Energy Fuels 2010, 24, 985–991 Published on Web 01/05/2010
: DOI:10.1021/ef900982c
Effects of Fuel Sulfur Content and Diesel Oxidation Catalyst on PM Emitted from Light-Duty Diesel Engine Hong Zhao,†,‡ Yunshan Ge,*,† Xiaochen Wang,§ Jianwei Tan,† Aijuan Wang,† and Kewei You§ †
National Lab of Auto Performance & Emission Test, Beijing Institute of Technology, Beijing 100081, China, ‡ College of Mechanical & Electronic Engineering, Qingdao University, Qingdao 266071, China, and § China Automotive Technology & Research Center, Tianjin 300162, China Received September 5, 2009. Revised Manuscript Received November 15, 2009
The effects of fuel sulfur content and diesel oxidation catalyst on number-size distribution, sulfate, and trace metals of particulate matter (PM) emitted from a Euro 3 light-duty diesel engine have been investigated. Three types of diesel fuel with sulfur content of 1000 ppm, 350 ppm and 19 ppm respectively were used in this study. According to the results, the number concentration of nanoparticles for low sulfur fuel compared to other two fuels decreased, but accumulation and coarse mode particles increased. With the use of DOC, the number concentration of different size range reduced at 50% load; while at full load, the reduction efficiency was 20-80% for 19 ppm sulfur fuel, and 30-50% only for nanoparticles for other two fuels. The results revealed that the presence of the catalyst and variations in fuel sulfur content altered the extent to which hydrocarbons and sulfates condense on the soot particles and the exhaust sampling methodology promoted the additional coagulation. Both sulfate emission rate and fuel consumption increased with sulfur content. Higher fuel consumption at higher load increased the concentration of SO2, and thus resulted in the generation of large concentration of sulfate. At low load, sulfate to PM mass ratio with DOC was less than that of without DOC; whereas at medium and high loads, the results were contrary. At medium and high loads, catalyst temperature was higher, which converted SO2 into SO3 effectively, and thus generated sulfate. The emission rates of Na, Ca, Mg, K, Al, Ni, and Cr for higher sulfur fuel were more than those for lower sulfur fuel. After engine was retrofitted with DOC, Na, K, and Fe emission increased regardless of load. The emission of Mg, Zn, Cu, and Ca were affected by DOC, as well as by load level.
Sulfate and ash (trace metals) also contribute to the emission of particulate matter. Most of the fuel sulfur is oxidized to sulfur dioxide during the combustion process. Sulfur dioxide is further oxidized to sulfur trioxide, which rapidly reacts with water to form sulfuric acid.4 Moreover, the gaseous sulfite reacts with the elements in the fuel and lubricating oil to form metal complexes at high combustion temperature.5 Trace metals are relevant to potential health effects, although they only make up a small fraction of PM.6 Recently, increasingly stringent regulations have been set forth in many locations around the world. However, the new PM emission limits are below what can be achieved solely by engine design and, therefore, require exhaust after-treatment devices, such as diesel oxidation catalyst (DOC) and diesel particulate filter (DPF). Sulfur in diesel fuel damages the performance of after-treatment devices in two ways: first, it acts as a catalytic inhibitor; second, it is a precursor of sulfate.7 Therefore, the use of after-treatment devices requires low sulfur or ultra low sulfur content fuel. Through with the development of engine and after-treatment technologies, the mass concentration of these particles has been significantly
Introduction Diesel exhaust particulate matter (PM) contributes to environmental and human health hazards. Variations of gaseous organic composition and PM are attributable to differences in test cycle, fuel composition, engine type, and sampling methodology.1,2 PM is composed of dry soot, soluble organic fraction, sulfate, and ash (trace metals). Currently, particle emissions from internal combustion engines have been regulated solely on the basis of total particulate matter mass. However, concerns have also been raised that particle number concentration or surface area, rather than mass concentration, may have a more direct relationship with adverse human health effects. Therefore, particle number and size distribution is more important in characterizing the physical properties of PM related to health effects. Diesel particulate matter is emitted in three usually distinct but overlapping size modes: the nucleation mode, typically 3-30 nm diameter, containing most of the particle number; the accumulation mode, roughly 30-500 nm, containing most of the particle mass; and the coarse mode consisting of larger particles and usually comprising less than 10% of the mass.3
(4) Schneider, J.; Hock, N.; Weimer, S.; Borrmann, S. Environ. Sci. Technol. 2005, 39, 6153–6161. (5) Lim, M. C. H.; Ayoko, G. A.; Morawska, L.; Ristovski, Z. D. Fuel 2007, 86, 1831–1839. (6) Miller, A.; Ahlstrand, G.; Kittelson, D.; Zachariah, M. Combust. Flame 2007, 149, 129–143. (7) Kweon, C.-B.; Okada, S.; Stetter, J. C.; Christenson, C. G. SAE Technol. Pap. Ser. 2003, No. 2003-01-1899.
*To whom correspondence should be addressed. Phone: þ86 10 6891 2035. Fax: þ86 10 6894 8486. E-mail:
[email protected]. (1) Shah, S. D.; Ogunyoku, T. A.; Miller, J. W.; Cocker, D. R. Environ. Sci. Technol. 2005, 39, 5276–5284. (2) Schauer, J. J.; Kleeman, M. J.; Cass, G. R.; Simoneit, B. R.T. Environ. Sci. Technol. 2002, 36, 1169–1180. (3) Kittelson, D. B. J. Aerosol Sci. 1998, 29, 575–588. r 2010 American Chemical Society
985
pubs.acs.org/EF
Energy Fuels 2010, 24, 985–991
: DOI:10.1021/ef900982c
Zhao et al.
Table 1. Properties of the 19 ppm Sulfur Fuel and Standards for Test Method in Chinaa fuel property sulfur content cetane number density at 20 °C (kg m-3) distillation 50% by vol °C distillation 95% by vol °C viscosity at 20 °C (10-6 m2 s-1) total aromatics (% by vol) a
diesel
standard
method
corresponding to ASTM
19 52 841 258 345 4 11
e50 51 820-845 300 325 4.0-6.0 11
GB/T380 GB/T386 GB/T1884-1885 GB/T6536 GB/T6536 GB/T265 GB/T11132
ASTM D4294 ASTM D6890 ASTM D1298/4052 ASTM D86:1995 ASTM D86:1995 ASTM D445 ASTM D1319-1999
GB/T is the standard method used in China.
reduced over the last years. At the same time, the interest in the particles number concentration and their chemical composition emanated from a diesel engine with after-treatment devices has increased. Some studies on the effects of sulfur content and aftertreatment devices on PM are reported.8-10 High fuel sulfur content and the presence of DOC are prerequisite conditions for the occurrence of nucleation mode particles.11-13 However, few studies have investigated the impact of after-treatment devices on the chemical composition such as sulfate and trace metals. Diesel particle emissions depend on many factors, such as the engine, after-treatment devices, fuel, lubricating oil and driving conditions, which interact with each other. However, a consistent conclusion of the effects of fuel sulfur content on diesel particulate matter emissions has not been reached so far due to the different test methods. This work aims at the particle number concentrations and size distributions, sulfate and trace metals emitted from a diesel engine fueled with three different sulfur content fuels, operating with and without DOC.
Table 2. Metal Compositions of Diesel Fuel and Lubricating Oil (ppm) Al Ca Fe Mg Na Zn Mo
diesel fuel
lubricating oil
0.2 0.8 0.6 1.6 0.4 4.4 n.d.
1.6 >1000 0.6 15.3 3.3 353 63.9
distribution. The ELPI consists of a corona charger, a 12-stage cascade low-pressure impactor, and a multichannel electrometer. Exhaust gas with volume flow of 10 L min-1 first passes through a unipolar positive polarity charger where the particles in exhaust gas are charged electrically. Then the charged particles are size classified according to their aerodynamic diameter in a lowpressure impactor. The charged particles collected in a specific impactor stage produce an electrical current, which is recorded by the respective electrometer channel. The ELPI measures particle size distribution in the size range 0.03-10 μm with the following 13 cut sizes: 0.007, 0.029, 0.057, 0.101, 0.165, 0.255, 0.393, 0.637, 0.99, 1.61, 2.46, 3.97, and 10.15 μm. Two tandem ejector diluters (Dekati, Finland) are used to simulate the reactions that occur when hot combustion products mix with cooler atmospheric air. The first stage is heated to 200 degree centigrade and the second stage is left at ambient temperature. Two stages are used in series to provide an overall dilution ratio of 64. In this study, the dilution ratio was determined from CO2 concentrations before and after dilution. Part of exhaust gas was diluted by these two tandem ejector diluters and then was sampled into the ELPI for particle size measurement. Compared to atmospheric dilution, this dilution system suppressed the formation of nucleation mode of PM. On the other hand, another part of engine exhaust was diluted by an ejector diluter, which is same to the first stage diluter used for real-time measurement. The diluter was heated to 100 degree centigrade. Teflon filter membranes (47 mm in diameter and nominal pore size of 0.2 μm supplied by Pall Corporation) housed in an ordinary filter holder were used to collect the exhaust particles. To sample enough particulate matter, a sampling pump was operated at a constant flow rate of 80 Lmin-1. Afterward, all filters collecting samples were immediately stored in parchment paper bag and sealed in drying bottle until digestion. Field blanks obtained at the sampling site were stored in the same way. The effects of field blanks were all subtracted from the final results. To analyze sulfate, half of each filter was cut into pieces and put into a centrifuge tube. Samples were immersed into 15 mL of high purity deionized water and sonicated for 20 min. Then, the extract was filtered by microcellular membrane filter. The above steps were repeated once again and the two extracts were merged together for analysis. Then the sulfate fraction was determined by ion chromatograph(IC, Dionex America). The other half of each filter was cut into pieces and transferred into Teflon vessels with a plastic tweezer. Samples were immersed into 2 mL of highpurity nitric acid for 5 min and dissolved by using 1 mL of highpurity hydrochloric acid. After digestion, the solution was made up to 10 mL in a standard flask. Trace metals were analyzed by a
Experimental Section A light-duty 2.771 L Euro3 diesel engine retrofitted with DOC was used in this study. The engine was a model year 2005, electronically controlled four cylinder diesel engine with intercooler turbocharger. This engine has 85 kW maximum power and 270 N m maximum torque at 3600 and 1900 rpm, respectively. The engine was fueled with fuels having sulfur levels of 19 ppm, 350 ppm and 1000 ppm and was tested on a test-bench based on an AC dynamometer (Schenck HT350, Germany). The higher sulfur fuels (350 ppm and 1000 ppm) were derived from the lower sulfur one (19 ppm) by doping with thiophene. The only difference in fuel composition is their sulfur content. Properties of the test fuel of 19 ppm sulfur as well as the standard test methods are listed in Table 1. Table 2 shows metal compositions of the 19 ppm sulfur fuel and lubricating oil. The DOC is 143.8 mm in diameter and 152.4 mm long. The DOC uses cordierite substrates with a 400 cell-per-square-inch (cpi) cell density, and have a platinum loading. Experiments were performed at European steady state 13 modes test. The regulated gaseous pollutants were measured by AMA4000 of AVL. CO and CO2 were monitored with a nondispersive infrared analyzer; NOx was monitored with a chemiluminescence detector; THC was monitored with a flame ionization detector (FID). An electrical low-pressure impactor (ELPI, Dekati, Finland) was used to measure particle number concentration and size (8) Grose, M.; Sakurai, H.; Savstrom, J.; Stolzenburg, M. R. Environ. Sci. Technol. 2006, 40, 5502–5507. (9) Bikas, G.; Zervas, E. Energy Fuels 2007, 21, 1543–1547. (10) Vogt, R.; Scheer, V.; Casati, R.; Benter, T. Environ. Sci. Technol. 2003, 37, 4070–4076. (11) Vaaraslahti, K.; Virtanen, A.; Ristim€aki, J.; Keskinen, J. Environ. Sci. Technol. 2004, 38, 4884–4890. (12) Tobias, H. J.; Beving, D. E.; Ziemann, P. J. Environ. Sci. Technol. 2001, 35, 2233–2243. (13) Maricq, M. M.; Chase, R. E.; Xu, N.; Laing, P. M. Environ. Sci. Technol. 2002, 36, 283–289.
986
Energy Fuels 2010, 24, 985–991
: DOI:10.1021/ef900982c
Zhao et al.
Table 3. Emissions of Regulated Gaseous Pollutants with and without DOC at Different Modes Without DOC sulfure level 19 ppm
350 ppm
1000 ppm
With DOC
rpm, load
CO (ppm)
NOX (ppm)
THC (ppm)
CO (ppm)
NOX (ppm)
THC (ppm)
2690, 50% 2690, 100% 3200, 50% 3200, 100% 2690, 50% 2690, 100% 3200, 50% 3200, 100% 2690, 50% 2690, 100% 3200, 50% 3200, 100%
309.1 168.9 362.0 167.0 99.0 66.0 70.0 65.0 79.0 74.2 76.5 59.4
165.8 299.0 159.0 322.0 187.0 328.0 196.0 361.0 198.0 379.0 215.0 392.0
73.6 60.5 115.0 56.0 282.0 168.4 300.0 145.0 273.0 160.0 291.0 144.0
11.5 11.5 13.6 13.5 60.1 57.0 45.3 42.8 49.8 60.5 46.0 55.0
169.0 306.0 164.0 322.0 188.0 331.0 206.0 349.0 203.0 370.0 219.0 390.0
43.1 31.2 76.3 45.1 12.4 11.2 12.9 12.2 12.0 11.3 13.9 12.8
At 50% load, for the three fuels, DOC reduces the number concentration of different size range. In this study, DOC conversion efficiency is used for particle number reduction. Under those operating conditions, the conversion efficiency is about 20-60%. When the sulfur content increases, the conversion efficiency of DOC reduces by 5-20%. High sulfur content has profound effects on number concentrations of accumulation mode and coarse mode particles. Conversion efficiency of DOC reduces with the increase of particle size. At 100% load, for the 19 ppm sulfur fuel, particle number emissions reduce about 20-80% with DOC compared to those without DOC. But, for the 350 and 1000 ppm sulfur fuel, nanoparticles number emissions exhibit a 30-50% decrease, while accumulation mode and coarse mode particles exhibit a 20-350% increase. For the 1000 ppm sulfur fuel, at the engine speed of 2690 rpm, the conversion efficiency of coarse mode reaches to a maximum of 350%. Furthermore, at 100% load, with DOC, the number and size of the particles increase as fuel sulfur content is increased. At high load, hence at high temperature, the DOC oxidizes the SO2 to form sulfuric acid. The sulfuric acid then condenses onto the soot particles. This increases their density and aerodynamic size. The presence of the catalyst and variations in fuel sulfur content alters the extent to which hydrocarbons and sulfates condense on the soot particles, and the exhaust sampling methodology also promote the additional coagulation.13 Emission of Sulfate. The sulfate emission rate and fuel consumption are plotted against sulfur content in Figure 2. The results show that the sulfur content in the fuel significantly affects the production of sulfates, especially at high load conditions.6 At different engine operating conditions, the emission rates of sulfate increase with sulfur content, and the variations are high. At engine speed of 2690 rpm and 50% load, sulfur emission rate for the 1000 ppm sulfur fuel is 4.3 times higher than that of the 19 ppm sulfur fuel. But at full load operating condition, this rate becomes 17.5 times higher than that of the19 ppm sulfur fuel. It means that with the same fuel, the emission rate of sulfate increases when engine load increases. Additionally, the increase rate also increases with load, which varies from 3.9 times (for the 19 ppm fuel) to 16.4 times (for the 1000 ppm fuel). From Figure 2, it is also evident that fuel consumption increases with the increase in sulfur content at the same operating condition. In addition, fuel consumption at high load is higher than that at low load. At high speed and load, fuel consumption increases and thus the total sulfur, that will form sulfate,
VARIN VISTA-MPX inductive coupled plasma-atomic emission spectroscopy.
Results and Discussion Emissions of Regulated Gaseous Pollutants. Emissions of regulated gaseous pollutants with and without DOC at different modes are listed in Table 3. Almost at all modes, DOC reduces THC and CO emissions by 90%. As expected, DOC has practically no effect on the NOx emissions. The THC concentrations of low sulfur diesel are higher than those of high sulfur diesel. This might be caused by more carbonaceous compounds being converted into the gaseous phase. Particle Size Distribution. Figure 1 represents the number and size distribution of PM with and without DOC for the three fuels at different modes. It can be seen that the size distributions are single log-normal. Generally, at different engine speeds and loads, without DOC, the number concentration of nanoparticles for the 19 ppm sulfur fuel decrease, but accumulation mode particles and coarse mode particles increase relative to the 350 ppm and 1000 ppm sulfur fuels. Schneider also found that the production of nucleation particles could be suppressed even at high engine load by using low sulfur fuel.4 Sulfuric acid is the nucleating agent in diesel nanoparticle formation.12 The organic compounds (volatile and low volatile) condense only on preexisting particles, such as sulfuric acid nucleation particles and larger accumulation mode soot particles. If the conditions for nucleation are not given, sulfuric acid also condenses on the larger accumulation mode soot particles. The nucleation mode arises from semivolatile organic gases or sulfates that nucleate and condense during exhaust dilution and cooling. This mode can exhibit order of magnitude fluctuations originating from small changes in engine load, fuel sulfur content, exhaust dilution, and PM sampling conditions.14 In the engine test bed measurements, it was found that engine load, fuel sulfur content and dilution conditions such as humidity of dilution air, dilution ratio, and residence time profoundly influenced the particle size distribution.15,16 Therefore, the nucleation mode can exhibit order of magnitude fluctuations originating from above factors. (14) Giechaskiel, B.; Ntziachristos, L.; Samaras, Z.; Scheer, V. Atmos. Environ. 2005, 39, 3191–3198. (15) Shi, J. P.; Harrison, R. M.; Brear, F. Sci. Total Environ. 1999, 235, 305–317. (16) Mohr, M.; Lehmann, U.; Margaria, G. SAE Technol. Pap. Ser. 2003, No. 2003-01-1890.
987
Energy Fuels 2010, 24, 985–991
: DOI:10.1021/ef900982c
Zhao et al.
Figure 1. Comparison of particle size distribution measured for three fuels with and without DOC at different engine speeds and loads.
manifolds. It is believed that increased fuel consumption at higher load would increase the concentration of SO2 available for the formation of sulfuric acid, thus generating large concentration of sulfate. In the present work, the emission rate of sulfate emitted from the diesel engine used with and without DOC as a function of engine speed at full load has been investigated. Without DOC, the emission rate of sulfate increases slightly when the engine speed increases. But, with DOC, this increase in sulfate emission rate is appreciable. Sulfate to PM mass ratio was measured at different modes for three fuels. At engine speed of 3200 rpm and 50% load, the percentage of sulfate was 0.04%, 0.09%, and 0.43% for the 19, 350, and 1000 ppm fuels, respectively. Similarly, at
engine speed of 3200 rpm and 100% load, this percentage of sulfate was 0.06%, 0.27%, and 2.1%, respectively. Figure 3 shows sulfate to PM mass ratio at engine speed of 2690 rpm and different loads with and without DOC. At low load, sulfate to PM mass ratio with DOC is less than that of without DOC. But at medium and high loads, the results are contrary to that of low load. The catalyst temperatures of DOC are also shown in Figure 3. At high load, catalyst temperature of DOC is higher than that at lower loads. The catalyst temperature is not high at low load and cannot reach the required temperature, so SO2 cannot effectively be converted into SO3. On the contrary, at medium and high load, catalyst temperature is higher, which can effectively convert SO2 into SO3, and thus generate sulfate. Sulfur in diesel fuel acts as a catalytic inhibitor, which reduces 988
Energy Fuels 2010, 24, 985–991
: DOI:10.1021/ef900982c
Zhao et al.
Figure 2. Sulfate emission rate and fuel consumption as a function of sulfur content at engine speed of 2690 rpm.
Figure 3. Sulfate to PM mass ratio and catalyst temperature at engine speed of 2690 rpm and different loads for the 19 ppm sulfur fuel.
Figure 4. Trace metals emission rate for three fuels.
conversion efficiency of oxidation catalysts and increases their light-off temperatures.17 During the combustion process, most of the fuel sulfur is oxidized to SO2. However, on the surface of the oxidation catalyst, SO2 is further oxidized to SO3, which rapidly reacts with H2O to form H2SO4. The extent of this undesired reaction depends on the catalyst formulation. To some extent, the conversion efficiency of SO2 to SO3 depends on the temperature of the oxidation catalyst, which in turn depends on the engine load.
Emission of Trace Metals. Most trace metals come from fuel, lubricating oil, additives, and detergents. Figure 4 presents the effects of sulfur content on trace metals emission rate, which was captured at engine speed of 2690 rpm and 100% load. The metals sodium (Na),calcium (Ca), iron (Fe), magnesium (Mg), potassium (K), sulfur (S), zinc (Zn), aluminum (Al), titanium (Ti), manganese (Mn), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and strontium (Sr) are shown. The emission rates of Na, Ca, Mg, K, Al, Ni, and Cr for higher sulfur fuel are higher than those for lower sulfur fuel. No noticeable differences in the emission rates of Pb, Cu, and Mn are observed for the test fuels. Ca and Fe are the two most abundant trace metals for three fuels as shown in the Figure 4. Calcium is found to be
(17) Ntziachristosa, L.; Samaras, Z.; Zervas, E.; Dorlhene, P. Atmos. Environ. 2005, 39, 4925–4936.
989
Energy Fuels 2010, 24, 985–991
: DOI:10.1021/ef900982c
Zhao et al.
Figure 5. Emission rate of trace metals with and without DOC at different loads.
the most abundant of the trace metals except for the 350 ppm sulfur fuel, while iron has the maximum emission rate for this fuel. This higher Fe is attributed to the fact that engine wears severely because iron most likely comes from engine wear, such as abrasion of the cylinder liner or piston.18 When fuel ignites in the cylinder, the sulfur in the oil and fuel prompts the formation of SO3, which in turn enhances the formation of sulfate complexes with the elements present in the oil and fuel, and facilitates the emission of such metal complexes in the form of particles or smoke. However, the exact mechanism by which fuel sulfur content enhances metal emission is still not fully understood. Figure 5 shows the emission rates of trace metals with and without DOC at two different loads for the 19 ppm sulfur fuel. The emission rates of Ca, Fe, Mg, and Na are higher than those of Cu, Mn, Ti, Ni, Pb, and Zn. For S, the emission rate increases 40-90% downstream of DOC, and when the load increase, the rate of increase becomes smaller. At engine speed of 2690 rpm and 25% load, the emission rates of the elements increase with DOC except for Ca and Zn. Ca and Zn have high contents in lubricating oil, above 1000 ppm and 353 ppm respectively. Na, K and Mg increase ranging from two to four times, while Fe shows modest increase. In addition, Sr and Ti increase considerably, about two times. On the contrary, Ca emission exhibits a sharp decrease. On the other hand, at full load with DOC, only the emission rates of Na, K and Fe increase significantly and other elements such Mg, Zn, Cu and Ca reduce at different degrees. This implies that DOC can increase the emission of Na, K and Fe regardless of load. The emission of Mg, Zn, Cu, and Ca are affected by DOC, as well as by load level. Fe is
assumed to come from the engine and the exhaust system (via wear, corrosion) and Fe is always found as oxide in emission. After the oxidation of DOC, more Fe form oxide and results in the increase of Fe emission rate. Ca, Mg, and Zn originate mainly from lubricating oil, which is shown in Table 3. Zn and Mg form mainly phosphates, so their emissions reduce with the PM mass when using DOC. But Ca was the only element observed to form sulfate, as well as oxide and phosphate, its decrease is slighter than Zn and Mg. Conclusions A diesel engine with and without diesel oxidation catalyst (DOC) was used to conduct the tests to study the effects of sulfur content on particulate matter. Three types of diesel fuels with 1000, 350, and 19 ppm sulfur contents respectively were used. Number concentration and size distribution, sulfate and trace metals were measured. The results indicate that the number concentration of nanoparticles of low sulfur fuel decreased but accumulation and coarse mode particles increased. With the use of DOC, the number concentration of different size range reduced at 50% load; while at full load, the reduction efficiency was 20-80% for 19 ppm sulfur fuel and 30-50% only for nanoparticles for other two fuels. The results revealed that the presence of the catalyst and variations in fuel sulfur content altered the extent to which hydrocarbons and sulfates condense on the soot particles and the exhaust sampling methodology promoted the additional coagulation. Both sulfate emission rate and fuel consumption increased with sulfur content. Higher fuel consumption at higher load increased the concentration of SO2, and thus resulted in the generation of large concentration of sulfate. At low load, sulfate to PM mass ratio with DOC was less than that of without DOC; whereas at medium and high loads, the results were contrary. At medium and high loads, catalyst temperature was higher, which converted SO2 into SO3 effectively, and thus
(18) Okada, S.; Kweon, C.-B.; Stetter, J. C.; Foster, D. E. SAE Technol. Pap. Ser. 2003, No. 2003-01-0076.
990
Energy Fuels 2010, 24, 985–991
: DOI:10.1021/ef900982c
Zhao et al.
generated sulfate. The emission rates of Na, Ca, Mg, K, Al, Ni, and Cr for higher sulfur fuel were more than those for lower sulfur fuel. After engine was retrofitted with DOC, Na, K, and Fe emission increased regardless of load. The emission of Mg, Zn, Cu, and Ca were affected by DOC, as well as by load level. This corroborates previous suggestion that low sulfur fuel can decrease diesel emission greatly. Reduction in diesel sulfur content and the using of after-treatment devices affect not only particle size distribution of PM, but also
affect the chemical composition of PM such as sulfate and trace metals. Thus, the use of low metal fuels and lubricating oil is as important to the environment and human health as low sulfur fuels, especially for engines with after-treatment devices. Acknowledgment. The authors gratefully acknowledge financial support from National Natural Science Foundation of China (NSFC, 50876013).
991
