A-LEVEL PHYSICS: 11.2.7: Power Output of an Engine (SaveMyExams) Flashcards
an engine’s efficiency depends on its…
this is determined by the…
power output
this is determined by the fuel
calorific value of fuel:
the amount of energy stored per unit volume or mass
calorific value of liquid fuel is measured in:
J kg ^-1
calorific value of gas fuel is measured in:
J m^-3
flow rate of fuel:
volume or mass of fuel that flow per second
flow rate of liquid fuel is measured in:
kg s^-1
flow rate of gas fuel is measured in:
m^3 s^-1
input power = …
calorific value * flow rate
indicated power:
the power developed in the cylinder of an engine.
depends on the number of cycles (strokes) per second
number of cycles (strokes) per second = …
1 / time for one cycle
in a four-stroke engine, 1 cycle is equal to…
2 revolutions
indicated power = …
indicated power = area of p-V loop * no. cycles per second * no. cylinders in engine
brake power:
power output by the engine, and is the same as the rotational power
output power (P) = …
P = Tω
friction power:
due to this, :
part of the indicated power that is used to overcome friction within the engine
due to this, this means that brake power is lower than he indicated power
why is brake power lower than the indicated power?
because some of the indicated power is used to overcome friction within the engine (friction power)
friction power = …
friction power = indicated power - brake power
