port timing diagram

The port timing has great influence on engine performance. A well tuned port timing results the better performance of engine, while badly tuned port time cause decreasing the efficiency of  engine. Incorrect port timing cause the leakage of fresh charge, cause partially burning of fuel, unwanted drop and rise of pressure inside the engine cylinder.

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