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Combustion characteristics and NOx emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine
Accepted Manuscript Research Paper Combustion characteristics and NOx emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine Peng Geng, Hongjun Mao, Yanjie Zhang, Lijiang Wei, Kun You, Ji Ju, Tingkai Chen PII: DOI: Reference:
S1359-4311(16)34379-4 http://dx.doi.org/10.1016/j.applthermaleng.2016.12.113 ATE 9733
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
28 September 2016 18 December 2016 26 December 2016
Please cite this article as: P. Geng, H. Mao, Y. Zhang, L. Wei, K. You, J. Ju, T. Chen, Combustion characteristics and NOx emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine, Applied Thermal Engineering (2016), doi: http://dx.doi.org/10.1016/j.applthermaleng.2016.12.113
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Combustion characteristics and NOx emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine Peng Geng a,*, Hongjun Mao b, Yanjie Zhang b, Lijiang Wei a, Kun You a, Ji Ju a, Tingkai Chen a a
Merchant Marine College, Shanghai Maritime University, Shanghai 201306, PR China
b
College of Environmental Science and Engineering, Nankai University, Tianjin 300072, PR China
Abstract: The International Maritime Organization (IMO) has enacted the Maritime Agreement Regarding Oil Pollution (MARPOL) VI to regulate the ship emissions. In the large ocean-going ship, the marine auxiliary diesel engine is widely used to produce electricity, and it could also generate large amounts of harmful emissions. In order to reduce these emissions, some alternative fuels were used in the marine diesel engine. In
term of this, the combustion and emissions
characteristics and emissions of a 6-cyclinder turbocharged inter-cooling direct-injection marine auxiliary diesel engine was investigated in this study when using Ultralow Sulfur Diesel (ULSD), B70 (diesel containing 70 vol.% of biodiesel), B90 and neat waste cooking oil biodiesel (B100), respectively.
The influence of high biodiesel to diesel ratio on the combustion
characteristics and NOx (NO and NO2) emissions was studied, under 25%,50%,75% engine load at 1050rev/min and 1500rev/min (Rated speed) conditions. The experimental results indicated thatthe cylinder pressure decreases slightly with
increasing the biodiesel content in
the test fuels, while the ignition advances, ignition delay reduces and combustion duration becomes longer. When the test engine operated at low load, the maximum percent peak heat release rate(HRR) decreases is about 14.3%, while the maximum percent can reach to 21.3% at high load condition. For each test fuel, the cylinder pressure and peak heat release rate increase significantly with the increase of engine load. The temperature of the exhaust manifold decreases with the increases of biodiesel content in the test fuels. Moreover, the NOx emissions decrease significantly when using the high substitution ratio of biodiesel, which is due to the decrease of the cylinder temperature in the
diffusion combustion mode.
The NO emission
increases with the increases of the engine torque, while the NO2 emission decreases. Consequently, the ratio of NO2 to NO decreases sharply with the increases of engine load, due to the increase of the cylinder temperature. Keywords: Marine auxiliary diesel engine;
waste cooking oil; biodiesel; combustion
characteristics; NOx emissions 1. Introduction Large ocean-going ship is the main power source of the logistics, passenger transport and national defense. Moreover, more than 90% of international trade is now conducted via the ocean-going shipping [1,2]. The large ocean-going shipping has three typical characteristics, which are the high fuel consumption rate, the long operation and the high level of harmful emissions [3]. Compared with the vehicle, the shipping would lead to worse environmental pollution
[4,5,6]
. In
order to decrease these harmful emissions, the IMO (International Maritime Organization) has
established the rules and regulations to strengthen the laws regulating NOx and SOx emissions [7,8,9]
. Since 2016, IMO Tier III regulations have been applied to new ocean-going shipping that
sail in three Emission Control Areas (ECAs) in China, which are Yangtze River Delta, Pearl River Delta and Bohai Rim, respectively. In recent years, both marine diesel engine manufacturing and shipping companies from all over the world have been focusing on the reduction of NOx and SOx emissions strategies [10,11,12,13]
. For most of the ocean-going ships, the heavy fuel oil (HFO), which is the lowest-grade
of oil, is used in both the main and auxiliary marine diesel engines,[14]. The diesel engines using the HFO can generate a large amount of harmful exhaust emissions during the combustion Many countries have adjusted the energy policies to search for the clean fuels
[15]
.
[16]
. One of the
alternative fuels is biodiesel, which is renewable, economical and environmentally conscious[17]. It can also be widely used in the marine diesel engine which has the highest demand for petroleum fuels
[18]
. The advantages of biodiesel as the alternative fuels, in addition to its renewability, are
the minimal aromatic hydrocarbon and sulfur content, high cetane number, high lubricity, high flash point, non-toxicity and high biodegradability[19]. Furthermore, there is about 10-11% oxygen by weight contained in the biodiesel. Additionally, it is no need to modify the diesel engine because the biodiesel can be used in either the neat form or in the blended form. However, there are also some disadvantages, such as low calorific value, low volatility, high viscosity and high pour point. In the previous studies, some researchers have investigated the environmental effects of the biodiesel fuel. They found that, the CO emission, sulfur levels, unburned hydrocarbons and particulate matter (PM) in the exhaust gas were decreased significantly compared with those from the conventional diesel fuel[20,21,22,23]. Biodiesel can be completely dissolved in the diesel fuel, and thus it can be blended in any proportion with diesel fuel. In the United States,about 90% of biodiesel is extracted from methyl or soybean methyl ester since it is the largest producer of soybeans worldwide
[24]
. Because of its
good balance between costs, performance and emission benefits, the blend fuel with 80% diesel and 20% biodiesel are widely used in the United States[25]. In Europe, the rapeseed oil is the major material of the biodiesel and it is complied with the applicable standard EN14214 [26]. In southeast Asia, biodiesel is mainly produced from jatropha tree [27]. In recent years, the waste cooking oil is more and more popular to be used as a biodiesel source inChina [28,29,30]. However, most of the previous studies for the biodiesel application were limited on the vehicle diesel enginesand the proportion of the biodiesel content in the blended fuels is low[31,32]. Since the marine auxiliary diesel engine has been widely used to produce electricity in the large ocean-going ship, the emissions from the marine auxiliary diesel engine also need to be noticed. In addition, the relation between NO emission and NO2 emission when using the biodiesel and diesel blended fuels has not been understood well. Lack of new research activities concerning the impact of biodiesel on the marine auxiliary diesel engine combustion and emissions forced the author to undertake this research work. Blended fuels with different biodiesel to Ultralow Sulfur Diesel (ULSD) ratios were used for
the engine tests. The main goal is to find out the effects of thehigh ratio of biodiesel and diesel blended fuels on the combustion and NOx emissions of a marine auxiliary diesel engine. This paper presents the results of laboratory tests on the effects of selected waste cooking oil biodiesel and ultralow sulfur light fuel on the level of emissions. 2. Experimental apparatus and procedure 2.1 Test engine and fuels In this study, the experiments were carried out on a 6-cylinder turbocharged inter-cooling direct-injection marine auxiliary diesel engine. Fuels with different blended proportions of waste cooking oil biodiesel and ULSD were used. Fig.1 shows the schematic of the experimental setup used in this study. The main specifications of the test diesel engine are listed in Table 1. The marine auxiliary diesel engine was coupled with a hydraulic dynamometer, and a control engine test system (Changtong system) was used to adjust the diesel engine speed and torque. This system allows adjustment of engine load at a fixed engine speed or adjustment of engine speed at a fixed engine load. In this study, the ULSD contains less than 10 ppm by the weight of sulfur. The biodiesel used in this study was manufactured from the waste cooking oil by Pusheng petroleum chemical industry Ltd, comply with EN4214. The biodiesel contains mainly Methyl palmitate, Methyl oleate and Methyl linoleate. The test fuels contained 0%, 70%, 90% and 100% by volume of biodiesel in light diesel fuel, and are identified as B0 (ULSD), B70, B90 and B100 (neat waste cooking oil biodiesel). Table 2 shows the main properties of ULSD and the biodiesel. For each case, fuel consumptions were measured gravimetrically using an electronic balance with a precision of 0.1g (Shimadzu Balance, Model BX-32KH). The standard errors were 2.9% and 1.6% for NOx emission and mass consumption of fuel, respectively. The mass consumption of fuel and detailed diesel engine operating conditions are shown in Table 3. Table 1 Test engine specifications Model
6135G128ZCa
Type
6-Cylinder, in-line, water-cooled, DI engine
Compression ratio
17.0:1
Bore/stroke (mm)
135/150
Displacement (L)
12.88
12h maximum power (kW) (PS)
178.2 (242)
Continuous output (kW) (PS)
162 (220)
Rated speed (rev/min)
1500
Ignition order
1-5-3-6-2-4
Intake type
Turbocharged, inter-cooling
Fresh air Inter-cooler
Air
Combustion analyzer
Exhaust gas Air filter
Cylinder Pressure Sensor
Hydraulic dynamometer
Shaft encoder
marine auxiliary diesel engine
Exhaust gas Engine control system
Exhaust gas turbocharger
Gaseous analyzers Fig.1 Schematic diagram of experimental system Table 2 Properties of ultralow sulfur diesel (ULSD) and biodiesel Properties
ULSD
Biodiesel
3
839
873.8
2
Viscosity (40 C) (mm /s)
2.4
4.395
Cetane number
53
55.3
Sulfur content (mg/kg)
＜10
＜10
Heat of evaporation (kJ/kg)
250-290
300
Lower heating value (MJ/kg)
42.5
37.5
Flash point (OC)
82
182.5
Carbon content (wt%)
86.6
77.1
Density (20 C) (kg/m ) O
O
Table 3 Fuel consumption (FC) forULSD, B70, B90 and B100 under various engine loads Mode Engine Speed
1050r/min
1500r/min
Diesel
B70
B90
Biodiesel
FC (kg/h)
FC (kg/h)
FC (kg/h)
FC (kg/h)
125N.m (25%)
4.24
4.70
4.82
4.84
250N.m(50%)
6.50
7.13
7.32
7.44
375N.m(75%)
8.80
9.73
9.96
10.17
273N.m(25%)
11.48
12.36
12.71
12.83
546N.m(50%)
19.29
20.84
21.47
21.79
819N.m(75%)
25.91
28.05
29.17
29.39
Engine Load
2.2 Engine test and measurement A pressure transducer (Kistler 6613CG1, 0.5% resolution) was used to measure the cylinder pressure, which was installed in the first cylinder of the test diesel engine. The pressure sensor was used with a charge amplifier and a shaft encoder(AVL 364C) to obtain the cylinder pressure data at 0.5 crank angle intervals. The averages of the pressure data were analyzed with a combustion analyzer to obtain the heat release rate. The NOx (NO and NO2) emissions from the test marine auxiliary
diesel
engine
were
measured
with
a
mobile
emissions
test
system
(SEMTECH-ECOSTAR, Sensor, Inc.) The precision of the NOx measure instrumentation is less than 1% of full scale when the range of measurement is
higher than 155ppm, while it is less
than 2% of full scale when the range of measurement is lower than 155ppm.The principle of the test system is based on the Beer-Lambert law. 2.3 Test mode and procedure In this research, the experiments were conducted at steady states to investigate the influence of the high substitution ratio of biodiesel to diesel on the combustion characteristic and NOx emissions. The test diesel engine was operated at the two steady engine speeds of 1050r/min and 1500r/min (rated engine speed) but different engine loads, as shown in Table 3. In order to obtain the high repeatability of the measurements, the test diesel engine was allowed to run for some minutes until the cooling water temperature, lubricating oil temperature and exhaust gas temperature had reached steady-state values The cooling water temperature was kept between 80 C and 85 OC, and the lubricating oil temperature was kept between 90 OC and 100 OC, depending
O
on the engine conditions. Fuel consumption, exhaust gas temperature and NOx emissions were continuously measured for three minutes when the test diesel engine was fueled with different test fuels and the average experimental results were obtained.
To ensure the experimental
uncertainty less than 5%, each steady state experiments were repeated at least twice. Moreover, the two-sided Student’s T-test was used to compare the testing results obtained from different test fuels if these results were different from each other at 95% significance level. 3
Results and discussion
3.1 Effect of high biodiesel to diesel ratio on the combustion characteristics Fig.2 shows the averaged cylinder pressure and heat release rate curves for different
test
fuels. In this study, the cylinder pressure data was obtained by averaging over 100 cycles data to diminish the influence of cycle-by-cycle variation and used to calculate the heat release rate. As shown in Fig.2, in all engine conditions, the cylinder pressure decreases slightly with the increase of biodiesel content in the test fuels. The cylinder pressure and heat release rate curves are similar for combustion in both ULSD mode and biodiesel additive diesel mode. The cylinder pressure
with the use of biodiesel-diesel blends began to increase earlier than neat ULSD. It is known that the octane number and laminar flame speed of biodiesel are higher than ULSD[33], and thus the combustion duration was shorten when the test diesel engine operated in the biodiesel-diesel blends mode[34]. It can be observed that the peak heat release rate(HRR) decreases significantly with the increase of the biodiesel content in the test fuels. When the test engine operated
at low
load, the maximum percent it decreases is about 14.3%, while the maximum percent can reach to 21.3% at high load condition. The ignition delay decreases with the increase of the biodiesel content in the test fuels. When the test engine operated on 25% of the maximum torque, the ULSD started to combust when the crank angle is -1°CA，while the B100 started to combust when the crank angle is -3°CA. Meanwhile, when the test engine operated on 75% of the maximum torque, the ULSD started to combust when the crank angle is -4°CA，while the B100 started to combust when the crank angle is -6°CA. It indicated that the ignition delay decreased about 2°CA. Moreover, the higher ratio of biodiesel and diesel fuel leads to the decrease of the instantaneous peak heat release rate and the start timing of the combustion advances. The mixture in the cylinder decreases and then lead to the reduction of the peak heat release rate. Meanwhile, the low cylinder temperature might be a major factor to decrease the diffusion combustion rate[35].
40
180 160
3
Cylinder Pressure (bar)
50
200
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 25%
140 30
120
20
100 80
10
60 0 40 -10 -20 -50
Rate of Heat Release (kJ/m /deg)
60
20 -40
-30
-20
-10
0
10
20
30
40
0 50
Crank Angle (deg)
30
140
20
120
10
100
0
80
-10
60
-20
40
-30
20
-40 -50
-40
-30
-20
-10
0
10
Crank Angle (deg)
20
30
40
0 50
ULSD B70 B90 B100
60
180 160
3
160
200
Engine speed: 1500r/min Engine load: 50% Cylinder Pressure （ bar）
Cylinder Pressure (bar)
40
80
180
140
40
120 20
100 80
0
60 40
-20
20 -40 -50
-40
-30
-20
-10
0
10
Crank Angle (deg)
20
30
40
Rate of Heat Release (kJ/m /deg)
200
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 50%
3
50
Rate of Heat Release (kJ/m /deg)
60
0 50
160 140
30
120
20
100 80
10
60 0 40
200
Engine Speed: 1500r/min Engine Load: 75%
ULSD B70 B90 B100
60 50
20
-20
30
120
20
100
10
80
0
60
-10 40
-50
-40
-30
-20
-10
0
10
20
30
40
20
-30
0 50
160 140
40
-20
-10
180
-40 -50
3
70
Rate of Heat Release (kJ/m /deg)
80
180
3
40
200
Cylinder Pressure (bar)
Cylinder Pressure (bar)
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 75%
50
Rate of Heat Release (kJ/m /deg)
60
-40
-30
Crank Angle (deg)
-20
-10
0
10
20
30
40
0 50
Crank Angle (deg)
Fig.2 Effect of high ratio of biodiesel and diesel fuel on cylinder pressure and heat release rate
3.2 Effect of high biodiesel to diesel ratio on the exhaust temperature The exhaust temperature reflects the combustion efficiency and affects the engine emissions generation[36]. The exhaust manifold temperatures for different ratios of biodiesel content in the test fuels are shown in Fig.3. As shown in Fig.3, the temperature of exhaust manifold decreases slightly with the increase of the biodiesel content in the test fuels, while increases significantly with the increase of engine speeds and loads. For all test fuels, when the test diesel engine operates at the low engine speed and load, the exhaust temperature is less than 150 OC, while the temperature could reach more than 400 OC when the engine operates at the high speed and load. The NOx emissions from the diesel engine are influenced by the temperature of exhaust manifold and there are also some chemical reactions between NO and NO2 emissions due to the changes of the rate of conversion[37]. Fig.3 also shows that the exhaust temperature of high ratio of biodiesel and diesel fuel mode is lower than that of pure ULSD mode. Because of the low heating value of biodiesel, the heat release decreases after the main injection period[38]. Moreover, due to the high rate of the heat release, the complete combustion became earlier and thus the heat transfer might occur before the exhaust valve opening. All of these factors lead to the reduction of the exhaust temperature. 450
450
Engine Speed： 1500r/min
Engine Speed: 1050r/min 400
Exhaust Temperature ( C)
O
300
ULSD B70 B90 B100
350
O
350
Exhaust Temperature ( C)
400
ULSD B70 B90 B100
250 200 150 100 50
300 250 200 150 100 50
0
0
25%
50%
75%
25%
Engine Load
50%
75%
Engine Load
Fig.3 Effect of high ratio of biodiesel and diesel fuel on exhaust manifold temperature
3.3 Effect of high biodiesel to diesel ratio on the NOx emissions The NOx emission is one kind of the major pollutants of the diesel engine, and it is consist of
NO (nitric oxide), NO2 (nitrogen dioxide) and N2O (nitrous oxide)[39]. For these emissions, NO emission is the main component and accounts for more than 60% of the total NOx emissions, while the proportion of NO2 emission is less than 40% and the N2O emission is less to be negligible. Thus, in this study,
the NO and NO2 emissions are considered as the
NOx
emissions. The NOx emissions from diesel engines are influenced by the air/fuel ratio, the residence time at the elevated temperature in the cylinder and the temperature in the burned mixture. Fig.4 shows that the high ratio of biodiesel and diesel fuels influences the formation of NOx emissions significantly. As shown in Fig.4, the NOx emissions decrease significantly with the increase of the biodiesel content in the test fuels. At the low engine speed and load condition, the NOx emissions are about 140 ppm in pure ULSD mode, while the NOx emissions are less than 100 ppm in pure biodiesel mode. For all test fuels, with the increase of engine speed and load, the total NOx emissions increase significantly. When the test diesel engine operates at the high engine speed and load, the total NOx emissions in pure ULSD mode can reach 800 ppm, and the NOx emissions in pure biodiesel mode can also reach 700ppm. The cylinder temperature increases significantly with the increase of engine speed and load, and this is the main factor leading to the increase of the total NOx emissions. There are also several reasons resulting in the decrease of the total NOx formation when the test engine operates in the biodiesel and diesel blended mode. Compared with diesel fuel, biodiesel with high cetane number leads to the smaller premixed combustion and ignition delay. Additionally, the lower cylinder temperature also decreases the total NOx concentration in the combustion process[40]. 900
500 450
Engine Speed: 1500r/min
Engine Speed: 1050r/min
400
700 600 -6
300
NOx/10
NOx/10
-6
350
ULSD B70 B90 B100
800
ULSD B70 B90 B100
250 200
500 400 300
150 200
100 100
50 0
0 25%
50%
Engine Load
75%
25%
50%
75%
Engine Load
Fig.4 Effect of high ratio of biodiesel and diesel fuel on NOx emissions
3.4 Effect of high biodiesel to diesel ratio on the NO and NO2 emissions The influences of high ratio of biodiesel and diesel fuels on the NO, NO2 emissions and the ratio of NO2/NO are shown in Fig.5 and Fig.6. As shown in Fig.5, the NO emission increases significantly with the increase of the engine loads, while the NO emission decreases with the increase of biodiesel content in the test fuels. Meanwhile, the NO2 emission decreases significantly with the increase of the engine loads, and also decreases with the increase of biodiesel content in the test fuels. Fig.6 shows the ratio of NO2/NO when the test diesel engine
operates on different engine conditions for all test fuels. When the test diesel engine operates on the low engine load, the ratio of NO2/NO is about 3:7, due to the low cylinder temperature, while the ratio of NO2/NO decreases significantly with the increase of engine loads. When the test engine operates on the high load, the proportion of NO2 in the total NOx concentration is less than 3%. As shown in Fig.5, the ratio of NO2/NO decreases slightly with the increase of biodiesel content in the test fuels. In the previous studies[41,42], the reactions between NO and NO2 are: (1) O2⇌2O; (2) N2+O⇌NO+N; (3) O2+N⇌NO+O; (4) N+OH⇌NO+H; (5) NO+HO2→NO2+OH; (6) NO2+O→NO+O2. 800
100
Engine Speed: 1500r/min 700
90
ULSD B70 B90 B100
600
ULSD B70 B90 B100
80 70
500 -6
60
NO2/10
-6
NO/10
Engine Speed: 1500r/min
400 300
50 40 30
200 20 100
10
0
0 25%
50%
75%
25%
50%
Engine Load
75%
Engine Load
(a) NO emission
(b) NO2 emission
Fig.5 Effect of high ratio of biodiesel and diesel fuel on NO and NO2 emissions 1.0
1.0
n=1500r/min Test fuel: B70
n=1500r/min Test fuel: Diesel 0.8
0.8
NO2 NO
0.6
NO2/NO
0.6
NO2/NO
NO2 NO
0.4
0.4
0.2
0.2
0.0
0.0 25%
50%
Engine Load
75%
25%
50%
Engine Load
75%
1.0
1.0
n=1500r/min Test fuel: B100
n=1500r/min Test fuel: B90 0.8
NO2 NO
0.8
0.6
NO2/NO
NO2/NO
0.6
NO2 NO
0.4
0.2
0.4
0.2
0.0 25%
50%
75%
0.0 25%
Engine Load
50%
75%
Engine Load
Fig.6 Effect of high ratio of biodiesel and diesel fuel on NO2/NO emissions
4
Conclusions This study focuses on the influence of the high ratio of biodiesel and diesel fuels on the
combustion characteristic (cylinder pressure and heat release rate) and NOx emissions (NO and NO2) from a marine auxiliary diesel engine. Experiments were conducted on a 6-cyclinder turbocharged inter-cooling direct-injection
diesel engine fueled with Ultralow Sulfur Diesel
(ULSD), B70 (diesel containing 70 vol.% of biodiesel), B90 and neat waste cooking oil biodiesel (B100). The test modes were under the 1050r/min & 1500r/min (Rated speed) and 25%-75% engine torques. Based on the experimental data, the major conclusions are shown as follows: 1. By the use of waste cooking oil biodiesel, the cylinder pressure increases slightly with the increase of biodiesel content in the test fuels, while the heat release rate decreases significantly. When the test engine operated at low load, the maximum percent peak heat release rate(HRR) decreases is about 14.3%, while the maximum percent can reach to 21.3% at high load condition. 2. The ignition delay was shortened with the increase of the biodiesel content in the test fuels, and the complete combustion became earlier. The ignition delay was shorten about 2°CA. 3. For all test fuels, the total NOx emissions increase significantly with the increase of the engine speeds and loads; for all engine conditions, the total NOx emissions decrease significantly with the increase of biodiesel content in the test fuels. 4. The NO emission increases significantly with the increase of engine loads, but decreases with the increase of biodiesel content in test fuels; while the NO2 emission decreases significantly with the increase of both engine loads and biodiesel content in the test fuels. 5. Additionally, the ratio of NO2/NO also decreases with the increase of the engine loads and biodiesel content in the test fuels. In our further research, we will evaluate the factors resulting in the influence of NO and NO2 emissions by the use of the numerical simulation with 0-D chemical kinetic. Acknowledgements The authors would like to acknowledge the financial support from Shanghai Maritime
University (2015 top journals cultivation fund). References [1] IMO (International maritime organization).
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[31] Fang Q., Fang J.H., Zhuang J., et al. Effects of ethanol-diesel-biodiesel blends on combustion and emissions in premixed low temperature combustion. Applied Thermal Engineering, 2013;54:541-548. [32] Atmanli A. Comparative analyses of diesel-waste oil biodiesel and propanol, n-butanol or 1-pentanol blends in a diesel engine. Fuel, 2016;176:209-215. [33] Fang Q., Fang J.H., Zhuang J., et al. Effect of ethanol-diesel-biodiesel blends on combustion and emissions in premixed low temperature combustion. Applied Thermal Engineering, 2013, 54: 541-548. [34] Ng H.K., Gan S. Combustion performance and exhaust emissions from the non-pressurised combustion of palm oil biodiesel blends. Applied Thermal Engineering, 2010, 30: 2476-2484. [35] Tashtoush G., Al-Widyan M.I., Al-Shyoukh A.O. Combustion performance and emissions of ethyl ester of a waste vegetable oil in a water-cooled furnace. Applied Thermal Engineering, 2003, 23: 285-293. [36] Prabhu S.S., Nayak N.S., Kapilan N., et al. An experimental and numerical study on effects of exhaust gas temperature and flow rate on deposit formation in Urea-Selective Catalytic Reduction (SCR) system of modern automobiles. Applied Thermal Engineering, 2017, 111: 1211-1231. [37] Guardiola C., Martin J., Pla B., et al. Cycle by cycle NOx model for diesel engine control. Applied Thermal Engineering, 2017, 110: 1011-1020. [38] Lapirattanakun A., Charoensuk J. Development of porous media burner operating on waste vegetable oil. Applied Thermal Engineering, 2017,110: 190-201. [39] Zhang G.Y., Zhu C.Q., Ge Y.X., et al. Fluidized bed combustion in steam-rich atmospheres for high-nitrogen fuel: Nitrogen distribution in char and volatile and their contributions to NOx. Fuel, 2016, 186: 204-214. [40] Reijnders J., Boot M., Goey P. Impact of aromaticity and cetane number on the soot-NOx trade-off in conventional and low temperature combustion. Fuel, 2016, 186: 24-34. [41] He B.Q. Advances in emission characteristics of diesel engines using different biodiesel fuels. Renewable and Sustainable Energy Reviews. 2016;60:570-586. [42]Cheng A.S, Upatnieks A,Mueller C.J. Investigation of the impact of biodiesel fuelling on NOx emissions using an optical direct injection diesel engine. Int J Engine Res.2006;7:297-318.
graphical abstract Fresh air Inter-cooler
Air
Combustion analyzer
Exhaust gas Air filter
Cylinder Pressure Sensor
Hydraulic dynamometer
Shaft encoder
marine auxiliary diesel engine
Exhaust gas Exhaust gas turbocharger
Engine control system
Gaseous analyzers
Fig.1 Schematic diagram of experimental system
60
200
ULSD B70 B90 B100
Cylinder Pressure (bar)
40
180 160
3
Engine Speed: 1050r/min Engine Load: 25%
140 30
120
20
100 80
10
60 0 40 -10 -20 -50
Rate of Heat Release (kJ/m /deg)
50
20 -40
-30
-20
-10
0
10
20
30
40
0 50
Crank Angle (deg)
140
20
120
10
100
0
80
-10
60
-20
40
-30
20 -20
-10
0
10
20
30
40
140 120
20
100 80
0
60 40
-20
20
0 50
-40 -50
-40
-30
-20
80
180
70
160
0
10
20
30
40
140 30
120
20
100 80
10
60 0 40
ULSD B70 B90 B100
50
20
-20 -30
-20
-10
0
10
Crank Angle (deg)
20
30
40
0 50
180 160 140
40 30
120
20
100
10
80
0
60
-10 40
-20
-10
-40
0 50
200
Engine Speed: 1500r/min Engine Load: 75%
60
Cylinder Pressure (bar)
40
200
3
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 75%
Rate of Heat Release (kJ/m /deg)
Cylinder Pressure (bar)
-10
Crank Angle (deg)
60
-50
160
40
Crank Angle (deg)
50
180
20
-30 -40 -50
-40
-30
-20
-10
0
10
20
30
40
Crank Angle (deg)
Fig.2 Effect of high ratio of biodiesel and diesel fuel on cylinder pressure and heat release rate
0 50
3
-30
60
Rate of Heat Release (kJ/m /deg)
-40
ULSD B70 B90 B100
3
160
30
-40 -50
200
Engine speed: 1500r/min Engine load: 50% Cylinder Pressure （ bar）
Cylinder Pressure (bar)
40
80
180
Rate of Heat Release (kJ/m /deg)
200
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 50%
3
50
Rate of Heat Release (kJ/m /deg)
60
450
450
Engine Speed： 1500r/min
Engine Speed: 1050r/min 400
O
O
300
ULSD B70 B90 B100
350
Exhaust Temperature ( C)
350
Exhaust Temperature ( C)
400
ULSD B70 B90 B100
250 200 150 100
300 250 200 150 100
50
50
0
0
25%
50%
75%
25%
50%
75%
Engine Load
Engine Load
Fig.3 Effect of high ratio of biodiesel and diesel fuel on exhaust manifold temperature 900
500
Engine Speed: 1500r/min
Engine Speed: 1050r/min
450 400 350
700 600 -6
500
NOx/10
-6
300
NOx/10
ULSD B70 B90 B100
800
ULSD B70 B90 B100
250 200
400 300
150 200
100 100
50 0
0 25%
50%
25%
75%
50%
75%
Engine Load
Engine Load
Fig.4 Effect of high ratio of biodiesel and diesel fuel on NOx emissions 800
100
Engine Speed: 1500r/min 700
90
ULSD B70 B90 B100
600
ULSD B70 B90 B100
80 70
500 -6
60
NO2/10
-6
NO/10
Engine Speed: 1500r/min
400 300
50 40 30
200 20 100
10
0
0 25%
50%
Engine Load
(a) NO emission
75%
25%
50%
Engine Load
(b) NO2 emission
Fig.5 Effect of high ratio of biodiesel and diesel fuel on NO and NO2 emissions
75%
1.0
1.0
n=1500r/min Test fuel: B70
n=1500r/min Test fuel: Diesel 0.8
0.8
NO2 NO
0.6
NO2/NO
0.6
NO2/NO
NO2 NO
0.4
0.4
0.2
0.2
0.0
0.0 25%
50%
25%
75%
n=1500r/min Test fuel: B100
n=1500r/min Test fuel: B90 NO2 NO
0.8
0.6
NO2 NO
0.6
NO2/NO
NO2/NO
75%
1.0
1.0
0.8
50%
Engine Load
Engine Load
0.4
0.2
0.4
0.2
0.0 25%
50%
75%
0.0
Engine Load
25%
50%
75%
Engine Load
Fig.6 Effect of high ratio of biodiesel and diesel fuel on NO2/NO emissions
Highlights (for review) 1. Higher waste cooking oil biodiesel-diesel blends were applied in the marine auxiliary diesel engine; 2. Effects of the test fuels on combustion and emissions clearly depends on engine conditions; 3. Higher waste cooking oil biodiesel-diesel blends increase the cylinder pressure slightly, while decrease the ignition delay. 4. Higher waste cooking oil biodiesel-diesel blends have potential for reducing the NOx emissions. 5. The ratio of NO2/NO decreases with the increase of the engine loads and biodiesel content in the test fuels.
S1359-4311(16)34379-4 http://dx.doi.org/10.1016/j.applthermaleng.2016.12.113 ATE 9733
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
28 September 2016 18 December 2016 26 December 2016
Please cite this article as: P. Geng, H. Mao, Y. Zhang, L. Wei, K. You, J. Ju, T. Chen, Combustion characteristics and NOx emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine, Applied Thermal Engineering (2016), doi: http://dx.doi.org/10.1016/j.applthermaleng.2016.12.113
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Combustion characteristics and NOx emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine Peng Geng a,*, Hongjun Mao b, Yanjie Zhang b, Lijiang Wei a, Kun You a, Ji Ju a, Tingkai Chen a a
Merchant Marine College, Shanghai Maritime University, Shanghai 201306, PR China
b
College of Environmental Science and Engineering, Nankai University, Tianjin 300072, PR China
Abstract: The International Maritime Organization (IMO) has enacted the Maritime Agreement Regarding Oil Pollution (MARPOL) VI to regulate the ship emissions. In the large ocean-going ship, the marine auxiliary diesel engine is widely used to produce electricity, and it could also generate large amounts of harmful emissions. In order to reduce these emissions, some alternative fuels were used in the marine diesel engine. In
term of this, the combustion and emissions
characteristics and emissions of a 6-cyclinder turbocharged inter-cooling direct-injection marine auxiliary diesel engine was investigated in this study when using Ultralow Sulfur Diesel (ULSD), B70 (diesel containing 70 vol.% of biodiesel), B90 and neat waste cooking oil biodiesel (B100), respectively.
The influence of high biodiesel to diesel ratio on the combustion
characteristics and NOx (NO and NO2) emissions was studied, under 25%,50%,75% engine load at 1050rev/min and 1500rev/min (Rated speed) conditions. The experimental results indicated thatthe cylinder pressure decreases slightly with
increasing the biodiesel content in
the test fuels, while the ignition advances, ignition delay reduces and combustion duration becomes longer. When the test engine operated at low load, the maximum percent peak heat release rate(HRR) decreases is about 14.3%, while the maximum percent can reach to 21.3% at high load condition. For each test fuel, the cylinder pressure and peak heat release rate increase significantly with the increase of engine load. The temperature of the exhaust manifold decreases with the increases of biodiesel content in the test fuels. Moreover, the NOx emissions decrease significantly when using the high substitution ratio of biodiesel, which is due to the decrease of the cylinder temperature in the
diffusion combustion mode.
The NO emission
increases with the increases of the engine torque, while the NO2 emission decreases. Consequently, the ratio of NO2 to NO decreases sharply with the increases of engine load, due to the increase of the cylinder temperature. Keywords: Marine auxiliary diesel engine;
waste cooking oil; biodiesel; combustion
characteristics; NOx emissions 1. Introduction Large ocean-going ship is the main power source of the logistics, passenger transport and national defense. Moreover, more than 90% of international trade is now conducted via the ocean-going shipping [1,2]. The large ocean-going shipping has three typical characteristics, which are the high fuel consumption rate, the long operation and the high level of harmful emissions [3]. Compared with the vehicle, the shipping would lead to worse environmental pollution
[4,5,6]
. In
order to decrease these harmful emissions, the IMO (International Maritime Organization) has
established the rules and regulations to strengthen the laws regulating NOx and SOx emissions [7,8,9]
. Since 2016, IMO Tier III regulations have been applied to new ocean-going shipping that
sail in three Emission Control Areas (ECAs) in China, which are Yangtze River Delta, Pearl River Delta and Bohai Rim, respectively. In recent years, both marine diesel engine manufacturing and shipping companies from all over the world have been focusing on the reduction of NOx and SOx emissions strategies [10,11,12,13]
. For most of the ocean-going ships, the heavy fuel oil (HFO), which is the lowest-grade
of oil, is used in both the main and auxiliary marine diesel engines,[14]. The diesel engines using the HFO can generate a large amount of harmful exhaust emissions during the combustion Many countries have adjusted the energy policies to search for the clean fuels
[15]
.
[16]
. One of the
alternative fuels is biodiesel, which is renewable, economical and environmentally conscious[17]. It can also be widely used in the marine diesel engine which has the highest demand for petroleum fuels
[18]
. The advantages of biodiesel as the alternative fuels, in addition to its renewability, are
the minimal aromatic hydrocarbon and sulfur content, high cetane number, high lubricity, high flash point, non-toxicity and high biodegradability[19]. Furthermore, there is about 10-11% oxygen by weight contained in the biodiesel. Additionally, it is no need to modify the diesel engine because the biodiesel can be used in either the neat form or in the blended form. However, there are also some disadvantages, such as low calorific value, low volatility, high viscosity and high pour point. In the previous studies, some researchers have investigated the environmental effects of the biodiesel fuel. They found that, the CO emission, sulfur levels, unburned hydrocarbons and particulate matter (PM) in the exhaust gas were decreased significantly compared with those from the conventional diesel fuel[20,21,22,23]. Biodiesel can be completely dissolved in the diesel fuel, and thus it can be blended in any proportion with diesel fuel. In the United States,about 90% of biodiesel is extracted from methyl or soybean methyl ester since it is the largest producer of soybeans worldwide
[24]
. Because of its
good balance between costs, performance and emission benefits, the blend fuel with 80% diesel and 20% biodiesel are widely used in the United States[25]. In Europe, the rapeseed oil is the major material of the biodiesel and it is complied with the applicable standard EN14214 [26]. In southeast Asia, biodiesel is mainly produced from jatropha tree [27]. In recent years, the waste cooking oil is more and more popular to be used as a biodiesel source inChina [28,29,30]. However, most of the previous studies for the biodiesel application were limited on the vehicle diesel enginesand the proportion of the biodiesel content in the blended fuels is low[31,32]. Since the marine auxiliary diesel engine has been widely used to produce electricity in the large ocean-going ship, the emissions from the marine auxiliary diesel engine also need to be noticed. In addition, the relation between NO emission and NO2 emission when using the biodiesel and diesel blended fuels has not been understood well. Lack of new research activities concerning the impact of biodiesel on the marine auxiliary diesel engine combustion and emissions forced the author to undertake this research work. Blended fuels with different biodiesel to Ultralow Sulfur Diesel (ULSD) ratios were used for
the engine tests. The main goal is to find out the effects of thehigh ratio of biodiesel and diesel blended fuels on the combustion and NOx emissions of a marine auxiliary diesel engine. This paper presents the results of laboratory tests on the effects of selected waste cooking oil biodiesel and ultralow sulfur light fuel on the level of emissions. 2. Experimental apparatus and procedure 2.1 Test engine and fuels In this study, the experiments were carried out on a 6-cylinder turbocharged inter-cooling direct-injection marine auxiliary diesel engine. Fuels with different blended proportions of waste cooking oil biodiesel and ULSD were used. Fig.1 shows the schematic of the experimental setup used in this study. The main specifications of the test diesel engine are listed in Table 1. The marine auxiliary diesel engine was coupled with a hydraulic dynamometer, and a control engine test system (Changtong system) was used to adjust the diesel engine speed and torque. This system allows adjustment of engine load at a fixed engine speed or adjustment of engine speed at a fixed engine load. In this study, the ULSD contains less than 10 ppm by the weight of sulfur. The biodiesel used in this study was manufactured from the waste cooking oil by Pusheng petroleum chemical industry Ltd, comply with EN4214. The biodiesel contains mainly Methyl palmitate, Methyl oleate and Methyl linoleate. The test fuels contained 0%, 70%, 90% and 100% by volume of biodiesel in light diesel fuel, and are identified as B0 (ULSD), B70, B90 and B100 (neat waste cooking oil biodiesel). Table 2 shows the main properties of ULSD and the biodiesel. For each case, fuel consumptions were measured gravimetrically using an electronic balance with a precision of 0.1g (Shimadzu Balance, Model BX-32KH). The standard errors were 2.9% and 1.6% for NOx emission and mass consumption of fuel, respectively. The mass consumption of fuel and detailed diesel engine operating conditions are shown in Table 3. Table 1 Test engine specifications Model
6135G128ZCa
Type
6-Cylinder, in-line, water-cooled, DI engine
Compression ratio
17.0:1
Bore/stroke (mm)
135/150
Displacement (L)
12.88
12h maximum power (kW) (PS)
178.2 (242)
Continuous output (kW) (PS)
162 (220)
Rated speed (rev/min)
1500
Ignition order
1-5-3-6-2-4
Intake type
Turbocharged, inter-cooling
Fresh air Inter-cooler
Air
Combustion analyzer
Exhaust gas Air filter
Cylinder Pressure Sensor
Hydraulic dynamometer
Shaft encoder
marine auxiliary diesel engine
Exhaust gas Engine control system
Exhaust gas turbocharger
Gaseous analyzers Fig.1 Schematic diagram of experimental system Table 2 Properties of ultralow sulfur diesel (ULSD) and biodiesel Properties
ULSD
Biodiesel
3
839
873.8
2
Viscosity (40 C) (mm /s)
2.4
4.395
Cetane number
53
55.3
Sulfur content (mg/kg)
＜10
＜10
Heat of evaporation (kJ/kg)
250-290
300
Lower heating value (MJ/kg)
42.5
37.5
Flash point (OC)
82
182.5
Carbon content (wt%)
86.6
77.1
Density (20 C) (kg/m ) O
O
Table 3 Fuel consumption (FC) forULSD, B70, B90 and B100 under various engine loads Mode Engine Speed
1050r/min
1500r/min
Diesel
B70
B90
Biodiesel
FC (kg/h)
FC (kg/h)
FC (kg/h)
FC (kg/h)
125N.m (25%)
4.24
4.70
4.82
4.84
250N.m(50%)
6.50
7.13
7.32
7.44
375N.m(75%)
8.80
9.73
9.96
10.17
273N.m(25%)
11.48
12.36
12.71
12.83
546N.m(50%)
19.29
20.84
21.47
21.79
819N.m(75%)
25.91
28.05
29.17
29.39
Engine Load
2.2 Engine test and measurement A pressure transducer (Kistler 6613CG1, 0.5% resolution) was used to measure the cylinder pressure, which was installed in the first cylinder of the test diesel engine. The pressure sensor was used with a charge amplifier and a shaft encoder(AVL 364C) to obtain the cylinder pressure data at 0.5 crank angle intervals. The averages of the pressure data were analyzed with a combustion analyzer to obtain the heat release rate. The NOx (NO and NO2) emissions from the test marine auxiliary
diesel
engine
were
measured
with
a
mobile
emissions
test
system
(SEMTECH-ECOSTAR, Sensor, Inc.) The precision of the NOx measure instrumentation is less than 1% of full scale when the range of measurement is
higher than 155ppm, while it is less
than 2% of full scale when the range of measurement is lower than 155ppm.The principle of the test system is based on the Beer-Lambert law. 2.3 Test mode and procedure In this research, the experiments were conducted at steady states to investigate the influence of the high substitution ratio of biodiesel to diesel on the combustion characteristic and NOx emissions. The test diesel engine was operated at the two steady engine speeds of 1050r/min and 1500r/min (rated engine speed) but different engine loads, as shown in Table 3. In order to obtain the high repeatability of the measurements, the test diesel engine was allowed to run for some minutes until the cooling water temperature, lubricating oil temperature and exhaust gas temperature had reached steady-state values The cooling water temperature was kept between 80 C and 85 OC, and the lubricating oil temperature was kept between 90 OC and 100 OC, depending
O
on the engine conditions. Fuel consumption, exhaust gas temperature and NOx emissions were continuously measured for three minutes when the test diesel engine was fueled with different test fuels and the average experimental results were obtained.
To ensure the experimental
uncertainty less than 5%, each steady state experiments were repeated at least twice. Moreover, the two-sided Student’s T-test was used to compare the testing results obtained from different test fuels if these results were different from each other at 95% significance level. 3
Results and discussion
3.1 Effect of high biodiesel to diesel ratio on the combustion characteristics Fig.2 shows the averaged cylinder pressure and heat release rate curves for different
test
fuels. In this study, the cylinder pressure data was obtained by averaging over 100 cycles data to diminish the influence of cycle-by-cycle variation and used to calculate the heat release rate. As shown in Fig.2, in all engine conditions, the cylinder pressure decreases slightly with the increase of biodiesel content in the test fuels. The cylinder pressure and heat release rate curves are similar for combustion in both ULSD mode and biodiesel additive diesel mode. The cylinder pressure
with the use of biodiesel-diesel blends began to increase earlier than neat ULSD. It is known that the octane number and laminar flame speed of biodiesel are higher than ULSD[33], and thus the combustion duration was shorten when the test diesel engine operated in the biodiesel-diesel blends mode[34]. It can be observed that the peak heat release rate(HRR) decreases significantly with the increase of the biodiesel content in the test fuels. When the test engine operated
at low
load, the maximum percent it decreases is about 14.3%, while the maximum percent can reach to 21.3% at high load condition. The ignition delay decreases with the increase of the biodiesel content in the test fuels. When the test engine operated on 25% of the maximum torque, the ULSD started to combust when the crank angle is -1°CA，while the B100 started to combust when the crank angle is -3°CA. Meanwhile, when the test engine operated on 75% of the maximum torque, the ULSD started to combust when the crank angle is -4°CA，while the B100 started to combust when the crank angle is -6°CA. It indicated that the ignition delay decreased about 2°CA. Moreover, the higher ratio of biodiesel and diesel fuel leads to the decrease of the instantaneous peak heat release rate and the start timing of the combustion advances. The mixture in the cylinder decreases and then lead to the reduction of the peak heat release rate. Meanwhile, the low cylinder temperature might be a major factor to decrease the diffusion combustion rate[35].
40
180 160
3
Cylinder Pressure (bar)
50
200
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 25%
140 30
120
20
100 80
10
60 0 40 -10 -20 -50
Rate of Heat Release (kJ/m /deg)
60
20 -40
-30
-20
-10
0
10
20
30
40
0 50
Crank Angle (deg)
30
140
20
120
10
100
0
80
-10
60
-20
40
-30
20
-40 -50
-40
-30
-20
-10
0
10
Crank Angle (deg)
20
30
40
0 50
ULSD B70 B90 B100
60
180 160
3
160
200
Engine speed: 1500r/min Engine load: 50% Cylinder Pressure （ bar）
Cylinder Pressure (bar)
40
80
180
140
40
120 20
100 80
0
60 40
-20
20 -40 -50
-40
-30
-20
-10
0
10
Crank Angle (deg)
20
30
40
Rate of Heat Release (kJ/m /deg)
200
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 50%
3
50
Rate of Heat Release (kJ/m /deg)
60
0 50
160 140
30
120
20
100 80
10
60 0 40
200
Engine Speed: 1500r/min Engine Load: 75%
ULSD B70 B90 B100
60 50
20
-20
30
120
20
100
10
80
0
60
-10 40
-50
-40
-30
-20
-10
0
10
20
30
40
20
-30
0 50
160 140
40
-20
-10
180
-40 -50
3
70
Rate of Heat Release (kJ/m /deg)
80
180
3
40
200
Cylinder Pressure (bar)
Cylinder Pressure (bar)
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 75%
50
Rate of Heat Release (kJ/m /deg)
60
-40
-30
Crank Angle (deg)
-20
-10
0
10
20
30
40
0 50
Crank Angle (deg)
Fig.2 Effect of high ratio of biodiesel and diesel fuel on cylinder pressure and heat release rate
3.2 Effect of high biodiesel to diesel ratio on the exhaust temperature The exhaust temperature reflects the combustion efficiency and affects the engine emissions generation[36]. The exhaust manifold temperatures for different ratios of biodiesel content in the test fuels are shown in Fig.3. As shown in Fig.3, the temperature of exhaust manifold decreases slightly with the increase of the biodiesel content in the test fuels, while increases significantly with the increase of engine speeds and loads. For all test fuels, when the test diesel engine operates at the low engine speed and load, the exhaust temperature is less than 150 OC, while the temperature could reach more than 400 OC when the engine operates at the high speed and load. The NOx emissions from the diesel engine are influenced by the temperature of exhaust manifold and there are also some chemical reactions between NO and NO2 emissions due to the changes of the rate of conversion[37]. Fig.3 also shows that the exhaust temperature of high ratio of biodiesel and diesel fuel mode is lower than that of pure ULSD mode. Because of the low heating value of biodiesel, the heat release decreases after the main injection period[38]. Moreover, due to the high rate of the heat release, the complete combustion became earlier and thus the heat transfer might occur before the exhaust valve opening. All of these factors lead to the reduction of the exhaust temperature. 450
450
Engine Speed： 1500r/min
Engine Speed: 1050r/min 400
Exhaust Temperature ( C)
O
300
ULSD B70 B90 B100
350
O
350
Exhaust Temperature ( C)
400
ULSD B70 B90 B100
250 200 150 100 50
300 250 200 150 100 50
0
0
25%
50%
75%
25%
Engine Load
50%
75%
Engine Load
Fig.3 Effect of high ratio of biodiesel and diesel fuel on exhaust manifold temperature
3.3 Effect of high biodiesel to diesel ratio on the NOx emissions The NOx emission is one kind of the major pollutants of the diesel engine, and it is consist of
NO (nitric oxide), NO2 (nitrogen dioxide) and N2O (nitrous oxide)[39]. For these emissions, NO emission is the main component and accounts for more than 60% of the total NOx emissions, while the proportion of NO2 emission is less than 40% and the N2O emission is less to be negligible. Thus, in this study,
the NO and NO2 emissions are considered as the
NOx
emissions. The NOx emissions from diesel engines are influenced by the air/fuel ratio, the residence time at the elevated temperature in the cylinder and the temperature in the burned mixture. Fig.4 shows that the high ratio of biodiesel and diesel fuels influences the formation of NOx emissions significantly. As shown in Fig.4, the NOx emissions decrease significantly with the increase of the biodiesel content in the test fuels. At the low engine speed and load condition, the NOx emissions are about 140 ppm in pure ULSD mode, while the NOx emissions are less than 100 ppm in pure biodiesel mode. For all test fuels, with the increase of engine speed and load, the total NOx emissions increase significantly. When the test diesel engine operates at the high engine speed and load, the total NOx emissions in pure ULSD mode can reach 800 ppm, and the NOx emissions in pure biodiesel mode can also reach 700ppm. The cylinder temperature increases significantly with the increase of engine speed and load, and this is the main factor leading to the increase of the total NOx emissions. There are also several reasons resulting in the decrease of the total NOx formation when the test engine operates in the biodiesel and diesel blended mode. Compared with diesel fuel, biodiesel with high cetane number leads to the smaller premixed combustion and ignition delay. Additionally, the lower cylinder temperature also decreases the total NOx concentration in the combustion process[40]. 900
500 450
Engine Speed: 1500r/min
Engine Speed: 1050r/min
400
700 600 -6
300
NOx/10
NOx/10
-6
350
ULSD B70 B90 B100
800
ULSD B70 B90 B100
250 200
500 400 300
150 200
100 100
50 0
0 25%
50%
Engine Load
75%
25%
50%
75%
Engine Load
Fig.4 Effect of high ratio of biodiesel and diesel fuel on NOx emissions
3.4 Effect of high biodiesel to diesel ratio on the NO and NO2 emissions The influences of high ratio of biodiesel and diesel fuels on the NO, NO2 emissions and the ratio of NO2/NO are shown in Fig.5 and Fig.6. As shown in Fig.5, the NO emission increases significantly with the increase of the engine loads, while the NO emission decreases with the increase of biodiesel content in the test fuels. Meanwhile, the NO2 emission decreases significantly with the increase of the engine loads, and also decreases with the increase of biodiesel content in the test fuels. Fig.6 shows the ratio of NO2/NO when the test diesel engine
operates on different engine conditions for all test fuels. When the test diesel engine operates on the low engine load, the ratio of NO2/NO is about 3:7, due to the low cylinder temperature, while the ratio of NO2/NO decreases significantly with the increase of engine loads. When the test engine operates on the high load, the proportion of NO2 in the total NOx concentration is less than 3%. As shown in Fig.5, the ratio of NO2/NO decreases slightly with the increase of biodiesel content in the test fuels. In the previous studies[41,42], the reactions between NO and NO2 are: (1) O2⇌2O; (2) N2+O⇌NO+N; (3) O2+N⇌NO+O; (4) N+OH⇌NO+H; (5) NO+HO2→NO2+OH; (6) NO2+O→NO+O2. 800
100
Engine Speed: 1500r/min 700
90
ULSD B70 B90 B100
600
ULSD B70 B90 B100
80 70
500 -6
60
NO2/10
-6
NO/10
Engine Speed: 1500r/min
400 300
50 40 30
200 20 100
10
0
0 25%
50%
75%
25%
50%
Engine Load
75%
Engine Load
(a) NO emission
(b) NO2 emission
Fig.5 Effect of high ratio of biodiesel and diesel fuel on NO and NO2 emissions 1.0
1.0
n=1500r/min Test fuel: B70
n=1500r/min Test fuel: Diesel 0.8
0.8
NO2 NO
0.6
NO2/NO
0.6
NO2/NO
NO2 NO
0.4
0.4
0.2
0.2
0.0
0.0 25%
50%
Engine Load
75%
25%
50%
Engine Load
75%
1.0
1.0
n=1500r/min Test fuel: B100
n=1500r/min Test fuel: B90 0.8
NO2 NO
0.8
0.6
NO2/NO
NO2/NO
0.6
NO2 NO
0.4
0.2
0.4
0.2
0.0 25%
50%
75%
0.0 25%
Engine Load
50%
75%
Engine Load
Fig.6 Effect of high ratio of biodiesel and diesel fuel on NO2/NO emissions
4
Conclusions This study focuses on the influence of the high ratio of biodiesel and diesel fuels on the
combustion characteristic (cylinder pressure and heat release rate) and NOx emissions (NO and NO2) from a marine auxiliary diesel engine. Experiments were conducted on a 6-cyclinder turbocharged inter-cooling direct-injection
diesel engine fueled with Ultralow Sulfur Diesel
(ULSD), B70 (diesel containing 70 vol.% of biodiesel), B90 and neat waste cooking oil biodiesel (B100). The test modes were under the 1050r/min & 1500r/min (Rated speed) and 25%-75% engine torques. Based on the experimental data, the major conclusions are shown as follows: 1. By the use of waste cooking oil biodiesel, the cylinder pressure increases slightly with the increase of biodiesel content in the test fuels, while the heat release rate decreases significantly. When the test engine operated at low load, the maximum percent peak heat release rate(HRR) decreases is about 14.3%, while the maximum percent can reach to 21.3% at high load condition. 2. The ignition delay was shortened with the increase of the biodiesel content in the test fuels, and the complete combustion became earlier. The ignition delay was shorten about 2°CA. 3. For all test fuels, the total NOx emissions increase significantly with the increase of the engine speeds and loads; for all engine conditions, the total NOx emissions decrease significantly with the increase of biodiesel content in the test fuels. 4. The NO emission increases significantly with the increase of engine loads, but decreases with the increase of biodiesel content in test fuels; while the NO2 emission decreases significantly with the increase of both engine loads and biodiesel content in the test fuels. 5. Additionally, the ratio of NO2/NO also decreases with the increase of the engine loads and biodiesel content in the test fuels. In our further research, we will evaluate the factors resulting in the influence of NO and NO2 emissions by the use of the numerical simulation with 0-D chemical kinetic. Acknowledgements The authors would like to acknowledge the financial support from Shanghai Maritime
University (2015 top journals cultivation fund). References [1] IMO (International maritime organization).
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graphical abstract Fresh air Inter-cooler
Air
Combustion analyzer
Exhaust gas Air filter
Cylinder Pressure Sensor
Hydraulic dynamometer
Shaft encoder
marine auxiliary diesel engine
Exhaust gas Exhaust gas turbocharger
Engine control system
Gaseous analyzers
Fig.1 Schematic diagram of experimental system
60
200
ULSD B70 B90 B100
Cylinder Pressure (bar)
40
180 160
3
Engine Speed: 1050r/min Engine Load: 25%
140 30
120
20
100 80
10
60 0 40 -10 -20 -50
Rate of Heat Release (kJ/m /deg)
50
20 -40
-30
-20
-10
0
10
20
30
40
0 50
Crank Angle (deg)
140
20
120
10
100
0
80
-10
60
-20
40
-30
20 -20
-10
0
10
20
30
40
140 120
20
100 80
0
60 40
-20
20
0 50
-40 -50
-40
-30
-20
80
180
70
160
0
10
20
30
40
140 30
120
20
100 80
10
60 0 40
ULSD B70 B90 B100
50
20
-20 -30
-20
-10
0
10
Crank Angle (deg)
20
30
40
0 50
180 160 140
40 30
120
20
100
10
80
0
60
-10 40
-20
-10
-40
0 50
200
Engine Speed: 1500r/min Engine Load: 75%
60
Cylinder Pressure (bar)
40
200
3
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 75%
Rate of Heat Release (kJ/m /deg)
Cylinder Pressure (bar)
-10
Crank Angle (deg)
60
-50
160
40
Crank Angle (deg)
50
180
20
-30 -40 -50
-40
-30
-20
-10
0
10
20
30
40
Crank Angle (deg)
Fig.2 Effect of high ratio of biodiesel and diesel fuel on cylinder pressure and heat release rate
0 50
3
-30
60
Rate of Heat Release (kJ/m /deg)
-40
ULSD B70 B90 B100
3
160
30
-40 -50
200
Engine speed: 1500r/min Engine load: 50% Cylinder Pressure （ bar）
Cylinder Pressure (bar)
40
80
180
Rate of Heat Release (kJ/m /deg)
200
ULSD B70 B90 B100
Engine Speed: 1050r/min Engine Load: 50%
3
50
Rate of Heat Release (kJ/m /deg)
60
450
450
Engine Speed： 1500r/min
Engine Speed: 1050r/min 400
O
O
300
ULSD B70 B90 B100
350
Exhaust Temperature ( C)
350
Exhaust Temperature ( C)
400
ULSD B70 B90 B100
250 200 150 100
300 250 200 150 100
50
50
0
0
25%
50%
75%
25%
50%
75%
Engine Load
Engine Load
Fig.3 Effect of high ratio of biodiesel and diesel fuel on exhaust manifold temperature 900
500
Engine Speed: 1500r/min
Engine Speed: 1050r/min
450 400 350
700 600 -6
500
NOx/10
-6
300
NOx/10
ULSD B70 B90 B100
800
ULSD B70 B90 B100
250 200
400 300
150 200
100 100
50 0
0 25%
50%
25%
75%
50%
75%
Engine Load
Engine Load
Fig.4 Effect of high ratio of biodiesel and diesel fuel on NOx emissions 800
100
Engine Speed: 1500r/min 700
90
ULSD B70 B90 B100
600
ULSD B70 B90 B100
80 70
500 -6
60
NO2/10
-6
NO/10
Engine Speed: 1500r/min
400 300
50 40 30
200 20 100
10
0
0 25%
50%
Engine Load
(a) NO emission
75%
25%
50%
Engine Load
(b) NO2 emission
Fig.5 Effect of high ratio of biodiesel and diesel fuel on NO and NO2 emissions
75%
1.0
1.0
n=1500r/min Test fuel: B70
n=1500r/min Test fuel: Diesel 0.8
0.8
NO2 NO
0.6
NO2/NO
0.6
NO2/NO
NO2 NO
0.4
0.4
0.2
0.2
0.0
0.0 25%
50%
25%
75%
n=1500r/min Test fuel: B100
n=1500r/min Test fuel: B90 NO2 NO
0.8
0.6
NO2 NO
0.6
NO2/NO
NO2/NO
75%
1.0
1.0
0.8
50%
Engine Load
Engine Load
0.4
0.2
0.4
0.2
0.0 25%
50%
75%
0.0
Engine Load
25%
50%
75%
Engine Load
Fig.6 Effect of high ratio of biodiesel and diesel fuel on NO2/NO emissions
Highlights (for review) 1. Higher waste cooking oil biodiesel-diesel blends were applied in the marine auxiliary diesel engine; 2. Effects of the test fuels on combustion and emissions clearly depends on engine conditions; 3. Higher waste cooking oil biodiesel-diesel blends increase the cylinder pressure slightly, while decrease the ignition delay. 4. Higher waste cooking oil biodiesel-diesel blends have potential for reducing the NOx emissions. 5. The ratio of NO2/NO decreases with the increase of the engine loads and biodiesel content in the test fuels.