Effect of hot spots on HCCI combustion

1
Effect of hot spots on HCCI combustion
Reference group meeting, KC FP Sept. 18, 2007

• T. Joelsson, R. Yu, X.S. Bai
• Division of Fluid Mechanics
• Lund Institute of Technology

2
Motivation

• Temperature stratification has strong effect on
  HCCI combustion.
• How does the length scale of temperature
  stratification affect the combustion phasing and
  duration?
• How does the amplitude of temperature
  stratification affect HCCI combustion?

3
Test engine
Scania D12 Engine with flat disc piston
Vressner et al., SAE 2007-01-0217
4
Flow and temperature field, flat disc engineLES
result
Yu et al., SAE 2007-01-0183
5
In-cylinder Pressure from LES and Experiments,
Disc engine, Sensitivity tests
Case A, T550K, T 10K
Case B, T547K, T15K
Case C, T540K, T20K
Case D, T540K, T30K
Case E, T535K, T30K
Yu et al., SAE 2007-01-0183
6
LES of hot spot growth

• Initial hot spots at 0 CAD sine waves
• Initial mean temperature at 0 CAD 1030 K
• Initial velocity at 0 CAD from LES
• Amplitude of temperature stratification 0 250
  K

7
Initial hot spots
8
Large hot spots
Hotspot size 64 mm
9
Temperature field, a/L1
CAD 1 ATDC
Hot spot size 64mm
10
Temperature field, a/L1
CAD 5 ATDC
Hot spot size 64mm
11
Temperature field, a/L1
CAD 10 ATDC
Hot spot size 64mm
12
Temperature field, a/L1
CAD 15 ATDC
Hot spot size 64mm
13
Temperature field, a/L1
CAD 20 ATDC
Hot spot size 64mm
14
Heat release a/L 1
Hot spot size 64mm
15
Incylinder pressure a/L1
Hot spot size 64mm
16
Small hot spots
Hotspot size 10,58 mm
17
Temperature field, a/L6
CAD 1 ATDC
Hot spot size 10,58 mm
18
Temperature field, a/L6
CAD 5 ATDC
Hot spot size 10,58 mm
19
Temperature field, a/L6
CAD 10 ATDC
Hot spot size 10,58 mm
20
Temperature field, a/L6
CAD 15 ATDC
Hot spot size 10,58 mm
21
Temperature field, a/L6
CAD 20 ATDC
Hot spot size 10,58 mm
22
Heat release a/L 6
Hot spot size 10,58 mm
Increase in temperature stratification
23
Incylinder pressure a/L6
Hot spot size 10,58 mm
Increase in temperature stratification
24
Very small hot spots
Hotspot size 6,35 mm
25
Temperature field, a/L10
CAD 1 ATDC
Hot spot size 6,35 mm
26
Temperature field, a/L10
CAD 5 ATDC
Hot spot size 6,35 mm
27
Temperature field, a/L10
CAD 10 ATDC
Hot spot size 6,35 mm
28
Temperature field, a/L10
CAD 15 ATDC
Hot spot size 6,35 mm
29
Temperature field, a/L10
CAD 20 ATDC
Hot spot size 6,35 mm
30
Heat release a/L 10
Hot spot size 6,35 mm
Increase in temperature stratification
31
Incylinder pressure a/L10
Hot spot size 6,35 mm
32
CA10
33
CA50
34
Total heat release 20 ATDC
35
Conclusions

• Larger hot spots are easier to cool down by
  turbulence heat transfer, difficult to ignite.
• With moderate temperature amplitude, very small
  hot spots are not easier to ignitie due to faster
  turbulence heat transfer within the hot spots
  that tend to smear out the hot spots.
• With very high temperature amplitude, very small
  hot spots can be ignited very fast. Heat
  transfer between hot spots are not fast enough
  to be in effect of the ignition.

36
Ongoing work

• How fast a hot spot is disturbed/dissipated by
  turbulence
• How are how spots generated in the cylinder