Lesson 1 Piston Engines Flashcards
What is the equation for calculating power in a piston engine?
Power = Torque x RPM
Piston engines produce power by converting what two types of energy?
Chemical energy into Mechanical energy
Fuel and air are burned in a confined space (cylinder) to release energy in the form of heat which raises pressure and moves the piston to create a mechanical movement. Mechanical energy drives the propeller which accelerates air rear wards to produce thrust
CHEMICAL to HEAT to PRESSURE to MECHANICAL
POWER = ____ x ____
TORQUE X RPM
TORQUE = ____ x ____
FORCE x DISTANCE
FORCE = ____ x ____
PRESSURE x AREA
A piston engine draws in air and mixes it with fuel to create what?
Charge
The charge combusts and is ignited by a spark plug to generate heat.
Heat generates pressure
Pressure drives piston downwards
How many full rotations are there if the crankshaft in a 4 stroke cycle?
Two full turns through 720deg
One movement between TDC and BDC is called what?
Stroke
Name the four cycles of a stroke:
INDUCTION
COMPRESSION
POWER
EXHAUST
I . C . P . E .
Are torque and speed proportional or inversely proportional?
Inversely proportional
The rated output of a motor is a fixed value. As speed increases the torque decreases to maintain a constant power output. As speed decreases, torque increases proportionally to maintain the same output.
The “working fluid” of all combustion engines is ____?
Air
A piston engine has what type of movement?
Reciprocal.
The crankshaft converts linear motion into rotary motion. The up and down motion of the piston is called reciprocal movement hence RECIPROCATING ENGINE
Does ignition take place before, at or after TDC?
Just before to take advantage of INEFFECTIVE CRANK ANGLE
The part of the piston movement around TDC and BDC where there is very little movement compared to rotation of crankshaft is called what?
Ineffective crank angle
Name the Piston Cycle:
Inlet valve still open as compression stroke begins and beyond BDC.
As piston comes out of BDC inlet valve starts to close and combustion can happen
INLET VALVE LAG
Keeping the valve open beyond BDC ensures that the mixture continues to flow into the cylinder even though the piston is barely moving.
Name the Piston Cycle:
As exhaust stroke comes to an end, but before TDC, the inlet valve opens.
INLET VALVE LEAD
Opening the valve before TDC is valve lead. This allows fresh mixture into the cylinder before the start of the induction stroke.
Name the Piston Cycle:
Both valves closed at start of power stroke
Most work done before BDC in power stroke
Exhaust valve opens before end of power stroke
EXHAUST VALVE LEAD
Name the Piston Cycle:
Exhaust valve remains open until slightly after TDC
Remaining exhaust gas exits under its own momentum
EXHAUST VALVE LAG
Longer period available to clear cylinder of waste gas helped by residual pressure
Where does valve overlap happen?
Around TDC between EXHAUST and INDUCTION stroke
The period when both inlet and exhaust valves are open at the end of the exhaust stroke and start of the induction stroke is known as what?
VALVE OVERLAP
Overlap of exhaust gases exiting the cylinder helps to draw in fresh mixture.
When is ignition timed to occur during the stroke to maximise ignition occurring at peak pressure?
Just before TDC.
This increases peak pressure and maximises power generated on the power stroke
What speed does the camshaft rotate in relation to the crankshaft?
Half, 50%
The distance from the centre of the crankshaft to the centre of the crank pin is called what?
The THROW
How many Throws in a Stroke
Two
