Interesterification optimization of waste cooking oil and ethyl acetate over homogeneous catalyst for biofuel production with engine validation

Applied Energy xxx (xxxx) xxx–xxx

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Interesterification optimization of waste cooking oil and ethyl acetate over homogeneous catalyst for biofuel production with engine validation Sathaporn Chuepenga, Cholada Komintarachatb, a b

⁎

ATAE Research Group, Department of Mechanical Engineering, Faculty of Engineering at Sriracha, Kasetsart University, 199 Sukhumvit Road, Chonburi 20230, Thailand Department of Basic Science and Physical Education, Faculty of Science at Sriracha, Kasetsart University, 199 Sukhumvit Road, Chonburi 20230, Thailand

H I GH L IG H T S

G R A P H I C A L A B S T R A C T

cooking oil and ethyl acetate • Waste interesterification over homogeneous catalysts.

on low-cost feedstock, gly• Benefits cerol-free yields, and mild reaction conditions.

of sodium hydroxide/oil • Optimization and ethyl acetate/oil at temperature and time.

optimized biofuel validation in a • The diesel engine for combustion and efficiency.

exhaust gas emissions, smoke, and • The particle number were explored and discussed.

A R T I C LE I N FO

A B S T R A C T

Keywords: Biofuel Catalyst Ethyl acetate Glycerol-free Homogeneous Waste cooking oil

The interesterification of waste cooking oil (WCO) and ethyl acetate (ETA) are investigated in homogeneous catalyst system using sodium hydroxide (NaOH) and acetic acid (CH3COOH). Later on, the subsequent biofuel has been investigated for the combustion characteristics, gaseous and particulate matter related emissions in a single-cylinder agricultural diesel engine. In the reaction, fatty acid ethyl esters were the main product whereas triacetin by-product was formulated in a single phase biofuel. The parameters affected the free fatty acid (FFA) conversion were studied such as catalyst system, molar ratio of ETA:WCO, molar ratio of catalyst:WCO, reaction time, and temperature. The experimental results revealed that NaOH was more favorable than the acid catalyst counterpart. The 92% biofuel yield was reached from the optimization at the NaOH:WCO of 0.015:1 M ratio and the ETA:WCO of 30:1 M ratio at 80 °C in 3 h. In the engine validation at 3.4 and 6.6 bar IMEP loads, 1700 rpm speed, the results from the combustion analysis using an indicating system reveal that the WCO biofuel initiates the combustion faster with pronounce premixed combustion regime than that of diesel fuel. The specific fuel consumption of WCO biofuel was greater, leading to a slight reduction in brake thermal efficiency by 4% and 10% at 3.4 and 6.6 bar IMEP loads, respectively compared with diesel fuel. The nano-particle emissions was characterized by an electrical mobility spectrometer and analyzed in terms of particle number. The total particle number increased with smaller size when fueling with WCO biofuel. In comparison over the loads tested, the total particle number concentrations were in the ranges of 8.1 × 1011 to 1.1 × 1012 m−3 for WCO biofuel and 4.8 × 1011 to 5.7 × 1011 m−3 for diesel fuel. Meanwhile, the particle sizes were in the ranges of 182–251 nm for WCO biofuel and 279–402 nm for diesel fuel. Summarily, for the biofuel production, this homogeneous process is beneficial in terms of low-cost feedstock, glycerol-free and mild reaction condition.

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Corresponding author. E-mail address: [email protected] (C. Komintarachat).

https://doi.org/10.1016/j.apenergy.2018.09.085 Received 4 May 2018; Received in revised form 6 July 2018; Accepted 8 September 2018 0306-2619/ © 2018 Published by Elsevier Ltd.

Please cite this article as: Chuepeng, S., Applied Energy, https://doi.org/10.1016/j.apenergy.2018.09.085

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N (m−3) number concentration n diluted multiple of ethyl ester N (m−3) total number concentration N (rpm) engine speed Na+ sodium ion NaOH sodium hydroxide Na2SO4 sodium sulfate NO (g/kW h) nitric oxide NOx (g/kW h) nitrogen oxides P (bar) in-cylinder pressure Pb (kW) brake power Pi (kW) indicated power PM particulate matter POP persistent organic pollution QHV (MJ/kg) lower heating value rpm revolution per minute SOC (deg) start of combustion SOI (deg) start of injection TA triacetin TG triglyceride TGA thermogravimetric analysis THC (g/kW h) total unburned hydrocarbon u (nm) maximum particle size V (m3) cylinder volume Vd (m3) displaced volume VOF volatile organic fraction WCO waste cooking oil γ specific heat ratio ηth (%) brake thermal efficiency θ (deg) crank angle ρoil (g/ml) density of waste cooking oil

Nomenclature AV acid value bsfc (g/kW h) brake specific fuel consumption CaO calcium oxide CH3COOH acetic acid Cester (g/ml) mass concentration of fatty acid ethyl ester CMD (nm) count mean diameter CO (g/kW h) carbon monoxide DMC dimethyl carbonate Dp (nm) equivalent diameter DOC diesel oxidation catalyst DPF diesel particulate filter dQn/dθ (J/deg) heat release rate EGR exhaust gas recirculation EMS electrical mobility spectrometer EOC (deg) end of combustion ETA ethyl acetate FFA free fatty acid FAEE fatty acid ethyl ester FAME fatty acid methyl ester FID flame ionization detector FT-IR fourier transform infrared GC gas chromatographer IMEP (bar) indicated mean effective pressure IPA isopropyl acetate L (nm) minimum particle size mactual (g)actual mass of ethyl acetate MTA methyl acetate mtheoretical (g) theoretical mass of ethyl acetate ṁ f (g/h) fuel mass consumption rate

1. Introduction

of the transesterification reactions that has to be removed prior to use the product as the biofuel [12]. The contaminated glycerol separated from biofuel production contains impurities such as alcohols, fatty acid alkyl esters, and some salts from the reaction processes [13], leading to decrease the biofuel yields [14]. To eliminate the glycerol, removal step for attaining high yield is crucially required [15]. One promising technique is the immobilize lipase catalyze interesterification of oil and ethanol in a fluidized bed reactor coupling with a column of glycerol removing simultaneously [16] or even using a tri-component of methanol, oil and dimethyl carbonate (DMC) as reactants over calcium oxide (CaO) catalyst [17]. Recently, some acyl acceptors such as methyl acetate (MTA) [18], isopropyl acetate (IPA) [19], ethyl acetate (ETA) [20] have been trial into the reactions to produce biofuel without glycerol formation. The interesterification reaction of oil with MTA or ETA produces esters and glycerol triacetate by-product [21]. Glycerol triacetate (commonly known as triacetin, TA) is an oxygenated compound that can be widely used as plasticizer in plastic molding [22], food [23], and pharmaceutical [24] industries and can be also included in biofuel formulation [24]. TA can be directly produced from esterification of glycerol and acetic acid using Amberlyst-15 as a catalyst [25]. Furthermore, TA can be miscible in FAEE and improves biofuel quality as an additive [26]. It can be, therefore, blended without additional separation step to remove this by-product. In addition, the ETA is commonly used with enzyme to produce biofuel at a cost [20]. ETA and oil feedstock can be synthesized under non-catalytic supercritical condition. However, suitable production methods for the latter are involve to energy utilization [27]. From the previously mentioned advantages and technological advance, WCO becomes more favorable in terms of environmental

Depletion and fluctuated price of fossil fuel in the past few decades have led worldwide intensification to find and seek for the alternative fuels [1]. Biofuel is one of the liquid fuels that can be used in diesel engine vehicles [2]. The initial generation of biofuel is directly produced from food crops through fermentation such as bioethanol [3] or transesterification as biodiesel [4]. The second generation biofuels are produced from agricultural products [5] and wastes such as wood, straw, corn and specific biomass crops, consequently avoiding the global concerns in food price and scarcity. Due to their biological source derivatives, main advantages of these biofuels in replacing petroleum fuels are their renewability, combustion-generated exhaust gas emissions [2], and biodegradability [6]. An important issue affected on large-scale biofuel production is a cost of oil-bearing raw materials that account for the total manufacturing costs [7]. To overcome the cost barrier of feedstock, waste cooking oils (WCO) is one of the attractive options to produce biofuel [8]. Biofuel can be synthesized from biomass conversion processes through esterification and transesterification with biocatalyst [9] and acid or base catalysts. In the latter process, triglyceride or free fatty acid (FFA) in oil can be reacted with acyl acceptor solvent as short chain alcohols (ethanol or methanol) in the presence of a strong base. In comparison, ethanol is preferred for the reaction as it can be derived from renewable non-toxic resources [10]. Furthermore, its derivative fatty acid ethyl ester (FAEE) contains higher heat content and cetane number. These fuel properties are surpass to fatty acid methyl ester (FAME) where the superfluous carbon is contained in ethanol [11]. In the first generation of biofuel production, glycerol is a by-product 2

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examined [38]. WCO biofuel reduces the total number of particles emitted from the engine with respect to the diesel fuel. By this consequence, there are some knowledge gaps of WCO biofuel production and usage that could affect to diesel engine operation. The novelty of this work associates to a source and methodology for biofuel production in relevance to applied energy as well as the utilization effects on a real diesel engine application. A source of low FFA (FFA < 3%) WCO was under the batch reaction in mild condition with ETA over basic or acid catalyst that gives soap-free and glycerol-free yields. The subsequent biofuel was tested for properties and run in a single cylinder diesel engine equipped with precise engine control system for verification. Unlike other published work, other factors concerning to cylinder-to-cylinder variation can be segregated. By this theme, the combustion characteristics and combustion related exhaust gas emission can be quantified and compared without perturbation from other cylinders. The main objective of this work is to examine the WCO based biofuel production with ETA as an acyl acceptor that leads to the determination of interesterification kinetics under the variation of catalyst system, molar ratio of ETA:WCO, molar ratio of catalyst:WCO, reaction time, and temperature. The scope of this work is to optimize the key parameters of interesterification using ETA as an acyl acceptor for the preparation of biofuel from WCO. The experiments were accomplished in a batch reactor to evaluate the effects of those parameters on biofuel yields without glycerol formation. The advantage of these reactants is to simultaneously synthesize biofuel and its additive. Later on, this work also aims to study the combustion characteristics, fuel consumption and efficiency, and exhaust emissions from the WCO biofuel combustion. The experimental will be conducted using an agricultural single cylinder diesel engine running at a constant speed, low and medium loads. Smoke opacity and particle number-size distribution with their corresponding total number-concentrations will be analyzed and compared. The key findings of this work will be explained and discussed.

concerns incorporated with the ETA that exhibits a promising substance to produce biofuel. The WCO at low cost as a raw material inherently contains high FFA, moisture, and some residual burnt foods. It should be, therefore, prepared for the interesterification [28] as the high FFA tends to form soap with the base catalyst that reduces the reaction yield and significantly interferes the purifying process [29]. Practically, FFA content in oil should be less than 3%w/w, but if the oil having higher FFA > 3% w/w, acid esterification process is necessary prior to the interesterification process [30]. Previous published work concerning the use of WCO biofuel in diesel engine with or without engine modification have been revealed. WCO biofuel burned in diesel engine resulted in different combustion characteristics. Geng et al. [31] verified a large marine diesel engine using WCO biofuel at various loads and speeds. When the test engine operated at low load, the heat release rate was decreased by 14.3%. In other application, Buffi et al. [32] found out that the heat release and exhaust gas emissions from the combustion of hydro-treated renewable jet fuel derived from used cooking oil and its blends were different from the conventional fossil Jet A-1 fuel. The hydro-treated renewable jet fuel can reduce emissions by generating a more homogenous heat release zone, reducing localized hot-spots that lead to the generation of soot and thermal NOx (nitrogen oxides) and increasing combustion pressure that compacts the flame at constant thermal power. Meanwhile, García-Martín et al. [33] produced waste cooking oil based biofuel in an oscillatory flow reactor and tested in a TDI diesel engine for performance. In the biofuel production, biofuel yield in oscillatory flow reactor was higher than in stirred tank reactor under the same experimental conditions. The composition and properties of the resulting biofuel did not depend on reactor type. For the engine test, specific fuel consumption, particle size distribution and concentration of exhaust gas emissions were analyzed and quantified to ensure the viability of using this biofuel in vehicle engines. In aspect of environment, many methods for mitigating diesel exhaust toxics have been developed. Both regulated and unregulated emissions were quantified in a 4-cyclinder natural aspirated DI diesel engine fueled with neat diesel, biofuel and their blends under the Japanese 13-mode test cycle [34]. With an increase of biofuel in the blended fuel, there were reductions of total unburned hydrocarbon (HC), carbon monoxide (CO) and particle mass concentrations but an increase in NOx. For the unregulated emissions, formaldehyde, acetaldehyde, propene, and ethene emissions increased with increasing biofuel content. For the aromatics emissions, biofuel addition led to an increase in benzene emission but reductions in toluene and xylene emissions. Key findings about diesel particulate matter have been extensively revealed. The typical particle size characterization of diesel particulate matter is in form of tri-modal and log-normal distribution [35]. Ranging from 5 to 50 nm diameter, spherical primary particles in light-weight are commonly known as the nucleation mode. Subsequently, primary particles are agglomerated into aggregates, fractal-like particles with equivalent diameter ranging from 50 to 1000 nm, called the accumulation mode. Lastly, the coarse mode contains particles larger than 1000 nm in equivalent diameter. A number of published work versatilely studied on particulate matter (PM) from the combustion of neat or blended WCO biofuel. Chen et al. [36] investigated the persistent organic pollutant (POP) emissions from a diesel engine equipped with a diesel oxidation catalyst (DOC) combined with an uncatalyzed diesel particulate filter (DPF) using WCO biofuel blends (B10 and B20). The WCO biofuel with a lower aromatic content reduced the precursors for POP formation, and its higher oxygen content compared to diesel promoted more complete combustion. The PM nanostructure from diesel engine fueled with WCO biofuel was extensively studied [37]. By thermogravimetric analysis (TGA), when WCO biofuel quantity increases in the fuel, PM shows a higher volatile organic fraction (VOF). In a diesel city car, the particle number – size distributions from the combustion of WCO biofuel were also

2. Experimental apparatus 2.1. Materials The WCO was collected from local restaurants in the university canteen without segregation of animal fats or vegetable oils whereas its acid value was determined regarding the methodology described in Section 2.3. All chemical reagents for gas chromatographer (GC) standards such as ethyl palmitate, ethyl oleate, ethyl linoleate and TA were analytical grade from Sigma-Aldrich. For solvents, ETA and n-hexane were from Fisher Chemicals. Homogeneous catalysts used in this work are sodium hydroxide (NaOH) and acetic acid (CH3COOH) from Merck. Anhydrous sodium sulfate (Na2SO4) was supplied by Ajax Fine Chemicals.

2.2. Catalytic interesterification reaction The interesterification reaction was performed at specified temperature in a 250 ml two-neck round bottom flask equipped with a water-cooled condenser by refluxing of ETA with WCO and catalyst at different reaction times, immersed in a temperature-controlled bath. After completion of the reaction, the excess ETA in a single phase of mixture was removed by rotary evaporator. The yield was later washed by distilled water (1:1 v/v) in a separated funnel until neutral; the yield was subsequently filtered through Na2SO4 to remove water, and the final product was then obtained. All reactions were conducted in triplicate and their standard deviation values are used to present as error bars in Section 3.

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2.3. Analysis of products by gas chromatography

Table 1 Engine specification.

The FAEE and TA compositions in the product were analyzed using GC (Varian, Model CP-3800) [39], equipped with a flame ionization detector (FID) and a capillary column (CB, Model CP WAX 52) in 30 m × 0.25 mm × 0.25 μm size at 1:20 split injection ratio. The temperature of the injector and the detector were kept at 230 °C and 290 °C, respectively. The column oven was initially kept at 150 °C for 5 min, then heated up to 245 °C at a rate of 20 °C/min, and kept constant at the final temperature for 10 min. Hydrogen was used as the carrier gas of the GC operating at a flow rate of 2.8 ml/min while the pressure in the column was set at 15 psi. To get access to the test data, a computer loaded with the Star Workstation 6.2 software was connected to the GC by a Star 800 Module Interface. The TA dissolved in n-heptane was quantified by external calibration curves of standard. The FAEE were identified by comparing their retention times of ethyl esters standard and the FAEE quantification were based on external calibration using standard solutions of FAEE (ethyl palmitate, oleate, stearate, and linoleate) at a 0.01 to 5 mg/ml concentration range in n-hexane. The FAEE yield in each experiment was calculated by Eq. (1) [40]:

FAEE =

mactual n × Cester × 100% ≈ mtheoretical ρoil

Properties

Specification

Engine type Combustion type Bore × Stroke Displaced volumeMaximum torque Maximum power Maximum torque Compression ratio Fuel injection system

1-cylinder, water cooled Direct injection 88 mm × 90 mm 547 cc 7.4 kW at 2,400 rpm 33.4 Nm at 1,600 rpm 18:1 Pump-line-nozzle type

range of 4000 cm−1 down to 400 cm−1 with 4 cm−1 resolution. All transmittance measurements were compared with the FAEE spectra [41,42]. 2.5. Engine test rig The synthesized WCO biofuel was validated in an agricultural diesel engine (Kubota, Model RT 100) on the test bench equipped with measurement apparatus as shown in Fig. 1 while the engine specification is concisely shown in Table 1. The engine was loaded by an engine dynamometer with the maximum capacity of 15 kW. A load cell (Vishay Tedea - Huntleigh, Model 613) for the engine dynamometer insists the maximum capacity of 50 kg load with its 2 mV/V sensitivity and ± 0.02% total error of rated output. The measurement accuracy for revolution speed from the engine dynamometer in speed control mode was ± 10 rpm. The engine validation system also involved other standard engine test rig instrumentation, i.e. several local temperature measurement devices. Atmospheric conditions in terms of temperature, pressure, and humidity were also recorded in order to use for cylinder pressure and exhaust gas emission corrections. All these data were recorded by a data

(1)

where both mactual and mtheoretical are the actual and theoretical masses of ethyl esters, respectively in g, Cester is the mass concentration of FAEE in g/ml acquired by the GC, n is the diluted multiple of ethyl ester, and ρoil is the density of the WCO in g/ml. 2.4. Analysis of products by Fourier transform infrared spectroscopy A Fourier transform infrared (FT-IR) spectrometer (JASCO, Model4100) was applied to qualify the biofuel from the production. The measurement of transmission was performed using 16 scans in the

Electrical signals Cooling water Diesel fuel Exhaust Air

1

2 3

4

Computer 10, 11

7 12

6

14 8 5

17

16

9

15

13 20 21 18

22

19

Fig. 1. Diagram of the engine test rig. 4

1: Diesel fuel reservoir 2: Submersible fuel pump 3: Fuel heat exchanger 4: Fuel measurement unit 5: Fuel injector 6: Air flow sensor 7: Charge amplifier 8: Pressure transducer 9: Incremental shaft encoder 10: Combustion analyzer 11: Data acquisition software 12: Air filter 13: Test engine 14: Dynamometer controller 15: Engine dynamometer 16: Direct connection 17: Air-to-liquid heat exchanger 18: Silencer 19: Tailpipe 20: Particle sampler 21: Exhaust gas analyzer 22: Smoke meter

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Furthermore, the constant engine loads of 3.4 and 6.6 bar IMEP (indicated mean effective pressure, see Section 2.11 for definition) were respectively tested as to simulate for 25% and 50% of the maximum engine load, regularly used in real engine operating conditions.

acquisition board (National Instruments, Model USB-6218) installed in a Windows-based PC with the in-house developed LabVIEW based software. 2.6. Air and fuel metering systems

2.11. Definition of the engine operating parameters The air consumed by the engine was measured by a flow meter (Benetech, Model GM8901) with accuracy in the range of ± 3% of reading. Diesel fuel flow rate was measured on mass basis using a balance (CST, Model CDR-3) with accuracy of ± 0.05 g. The fuel temperature was controlled at 40 ± 1 °C using a liquid-to-liquid heat exchanger immersed in a bath (Lauda, Model Ecoline 011) with temperature controller (Lauda, Model E200).

Indicated mean effective pressure (IMEP) is the value of pressure indicating the performance of an engine. The IMEP value is used to compare performance of two engines having different displaced volume (Vd) and speed (N), obtained from

IMEP=

2Pi Vd N

(2)

where Pi is indicated power, the rate of the work transferred from pressurized gas inside the engine cylinder to the piston. The brake specific fuel consumption (bsfc) is the fraction between fuel mass consumption rate (ṁ f ) and brake power (Pb), obtained from

2.7. Combustion analyzer The combustion in the engine validation was examined by means of cylinder pressure data corresponding to the position of the crankshaft. The combustion pressure in the cylinder was measured by a pressure transducer (Kistler, Model 6052C) with its sensitivity of −19.90 pC/bar at 200 °C and linearity of ± 0.4% FSO. The signal has been sent to the charge amplifier (Dewetron, Model DEWE-30-4) in order to magnify and filter the signal from the pressure transducer. Meanwhile, an incremental shaft encoder (Baumer Electric, Model BDK 16.05A360-5-4) was used to determine the position of the engine crankshaft rotation at the rate of 360 pulses per revolution. All signals were sent to the data acquisition system (Dewetron, Model DEWE-ORION-0816-100x) at the sampling rate of 1 MS/s. The cylinder pressure traces were analyzed using the DEWEsoft V6.6.9 software. Cylinder pressure traces of 100 consecutive cycles were averaged and were then used to represent the values of the combustion characteristics in each test condition.

bsfc=

ṁ f Pb

(3)

The brake thermal efficiency (ηth) is the ratio between produced work per cycle and chemical energy in the fuel, calculated from

ηth =

Pb ṁ f QHV

(4)

where QHV is the fuel lower heating value and Pb is brake power. The values of in-cylinder pressure corresponding to crankshaft angle position are used to calculate the heat release rate (dQn/dθ) of the combustion in the engine: the fuel chemical energy suppressed by the heat loss to cooling system. The calculation condition is assumed to be the ideal gas condition in angle position domain, following:

2.8. Engine exhaust analyzer

dp γ dV 1 dQn = p + V dθ γ −1 dθ γ −1 dθ

The combustion generated exhaust gas from the test engine composed of total unburned hydrocarbon (THC), carbon monoxide (CO), and nitric oxide (NO), the main constituent of nitrogen oxides (NOx), were measured by an analyzer (Horiba, Model MEXA-584L) on a dry basis. Black smoke was measured by a smoke meter (Motorscan, Model Smoke Module 9010) based on the light intensity absorbed and will be reported in term of opacity percentage. The measurement range and accuracy of the exhaust gas and smoke emissions are gathered in Table 2.

(5)

where θ is crank angle in degree and γ is specific heat ratio. The latter was directly obtained from each experimental condition assuming that the pVγ was constant in the compression and expansion strokes. The ignition delay is defined as the time interval in degree of the crankshaft from the start of injection (SOI) of the diesel fuel to where the rate of heat release turns to the positive value, called the start of combustion (SOC). The latter occurs after the diesel fuel is injected and absorbs heat from surrounding to vaporize (negative value of the heat release rate). The combustion duration is defined as the time interval in degree of the crankshaft from the start of combustion to the end of combustion (EOC) where the heat release rate turns into zero in the expansion stroke. For the PM characterization, the number concentration (n) can be directly obtained by the measurement in each specified size range. The total number concentration (N) is the summation of number concentration in all size ranges calculated by:

2.9. Particulate matter number determination The measurement of particle number and size was a full-flow sampling of a small portion of the exhaust gas, approximately 40 cm downstream of the exhaust manifold. The PM contained exhaust gas was isokinetically drawn at the constant volumetric flow rate of 3 lpm into an Electrical Mobility Spectrometer (EMS) (Fabix, Model DusTEC). The EMS is able to measure particles in ten size ranges between 18 and 2200 nm at 60 s time response [43]. The particle number size distributions shown in the following sections are one minute averages that are representatives for each steady state engine test condition. The distribution of particle number concentration is presented in the unit of number per cubic meter, over the interval of particle size. The particle size is shown as an equivalent diameter (Dp) of count mean diameter (CMD) as the particle is not apparently spherical.

u

N=∑ n

(6)

l

where l and u are the minimum and maximum particle sizes, respectively. The PM mean diameter can be calculated in count mean diameter Table 2 Exhaust analyzer measurement range and accuracy.

2.10. Engine test condition

Component

Range

Accuracy

The engine was tested without exhaust gas recirculation (EGR) and without engine modification. The engine speed of 1700 rpm chosen is by the frequent use of loaded application (agricultural purposes) and is near by the maximum torque occurrence produced by the engine.

THC CO NO Smoke

0–10,000 ppm vol. 0–10% vol. 0–4000 ppm vol. 0–100% opacity

1.7% of reading 1.7% of reading 4% of reading ± 0.1% opacity

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ETA is beneficial for the interesterification reaction due to its reverse reaction that can escalate the yield of ethyl esters. Generally, a molar ratio of ETA to TG is 3:1, equivalent to three-mole FAEE and one-mole TA. By this fact, it is therefore in this work, that the molar ratio of ETA and oil were trail to increase from 10:1 to 40:1as an envelope for the reaction condition in order to examine the effects of ETA for the reaction to attain biofuel. Fig. 5 shows the biofuel yields under different amounts of ETA:WCO at 80 °C by 0.015:1 M ratio of NaOH to WCO in 3 h. The NaOH to WCO molar ratio of 0.015 was chosen for the analysis as by the results obtained from the previous optimization. In Fig. 5, the conversion of FFA was achieved by 78% and at this point, the FAEE yield was up to 80% w/w in 3 h when the ratio of ETA to WCO was at 30:1. More or less other than this ETA to WCO ratio, no biofuel yields can be further improved. The optimum amount of ETA at 30 folds over an oil molar ratio is therefore suitable for this study.

(CMD) following:

CMD=

u ∑l

nDp (7)

N

3. Results and discussion 3.1. Identifying the free fatty acid in the WCO feedstock The collected WCO was preconditioned as previously described and determined for key properties. Hundred samples of WCO with one liter each were measured for acid value (AV) by titration using a standard sodium hydroxide solution. In accumulation, the WCO used in this study was statistically averaged by normal distribution. The resultant AV of the collected WCO was by 3.92 AV, equivalent to 2.764% w/w of FFA content determined by the AOCS official method Ca 5a-40 based on oleic acid and saponification value which calculated from the AOCS official method Cd 3–25. The relationship of FFA and AV can be calculated by:

%FFA(w /w ) = Acid value ×

3.4. Effect of reaction time and temperature on biofuel production The reaction temperature was also examined for biofuel yields. The conditions for the evaluation were at 60, 80 and 100 °C in 1, 2 and 3 h of reaction time by keeping the remaining reactions parameters to be constant; the molar ratios of NaOH to WCO and ETA to WCO were by 0.015:1 and 30:1, respectively. In effects of reaction time and temperature, biofuel yields results are presented in Fig. 6. Fig. 6 shows the biofuel yields for the condition: 0.015:1 M ratio of NaOH to WCO, 30:1 M ratio of ETA to WCO under the variation of reaction times and temperatures. It can be seen from the graphs that the TG and FFA rapidly converted to biofuel within the first 3 h whereas the yield significantly increased up to 82% for 80 °C reaction temperature. During the reaction with ETA at its boiling point (75 °C) the maximum yield (72% w/w) was reached in 30–35 min. Meanwhile, the reaction with isopropyl acetate at its boiling point (87 °C) proceeds so fast; the ester content (71% w/w) was raised to approximately the same as of ethyl acetate at its boiling point. This unexpected result can conclude that all the investigated interesterification reactions at the boiling point of alkyl acetate reached equilibrium in one hour by the use of optimal concentration of catalyst and alkyl acetate to oil molar ratio.[19] In addition, the biofuel yields were increasing over the time for reaction as set to the maximum of 3 h. Depending on the test condition and quality of the WCO used, the subsequent results are similar to those accomplished by Elsheikh et al. [47] in that this condition reached steady state. Accordingly, with the fixed operation conditions applied to the present study, the reaction time of 3 h at 80 °C assigned for the reaction condition was satisfied by reducing the acid WCO down to 0.41% and the biofuel yield of up to 90% was obtained. In the aspect of reaction temperature, the homogeneous system of WCO and ETA reactants over the NaOH catalyst has no limitation of the phase whereas the increasing reaction temperature accelerates the chemical reaction [48] that enhances the miscibility and mass transfer of the substances. The results shown in Fig. 6 also indicate that the conversion of FFA increased as the reaction temperature increased from 60 to 80 °C in 3 h of reaction time. When the reaction temperatures were reaching to 100 °C, the rate of the FFA conversion can be noticed. In this circumstance, the overheated temperature causes thermal deactivation of ETA where its boiling point is approximately 77 °C [49].

Oleic acid molecular weight Potassium hydroxide molecular weight (8)

The parameters influencing to biofuel yields are revealed and discussed as the followings. 3.2. Effects of catalyst on biofuel production The different types of catalyst for the presented WCO at the FFA of 2.764% w/w were first investigated. In the homogeneous system of mixture for interesterification used in this work, sodium hydroxide (NaOH) and acetic acid (CH3COOH) were chosen for two different types of catalyst: basic and acidic systems, respectively. The reactions were carried out under the condition of 0.01:1 M ratio of catalyst to oil and 30:1 M ratio of ETA to oil for 3 h of reaction time at 80 °C. The temperature chosen was at which the transesterification reaction of ethanol and used frying oil on NaOH catalyst reached the optimum ethyl ester [40]. As a result, Table 3 shows the conversion of FFA using NaOH and CH3COOH as a catalyst. In Table 3, it has shown that the base catalyst NaOH gave a higher yield than that of the acid catalyst (CH3COOH). By this situation, nucleophilic substitution was effective than proton attack in triglyceride [44]. NaOH was therefore used as a catalyst for further investigation. The NaOH was subsequently trial for optimum catalyst to oil ratio. By controlling the reaction condition to be at 80 °C, 3 h in a 30:1 M ratio of ETA to WCO, the results are shown in Fig. 2 with the error bars representing 95% confidence. To maximize biofuel yield, the catalyst to oil ratios in the range of 0.005–0.020 M ratio of NaOH to WCO were chosen regarding the data obtained by previous experimental investigation [31]. The increment of NaOH to WCO ratios from 0.005 to 0.015 leads to the increasing biofuel yields from 63 %w/w to the maximum value of biofuel yields at 75% w/w. The increased FFA is directly affected by the NaOH catalyst amounts that enhanced the biofuel yields of WCO. Afterwards, the biofuel yields have shown to decline to 65% w/w at the NaOH to WCO ratio of 0.020. It is noticed at this point that the conversion of FFA dropped due to water formation during the reaction that possibly inhibited the interesterification [45]. Water can break the base molecule apart, producing free sodium ions (Na+), that can then combine with free fatty acids to produce soap which can deactivate the catalyst [46] (Fig. 3).

Table 3 Biofuel yield in homogeneous catalyst system of CH3COOH and NaOH.

3.3. Effect of ETA on biofuel production Fig. 4 shows the interesterification reaction of triglyceride (TG) and ETA to biofuel (in terms of FAEE) with TA by-product [27]. The excess

Catalytic system

Biofuel yield (%)* (FAEE + TA)

NaOH CH3COOH

77.5 52.4

* Condition: Reaction temperature at 80 °C in 3 h, molar ratio of ETA to WCO = 30:1 and molar ratio of catalyst to WCO = 0.01:1. 6

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100

Table 4 shows the fuel properties of diesel and WCO biofuel. It was found that the WCO biofuel density was higher than diesel fuel (0.8255 kg/l) due to the presence of TA by-product. TA has a high density of 1.183 kg/l, making WCO biofuel denser than diesel [26]. Viscosity affects the fuel injection duration and the increase in fuel injection rate and pressure. The WCO biofuel is slightly thicker than diesel and considered insignificantly affect to the start of combustion. Cetane number shows flammable properties by which the WCO biofuel has a higher cetane number, indicating that the shorter ignition delays may be observed [53]. Heating value is the value for the energy release from the combustion per unit mass. WCO biofuel has a heating value lower than diesel as its structure of hydrocarbon is substituted by oxygen atom. In addition, the WCO biofuel has a larger amount of contaminated water. The water molecules become vaporized while burning. As a result, the amount of energy released is lower [26]. Sulfur content is related to particle and sulfur dioxide emissions [54]. Sulfur compounds can be a solid core of particulate matter within a volatile organic fraction of hydrocarbon compounds. In this case, when the lower sulfur content WCO biofuel is used, a smoke opacity may be seen in lower level.

TA FAEE

Biofuel yields (%)

80

60

40

20

0

0.005

0.010

0.015

0.020

Molar ratio of NaOH:WCO

Fig. 2. Effects of NaOH catalyst to WCO ratio on biofuel yield at 80 °C, 3 h in a 30:1 M ratio of ETA to WCO.

One can explain that when the reaction temperature adjacent to the boiling point of acyl acceptor, the acyl acceptor will vaporize to form bubbles which inhibit the reaction [50].

3.7. WCO biofuel combustion characteristics and performance The WCO biofuel produced at the optimum condition was subsequently validated in the diesel engine described in Section 2.5. The analysis of combustion characteristics and performance presented in the section includes the cylinder pressure traces, peak pressure, heat release rate, start and end of combustion, combustion duration, mass fraction burnt, brake specific fuel consumption, and thermal efficiency. Fig. 8 illustrates the traces of cylinder pressure and the rates of heat release versus crank angle over the late compression and the early expansion strokes of the engine running on WCO biofuel at 3.4 and 6.6 bar IMEP loads, 1700 rpm with those of diesel fuel for comparison. The results in Fig. 8 are clearly shown that, for the same load, the combustion of WCO biofuel increased rate of the fuel burning in the premixed phase, advanced the combustion to earlier crank angle positions, and increased peak pressure values over the diesel combustion. These effects can also be seen for both engine loads with the different data values. The negative heat release rates for both fuels obviously seen after the start of injection denotes the fuel that requires heat for vaporization prior to combustion. The starts of combustion for WCO biofuel combustion are shown in Fig. 9. It is apparently that the start of combustion for WCO biofuel was taken place earlier than that of diesel combustion, by 0.11° and 2.13° crank angle at 3.4 and 6.6 bar IMEP loads, respectively. Regardless of fuel type used, the start of combustion was more advanced when running the engine at higher load. Ignition delay can be represented by comparing the start of combustion; the obtained results indicate the shorter ignition delay of WCO biofuel than diesel combustion. The advanced start of combustion and increased heat release rate and pressure have been frequently reported for the use of biofuel [53]. Fig. 9 also illustrates the combustion duration for WCO biofuel and diesel combustion for the two engine loads. At the higher load, the diesel burned longer (3.3° crank angle) than WCO biofuel while at the lower load, the difference in combustion duration was insignificantly seen (0.1° crank angle). The WCO biofuel combustion was prone to be shorter in combustion duration, due to the earlier start of combustion under the same engine load with the increased rate of the fuel burning

3.5. FT-IR spectroscopy The interesterification reaction of biofuel at the optimum condition of 0.015:1 M ratio of NaOH to WCO, 30:1 M ratio of ETA to WCO at 80 °C in 3 h were analyzed by FT-IR spectrometer. The infrared spectra of FAEE and TA are shown in Fig. 7 for transmittance percentage over the wavelength. The FT-IR spectrum of biofuel appeared at 3248, 2920, 2852, 2354, 1743, 1457 and 1156 cm−1. The characteristic bands at 3238–2852 cm−1 represented the hydroxyl (eOH) group and eCeHe stretching, respectively. The strong peaks around 1743 cm−1 was a signal from the carbonyl (C]O) stretching of esters, confirming that the triacetin was obtained [51] and 1156 cm−1 wavelength clearly presented the spectra of FAEE (CeO) [42]. The peak at 1457 cm−1 corresponded to the presence of eCH3 group in the production. The presence of eCeOe in the ester group was appeared at 1156 cm−1. The appearance of strong peak of CO2 at 2354 cm−1 of WCO was due to long storage before FT-IR analysis. The absence of 1500–1600 cm−1 absorption in biofuel spectrum indicates that there was no soap presented. In fact, soap can be formed during the base catalysis step and in the interesterification reaction of WCO and ETA over strong base NaOH catalyst. However, the sodium metal catalyst additionally binds any water traces to inhibit the formation of free glycerol and its partial acetyl esters [52], without sodium salt of fatty acid (soap) formation. Therefore, the spectral data from the transesterification products obtained via FT-IR spectroscopy indicate highly pure ethyl ester products. 3.6. WCO biofuel property comparison There were two types of fuel used in the test: diesel and WCO biofuel. The diesel fuel contains a trace of FAME by local regulation (volumetric blend of 95% petroleum diesel and 5% palm-based biodiesel). Meanwhile, the WCO biofuel was derived from the optimum production condition. Some of their key properties are numerated in Table 4.

O

O H2O Water

+

NaOH

Sodium hydroxide

Na + + Ions

OH- +

H2O + Na-O-C-R

HO-C-R Free fatty acid

Water 7

Soap

Fig. 3. Water – sodium hydroxide reaction [46].

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O H2C

O

O

O

C O

R1 O

HC

O

C O

R2

H2C

O

C

R3

+

3 CH3 COCH2CH3

Triglyceride

C2H5

O

C O

R1

C2H5

O

C O

R2

C2H5

O

C

R3

Ethyl acetate

+

H2C

C O

O

CH3

HC

C O

O

CH3

H2C

C

O

CH3

Triacetin

FAEE

Fig. 4. Interesterification of triglycerides and ethyl acetate for biofuel production [27] (R1, R2, R3 = alkyl chain of fatty acids). 100

100

TA

90

FAEE % Transmittance

Biofuel yields (%)

3248

80

80

60

40

1457

70 60

1156

40

10 0 1000

0 10

20 30 Molar ratio of ETA:WCO

40

Biofuel yield (%)

80

2920

WCO biofuel 1500

2000

2500

3000

3500

4000

Fig.7. FT-IR spectra of biofuel production from the optimum condition of 0.015:1 M ratio of NaOH to WCO, 30:1 M ratio of ETA to WCO at 80 °C in 3 h. Table 4 Fuel properties.

FAEE at 60°C FAEE at 80°C FAEE at 100°C TA

60

40

0 2 Reaction time (h)

Analysis

Method

Diesel

WCO biofuel

Density at 15 °C (kg/l) Kinematic viscosity at 40 °C (cSt) Water and sediment (%vol.) Cetane number Lower heating value (MJ/kg) Sulfur content (% w/w)

ASTM ASTM ASTM ASTM ASTM ASTM

0.8255 2.9 < 0.005 58.8 42.8 0.0037

0.9311 3.1 0.3 63.5 37.3 0.0002

D4052-11 D445-11a D2709-96 D613-10a D4809-13 D2622-10

of the fuel burnt (50% mass fraction burnt) frequently used to compare burning rate of fuel and air took 8.7° and 12.5° crank angle, for WCO biofuel, respectively at 3.4 and 6.6 bar IMEP. Meanwhile, the diesel fuel took longer time for 50% mass fraction burnt, by 11.8° and 14.4° crank angle, respectively at 3.4 and 6.6 bar IMEP. The brake specific fuel consumption is shown in Fig. 11. Apparently, the WCO biofuel consumed more fuel than the diesel fuel as the heating value of the WCO biofuel is lower than that of the diesel fuel by 12% (see Table 4 for comparison). Therefore, WCO biofuel requires a larger amount of fuel injected into the combustion chamber to produce the same power. This has caused the slight decrease in brake thermal efficiency (Fig. 11) compared to the case of diesel by 4% and 10% at the engine loads of 3.4 and 6.6 bar IMEP, respectively.

20

1

WCO feedstock

Wave number (cm-1)

Fig. 5. Effects of different amounts of ETA:WCO ratio on biofuel yield at 80 °C in 0.015:1 M ratio of NaOH to WCO in 3 h.

100

2852

1743

30 20

20

2354

50

3

Fig. 6. Effects of different reaction time and temperature on biofuel yield at 0.015:1 M ratio of NaOH to WCO and 30:1 M ratio of ETA to WCO.

in the premixed phase (Fig. 8). Regardless of the fuel type used at the higher load, the engine consumes more fuel into the combustion chamber. This causes a longer time for fuel to burn in the combustion chamber, and hence longer combustion duration. The cylinder pressure data shown in Fig. 8 were used to calculate the mass fraction burnt as appeared in Fig. 10. As previously described, the starts of combustion were different depending on fuel type and engine load used. Therefore, with the purpose of comparison on the rate of fuel burning, the starts of combustion are neglect by plotting the mass fraction burnt starting from the same timing, depicted in Fig. 10. After the start of combustion, the mass of WCO biofuel rapidly burned as shown by the steeper slope of the mass fraction burnt. The first half

3.8. WCO biofuel exhaust emissions The exhaust gas emissions described in this section are associated to total unburned hydrocarbon (THC), carbon monoxide (CO), nitric oxide (NO), and smoke opacity. Fig. 12 quantifies carbon-derived gaseous emission THC and CO. The combustion of WCO biofuel tends to reduce unburned hydrocarbon and carbon monoxide. On mass basis, WCO biofuel combustion reduced the THC emission by 41.8% and 40.5%, 8

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60

Diesel WCO biofuel

50 40

40

30

30

20

20

10

10

0

0 -40

Cylinder Pressure (bar)

(a)

50

-10 -20

0

20 40 60 Crank Angle (deg)

80

100

60

Diesel WCO biofuel

60 Heat Release Rate (J/deg)

Cylinder Pressure (bar)

60

70

(b)

50

40

40

30

30

20

20

10

10

0

0 -40

120

50 Heat Release Rate (J/deg)

70

-10 -20

0

20 40 60 Crank Angle (deg)

80

100

120

Fig. 8. Cylinder pressure and heat release rate (a) 3.4 bar IMEP and (b) 6.6 bar IMEP, 1700 rpm.

45 40

Diesel: SOC Diesel: EOC Diesel: Duration

300

WCO biofuel: SOC WCO biofuel: EOC WCO biofuel: Duration

bsfc (g/kWh), Thermal Efficiency (%)

Start and End of Combustion, Duration (deg)

50

35 30

25 20 15 10 5 0

200

150 100 50 0

6.6

3.4

Load (bar IMEP)

Fig. 11. Brake specific fuel consumption and thermal efficiency.

100

40

90

Diesel: THC Diesel: CO

35

80

WCO biofuel: THC WCO biofuel: CO

30

70

THC, CO, (g/kWh)

Mass Fraction Burnt (%)

6.6 Load (bar IMEP)

Fig. 9. Start and end of combustion, and combustion duration.

60 50 40 30

Diesel: 3.4 bar Diesel: 6.6 bar WCO biofuel: 3.4 bar WCO biofuel: 6.6 bar

20 10

0

WCO biofuel: bsfc WCO biofuel: Efficiency

250

-5

3.4

Diesel: bsfc Diesel: Efficiency

0

10

20

30 40 Crank Angle (deg)

50

60

25 20

15 10 5 0

70

3.4

6.6 Load (bar IMEP)

Fig. 10. Mass fraction burnt. Fig. 12. Total unburned hydrocarbon and carbon monoxide.

and reduced the CO emission by 54.3% and 72.4% at 3.4 and 6.6 bar IMEP loads, respectively. The oxygen content of the biofuel partly presented in the fuel may contribute to improved fuel oxidation resulting in the reduction in THC and CO emissions. The difference in engine operating conditions (3.4 and 6.6 bar IMEP) for the two fuels resulted in different amount of THC and CO emissions. Fig. 13 shows the trade-off emissions of smoke opacity and nitric oxide from the combustion of WCO biofuel and diesel at the two engine loads. For both loads, WCO biofuel combustion resulted in the lower

level of smoke opacity than that of the diesel combustion while emitting higher level of nitric oxide. In the meantime, regardless of fuel type, the engine running at the higher load generated greater level of black smoke whereas the fuel was injected in greater amount within limited combustion time and oxidizer. Apart from the oxygen content of the biofuel that may contribute to improved fuel oxidation in locally rich in fuel combustion zones, resulting in the reduction of smoke, the reduction of smoke for WCO biofuel over diesel fuel can also be attributed by

9

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Total Particle Number Concentration (m-3)

10 9

Smoke (% opacity)

8

7 6 5 4 3

Diesel: 3.4 bar Diesel: 6.6 bar WCO biofuel: 3.4 bar WCO biofuel: 6.6 bar

2 1 0

0

10

20

30

40 50 NO (g/kWh)

60

70

1.2E+12 1.0E+12 8.0E+11 6.0E+11 4.0E+11 2.0E+11 0.0E+00

80

0

100

200 300 Dp (nm)

400

500

Fig. 15. Total particle number concentration.

Fig. 13. Smoke opacity and nitric oxide emissions.

concentration at larger size. The engine running at the higher load injected a greater fuel amount that was prone to emit the particles at higher amount and larger size. Apart from engine load effects discussed in the previous section, there is the second fold to explain for the relationship between total particle number concentration and particle size as appeared in Fig. 15. One of the main reasons for the higher total particle number concentration for biofuel combustion is oxygen content in the fuel. The WCO biofuel is one of the oxygenated fuels that, during injection, a bulk fuel and air mixture nearby the core of injected fuel is intensively surrounded by oxidizer. This yields better fuel atomization with oxidizer among bulk of the injected fuel. During burning in limited time, these atomized fuel droplets has more ability to oxidize and transform into particles by increasing the number and shifting the fuel droplets to smaller sizes. In fact, larger aggregates can be formed when the particle number is higher [35], i.e. by collision. However, the combustion at this load (25% and 50% of the maximum engine load, see Section 2.10 for details) in the agricultural single-cylinder engine did not reach the stage that the larger aggregates to be formed. Therefore, the WCO biofuel particles demonstrate higher particle number at smaller size compared to diesel fuel particles. Utterly, in the real application in terms of feedstock and reactants, the low cost feedstock waste cooking oil with FFA lower than 3% w/w are crucially be supplied for batch biofuel production while ETA is readily available. For the production condition that gives soap-free and glycerol-free yields, the results from this work proved for the optimized condition for biofuel production in homogeneous catalytic system at

its significantly lower sulfur content in the fuel (see Table 4 for comparison). By this key factor, sulfur compound has been recognized for being a part of a solid carbon contained core of the particulate matter. 3.9. PM number Fig. 14 shows the distribution of particle number concentration over the range of count mean diameter (CMD) from WCO biofuel and diesel combustions at 3.4 and 6.6 bar IMEP loads, 1700 rpm. The WCO biofuel particles show a greater concentration in the nucleation and accumulation modes for both loads. One of the main parameters related to the increased concentration of particles at small sizes is the increase in fuel injection pressure for WCO biofuel. In a pump-line-nozzle fuel injection system, the increased injection pressure of biofuel was due to its higher density, viscosity and bulk modulus of compressibility. This yields better fuel atomization with smaller droplet sizes that increase PM number after combustion. Fig. 15 shows the plots of the total particle number concentration calculated using Eq. (6) and the corresponding CMD calculated using Eq. (7). The total particle number concentrations have shown to be higher for WCO biofuel at smaller size for the two load conditions tested. The total particle number concentrations for WCO biofuel and diesel were in the ranges of 8.1 × 1011 to 1.1 × 1012 m−3 and 4.8 × 1011 to 5.7 × 1011 m−3, respectively. The count mean diameter for WCO biofuel and diesel were in the ranges of 182–251 nm and 279–402 nm, respectively. Furthermore, the engine running on the higher load generated higher amount of total particle number

3.5E+11

3.5E+11 Diesel 3.0E+11

Particle Number Concentration (m-3)

Particle Number Concentration (m -3)

Diesel: 3.4 bar Diesel: 6.6 bar WCO biofuel: 3.4 bar WCO biofuel: 6.6 bar

WCO biofuel

2.5E+11

(a)

2.0E+11 1.5E+11 1.0E+11 5.0E+10

Diesel 3.0E+11

WCO biofuel

2.5E+11

(b)

2.0E+11

1.5E+11 1.0E+11 5.0E+10 0.0E+00

0.0E+00 18

38

63

96

141 211 Dp (nm)

337

18

644 1238 2200

38

63

96

141 211 Dp (nm)

337

Fig. 14. Particle number concentration – size distribution (a) 3.4 bar IMEP and (b) 6.6 bar IMEP, 1700 rpm. 10

644 1238 2200

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mild condition over the basic catalyst NaOH. The WCO biofuel derived from the optimum production condition was comparable to diesel fuel standard and viable to fuel the pump-line-nozzle diesel engine. However, material compatibility must be further investigated for durability and reliability of an engine to be fueled. In terms of usage effect, a difference in WCO biofuel properties compared to those of diesel fuel posed a difference in combustion characteristics and exhaust gas emissions as previously described. Therefore, if the WCO to be fueled in multi-cylinder diesel engines, further calibration of engine management system and/or after-treatment devices may be required to conform to emission regulations.

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4. Conclusion The biofuel production from a low cost feedstock waste cooking oil and ETA in homogeneous catalytic system was investigated for biofuel yields through interesterification. The results showed that the highest biofuel yields of 92% was attained after 3 h of reaction at 80 °C using 30:1 ETA to WCO and 0.015:1 NaOH to WCO molar ratios. The optimal parameters for achieving maximum conversion of FFA to product were dependent on the chemical and physical properties of WCO and ETA. The parameters can be recommended to complete conversion of FFA to biofuel without glycerol formation. In the engine validation, the produced WCO biofuel resulted in greater premixed combustion for both engine loads at 3.4 and 6.6 bar IMEP, 1700 rpm with the start of combustion advanced to the earlier crank angle and thus shorter combustion duration. The WCO biofuel with lower heating value consumed more fuel than that of diesel at the same load whereas the engine brake thermal efficiency slightly decreased. The brake specific fuel consumptions of the WCO biofuel were greater than those of diesel fuel by 12.9% and 18.9%, respectively at 3.4 and 6.6 bar IMEP loads. On mass basis, WCO biofuel combustion reduced the THC emission by 41.8% and 40.5%, and reduced the CO emission by 54.3% and 72.4% at 3.4 and 6.6 bar IMEP loads, respectively. The WCO biofuel combustion resulted in the lower level of smoke opacity than diesel combustion due to inherit oxygenated fuel with near zero sulfur content. On opacity basis, the smoke reductions for the WCO biofuel were by 42.3% and 10.3%, respectively at 3.4 and 6.6 bar IMEP loads, compared to diesel fuel smoke opacity. In terms of particle number, the WCO resulted in greater concentration in the nucleation and accumulation modes while the total particle numbers have shown to be higher for WCO biofuel at smaller size. For the engine loads and speed tested, the total particle number for WCO biofuel and diesel fuel were up to 1.1 × 1012 m−3 and 5.7 × 1011 m−3, respectively while the count mean diameter for WCO biofuel and diesel fuel were up to 251 nm and 402 nm, respectively. Acknowledgement The authors would like to acknowledge Kasetsart University through Kasetsart University Research and Development Institute for the research funding (Grant Number: V-P(D)42.60) and the Faculty of Science at Sriracha for the support of experimental apparatus. References [1] Khanna M, Crago CL, Black M. Can biofuels be a solution to climate change? The implications of land use change-related emissions for policy. Interface Focus 2011;1(2):233–47. [2] Han X, Yang Z, Wang M, Tjong J, Zheng M. Clean combustion of n -butanol as a next generation biofuel for diesel engines. Appl Energy 2017;198:347–59. [3] Saha P, Baishnab AC, Alam F, Khan MR, Islam A. Production of bio-fuel (bioethanol) from biomass (Pteris) by fermentation process with yeast. Procedia Eng 2014;90:504–9. [4] Luque R, Herrero-Davila L, Campelo JM, Clark JH, Hidalgo JM, Luna D, et al. Biofuels: a technological perspective. Energy Environ Sci 2008;1(5):542. [5] Sanz Requena JF, Guimaraes AC, Quirós Alpera S, Relea Gangas E, HernandezNavarro S, Navas Gracia LM, et al. Life Cycle Assessment (LCA) of the biofuel production process from sunflower oil, rapeseed oil and soybean oil. Fuel Process Technol 2011;92(2):190–9.

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