The effect of biodiesel and bioethanol blended diesel fuel on nanoparticles and exhaust emissions from CRDI diesel engine

Renewable Energy 35 (2010) 157–163

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The effect of biodiesel and bioethanol blended diesel fuel on nanoparticles and exhaust emissions from CRDI diesel engine Hwanam Kim a, Byungchul Choi b, * a b

Automobile Research Center, Chonnam National University, Gwangju 500-757, Republic of Korea School of Mechanical Systems Engineering, Chonnam National University, Gwangju 500-757, Republic of Korea

a r t i c l e i n f o

a b s t r a c t

Article history: Received 10 November 2008 Accepted 19 April 2009 Available online 15 May 2009

Biofuel (biodiesel, bioethanol) is considered one of the most promising alternative fuels to petrol fuels. The objective of the work is to study the characteristics of the particle size distribution, the reaction characteristics of nanoparticles on the catalyst, and the exhaust emission characteristics when a common rail direct injection (CRDI) diesel engine is run on biofuel-blended diesel fuels. In this study, the engine performance, emission characteristics, and particle size distribution of a CRDI diesel engine that was equipped with a warm-up catalytic converters (WCC) or a catalyzed particulate filter (CPF) were examined in an ECE (Economic Commission Europe) R49 test and a European stationary cycle (ESC) test. The engine performance under a biofuel-blended diesel fuel was similar to that under D100 fuel, and the high fuel consumption was due to the lowered calorific value that ensued from mixing with biofuels. The use of a biodiesel–diesel blend fuel reduced the total hydrocarbon (THC) and carbon monoxide (CO) emissions but increased nitrogen oxide (NOx) emissions due to the increased oxygen content in the fuel. The smoke emission was reduced by 50% with the use of the bioethanol–diesel blend. Emission conversion efficiencies in the WCC and CPF under biofuel-blended diesel fuels were similar to those under D100 fuel. The use of biofuel-blended diesel fuel reduced the total number of particles emitted from the engine; however, the use of biodiesel–diesel blends resulted in more emissions of particles that were smaller than 50 nm, when compared with the use of D100. The use of a mixed fuel of biodiesel and bioethanol (BD15E5) was much more effective for the reduction of the particle number and particle mass, when compared to the use of BD20 fuel. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: Diesel engine Biodiesel Bioethanol Particulate matter Catalyzed particulate filter (CPF) Particle size distribution

1. Introduction Since diesel engines have higher thermal efficiency than gasoline engines, they have an advantage in reducing global warming and in using less fossil fuel. However, they emit more diesel PM (particulate matter) than gasoline engines because of the relatively low rate of utilization of air. The after-treatment of the diesel engine exhaust was a very effective method to reduce CO (carbon monoxide) and THC (total hydrocarbon) emissions and the SOF (soluble organic fraction) of PM emissions. Recently, the price of petroleum has been widely fluctuating and the strict regulation of pollutant emissions has increased the level of interest in biodiesel [1–10], natural gas [11,12], ethanol [13,14], dimethyl ether (DME) [15], hydrogen [16], etc., as alternatives to fossil fuels. Biodiesel fuel, which is applicable to diesel without

* Corresponding author. Tel.: þ82 62 530 1681; fax: þ82 62 530 1689. E-mail address: [email protected] (B.C. Choi). 0960-1481/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2009.04.008

modification of the engine, has been actively researched as a possible alternative fuel. Biodiesel is derived from various sources such as soybean oil, jatropha oil [3], vegetable oil [4], rapeseed oil [5], palm oil [6], sunflower oil [7], animal fats [8], and waste cooking oils [9]. With its high octane number, bioethanol is a gasolinealternative fuel that is made from various kinds of biomass such as corn, sugarcane, sugar beet, cassava, red seaweed, etc. The mixing of biodiesel and bioethanol with diesel significantly reduces the emission of particulate matter because the blended biofuel contains oxygen [10]. Particulate matter is currently regulated in terms of grams per kilometer or grams per kilowatt-hour but number-based PM regulation is under discussion for introduction in the near future. The smaller the emitted particle, the more harmful it is to the human body because particles under 100 nm (ultrafine particles) in diameter have a higher surface area per unit mass of particles; therefore, the smaller particles can more easily infiltrate into the respiratory organs [17]. The reduction in weight of PM under the use of biodiesel and bioethanol–diesel blends is known. However, there is a lack of research with regard to biodiesel

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and bioethanol–diesel blends about PM emission characteristics in terms of the particle size distribution and number concentration. The objective of this experimental study is to investigate the characteristics of the exhaust emission and particle size distribution and the number concentration of PM from a CRDI diesel engine through the ECE R49 and ESC tests and the use of biodiesel and bioethanol–diesel blends. 2. Experimental apparatus and methods 2.1. Experimental apparatus Fig. 1 shows a diagram of the main experimental device that is used to study the engine performance, emission characteristics, and particle size distribution of a CRDI diesel engine that uses biofuel-blended diesel fuel. The after-treatment system of each test cycle used a warm-up catalytic converter (WCC) or catalyzed particulate filter (CPF) to meet the EURO 4 diesel emission regulations. Catalysts were installed in the rear part of the exhaust manifold. The exhaust pipe leading to the after-treatment was completely insulated for fast activation. The diameter of the WCC was 76 mm and the volume was 0.51 L. A honeycomb-type monolithic substrate with a cell density of 600 cpsi was coated with g-Al2O3 and 3.18 g/L of platinum (Pt). A commercial CPF is composed of a diesel oxidation catalyst (DOC) in the front and a CPF in the rear of the catalytic system. An eddy current dynamometer (Fuchino, ESF-600) capable of adsorbing 440 kW was used to measure power performance. An exhaust gas analyzer (Horiba, MEXA-9100DEGR) was used to measure the CO, THC, and NOx concentrations. A Bosch-type smoke meter (World Env., ATF-2000) measured the amount of smoke emission. Table 1 shows the specifications of the test engine. Both the particle size distribution and the emission characteristics were measured at the inlet and outlet of the after-treatment system; for the former, a scanning mobility particle sizer (SMPS) (Model 3080, TSI. Inc) [18] was used. Exhaust gas was diluted in an ejector-type dilutor because of the high particle number concentration. In this study, a part of the exhaust gas and filtered ambient air were mixed in the ratio of 1:132 through a dilutor system that the authors developed. The first dilutor preheated the dilution air to about 150  5  C in order to prevent nucleation and condensation of the volatile components. For the second dilution, compressed air was filtered and kept at ambient temperature. The particle size distribution was measured over a range of diameters from 10 nm through to 385 nm by the SMPS, and the particle mass concentration was calculated from the

Exhaust Gas Analyzer

Engine Dynamo meter

Data logger Smoke meter

or

Table 1 Specifications of test engine. Items

Specifications

Engine Type Bore  Stroke (mm) Displacement (cc) Compression ratio Max. Power (PS@rpm) Max. Torque (N m@rpm) Aspiration

CRDI 4 Cylinder 91  96 2497 17.1 145@3800 324@2000 T/C & after cooler

measured size distribution assuming a particle density of 1.2 g/cm3. Table 2 shows the specifications of the SMPS and the ejector-type dilutor [19].

2.2. Experimental methods The engine performance, emission characteristics, and particle size distribution of a CRDI diesel engine that was equipped with a WCC or CPF in the ECE R49 test cycle and the ESC test cycle, as shown in Fig. 2, were examined. In the driving conditions for the ECE R49 test cycle for the engine that was equipped with a WCC, the test fuels were: a ultra-lower sulfur diesel fuel called D100; a blend of diesel fuel with 15% (by vol.) bioethanol (E15); a blend of diesel fuel with 15% bioethanol and cetane improver (EHN, 7500 ppm) [20] (E15CI); a blend of diesel fuel with 20% biodiesel (BD20); and a blended fuel with 5% biodiesel (BD05), respectively. Table 3 shows the test cycles used, the blending ratios of the test fuels, and symbols. Commercial diesel fuel that contains less than 30 ppm sulfur content, biodiesel produced from soybeans, and anhydrous bioethanol (99.5% purity) were used in this test. In the ESC test cycle, we measured the particle size distribution, differential pressure, and exhaust gas temperature in the upstream and downstream CPFs under the use of BD20 and BD15E5, which was a mix of 15% biodiesel and 5% bioethanol.

3. Results and discussion 3.1. Emissions characteristics The ECE R49 test cycle consists of engine loads of 25%, 50%, 75% and 100% at 2100 and 3800 rpm, which show the engine’s maximum torque, maximum output, and idling modes (750 rpm; modes 1, 7, and 13). Except for low-load driving conditions (modes 2 and 12), the fuel consumption rate was 220–400 kg/kWh at each mode. The fuel consumption rate of the bioethanol–diesel blends increased by 6.5% when compared to that of D100, whereas the fuel consumption rate of the biodiesel–diesel blends increased by 1–2%. This is due to the varying calorific values that result from the differential oxygen contents in the fuels. The engine’s maximum

WCC ECE 13 mode Dynamo Controller

DOC

CPF ESC 13 mode Comp. air

SMPS

Diluter

Diluter CPC

Heater Filter MFC MFC

Fig. 1. Diagram of experimental apparatus.

Table 2 Specifications of SMPS and ejector-type diluter. SMPS (model: 3080, TSI) Description Particle size range (L-DMA 3081) Upper concentration limit (3025A CPC) Scanning time

Specification Adjustable: 10–1000 nm (Measuring from 10.6 to 385 nm) 105 (particles/cm3) 30–300 s

Diluter (ejector type, CNU) Diluter 1st diluter 2nd diluter

Dilution ratio 1:12 (heating up to 200  C) 1:11 (TDR 1:132)

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159

1.4 6 25

8 9

10 8

8 10

2

75

2 8

5

6 5

4 10

12 5

9 2

4

5 5

3 10

13 5

10 10 2

3

7 5

9 10

11 5

11 11 2

ESC Load,

ECE

2

50

2

25 25

2

1, 7, 13 1

Normalized CO emission

100

50

75

1

0.8

0.6

12 12 2

2

1.2

D100

100

BD20

E15

E15CI

ECE R49 Cycle

Engine speed,

Idle 15

BD05

D100

BD20 BD15E5

ESC Test Cycle

Fig. 3. Normalized CO emission of the different fuels according to the test cycles. Fig. 2. Engine test cycles (ESC, ECE R49).

Table 3 Specifications of test fuels. Test cycle

Diesel

Biodiesel

Ethanol

Symbol

ECE R49

100% 85% 85% 95% 80% 100% 80% 80%

– – –

– 15% 15% – – – – 5%

D100 E15 E15CI BD05 BD20 D100 BD20 BD15E5

ESC test

5% 20% – 20% 15%

1.8

1.6

Normalized THC emission

torque and power output under biofuel-blended diesel fuel were the same or very slightly lower than under D100. Fig. 3 shows the total CO emissions for each fuel used in each experimental cycle, divided by the total CO emissions under the use of D100 fuel. In the case of the biodiesel–diesel blends, CO emissions decreased with the increase of the biodiesel content in the fuel because oxygen that was contained in the fuel favorably affected the combustion. However, in the case of the bioethanol– diesel blends, despite the high oxygen content in the fuel, high CO emissions resulted. This is because the ignition delay due to ethanol’s high latent heat of vaporization caused a rise in the premixed burning rate so that the premixed lean mixture was partially oxidized in the combustion chamber. In the case of E15CI in which a cetane number improver was added, CO emissions were reduced due to the decrease in the ignition delay by the cetane number improver. However, in the two test cycles, the bioethanol–diesel blends emitted more CO than D100 fuel. Fig. 4 represents the THC emissions in each test cycle from the biofuel-blended diesel fuels that were used, relative to THC that was emitted under D100 fuel. In the case of the biofuel–diesel blends, the THC emission characteristics were similar to those of CO emissions except that under high-load driving conditions, more THC was emitted, particularly during idling and the low-load region of driving. This is because ethanol’s high latent heat of vaporization slowed both air-fuel mixing and fuel evaporation [21]. However, under the biodiesel–diesel blends, the THC emission ratio reduced with the increase in the biodiesel mixture ratio. In the ESC test cycle, when the engine was equipped with a CPF, biofuel-blended diesel fuels exhibited lower THC emission ratios than D100. In particular, BD15E5 mixed fuel (15% biodiesel and 5% bioethanol) yielded the lowest THC emission ratio.

Fig. 5 shows the NOx emission ratios under biofuel-blended diesel fuels when compared to those under D100. One of the important characteristics of oxygenated fuel is the high emission of NOx that originates from the oxygen content in the fuel. The addition of a cetane number improver (E15Cl) to reduce the ignition delay results in an increase in the combustion temperature and in higher NOx emissions that originate from the oxygen content in the fuel. CO and THC that are emitted from the engine can be sufficiently oxidized by the after-treatment system but NOx is not easily reduced by the catalyst due to the high oxygen content in the exhaust gas. The NOx emissions under the biodiesel–diesel and bioethanol–diesel blends were higher than those under D100 by 0.4–3.7% and 6.5–13%, respectively. Increasing the oxygen content of the fuel in the ESC test cycle also increased NOx emissions by 2.3– 8%. The conversion efficiencies of THC and CO emissions in the WCC under D100 and biofuel-blended diesel fuels were about 50% and 80%, respectively; those in the CPF were about 70% and 84%, respectively. Thus, under the various biofuel-blended diesel fuels, the conversion efficiencies of exhaust emissions in the after-treatment device were vary similar. Fig. 6 represents the smoke that was emitted under biofuelblended diesels in the ECE R49 test. The smoke emission was found to significantly reduce when biofuel-blended diesel fuels were

1.4

1.2

1

0.8

0.6

D100

BD05

BD20

E15

ECE R49 Cycle

E15CI

D100

BD20 BD15E5

ESC Test Cycle

Fig. 4. Normalized THC emission of the different fuels according to the test cycles.

160

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30

700

25

600 500

ΔP (kPa)

20

1

400 15 300

Temp. (°C)

Normalized NOx emission

1.2

10 D100 BD20 BD15E5 Temp.

5

0.8

20 min.

0

1

0

2

3

4

60

5

6

7 120

8

9

10 180

11

200 100

0 12 13 mode 240

Time (minutes) 0.6 D100

BD05

BD20

E15

E15CI

ECE R49 Cycle

D100

BD20 BD15E5

Fig. 7. Differential pressure between front and rear of the CPF and exhaust gas temperature in front of the CPF according to 3 kinds of fuel (ESC test).

ESC Test Cycle

Fig. 5. Normalized NOx emission of the different fuels according to the test cycles.

used. Smoke reduction under biofuel-blended diesel fuels was greater in the 3800 rpm region of driving (single fuel injection, main fuel injection only) than in the 2100 rpm condition of driving (dual fuel injection, pilot and main fuel injection). This is because the high oxygen content of the biofuel-blended diesel fuels contributed to smoke reduction in spite of the insufficient time for air-fuel mixing during single fuel injection. In the case of the biodiesel–diesel blends, a higher biodiesel mixing ratio resulted in greater smoke reduction. This was due to the increase in oxygen content in the fuel; the increased smoke reduction under the bioethanol–diesel blends was due to the suppression of soot generation in the fuel-rich region. In the case of E15CI fuel, smoke emission was higher than under E15 because a shorter ignition delay with the addition of the cetane number improver reduced the premixed burning rate [20]. PM reduction rates under the biofuelblended diesel fuels were 3–18% for the biodiesel–diesel blends and 42–51% for the bioethanol–diesel blends. Fig. 7 shows the differential pressure in the upstream and downstream CPFs and the exhaust gas temperature at the entrance of the CPF for 20 min. at each mode in the ESC test cycle. It was determined that PM accumulated and regenerated repeatedly

depending upon the amount of PM emissions and the exhaust gas temperature conditions for each test mode. At modes 2 (elapsed time of 20–40 min.), 8 (elapsed time of 140–160 min.), and 10 (elapsed time of 180–200 min.), which were high-load test conditions (100% load, 2325 rpm, 2950 rpm, and 3575 rpm), the initial differential pressure was high due to a large amount of PM production from the rapid increase in the exhaust gas flow and the rapid load change at the beginning of the mode conversion. Later, as the high exhaust gas temperature was maintained, PM oxidized continuously in the CPF and a constant differential pressure was maintained. The descending order of the magnitude of the differential pressure of the engine for each type of fuel at modes 2, 8, and 10 was D100 > BD15E5 > BD20. The reason the differential pressure under BD15E5, which was expected to be the lowest, was higher than that under BD20 was the excessively injected fuel. However, considering the 5% increase in the power output under BD15E5 fuel when compared to D100, the lowest differential pressure can be said to have been maintained when BD15E5 fuel was used. At other test modes, the differential pressures under the BD15E5, BD20, and D100 fuels were in the same descending order. This means that PM emission under biofuel-blended diesel fuels was lower than that under D100. Differential pressures between the front and the rear of the CPF continuously increased at loads of 25% (modes 7, 9, and 11) and 50% (modes 3, 5, and 13) in the time that PM accumulated on

D100 BD05 After WCC

D100 After WCC BD20

BD05 BD20 After WCC

)

1.2

Normalized particle number (

100

Normalized smoke

1

0.8

0.6

0.4

0.2

D100

BD05

BD20

E15

E15CI

80

60

40

20

0

Dp<50

Dp<100

Dp<385

Diameter (nm) ECE R49 Cycle Fig. 6. Normalized smoke emission of the different fuels according the ECE R49 test.

Fig. 8. Normalized particle number for each size range using biodiesel–diesel blend fuels (ECE R49 test).

Normalized particle number ( )

H.N. Kim, B.C. Choi / Renewable Energy 35 (2010) 157–163

100

D100

D100 After WCC

E15CI

E15CI After WCC

E15

E15 After WCC

80

60

40

20

0

Dp<50

Dp<100

Dp<385

Diameter (nm) Fig. 9. Normalized particle number for each size range using bioethanol–diesel blend fuels (ECE R49 test).

the CPF. On the other hand, PM continuously decreased on the CPF at a 75% load (modes 4, 6, and 12). The exhaust gas temperature at the front of the CPF at a 75% load was 475–515  C. The exhaust gas temperatures at modes 2, 8, and 10 were 574–656  C. The temperatures in the CPF were high enough to allow PM to oxidize, not be trapped in the CPF, and regenerate completely. 3.2. Nanoparticle emissions Figs. 8 and 9 illustrate the particle number ratio for each particle size range under biodiesel–diesel blends and under bioethanol– diesel blends relative to the particle number concentration (10– 385 nm) for each size of PM that is emitted under D100 fuel in the ECE R49 test cycle. The particles emitted from the engine are generally classified into: nanoparticles (Dp < 50 nm); ultrafine particles (Dp < 100 nm); and fine particles (Dp < 2.5 mm). In this study, since measurement was limited to 10–385 nm, particle number concentrations were classified into: 10–50 nm; <100 nm; and <385 nm. The number of particles smaller than 50 nm was increased under biodiesel–diesel blends in comparison with D100. The number of particles smaller than 50 nm was increased by 8.7% (1.6%) when migrating from D100 to BD05 (BD20). With respect to particles smaller than 100 nm, the use of BD05 exhibited a

Normalized particle number (

)

D100 E/N BD20 E/N BD15E5 E/N

5.4%-higher particle number concentration than that of D100; however, under BD20, the corresponding value was 6.3% less than under D100. Therefore, compared with the particle number concentration under D100, more particles smaller than 50 nm – but fewer large particles – were emitted under BD20. The increased number of particles under 50 nm that were emitted through the use of biodiesel–diesel blends possibly originated from the increase in the SOF particles. Under BD05, the rate of reduction in particle numbers in the catalyst was higher than that under D100, probably because a large number of SOF particles were oxidized in the oxidation catalyst. The total number of particles emitted under BD05 in the entire range of measurement (10 < Dp < 385 nm) increased by 4.4%. However, under BD20, the corresponding number decreased by 9.4%, and in terms of the converted particle weight, the particle mass reduced by 25%. The use of bioethanol– diesel blends resulted in the emission of fewer particles smaller than 50 nm, compared with that of D100 fuel. With respect to particles smaller than 100 nm, which are harmful to the human body, biodiesel–diesel blends resulted in the emission of more particles than bioethanol–diesel blends. Under E15 fuel, 7% fewer particles that were smaller than 50 nm were emitted at all test modes despite the fuel’s high nanoparticle emission characteristics at mode 1, when compared with D100 [19]. The number of particles emitted under E15CI fuel was 1.5% less when compared with that under D100. With respect to ultrafine particles smaller than 100 nm, emissions under bioethanol–diesel blends (E15 and E15CI) were less by 13% and 9%, respectively, when compared to that under D100. The total number of particles emitted under bioethanol–diesel blends in the entire range of measurement decreased by 11.7–15%; in terms of the converted particle weight, the particle mass decreased by 19.2–26.9%. Fig. 10 represents the particle number ratio for emission under biofuel-blended diesel fuels in the ESC test cycle, relative to the particle number for each size of particulate matter that is emitted under D100 fuel. The number of particles under 50 nm in diameter for blended fuel containing 20% biodiesel in an engine that was equipped with a CPF, which is a PM reducing device, showed results similar to the experimental results in the ECE R49 test, wherein the engine was equipped with a WCC. Under BD20 fuel, the number of particles smaller than 50 nm showed a 3.5% higher particle number concentration compared to that under D100. However, under BD15E5 fuel, which is a blended fuel containing 15% biodiesel and 5% bioethanol, 22.3% fewer particles smaller than 50 nm were emitted compared to that under D100. This was a higher rate of

D100 After DOC BD20 After DOC BD15E5 After DOC

D100 After CPF BD20 After CPF BD15E5 After CPF

100

80

60

40

20

0

Dp<50

161

Dp<100

Dp<385

Diameter (nm) Fig. 10. Normalized particle number in the size range from biofuel-blended diesel fuels (ESC test).

Normalized particle mass (

)

162

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100

D100 E/N BD20 E/N BD15E5 E/N

D100 After DOC BD20 After DOC BD15E5 After DOC

D100 After CPF BD20 After CPF BD15E5 After CPF

Dp<100

Dp<385

80

60

40

20

0

Dp<50

Diameter (nm) Fig. 11. Normalized particle mass in the size range from biofuel-blended diesel fuels (ESC test).

reduction than that under bioethanol–diesel blends in the ECE R49 test. Under BD20, ultrafine particles smaller than 100 nm were similar to those under D100 because particles smaller than 50 nm, more of which were emitted under BD20 than under D100, were counted together. Under biodiesel–diesel blends, 2% fewer particles smaller than 385 nm were emitted than under D100. However, under BD15E5, 22.6% fewer particles smaller than 385 nm were emitted than under D100. The rate of reduction in the particle number through the DOC, a diesel after-treatment device, was 8–12%. The highest rate of reduction appeared under the use of BD20. This is because much of the emitted SOF oxidized in the DOC. The number of particles emitted from the engine was reduced by 98% in the CPF. When bioethanol blends with diesel fuel for the practical use in engine, a surfactant and a cetane number improver have to be added to the blended fuel [16] and these additives may increase the PM emission from engine combustion. On the other hand, under biodiesel and bioethanol blended with diesel, PM emission from the engine can reduce because the above-mentioned additives are not needed for these blends. The addition of lowconcentration (<10%) anhydrous ethanol to the diesel oil does not cause phase separation, and anhydrous ethanol enables the ternary blends (diesel–biodiesel–bioethanol) to dissolve as a homogeneous solution [22].

Calculated PM

Measured PM

Fig. 11 shows the particle mass ratio for the emission under biofuel-blended diesel fuels relative to particle mass for each size of particulate matter that is emitted under D100 in the ESC test cycle. Under BD20, 1% more particle mass was emitted of particles smaller than 50 nm, compared with the use of D100. On the other hand, under BD15E5, 22.8% less mass was emitted than under D100. Under BD20 and BD15E5, the emission of particles smaller than 100 nm was less by 3.3% and 22.7%, respectively. The rates of reduction in the mass for particle smaller than 385 nm were 16.2% and 20.3%, respectively. Through the DOC, the rate of reduction in the mass for particles smaller than 385 nm was about 10% under D100 fuel. Through the CPF, which is a PM elimination filter, the rate of reduction in the mass of particles was 97%, which was similar to the corresponding reduction in the particle number concentration. Fig. 12 indicates the comparison between the normalized mass of particles, as calculated from SMPS data, and the PM measured from engine-out emission for three kinds of fuel, as per the ESC test cycle. The number concentration of SMPS data (10–385 nm) at the inlet of the CPF was converted to the mass of the particles (Calculated PM). The weight of particles (Measured PM) emitted from the engine was directly measured by the trapping filter (70 mm diameter [Pall, T60A20]). The difference between the initial and final trapping filter weights is the total weight of PM. To measure the weight of particulate matter that is emitted from the engine, the exhaust gas was diluted by the two-stage dilutor. The filtering paper containing particles was weighed with an electronic balance (0.001 mg precision) for which a chamber was kept at a constant temperature and constant humidity of 22  3  C and 45  8%, respectively. The measured PM weight and calculated PM mass, as emitted under BD20, were 83.9% and 83.8%, respectively, of the corresponding values under D100. The measured (calculated) PM weight under BD15E5 relative to that under D100 was 75.6% (79.7%). The calculated PM mass as measured by SMPS was generally not greatly different from the directly measured PM weight but was slightly different when fuel containing bioethanol was used. This is probably because the number of large-size particles (>385 nm) was low when ethanol–diesel blends were used.

4. Conclusions The characteristics of exhaust emissions and particle size distributions of PM from a CRDI diesel engine were investigated under the ECE R49 and ESC test cycles and the use of biodiesel and bioethanol blended diesel fuels. The results of the study are summarized as follows.

Normalized PM mass ( )

100

80

60

40

20

0

D100

BD20

BD15E5

Fig. 12. Comparison between normalized mass calculated from SMPS data and measured PM from engine-out emission of 3 kinds of fuel according to the ESC test.

1. The engine performance under biofuel-blended diesel fuels was similar to that under D100 fuel; the slightly higher fuel consumption was due to the lower calorific value that was based on the biofuel mixture. 2. The use of biodiesel–diesel blends reduced the THC and CO emissions but increased NOx emissions, as the oxygen content of the fuel increased. Smoke emissions were reduced by 50% with the use of bioethanol–diesel blends. 3. The conversion efficiencies of THC and CO emissions in the WCC and CPF under biofuel-blended diesel fuels were very similar to those under D100 fuel. 4. The use of biofuel-blended diesel fuels reduced the total number of particles emitted from the engine. However, when compared to the use of D100, the use of biodiesel–diesel blends caused the emission of more particles smaller than 50 nm, which are harmful to human body.

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