Biodiesel production process optimization from Spirulina maxima ...

Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033 www.springerlink.com/content/1738-494x(Print)/1976-3824(Online)

DOI 10.1007/s12206-017-0546-x

Biodiesel production process optimization from Spirulina maxima microalgae and performance investigation in a diesel engine† M. A. Rahman1,*, M. A. Aziz1,2, A. M. Ruhul1,3 and M. M. Rashid2 1

Department of Mechanical Engineering, Rajshahi University of Engineering and Technology, Rajshahi-6204, Bangladesh Department of Mechatronics Engineering, International Islamic University Malaysia, Jalan Gombak, 53100 Kuala Lumpur, Malaysia 3 Department of Mechatronics Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

2

(Manuscript Received September 5, 2016; Revised December 23, 2016; Accepted February 27, 2017) ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Abstract Biodiesel is a renewable, easily biodegradable, eco-friendly and sustainable alternative energy source. In this investigation, crude oil was extracted from Spirulina maxima microalgae through biochemical conversion method with the help of soxhlet apparatus. Biodiesel production process parameters were optimized through base transesterification. Maximum biodiesel yield achieved was 87.75 % at optimal reaction condition after transesterification, when methanol to oil ratio was 6:1, catalyst loading was 1 % KOH (wt.%), temperature was 65 °C, and stirring speed was 600 rpm for a reaction time of 70 minutes. All the physicochemical properties of the produced biodiesel were determined and compared with the ASTM D6751 specification. Finally, performance and emission of an unmodified diesel engine was evaluated with 20 % and 40 % (v/v) biodiesel blends and compared the results with ordinary Diesel fuel (DF). Using biodiesel blends improves Hydrocarbon (HC) emission by 10-15 % and Carbon monoxide (CO) emission by 9.3-13.9 %. However, Brake specific fuel consumption (BSFC), Oxides of nitrogen (NOX), Carbon dioxide (CO2) and smoke opacity were found to be slightly higher for biodiesel blends, and Brake thermal efficiency (BTE) was found slightly lower than DF. Thus, Spirulina maxima serves as a potential feedstock for biodiesel production and prospective fuel in diesel engine application. Keywords: Spirulina maxima; Biodiesel; Transesterification; Optimization; Performance; Emission ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

1. Introduction The use of fossil fuel is expanding day by day to meet the rising energy demand worldwide and rapidly diminishing petroleum fuel reserves. In addition, extensive use of petroleum fuel causes many harmful emissions, which contributes to rising global warming. Researchers are working to discover renewable, sustainable and eco-friendly alternative energy sources which can replace or reduce the excess load on the petroleum based fuel. Thus, developing the renewable energy sources is always a burning issue throughout the world. Biodiesel from vegetable oil has become an acceptable alternative option for supplementing diesel because of interesting features compared to other types of energy sources. It can be blended with petroleum diesel in any ratio because of it’s properties, are very close to petro diesel and can be used in existing diesel engines without any modification [1]. The first and second generation biodiesel research is at saturated level, but third generation, i.e., biodiesel from algae research, is in the promising stage. *

Corresponding author. Tel.: +880 1 738451050 E-mail address: [email protected] † Recommended by Associate Editor Jeong Park © KSME & Springer 2017

Several researchers have taken challenge to utilize algal biomass as a source in an efficient manner and used in automotive vehicle. Mostafa and Gendy [2] investigated the physicochemical properties of Spirulina platensis algal biodiesel. They reported this biodiesel conforms ASTM specification and can be used in CI engine blended with petro diesel. ElShimi et al. [3] optimized reaction parameters for maximizing biodiesel yield from Spirulina platensis. They achieved maximum conversion of biodiesel of 84.7 % at optimum condition. Tsaousis et al. [4] investigated performance and emission behavior of algal biodiesel on a diesel engine, and reported that it reduced power output and NOX emissions, whereas increased BSFC, PM and CO2 emissions. Velappan and Sivaprakasam [5] did an experiment with various algal biodiesel blends in a diesel engine. Authors reported that BD20 showed the maximum NOX emissions than the other blends, but showed lowest smoke opacity. Microalgae can be considered as one of the most prominent alternative sources for the conventional feedstock. Biodiesel from Spirulina maxima is renewable, biodegradable, nontoxic, has low environmental impact and potential as a green alternative fuel for CI engine [6]. It has closed carbon cycle so it does not contribute to greenhouse gases. It has satisfactory combus-

3026

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

tion and emission profile, generating less CO, sulfur oxide (SOX), NOX and HC than conventional diesel [7]. So attempts have been made to supplement the diesel fuel and utilize algal biodiesel in the engine. The above literature shows that biodiesel from algae is well established to supplement fossil fuels. However, research on third generation biodiesel (Spirulina maxima) still in developing stage and limited to production level. It is very rare to find the production process optimization of Spirulina maxima biodiesel and its quality evaluation as sustainable fuel. In this study, Spirulina maxima biodiesel production process parameter was optimized in the context of yield and the performance and emission behavior was evaluated in an unmodified diesel engine.

2. Materials and methodology 2.1 Materials Raw material for biodiesel production, Spirulina maxima algae, was collected from Bangladesh Council of Scientific and Industrial Research (BCSIR) under controlled conditions of light and temperature (5000 lux, 14 h light and 10 h dark at 20 °C), and other relevant chemical were purchased from a local market. Highly pure analytical grade chemicals were selected for this investigation: 99.8 % pure CH3OH (methanol), 96 % pure H2SO4 (sulfuric acid), 86 % pure KOH (potassiumhydroxide), diethyl ether, methylene chloride, n-hexane. 2.2 Pretreatment At first, Spirulina maxima algae was cleaned properly in fresh water, dried in shade condition and heated in an oven at 70 °C for removing moisture. Secondly, the dry biomass was prepared into fine-grained powder by a mechanical crusher and mixed with water in 1:3 (v/v) ratio. Finally, an ultra-sonication process was employed for cell destruction of the algae biomass, where 24 kHz frequency and 50 °C temperature were maintained for 5 minutes. Then the sample was prepared to extract oil effectively for biodiesel production. 2.3 Extraction of crude algal oil Solvent extraction process with soxhlet apparatus was employed to extract the oil from the pretreated algae biomass sample. In this process, the pretreated biomass of Spirulina maxima was fed to a soxhlet apparatus with a round bottom flask with the condenser (see Fig. 1). Oil extraction was executed through percolation process of the algae biomass at 45 °C with the help of 15 % diethyl ether (DEE) and 10 % methylene chloride in n-hexane solution for 48 hours [8]. The diethyl ether functioned as a solvent for the extraction process, as it has a non-polar phenomenon. The role of methylene chloride was to separate oil content from water. The use of higher volume of methylene chloride refers to maximizing the oil extraction from biomass due to the higher polarity index of

Fig. 1. Schematic of experimental setup.

methylene chloride. Hexane was extensively used for oil extraction due to its low corrosiveness, low boiling point and high stability. After completing the reaction the products were poured into a rotary evaporator, evaporating the dissolved diethyl ether in crude oil. 2.4 Esterification and transesterification A fixed batch double jacket glass reactor was used to produce the biodiesel in laboratory scale. It is well established in biodiesel technology that acid catalyst esterification is recommended before alkaline transesterification when the vegetable oil contains high Free fatty acid (FFA) content (i.e., more than 2 % FFA). The acid esterification helps to reduce the FFA in the oil as well to prevent emulsified soap formation, which will inhibit biodiesel production yield; thus, a two stage production process was introduced. In esterification stage, 1 % (v/v) H2SO4 acid, 12:1 methanol to oil molar ratio, constant 400 rpm stirring speed and 60 °C reaction temperature was maintained for 90 minutes. The esterified oil was separated via a separation funnel and reduced % FFA was found from 5.7 % to 0.475 %. Transesterification process is sometimes treated as the main step of biodiesel production. The effect of all reaction parameters was investigated to optimize the production yield, so methanol to oil molar ratio was varied from 4:1 to 8:1, base catalyst (KOH) loading was varied from 0.25 % to 1.5 % (w/w), reaction temperature was varied from 45 °C to 75 °C, reaction time from 50 to 90 minutes as well as the mixing intensity from 600 to 700 rpm was varied throughout the experiment. 2.5 Post-treatment After completing the reaction, the mixture of reactant and product was poured into a separation funnel and glycerin was settling down at the bottom due to gravity. At the same time, methyl ester (biodiesel) was separated on the top of the funnel and waited until separation appeared not to be advancing anymore. The glycerin and other impurities were drawn off at the bottom of the separation funnel. It was washed with 60 °C temperature warm water for removing the soap and other im-

3027

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

Table 1. Test engine specification. Engine type

4-Stroke cycle CI engine

Manufacturer

Peter (England)

Number of cylinders

One

Bore×stroke

80×110 mm

Compression ratio

16.5

Method of cooling

Water cooling

Rated power

4.47 kW @ 1800 rpm

Injection timing

24° before TDC

Loading device

Eddy current dynamometer

Table 2. Technical features of gas analyzer. Equipment Fig. 2. Flow chart of biodiesel production.

purities like salt, free fatty acid. The process was repeated until raising the biodiesel pH of 6-7 and no soap bubbles appeared in it or the washed water became crystal in color. Then the biodiesel was evaporated with a rotary evaporator to remove dissolved methanol and water. Excess sodium sulfate (Na2SO4) anhydrous was utilized for chemical treatment, and finally pure biodiesel was obtained by filtering with filter paper. A flow chart of biodiesel production is shown in Fig. 2.

AVL DiCom 4000

Combustion product

Measuring range

Accuracy

O2

0-25% vol.

±0.01 % vol.

CO

0-10% vol.

±0.01 % vol.

CO2

0-20% vol.

± 0.1% vol.

UHC

0-20000 ppm

± 1 ppm

NOx

0-5000 ppm

±1 ppm

2.6 Characterization The physicochemical properties of produced biodiesel at optimum condition, its blends BD20 and BD40 along with Diesel fuel (DF), were determined according to ASTM standards and compared with ASTM D6751 specification. Some analysis, like Fourier transform infrared spectroscopy (FTIR), elemental analysis, was done according to ASTM standards. Perkin Elmer FT-IR 2000 equipment was used to analyze the % transmission by drop-casting on CaF2 optical windows in the range of 4000-500 cm-1 with resolution 4 cm-1. EA1108 elemental analyzer was used to analyze the Carbon, hydrogen, nitrogen, and sulfur (CHNS).

3. Engine test bed and experimental procedure The engine specifications and schematic of the experimental setup are shown in Table 1 and Fig. 3, respectively. The experiment was conducted with a 4-stroke cycle diesel engine. Initially, the engine was run with DF at no load for about five minutes until it reached steady-state conditions and then fixed the engine speed at 1500 rpm. After that, fuel consumption, various performance and emission parameters such as smoke opacity, NOX, HC, CO and CO2 emissions, were taken at various engine loading. Then the engine was operated with same operating condition fueled with BD20, BD40. Before going to change the fuel, engine was flashed with DF for a certain period until it reached the steady-state condition. Exhaust gas

Fig. 3. Schematic of engine test bed.

emission was measured by an AVL gas analyzer. The technical features of the gas analyzer along with measuring range and accuracy are shown in Table 2. Fuel consumption of the engine was measured with a stopwatch and a burette. This whole procedure was repeated three times and the average value of each measured parameter was presented as the result.

4. Results and discussion 4.1 Optimization of transesterification parameters 4.1.1 Molar ratio The important parameter for biodiesel production is the methanol to oil molar ratio. In this study, molar ratios were varied from 4:1 to 8:1 with an interval of two. The initial conditions of the reaction were fixed at 1 % KOH catalyst concentration, 50 °C temperature, 500 rpm mixing intensity for the reaction time of 90 minutes. The effect of molar ratio on biodiesel production is depicted in Fig. 4(a). Biodiesel yield was increased with an increasing in molar ratio, whereas glyc-

3028

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

(a)

(b)

(c)

(d)

(e) Fig. 4. (a) Effect of molar ratio on biodiesel yield; (b) effect of catalyst concentration on biodiesel yield; (c) effect of reaction temperature on biodiesel yield; (d) effect of mixing intensity on biodiesel yield; (e) effect of reaction time on biodiesel yield.

erol and soap formation was opposite for the formation of biodiesel. When the molar ratio increased from 4:1 to 6:1, biodiesel yield increased by 16.5 %, whereas glycerol and soap formation decreased by 21.5 % and 42.25 %. The maximum biodiesel yield 55.2 % was achieved for molar ratio at 6:1 with the minimal soap formation. Further increased in molar ratio beyond 6:1, biodiesel yield decreased but soap and glycerol formation again increased due to emulsification. Excess amount of methanol than required increases the solubility of glycerol, which impedes the separation of biodiesel and byproducts layer. As a result, soluble glycerol existing in the methyl ester phase caused foam formation and therefore apparent loss of biodiesel [9]. Abuhabaya et al. [10] achieved maximum yield of 94 % when reaction condition was metha-

nol to oil molar ratio 6:1, 1 % NaOH catalyst loading, 35 °C reaction temperature, and mixing intensity 200 rpm for the reaction time of 66 min. 4.1.2 Catalyst concentration The effect of catalyst concentration on reaction is depicted by Fig. 4(b). The effect of catalyst concentration on biodiesel yield was investigated by varying the KOH concentrations of 0.25, 0.5, 1 and 1.5 % wt. Initial operation conditions were fixed at a reaction temperature 50 °C, methanol: oil 6:1 and mixing intensity at 500 rpm for 90 min. The biodiesel yield was increased with an increasing in catalyst concentration up to a certain level, beyond that decreased the yield. The catalyst concentration of 0.25 % KOH was insufficient to complete the

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

reaction; thus, the yield of 42.5 % was very low, whereas soap formation was 6.12 %, which was very high. The maximum biodiesel yield 63.7 % was attained at 1.0 % KOH with the formation of 5 % glycerol and 2.1 % soap. Further increase in catalyst concentration, i.e., 1.5 % of KOH, the yields again decreased to 56 % with increasing soap formation. This was due to large amounts of soap formed by saponification when high concentrated KOH was added resulting in reduction of biodiesel yield [11]. Meher et al. [12] carried out the similar trend for maximum biodiesel yield of 96 % at methanol: oil 6:1, temperature 65 °C, 1 % KOH and stirring speed 600 rpm from Pongamia pinnata.

3029

Fig. 5. FTIR graph of algal biodiesel.

4.1.3 Temperature The effect of temperature on biodiesel production is shown in Fig. 4(c). The investigation was carried out at 45, 55, 65 and 75 °C with 1 % KOH, molar ratio 6:1 and mixing intensity of 500 rpm for 90 minutes. Temperature had a positive influence on reaction as biodiesel conversion was increased with increasing temperature. The reason behind that combination of oil and methanol increased the solubility of molecules, and hence increased biodiesel production [8]. The maximum biodiesel yield 81.38 % was at 65 °C, but beyond this further increase in temperature, there was no improvement of biodiesel yield. This was due to the solubility of solvent reached at saturated level with decreased diffusion level and the lower boiling point of methanol (64.7 °C), which has a tendency to escape from the reactor. Rashid and Anwar [13] investigated similar trends for maximum biodiesel production of 90.6 % using rapeseed oil at 65 °C, molar ratio 6:1, 1 % KOH, and rate of stirring 600 rpm.

4.1.5 Reaction time To observe the actual time needed to complete a transesterification reaction with maximum biodiesel production, investigation were carried out at a different times, such as 50, 60, 70 and 80 minutes with 1 % KOH, methanol to oil ratio 6:1 at temperature 65 °C and 600 rpm. After passing 50 minutes, biodiesel yield was 70 %, glycerin was 5.1 % and soap formation was 3 % (Fig. 4(e)). Maximum biodiesel yield of 87.75 % was achieved after 70 minutes with the formation of 9 % glycerol and 1 % soap. For further increase in reaction time beyond 70 minutes, there was no significant improvement in biodiesel yield due to decreased diffusion rate. Suganya et al. [8] also reported that the optimum time of 70 minutes for maximum biodiesel yield of 90.6 % from microalgae E. compressa and parameters was fixed at 1 % KOH, 55 °C, 9:1 molar ratio for 90 minutes.

4.1.4 Mixing intensity Mixing intensity has a strong influence on biodiesel production as it increases interact area between the catalyst and alcoholic oil. Due to the improper mixing, the reaction does not take place at the interface between the two layer and therefore lowers biodiesel yield [13]. The effect of mixing speed on biodiesel production is shown in Fig. 4(d). To evaluate the effect of mixing intensity on biodiesel production, the stirring speed was varied from 400 to 700 rpm. Initial operation conditions were fixed at temperature 65 °C, methanol: oil 6:1 and 1 % KOH for 90 minutes. Biodiesel yield was increased with an increasing in mixing intensity due to an increase of the homogenization of the reactant [8]. At stirring rate 400, 500, 600 and 700 rpm, the value of biodiesel yield was 60, 70.5, 85, 84.2 %, glycerol formation was 6.4, 7, 9, 6 % and soap formation was 3, 2.22, 1.12, 1.9 %, respectively. When stirring speed was increased from 400 to 600 rpm, biodiesel yield increased from 60 to 85 %. With further increase in stirring speed, there was no improvement in the biodiesel yield. The maximum biodiesel yield of 85 % was at 600 rpm. Vicente et al. [14] also achieved a maximum biodiesel yield of 97 % from Brassica carinata at 600 rpm, 6:1 molar ratio, 1.2 % KOH, and 25 °C reaction temperature for 60 minutes.

The fundamental analysis of biodiesel obtained at maximum yield condition is shown in Table 3. The biodiesel and its blends have higher viscosity than diesel fuel. The Higher calorific value (HCV) of the BD, BD20, BD40 and DF was 38.43, 43.13, 42 and 44.5 MJ/kg, respectively. The Cetane number (CN) of the biodiesel and its blends was comparatively higher than diesel fuel. The acid value of the biodiesel was higher than diesel fuel. The biodiesel has higher carbon content (67.91 %wt.) and oxygen content (19.86 %wt.). The higher oxygen content of bio-oil is attractive for the production of transport fuels. The moisture and carbon residue content was 0.04 % and 0.045 %wt., respectively. The measured biodiesel and diesel properties were found within ASTM standard limits. FTIR spectroscopy has proved to be a powerful analytical tool for the identification of the basic compositional group’s presence in the oil. FTIR analysis of biodiesel was performed to know what type of functional group existed in the oil. The FTIR spectroscopy of the biodiesel is shown in Fig. 5. The characteristic absorption bands for the vibrations of C-H, around 2922.1 & 2852.7 cm-1 corresponding to the asymmetric and symmetric vibration modes of methyl groups, respectively, indicate the presence of alkane and appearance is very

4.2 Analysis of diesel and biodiesel

3030

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

Table 3. Physicochemical properties of the biodiesel and tested fuel. Experimental results

ASTM standard method

Diesel

BD

BD20

BD40

ASTM D6751 biodiesel

Density (kg/m3) at 15 °C Kinematic viscosity (mm2/s) at 40 °C Higher calorific value (MJ/kg) Cetane number (CN) Pour point (°C ) Flash point (°C ) Carbon residue (% wt.) PH Moisture content (%) Ash content (%) Acid value (mg KOH/g)

D 4052 D 445 D 240 D 613 D 97 D 93 D 524 D 6751 D 482 D 664

0.851 2.83 44.5 48 n.d. 84 0.01 6.54 0.03 max. 0.02 max. 0.245

0.872 4.47 38.43 55 -10 178 0.045 7 0.04 n.d. 0.475

0.857 2.98 43.13 51 n.d. 92 n.d. n.d. n.d. n.d. 0.324

0.861 3.5 42 52 n.d. 96 n.d. n.d. n.d. n.d. 0.384

n.a. 1.9-6.0 40-68 -15 to 16 130 min. 0.05 max. n.a. n.a. 0.02 max. 0.50 max.

Elemental analysis (% wt.)

C (Carbon) H (Hydrogen) O (Oxygen) N (Nitrogen) S (Sulfur)

86.18 13.8 0.01 max. 0.034

67.91 10.69 19.86 1.54 -

Property/sample

n.a. n.a. n.a. n.a. n.a.

n.d.= Not determined, n.a.= Not available

strong. The peaks 1770.86 cm-1 and 1650 cm-1 represent the C=O (Aldehyde/ketone) stretching. The transmittance peaks 1063 cm-1 and 966.64 cm-1 represent alcohol, a functional group of stretching carbohydrates. The absorbance peaks 1465.2 cm-1 and 719.4 cm-1 for the vibrations of C-H represent alkane. In biodiesel spectra, the absence of a peak higher than 3000 cm-1 corresponding to -OH of carboxylic acid indicates complete transesterification [2]. Since, the major sharp transmittance peaks of FTIR spectra are an alkane, which indicates biodiesel is saturated hydrocarbon and potential to be used as a fuel [15]. 4.3 Engine performance parameters To evaluate the performance and emission parameters of biodiesel blends, a diesel engine with a constant speed 1500 rpm at different loads was tested. The performance parameters (BTE, BSFC) and emission characteristics (CO, CO2, NOX, HC and smoke opacity) were determined and compared to those with DF. 4.3.1 Brake thermal efficiency (BTE) The effect of biodiesel blends on BTE is shown Fig. 6(a). BTE of DF and BD blends was increased with an increasing in BP, but BTE of DF was comparatively higher than biodiesel blends. Thermal efficiency depends on the heating value and density of fuel. The higher the heating value, the higher the BTE, but higher viscosity and density retard BTE [16]. The BTE at lower load for all blends tested were very close to each other. At full load, BTE of DF, BD20 and BD40 was 24.4 %, 22.7 % and 20.9 %, respectively. The efficiency of DF was 7.4 % and 16.7 % higher than BD20 and BD40, respectively, at full load. The DF had better heating value compared to biodiesel blends.

4.3.2 Brake specific fuel consumption (BSFC) BSFC is also an important factor for evaluating the engine performance. Fig. 6(b) shows a variation of the BSFC with BP for diesel and biodiesel blends at constant engine speed. BSFC decreased with increasing in BP for diesel and biodiesel blends in terms of per unit power output. BD20 and BD40 showed higher BSFC compared to DF due to the higher density, lower heating value and higher flash point [4, 17]. The reason behind that the better atomization and combustion of BD20 at high speed by accelerating the reaction [18]. At full load operation, BSFC for DF was 0.33 kg/kW- hr, whereas for BD20 and BD40 were 0.37 kg/kW-hr and 0.41 kg/kW-hr, respectively. 4.3.3 Carbon monoxide (CO) emission Fig. 6(c) shows the variation of the CO emission with BP for DF and BD blends at constant speeds of the engine. Biodiesel blends showed lower CO emission than DF. CO emission depends on the improper combustion in low temperature and oxygen unavailability in combustion chamber. Since, BD blends contain superfluous oxygen content, which leads to better combustion of the fuel and generates higher temperature in the cylinder. This high temperature helps oxidation to convert CO to CO2 [19]. The trend of CO emission declined with increasing in engine load. The value of BD20 and BD40 at full load operation was 0.078 % and 0.074 % (by volume), which was 9.3 % and 13.9 %, respectively, lower than DF. 4.3.4 Hydrocarbon (HC) emission The variation of the HC emission with BP for DF and BD blends is shown in Fig. 6(d). HC emission decreased with increasing in BP and decreased with increasing percentage of BD blends. HC emission depends on the oxygen content of the fuel. Since, biodiesel contains higher oxygen content,

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

(a)

3031

(b)

(c)

(d)

(e)

(f)

(g) Fig. 6. (a) Variation of BTE with BP; (b) variation of BSFC with BP; (c) variation of CO emission with BP; (d) variation of hydrocarbon with BP; (e) variation of NOX emission with BP; (f) variation of CO2 emission with BP; (g) variation of smoke opacity with BP.

3032

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

which leads to better combustion of the fuel [20]. Initially, HC level of DF, BD20, BD40 was 60 ppm, 58.8 ppm and 53.4 ppm, respectively. At the full load conditions, HC of BD20 and BD40 was 10 % and 15 %, respectively, lower than DF. 4.3.5 Oxide of nitrogen (NOX) emission NOX is of prime importance when it comes to engine exhaust. The variation of the nitric oxide (NOX) emission with brake power for DF and BD blends is shown in Fig. 6(e). From the graph for all load condition, NOX emission increased with the increase of BP and NOX emission for biodiesel blends higher than DF. NOX emission depends on the oxygen concentration and higher temperature in combustion chamber. NOX emission was higher at all load conditions, due to higher cetane number, which leads to better combustion of the biodiesel. Since, a peak temperature is produced by the better combustion of fuels, which eventually increases the NOX formation [21]. At full load condition NOX emission of BD20 and BD40 was 571 ppm and 601 ppm, respectively. NOX emission of BD20, BD40 was 16.5 % and 22.6 %, respectively, higher than DF at full load condition. 4.3.6 Carbon dioxide (CO2) emission The variation of the CO2 emission with BP for DF and BD blends is shown in Fig. 6(f). CO2 emission depends on the effective combustion of fuel [22, 23]. BD contains 19.86 % oxygen content, whereas DF contains 0.01 % oxygen. This higher concentration of oxygen content in biodiesel favors the better combustion of fuel, which generates high combustion temperature and CO converted to CO2 by oxidation. At full load operation, CO2 emission for DF, BD20 and BD40 was 10.7 %, 12.03 % and 12.57 % (by volume), respectively. 4.3.7 Smoke opacity Fig. 6(g) shows variation of the smoke opacity with BP for DF and BD blends at constant speed of the engine. Smoke emission increased with the increase of BP for both of DF and BD blends. The smoke opacity increased due to the higher ignition delay and insufficient combustion usually at rich mixture zone in the combustion chamber [19]. Since BD has a higher viscosity, which resulted in poor atomization by producing larger droplets, increased ignition delay and consequently, produce higher smoke emission. At full load condition, the smoke opacity of DF, BD20 and BD40 was 72, 73, 78.1 BSU (Bosch smoke units), respectively. Smoke opacity of BD20, BD40 was 1.38 % and 8.4 %, respectively, higher than DF at full load condition.

5. Conclusion Based on our experimental investigation, the following conclusions can be drawn: ·Maximum biodiesel yield 87.75 % can be obtained at 6:1 methanol to oil molar ratio, 1 % wt. KOH catalyst load-

ing, 65 °C reaction temperature with 600 rpm stirring speed for 70 minutes. ·BD20 and BD40 showed improved HC emission (1015 %) and CO emission (9.3-13.9 %) compared to DF at full load condition. NOX emission was found higher about respectively at full load condition. BD20 and BD40 lowered BTE by 7.4-16.7 % compared to DF at full load. BSFC of biodiesel blends was found higher compared to DF due to higher density and lower energy density. ·The properties of algal biodiesel and its blends were close to ASTM standard limit.

Acknowledgment Authors would like to express sincere gratitude to International Islamic University Malaysia for the financial support and Rajshahi University of Engineering & Technology (RUET) for technical support. The authors would also like to thank Bangladesh Council of Scientific and Industrial Research (BCSIR) for laboratory assistance characterization for the tested fuel.

References [1] M. A. Rahman, A. M. Ruhul, M. A. Aziz and R. Ahmed, Experimental exploration of hydrogen enrichment in a dual fuel CI engine with exhaust gas recirculation, International J. of Hydrogen Energy, 42 (2017) 5400-5409. [2] S. S. M. Mostafa and N. S. El-Gendy, Evaluation of fuel properties for microalgae Spirulina platensis bio-diesel and its blends with Egyptian petro-diesel, Arabian J. of Chemistry (2013) 10.1016/j.arabjc.2013.07.034. [3] H. I. El-Shimi, N. K. Attia, S. T. El-Sheltawy and G. I. ElDiwani, Biodiesel production from Spirulina- Platensis microalgae by in-situ transesterification process, J. of Sustainable Bioenergy Systems, 3 (2013) 224-233. [4] P. Tsaousis, Y. Wang, A. P. Roskilly and G. S. Caldwell, Algae to energy: Engine performance using raw algal oil, Energy Procedia, 61 (2014) 656-659. [5] R. Velappan and S. Sivaprakasam, Investigation of single cylinder diesel engine using bio diesel from marine algae, International J. of Innovative Science, Engineering & Technology, 1 (2014) 399-403. [6] H. M. El-Mashad, R. Zhang and R. J. Avena-Bustillos, A two-step process for biodiesel production from salmon oil, Biosystems Engineering, 99 (2) (2008) 220-227. [7] S. Zheng, M. Kates, M. A. Dubé and D. D. McLean, Acidcatalyzed production of biodiesel from waste frying oil, Biomass and Bioenergy, 30 (2006) 267-272. [8] T. Suganya, N. N. Gandhi and S. Renganathan, Production of algal biodiesel from marine macroalgae Enteromorpha compressa by two step process: Optimization and kinetic study, Bioresource Technology, 128 (2013) 392-400. [9] A. N. Phan and T. M. Phan, Biodiesel production from waste

M. A. Rahman et al. / Journal of Mechanical Science and Technology 31 (6) (2017) 3025~3033

cooking oils, Fuel, 87 (2008) 3490-3496. [10] A. Abuhabaya, J. Fieldhouse and D. Brown, The effects of using biodiesel on CI (compression ignition) engine and optimization of its production by using response surface methodology, Energy, 59 (2013) 56-62. [11] D. Y. C. Leung and Y. Guo, Transesterification of neat and used frying oil: Optimization for biodiesel production, Fuel Processing Technology, 87 (10) (2006) 883-890. [12] L. C. Meher, V. S. S. Dharmagadda and S. N. Naik, Optimization of alkali-catalyzed transesterification of Pongamia pinnata oil for production of biodiesel, Bioresource Technology, 97 (12) (2006) 1392-1397. [13] U. Rashid and F. Anwar, Production of biodiesel through optimized alkaline-catalyzed transesterification of rapeseed oil, Fuel, 87 (3) (2008) 265-273. [14] G. Vicente, M. Martínez and J. Aracil, Optimization of Brassica carinata oil methanolysis for biodiesel production, J. of the American Oil Chemists’ Society, 82 (12) (2005) 899-904. [15] M. N. Nabi, M. S. Akhter and M. A. Rahman, Waste transformer oil as an alternative fuel for diesel engine, Procedia Engineering, 56 (2013) 401-406. [16] G. Tüccar and K. Aydın, Evaluation of methyl ester of microalgae oil as fuel in a diesel engine, Fuel, 112 (2013) 203-207. [17] D. Yuvarajan and M. Venkata Ramanan, Experimental analysis on neat mustard oil methyl ester subjected to ultrasonication and microwave irradiation in four stroke single cylinder Diesel engine, J. of Mechanical Science and Technology, 30 (1) (2016) 437-446. [18] H. Aydin and H. Bayindir, Performance and emission

3033

analysis of cottonseed oil methyl ester in a diesel engine, Renewable Energy, 35 (3) (2010) 588-592. [19] M. N. Nabi, M. M. Rahman and M. S. Akhter, Biodiesel from cotton seed oil and its effect on engine performance and exhaust emissions, Applied Thermal Engineering, 29 (2009) 2265-2270. [20] M. I. Al-Widyan, G. Tashtoush and M. Abu-Qudais, Utilization of ethyl ester of waste vegetable oils as fuel in diesel engines, Fuel Processing Technology, 76 (2) (2002) 91-103. [21] G. Paul, A. Datta and B. K. Mandal, An experimental and numerical investigation of the performance, combustion and emission characteristics of a diesel engine fueled with jatropha biodiesel, Energy Procedia, 54 (2014) 455-467. [22] R. Kumar, M. K. Mishra, S. K. Singh and A. Kumar, Experimental evaluation of waste plastic oil and its blends on a single cylinder diesel engine, J. of Mechanical Science and Technology, 30 (10) (2016) 4781-4789. [23] A. S. Ramadhas, C. Muraleedharan and S. Jayaraj, Performance and emission evaluation of a diesel engine fueled with methyl esters of rubber seed oil, Renewable Energy, 30 (12) (2005) 1789-1800.

M. A. Rahman received his B.Sc. in Mechanical Engineering from Rajshahi University of Engineering and Technology (RUET), Bangladesh. His research interest includes biodiesel research, IC engine combustion and emissions, combustion in IC engine and pyrolysis technology.