Effects of Fuel Aging on the Combustion Performance and Emissions

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Effects of Fuel Aging on the Combustion Performance and Emissions of a Pyrolysis Liquid Biofuel and Ethanol Blend in a Swirl Burner Milad Zarghami, Tommy Tzanetakis, Yashar Afarin, and Murray J. Thomson Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 04 Feb 2016 Downloaded from http://pubs.acs.org on February 7, 2016

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Effects of Fuel Aging on the Combustion Performance and Emissions of a Pyrolysis Liquid Biofuel and Ethanol Blend in a Swirl Burner Milad Zarghami, Tommy Tzanetakis, Yashar Afarin, Murray J. Thomson* Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, Ontario M5S 3G8, Canada KEYWORDS: Pyrolysis liquid biofuel (Bio-oil), Aging, Combustion, Fuel Properties, Emission

ABSTRACT. Pyrolysis liquid biofuel (also called bio-oil or pyrolysis oil) is a promising renewable fuel for stationary heat and power generation; however the fuel properties, combustion performance and combustion emissions degrade with fuel aging. The aging effects of softwood bark pyrolysis liquid biofuel on fuel properties and combustion performance are studied. In order to investigate the ageing effects on fuel properties, the solid content, viscosity, estimated SMD, and TGA residue of pure pyrolysis liquid are considered. Furthermore, the CO emission, unburned hydrocarbon (UHC), and organic fraction of particulate matter emissions (also called carbonaceous residue, CR) from combustion of aged pyrolysis liquid biofuel/ethanol blend are measured to investigate the effect of aging on the combustion performance in a swirl spray burner. All measurements are employed for two batches of pyrolysis liquid biofuel with

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two levels of solid content. Results show that pyrolysis liquid’s fuel properties, combustion emissions and combustion performance become degraded as it is stored for longer periods of time. The results also support the accelerated aging correlation from literature which is based on viscosity and can accurately predict the effect of natural aging on the fuel properties, combustion emissions and combustion performance.

1. Introduction Pyrolysis liquid biofuel (also called bio-oil or pyrolysis oil) is a type of biofuels which is a product of biomass thermal decomposition through the fast pyrolysis process in the absence of oxygen. Since the process cannot be fully controlled and the feed material varies widely, there is a wide range of physical and chemical properties for the liquid fuel.1 ASTM has developed standard specifications for pyrolysis liquid biofuel.2 The fuel’s properties such as acidity, high viscosity, low heating value, inherent water, solids content and ash content make pyrolysis liquid difficult to use. Therefore, special burner designs are required for stable combustion.3-5 Pyrolysis liquid biofuel can experience fuel degradation when stored for prolonged periods of time, also known as fuel aging.6,7 Several studies have been performed on the effects of storage time and storing conditions on pyrolysis liquid properties. In this regards, Oasmaa et al.8 studied the visual changes in one month stored pyrolysis liquid sample. Their results showed that flaky sediments form after one month of storage at a constant temperature. Chaala et al.7 performed a Thermogravimetric Analysis (TGA) on pyrolysis liquid and demonstrated that aging decreases the volatility and increases the non-evaporative TGA residue material. Garcia-Perez et al.9 analyzed the chemical changes in pyrolysis liquid during aging. They maintained the pyrolysis


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liquid biofuel samples at a constant temperature for a range of time periods. It was observed that the morphology of waxy materials change with time and these changes are accelerated by increasing the temperature to 80℃.9 Several researchers have studied the effect of storage temperature on the aging of liquid pyrolysis liquid biofuel.8,10,11 According to their results, increasing the temperature increases the rate of change of the viscosity and fuel structure. The effect of aging on the water content of the pyrolysis liquid was investigated by Czernik et al.12 and Diebold and Czernik13. Their results indicated that aging increases the pyrolysis liquid water content with significantly faster rates at higher temperatures.12,13 The thermal decomposition process of raw, aged, and Torrefied wood pyrolysis liquid biofuels through TGA were investigated by Ren et al.14. Based on the TGA results, a three-stage degradation process was proposed which consisted of devolatilization of the light component, transition of the heavy fraction to solid, and combustion of carbonaceous residues.14 They also found that aged pyrolysis liquid has more thermal instability compared to other ones. Jiang et al.15 studied the aging effect of pyrolysis liquid by measuring the fuel properties such as viscosity, water content, acid number, and averaged molecular weight before and after storing in a room with 80℃ for 180 hours. They also compared these results with the aging properties of the upgraded pyrolysis liquid (ether-soluble fraction of pyrolysis liquid biofuel with bio-diesel). Their results showed that upgrading the pyrolysis liquid reduces the rate of the aging process .15 Similar research has been done by Elliot et al.16. They studied changes in viscosity at different temperatures. Their results confirmed that the increase in viscosity during the aging in room temperature for 6 months is similar to the increase in the accelerated aging test of 24h at 80℃. Chen et al.17 reviewed different testing parameters and technologies which can be used for examining bio-oil stability and also research progress in this field. They also studied


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different bio-oil upgrading methods for improving the aging characteristics. Their studies showed that the storage temperature, storage time and bio-oil oxygen content have a noticeable effects on stability of bio-oil.17 A number of studies have performed to study the effect of pyrolysis liquid biofuel properties on the combustion performance and emission production. Tzanetakis et al.4 studied spray combustion tests with pyrolysis liquid/ethanol blends. They investigated the effect of swirl, atomization quality, ignition source energy, air and fuel preheats, and equivalence ratio on the combustion stability of emissions of cellulose based bio-oil spray combustion. They concluded that an increase in viscosity results in an increase of the droplet size which deteriorates the combustion performance and increases the emissions.4 Moloodi et al.18 showed that carbon monoxide and unburned hydrocarbon emissions increase with increasing solids and ash fractions of pyrolysis liquid.18 Furthermore, carbon monoxide and unburned hydrocarbon emissions decrease with both higher water and ethanol contents.18 They found that increasing the volatile content of fuel by blending in ethanol improves the flame stability. Also, a strong correlation was found between the organic fraction of particulate matter emissions and the TGA residue of the fuel.4,18 Although a few studies have been performed on studying the effect of aging on pyrolysis liquid biofuel properties, based on authors’ knowledge there is no research investigating this effect on the combustion performance. The present research focuses on the effect of storage time and conditions on the fuel properties, combustion performance and combustion emissions of pyrolysis liquid biofuel in a spray burner. 2. Experimental Methodology


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2.1 Experimental Setup In this section, a brief description of the pyrolysis liquid biofuel burner is provided. Complete details on the design and assembly of the system can be found in our last publication.4,5,19 Figure 1 shows a schematic of the main burner assembly. The main sections of the burner system are a variable swirl generator, an internal-mix air-blast atomizing nozzle and a pilot flame. Primary combustion air is heated to a temperature between 250 ℃ and 300℃ by passing through a 1.5 kW electric heater before entering the moveable block swirl box installed above the combustion chamber. This air flow is provided by a stack fan which is placed downstream of all instruments. Therefore, the whole system operates at a slight negative pressure to contain exhaust gases. Fuel is dispensed using peristaltic pumps since the flow rates for 10 kW operation conditions are very low (about 30 mL/min). A pilot flame from a methane-oxygen torch is used to stabilize the combustion. The pilot flame system is comprised of an oxy-fuel torch body and a standard tip with a 1.2 mm orifice diameter. Although originally designed for oxygen and natural gas, the pilot is run using pure methane and produces a premixed CH4/O2 flame. The tip also has a hexagonal slit or pattern that surrounds the central orifice. The multiple flames issuing from these small openings produce an overall well-distributed flame shape. The maximum methane flow rate through the pilot is 0.88 SLPM, corresponding to an energy input of 0.5 kW. The atomizing nozzle is placed along the centerline of the burner and near the pilot flame in order to spray the fuel-air mixture as close as possible to the ignition source. The atomizing air flow is provided by a compressed air source and is measured using a pressure regulator and a rotameter. Because of the extended nozzle body sheath, both the atomizing air and liquid fuel are subsequently heated by the incoming primary combustion air. Figure 2 shows the internal construction of the nozzle tip. Fuel is carried through a single liquid cap orifice to the internal


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mixing chamber, where it is mixed with the air. Then, the spray jet exits through six symmetrically spaced discharge orifices. The six individual jets each make an angle of 60˚ with the centerline of the burner and create a hollow cone pattern. This pattern is important to establish a recirculation zone and enhances the combustion stability. Another factor that affects the combustion stability is fuel boiling. In the system used for this study, boiling and bubble forming causes instability which occasionally ends in flame blow-out. Therefore, a water cooling system for the nozzle was designed by Moloodi et al.20 in order to prevent the fuel from boiling and avoid these instabilities. As shown in Figures 1 and 2, a thermocouple mounted inside the nozzle tip measures the fuel temperature just before injection into the burner. The extended exhaust section is also outfitted with various thermocouples and Borescope ports. The Borescopic probe is considered for taking unobstructed photographs of the flame that look up along the central axis of the burner. More detailed information about this section can be found in Tzanetakis et al.4 paper. All the burner sections downstream of the nozzle are built from 316 stainless steel in order to prevent corrosion. Beyond the nozzle and pilot flame, the burner opens up into a conical diffuser with a half angle of 35 degrees. As a general guideline, a half angle between 20 and 35 degrees is recommended by Gupta et al.21, in order to promote the onset of a central recirculation zone (CRZ) due to a sudden geometry expansion. In addition, a 3.2 mm thick quartz window enables the operator to directly view the flame and monitor the combustion quality during tests. 2.2 Fuel Analysis The fuel properties of the two pyrolysis liquid biofuel batches are summarized in Table 1. The methods employed for measuring the heating value, chemical composition, viscosity, water


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content, solids content, and the ash content are also provided in the table. The TGA tests were performed by heating a small sample of fuel (~20 mg) up to 600˚C under nitrogen atmosphere at a constant rate of 10˚C/min. As can be seen from this table, there are considerable differences between the two pyrolysis liquid biofuel batches in particular with their solids content. The higher heating value (HHV) of all pyrolysis liquid biofuel samples was measured prior to testing in order to determine the fuel flow rate corresponding to 10 kW operation conditions. Therefore, the tests were run based on equivalent energy throughput. Since small combustor’s flame is more unstable due to high heat loss, in this study, bio-oil was blended with 15% ethanol by volume prior to running the test. The primary reason for this was to increase the volatility of the fuel mixture and make the flame more stable. 2.3 Gas Phase Species Measurement To measure unburned hydrocarbons (UHC) and carbon monoxide (CO), as well as the equivalence ratio, a system consisting of a heated sample line, a heated filter, a flame ionization detector (FID), a Fourier transform infrared (FTIR) spectrometer, and an oxygen sensor was used.4 Figure 3 shows the inputs, outputs and sampling lines for the burner. Exhaust is extracted from the burner using a 6.4 mm diameter stainless steel heated sample line that maintains the gas at 195ºC in order to avoid water and hydrocarbon condensation. Before entering any gas phase species measurement instrument, the exhaust sample is passed through a heated glass microfiber/Teflon bounded filter element that removes most of the particulate matter. The UHC and O2 concentration in the exhaust were continuously monitored using DC analog output signals from the FID and the oxygen sensor, respectively. Before each combustion test, the FID is calibrated using two gases; the first is the zero gas consisting of purified air, and the second is the span gas


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consisting of 90.2 ppm of methane in air. The CO emissions were acquired by taking the average of five consecutive infrared spectra from the FTIR at steady state burner operating conditions. The equivalence ratio for each test was calculated using the measured O2 in the exhaust. 2.4 Particulate Matter Measurement Particulates were collected using an iso-kinetic sampling system placed in the burner exhaust.5The particulate matter (PM) was deposited on 47 mm borosilicate filters with an aerosol retention efficiency of 99.9% at 0.3 μm. The filters are made of pure quartz micro-fibers without any binding material and are therefore able to withstand temperatures up to 1100 °C. To separate water, ash, and unburned or partially burned carbonaceous residue (CR) fractions in the PM, the "loss on ignition" standard method (ASTM D4422-03) was used. Figure 4 shows the procedure steps of the loss on ignition method. Each weight measurement (labeled as M1 to M4) was carried out three times consecutively on a Scientech SM-128D microbalance in order to generate average values and perform the appropriate uncertainty analysis. 2.5 Test Procedure To study the effect of aging on the combustion performance and emissions of pyrolysis liquid biofuel, 14 tests were carried out over a 10-months period. Pyrolysis liquid was poured into several bottles and sealed with plastic caps. The samples were then separated into two categories: a number of sealed bottles were stored in a ventilated cabinet located in a room with a central climate control system which kept the temperature at 20℃. The cabinet door was kept closed and only opened when temperature measurements were done, in order to keep the pyrolysis liquid biofuel out of any direct lighting. This procedure is referred as “Natural Aging” in this study, since the temperature is representative of the room temperature. The rest of the bottles were


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stored at 5 ℃, in order to slow down the aging of pyrolysis liquid to a point that there is no changes associated with aging during this storage. These bottles were taken out one by one from the fridge and placed in a fume hood for five hours to reach room temperature before the “accelerated aging” procedure could begin. Equation.1 (Diebold and Czernik13) was used to mimic the natural aging in a shorter period of time. This correlation suggests that pyrolysis liquid can be heated up to higher temperatures and the equivalent changes in the viscosity and the average molecular weight can be achieved after a specific time. Aging rate = 2.317 × 10 exp(

)

(1)

In this study, the aging rate is defined as the change in viscosity over time and has a unit of cP/day and T is the storage temperature in Kelvin. In order to calculate the time required to heat the bio-oil and achieve an equivalent viscosity increase to the one obtained from the bio-oil stored at room temperature, Equation 1 was manipulated to obtain the following equation (Equation.2): −9659 −9659 t × exp ' = t ))***+ × exp ' T$ %&% T,))***+ %&%

(2)

Inputs for this equation are the temperature of the heated storage (a vacuum oven from Precision Scientific Inc.) that was kept at 80℃ (353 k) and time of natural aging. The outcome is the accelerated time required to heat the pyrolysis liquid which produces the equivalent amount of aging to those stored at room temperature (20℃). Table 2 presents the accelerated aging time (hours) compared to the time required for equivalent natural aging (months).


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Both the naturally aged and the accelerated aged pyrolysis liquid biofuels were tested in the burner. After the fuel aging and before the burner tests, the pyrolysis liquid was mixed with 15% ethanol on a volumetric basis. The burner parameters were optimized for the combustion of pyrolysis liquid/ethanol blends and are presented in the study by Tzanetakis19. This optimized condition is called the “base” operating point and is presented in Table 3. The ranges that are reported for equivalence ratio, air preheat temperature and primary combustion air flow rate are due to differences in the basic properties of the two batches and also the limit in control accuracy of the system. In all tests, the fuel flow rate is adjusted to provide a power input of 10 kW based on the heating value of the fuel. Since experiments with pure ethanol suggest that the combustor flow field, flame stability and recirculation configuration are extremely sensitive to the atomizing air flow rate, it was kept constant for all tests. 3. Results and Discussion 3.1 Fuel Properties Figure 5 shows the effect of aging on the pyrolysis liquid from batch one. A comparison of results from natural and accelerated aging procedure for a period up to nine months validates the accelerated aging correlation (Equation.1) which is based on the viscosity increase. The effect of aging on the physical properties becomes noticeable after the first three months of aging. As expected, the viscosity increases with storage time. This is mainly happening due to polymerization reactions among the larger molecules of the fuel.9 Figure 5 also shows that aging increases the estimated Sauter mean diameter (SMD) which has a negative influence on the combustion performance. The size of the fuel droplet in the combustion zone, represented here


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by SMD parameter, has a direct effect on the combustion quality. The correlation given by Lefebvre22 has been selected to estimate the SMD parameter (Equation.3). 9.:

SMD σ = 0.48 ' d1 ρ, U78 d1

(1 +

1 9.: μ8? 1 ) + 0.15( )(1 + ) ALR σρ? d1 ALR

(3)

where σ is the surface tension, ρ, and ρ? are the air and liquid densities, respectively. U7 is the

relative velocity between the air and liquid, d1 is the discharge orifice diameter and ALR is the

air to liquid mass flow ratio. The isentropic ideal gas assumption is used to calculate the density and air velocity through the nozzle orifice. The liquid density is assumed to be independent of the temperature and ALR is known from the measured air and liquid flow rates. Since the viscosity-shear behavior of the aged oils has not been measured directly, it is assumed that its behavior is independent of the aging. The ASTM standard test is used to measure the liquid viscosity at the nozzle temperature (Table 1), which is usually around 80˚C. For bio-oil blends, the surface tension of a wood derived bio-oil at 80˚C is 30mN/m which is taken from the literature.23 The solids content of the pyrolysis liquid also shows an increase over time. This behavior is attributed to the agglomeration of high molecular weight (HMW) molecules into solid particles. The solids content was measured through the MeOH-DCM solvent method, where the fuel is dissolved in methanol and the fraction that is not soluble is accounted for the solids content. The TGA residue is the mass remaining at 600 ℃ and is interpreted as a measure of the fuel’s tendency to polymerize.5 It is expected that the TGA residue increases over time, mainly because of the polymerization reactions taking place in the fuel which results in an increase in the HMW


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molecular fraction of the fuel. Furthermore, for the two-year aging case, there is a linear increasing relationship between the storage time and the values of each physical property. After validation of the accelerated aging procedure, a second batch was considered to investigate the effect of the initial solids content on the aging of pyrolysis liquid biofuel. The solids content of batch 2 was almost two orders of magnitude larger than the first batch. Figure 6 shows the aging effect over 24 months on the fuel solids content, the viscosity, the estimated SMD, and the TGA residue resulting from batch 2. Similar to batch 1, aging increases the values of fuel properties; however, the rate of changes on viscosity and solids content for batch 2 is larger than batch 1. The abundance of solids in this batch accelerates the polymerization reactions and enhances the agglomeration of the particles in a way that gel-like solid chunks in the liquid are easily visible for the 24 months aged pyrolysis liquid. The solids content of batch 2 increases steadily with the aging time and the trend can be approximated by a linear function. The rate of increase in TGA residue for batch 2 is lower than batch 1. 3.2 Gaseous and Particulate Emissions Measurements of gaseous and particulate emissions are employed to evaluate the effect of fuel aging on the combustion performance. The considered emissions are carbon monoxide (CO), unburned hydrocarbon (UHC) and the carbonaceous residue (CR). Since the energy throughput of the burner is fixed to 10 kW for all tests, the carbonaceous residue emissions of combustion of pyrolysis liquid biofuel blends are normalized by the energy of the fuel that goes through the system and is presented in units of mg/MJ. Figure 7 shows the variations of CO, UHC and CR concentrations under the aging process for batch 1. This figure also investigates the capability of accelerated aging equation for predicting


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the aging effect on the combustion performance. As can be seen from Figure 7, the emission values of natural and accelerated aged pyrolysis liquid are very close which suggests that the accelerated aging produces a very similar liquid compared to the natural aging process. Furthermore, it can be observed that aging increases the CR emissions due to having larger droplet, loss of volatiles and polymerization reactions. The burning time of fuel droplets typically increases with the square of the SMD. The loss of volatiles during aging makes the combustion of the fuel more difficult due to the fact that the high energy volatile materials decrease in volume with aging. Also, the polymerization reactions increase the HMW fraction of the fuel which increases char formation. Char burnout is typically much slower than liquid droplet combustion and leads to CR emissions. Moloodi et el.18 showed that the CR emission strongly correlates with TGA residue and the solids content. They also stated that the TGA residue is believed to measure the tendency of the fuel to polymerize. This is consistent with the current study where the CR, TGA residue and solids content of the two years aged pyrolysis liquid are all significantly higher compared to the base condition. Figure 7 also shows the effect of aging on CO and UHC emissions for batch 1. There is almost no change in the CO emissions during the first 3 months corresponding to the small changes in physical properties over this period, but the major increase occurs after this time through the 9 months data point. However, the CO emission value at two years does not follow this trend and is actually lower than the value after 6 months. Previous studies have shown that CO and UHC trends follow each other closely.10 Figure 7 confirms this observation, where a slight increase in UHC emissions is detected in the first 3 months and after that an increase in values are observed from 6 and 9 months, followed by a decline for the 24 months. The behavior that is seen for two years of aging can be explained using the CR emissions of the fuel. For batch 1 aged 24 months, the fuel quality


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and the combustion performance is so poor that fuel droplets form an abundance of char particles without adequate residence time to burn the carbon fraction through heterogeneous combustion. Therefore, with two years of aging, a great portion of the fuel escapes in the form of particulate matters or deposits on the wall resulting in reduced gaseous CO and UHC. Figure 8 presents the effect of aging on the combustion emissions for batch 2. The UHC, CO and CR emissions increase steadily with the aging time which is consistent with results from batch 1. Similar to batch 1, the increase in CR emission strongly correlates with TGA residue and the solids content as proposed by Moloodi et el.18. For this batch, the 24 months aged pyrolysis biofuel was almost degraded and fuel quality was very poor in a way that its combustion was very unstable. 4. Conclusion Aging effects of pyrolysis liquid biofuel on fuel properties and combustion performance were studied. Measurements were employed for two batches of pyrolysis liquid biofuel with two different solid contents (0.034% for batch 1 versus 1.9% for batch 2). The 24 months natural aging of pyrolysis liquid biofuel was simulated with the accelerated aging process. To confirm the simulation correlation, the fuel properties and combustion performance under natural aging were compared with accelerating aging results for the first 9 months. After 3 months aging, results showed a linear increase in viscosity versus storage time. Having two orders of magnitude larger solid content for batch 2 led to almost a two times larger rate of increase in viscosity compare to batch 1. The increase in viscosity increased the estimated SMD value as well. Furthermore, aging for 24 months caused two times increase in the solid content for batch 2 compared to negligible increase for batch 1. Results from the combustion of aged


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pyrolysis liquid/ethanol blend showed that aging also increased the CR emissions which correlate with the increase in the TGA residue. The same behavior was observed for CO and UHC measurements during the 9 months for both batches. For the two years aged pyrolysis liquid from batch 1, the fuel was considerably degraded and the combustion performance was poor. Hence, a great portion of the fuel escaped in the form of particulate matters or deposited on the wall, resulting in reduced gaseous CO and UHC. This situation was worst for batch 2, in which it was not possible to have a stable combustion for the 2-year aged pyrolysis liquid/ethanol blend. It can be concluded that aging time of pyrolysis liquid biofuel significantly affects the fuel quality and combustion performance. These degradations are much more severe for fuels with larger initial amount of solid content.


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FIGURES

Figure 1. Main burner assembly [8]

Figure 2. Internal Mix nozzle tip assembly [8]


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Figure 3. Overall schematic of experimental setup [8]

Figure 4. Loss on Ignition Gravimetric Analysis Method [8]


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200 300 400 500 Estimated SMD (micro meter)

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Figure 5. Fuel (pyrolysis liquid biofuel/ethanol) properties versus natural aging time for batch 1. The solid and dashed lines are related to the natural aging and the accelerating aging, respectively.

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Aging Time (Month)

Figure 6. Fuel (pyrolysis liquid biofuel/ethanol) properties versus natural aging time for batch 2. The dashed lines are related to the accelerating aging.


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Figure 7. Effect of aging on combustion emissions versus equivalent natural aging time for batch 1. The solid and dashed lines are related to the natural aging and the accelerating aging, respectively.

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Aging Time [Month]

Figure 8. Effect of accelerated aging on combustion emissions versus equivalent natural aging time for batch 2.


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TABLES Table 1. Properties of pure pyrolysis liquid biofuel for different batches Properties

Measuring method

Batch 1

Batch 2

C-H-O-N (wt %) dry

ASTM-D5291

40.78-7.67-51.43-0.12

43.45-7.38-48.90-0.27

Solids (wt %)

MeOH-DCM

0.034

1.9

Ash (wt %)

ASTM-482

0.24

0.26

Water (wt %)

ASTM-E203

26.5

23

HHV (MJ/kg)

ASTM-4809

16.9

18.3

18.4

17

40.14

50.47

TGA residue (wt %) kinematic viscosity at 40 ℃ (cSt)

ASTM-445

Table 2. Natural and accelerated aging times of pyrolysis liquid biofuel Natural Time at T=20oC (Months)

Accelerated Time at T=80oC

3

7.96

6

15.92

9

23.88

12

31.85

24

63.69

(Hours)


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Energy & Fuels

Table 3. Base Operating Point Conditions Parameter

Value (s)

Swirl number

5.41

Power input from the blend

10 kW

Pilot power input

0.5 kW

Primary air pre-heater power

1.5 kW

Primary air temperature at swirl box

320-337 ℃

Fuel (pyrolysis liquid/ethanol) flow rate

33.3 mL/min

Primary air flow rate

241-255 SLPM

Equivalence ratio

0.6-0.63

Atomizing air flow rate

23.2 SLMP

AUTHOR INFORMATION Corresponding Author *Telephone: + 1-416-580-3391. Fax: +1-416-978-7753. Email: [email protected] Present Addresses Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, OntarioM5S 3G8, Canada Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally.


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NOMENCLATURE ALR=air-to-liquid mass flow ratio in the nozzle [(kg/s)air/(kg/s)fuel] ASTM=American Society for Testing and Materials CRZ=central recirculation zone FID=flame ionization detector FTIR=Fourier transform infrared (spectrometer) HMW=high molecular weight PM=particular matter SLPM=standard liters per minute SMD=Sauter mean diameter (µm) TG=thermogravimetric THC=total hydrocarbon d= orifice diameter (mm) U=velocity (m/s) µ=dynamic viscosity (Pa s or Kg m-1S-1)


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REFERENCES [1] A. V. Bridgwater, "Biomass Pyrolysis," Report IEA Bioenergy, 2007. [2] S. P. Krumdieck and J. W. Daily, "Evaluating the Feasibility of Pyrolysis Oil for Spray Combustion Applicatons," Combustion Science and Technology, vol. 134, no. 1, pp. 351365, 1998. [3] ASTM Standard ASTM D7544 - 12, 2003, “Standard Specification for Pyrolysis Liquid Biofuel," ASTM International, West Conshohocken, PA, 2012, DOI: 10.1520/D7544-12, www.astm.org [4] T. Tzanetakis, N. Farra, S. Moloodi, W. Lamont, A. McGrath and M. J. Thomson, "Spray Combustion Characteristics and Gaseous Emissions of a Wood Derived Fast Pyrolysis Liquid-Ethanol Blend in a Pilot Stabilized Swirl Burner," Energy & Fuels, vol. 24, pp. 5331-5348, 2010. [5] T. Tzanetakis, S. Moloodi, N. Farra, B. Nguyen and M. J. Thomson, "Spray Combustion and Particulate Matter Emissions of a Wood Derived Fast Pyrolysis Liquid-Ethanol Blend in a Pilot Stabilized Swirl Burner," Energy & Fuels, vol. 25, pp. 1405-1422, 2011. [6] C. Branca and C. Di Blasi, "Devolatilization and Heterogeneous Combustion of Wood Fast Pyrolysis Oils," Industrial & Engineering Chemistry Research, vol. 44, pp. 799-810, 2005. [7] A. Chaala, T. Ba, M. Garcia-Perez and C. Roy, "Colloidal Properties of Bio-oils Obtained byVacuum Pyrolysis of Softwood Bark: Aging and Thermal Stability," Energy & Fuels, vol. 18, pp. 1535-1542, 2004. [8] A. Oasmaa and E. Kuoppala, "Fast Pyrolysis of Forestry Residue. 3. Storage Stability of Liquid Fuel," Energy & Fuels, vol. 17, pp. 1075-1084, 2003. [9] M. Garcia-Perez, A. Chaala, H. Pakdel, D. Kretschmer, D. Rodrigue and C. Roy, "Multiphase Structure of Bio-Oils," Energy & Fuels, vol. 20, pp. 364-375, 2006. [10] M. E. Boucher, A. Chaala, H. Pakdel and C. Roy, "Bio-Oils Obtained by Vacuum Pyrolysis of Softwood Bark as a Liquid Fuel for Gas Turbines. Part II: Stability and Ageing of Bio-oil and its Blends with Methanol and a Pyrolytic Aqueous Phase," Biomass & Bioenegy, vol. 19, pp. 351-361, 2000. [11] D. C. Elliott, "Water, alkali and char in flash pyrolysis oils," Biomass and Bioenergy, vol. 7,


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pp. 179-185, 1994. [12] S. Czernik, D. K. Johnson and S. Black, "Stability of Wood Fast Pyrolysis Oil," Biomass and Bioenergy, vol. 7, pp. 187-192, 1994. [13] J. P. Diebold and S. Czernik, "Additives to Lower and Stabilize the Viscosity of," Energy & Fuels, vol. 11, pp. 1081-1091, 1997. [14] X. Ren, J. Meng, A. M. Moore, J. Chang, J. Gou and S. Park, "Thermogravimetric Investigation on the Degradation Properties and Combustion Performance of Bio-oils," Bioresource Technology, Vol. 152, pp. 267-274, 2014.S. [15] X. Jiang, Z. Zhong, N. Ellis and Q. Wang, "Aging and Thermal Stability of the Mixed Product of the Ether-Soluble Fraction of Bio-oil and Bio-diesel," Chemical Engineering Technology, Vol. 34, No. 5, pp. 727-736, 2011. [16] D.C. Elliott, A. Oasmaa, D. Meier, F. Preto, A. Bridgwater, “Results of the IEA Round Robin on Viscosity and Aging of Fast Pyrolysis Bio-oils: Long-Term Tests and Repeatability” Energy and Fuels, vol. 26, pp.7362-7366, 2012. [17] D. Chen, J. Zhou, Q. Zhang, X. Zhu, "Evaluation methods and research progresses in bio-oil storage stability," Renewable and Sustainabl Energy Reviews, vol. 40, pp. 69-79, 2014. [18] S. Moloodi, T. Tzanetakis, B. Nguyen, M. Zarghami-Tehran, U. Khan and M. J. Thomson, "Fuel Property Effects on the Combustion Performance and Emissions of HardwoodDerived Fast Pyrolysis Liquid-Ethanol Blends in a Swirl Burner," Energy & Fuels, vol. 26, no. 9, pp. 5452-5461, 2012. [19] T. Tzanetakis, "Spray Combustion Characteristics and Emissions of a Wood Derived Fast Pyrolysis Liquid-Ethanol Blend in a Pilot Stablizied Swirl Burner," Mechanical and Industrial Engineering, University of Toronto, PhD Thesis 2011. [20] S. Moloodi, "Experimental Investigation of the effects of Fuel Properties on Combustion Performance and Emissions of Biomass Fast Pyrolysis Liquid-Ethanol Blends in a Swirl Burner," Mechanical and Industrial Engineering, University of Toronto, MASc Thesis 2011. [21] Gupta, A. K.; Lilly, D.G.; Syred, N. swril Flows; Abacus Press: Tunbridge Wells, Kent, England, 1984. [22] Lefebvre, A.H. Atomization and Sprays; Taylor & Francis New York, 1989.


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[23] T. Tzanetakis, N. Ashgriz, D.F. James, and M.J. Thomson, "Liquid fuel properties of a hardwood-derived bio-oil fraction," Energy and Fuels, vol. 22, no. 4, pp. 2725-2733, 2008.


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Effects of Fuel Aging on the Combustion Performance and Emissions

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