4 stroke engine stroke is defined as the movement of the piston from the 'bottom dead...

4 Stroke engine4 Stroke engine

Stroke is defined as the Stroke is defined as the movement of the piston movement of the piston from the 'bottom dead from the 'bottom dead center' (BDC) to the 'top center' (BDC) to the 'top dead center' (TDC) or the dead center' (TDC) or the other way round, that is other way round, that is from TDC to BDC. A four from TDC to BDC. A four stroke engine has 4 stroke engine has 4 strokes. strokes.

1º 1º Intake.Intake. 2º 2º CompressionCompression 3º 3º PowerPower 4º 4º Exhaust.Exhaust.

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1º Intake1º Intake The piston is at its highest point The piston is at its highest point

(TDC), the inlet valve opening and (TDC), the inlet valve opening and the exhaust valve closed.the exhaust valve closed.

The piston moves downward and it The piston moves downward and it increases the volume between the increases the volume between the valves and the piston, so the valves and the piston, so the pressure inside the cylinder gets pressure inside the cylinder gets lower and lower. As the outside air lower and lower. As the outside air pressure is higher, this forces the pressure is higher, this forces the air-fuel mixture into the cylinder air-fuel mixture into the cylinder as the the piston is moving downas the the piston is moving down

A moment later, the piston reaches A moment later, the piston reaches the BDC ( bottom dead center) and the BDC ( bottom dead center) and the inlet valves closes. the inlet valves closes.

A new Stroke is coming A new Stroke is coming


2º Compression.2º Compression.

Both exhaust and intake Both exhaust and intake valves stay closed as the valves stay closed as the piston move upward from piston move upward from the BDC (bottom dead the BDC (bottom dead center) center)

The piston moves upward, The piston moves upward, squeeze the fuel-air mixture squeeze the fuel-air mixture into a smaller volume. The into a smaller volume. The pressure gets higher and pressure gets higher and this causes the fuel-air this causes the fuel-air mixture´s temperature to mixture´s temperature to rise. rise.

With high temperature, With high temperature, ignition is easier and ignition is easier and combustion more complete combustion more complete


Ignition and PowerIgnition and Power:: Just before the piston reach the TDC ( At the end of the Just before the piston reach the TDC ( At the end of the

compression stroke ) the spark plug fires.compression stroke ) the spark plug fires. The fuel-air mixture explodes forcing the piston down the The fuel-air mixture explodes forcing the piston down the

cylinder.cylinder. The Power stroke drives the engine The Power stroke drives the engine


4º Exhaust.4º Exhaust. At the bottom of the power At the bottom of the power

stroke, the exhaust valve is stroke, the exhaust valve is opened by the cam/lifter opened by the cam/lifter mechanism. mechanism.

The piston now moves from The piston now moves from BDC to TDC. The inlet BDC to TDC. The inlet valve is closed, the valve is closed, the exhaust valve opens, and exhaust valve opens, and the piston, moving upward, the piston, moving upward, pushes the leftover gases pushes the leftover gases out of the cylinder. out of the cylinder.

BDC = bottom dead center BDC = bottom dead center TDC = top dead centerTDC = top dead center

4 stroke engine stroke is defined as the movement of the piston from the 'bottom dead...

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