Wanchen Sun1, Xin Zhang1, Liang Guo1, Yi Sun1, Yuying Yan2, Jun Li3, Hao Zhang1, Dongqi Fu1. 1. State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130025, China. 2. Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, U.K. 3. State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China.
Abstract
To assess the effects of intake components and n-butanol application on compression-ignition engines, an experiment was carried out based on a single-cylinder engine fueled with n-butanol/diesel-blended fuel. The results show that with the increased n-butanol fraction of the blended fuel, the emissions of particulate mass (PM) decrease significantly, but the NO x and hydrocarbon (HC) emissions deteriorate. For B15 and B30, the PM emissions are 66.2% and 74.4% lower than B0, respectively. Furthermore, exhaust gas recirculation (EGR) was introduced to reduce the NO x emissions. However, a large EGR rate significantly reduces the indicated thermal efficiency (ITE) of the engine. Compared with the non-EGR condition, the ITE of B15 and B30 decrease by 3.1% and 3.8%, respectively, when the EGR rate is 18%. At the same time, the PM and HC emissions are found to be increased greatly. The PM emission of B15 and B30 increases by 69% and 46% and the HC emission increase by 150% and 71%, respectively. To restrain the engine emissions caused by the EGR, pure oxygen is further introduced into the intake charge. It is found that both the PM and HC emissions are significantly reduced with the introduction of extra oxygen. Under the condition of the 18% EGR rate, increasing oxygen addition to 4% can reduce HC emissions by more than 50% and the total particle mass of B15 and B30 is reduced by 60.6% and 47.7%, respectively. Moreover, the ITE reduction and combustion deterioration caused by the large EGR are found to be alleviated. By adjusting the n-butanol ratio, EGR rate, and oxygen addition, the excellent performance of combustion and emission can be achieved in an n-butanol/diesel blend fueled engine.
To assess the effects of intake components and n-butanol application on compression-ignition engines, an experiment was carried out based on a single-cylinder engine fueled with n-butanol/diesel-blended fuel. The results show that with the increased n-butanol fraction of the blended fuel, the emissions of particulate mass (PM) decrease significantly, but the NO x and hydrocarbon (HC) emissions deteriorate. For B15 and B30, the PM emissions are 66.2% and 74.4% lower than B0, respectively. Furthermore, exhaust gas recirculation (EGR) was introduced to reduce the NO x emissions. However, a large EGR rate significantly reduces the indicated thermal efficiency (ITE) of the engine. Compared with the non-EGR condition, the ITE of B15 and B30 decrease by 3.1% and 3.8%, respectively, when the EGR rate is 18%. At the same time, the PM and HC emissions are found to be increased greatly. The PM emission of B15 and B30 increases by 69% and 46% and the HC emission increase by 150% and 71%, respectively. To restrain the engine emissions caused by the EGR, pure oxygen is further introduced into the intake charge. It is found that both the PM and HC emissions are significantly reduced with the introduction of extra oxygen. Under the condition of the 18% EGR rate, increasing oxygen addition to 4% can reduce HC emissions by more than 50% and the total particle mass of B15 and B30 is reduced by 60.6% and 47.7%, respectively. Moreover, the ITE reduction and combustion deterioration caused by the large EGR are found to be alleviated. By adjusting the n-butanol ratio, EGR rate, and oxygen addition, the excellent performance of combustion and emission can be achieved in an n-butanol/diesel blend fueled engine.
The compression-ignition
(CI) engines are widely used in transportation
and other fields due to their high thermal efficiency, excellent power
output, and durability. However, due to the inhomogeneous mixture
in the cylinder, various toxicological pollutants are inevitably generated
during the combustion process of the diesel engine.[1−4] As the number of engines keeps
growing, environmental problems are becoming more and more severe.
Research shows that among the nonroad mobile sources, such as CO,
hydrocarbon (HC), NO, and particulate
mass (PM) emissions, the proportion of diesel engines exhaust exceeds
66%, and countries around the world have also introduced increasingly
strict emission regulations to limit diesel engine pollutant emissions.[5,6] However, with the development of human society, the demand for nonrenewable
energy is also growing. Therefore, it is necessary to find alternative
renewable resources, improve the thermal efficiency of diesel engines,
and reduce pollutant emissions.[7−11]In recent years, butanol has been widely studied as a liquid
alternative
fuel with great development potential.[12−14] Butanol is an alcohol
fuel with four C atoms, and its molecular formula is C4H9OH. As a second-generation biofuel, butanol has the
advantages such as high energy density, low volatility, low corrosiveness,
and good miscibility with diesel and gasoline, making it a potential
alternative fuel.[15,16] At the same time, with the continuous
development of microbial fermentation technology, the manufacturing
process of biobutanol based on renewable raw materials has gradually
matured. Biobutanol has made great progress in terms of the raw material
adaptability and product conversion rate. Therefore, the production
cost of butanol has been greatly reduced, and it has a broad market
application prospect.[17,18] At present, extensive research
has been conducted on the application of butanol fuel to vehicle internal
combustion engines. Among them, blending butanol with diesel and then
injecting the blended fuel into the cylinder is the main method of
butanol application in the CI engines.[19−21] Rakopoulos et al.[22] experimentally studied the effects of butanol/diesel-blended
fuels on the combustion and emissions of CI engines. The results showed
that compared with diesel, the soot, NO, and CO emissions were reduced in different degree, but the HC emissions
increased when using the butanol/diesel-blended fuels. Gu et al.[23] and Yao et al.[24] compared
the effects of butanol and its isomers on the emission characteristics
of a CI engine, and they concluded that the NO and soot emissions can be further reduced by the coordination
of exhaust gas recirculation (EGR) and injection strategies. However,
owing to the higher latent heat of vaporization and the lower cetane
number of the blended fuel, the load range of the butanol/diesel engine
was narrow. Some results showed that burning n-butanol/diesel-blended
fuel cause the increase in emissions such as HC and CO, and these
problems are more obvious after the introduction of EGR.[25,26]To solve the problems of engine burning n-butanol/diesel-blended
fuel, it is necessary to adopt oxygen-enriched combustion technology.
Oxygen-enriched combustion of diesel engines has a positive effect
on improving the thermal efficiency and reducing pollutant emissions.
Early studies have found that oxygen has a direct and significant
effect on the in-cylinder combustion process. Therefore, increasing
the oxygen content of the intake gas can improve the combustion efficiency
and reduce fuel consumption and pollutant emissions such as HC, PM,
and CO.[27,28] Moreover, the activation atmosphere produced
by adding oxygen is conducive to the combustion of the mixed gas,
which is beneficial to alleviating the problem of narrow load range
when the engine is fueled with the n-butanol/diesel-blended
fuel. In the early days, due to the limitation of the cost for oxygen-enriched
technology, oxygen-enriched combustion was mainly used in the field
of thermal power generation. In recent years, profiting from the rapid
development of the gas membrane separation technology, it has the
basics for the application of oxygen-enriched combustion technology
on engines.[29−32]A number of studies showed that the combination of n-butanol/diesel blends and EGR can reduce the NO and soot emissions of the engine, but with
an increased
EGR rate, the thermal efficiency and HC emission of the engine deteriorate
gradually. To restrain the adverse effects of the large EGR rate,
oxygen-enriched technology was adopted in the experiment by a modified
intake system. The combined effects of the n-butanol/diesel-blended
fuel and intake components on combustion and emission of the engine
were explored in this study.
Results and Discussion
Effects of Fuel Characteristics on Combustion
and Emissions
Figures and 2 show the combustion characteristics
of the engine for different fuels. It can be seen from the figures
that with the increased n-butanol-blended ratio,
the maximum cylinder pressure and the rate of heat release (RoHR)
are obviously increased, and the reason is that the n-butanol addition leads to a larger proportion of premixed combustion.
It can also be seen from the figures that with the increased n-butanol-blended ratio, the ignition delay (ID) is obviously
prolonged and the combustion duration (CD) is shortened. Compared
with fuel B0, the ID of fuel B15 and B30 is prolonged by 2.9 and 4.6
deg CA, respectively, and the CD is shortened by 2.8 and 4.9 deg CA,
respectively. The lower cetane number and higher latent heat of vaporization
of the blended fuel are the two major factors that contribute to a
lower cylinder temperature during the fuel atomization stage; hence,
the ID is obviously prolonged with the increased n-butanol-blended ratio. In addition, the longer ID is conducive to
increasing the proportion of premixed combustion and thereby shortening
the CD. It can improve the fuel atomization effect and thus reduce
the engine pollutant emissions.
Figure 1
Cylinder pressure and RoHR of different
fuels.
Figure 2
ID and CD of different fuels.
Cylinder pressure and RoHR of different
fuels.ID and CD of different fuels.Figure shows
the
NO and HC emissions of different fuels.
It can be observed that both the NO and
HC emissions are increased for B15 and B30 compared with the pure
diesel. The higher n-butanol-blended ratio increases
the maximum RoHR, which leads to a higher combustion temperature.
The n-butanol addition increases the oxygen content
in the cylinder, and the effects of combustion temperature and oxygen
concentration promote the production of NO. The reason for the increase in HC emissions is that the long ID
of the blended fuels leads to a large amount of fuel adhering to the
wall of cylinder chamber, and it is difficult to burn completely due
to the low temperature and oxygen concentration near the wall. Figure shows the PM emissions
of different fuels. In this paper, the particle whose size is in 0–35
nm is defined as a nuclear mode particle (NMP), and the particle whose
size is larger than 35 nm is defined as the accumulation mode particle
(AMP). For B15 and B30, the total PM emissions are 66.2% and 74.4%
lower than B0, respectively, but the NMP mass emissions increase with
the increased n-butanol-blended ratio. It illustrates
that the higher oxygen content of n-butanol/diesel
blends promote the oxidation of AMP. However, the reason why the NMP
increases is that the HC emissions of n-butanol/diesel
blends are higher, and the saturated HC components condense to the
NMP during the cooling and dilution processes of the exhaust gas.
Figure 3
NO and HC emissions of different fuels.
Figure 4
PM emissions of different fuels.
NO and HC emissions of different fuels.PM emissions of different fuels.In summary, burning n-butanol/diesel blends increases
the proportion of premixed combustion, improves the volumetricity
of combustion, and reduces particulate emissions significantly, but
at the same time it increases the NO and
HC emissions.
Effects of EGR on Combustion
and Emissions
of n-Butanol/Diesel Blends
To avoid the deterioration of
NO emissions when burning n-butanol/diesel blends, the effects of different EGR rates on the
combustion and emissions for n-butanol/diesel blends
were experimentally studied. B15 and B30 were selected as the tested
fuels for the EGR rates including 0%, 10%, 14%, and 18%.Figure shows the ID and
CD of B15 and B30 at different EGR rates. It can be seen from Figure a that the ID for
both blended fuels is prolonged with the increased EGR rate. It is
because that the introduction of EGR gas increases the specific heat
capacity of the working medium in the cylinder, thereby reducing the
in-cylinder temperature. Moreover, the introduction of EGR gas also
reduces the oxygen concentration in the cylinder. Both the reasons
are not conducive to achieving the ignition conditions of the mixture.
In addition, due to the lower cetane number and higher latent heat
of vaporization, the ID for B30 is about 2–3 deg CA longer
than that of the B15 at all EGR rates. Figure b shows that the CD of both fuels decreases
with an increase in the EGR rate. The main reason for this result
is that the increase in the EGR rate prolongs the ID, which leads
to an increasing premixed combustion ratio and a higher combustion
speed. Furthermore, the low oxygen concentration caused by EGR may
lead to incomplete combustion of the fuel at the last stage of the
combustion process and shortens the CD. Comparing the CD for two fuels
at different EGR rates, it can be found that the CD for B30 is 2–3
deg CA shorter than B15, and because of this more fuel is consumed
in the premixed combustion for B30.
Figure 5
(a) ID of B15 and B30 at different EGR
rates and (b) CD of B15
and B30 at different EGR rates.
(a) ID of B15 and B30 at different EGR
rates and (b) CD of B15
and B30 at different EGR rates.Figure shows the
thermal efficiency and pollutant emissions of B15 and B30 at different
EGR rates. It can be found that the indicated thermal efficiency (ITE)
decreases significantly with the increased n-butanol-blended
ratio and EGR rate. Compared with non-EGR conditions, the ITE of B15
and B30 decreases by 3.1% and 3.8%, respectively, when the EGR rate
is 18%. The reason for the decrease in the ITE should be that the
lower heat value and the higher latent heat of vaporization of n-butanol result in a decrease in the cycle heat release
and an increase in the heat absorption. Moreover, the decrease in
the ITE caused by EGR could be explained by the fact that EGR can
reduce the oxygen content in the cylinder, and the specific heat capacity
of triatomic molecular gases in EGR is larger than diatomic molecular
gases (air), which leads to a decrease in combustion temperature and
combustion efficiency. In addition, the effects of EGR are beneficial
to suppressing the generation of NO but
not conducive to improving the particulate and HC emissions. At an
EGR rate of 18%, the NO emission of B15
and B30 decreases by 55% and 53%, the total particle mass concentrations
of B15 and B30 increase by 69% and 46%, and the HC emission of B15
and B30 increases by 150% and 71%, respectively, compared with the
non-EGR condition. Among them, the increase in HC and particulate
emissions verify that the low oxygen concentration caused by EGR can
indeed reduce the completeness of combustion.
Figure 6
(a) Thermal efficiencies
of B15 and B30 at different EGR rates.
(b) Pollutant emissions of B15 and B30 at different EGR rates.
(a) Thermal efficiencies
of B15 and B30 at different EGR rates.
(b) Pollutant emissions of B15 and B30 at different EGR rates.From the analysis above, it can be concluded that
when burning
the n-butanol/diesel blends, EGR is an effective
technique to reduce the NO, but it also
leads to combustion deterioration and thermal efficiency reduction.
Effects of EGR and Intake Oxygen Addition
on Combustion and Emissions of n-Butanol/Diesel Blends
To
alleviate the negative effects of EGR in the case of burning the n-butanol/diesel blends, the effects of oxygen introduction
together with the EGR gas on combustion and emissions characteristics
of the engine were experimentally studied.Figures and 8 illustrate the ID and CD of B15 and B30 with different intake components.
Under the same EGR rate conditions, different oxygen addition rates
were tested. It is found that the ID is shortened with the increased
oxygen addition for all conditions. Comparing the effects of different
oxygen addition rates under different EGR rates, it can be observed
that the ID is more sensitive to the change in oxygen addition at
all EGR levels and fuels. This can be explained by the fact that in-cylinder
oxygen concentration is an important condition for CI, and higher
in-cylinder oxygen concentration facilitates autoignition of the oil–gas
mixture. However, although increasing the in-cylinder oxygen concentration
shortens the ID and reduces the premixed combustion fraction and higher
in-cylinder oxygen concentration can promote the combustion process,
the combined effects of the two reasons cause slight changes in the
CD with the increased oxygen addition.
Figure 7
ID of B15 and B30 burning
with different intake components: (a)
B15 and (b) B30.
Figure 8
CD of B15 and B30 burning
with different intake components: (a)
B15 and (b) B30.
ID of B15 and B30 burning
with different intake components: (a)
B15 and (b) B30.CD of B15 and B30 burning
with different intake components: (a)
B15 and (b) B30.Since the oxygen addition
rate affects ID and CD, the engine thermal
efficiency can also be changed accordingly. Figure shows the ITE of the engine with different
intake components. As can be seen from the figures, oxygen addition
is beneficial to improving the combustion process and compensating
for the thermal efficiency reduction caused by the large proportion
EGR and burning the n-butanol/diesel blends. Taking
the 18% EGR as an example, the ITE of B15 and B30 increases by 2.4%
and 2.5%, respectively, when 4% oxygen addition is introduced. This
can be explained by the fact that the addition of oxygen can shorten
the ID and reduce the premixed combustion fraction while maintaining
a short CD. Since the in-cylinder combustion temperature is positively
correlated with the premixed combustion fraction, the addition of
oxygen can reduce the combustion temperature, thus reducing the heat
transfer loss on the basis of maintaining the volumetricity of combustion.
Additionally, the addition of oxygen is also conducive to improving
incomplete combustion caused by the large proportion EGR and burning
the n-butanol/diesel blends.
Figure 9
ITE of B15 and B30 burning
with different intake components: (a)
B15 and (b) B30.
ITE of B15 and B30 burning
with different intake components: (a)
B15 and (b) B30.The addition of oxygen
not only improves the thermal efficiency
of the n-butanol/diesel blend fueled engine but also
has a significant impact on the pollutant emissions. Figures and 11 show the HC and NO emissions of B15
and B30 with different intake components. As can be seen from Figure , the oxygen addition
into the intake can effectively reduce the high HC emissions caused
by excessive EGR and n-butanol blending. Under the
condition of 18% EGR rate, increasing oxygen addition to 4% can reduce
HC emissions by more than 50%. This can be explained by the fact that
the significant increase in the oxygen content in the cylinder is
conducive to promoting HC oxidation, also increasing the in-cylinder
reaction rate and temperature at the same time. As for the NO emissions, it can be seen from Figure that the NO emissions increase with an increase in the oxygen addition.
Under all conditions, when 4% oxygen addition is introduced into the
intake, the NO emission is 71–150%
higher than that with nonoxygen supplementation. According to Zeldovich’s
principle, the formation of NO is greatly
affected by oxygen concentration, in-cylinder temperature, and its
duration. The oxygen supplementation provides favorable conditions
for the NO formation, thus promoting
the chemical reaction to move toward the direction of NO formation.[33] Generally
speaking, although increasing the oxygen content in the blended fuel
and intake gas leads to the NO emission
deterioration, the deterioration level is not very high when the EGR
is applied, due to the alleviating effect of EGR on the NO emission.
Figure 10
HC emissions of B15 and B30 burning with
different intake components:
(a) B15 and (b) B30.
Figure 11
NO emissions of different fuels with
different intake components: (a) B15 and (b) B30.
HC emissions of B15 and B30 burning with
different intake components:
(a) B15 and (b) B30.NO emissions of different fuels with
different intake components: (a) B15 and (b) B30.
Effects of EGR and Intake Oxygen Addition
on Particulate Characteristics of n-Butanol/Diesel Blends
Since particulate emission control has always been a difficult task
for CI engines, and the harm of particles of different sizes to the
human body are also different, it is meaningful to analyze the particle
size distribution (PSD) in detail. To further investigate the effects
of EGR and oxygen addition on particulate emission of the n-butanol/diesel blends, the particulate emission characteristics
at different intake components were studied under the EGR rates of
10% and 18%.Figure shows the PSD of B15 and B30 with different intake components.
As can be seen from Figure , the PSD presents a two-peak shape under all conditions,
and the two peaks represent the different modes of particles, within
the range of 5–35 nm (NMP) and 35–1000 nm (AMP), respectively.
Moreover, the peak of NMP is an order of magnitude higher than the
peak of AMP under all conditions, which indicates that the number
concentration of NMP is accounted for the majority of particle number
emissions when the blended fuels are used. It can also be seen that
the NMP distributions almost remain constant with a change in the
oxygen concentration, but the AMP decreases with an increase in the
oxygen concentration, which means that the addition of oxygen can
effectively promote the late oxidation of AMP. In addition, the number
of the particles larger than 150 nm when burning B30 is significantly
lower than that when burning B15 at the same EGR rates and oxygen
addition. This indicates that the addition of n-butanol
is particularly effective in reducing the particles with a large size.
Figure 12
PSD
of B15 and B30 with different intake components: (a) B15-10%
EGR, (b)B30-10% EGR, (c) B15-18% EGR, and (d) B30-18% EGR.
PSD
of B15 and B30 with different intake components: (a) B15-10%
EGR, (b)B30-10% EGR, (c) B15-18% EGR, and (d) B30-18% EGR.To quantify the particle emissions in different modes, the
mass
concentration of NMP, AMP, and total particles calculated from the
PSD are shown in Figure . It can be found that with an increase in EGR, the mass of
NMP gradually decreases and the mass of AMP gradually increases for
B15 and B30. As can be seen from Figure , increasing the oxygen concentration can
effectively reduce the total PM at all EGR rates and fuels. Moreover,
the effects of oxygen concentration on total PM are more obvious under
the conditions of the high EGR rate and low n-butanol-blended
ratio whose total particle mass emission is relatively high. For the
B30 fuels, when the addition oxygen concentration increased from 0%
to 4%, the total particle mass at 10% EGR and 18% EGR decreased by
36.1% and 47.7%, respectively. For the 18% EGR rate, when the addition
oxygen concentration increased from 0% to 4%, the total particle mass
at B15 and B30 is reduced by 60.6% and 47.7%, respectively. In addition,
the mass of AMP decreases continuously with an increase in the oxygen
concentration, but the change in NMP mass with the oxygen concentration
shows different trends at different EGR rates and fuels. This is because
AMP is mainly formed in the local hypoxic zone due to the uneven distribution
of oxygen concentration during the diffusion combustion process.[34,35] Introducing oxygen into the intake is conducive to improving the
in-cylinder oxygen concentration distribution, reducing the local
hypoxic zone, thereby suppressing the formation of AMP. For NMP, although
increasing the in-cylinder oxygen concentration is beneficial to reducing
the unburned HC and thus suppressing the generation of nuclear particles,
but at the same time, oxygen addition reduces the mass concentration
of AMP, so it stunts the adsorption of gaseous precursors such as
sulfuric acid and HC on the surface of AMP, thus increasing the NMP
emission. The synergistic effects of these two reasons cause NMP to
show different trends with the increased oxygen concentration under
different conditions.
Figure 13
Mass concentration of the particles obtained with different
intake
components: (a) B15-10% EGR, (b) B30-10% EGR, (c) B15-18% EGR, and
(d) B30-18% EGR.
Mass concentration of the particles obtained with different
intake
components: (a) B15-10% EGR, (b) B30-10% EGR, (c) B15-18% EGR, and
(d) B30-18% EGR.In summary, oxygen addition
can effectively improve the ITE and
suppress HC and particle emission, but the NO emission can be increased. Compared with using EGR only, the combination
of EGR and oxygen addition can improve the thermal efficiency and
maintain relatively low pollutant emissions when burning the n-butanol/diesel blends.
Comparative
Analysis for This Study
To intuitively evaluate the effects
of blending n-butanol, EGR, and oxygen addition on
the combustion and emissions
performance of the engine, the thermal efficiency and main emissions
of the engine are listed in Table when the abovementioned technologies are used.
Table 1
Comparison of the ITE and Emission
Result Obtained Using Different Technologies
fuel
EGR rate
(%)
O2 addition (%)
ITE (%)
NOx (ppm)
PM (μg/cm3)
HC (ppm)
diesel
0
0
49.5
1150
8.71 × 10–11
25
B15
0
0
48.6
1340
2.94 × 10–11
42
B30
18
0
44.1
785
3.25 × 10–11
125
B15
18
2
47.2
800
3.04 × 10–11
60
As can be seen from Table , burning the n-butanol/diesel
blends can
significantly reduce particulate emissions, but it causes an increase
in NO and HC and a decrease in ITE. For
the combination of n-butanol blends and EGR, the
use of a large proportion of n-butanol and a high
EGR rate can simultaneously reduce NO and PM compared to the original condition, but the ITE and HC emissions
further deteriorate under that condition. Moreover, compared with
the combination of n-butanol/diesel blends and EGR,
further adding oxygen into the intake can achieve excellent engine
performance. By adjusting the n-butanol ratio, EGR
rate, and oxygen concentration, the ITE can be restored and lower
PM and HC emissions are achieved on the basis of a slight change in
NO emission.
Conclusions
Combining different intake components, the combustion and emissions
characteristics of CI engine fueled with n-butanol/diesel
blends were studied and analyzed in this paper. The results show that
when burning the n-butanol/diesel blends, the synergistic
effect of EGR and oxygen addition can effectively reduce the emissions
of NO and particle, while keeping the
thermal efficiency basically unchanged. The conclusions were drawn
as follows:(1) At medium speed and load, with the increased n-butanol volume fraction of the n-butanol/diesel
blends, the ID prolongation and CD shortening lead to a significant
decrease in particulate emission. However, the NO and HC emissions of B15 and B30 are higher than that of
diesel.(2) With the increased EGR rate, the n-butanol/diesel
blend fueled engine can effectively suppress NO emissions, but it causes the deterioration of HC and particulate
emissions. Naturally, ITE decreases accordingly.(3) With an
increase in oxygen addition, the ID is shortened but
the CD is not changed significantly. Compared with the combination
of n-butanol/diesel blends and EGR, by further adding
oxygen into the intake, the ITE can be restored with lower PM and
HC emissions being achieved on the basis of a slight change in NO emission.(4) With an increase in the
EGR rate, the AMP and total PM emission
of B15 and B30 increase significantly, but the mass concentration
of NMP is decreased. Benefiting from the high oxygen concentration
can effectively reduce the number and mass concentration of AMP particles,
and the addition of oxygen can significantly suppress the total exhaust
particle mass concentration, especially for the conditions of high
EGR rates and low n-butanol-blended ratios.
Experimental System and Test Procedure
Experimental
Engine and Apparatus
The experimental engine was a single-cylinder
engine modified from
a four-cylinder, four-valve, common-rail diesel engine. The main engine
specifications are shown in Table . The third cylinder of the engine was kept as the
working cylinder with independent intake/exhaust system and fuel supply
system; the valve and fuel injector of the other cylinders are removed
and the others remain unchanged. An opened ECU (NI2106), which can
modify the fuel injection parameters flexibly, was used in the engine. Figure shows the schematic
diagram of the experimental setup. To adjust the intake components
and intake pressure flexibly, a two-stage supercharging system and
an intake component control system were designed and fixed to the
engine. In this study, pure CO2 was used to simulate the
EGR gas. A compressor together with a pressure sensor and a current
limiting valve were employed to adjust the intake air pressure within
a range of 0.1–0.3 MPa. Intake component control equipment
was developed based on a FX5U-32M programmable logic controller (PLC)
worked under a self-edited program. PLC was used to adjust the proportions
of the pure O2 and pure CO2 both supplied with
the high-pressure tank. The flux of O2 and CO2 can be adjusted flexibly by magnetic valves in the range of 0–100
L/min. Figure shows
the main structure of the intake oxygen system.
Table 2
Engine Specifications
category
properties
geometric compression ratio
17.7
cylinder diameter (mm)
95.4
piston stroke (mm)
104.9
connecting rod length (mm)
162
intake valve closing moment (deg CA ATDC)
–143
exhaust valve closing moment (deg CA ATDC)
366
injector orifice number
6
injector orifice diameter
(mm)
0.12
oil jet cone angle
(°)
12
Eddy current
ratio
0.97
Figure 14
Schematic diagram of
the experimental setup: 1: high-pressure oxygen
cylinder; 2: pressure-reducing valve; 3: intake oxygen control machine;
4: high-pressure oil rail; 5: ECU; 6: high-pressure oil pump; 7: alternating
current motor; 8: injector; 9: fuel tank; 10: compressor; 11: pressure-stabilizing
tank; 12: CO2 cylinder; 13: intake CO2 control
machine; 14: engine; 15: engine exhaust particle sizer; and 16: fast
engine exhaust analyzer.
Schematic diagram of
the experimental setup: 1: high-pressureoxygen
cylinder; 2: pressure-reducing valve; 3: intake oxygen control machine;
4: high-pressure oil rail; 5: ECU; 6: high-pressure oil pump; 7: alternating
current motor; 8: injector; 9: fuel tank; 10: compressor; 11: pressure-stabilizing
tank; 12: CO2 cylinder; 13: intake CO2 control
machine; 14: engine; 15: engine exhaust particle sizer; and 16: fast
engine exhaust analyzer.Schematic representation
of the intake oxygen system: 1: O2 decompression valve;
2: PLC; 3: pressure sensor; 4: high-pressureoxygen tank; 5: solenoid valve; 6: pressure regulator; 7: O2 distributor; 8: high-frequency solenoid valve; and 9: engine.The main instruments
and equipment of the measuring and control
system are shown in Table . Among them, the characteristics of the particulate emission
were measured using the DMS500 fast particle analyzer. When the cyclone
separator is introduced in DMS500, large particles (particle diameter
larger than 1000 nm) of engine exhaust are removed, and then the sample
gas enters the classifier to classify the charged particles according
to the electron mobility. Finally, the classified particles generate
corresponding currents in the electrometer to determine the concentration
of particles with different sizes.[36] The
particle mass can be calculated based on the number of the particles
using the following formula:where dp is the
particle size, massagg is the mass of the particles with
the size dp, and nagg is the number of particles with the size dp.
Table 3
Main Equipment
category
measuring
instruments
manufacturer
accuracy
dynamometer
CW260
CAMA
torque: ±0.5 NM
speed: ±2 rpm
fuel flow meter
FX-100
ONO-SOKKI
±0.12%
air flow meter
20R100
TOCEL
±1%
CO and CO2
NDIR500
Cambustion
<2% FS/h
HC
HFR500
Cambustion
<1% FS/h
NOx
CLD500
Cambustion
<5 ppm/h
particle
DMS500
Cambustion
Methodology and Test Conditions
The
ultralow sulfurdiesel was used as the baseline fuel. The pure baseline
diesel was defined as B0. One comparative fuel was made of 85% baseline
diesel and 15% n-butanol (by volume), defined as
B15. Another comparative fuel was composed of 70% baseline diesel
and 30% n-butanol (by volume), defined as B30. Table shows the main properties
of the fuels for test. Table summarizes the experimental conditions of this study. The
engine runs with a maximum torque speed of 1400 rpm, under a load
rate of 50%. The indicated mean effective pressure (IMEP) was about
0.85 MPa. For different fuels and intake components, the fuel injection
timing was adjusted to ensure that the heat release center (CA50)
was 8 deg CA ATDC, and the injection pressure was kept at 100 MPa.
The different intake components were achieved by changing the oxygen
addition and EGR rate. Without the oxygen addition, the EGR rate determines
the oxygen concentration in the intake gas, and the existing research
results show that the excessive oxygen introduction leads to a significant
deterioration of the NO emissions.[37] Therefore, depending on the actual situation,
this experiment supplies oxygen in moderation (1–4% with the
step of 1%) for all of the EGR rate conditions including 0%, 10%,
14%, and 18%, respectively. All the tests were repeated three times,
and the data used in this paper are the average of the three tests.
Among them, the EGR rate was defined as the mass ratio of the CO2 content in the intake to the exhaust of the engine, and 1–4%
oxygen addition refers to the introduction of oxygen with a mass fraction
addition of 1–4% on the basis of the intake oxygen concentration
when EGR is introduced. The difference between the combustion start
point (CA10) and the fuel injection start point is defined as ID,
and the difference between the combustion end point (CA90) and the
CA10 is defined as CD.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15