Effects of Biodiesel Blending on Particulate and Polycyclic Aromatic Hydrocarbon Emissions in Nano / Ultrafine / Fine / Coarse Ranges from Diesel Engine

The influences of different blending percentages of biodiesel on the size distributions of particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) are not well known. In this study, commercial pure petroleum-based diesel (D100) and three biodiesel blends of 20% (B20), 60% (B60), and 100% (B100) were tested in an engine operated on a dynamometer following the US transient-cycle test procedure. PM size distributions were measured with micro-orifice uniform deposit impactor (MOUDI) and Nano-MOUDI of 0.01-10 m aerodynamic diameter. The collected samples were extracted then analyzed for PAHs by GC/MS. The results revealed that PM emissions decrease apparently as the blending percentages of biodiesel increase. For D100, B20, B60 and B100, PAH emission factors were 3704, 2720, 1709 and 1514 μg/Hph (horsepower per hour), respectively. Increasing the biodiesel blending percentage reduces the emission of both PAHs and PM. As the blending fractions of biodiesel increased, the PM emissions for the four size ranges decreased. The reductions were significant especially for ultrafine (41.3%) and fine (44.8%) PM. The PAH mass was 32.5%, 32.6%, 34.5%, 30.0% in the ultra-fine size range and 23.8%, 24.3%, 29.2%, 34.5% in the nano size range for D100, B20, B60 and B100, respectively. The addition of biodiesel would cause higher percentages of ultra-fine and nano particulates in exhaust gas. For most biodiesel blending mixtures in the four size ranges, the percentages of PAH emission reduction were higher than those of PM emission. The reduction percentages reached 45.1% and 63.7% for B60, 66.5% and 68.3% for B100, respectively in ultrafine and fine size ranges. The BaPeq emission factors for B100 were 27.2, * Corresponding author. TEL.: +886-423323000 ext. 4451; Fax: +886-423742365 E-mail address: hhyang@cyut.edu.tw Chien et al., Aerosol and Air Quality Research, Vol. 9, No. 1, pp. 18-31, 2009 19 49.5, 74.2 and 13.0 g/Hph in nano, ultrafine, fine and coarse size ranges. Biodiesel can reduce both PAH emission factors and the PAH corresponding carcinogenic potency in the full size ranges.


INTRODUCTION
In recent years, due to increasing fuel prices and diminishing petroleum reserves, considerable concern has been raised over diesel-powered vehicles using biodiesel as fuel in many countries.Biodiesel, a fuel that can be made from renewable biological sources, such as vegetable oils, animal fats and waste cooking oils, may have the potential to reduce the reliance on imported oil and reduce air pollutant emissions from diesel engines (Wang et al., 2000;Durán et al., 2005).Many studies on air pollutant emissions with biodiesel have been carried out worldwide.Most studies have shown that emissions of carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) are reduced by using biodiesel instead of diesel (e.g.McCormick et al., 2001;Ramadhas et al., 2004;Rakopoulos et al., 2008).
It has been shown that vehicles are important contributor of air pollution in urban areas (Srivastava et al., 2008;Tsang et al., 2008;Zhang et al., 2008).PM emissions from diesel-powered vehicles are typically 10-100 times higher than those from gasoline-powered vehicles (Kittelson, 1998).
Previous studies have shown that diesel-powered vehicles are the major contributors of PM in urban areas (Fushimi et al., 2008;Takahashi et al., 2008).The size of PM is an important factor affecting human health, because it determines the deposition position in the respiratory tract.
Fine particulates are especially important in regard to adverse health outcomes, such as increased cardiovascular, respiratory morbidity and mortality rates, due to their larger active surface and the higher likelihood of deposition in the alveolar region of the lungs (Schwartz et al., 2002;Hartog et al., 2003).
The influence of biodiesel used in diesel engines on PM size distribution has been investigated.Bagley et al. (1998)  and pure biodiesel, respectively.Fine particulates were found to cause a stronger toxic effect than coarse particulates at the same mass level (Donaldson et al., 1998;Obersdörster et al., 2001).Hence, researchers have paid increasing attention to ultrafine and nano particulates (Hitchins et al., 2000;Shi et al., 2001;Kittelson et al., 2004).Although several studies have been performed on the effects of biodiesel blending on PM size distribution, investigation on PM in nano size range is still lacking.
Diesel-powered vehicle is also an important source of PAHs.Some PAHs have been proven to be carcinogenic (IARC, 1987).Most PAHs are found to be associated with particulate, predominately fine or nano particulate (Kahandawala et al., 2004;Westerdahl et al., 2005)  The details of the driving cycle are described elsewhere (Yang et al., 2007).

Dilution Tunnel and Sampling System
The

Analysis of PM and PAHs
Before and after sampling, the filters were stored for 24 h in a desiccator at 25°C in The recovery efficiencies of two internal standards were between 83.0% and 88.0%, and were fairly constant.

PM Emissions and Size Distributions
The weights of particulates collected on the 13 stage filters of the MOUDI and nano-MOUDI were recorded and added together as total PM emission.The emission factors (mass emitted per horsepower hour) of PM with the four fuels are listed in Table 2. PM emission factors were 0.052, 0.044, 0.041 and 0.037 g/Hph for D100, B20, B60 and B100, respectively.PM emissions decrease as the blending percentages of biodiesel increase.This result agrees with those of the previous studies (Haas et al., 2001;Lapuerta et al., 2008).Reduction of PM emission for biodiesel can be attributed to the fact that biodiesel contains no aromatic constituent and much less sulfur in comparison to diesel (Wang et al., 2000;Dorado et al., 2006).
The PM size distributions (df/dlog dp versus dp: f is the mass fraction of PM in a certain size interval) from 0.0018 to 10 m for the test fuels are shown in Fig. 3.Of the four size ranges (i.e.nano, ultra-fine, fine and coarse) adopted in this study, approximately 80% of PM is smaller than 1.0 m for all the four fuels, which indicates that the particulates emitted from diesel engine are primarily inhalable particulates.
There is no significant difference for the PM size distribution between D100 and B20.As   blending fractions is similar to those of the previous studies (Bagley et al., 1998;Jung et al., 2006).

PAH Emissions and Size Distributions
Emission factors of the 16 PAHs for the test fuels are listed in Table 2.For D100, B20, B60 and B100, PAH emission factors are 3704, 2720, 1709 and 1514 μg/Hph, respectively.Increasing the biodiesel blending percentage reduces PAH emission, which agrees with the results of PM.In comparison with D100, the reduction of PAH emissions for B20, B60 and B100 are 11.7%, 53.9%, 56.4%, respectively.The results also agree with previous studies (Corrêa and Arbilla, 2006).Reduced PAH emission was caused by the fact that PAHs are derived from unburned fuel and from lubricating oil of physical and/or chemical condensation (Tancell et al., 1995;Miguel et al., 1998).The nil or very little aromatic emissions.The PAH mass are 32.5%, 32.6%, 34.5%, 30.0% in ultra-fine size range and are 23.8%,24.3%, 29.2%, 34.5% in nano size range for D100, B20, B60 and B100, respectively.The addition of biodiesel would cause a higher percentage of ultra-fine and nano particulates in exhaust gas.

Influences of Biodiesel Blending on PM and PAH Emissions
The influences of biodiesel blending on PM and PAH emissions are assessed by comparing the effects of the various ratios of blended biodiesel fuels with D100.These reduction percentages (, %) were calculated using the formula: Biodiesel contains much lower PAH content, which is the main reason why PAH emissions were reduced (Agarwal, 2007).It is worth noting that for pure biodiesel (B100), PAHs were still emitted.Previous studies have proposed that PAH emissions can arise from fuel PAH surviving and synthesizing during the combustion process (Tancell et al., 1995;Rhead and Hardy, 2003).The results indicate that thermal synthesis plays an important role for PAH generation in the process of diesel/biodiesel combustion.

PAH Corresponding Carcinogenity
In this study, toxic equivalency factors found that 65% of submicron (0.01-0.1 μm) PM was reduced when using soybean-oil biodiesel in an indirect injection diesel engine.Turrio-Baldassrri et al. (2004) blended 20% rapeseed-oil with diesel and used it as fuel for buses.The results indicated that most of the emitted PM was in the size range of 0.06-0.3μm.Jung et al. (2006) used pure rapeseed-oil biodiesel as fuel and found a 38% PM reduction.The mean diameter was reduced from 0.08 m with diesel to 0.062 m with rapeseed-oil diesel.Lin et al. (2007) used a palm-biodiesel/diesel blend as fuel.Their results indicated mass median diameters of 0.439, 0.380 and 0.465 m for diesel, B20 (20% biodiesel + 80% diesel) was in accordance with the U.S. Code of Federal Regulations 40, Part 86, Subpart N (U.S. transient cycle).The U.S. transient cycle includes a wide variety of speeds and loads sequenced to simulate real-traffic on an expressway in congested and uncongested urban driving.
Fig. 1.Schematic diagram of the test equipment.
45% relative humidity.They were then weighed on an electronic balance (Sartorius CP225D) with a resolution of 1.00 g.The emission factor of PM was determined by dividing the mass emitted by the horsepower-per-hour of that driving test.After weighing, the combined filter samples were Soxhlet-extracted with a mixed solvent (n-hexane 125 mL and dichloromethane 125 mL) for 24 h.The extract was then concentrated by purging with ultra-pure nitrogen to 2 mL for the cleanup procedure and then reconcentrated to 0.5 mL with ultra-pure nitrogen.The concentrations of the following PAHs were determined: naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, cyclopenta[c,d]pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo-[e]pyrene, benzo[a]pyrene, perylene, indeno[1,2,3,cd]pyrene, dibenz[a,h]anthracene, benzo[b]chrysene, benzo[ghi]perylene and coronene.A gas chromatograph (GC) (Agilent 6890) with a mass selective detector (MS) (Agilent 5973N) and a computer workstation was used for the PAH analysis.This GC/MS was equipped with an Agilent capillary column (Agilent Ultra 2 -50 m  0.32 mm  0.17 m), an Agilent 7673A automatic sampler, with an injection volume of 1 L, splitless injection at 310 o C, ion source temperature at 310 o C, oven, from 50 o C to 100 o C at 20 o C /min; 100 o C to 290 o C at 3 o C /min; hold at 290 o C for 40 min.The masses of primary and secondary ions of PAHs were determined by using the scan mode for pure PAH standards.Qualification of PAHs was performed by using the selected ion monitoring (SIM) mode.The analysis ofPAHs is described in detail in our previous study(Yang et al., 2005).In this study, two internal standards (phenanthrene-d10 and perylene-d12) were used to check the response factors and the recovery efficiencies for PAH analysis.The recovery efficiencies of 16 individual PAHs and these two internal standards were determined by processing a solution containing known PAH concentrations through the same experimental procedure used for the samples.
the biodiesel blending percentage increases to 60% (B60), the ultra-fine and nano particulates increase.While pure biodiesel (B100) was used, nano particulates predominated in the size distribution.The calculated mass median diameters (MMDs) of PM shown in Fig. 2 are 0.146, 0.144, 0.134 and 0.124 μm for D100, B20, B60 and B100, respectively.The results show that as the blending percentage of biodiesel increase, the emitted particulates shift to ultrafine size range.The results also show that the PM size distribution of the biodiesel

Fig. 2 .
Fig. 2. PM size distributions for the four size ranges.

Fig. 3 .
Fig. 3. PAH size distributions for the four size ranges.

Fig. 4 .
Fig. 4. Reduction percentages of (a) PM and (b) PAH emissions by biodiesel blending mixtures compared with D100.

(Fig. 5 .
Fig. 5. BaP eq emission factors for the four size ranges with four test fuels.

Engine, Dynamometer and Driving Cycle
DC-IV control system.The DC-current dynamometer with a fully automatic control system is capable of supplying maximum power and torque at 335 kW and 800 Nm,

Table 2 .
Emission factors of PM and PAHs.