Modeling of Alternative Fuels

and Fuel Blends Using Surrogates

Anne Lown

Lars Peereboom

Carl T. Lira

5/14/2014

Department of Chemical Engineering and

Materials Science

UNCLASSIFIED: Distribution statement A. Approved for public release

Outline

• Introduction

• Fuels of Interest

• Fuel Composition

• Surrogate Development and Modeling

• Cloud point

• Distillation curve

• Cetane number

• Compressibility

• Conclusions

2

Introduction• Alternative fuels important research

• Projected 60 billion gal required by 2022[1]

• Mandated deadlines for renewable content in diesel

and jet fuels approaching[2]

• Second generation biofuels produce a wide

variety of molecules

• Ethanol from lignocellulosic sources

• Hydrocarbons from Fischer-Tropsch

• Butanol or mixed alcohols

3

1. Biofuels Digest. “Biofuels Mandates Around the World” http://www.biofuelsdigest.com/bdigest/2011/07/21/biofuels-mandates-

around-the-world/

2. St. Paul Pioneer Press (MN) - November 5, 2011 - A14 Business. “Officials urge delay in biodiesel boost”

Project Goals• Use of surrogates to predict mixture

properties

• Improve property prediction for fuels and

blends

• Minimize number of tests for a fuel/blend

• Minimize number of surrogate components

• Wide range of fuel specifications

4

Fuels of Interest

• JP-8 – Aviation fuel

• IPK – Fischer-Tropsch fuel

• Highly branched, gas-to-liquid (GTL) process

• HRJ-8 – Hydrotreated plant oil

• UOP process

• 4 additional alternative fuels in research

set

5

Fuel Composition

6

Petroleum Fuels

• Petroleum fuels have 5 classes of

components• Paraffins (n-alkanes)

• Isoparaffins

• Aromatics

• Naphthenes (cycloparaffins)

• Olefins

• Paraffins important for cold flow

• Ratio between alkanes, isoparaffins, and

aromatics important for cetane number

7

Composition Profile for JP-8

Experimental data provided by J. T. Edwards, AFRL, Wright Patterson AFB,

2014

UNCLASSIFIED

8

Composition Profile for IPK

9Experimental data provided by J. T. Edwards, AFRL, Wright Patterson AFB,

2014

UNCLASSIFIED

Composition Profile for HRJ-8

10Experimental data provided by J. T. Edwards, AFRL, Wright Patterson AFB,

2014

UNCLASSIFIED

Surrogate

Development

11

Surrogate Development

• Most literature surrogates optimized to fit

one fuel property

• Need extension of surrogates to represent

multiple properties

• Surrogate composition guided by testing of

neat fuel batches

• Goals

• Identify key components to include in surrogate

• Develop code for predicting blend properties

12

MSU JP-8 Surrogate

Component StructureWeight % in

Surrogate

n-Octylbenzene 14.8

2,2,5,5-

Tetramethylhexane20

n-Butylcyclohexane 23

3-Methylundecane 2313

• 16 components total, only 4 adjusted

• 11 paraffins, total 17.8wt%

• 1-Methyl naphthalene for di-aromatic,

1.2wt%

Cloud Point TemperatureTemperature at which the first solid forms in a fuel

14

Cloud Point Model• Solid Solution[3]

• Change T until ΣxiS = 1

• Can model selective precipitation by limiting

which components solidify

• UNIFAC model used for activity coefficients

in liquid phase

15

−

∆−==

im

fus

i

S

i

L

i

L

ii

TTR

H

x

xK

,

11exp

γ

3. Hansen et al. AIChE Journal. 1988, Vol. 34, pg 1937.

Jet Fuel Surrogates' Predicted Cloud Points

16

Fuel Cloud Point

MSU JP-8 Surrogate

4. Huber, M.L., E. W. Lemmon, and T. J. Bruno, Surrogate Mixture Models for the

Thermophysical Properties of Aviation Fuel Jet-A. Energy and Fuels, 2010. 24: p. 3565–3571

Distillation CurveChange in boiling temperature as more fuel is distilled

17

Distillation Curve Model• Single-stage batch distillation model

• Raoult’s law used to calculate bubble point

temperature

• Pre-set number of moles evaporated at

equilibrium concentration

• Change in liquid phase calculated

18

MSU Surrogate Distillation Curve

19

ASTM D-86Surrogate Model

80 90 1000 60 7040302010 50Volume Percent Distilled

Te

mp

era

ture

(˚C

)300

275

250

225

200

175

150

Cetane NumberMeasurement of the ignition delay in a compression-ignition

engine

20

Cetane Number Model• Cetane number – measure of ignition delay

in a compression ignition engine

• Use the correlation of Ghosh and Jaffe (ExxonMobil)[5]

• β is an empirical parameter dependent on the molecular class

• Mixtures of fuels can also be calculated using surrogate β values

215. Ghosh P., Jaffe S.B., Detailed Composition-Based Model for Predicting the Cetane Number

of Diesel Fuels, Industrial & Engineering Chemistry Research, 45 (2006) 346-51.

Cetane Number vs Carbon Number

22

Only Mono-Iso

Only Multi-Iso

Average Iso

Cetane Number for IPK and JP-8

Experimental data provided by N. Hubble TARDEC, Warren, MI, 2014

UNCLASSIFIED23

CompressibilityChange in volume of a fluid as the pressure is increased

24

Compressibility Model• Compressibility of a fuel affects:• Injection timing

• Injected mass

• Emissions

• Prediction requires an EOS

25

ESD and SAFT-BACK

ESD (cubic)

0 2000 4000 60000

2

4

6

8

10

12

14

16

18

Density (mol/m3)

P (MPa)

298.15 K

410.93 K

510.93 K

675 K

SAFT-BACK

0 2000 4000 60000

2

4

6

8

10

12

14

16

18

Density (mol/m3)

P (MPa)

298.15 K

410.93 K

510.93 K

675 K

26

• Prediction for the density of n-decane using two

different models

Conclusions• Alternative fuel blend properties can be

modeled with appropriate surrogates

• PIAN distribution necessary for the representation of both distillation curve and cloud point

• Cetane model not dependent on detailed composition information

• Current surrogate results provide good estimates for CP, molecular weight, distillation curve, cetane number

27

Acknowledgements• B. Windom, M.L. Huber, and T.J. Bruno –

National Institute of Standards and Technology

• N. Hubble – TARDEC

• R. W. Morris and J. T. Edwards – AFRL, Wright Patterson AFB

• Defense Logistics Agency• Contract Number SP4701-09-C-0037

• Contract Number SP4701-11-C-0011

• Tank Automotive Research, Development, and Engineering Center• Contract Number W56HZV-13-C-0340

Questions?28

References1. Biofuels Digest. “Biofuels Mandates Around the World”

http://www.biofuelsdigest.com/bdigest/2011/07/21/biofuel

s-mandates-around-the-world/

2. St. Paul Pioneer Press (MN) - November 5, 2011 - A14

Business. “Officials urge delay in biodiesel boost”

3.Hansen et al. AIChE Journal. 1988, Vol. 34, pg 1937.

4. Huber, M.L., E. W. Lemmon, and T. J. Bruno,

Surrogate Mixture Models for the Thermophysical

Properties of Aviation Fuel Jet-A. Energy and Fuels,

2010. 24: p. 3565–3571.

5. Ghosh P., Jaffe S.B., Detailed Composition-Based

Model for Predicting the Cetane Number of Diesel Fuels,

Industrial & Engineering Chemistry Research, 45 (2006)

346-51.

29