Download Auto-Ignition Characteristics of Different Fuels with IQT, and Pentane

Auto-Ignition Characteristics of Different Fuels with
IQT, and Pentane Isomers Research with CFR
Engine.
ME 490 Project Report
Iljin Eum,
Mechanical Engineering
University of Michigan
Mentored by:
Prof. Andre Boehman
Submitted to:
Prof. Andre Boehman
Mechanical Engineering
College of Engineering
University of Michigan
Dec. 16th 2015
ACKNOLDGEMENTS
First, I would like to express my gratitude to Prof. Andre Boehman for offering me such a great
opportunity. His advice and guidance helped me set a correct direction and goal throughout the
project. In addition, it was a semester which I could learn a lot and expand my experiences above
the undergraduate level of learnings while participating his research group.
Also, I would like to thank Prof. Diann Brei, Chair of RISE program, for allowing me to modify
the project in the middle of the semester and thoughtful advice for MEUS preparation.
Lastly, I really appreciate my research lab-mates: Dongil Kang and Karthik Kandappan. Without
their support and help, it would not be possible to conduct and accomplish the project.
1
Table of Contents
ABSTRACT.....................................................................................................................................3
INTRODUCTION........................................................................................................................4-5
Fuel Research with IQT…………………………………………………………………...4
Pentane Isomers Auto-Ignition Characteristics with CFR Engine………………………..5
METHODOLOGY…………………………………………………………………………….6-10
Fuel Research with IQT………………………………………………………………....6-7
Pentane Isomers Auto-Ignition Characteristics with CFR Engine…………………….8-10
RESULTS/DISCUSSION……………………………………………………........................11-17
Fuel Research with IQT………………………………………………………………11-12
Pentane Isomers Auto-Ignition Characteristics with CFR Engine…………………...13-17
CONCLUSION/RECOMMENDATION…………………..........................................................18
REFERENCES……………………………………………………..............................................19
2
ABSTRACT
This report consists of two main parts: analysis of auto-ignition characteristics of different fuels
using the ignition quality tester (IQT), and auto-ignition characteristics of pentane isomers using
the cooperative fuel research (CFR) engine. The ignition delay (ID) and derived cetane number
(DCN) measured from IQT are important in diesel fuel formulation since the rate of burning is
essential in compression ignition and also closely related to the performance of an engine: knock,
efficiency, and emissions. Thus, different types of hydrocarbons and oxygenated diesel fuels are
analyzed in a constant volume combustion chamber (CVCC) under a temperature of 575 °C.
Another research about pentane isomers are important to enhance understanding of the
relationship between the chemical structure and auto-ignition characteristics. To observe the
differences in auto-ignition characteristics, the heat release rate and emissions are analyzed. The
CFR engine varies the compression ratio while keeping the engine speed at 600 rpm and the
intake temperature at 120 °C. Intermediate species are analyzed using exhaust gas samples with a
gas chromatography flame ionization detector (GC-FIC). The results show that the unique
structures of pentane isomers impact differently on intermediate species as well as auto-ignition
characteristics. The study has led to an improved understanding of the ignition characteristics of
diesel fuels and pentane isomers.
3
INTRODUCTION
Fuel Research with IQT
The compression ignition engine uses auto-ignition of fuels to produce the required power
output. In auto-ignition, the time duration between the start of injection (SOI) and the start of
combustion (SOC) are essential, and it is defined as the ignition delay (ID). Based on the
measured ID, the derived cetane number (DCN) can be calculated. These measured ID and DCN
can be utilized in many different applications: formulation of alternative diesel fuels, design of
engine geometry, and basis for the improvement in efficiency and emissions.
The goal of the research is to investigate ID and DCN using the ignition quality tester (IQT).
Potentially, the results of the research can help users determine an appropriate fuel with target
cetane number; for example, high cetane fuels can provide cold starts, more complete
combustion, lower misfires, and lower engine-out emissions. Based on the ASTM D6890-08, the
following fuels are analyzed in a constant volume combustion chamber under the temperature of
575 °C.











N-heptane
Ford Tier 2 Diesel
Tri-propylene glycol methyl ether (TPGME)
Di-propylene glycol methyl ether (DPGME)
Methyl Decanoate
Heptamethylnonane (HMN)
N-hexadecane + TPGME (50:50 volume basis)
Heptamethylnonane + TPGME (50:50 volume basis)
Surrogate fuel (SR) + TPGME (50:50 volume basis)
N-dodecane
PRF blends
To prepare the surrogate fuel (SR), 77% volume of n-dodecane and 23% volume of m-xylene are
blended.
For PRF fuels of target CN, the following equation is used.
𝐶𝑁 = % 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑛 − ℎ𝑒𝑥𝑎𝑑𝑒𝑐𝑎𝑛𝑒 + 0.15 × % 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐻𝑀𝑁
For the future and extended scope of the project, the CN rating results from IQT needs to be
validated using the different instrument: Cetane Ignition Delay (CID) 510 which is capable of
creating various test conditions by varying temperature and pressure of the chamber, and %EGR
of the working fluid.
4
Pentane Isomers Auto-Ignition Characteristics with CFR engine
To observe the variation in auto-ignition characteristics and chemical species of fuels before the
complete combustion, it is required to create low temperature conditions. Using the CFR engine
which is capable of varying the compression ratio, temperature regimes between the incomplete
and complete combustion are built by sweeping the compression ratio from 4 to 14.
For the fuel selection, especially, this study focuses on the pentane isomers, C5: n-pentane, isopentane, and neo-pentane. Since each pentane isomer has different unique structures and autoignition characteristics, it is possible to observe the behavior of intermediate species during the
low temperature combustion for better understanding of chemical structural impacts on autoignition.
CO emissions, unburned C5 fraction within the exhaust, and heat release are used to observe the
variation in reactivity of each isomer. Also, the exhaust gas samples are analyzed using gas
chromatography flame ionization detector (GC-FID) observing the differences in intermediate
species: especially, conjugate alkenes.
As observed in the previous study using a rapid compression machine (RCM) [1], the results of
low temperature incomplete combustion with C5 possesses three different regimes clearly: low
temperature oxidation (LTO), negative temperature coefficient (NTC), and high temperature
oxidation (HTO). Reactivity results show that n-pentane has the highest reactivity followed by
neo-pentane and iso-pentane. While all three isomers have similar conjugate alkenes behavior
during LTO, the NTC regime has obviously different intermediate species due to the various
structure and degree of H-atom abstraction.
For the future and extended scope of the project, a different GC-FID with capability of capturing
oxygenated species will be helpful for the better understanding of intermediate species
behaviors. Also, it is required to have better characterization of the oxidation processes
experimentally and numerically during the incomplete combustion.
5
METHODOLOGY
Fuel Research with IQT
Device
To measure the ignition delay (ID) and derived cetane number (DCN) of different fuels, the
ignition quality tester is used, shown in Figure 1.
Figure 1: Ignition Quality Tester (IQT) made by AET Ltd. [2].
The IQT is capable of measuring ID and DCN accurately based on the several test methods:
ASTM 6890 (method used in this research), ASTM D975, ASTM D6751, and ASTM D7467.
All the data of the results are automatically saved in the computer connected to the IQT through
the built-in software. Also, IQT is able to sweep temperature from 550 to 600 °C.
Compressed gas for testing
For the air of the actuator and injection process, the oil free compressed air of less than 0.1
volume % water is used at 175 psi.
The charge air for the combustion uses the compressed air of 20.9 ± 1.0 volume % oxygen, less
than 0.003 volume % hydrocarbons, and 0.025 volume % water at 310 psi.
Lastly, 99.9 volume % nitrogen at 50 psi is required to pressurize the fuel tank and injection.
Calibration of IQT
Based on the ASTM D6890 [3], the derived cetane number (DCN) is calculated using the
following equation.
186.6
𝐷𝐶𝑁 = 4.460 +
𝐼𝐷
where ID in milliseconds (ms).
6
For calibration of the machine, n-heptane of purity with 99.5 volume % was used. The chamber
temperature was determined when the measured ignition delay of n-heptane was same as the
standard value of 3.78 ms according to the ASTM D6890.
Test procedure
First, the coolant ran through the injection system and all other sensors to protect from
damaging. Then, the chamber was heated up to the target temperature, 575 °C, which was set by
the built-in software.
Once the temperature reached the target value, the leakage test was performed. The required
values for the pressure tests are listed below.
Table 1: The maximum allowable rate of change of combustion chamber pressure
Pressure Test
With Charge
Without Charge
Maximum allowable rate of change of combustion
0.50 psi/s
0.10 psi/s
chamber pressure
After the leakage test, fuels to be tested were injected into the fuel reservoir. Before injecting the
fuel, all the fuels were filtered using 3 to 5 micron Teflon filter with a syringe. Once the fuels
were injected into the reservoir, nitrogen was used to pressurize the fuel injection system.
Whenever a different fuel was tested, the injection system and fuel tank were purged using the
torque bleed valves and nitrogen gas.
Before starting the test, the sensor diagnostics was conducted. By adjusting the position of the
needle valve manually, the needle lift and pressure profiles were checked on the monitor.
For each fuel, 15 pre-injections and 32 actual injections were performed. The ID and DCN were
averaged from 32 actual injections data only. All the ID and DCN values were automatically
saved in the software.
7
Pentane Isomers Auto-Ignition Characteristics with CFR engine
All the tests were conducted using the cooperative fuel research (CFR) engine. Tenax trap and
self-designed test rig were used to capture the exhaust gas. The collected exhaust gas samples
were analyzed by a NDIR emission analyzer and gas chromatography flame ionization detector
(GC-FID). All the details are listed below.
Test fuels
The specifications of three fuels are listed below.
 n-pentane: 109-66-0, 99%
 iso-pentane: 78-78-4, 99%
 neo-pentane: 463-82-1, 99%
Engine setup
The CFR engine was modified to utilize the direct injection system. The fuel was injected into
the upstream of the intake system which was heated at 120 °C. Therefore, the air/fuel mixture was
premixed and homogeneous.
Fuel injection
CFR Engine
Cylinder
Injection line
Figure 2: CFR engine and the intake system.
Engine speed was kept at 600 rpm throughout the entire experiments. Also, the equivalence ratio
was constant at 0.25 during the experiments. To calculate the equivalence ratio, a Delphi hotwire mass air flow sensor was used for the air flow rate. A Max Model 213 piston flow meter
measured the fuel flow rate of n-pentane and iso-pentane. For neo-pentane, a Sierra Top-Trak
Model 826 was used. All the temperatures and pressures of the line and cylinder were measured
and saved through the labview program. For the cylinder chamber, especially, the temperatures
were measured by a MEDTHERM coaxial thermocouple on the side of combustion chamber.
The in-cylinder pressure was recorded by a Kistler 6052B piezoelectric pressure transducer in
the cylinder head.
Exhaust gas sampling setup
CO and CO2 emissions were recorded and monitored using a NDIR analyzer. The exhaust gas
was collected at 2.35 L/min through the line heated at 190 °C. Before capturing the exhaust sample,
it was filtered by Tenax trap to remove the heavy hydrocarbons or lubricant oils.
8
Tenax Trap
Figure 3: Exhaust gas sampling setup and a gas sampling bag.
The exhaust samples were diluted with the internal standard gas at 10:1 ratio (total
volume:exhaust gas volume). To avoid the residuals within the exhaust lines, 10:1 ratio capturing
was performed as 9 min 36 sec of the internal standard, 1 min 12 sec of the exhaust, and again 1
min 12 sec of the internal standard. 9.3 ppm propane and nitrogen gas were used as an internal
standard to quantify the species within the exhaust gases.
The analysis was conducted using Shimadzu GC-17A (GC-FID). The oven temperature started
from -80 °C to 238 °C to quantify C1-C10 hydrocarbons using a 130 species retention library [4].
Figure 4: GC-FID made by Shimadzu, model number is GC-17A.
Knowing the concentration of the internal standard, the area of the propane from GC-FID result
was converted into the value of concentration/area. By multiplying this factor to all other species,
the actual ppm of each species was calculated.
9
Compression ratio determination
To determine six different compression ratios where the exhaust samples were collected, the CO
emission was observed using each fuel while sweeping the compression ratio.
LTO
NTC
HTO
CCR
Figure 5: CO emissions and in-cylinder maximum temperature of neo-pentane.
As shown in Figure 5, the in-cylinder temperature increases as the compression ratio increases.
The temperature and pressure variation within the chamber influences the CO emission. From
the very beginning of the CO emission to the point where CO becomes stabilized, it is called
“Low Temperature Oxidation” (LTO) regime. The regime where the CO emission remains
constant is called “Negative Temperature Coefficient” (NTC). Lastly, CO emission increases
sharply up to the point where the complete combustion starts. This compression ratio is called
“Critical Compression Ratio” (CCR), and the regime is called “High Temperature Oxidation”
(HTO). 1 – 3 compression ratios from each regime were selected (total 6 points) to see the
changes in the intermediate species from the exhaust gas sample analysis.
Test procedure
For each fuel, the CO emission was recorded and considered to determine 6 compression ratios.
Once 6 points were determined, each pentane isomer was injected and burned during the
incomplete combustion to collect the exhaust sample at those 6 points of compression ratios.
Using the GC-FID and heat release calculation, the 6 exhaust samples for each pentane isomer
were analyzed.
10
RESULTS/DISCUSSION
Fuel Research with IQT
First, n-heptane was used to calibrate the IQT by varying the in-cylinder temperature. The results
are shown in Table 2 below.
Table 2: Calibration results using n-heptane at different set temperatures.
Derived Cetane
Fuel
Ignition Delay (ms)
Tset (°C)
Number ()
n-heptane
3.266
61.58
590
n-heptane
3.131
64.72
600
n-heptane
3.534
57.27
575
n-heptane
3.832
53.16
590
n-heptane
3.293
61.00
595
n-heptane
3.432
58.94
585
n-heptane
4.236
48.51
565
n-heptane
3.928
51.97
570
n-heptane
3.863
52.77
572.5
n-heptane
3.844
53.00
573.5
n-heptane
3.806
53.49
575
n-heptane
3.694
54.98
576.5
n-heptane
3.780
53.82
575.5
At the beginning of the test, the IQT system was unstable due to the exchange of gaskets, coolant
system, and needle lift sensor. Thus, the ID and DCN values at 575 °C were significantly different
from the final calibration value and temperature which is noted in red color at the bottom row. As system
became stable by adjusting the position of the sensor and other systems, the ID and DCN values started to
have a trend and consistent. Thus, the IQT system was determined to use 575 °C as a calibrated
temperature for other fuels since ID at 575.5 °C was 3.78 which was within the error range of the standard
value for n-heptane: 3.78 ± 0.01 ms.
The following table shows the results of ID and DCN for all other fuels (page 12).
11
Table 3: ID and DCN for all other diesel hydrocarbon and oxygenated fuels at 575 °C.
Ignition Delay
Derived Cetane
Fuel
Tset (°C)
(ms)
Number ()
Ford tier 2 diesel
4.54 ± 0.27
45.57 ± 2.52
575
TPGME
2.39 ± 0.56
96.87 ± 31.5
575
Ford tier 2 diesel +
2.79 ± 0.28
75.08 ± 10.1
575
TPGME
Methyl Decanoate
3.71 ± 0.39
54.79 ± 5.32
575
DPGME
3.96 ± 0.47
51.62 ± 5.80
575
n-dodecane
2.59 ± 0.17
83.92 ± 8.75
575
n-hexadecane
2.05 ± 0.08
130.74 ± 13.7
575
Heptamethylnonane
18.75 ± 3.47
16.46 ± 1.77
575
(HMN)
Surrogate fuel + TPGME
2.47 ± 0.16
89.82 ± 9.65
575
(50:50 volume)
n-hexadecane + TPGME
1.98 ± 0.11
142.96 ± 20.7
575
(50:50 volume)
HMN + TPGME
3.09 ± 0.25
65.78 ± 6.60
575
(50:50 volume)
PRF 85
(HMN 82 % volume + n2.50 ± 0.14
88.48 ± 8.06
575
hexadecane 18 % volume)
PRF 65
(HMN 59 % volume + n2.97 ± 0.17
69.36 ± 5.19
575
hexadecane 41 % volume)
PRF 45
(HMN 65 % volume + n4.95 ± 0.53
42.21 ± 3.10
575
hexadecane 35 % volume)
All the ID and DCN were calculated using the measured values from 32 actual injections at each
test run. The error analysis has 95% reliability.
As shown in Table 3, some fuels do not match with the expected DCN values. For example, PRF
85, 65, and 45 are expected to have DCNs of 85, 65, and 45 respectively. Nonetheless, the actual
DCN measured from the IQT do not coincide with them. Also, during the test runs, it was
observed that the pressure had some instability issues. In addition, the actual chamber
temperature was kept at 525 °C although the set temperature was 575 °C throughout the tests. Thus,
some fuels exhibit large uncertainties: the error of TPGME is about 30% of the actual values.
Further testing with the IQT and some other methods are required to validate the values
measured from the IQT.
12
Pentane Isomers Auto-Ignition Characteristics with CFR engine
To observe the reactivity and intermediate species variation at each compression ratio, CO
emissions, unburned C5 concentration, heat release, and conjugate alkenes were analyzed.
Concentration analysis
For all the analyses in this section, the concentration was calculated in ppm of C1 value. If the
captured species from GC-FID is C4, ppm C1 is 4 times of the ppm of C4 value.
For GC-FID analysis, the internal standard of 9.3 ppm, C1 propane was used as a conversion
factor. Since the entire exhaust sample was diluted as 10:1 ratio (total volume:exhaust sample),
the actual concentration of propane in the exhaust gas was 90% of the total volume.
𝐴𝑐𝑡𝑢𝑎𝑙 𝑝𝑝𝑚, 𝐶1 𝑜𝑓 𝑝𝑟𝑜𝑝𝑎𝑛𝑒 = 9.3 𝑝𝑝𝑚, 𝐶1 ×
9
= 8.37 𝑝𝑝𝑚, 𝐶1
10
If the area of propane measured from GC-FID analysis is 3000, the conversion factor becomes
𝐶𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 =
8.37 𝑝𝑝𝑚, 𝐶1
3000
Now, if a captured species from GC-FID has an area of 6000, the concentration of the species
becomes
8.37 𝑝𝑝𝑚, 𝐶1
× 6000 = 16.74 𝑝𝑝𝑚, 𝐶1
3000
Again, since the exhaust gas was diluted as 10:1, the actual concentration of the species needs to
be multiplied by 10. Therefore, it is 167.4 ppm, C1.
To calculate the % concentration of a species, it is required to find the actual concentration of
input fuel (C5).
Global reaction of pentane (C5H12) is as follows.
𝐶5 𝐻12 + 𝑎(𝑂2 + 3.76𝑁2 ) → 5𝐶𝑂2 + 6𝐻2 𝑂 + 3.76 · 𝑎 · 𝑁2
Under the stoichiometric condition, a = 8.
With the equivalence ratio (𝜙) of 0.25, a = 32.
The mole fraction of carbon is
1 (𝑚𝑜𝑙𝑒 𝑜𝑓 𝑓𝑢𝑒𝑙)
= 0.006522 = 6522 𝑝𝑝𝑚, 𝐶1
1 + 32 · 4.76 (𝑚𝑜𝑙𝑒 𝑜𝑓 𝐴/𝐹 𝑚𝑖𝑥𝑡𝑢𝑟𝑒)
This 6522 ppm, C1 means the total input concentration of fuel (C5). This number was used as a
denominator for the entire exhaust gas species analysis.
For example, if the unburned C5 concentration analyzed from GC-FID is 652 ppm, C1,
13
𝑈𝑛𝑏𝑢𝑟𝑛𝑒𝑑 𝐶5 % 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
652 𝑝𝑝𝑚, 𝐶1
= 0.099 = 9.9 %
6522 𝑝𝑝𝑚, 𝐶1
CO emissions and unburned C5 (fuel) concentration
Figure 6 shows the results of CO emissions recorded by a NDIR analyzer, and calculated %
concentration of unburned C5 (fuel).
neo-pentane
neo-pentane
iso-pentane
iso-pentane
n-pentane
n-pentane
Figure 6: CO emissions (left) and unburned C5 concentration (right) at different
compression ratios.
As shown in Figure 6, CO emission result and % concentration result both agree. All three
isomers have three distinct regimes: LTO, NTC, and HTO. The reactivity from CO emission
profiles show that n-pentane has the highest reactivity, followed by neo- and iso-pentane. This
also can be observed in the unburned % concentration plot. While n-pentane is consumed fastest,
iso-pentane shows the slowest consumption rate with the longest NTC regime.
Heat release
The following figure shows the heat release rate of each isomer at different compression ratio to
observe the differences in reactivity and auto-ignition characteristics.
n-pentane
neo-pentane
n-pentane
neo-pentane
iso-pentane
iso-pentane
Figure 7: Heat release rate of each isomer at 8.5 compression ratio (left), and critical
compression ratio (right).
14
From the left side of the graph, it is observed that n-pentane has distinct two stage of heat
releases: small one on the left = low temperature heat release, and the other on the right = high
temperature heat release (although the entire process occurred during the low temperature
incomplete combustion, words of low and high temperature were used to differentiate two
different heat release stage). While n-pentane was close to the critical compression ratio of 8.55,
neo- and iso-pentane were both at NTC regime at 8.5 compression ratio. Therefore, it is observed
that neo only has a low temperature heat release while iso, which has the lowest reactivity, has
almost no heat release.
The graph on the right side shows the heat release rate of each isomer at its own CCR. Both nand neo-pentane have two stage heat releases. However, iso-pentane shows only single stage
heat release.
Conjugate Alkenes
In pentane isomer reactions, the conjugate alkenes mean the formation of one double bond from
the original pentane isomers by losing 2 hydrogen atoms.
For example, one of the conjugate alkenes is trans-2-pentene from n-pentane.
n-Pentane (C5H12)
trans-2-pentene (C5H10)
Since the conjugate alkenes are the dominant chemical reaction during the NTC regime, this GCFID analysis specifically focuses on them to observe how different structure of each isomer
affects the intermediate species during the incomplete combustion.
(n-pentane)
trans-2-pentene
1-pentene
cis-2-pentene
Figure 8: Conjugate alkenes variations of n-pentane at different compression ratio.
As shown in Figure 8, all conjugate alkenes increase from LTO through the NTC regime, and
decrease in HTO. Among the conjugate alkenes, there exists a variation as well.
15
Before talking about conjugate alkenes, the bond strength between the carbon and hydrogen
atoms needs to be stated. When a carbon has another carbon connected to itself, it is called a
primary carbon. Likewise, a carbon with two other carbons is secondary, and a carbon with three
other carbons is tertiary. Now, if a hydrogen atom is connected to a primary carbon, it is called a
primary hydrogen and has the largest bond strength, followed by the secondary and the tertiary.
Since n-pentane has 2 primary and 3 secondary carbons, it is likely to form a double bond
between two secondary carbons. This is why trans-2-pentene has the highest concentration. It is
followed by 1-pentene which has a double bond between a primary and a secondary. Although
cis-2-pentene has an exactly same structure as a trans-2-pentene, it is unlikely to be formed
because cis-2-pentene is a very unstable material.
This mechanism was observed in iso-pentane as well. The following figure shows the conjugate
alkenes profile of iso-pentane.
(iso-pentane)
2-methyl-1-butene
3-methyl-1-butene
2-methyl-2-butene
Figure 9: Conjugate alkenes variations of iso-pentane at different compression ratio.
Similarly, conjugate alkenes increase from LTO through NTC regime, and decrease in HTO.
Differences in concentration of conjugate alkenes can be explained similarly again. Iso-pentane
has 3 primary, 1 secondary, and 1 tertiary carbons. Therefore, a double bond formation is likely
to happen at the tertiary carbon which has the weakest bond strength. Unlike the previous case,
however, one tertiary bond has 2 options: a double bond with one of 2 primary carbons (2methyl-1-butene) or a double bond with 1 secondary carbon (2-methyl-2-butene). Although the
secondary bond has a weaker strength, the actual concentration shows that 2-methyl-1-butene
(double bond between 1 tertiary and one of 2 primary) has a higher concentration because the
probability of 2-methyl-1-butene is higher. From the tertiary carbon perspective, it has 3
neighbors: 2 primary and 1 secondary. It is true that a double bond formation is more active with
the secondary, but the number of double bond formation with 2 primary is larger than that of 1
secondary. This is why 2-methyl-1-butene has the highest concentration. 3-methyl-1-butene has
a double bond between a secondary and a primary, so it ranks the second highest concentration.
16
Lastly, Figure 10 shows the results of neo-pentane analysis.
(neo-pentane)
C2-C3
(iso-butene, C4H8)
Figure 10: Conjugate alkenes variations of neo-pentane at different compression ratio
Unlike the previous two cases (n-, and iso-pentane), neo-pentane shows different results. As
shown in Figure 10, it does not have any conjugate alkenes in the exhaust gas. Since neo-pentane
has all primary carbons, it is hardly to form conjugate alkenes from neo-pentane. Instead of
conjugate alkenes, 2-methylpropene (iso-butene) is a major species and follows the same trend as
conjugate alkenes. It increases from LTO through NTC, and then decreases in HTO regime.
From the GC-FID data analysis, it can be observed that the unique structure of each isomer has
all different intermediate species paths.
17
CONCLUSION/RECOMMENDATION
Fuel Research with IQT
During the test, IQT was calibrated with n-heptane and kept at 575 °C. While observing the
results of the test and performing literature reviews, it can be concluded that there is no one strict
way to define or measure the cetane number of fuels. Since the IQT possesses some limits: short
range of temperature sweeps, no pressure variation, and discrepancy between the set and actual
chamber temperature, it is highly recommended to validate the ID and DCN values by
comparing those from other methodology.
Pentane Isomers Auto-Ignition Characteristics with CFR engine
Based on the results of CO emissions, unburned C5 % concentration, and heat release rate at
each compression ratio, it is observed that the reactivity of n-pentane is the highest followed by
neo-pentane and iso-pentane.
About the heat release rate, iso-pentane shows only single stage heat release while the other two,
n- and neo-pentane, have two stage heat releases.
From the GC-FID analysis, it is observed that n- and iso-pentane have conjugate alkenes as
dominant species during the NTC regime. However, neo-pentane does not have any conjugate
alkene formation during the NTC regime due to its unique structure.
Lastly, the position of hydrogen (primary, secondary, and tertiary) causes the different bonding
strength resulting in the different concentration of intermediate species and reactivity of each
isomer.
During the experiments, only conjugate alkenes were analyzed since the GC-FID used was not
able to capture other important species like oxygenated ones. For the future work, analysis with
another GC-FID of different range of capturing will be beneficial to strengthen the exhaust gas
analysis. Also, more detail understanding of chemical reaction will be helpful to explain the
intermediate chemical reaction qualitatively and numerically.
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REFERENCES
[1] M. Ribaucour, R. Minetti, L.R.Sochet, H.J.Curran, W.J.Pitz, and C.K.Westbrook, Proc.
Combust. Inst. 28 (2000) 1671-1678.
[2] Photo of Ignition Quality Tester (IQT) made by AET Ltd.,
http://www.aet.ca/index.php?section=20.
[3] Standard Test Method for Determination of Ignition Delay and Derived Cetane Number
(DCN) of Diesel Fuel Oils by Combustion in a Constant Volume Chamber, ASTM D6890 – 15a,
ASTM International.
[4] T. Jensen, W. Siegl, J. Richert, F. Lipary, J. Loo, A. Prostak, J. Sigsby, SAE Paper 920320
(1992).
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