Overview Experimental Data Analysis and Modeling

Ignition Quality Tester (IQTTM)

Objective

Develop a pathway to use easily 

measured ignition properties as 

metrics for characterizing fuels in 

advanced combustion engine 

research

- Correlate IQTTM measured 

parameters with engine data

The information contained in this poster is subject to a government license; NREL/PO-540-40427; 2006 Diesel Engine-Efficiency and Emissions Research (DEER) Conference, Detroit, MI, August 20-24, 2006.

In HCCI engines, ignition timing 

depends on the reaction rates 

throughout compression stroke

- Need to understand 

sensitivity to T, P, and [O2]

- Need to rank fuels based on 

more than one set of conditions

- Need to understand how fuel 

composition (molecular species) 

affect ignition properties

3.5

3.0

2.5

2.0

1.5

1.0

0.5

1.1 1.2 1.3 1.4 1.5

In(Ignition Delay [ms])

1000/T

T = 550oC

T = 405oC

DCN = 42

DCN = 46

DCN = 53

DCN = 58

DCN = 81

DCN = 100

CARB Diesel

Heptane

Diesel w/EHN

Cetane

DPGME (oxy)

TPGME (oxy)

1200

1000

800

600

400

200

0

0 5 10 15 20

16

12

8

4

0

Pressure (psi)

Time (ms)

Needle Lift (mm)

Injector Needle

Pressure Trace

Ignition Delay

 Constant volume spray combustion chamber 

- Requires ~50 mL fuel

 Ignition delay can be measured 

over a range of conditions:

- T ~ 300 – 580°C

- P ~ 5 – 30 bar

- [O2]: Up to 21% or beyond

• Can measure derived 

cetane number (DCN) 

at specified conditions

3.5

3.0

2.5

2.0

1.5

1.0

0.5

1.1 1.2 1.3 1.4 1.5

In(Ignition Delay [ms])

1000/T(K)

T = 575oC

T = 405oC

PRF 30

PRF 50

PRF 100

Cetane - HMN

Cetane - AMN

3.5

3.0

2.5

2.0

1.5

1.0

0.5

1.1 1.2 1.3 1.4 1.5

In(Ignition Delay [ms])

1000/T

T = 575oC

Soy Biodiesel

Methyl Linoleate

Methyl Decanoate

CARB Diesel

PRF 30

PRF 50

PRF 100

3

2.5

2

1.5

1

1.2 1.25 1.3 1.35 1.4

25

20

15

10

5

0

0 5 10 15 20 25

In(Delay [ms])

1000/T (K)

Model Delay (ms)

Experimental Delay (ms)

18% Oxygen (14% EGR)

y = 0.9918x

R2 = 0.9888

10 bar

20 bar

30 bar

5

4

3

2

1

0

1.2 1.25 1.3 1.35 1.4

In(Delay [ms])

1000/T

0.5

0.6

0.7

0.8

0.9

1

Data

P = 21 bar

 Some oxygenates have a 

lower activation energy 

than normal hydrocarbons

- Higher effective cetane 

number at reduced 

temperature 

• Cold-start implications

• Impact on HCCI ignition

 Molecules with weakest 

C-H bonds have the lowest 

activation energy

- Tertiary < Secondary < Primary

- Adjacent to ether or carbonyl 

weaken C-H bonds

 Branching in hydrocarbons decreases activation energy

- Tertiary C-H bonds

 Aromatic compounds increase activation energy

- Resonance stabilization

 Biodiesel fuels have a higher 

activation energy for ignition

- Unsaturated bonds result in 

resonance-stabilized radicals

Mixing Factor Calculations

 Assumes fuel “perfectly” mixes with fraction of air in IQT

- Ignores spray and mixing time

- Accounts for temperature drop due to evaporation

 Data shows how mixing increases with ignition delay

- Lower mixing factor as pressure increases for fixed delay

Integrated CFD Model 

of IQTTM

 Spray: simplified cone model

 Evaporation and mixing

 Detailed chemistry w/ CHEMKIN 

- three mechanisms tested

 Ignition delays are too fast!

Rate = A exp ( -Ea

RT ) [O2]b

Heptane: Ea = 50.2 kJ/mol, b = 0.74

Developed set of 27 points

- T = 450, 500, 550 °C

- P = 10, 20, 30 bar

- [O2] = 15, 18, 21%

Fit empirical rate model

- To deconvolute [O2] 

and T effects

R• + O2 ⇔ RO2•

1000

800

600

400

200

-180 -130 -80 -30

60

50

40

30

20

10

0

Temperature (K)

Crank Angle Degree

Pressure (bar)

Pressure

Temperature

CIDI

HCCI

Fuel Sensitivity Parameters

DPGME

Tertiary C-H

adj. to -OSecondary C-H

adj. to -OTPGME

TEGME

2-Heptanone Methyl Caproate

HME 1-Heptanol

OH

OH

HO

O

O

O

O O

O

O

O

O

O O

O

OH

Increasing Activation Energy

Fuel Effects on Ignition and Their Impact on Advanced Combustion Engines

Joshua Taylor • National Renewable Energy Laboratory

Hailin Li and W. Stuart Neill • National Research Council Canada