Engines 2

Piston engines turn

Chemical energy to mechanical energy (Chemical - Thermal - Pressure - Mechanical)

Petrol engines need ______ plugs to ignite the fuel in the cylinders

Spark

Thermal Efficiency

The ratio between useful output of energy and the total input of fuel energy

When ____ and _____ mix, it’s called a mixture

Air, fuel

Charge

The amount of mixture drawn

Reciprocating movement

The up and down motion of the piston

Crankshaft

The rotating axis that the piston turns

Mechanical efficiency

Ratio of energy input to energy output in a piston

Cylinder

The area that the piston reciprocates

Induction

The mixture is drawn into the cylinder

Compression

The mixture is compressed

Power

The mixture ignites

Exhaust

The burnt fuel is drawn out

Top Dead Centre (TDC)

The top of the stroke

Bottom dead centre (BDC)

The bottom of the stroke

Stroke

The length that the piston can move

Crank angle

The angle of the crankshaft which describes where the piston is (e.g 15 degrees after TDC)

Ineffective Crank angle

At the top and bottom of the stroke, where the piston doesn’t move as much for the angle of the crankshaft

Valve lead

At the end of the exhaust stroke, the inlet valve open before TDC

Inlet valve lag

Allowing the inlet valve to remain open after BDC allows more compression

Ignition timing

The ignition happens before TDC to allow time for the flame to reach the piston to push it down

Exhaust valve lead

The valve opens before BDC to prevent back pressure

Exhaust valve lag

The valve closes after TDC where the momentum of the gas removes the last of it

Valve overlap

Where both valves are open which means mixture escapes the exhaust

We can change ________ timing

Ignition