Termodinâmica aplicada AULA-4

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THERMODYNAMIC CYCLES
 Cycle comparison
 For cycles with the same compression ratio, the most efficient 
cycle is the Otto cycle (lower heat, higher expansion)
ηth
Otto 0,525
Sabathe 0,500
Diesel 0,380
γ = 1,3
rc = 12
Q/(cvT) = 8,525
 Cycle comparison
 For Otto and Diesel cycles with the same maximum operating pressure, the most 
efficient cycle is the Diesel cycle (less heat, higher expansion)
THERMODYNAMIC CYCLES
 Cycle comparison
 The compression ratio of the Otto cycle is 
limited by knock occurrence
THERMODYNAMIC CYCLES
REAL CYCLES & IN CYLINDER PRESSURE
THERMODYNAMIC CYCLES
 Otto Cycle - Real
 Differences:
A – Wall heat losses
B – Finite Burn
C – Early Exhaust Valve Opening
D – Pumping Losses
Full Load Parcial Load
 Otto Cycle - Real
Inlet and exhaust valves effect
Spark Timing Effect
THERMODYNAMIC CYCLES
 Otto Cycle - Real
 In CyliIn-Cylinder pressure of SI engine
THERMODYNAMIC CYCLES
 Otto Cycle - Real
 In Cylinder 
pressure of SI 
engine Lambda 
effect.
THERMODYNAMIC CYCLES
 Diesel Cycle - Real
 Differences:
A – Wall heat losses
B – Finite Burn
C – Early Exhaust Valve Opening
D – Pumping Losses
THERMODYNAMIC CYCLES
VALVE TIMING
file:///C:/Users/Baeta/Documents/BAETA/UNIVERSIDADES/UFMG/TERMODINÂMICA APLICADA/MotorOTTO.exe
STIRLING & ERICSSON CYCLES
 There are two other cycles that involve an isothermal heat-addition process at TH and an isothermal heat-
rejection process at TL: the Stirling cycle and the Ericsson cycle. They differ from the Carnot cycle in that the 
two isentropic processes are replaced by two constant-volume regeneration processes in the Stirling cycle and 
by two constant-pressure regeneration processes in the Ericsson cycle. Both cycles utilize regeneration, a 
process during which heat is transferred to a thermal energy storage device (called a regenerator) during one 
part of the cycle and is transferred back to the working fluid during another part of the cycle.
The Stirling cycle, which is made up of four totally reversible processes:
1-2 Isothermal expansion (heat addition from the external source);
2-3 Isovolumetric regeneration (internal heat transfer from the working fluid to the regenerator);
3-4 Isothermal compression (heat rejection to the external sink);
4-1 Isovolumetric regeneration (internal heat transfer from the regenerator back to the working fluid).
STIRLING & ERICSSON CYCLES
1 2
3
4