Page 382 - Advanced thermodynamics for engineers

16.6 SIMULATION OF COMBUSTION IN SPARK-IGNITION ENGINES 371

100
Equivalence
ratio
80 λ = 1.0
Pressure (bar) 60 λ = 1.2
λ = 1.1
λ = 0.9
λ = 1.3
λ = 0.7
40 λ = 0.8
λ = 0.6
20

-40 -20 0 20 40 60 80 100 120 140
Crankangle (deg atdc)
FIGURE 16.15
Effect of equivalence ratio on pressure–crank angle diagram.

charge in the cylinder and there is still some unburned charge in the cylinder at evo. This effect can be
overcome by increasing the turbulence in the cylinder by various means, including the use of variable
valve porting and timing at part-load. The flame radius continues to increase as the flame follows the
piston down the cylinder. This is also indicated on Fig. 16.16, where it can be seen that the unburned
charge, as evidenced by the temperature associated with it, still exists at evo.

Equivalence
ratio
3000 λ = 1.0
λ = 1.1
λ = 1.2
2500 λ = 0.9
λ = 1.3
Temperature (K) 2000 Burned zone λ = 0.7
λ = 0.8
λ = 0.6
1500

1000

500
Unburned zone

-40 -20 0 20 40 60 80 100 120 140
Crankangle (deg atdc)
FIGURE 16.16
Effect of equivalence ratio on temperature–crank angle diagrams.