Chp2 Construction Flashcards
(29 cards)
What type of engine is a piston engine
Internal combustion engine
What is an internal combustion engine
An engine that uses a mix of air and fuel within to be burnt, the heat generated by this provides pressure which pushes the pistons
What principle does a piston engine work upon
A 4 stroke cycle
What is the 1st stage of the 4 stroke cycle
Intake
This is where the piston descends and the intake valve opens to allow a mix of fuel and air to enter
What is the 2nd stage of the 4 stroke cycle
Compression
This is where the intake valve closes as the piston ascends, forcing the mixture upwards
What is the 3rd stage of the 4 stroke cycle
Power/combustion
This is where a spark is created, igniting the mixture which forces the piston downwards
What is the final stage of the 4 stroke cycle
Exhaust
This is where the gases created from the combustion (Co2 ect…) are allowed to escape through the exhaust valve then the piston ascends again restarting the cycle
How many degrees is each stroke
180°
What is the total amount of degrees the crankshaft has turned after the 4 stroke cycle
720°
Does the number of pistons affect the total degrees of rotation in a cycle
No
The number of pistons and degrees turned through are independent
Eg. 4 pistons = 720° and 6 pistons. = 720°
What are the three cylinder arrangements for a piston engine
In line / inverted in line
Radial
Horizontally opposed
What are the disadvantages of an in-line cylinder arrangement
Long and heavy crankshaft
Poor visibility as line of sight can be interfered with
What is the positive abs negative of an inverted in-line arrangement
There is improved visibility
Hydrolock can occur
What is hydrolock
When oil pools inside a cylinder, stopping the piston from fully extending downwards.
Extremely inefficient and harmful to the engine
What is a positive and negative of a radial arrangement
It can accommodate a large number of cylinders in multiple rows so there is a large power output
However larger surface area = more drag
And it is a complex valve actuation mechanism
What are the positives of a horizontally opposed arrangement
It has a short and light crankshaft
There is good visibility
Reduced drag
No hydrolocking
What is the crankcase
The main engine casing and support for other components (crankshaft, cylinders, sump and accessories)
What is a breather
A component that ensures pressure is kept equal to ambient pressure
Allows excess gases (eg. Oil vapours) to escape
Why is a flywheel needed on a crankcase
To allow for smoother rotation as there will be greater inertia
What is the crankshaft
The component which converts linear movement of the pistons into rotary movement
Why is the crankshaft kept as short as possible
To reduce its weight and to avoid it twisting too much
Why does a crankshaft need to be strong and rigid
To withstand high torque loads
What is the main journal om a crankshaft
The main bar that stays fixed in the same place even when the other parts are moving up and down
Why are there holes along the crankshaft and pins
To allow for free oil flow therefore lubrication of all the main parts
