Two-Stroke Spark Ignition Engine Process

Study Notes

Two-Stroke Spark Ignition Engine

The power stroke is produced in the following sequence:
- Piston is forced downward from TDC, opening the exhaust port and allowing burnt gases to escape into the atmosphere.
- Further downward movement of the piston opens the transfer port, allowing the partially compressed mixture to reach the combustion chamber.
The piston head has a special shape that deflects a fresh change of fuel mixture up into the cylinder.
The process of scavenging occurs, where the fresh mixture flows down and pushes the burnt gas out through the exhaust port.
One power stroke is obtained in two revolutions of the crankshaft.

First Stroke (Suction and Compression)

The piston moves up from BDC, closing the inlet port, exhaust port, and transfer port.
The upward motion of the piston creates a partial vacuum inside the crankcase, drawing the air/fuel mixture into the crankcase through the inlet port.
The exhaust and transfer ports remain closed during this operation.

Four-Stroke Spark Ignition Engine

The sequence of operations is:
- Suction stroke: Piston moves from TDC to BDC, creating a vacuum inside the cylinder, and the inlet valve opens while the exhaust valve remains closed.
- Compression stroke: Piston moves from BDC to TDC, compressing the charge and increasing pressure and temperature.
The four operations take place in the four strokes of the piston, giving one power stroke in four strokes, i.e., in two revolutions of the crankshaft.
Three strokes are idle strokes, requiring a heavier flywheel due to non-uniform load on the crankshaft.

Comparison between Four-Stroke Engine and Two-Stroke Engine

Four-stroke engine: Four operations take place in four strokes, giving one power stroke in two revolutions of the crankshaft.
Two-stroke engine: Four operations take place in two strokes, giving one power stroke in one revolution of the crankshaft.
Four-stroke engine has a heavier flywheel due to non-uniform load, while two-stroke engine has a lighter flywheel due to more uniform load.

Two-Stroke Diesel Engine

The sequence of operations is:
- First stroke: Piston at BDC, scavenging port and outlet valve open, and a root blower sucks in pure air and presses it through the scavenging port into the cylinder.
- The air is brought into a turbulent motion, and the cylinder is completely flushed out and filled with fresh air.
- The exhaust gases flow out towards the outlet valve.
- Second stroke: Piston at TDC, scavenging port and outlet valve closed, and fuel is directly injected into the cylinder, vaporized into an ignitable fuel-air mixture, and automatically ignited and burned.

Description

This quiz covers the process of a two-stroke spark ignition engine, including the power stroke sequence, piston movement, and scavenging. Learn about the different stages involved in the engine's operation.