Engineering Flashcards
Work done by Gas (sign of W)
+ve expansion
Work done on Gas (sign of W)
-ve compression
Isothermal
W is +ve
Δu = 0
Q=W
Isobaric
W is +ve
Δu is +ve
Q = W + Δu
Adiabatic
W is +ve
Δu is +ve
Q = 0
W = Δu
Isovolumetric
W = 0
Δu increases
Q = Δu
Increase of Thermal energy (sign of Q)
+ve
Decrease of Thermal energy (sign of Q)
-ve
Increase in internal energy (sign of Δu)
+ve
Decrease in internal energy (sign of Δu)
-ve
Isothermal expansion
Q=W
Adiabatic expansion
W=-Δu
Isothermal compression
-Q=-W
Adiabatic compression
-W=Δu
A to B
Piston moves up
Adiabatic compression stroke
B to C
Spark plug ignites gas mixture
Increase in pressure at constant vol
C to D
Piston pushed down by increase in pressure
Adiabatic expansion
Power stroke
D to A
Exhaust valve opens
Burnt gas mixture released
A to A’
Piston moves up
Gas mixture expelled
Exhaust stroke
A’ to A
Air drawn in
Piston moves down
Induction stroke
A to B
Piston moves up
Air compressed adiabatically
Temp increases to 700 Cels
Compression stroke
B to C
Diesel sprayed into cylinder
Ignited by hot air
Piston moves down at constant pressure
C to D
Fuel supply cut off at C
Adiabatic expansion
Temp falls and piston moves down
D to A
Exhaust valve opens
Gas releases
A to A’
Piston moves up
Exhaust stroke
Adiabatic definition
Transfer of thermal energy to gas is 0
Thermal efficiency
ε = indicated power/input power
Mechanical efficiency
η = brake (output) power/indicated power
Overall efficiency
brake (output) power/Input power
