Relationship between Threshold Soot Index and Soot Levels for Surrogate Fuels

Venkatesh Iyer, Suresh Iyer, Milton Linevsky, Thomas Litzinger, and Robert Santoro

The Pennsylvania State University, University Park, PA 16802

Smoke point measurement is required for characterization of jet fuels

• Smoke Point = maximum height of a smoke free laminar diffusion flame

Increasing fuel flow

Smoke Point

Up to smoke point:

Production = Oxidation

Above smoke point:

Production > Oxidation

Kent and Wagner, 1984 Z = z (D/Q)

Calcote and Manos created Threshold Soot Index (TSI) to correlate smoke point data

SP = smoke point heightMW = molecular weighta & b = constants dependent on the experiment.

bSP

MWaTSI +⎟⎠⎞

⎜⎝⎛=

Linear behavior of TSI for mixtures facilitates matching of surrogate to actual fuels

R2 = 0.9775

0

2

4

6

8

10

12

14

16

0 0.2 0.4 0.6 0.8 1Iso-octane mole fraction

MW

/Sm

oke

Poi

nt

Calibration of Smoke Point apparatus is done with mixture of iso-octane and toluene

Peak Centerline Soot fv vs. TSI (Olson et al., 1985)

n-propylbenzene

1,3,5-trimethylbenzene

Wick burner for studies of soot fields of surrogates and jet fuels

Inner tubeOuter tube

Ceramic honeycomb

3mm glass beads

ASTM Standard wick

Translation stage

Soot measured with light extinction

Fuel Matrix for Wick Burner Studies

Smoke Height ASTM Burner 

(mm)

TSI ASTM Burner

H/C ratio

Jet A (4658) 22.1 21.4 1.957

2nd generation surrogate

22.5 20.4 1.95

D95 38.5 13.9 2.1*

JP8 (5699) 23 22.3 1.935

D95 + toluene 23 21.7 1.913

*estimated

Exxsol D95: Narrow cut (C12-C16), de-aromatized solvent

Carter et.al. (2000)

15.0 20.0 25.0 30.0 35.0

n-C12

n-C13

n-C14

n-C15

iso-C13

iso-C14

15.0 20.0 25.0 30.0 35.0

n-C12

n-C13

n-C14

n-C15

iso-C13

iso-C14

Approximate composition

Normal paraffins 23%

Iso-paraffins 33%

Cyclo-paraffins 44%

Fuel Matrix for Wick Burner Studies

Smoke Height ASTM Burner

(mm)

TSI ASTM Burner

H/C ratio

Jet A (4658) 22.1 21.4 1.957

2nd generation surrogate

22.5 20.4 1.95

D95 38.5 13.9 2.1*

JP8 (5699) 23 22.3 1.935

D95 + toluene 23 21.7 1.913

*estimated

10mm height

12.5mm height

Soot volume fractions distribution:Jet A (4658) and MURI 2nd generation surrogate

2nd gen. surrogateJet A (4658)

Fuel Matrix for Wick Burner Studies

Smoke Height ASTM Burner

(mm)

TSI ASTM Burner

H/C ratio

Jet A (4658) 22.1 21.4 1.957

2nd generation surrogate

22.5 20.4 1.95

D95 38.5 13.9 2.1*

JP8 (5699) 23 22.3 1.935

D95 + toluene 23 21.7 1.913

*estimated

Soot volume fractions distribution:JP8 (5699) and D95 – Toluene surrogate

D95-TolueneJP8 (5699)

5mm height

7.5mm height

Soot volume fractions distribution:JP8 (5699) and D95 – Toluene surrogate

D95-TolueneJP8 (5699)

10mm height

12.5mm height

Soot volume fractions distribution:JP8 (5699) and D95 – Toluene surrogate

D95-TolueneJP8 (5699)

15mm height

17.5mm height

TSI Summary• Jet A (4658) / 2nd generation surrogate

– Different smoke heights on the wick burner: 21mm v 23 mm– Similar peak volume fractions– Different radial soot profiles: offset axially by ~2mm

• JP8 (5699) / D95 + Toluene surrogate– Same smoke heights on the wick burner– Similar peak volume fractions– Similar radial soot profiles

Comparison of Surrogate and JP8 in Dump Combustor

Dump Combustor

Optical access --soot via light extinction

Fuels for Dump Combustor Study

Smoke Height ASTM Burner

TSI ASTM Burner

H/C ratio

JP8 (5699) 23 22.3 1.935

D95 + toluene 23 21.7 1.913

2nd generation surrogate is too expensive to run in these experiments

19

P=5 atm

Inlet T=510K

Possible causes of difference in soot levels for JP8 and surrogate

• H/C ratio

• Soot production from toluene compared to larger alkyl aromatics

• Differences in physical properties

What next?

• Soot production in dump combustor– Understand difference between D95 surrogate and

JP8– Studies of next gen surrogates

• Soot fields in wick burner flames– Understand different behavior of D95 surrogate and

2nd generation surrogate– Understand differences in peak fv, soot formation and

oxidation rates among aromatic compounds

Penn State teaming with Innosense, LLC to design rapid smoke point apparatus (Army STTR A10a-T010)