engineering- heat engines Flashcards
what is the working substance?
the fluid on which thermodynamic process are performed, these include changes in temperature, pressure or volume
what is in the cylinder?
the working substance is contained in the cylinder (usually with a circular cross section)
what does a piston do?
the piston seals off the container but can move in and out
what does a crankshaft do?
this changes up and down motion into rotational motion
whats a cycle?
a series of thermodynamic processes which return to starting conditions
how many cylinders do cars usually have and can have?
most cars have four cylinders although some have 3,6 pr 8
what do cylinders do?
they help to make the operation smooth and ensure a continuous power output
what cycle does the engine work on?
the Otto cycle
what are the 4 stages of a 4 stroke petrol engine?
- induction
- compression
- power
- exhaust
what happens in the induction stage of a four stroke petrol engine?
a mix of 7% petrol and 93% air is drawn into the cylinder as the piston moves out and the the inlet valve is shut
what happens in the compression stage of a four stroke petrol engine?
the mixture is compression adiabatically as the piston moves in
the temperature rises to about 300’C
work is done on the working substance
what happens in the power stage of a four stroke petrol engine?
ignition- a spark ignites the working substance and
the temperature increases to about 2000’C and the pressure rises
expansion- the pressure in the working substances pushes the piston out causing adiabatic expansion
work is done by the working substance
what happens in the exhaust stage of a four stroke petrol engine?
the exhaust valve opens and much of the working substance is expelled by its own pressure
the piston moves in with the exhaust valve still open, pushing the rest of the spent fuel mixture out
at the the end of this stroke the valve closes
ignition and expansion are part of what stage of the four stroke petrol engine/
power