The Swedish and Finnish National
Committees of the International Flame
Research Foundation – IFRF
Studying Equivalence ratio – Temperature Maps in a HeavyDuty Diesel Engine
Ossi Kaario1*, Anders Brink2, Kalle Lehto1, Karri Keskinen1, and Martti Larmi1
1
Aalto University School of Science and Technology
Puumiehenkuja 5A
Espoo
Finland
firstname.lastname@tkk.fi
2
Åbo Akademi
Tuomiokirkontori 3
Turku
Finland
firstname.lastname@abo.fi
* corresponding author
Abstract
New measurements have been done in order to obtain information concerning the effect of EGR
and a paraffinic hydro-treated fuel for the smoke and NOx emissions of a heavy-duty diesel
engine. The measured smoke number and NOx emissions are explained using detailed chemical
kinetic calculations and CFD simulations. The local conditions in the research engine are
analyzed by creating equivalence ratio – temperature (Phi-T) maps and analyzing the CFD
results within these maps. The study uses different amount of EGR, Miller cycle, and two
different diesel fuels; standard EN590 diesel fuel and a paraffinic hydrotreated vegetable oil
(HVO). The detailed chemical kinetic calculations take into account the different EGR rates and
the properties of the fuels. It was observed that NOx emission trends can be well captured with
the Phi-T maps but the situation is more difficult with the engine smoke.
Keywords: Phi-T maps, combustion simulation, diesel engine, emissions
1. Introduction
Phi-T maps were first introduced by Kamimoto and Bae [1]. Afterwards Phi-T maps have mainly
been used in theoretical studies to identify beneficial trajectories [2], clarify soot formation paths
[3] and to understand the local conditions in the engine combustion chamber [4]. Phi-T maps are
useful tools but they lack some exactness as pointed out by Bergman et al. [4]. This is because
the Phi-T maps do not take into account mixing between different parts of the map. In addition,
as observed by Pickett et al. [3], the path that leads to soot formation matters; not only the end
state of combustion. Nevertheless, Phi-T maps can be used to study the local combustion
conditions in the combustion chamber.
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In this study experimental data is utilized to explain how Phi-T maps can be interpreted. New
measurements have been carried out in order to obtain information concerning the effect of EGR
and a paraffinic hydro-treated fuel for the smoke and NOx emissions of a heavy-duty diesel
engine. The bio-derived hydrotreated vegetable oil (HVO) used in the study is available as a
commercial product under the name NexBTL from the Finnish oil company Neste Oil. The HVO
oil contains mainly parafinic compounds and it has no aromatic components, and it also has very
high cetane number (>90). Using the HVO fuel,the smoke emissions are lower than with
standard EN590 diesel fuel. NOx emissions are also lower due to high cetane number (low
ignition delay) and lower density (longer injection duration)
The Phi-T maps have been constructed using detailed chemical kinetics and taking the EGR rate
into account. CFD results have been plotted onto the maps and the observed trends from the PhiT maps have been compared with the experimental results. Furthermore, Miller cycle has been
compared to the above mentioned EGR addition. The idea of Miller cycle is to lower the charge
air temperature before combustion. With the lower gas temperature a decrease in NOx emissions
is aimed at. The lower top dead center (tdc) temperature is typically achieved by changing the
valve timing in the engine. The utilization of the Miller cycle may sometimes cause increased
soot emissions. The combination of detailed kinetic calculations, the new measured data, and the
CFD analysis is found valuable in analyzing the Phi-T maps together with the measured engine
emissions. This paper suggests that rather accurate NOx trend predictions can be made by using
Phi-T maps. On the other hand, the accuracy of sooting behavior seems to be on a more vague
state.
2. Experimental Engine
The single-cylinder research engine is based on a commercial 6-cylinder off road common rail
diesel engine. Cylinder dimensions are standard from the production engine, see Table 1.
The research configuration consists of the engine and an electrical motor for braking and
motoring the engine. The control and measurement system is made in house at Aalto University.
The engine has a very flexible control system. It has a completely independent charge air system
equipped with an independent EGR system using pure nitrogen. The control system allows full
control over rpm, charge air pressure and temperature, exhaust back pressure, EGR percentage,
injection timing, injection pressure, and injection duration. Also multiple injections per cycle are
possible. The engine is equipped with common rail fuel injection system.
In addition, the engine has been equipped with hydraulic valve actuators in order to have full
freedom of the opening and closing times of the valves as well as the opening duration and
magnitude of the valves.
Smoke emissions have been measured by Fuel Smoke Number (FSN) meter by AVL 415S. This
method uses a filter in the exhaust pipe. The darkness of the filter color is measured optically
after each measurement point. NOx is measured with Ecophysics CLD 822Sh.
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Table 1 – Experimental engine parameters
Displaced volume
Stroke
Bore
Connecting Rod
Compression ratio
Number of Valves
Nozzle holes
Nozzle hole diam
1.40 liters/cylinder
145 mm
111 mm
232 mm
16.7:1
4
8
0.162 mm
3. Chemical mechanism
The mechanism to describe the PAH formation and destruction is based on a mechanism
developed by Naydenova [5]. In this mechanism the C1-C4 hydrocarbon oxidation
mechanism originates from Hegesh [6], the C2 mechanism from Wang and M. Frenklach [7].
Reactions for C3-, C5- to C8-hydrocarbons are based on the work of Richer and Howard [8],
Skjoth-Rasmusseen et al. [9] and Frenklach and Warnatz [10]. The n-hepthane model was
adopted from Correa etr al. [11] The formation and growth of polycyclic aromatic hydrocarbons
is based on the HACA model [12], Additional reaction paths of PAH formation and growth for
PAH between benzene and pyrene were adopted from Richter et al. [13], together with several
reaction paths for large polycyclic aromatics up to coronene. In this work, the mechanism of
Naydenova [5] was extended with a set of reaction describing nitrogen chemistry from Coda
Zabetta et al.[14] The complete mechanism contains 238 species and 1505 reactions. The subset
describing the nitrogen chemistry consists of 194 reactions.
4. CFD Model
The engine was modeled with a sector mesh that represents one fuel spray in the engine. The
mesh at tdc is shown in the Figure 1. The k-ε RNG turbulence model is used. The ReitzDiwakar drop breakup model [15] is used together with the O’Rourke droplet collision model
[16] with some improvements and additions as discussed in [17]. The mass transfer from the
droplets due to evaporation is modeled according to Bird et al. [18]. The mass transfer
coefficient is modeled according to Ranz and Marshall [19]. The initial half spray opening angle
was set to a constant value of 10 degrees.
The fuel injection profile obtained from 1-D simulations [20]. The mass flow rate of injected fuel
has been simulated with GT-Fuel. The model consists of rail and high pressure pipe and an
injector. A rail pressure of 450bar was used in the study. Discharge coefficient of the nozzle
holes was calculated using combined Giffen-Muraszew and Schmitt model, in Figure 2. The
obtained mass flow rate is also shown in the Figure 2. This mass flow rate curve was used as a
boundary condition in the fuel injection CFD modeling.
The combustion model used is ecfm-3z that is described e.g. in [21]. The model divides the
reactions between premixed and mixing controlled combustion, and between non-reacting and
reacting parts. The premixed combustion is computed from flame surface density equation. The
reaction rate in the mixing controlled phase is related to the turbulent characteristic time. Threestep main chemistry is used with this model.
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Figure 1 - Computational sector mesh (1/8 of the total cylinder) in the CFD simulations at top dead center
position. The mesh has 12760 cells at tdc position.
4.0E-02
Mass flow rate (kg/s)
3.5E-02
3.0E-02
2.5E-02
2.0E-02
1.5E-02
1.0E-02
5.0E-03
0.0E+00
-5
0
5
10
15
20
25
30
35
Crank angle
Figure 2 - Combined Giffen-Muraszew and Schmitt –model for flow coefficient of nozzle hole (left). Fuel
injection profile used in the CFD simulations obtained from 1-D simulations (right). The engine load is 50%
and the maximum injection pressure is 450bar.
Mixture fraction is frequently used in combustion models used in CFD. The mixture fraction is a
conserved scalar that describes the mass fraction of the mixture that originates from the fuel.
When the stoichiometric mixture fraction is known, lambda and equivalence ration can be
calculated from the stoichiometric mixture fraction and the local mixture fraction. Using this
approach lambda represents the lambda of the fresh mixture and will not change as the
combustion process proceeds.
Miller cycle is simulated so that the tdc average temperature is 97K lower than in the normal
cycle (952K vs 855K). The charge air mass was increased by about 10% and bottom dead center
pressure was decreased 0.067bar in the Miller cycle simulation compared to the standard cycle.
In experiments, this is achieved by closing the intake valve earlier than in the standard cycle.
This results in gas expansion that lowers the gas temperature. At the moment, no directly
comparable Miller cycle experiment is available,
5. Results
5.1
Smoke number (FSN) and NOx emissions
Figure 3 shows the measured fuel smoke number (FSN) and NOx emissions. The figure shows
that EGR strongly reduces NOx emissions but also increases smoke. Using the paraffinic HVO
fuel seems to suppress the smoke production. It also has positive influence to the NOx emissions.
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The EGR rate is defined in the experiments and in the simulations as
EGR % =
m& N 2 EGR
m& Tot
x100
(1)
where m& N 2 EGR is the EGR nitrogen mass flow rate and m& Tot is the total mass flow to the engine.
In the experiments and simulations, pure nitrogen is used as EGR. Both in the experiments and
simulations, 20% EGR has been used. This means that the oxygen content in the oxidizer stream
is about 18.6 % on mass bases. If the exhaust gases from the research engine would be used
instead of synthetic EGR, the EGR rate would be close to 40% in order to keep the oxygen level
the same.
3
6
HVO
5
HVO
2.5
EN590
2
NOx (g(kWh)
4
FSN
EN590
1.5
3
2
1
0.5
1
0
0
1
Air
2
1
EGR
Air
2
EGR
Figure 3 - Measured smoke number (left) and measured NOx emissions in the diesel experiments with 50%
engine load (right). In the EGR case, 20% EGR (pure N2 ) has been used.
5.2
Pressure and temperature fields
Measured and computed pressure curves are shown in the Figure 4. In the same figure also heat
release rates are shown. It is seen that the measured and computed pressures are in good
agreement. The 20% EGR case has lower heat release rate and hence lower pressure. The
measured pressure curve is obtained with 0% EGR. The Miller cycle pressure curve is very close
to the measured pressure curve. Computed mean and maximum gas temperatures are shown in
the Figure 5. It is seen that 20% EGR lowers the maximum temperature by about 200K. The
mean temperature is lowered also, at maximum about 80K. Miller cycle is seen to lower the
average temperature throughout the combustion and expansion stroke whereas EGR lowered the
mean temperature mainly during the most intense phase of combustion. On the other hand,
Miller cycle does not affect the maximum temperature significantly.
Figure 6 shows the combustion regimes using simplified Phi-T map at the crank angle 24 after
top dead centre. Also shown in the figure are the local temperatures and equivalence ratios. The
sooting area (red area) is seen to be much larger in the 0% EGR case than in the 20 EGR case. It
is also seen that the local equivalence ratios are very close to each other between 0% and 20%
EGR cases. Hence, the reason for the different sooting tendencies is in the different local
temperatures. The 20% EGR case has lower temperatures, so the soot peninsula in the Phi-T map
is avoided. The 0% EGR case, on the other hand, has more combustion areas in the sooting
peninsula. However, this computational result is contradictory to the experimental result seen in
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the Figure 3 where much more soot is produced when EGR is used. In the Miller cycle plot the
ambient gas temperature that has not been heated up by combustion is seen to be lower than in
the other cases.
100.00
3.0E+06
Experimental
EGR 0%
N2 EGR 20%
Miller cycle
90.00
2.5E+06
Pressure (bar)
2.0E+06
70.00
1.5E+06
60.00
1.0E+06
50.00
5.0E+05
40.00
-10.00
Heat release rate (W)
80.00
30.00
0.00
10.00
20.00
30.00
40.00
50.00
0.0E+00
60.00
Crank angle
Figure 4 – Measured and computed pressure curves and heat release rates. The measured pressure is with
0% EGR.
2400
EGR 0%
2300
2200
EGR 20%
2100
2000
Miller cycle
Temperature (K)
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
800
0
10
20
30
40
50
60
70
80
Crank angle
Figure 5 – Computed mean and maximum temperatures.
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100
110
120
130
140
The Swedish and Finnish National
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EGR 0%
EGR 20%
Miller
Temperature
Temperature
800-2200 K
800-2200 K
Phi
Phi
0-8 (-)
0-8 (-)
Combustion
regimes
Combustion
regimes
Figure 6 – Temperature (top), equivalence ratio (middle), and combustion regimes (bottom) without EGR
(left), with20% EGR (middle) or with Miller cycle (right) at the crank angle 24 after top dead center. The
combustion regimes are plotted roughly according to the Phi-T maps. Red color indicates soot production
area, light green corresponds to Low temperature combustion area and light blue means no combustion.
5.3
Phi-T maps of PAH and NOx
The Phi-T maps, or better T-Phi maps, were constructed using the chemical mechanism
described earlier. Based on experimentally obtained pressure curves and temperature obtained
from CFD simulations, the maps were constructed using a pressure of 80 bars and a residence
time of 2 ms. The calculations were done using the closed reactor model in CHEMKIN 4. The
reaction mechanism does not include heterogeneous reactions. Hence, the sum of PAH from
pyrene to corone was used to indicate the soot formation areas. In this case, when the
experimental soot measurements are based on the smoke number, quantitative comparisons
would not be possible even if a comprehensive soot mechanism was utilized.
In the calculations, the paraffinic HVO was model as n-heptane. The EN590 was modeled using
a mixture of n-heptane, benzene and naphthalene. The molar composition of the EN590 model
mixture was 65% n-heptane, 27% benzene and 8% naphtalene. On mass bases this corresponds
to a fuel with 70 mass-% aliphatic hydrocarbons, 20 mass-% aromatics and 10 mass-% polyaromatics.
Figure 7 a-d shows Phi-T maps calculated for the two fuels with air as oxidizer. Superimposed
on the maps are the Phi-T values in the CFD simulations of the engine. In the CFD simulations,
the same overall hydrocarbon was used to describe the paraffinic hydrocarbon based fuel and the
EN590. The figures show that at a crank angel of 20º, many of the computational cells are in the
region where high concentrations of PAH are predicted. At this instance, there is not a big
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difference between the fuels. At 60 º the difference between the two fuels is clearer. For the nheptane case, the branch of computational cells being fuel rich extends into the PAH formation
area in such a way that the computed PAH mole fraction is approximately 10 times lower
compared to the case where a mixture of n-heptane, benzene and naphthalene was used.
However, it should be noted that the temperature in the most fuel rich cells are around 1800 K.
Although an influence of the fuel mixture composition on the NOx formation is possible, the PhiT maps do not reveal such a difference. Both in the n-heptane and in the n-heptane, benzene and
naphthalene mixture case several of the cells in the CFD calculation is in the NOx formation zone
at 60º.
Figures 8a-d shows corresponding Phi-T maps for the case when the diesel engine was run in
EGR mode. In these runs the O2 content of the oxidizer stream was 18.6 mass-%. The figures
show that the in this case the peak temperature is lowered approximately 200 K. In this case too,
the difference between the PAH levels in the Phi-T locations obtained in the CFD simulations is
approximately a factor 10, being lower in the n-heptane case.
Figure 9a-d shows Phi-T maps for the case when the Miller cycle has been applied. The figure
shows that compared to the standard case, the NOx producing region is slightly less entered.
However, compared to the EGR case, a large fraction of the fluid inside the cylinder is entering
the NOx producing region.
Based on Figure 7 and 9 a likely sooting tendency ranking is EN590/air & EN590/air+Miller >
HVO/air & HVO/air+Miller > EN590/EGR > HVO/EGR. Based on the figure, there is no
influence of the fuel quality on the NOx formation tendency. However, significantly lower NOx
emissions can be expected using EGR. For the Miller case, no experimental data is available.
Comparing with the results in Figure 3, one can conclude that for the NOx formation tendency
the interpretation of the Phi-T maps agrees well with the measurements. For the sooting
tendency, on the other hand, the results are contradicting. According to Figure 3, less smoke is
formed in the air case compared to the EGR case. Based on this, the Phi-T maps are not very
useful for predicting the sooting tendencies. However, these results should be reviewed critically,
since the relation between the smoke number and the sum of PAH consisting of pyrene to corone
may be debatable.
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8
PAH
0.00
01
7
3
1600
05
5e.-0000 1
0
00 5
0.0
0.001
0.005
NOx
-005
5e
0.0001
00 51
0. 00.00
1
1400
1800 2000 2200
Temperature (K)
2400
2600
2800
3000
1400
1600
1800 2000 2200
Temperature (K)
0.000 1
1e -0
05
1e-006
2600
2800
3000
d)
1
1e 005
1e -006
4
3
1200
1400
1600
05
00
0.
1800 2000 2200
Temperature (K)
2400
2600
2800
1e 005
1e-006
1
3000
1000
0.000 1
1200
1400
1600
05
5e -0
00 1
0
.
0
00051
0.00.0
5
-00
1e
-0
06
2
05 1
5
5e -00.000 0.00000
0. 1
5
0
NOx
0.0
5e -005
0.000 100051
0.00.0
1e
1e -006
0.
00
1
1
1
0.000
5e -0
0
0.0 5
00
1
2
05
-0
1e
6
1e
-00
5
6
0
1e -0
0
1e -0
3
2400
0.00
0
Phi (-)
1e -006
0.000 1
1e-006
1e-005
1e -006
0. 0
00 1
1e
-00
6 1e -005
5
1
0.000
1
1e-006
4
6
PAH
1e-005
0
0.00
5
8
7
1e-005
Phi (-)
1200
0.0001
0.0001
PAH
6
1000
1000
9
c)
05
5e -0.000 1
0
05
0.0
0.0001
0.005
NOx
5
5e0-0
.0000 1 0 51
0 0
0.0 0. 0
1
10
9
7
00
1
1e -0
1e -006 05
2
10
8
0.
0
3
1e -005
1e -006
1200
5
4
00 1
0.0
2
1000
Phi (-)
1
1e e -005
-00
6
4
6
1e -005 06
1e -0
5
1
0.000
1e -005 -006
1e
Phi (-)
6
b)
0.0
1e 1e 00 1
-00 -005
6
0.0001
7
PAH
9
a)
1e1e
-0-00
06 5
8
1e-005
1e-006
9
0.000 1
1e -005
1e -006
10
0.000 1
1e-005
1e-006
10
1800 2000 2200
Temperature (K)
2400
0.005
NOx
2600
Figure 7 - Phi-T maps of PAH and NOx. a) CA = 20º, n-heptane/air. b) CA = 60º, n-heptane/air.
c) CA = 20º, n-heptane, benzene, naphthalene/air, d) CA = 60º, n-heptane, benzene, naphthalene/air.
Superimposed a cell values from the CFD calculation with air.
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The Swedish and Finnish National
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PAH
1
1200
1400
0. 0 1
1e -000
05
1e-006
1e-006
3000
9
c)
7
1600
PAH
1400
1600
1800 2000 2200
Temperature (K)
2400
05 1
5e -00.000
00 5
00.0
.001
0.005
NOx
2600
2800
3000
2600
2800
3000
d)
1e 1e 0.000
1
-00 -00
5
6
1
0.000
5
1e -00
1e -006
2
1
1000
1e
-00
6
1200
1400
1600
05
50e.0-000 1
-005
5e 0
0. 0050 1
0
0
0.
0.
00
1
1e-006
Phi (-)
0.0
00 1
1e 0
1e 05
-00
6
0.000 1
5
1e -001e -006 -005 1
5e 0. 000 5
01
0. 0.000
0
06
1e -0
1200
05
1e -0
05
1e -0
1e-006
1000
4
3
2
1
5
1
0.000
1
0.000
Phi (-)
1400
6
5
3
1200
8
6
4
1000
1e-005
7
PAH
1e-005
8
2800
0.000 1
9
2600
10
0.000 1
10
1600
05
00
0.
1800 2000 2200 2400
Temperature (K)
005 0 1
5e - 0. 00 .000 5
0 0.001
0.005
NOx
0.0001
1e -0 1e -005
06
1000
1
NOx
01
05
5e -00.000 1 00 051
5
0.00. 0
00
0.
1800 2000 2200 2400
Temperature (K)
5
1e -00
1e-006
2
0.
0
1e -005
1e-006
2
01
00
0.
3
005 1
5e -0.000
05
0.00.0001
0. 0
00 1
1e - 1e 006 005
4
0.
00
01
3
5
5e
0. 005
00
01
4
Phi (-)
0.0
00
1e 1e -00 1
-00
5
6
5
b)
6
05
1e -0 006
1e-
05
1e -0
1e -006
Phi (-)
6
PAH
0.000 1
7
0.000 1
7
8
1e-006
8
9
a)
1e-005
1e-006
1e-005
1e-006
9
0.0001
1e -005
1e -006
10
0. 0001
-0
1e -01e
06 05
10
1800 2000 2200
Temperature (K)
05
0.000.001
0.005
2400
NOx
2600
2800
3000
Figure 8 - Phi-T maps of PAH and NOx. a) CA = 20º, n-heptane/EGR. b) CA = 60º, n-heptane/EGR. c) CA =
20º, n-heptane, benzene, naphthalene/EGR, d) CA = 60º, n-heptane, benzene, naphthalene/EGR.
Superimposed a cell values from the CFD calculation with 20% EGR (pure N2).
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10
8
4
5
05 01
- 0 00 .00 0
0
5e 0.
00
1
x
0.
1600
1800 2000 2200
Temperat ure (K)
2400
2600
2800
3000
1000
0.000 1
1e -005
1e-006
9
c)
8
1 e-0 05
1e -0
1 e -00 6
Phi (-)
0 .0
00 1
1e
-0
05
1e
-
00
6
1 e-0 06
5
01
1000
1 e -0
-0 0
5
06
1200
1400
1600
1
0 .0 00
1e -00 6
3
5
-000 1
5 e.0
0 0
05
0 .00.0001
0.0 05
NOx
05
5e -00 00 1 0 5
0
0.
0.0
0.
00
1
1e
1800 2000 2200
Temperat ure (K)
2400
NO
x
2400
2600
2800
3000
d)
6
1e-005
2
1
7
4
3
PAH
0 .00
01
4
0 .00
5
1e-005
Phi (-)
6
1800 2000 2200
Temperat ure (K)
1e-005
06
PAH
7
1600
0.0001
0.0001
8
1400
10
10
9
1200
0.000 1
1400
0. 005
2600
2800
1e 1
0
-00 e-00 .000 1
5
6
1200
1
00
0 .0
1e -0 05
0501
006
1e5e0.-000
05
00
0.
2
1
3000
1000
1e 00 6
1200
0.
00
1
1000
5e -005
01 5
0. 00 .00 0001
0 0.
1
1e -006
1
0 05
5e 01
0
0
0.
05
0 .00.000 1
1e
1 e -0 -00 5
06
2
0 05 0 1
5 e -0 .00
05
0 .00.000 1
0 .0 05
NO
1e - 1e -0 05
006
-00 5
1e -010e6
2
0.
00
01
3
b)
1e
0
-00 1e - .0 00 1
6 00 5
01
-00 1e -0
05
6
0. 0
0
1
00
3
5
1e
0
0.
4
1e -0 05 6
1 e -00
5
Phi (-)
6
5
1 e -0000 6
1 e-
Phi (-)
PAH
7
6
0 .00 0
1
1 e-0 061e -0 05
9
a)
0.0 00 1
7
1e-005
1e-006
PAH
0. 000 1
1e-006
8
1e-005
9
0.000 1
1e -0 061e -00 5
10
1400
1600
1800 2000 2200
Temperature (K)
05 1
5e -0
0
0. 00
5
00 01
.0
0 0.0
05
0 .0
2400
NOx
2600
2800
3000
Figure 9 - Phi-T maps of PAH and NOx. a) CA = 20º, n-heptane/air. b) CA = 60º, n-heptane/air. c) CA = 20º,
n-heptane, benzene, naphthalene/air, d) CA = 60º, n-heptane, benzene, naphthalene/air. Superimposed a cell
values from the CFD calculation with Miller cycle.
6. Conclusions
New measured engine data has been obtained from a heavy-duty diesel engine for off-road
applications. The Miller cycle test showed that it lowers the mean temperature very effectively
throughout the expansion stroke whereas EGR lowered the mean temperature only during the
most intense phase of combustion. Maximum gas temperature was lowered more effectively by
using EGR. The fuels used were the standard EN590 diesel fuel and a paraffinic hydrotreated
vegetable oil (HVO) which has no aromatics in it. Different EGR rates were also used in the
experiments. The effects of EGR and those from the paraffinic diesel fuel have also been used in
the creation of Phi-T maps by detailed chemistry calculations. CFD was used to analyze the local
combustion conditions in the combustion chamber by utilizing the created Phi-T maps. This
combination of detailed kinetic calculations, the new measured data, and the CFD analysis was
found valuable in analyzing the Phi-T maps together with the measured engine emissions.
Combining Phi-T maps, superimposed with Phi-T values of computational cells in CFD
calculations, with the information about the critical mixing time obtained from the kinetic mixing
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The Swedish and Finnish National
Committees of the International Flame
Research Foundation – IFRF
calculations, is likely a good way to qualitatively predict sooting tendencies. If the sooting
peninsula is completely avoided, sooting is unlikely. If the sooting peninsula is entered during
the combustion cycle, complete mixing should be obtained before entering temperatures too low
for PAH (and soot) oxidation. Tracking the fraction of cells that have been in the sooting area,
and that still are fuel rich when the local temperature drops below 1300K is probably a useful
approach.
7. References
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The Swedish and Finnish National
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