Experimental assessment of performance, combustion and emissions of a compression ignition engine fuelled with Spirulina platensis biodiesel

Journal Pre-proof Experimental assessment of performance, combustion and emissions of a compression ignition engine fuelled with Spirulina platensis biodiesel Piyushi Nautiyal, K.A. Subramanian, M.G. Dastidar, Ashok Kumar PII:

S0360-5442(19)32556-3

DOI:

https://doi.org/10.1016/j.energy.2019.116861

Reference:

EGY 116861

To appear in:

Energy

Received Date: 27 June 2019 Revised Date:

9 December 2019

Accepted Date: 25 December 2019

Please cite this article as: Nautiyal P, Subramanian KA, Dastidar MG, Kumar A, Experimental assessment of performance, combustion and emissions of a compression ignition engine fuelled with Spirulina platensis biodiesel, Energy (2020), doi: https://doi.org/10.1016/j.energy.2019.116861. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Word Count: 8982

Experimental assessment of performance, combustion and emissions of a compression ignition engine fuelled with Spirulina platensis biodiesel Piyushi Nautiyal, [a], [b]* K.A. Subramanian, [a] M.G.Dastidar, [a] and Ashok Kumar [a], [c] [a]

Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi, 110016, India Department of Chemistry, New Horizon College of Engineering, Bengaluru, Karnataka, 560103, India [c] Department of Mechanical Engineering, New Horizon College of Engineering, Bengaluru, Karnataka, 560103, India * Corresponding author Email: [email protected] [b]

Graphical Abstract

ABSTRACT The investigation was conducted with an aim to explore the potential of novel, less explored biodiesel from Spirulina platensis algae, which can be used as an alternate fuel for conventional diesel. The effect of biodiesel on performance, combustion and emission characteristics of diesel engine was experimentally investigated. The ignition delay period declined to 7.3 °CA for B100 blend compared to 10 °CA for diesel. The heat release rate with biodiesel-diesel blends was lower than base diesel. The duration of combustion for base diesel, B10, B20 and B100 algae biodiesel-diesel blends was found out to be 37.5 ° CA, 38 ° CA, 38 ° CA and 40 ° CA respectively. The carbon monoxide (CO), hydrocarbon (HC) and smoke emissions were reduced significantly as the percentage of biodiesel in fuel blend is increased. The CO emission decreased from 3.10 g/kWh with diesel to 1.20 g/kWh for B100 at full load. The HC emission showed the decrease from 0.06 g/kWh with diesel to 0.04 g/kWh for B100 whereas smoke emission reduced from 0.7% with diesel to 0.6% for B100 at full load. NOx emission with biodiesel and its blends increased significantly. NOx was 16.19 g/kWh and 13.3 g/kWh with B100 and base diesel. Keywords: Algae, Spirulina platensis, biodiesel, performance, emission, combustion 1. Introduction

Developing countries are in perilous energy crisis. As of today, 80% of the total energy consumed globally is derived from fossil fuels alone. This over dependency on fossil fuels causes threats: exhaustion of fossil fuel reserves and global warming posing worldwide climatic changes (Raheem et al., 2018; Saravanan et al., 2018). The use of biomass for energy production has gained a considerable attention from past decade, since it is renewable, viable and environmentally friendly basis of energy. At present, about 8-15% of world’s energy is contributed by biomass derived fuels for transportation and it is expected to increase upto 33-50% by the year 2050 (Vassilev et al., 2013). India consumes about 3.5 times more diesel as compared to gasoline, which is unique because most of the countries use more gasoline as compared to diesel (MoPNG, 2016). About 75–80% of total petroleum requirement in India is met through imports. Therefore, immediate efforts are required for a switch towards renewable alternate fuel for diesel. A huge amount of literature can be found dealing with the studies of performance, combustion and emissions characteristics of biodiesel (from edible and non-edible sources) fuelled engine. Scanty information can be found on the use of biodiesel produced from algae in diesel engines. Therefore, more concentrated efforts are needed to study the engine characteristics of a compression ignition engine using algae biodiesel-diesel blends. Tripathi and Subramanian, 2017 investigated the performance, combustion and emissions characteristics of a diesel engine fuelled with soya soap stock-based acid oil derived biodiesel. The results showed the drop-in power in range of 1.4% to 15.9% with biodiesel compared to base diesel. The emissions characteristics showed the significant reduction of CO and HC emissions. However, NOx emissions showed an increase of 3.23 g/kW with diesel to 4.43 g/kW h

with biodiesel. Moreover, biodiesel fuelled engine showed the decrease in brake thermal efficiency from 28.12% using diesel to 21.38% with B100 blend. Vedaraj et al., 2016 utilized B20 blend of catalytically cracked cashew nut shell liquid in an engine to examine its performance and emissions characteristics. They reported that only the oxidation stability of B20 blends of liquid met the benchmarks laid down by American and European standards. The blend showed engine performance much closer to diesel while the brake thermal efficiency and brake specific fuel consumption improved with blend compared to diesel. Leevijit et al., 2017 studied the performance and emission characteristics of B20, B30 and B100 blends of esterified mixed palm oil- diesel blends utilized in a diesel engine. They reported that blends showed marginally higher BSFC and lower BTE (0.9% and 1.2%) and there was decrease in HC and smoke emissions in comparison to base diesel. Kumar et al., 2016 used Artificial Neural Networks for predicting the characteristics of compression ignition engine fuelled with biodiesel derived from waste cooking oil. Kumar et al, 2019 reported that engine fuelled with Chakotara biodiesel resulted in increase in efficiency and performance of engine when n-butanol is added to the fuel. Damodharan et al., 2018 studied the effect of alcohol additives in waste plastic oil on the emission characteristics of diesel engine. The investigation reported that with pentanol addition to oil at 21° CA BTDC and 10% EGR, the smoke emissions dropped by 74.2%, however the NOx emission increased by 9.7% and the slim improvement observed in BSFC by 3.2%. Debnath et al., 2019 studied the performance and emission characteristics of diesel engine when fuelled with B20 blend of Thumba biodiesel. The brake thermal efficiency and unburnt hydrocarbons showed the better results with biodiesel blend compared to diesel, whereas NOx emissions showed an increase. Mathimani et al., 2017 assessed the performance of biodiesel from Chlorella vulgaris algae on diesel engine and found that the engine performance was appreciable when it was running on B40 or B50 blend as the brake thermal efficiency improved while CO, HC and smoke emissions dropped. Narayanswamy and Jeyakumar, 2019 investigated the effect of addition of nano-additives of TiO2 in Azolla algae biodiesel on the characteristics of diesel engine and reported the nano-additives helped in further decreasing the HC, CO and smoke emissions but NOx emission increases. Moreover, with increase in dosage of nano-additives in B20 blend of biodiesel, the brake thermal efficiency increased, and brake specific fuel consumption decreased linearly. This is due to the catalytic activity of the nanoparticle which improves the combustion process by improving the rate of evaporation, shortens the ignition delay period and encourages the secondary atomization. Algae, photosynthetic beings, derive the solar energy and CO2 from atmosphere for their biomass formation (Demirbas, 2010). They are the potential contenders to produce biodiesel attributable to their high photosynthetic efficacy, rapid growth and extraordinary productivity (Demirbas and Demirbas, 2011; Amaro et al., 2011; Slade and Bauen, 2013; Piemonte et al., 2016; Nautiyal et al., 2017). Algae grow faster than the fastest growing terrestrial plant, switch grass. The yield of algae biomass per acre is 200 times above as compared to the yield of the finest performing terrestrial plant (Sheehan et al., 1998). Some algae species can even complete their growing cycle in few days (Demirbas, 2008). The other attractive applications of algae biomass other than lipid conversion to

biodiesel are adsorbent for wastewater treatment, production of energy from remaining carbon and hydrogen after lipid extraction, carbon dioxide sequestration, bio-manure and food supplement (Adeniyi et al., 2018). In the light of literature, several studies on biodiesel utilization in diesel engine from edible as well as non-edible sources and their effects on engine’s performance, combustion and emissions can be found. Nevertheless, to the best of authors’ knowledge, no study has been reported yet dealing with utilization of Spirulina platensis algae biodiesel in engine with the detailed investigation on the performance, combustion and emission exhaust behavior of engine. The novelty of the work lies in the exploration of new biodiesel feedstock, Spirulina platensis, which has not drawn much attention till now by the researchers. Spirulina is the blue-green algae and is best known to produce high amounts lipids which makes it an attractive feedstock for biodiesel industry (Avagyan and Singh, 2019; Chia et al., 2018, Rajak et al., 2019a). The fatty acid profile of S.platensis constitutes the optimum percentage ratio of saturated fatty acids and unsaturated fatty acids (approximately 1: 1 percentage ratio), which is the appropriate balance in the percentage composition of both saturated as well as unsaturated fatty acids required for the efficient performance of biodiesel (Chojnacka et al., 2018). The saturated fatty acids will improve the oxidative stability of biodiesel, whereas unsaturated fatty acids will improve the poor cold flow properties of biodiesel (Chen et al., 2018). In spite of the fact that various studies have been contemplated using variety of biodiesel feedstocks but to date, no systematic and comprehensive technical analysis is found in literature with Spirulina platensis algae biodiesel. To meet this gap, the present work is intended to highlight and achieve the broad accompanying objective of establishing the potential of algae as a sustainable feedstock for the production of biodiesel as well as to provide further insights which elucidate the effects of biodiesel on performance, combustion and emission characteristics of diesel engine. The biodiesel was obtained via simultaneous oil extraction and transesterification from Spirulina platensis algae using methanol, hexane and conc. sulphuric acid as an alcohol, solvent and catalyst respectively. The physicochemical properties of the biodiesel were examined and compared with ASTM an EN standards to determine its suitability as a biodiesel feedstock. The study investigated the utilization of biodiesel produced from Spirulina platensis algae (10%, 20% and 100% biodiesel-diesel blends on volume basis) in compression ignition engine, having alternate 5 kW power output running at 1500 rpm. The engine performance pertaining to brake thermal efficiency was determined and compared with base diesel. Likewise, detailed combustion characteristics such as in-cylinder pressure, heat release rate (HRR), cumulative heat release (CHR), combustion duration, ignition delay, in-cylinder temperature operating on different algae biodiesel blends were also systematically investigated. The effect on emissions such as CO, HC, NOx and smoke were also studied and compared. The results were compared and analyzed with engine behavior operated with base diesel.

2. Experimental methodology

2.1.

Biodiesel production and its characterization

The previous reported study (Nautiyal et al., 2014) by our research group dealt with the optimization of biodiesel production from Spirulina platensis algae and its characterization. The present study is the continuation of aforementioned work where the biodiesel produced was tested in engine to establish its potential as a substitute to conventional diesel. The dried and powdered biomass of algae Spirulina platensis was procured from local supplier in India. Spirulina platensis algae is single celled autotrophic microbe which belongs to the family of blue green algae. It can grow both in fresh and saline water. The lipid content in Spirulina varies from 10-25% by weight. Figure 1 shows the image of Spirulina algae growing in fresh water. The experiment for biodiesel production was performed using Remi MLH series heating mantle. The dried sample of Spirulina platensis algae biomass post pulverization was added to the glass reactor of the transesterification unit. The solvent (hexane) and alcohol (methanol) with acid catalyst (conc. H2SO4) were transferred to the glass reactor. The temperature of the reactor was maintained at 55oC for 50min with constant stirring at 450 rpm. After the stipulated time required for reaction completion, the products of the reactor were made to cool and settle down to room temperature followed by addition of distilled water to the reactor. The contents of reactor were transferred to the separating funnel leaving behind the solid residue of algae biomass in the reactor. After 10-15 min, the two layers were observed. The upper layer comprised of biodiesel with solvent which was isolated from the lower layer of glycerol, unreacted methanol and catalyst. Finally, using simple distillation biodiesel was recovered from hexane solvent. The biodiesel obtained was then weighed gravimetrically. The percentage yield of biodiesel, as proposed by Xu and Mi, 2011, was determined by using Eq. 1.    


    % =  100 1     



where oil present in biomass= weight of lipid/oil content present in algae The optimization of process parameters for simultaneous oil extraction and transesterification to produce algae biodiesel showed that the most suitable conditions to achieve maximum algae biodiesel yield (78 wt%) were: 55°C reaction temperature, 450 rpm stirring intensity, 60% catalyst concentration and 1:4 algae biomass to methanol ratio (Nautiyal et al., 2014).

Fig. 1. Pictorial image of freshwater Spirulina platensis algae

The chemical profile of biodiesel produced was tested via gas chromatography in our previous study (Nautiyal et al., 2014). The results depicted that algae biodiesel was comprised of almost 41% of palmitic acid methyl esters, followed by linolenic (18%), linoleic (13%), oleic (4%), caprylic (4%), myristic (2.5%), lauric (1%), etc. The spectra of NMR and FTIR spectral analysis data showed very clearly that Spirulina algae biodiesel were composed of fatty acid methyl esters. A characteristic peak at 3.6 ppm in the NMR spectra biodiesel was due to methyl group of esters which ensures the good conversion of oil to biodiesel. The absorption band in the FTIR spectra of algae biodiesel in the range of at 1437–1460 cm−1 appeared due to the methyl ester moiety and at 1743 cm−1 due to the >C=O stretching. The presence of the two absorption peaks validates the conversion of oil to biodiesel. The TGA analysis presented the good thermal stability of the algae biodiesel with the onset and offset temperature of 140°C and 246°C respectively. The physical properties of fuel such as density, viscosity and the calorific value of algae biodiesel and its blends were determined as per recommended ASTM standards.

2.2. Blends preparation The commercial grade No. 2 diesel fuel, having the elemental composition by weight of 84.92% carbon and 13.18% hydrogen, was used in the preparation of algae biodiesel-diesel blends. At present, to get algae oil from algae biomass is difficult and expensive process, therefore the study was conducted with two algae biodiesel-diesel blends, B10 and B20, due to their widespread use. According to Energy Policy Act of 1992 (EPAct) compliance, the popular biodiesel blends B20 and below can only be used in diesel engine with few or no modifications. The ASTM specification for pure biodiesel was approved only for blends up to B20 and not for higher blends. With an aim to test the applicability of pure form of biodiesel, neat fuel designated as B100 was also tested. The blends were prepared on a volume basis at 25 °C. Although, if the blends are prepared on a weight basis, the weight fractions will not change with change in temperature, however the universally followed practice in the fuel business is to prepare the blends on a volume basis at ambient temperature conditions. There was no phase separation observed in the blends may be due to the emulsifying property that biodiesel possess. Besides this, the miscibility of any fuel blend is mainly governed by the water content present in it. To avoid any phase separation, every precaution was taken while preparing the biodiesel. The biodiesel obtained was treated with anhydrous sodium sulphate and subjected to heating at 100-110°C for 10-15 min for removal of any traces of moisture.

2.3. Engine set-up and test procedure The studies were performed on a compression ignition engine to examine the effect of biodiesel and its blends on performance, combustion and emission characteristics of the engine. The experimentation tests were conducted with B10, B20 and B100 algae biodiesel-diesel blends on a compression ignition engine.The specifications of the test engine used are summarized in Table 1. The schematic layout of the experimental set-up is presented in Fig. 2. The test engine’s performance, combustion and emissions were evaluated at varying loads (20%, 40%, 60%, 80% and 100%). The AVL Indicom system comprising data acquisition system, charge amplifier and post processing software was taken for the measurement of crank-angle data. The combustion analysis system was equipped with piezoelectric transducer, optical encoder and piezoelectric strain gauge. The voltage and charge amplifiers were used to amplify the input signals and data was recorded from data acquisition system. The data was used to calculate the combustion characteristics, namely in-cylinder pressure, HRR, CHR, ignition delay, maximum rate of pressure rise, in-cylinder temperature and combustion duration. The CO, HC and NOx emissions were measured with online digas analyzer (AVL) while the smoke opacity was measured by with smoke meter (AVL 437). An error analysis for the engine measurements was carried out using root mean square

method proposed by Holman and Gajda, 1994. The error analysis was based on the accuracy of the measurement equipment. The experimental error is shown in the graphs (Refer supplementary material).

Table 1 Details of engine Description Fuel Engine Aspiration Number of Cylinders Bore x stroke (mm) Displacement volume (mm) Compression ratio Rated power output (kW) Alternate power output (kW) Engine speed (rpm) Intake valve opening and closing Exhaust valve opening and closing Connecting rod length (mm) Emission certificate

Compression ignition engine Diesel Four stroke Natural 1 102 x 116 947.3 19.5:1 7.35 5 1500 43°BTDC and 67°ABDC 87°BBDC and 39°ATDC 232.6 CPCB compliance

Fig. 2. Schematic layout of experimental setup for diesel engine

3. Results and discussion

3.1. Fuel properties Table 2 compares the fuel properties of Spirulina platensis algae biodiesel with other varieties of biodiesel. Table 3 summarizes the physico-chemical properties of the biodiesel-diesel fuel blends. It is clear that by increasing the percentage concentration of biodiesel in a blend, there is a linear increase in the fuel’s density. The analogous tendency was noted with viscosity trend too. The calorific value of the blend decreased with increasing percentage of biodiesel in the blend.

In compression ignition engine, the fuel properties significantly affecting the brake thermal efficiency are density, viscosity and calorific value. During fuel injection, the fuel quantity injected into the cylinder is controlled and measured volumetrically. Hence, higher the density of the fuel, more mass of the fuel gets injected. The high density and viscosity of the fuel often lead in an increase of in-line pressure. On the whole, as density and viscosity of the biodiesel is higher compared to diesel, the quantity of biodiesel injected in the combustion chamber is always more compared to diesel fuel. The high viscosity is indirectly indicating the high surface tension of biodiesel that can result in weakening of atomization and air-fuel mixture formation. The calorific value of biodiesel is slightly lower than that of diesel therefore it affects the power and fuel consumption adversely. Table 2 Comparison of fuel properties of biodiesel from various sources Properties

Density at 15 °C (kgm-3)

Feedstocks ASTM D 860-900 6751, EN 14214 Algae Feedstocks Chlorella 895 vulgaris Chlorella 900 protothecoid es Fresh water 792 pond algae Nannochloro psis salina Scenedesmus 803 incrassatulus

Specific gravity

Kinematic Viscosity (cSt)

Higher Calorific value (MJkg-1)

Acid number (mg KOHg-1)

Pour point (°C)

Flash point

CHNS

Total Glycer ol (%)

Copper strip corrosion

Reference

0.86-0.9

1.9-6

>35

0.50

-

Min. 100– 170

-

0.24

1-3

-

-

4.1

42.7

0.51

< -7

-

-

0.08

-

-

4.22

40.04

-

-

124

-

-

-

Mathimani et al., 2017 Islam et al., 2017

3.51

40.362

2.1

-18.3

92

-

-

-

0.85

4.6

39.2

-

-20

-

-

-

-

3.78

41

-

3

-

75.34, 11.3, 0.05, 0.02 -

-

-

Prabhu et al., 2018 Patil et al., 2017 AriasPeñaranda et al., 2013

Other Feedstocks Soybean 890

5.249

37.52

148

Can et al., 2016 Attia et al., 2016

Waste cooking oil

877

-

4.9

37.95

-

-

129

80.6, 12.6, nil, 0.00056

-

-

Waste fish oil

875

-

4.142

41

-

-

170

82.06, 8.64, -,-

-

-

Mustard

880

-

5.77

39.85

-

-12

158

-

-

-

Neem

844

-

4.28

37.51

-

-

140

-

-

-

Palm

801

-

3.85

39.385

-

-

146

-

-

-

Rice bran

880

-

39.54

-

-

-

-

-

-

Jatropha

880

-

5.66

40.07

-

-

160.5

-

-

-

Karanja

900

-

4.37

42.13

-

-

163

-

-

-

Rubber seed

880

-

4.84

-

0.35

-

184

-

-

1

D 1298

D287

D 445

D 240

D 664

D 97

D93

CHNS analyzer

D1275

-

±0.1 kg/m3 860

±0.001

±0.01 mm2 /s 5.66

±0.001 MJ/kg 41.36

±0.001 mg KOH/g 0.45

±0.1C

±0.1C

EN 14105 ±0.01%

-

-

-18

130

0.06

1

Nautiyal et al., 2015

This study Method Accuracy Spirulina platensis

0.865

78.44, 12.04, 020, 0.08

Gharehgha ni et al., 2017 Uyumaz, 2018 Devarajan et al., 2018 Devarajan et al., 2018 Bora and Saha, 2016 Patel et al., 2016 Sivaramakri shnan, 2018 Roschat et al., 2017

Table 3 Properties of tested fuels Fuel Density (kg/m3)

Viscosity

Higher Calorific

(mm2/s) at 400C

Value (MJ/kg)

Diesel Algae Biodiesel

B10 B20 B100

825

2.89

43.23

831 841 860

3.45 3.82 5.66

42.79 42.13 41.36

3.2. Performance characteristics 3.2.1. Brake thermal efficiency Brake thermal efficiency (BTE) is one of the most significant engine’s performance parameters. The variation of BTE with the change in load at 1500 rpm for algae biodiesel-diesel blends and diesel is presented in Fig. 3. It indicates how efficiently fuel burnt during combustion can be converted into useful work. The efficiency is majorly influenced by the calorific value, cetane number, density, viscosity and oxygen content present in the fuel. It is observed from the results that an increase in load leads to an increase in the efficiency in all cases due to the increase of in-cylinder temperature. The efficiency of algae biodiesel-diesel blends was slightly lower than that of base diesel at lower and part loads, and in the comparable range (within the uncertainty limits) to that of base diesel at higher loads. This is due to combined effect of low caloric value and high viscosity and density of blends which are accountable for spray characteristics leading to inferior air-fuel mixture formation and combustion resulting in lower brake thermal efficiency (Alptekin et al., 2008). Even though biodiesel has high density and viscosity compared to base diesel which can adversely affect its degree of atomization, but then again, the early start of combustion and improved lubricating properties of algae biodiesel annul the

adverse effects of atomization and thus efficiency of all the blends of biodiesel is comparable with diesel. The brake thermal efficiencies of different algae biodiesel-diesel blends (B10, B20 and B100) and base diesel at full load obtained were 26.79%, 25.97% 26.51% and 27.19% respectively, which were almost in the similar range. The oxygen in biodiesel assist in improved combustion but it is compensated with lower calorific value of biodiesel compared to base diesel. The results are in agreement with the reported works in the literature (Miri et al., 2017; Sanjid et al., 2016; Nautiyal et al., 2017; Datta and Mondal, 2016) Babu and Anand, 2017 studied the effect of biodiesel from waste frying oil on the characteristics of diesel engine. They reported that the high viscosity of biodiesel causes its poor atomization during spray which requires more energy for pumping the fuel. Moreover, the high density of biodiesel causes more discharge of fuel to uphold the equivalent energy input to engine. 35.00 30.00

BTE (%)

25.00 20.00

Diesel Algae B10

15.00

Algae B20

10.00

Algae B100

5.00 0.00 0

20

40

60

80

100

Load (%) Fig. 3. Variation of brake thermal efficiency at different loads 3.3. Combustion characteristics 3.3.1. In-Cylinder pressure and maximum rate of pressure rise

The combustion characteristics of the diesel engine are largely dependent on the physical and chemical properties of the fuel utilized. The cylinder pressure defines the capability of a fuel to blend homogeneously with air and burn efficiently. The variation of in-cylinder pressure with crank angle at full load for algae biodiesel-diesel blends is shown in Fig. 4. The pattern of variation of incylinder pressure with crank angle for algae biodiesel-diesel blends were similar to that of base diesel. The in-cylinder pressure was found to be marginally lower with biodiesel-diesel blends compared to that of base diesel. The results showed that the in-cylinder pressure and the percentage of biodiesel in a blend is inverse related to each other. This could be due to the lower volatility and higher viscosity of biodiesel leading to poor mixture preparation and atomization, thereby lowering of peak pressure. The addition of biodiesel in base diesel leads to early start of combustion which can be seen in figure showing the advance rise in pressure. The similar observations of early pressure rise were also reported by Ozturk, 2015 and Abedin et al., 2016 using canola oil- hazelnut soapstock biodiesel mixture and Calophyllum inophyllum biodiesel respectively. It is evident from the graph that combustion was early in the case of biodiesel and its blends compared to diesel because of the shorter ignition delay period and higher cetane number of biodiesel. Cetane number is another factor responsible for the advancement of pressure rise as start of combustion advances with increasing cetane number (Dhar and Aggarwal, 2014). Higher the cetane number, more is the advancement of pressure rise. Thus, high cetane number and more oxygen content in biodiesel led to rapid combustion during pre-mixed combustion phase which resulted in higher peak pressure values in biodiesel compared to base diesel. How et al., 2014 reported that the with biodiesel, the peak of in-cylinder pressure is marginally lower than compared to diesel which could be due to the combined effect of high viscosity and lower calorific value of biodiesel. Dhar and Agarwal, 2014 proposed the scientific explanation for lower in-cylinder pressure peak for biodiesel when compared to diesel which is attributable to the poor fuel–air mixing due to higher evaporation energy desired by biodiesel which plays the significant part in deteriorating the combustion and results in lower peak pressure. The similar findings were reported by Hwang et al., 2016 by using biodiesel produced from waste cooking oil where maximum in-cylinder pressure peak was lower for biodiesel compared to diesel. Besides, the knock-free operation of the diesel engine can be evidently seen in Fig. 4 as the graph is depicting smooth curve with no pulsation on the pressure. The maximum rate of pressure rise is an indicator of an engine rough running. The rate of pressure rises decrease with increasing concentration of biodiesel in the blend due to lower ignition delay period and hence less fuel accumulation during the premixed combustion phase for biodiesel blends. Similarly, algae biodiesel-diesel blends showed the lower rate of maximum pressure rise compared to that observed with base diesel. The maximum rate of pressure rise for base diesel, B10, B20 and B100 blends of algae biodiesel, as observed in Fig. 5, was 7.35 bar/ ° CA, 6.20 bar/ ° CA, 5.90 bar/ ° CA and 3.36 bar/ ° CA respectively.

In-cylinder pressure (bar)

80

Diesel

70

Algae B10 Algae B20

60

Algae B100

50 40 30 20 10 0

-100

-80

-60

-40

-20 0 -10 ° CA

20

40

60

80

100

Fig. 4. In-cylinder pressure of a diesel engine fuelled with different Spirulina algae biodiesel-diesel blends

Maximum rate of pressure rise (bar/deg.CA)

8 6 4 2

Diesel Algae B10 Algae B20 Algae B100

0

Fig. 5. Comparison of maximum rate of pressure rise for Spirulina algae biodiesel-diesel blends with base diesel

3.3.2. Ignition delay Ignition delay is one of the combustion characteristics which defines the time period between the start of injection and start of combustion. The delay period is composed of chemical and physical delay. The physical delay is due to the time required for atomization of fuel, vaporization and air-fuel mixing, whereas chemical delay comprises of pre-combustion reactions. It impacts the combustion phase by effecting the premixing of air-fuel vapor and the thermodynamic efficiency of the engine. It also has a substantial effect on the heat release rate and NOx emissions. It influences the in-cylinder pressure and the combustion phases as well. It is a known fact that the higher cetane number and more oxygen content of fuel lead to decrease in ignition delay. Moreover, low heat capacity of the biodiesel fuel results in its swift heating and evaporation which reduce the ignition delay. Ignition delay period is inversely related to cetane number. Higher the cetane number, lower will be the ignition delay and thus better will be the diffusion combustion as compared to pre-mixed combustion. The ignition delay period for biodiesel-diesel blends was lower in comparison to that of base diesel. This can be supported by the fact that the swift pre-flame reactions occur in biodiesel that lower the chemical ignition delay period in biodiesel (Das et al., 2018). The small ignition delay period hastens the flame propagation which lowers the carbon activation temperature and exhaust gas temperature (Ramanan and Yuvarajan, 2015). Due to the increase in the ignition delay period, fuel which gets accumulated in the combustion cylinder gets burnt rapidly which shortens the combustion duration. Buyukkaya, 2010 proposed the scientific explanation for lower ignition delay while using biodiesel in engine compared to base diesel. The chemical reactions which take place during biodiesel injection in the engine at high temperature results in the breakdown of the high molecular weight fatty acid alkyl esters present in biodiesel. These heterogeneous intricate chemical reactions lead to the formation of low molecular weight gases. Rapid gasification soon spreads from the peripheral of the spray throughout the jet stream, and therefore volatile combustion mixture ignites early and reduces the ignition delay period. Similar results were reported by How et al., 2014 while using coconut biodiesel in high pressure common rail biodiesel. The ignition delay period of base diesel, B10, B20 and B100 of algae biodiesel-diesel blends was 10 ° CA, 10 ° CA, 9.50 ° CA and 7.30 deg CA respectively (Fig. 6). Canacki, 2007 reported that biodiesel from soybean oil had the shorter ignition delay period of about 1.06 ° CA compared to that of base diesel with corresponding cetane number values of 42.6 and 51.5 for diesel and biodiesel respectively. Similarly, in another study, Ozsezen et al., 2009 reported the ignition delay period for palm biodiesel, canola biodiesel and base diesel equal to 7.50 ° CA, 8.0 °CA and 8.25 ° CA respectively. Shahabuddin et al., 2013 reported that the viscosity of the fuel used in the engine governs the ignition delay during the combustion process. Lower the viscosity of the fuel, lower will be the ignition delay and the advancement in the combustion. Another study, conducted by Ozsezen and Canakci, 2011 reported that with

waste palm oil biodiesel and canola biodiesel, there is early start of combustion with respect to conventional diesel. The average timing of start of combustion with palm and canola biodiesel was 1.21 CA and 0.41 CA, respectively as compared to diesel. 12

Ignition Delay (° CA)

10 8 6 4 2 0 Diesel

Algae B10

Algae B20

Algae B100

Fig. 6. Comparison of ignition delay for Spirulina algae biodiesel-diesel blends with base diesel at full load 3.3.3. Heat release rate and cumulative heat release Figure 7 shows the heat release rate with respect to degree crank angle at full load for the fuels. The combustion phenomena in the compression ignition engine can be split into two major phases. The first phase is the premixed combustion phase and the other is the diffusion combustion phase. The first phase (premixed combustion) begins with the start of injection of fuel followed by air-fuel mixing leading to high degree of homogeneous charge during the ignition delay period. This combustible mixture gets ignited resulting in triggering of rapid reactions and resulting in higher heat release rate (Ozener et al., 2014). During the diffusion combustion period, the burning is controlled with the air-fuel mixture available for combustion. Since, biodiesel blends have higher cetane number compared to diesel, it assists in improved diffusion combustion instead of premixed combustion. In addition to this, high viscosity and low calorific value of biodiesel compared to diesel are the factors which also contribute to heat release. The algae biodiesel and diesel showed the similar trends of heat release rate with respect to crank angle. It can also be observed from the

figure, as the curve for biodiesel shifted towards the left compared to diesel, this depicts that the combustion is earlier for biodiesel– diesel blends as compared to base diesel. This corresponds to the short period of ignition delay period in the case of biodiesel. In the beginning, heat release rate is observed to be negative due to the evaporation of fuel which gets accumulated during the ignition delay period and later becomes positive during further combustion process. Figure 7 shows that in premixed combustion phase, the rate of heat release for the blends is less with respect to diesel. This is a result of a lesser amount of fuel accumulation due to rapid burning of injected fuel as in-cylinder temperature is relatively higher in diffusion combustion phase than premixed combustion phase. Due to high volatility and exceptional mixing of base diesel with air, it leads to prolonged ignition delay of diesel compared to biodiesel. This intensifies the rate of pre-mixed combustion for base diesel, thus resulting in higher heat release rate. As a result of this advancement of heat release in the case of biodiesel, the in-cylinder temperature of biodiesel rises, and this leads to the increase in NOx emissions. Ozener et al., 2014 studied the effect of soybean biodiesel on heat release rate of diesel engine and stated that maximum HRR got lowered when the percentage of biodiesel content in the fuel blend is increased. This could be due to the longer ignition delay for diesel than for biodiesel which results in much better air and fuel mixing and caused the higher heat release rate. 80

Diesel Algae B10 Algae B20 Algae B100

70 60 HRR (J/° CA)

50 Diffusion combustion phase

40 30

After burning phase

20 10 0

-40

-20

-10 0 -20

20

40

60

Premixed ° CA

Fig. 7. Variation of heat release rate

80

100

Cumulative heat release (kJ)

1600 1400 1200 Diesel

1000

Algae B10

800

Algae B20

600

Algae B100

400 200 0 0

20

40 ° CA

60

80

100

Fig. 8. Cumulative heat release for Spirulina algae biodiesel-diesel blends and base diesel at full load Figure 8 shows the cumulative heat release with respect to crank angle for algae biodiesel-diesel blends. Cumulative heat release is the measure of chemical energy released by combustion of fuel. The pattern of cumulative heat release curve with change in crank angle for all the biodiesel fuels were similar compared to base diesel. As observed in figure, the cumulative heat release for biodiesel-diesel blends was lower in comparison to diesel. The calorific value of biodiesel is less in comparison to that of diesel which results in lower cumulative heat release. The release of heat for biodiesel was early when compared to diesel but very rapidly combustion of diesel fuel exceeds its cumulative heat release. The high surface tension and viscosity of biodiesel check the reasonable breakdown of the biodiesel during the injection which depreciates the appreciable amount of combustible mixture formation and leads to lower cumulative heat release (Prasath et al., 2010).

3.3.4. Combustion duration Figure 9 compares the combustion duration of algae biodiesel-diesel blends with that of base diesel. The combustion duration is the time interval between the beginning and end of combustion. Mass fraction burned (MFB) can be better understood as the fraction of fuel converted to energy which is the function of crank angle in a combustion cycle that is comprised of flame development angle considered at 10% of the total heat energy release (HRR) and rapid burning angle considered at 90% of HRR. This fuel burning duration which lie down in between 10% to 90% of HRR is defined as combustion duration. The beginning of combustion in the compression ignition engine is defined as the start of heat release, whereas the end of combustion is denoted by the 90% heat release of the total heat release. The duration of combustion for blends was longer than diesel. This could be due to the lower volatility and higher viscosity leading to poor atomization and slower combustion in case of biodiesel which prolongs the duration of combustion. Moreover, the longer injection duration in biodiesel also lead to prolongation of the combustion duration. Biodiesel fuel in comparison to base diesel does not evaporate adequately; therefore, evaporation of fuel continues upto the end of main combustion phase. According to Ozener et al., 2014, the high viscosity of biodiesel affects its atomization, spray characteristics and evaporation which are mainly responsible for lengthier combustion duration. It was 37.5 ° CA, 38 ° CA, 38 ° CA and 40 ° CA for base diesel, B10, B20 and B100 algae biodiesel-diesel blends respectively. This shows that the combustion duration increased upto 2.5 ° CA while using biodiesel compared to base diesel. Can, 2014 reported 3 ° CA increase in combustion duration when biodiesel from waste cooking oil was added to base diesel. With the view of retaining the similar or given power output with similar BTE, more fuel must be injected relatively to the engine. The late combustion of fuel results in fuel burning in the expansion stroke, of late the input of the heat energy to the overall engine work becomes quite low. Can et al., 2017 stated that increase in combustion duration using canola biodiesel is due to its higher fuel injection duration and low calorific value of biodiesel. Also, the slower combustion rate of biodiesel during the last stage of the diffusion combustion is contributed by the higher boiling point and viscosity of the canola biodiesel. Can et al., 2016 stated that the high density, high viscosity and high surface tension of biodiesel compared to diesel cause the deterioration of rate of evaporation of fuel as well as air–fuel mixing resulting in increase of droplet size. As a result, the combustion shifts towards the expansion period and causes increase in combustion duration. Lee et al., 2017 also reported the higher combustion duration for karanja biodiesel and blends compared to base diesel in a single cylinder compression ignition engine. According to Can et al., 2014, due to higher cetane number of biodiesel than diesel fuel, biodiesel possess shorten ignition delay period. On the other hand, high viscosity and high boiling point of biodiesel influence the fuel injection processes such as spray characteristics, evaporation rate and degree of atomization, which results in sluggish burning and extended combustion duration.

Combustion Duration (° CA)

Diesel

45

Algae B10

40

Algae B20

35

Algae B100

30 25 20 15 10 5 0

Fig. 9. Comparison of combustion duration for Spirulina algae biodiesel-diesel blends with base diesel at full load 3.3.5. In-cylinder temperature Figure 10 shows change in in-cylinder temperature for algae biodiesel blends. The graph shows the similar trends of in-cylinder temperature with change in crank angle for diesel and biodiesel blends. However, the peak of in-cylinder temperature was higher for biodiesel compared to that of base diesel. This could be due to a higher oxygen content of biodiesel. The more fuel accumulation during the ignition delay period in case of biodiesel also leads to higher in-cylinder temperature. Biodiesel has higher bulk modulus which means it is less compressible, leading to advance injection timing. This results in premature combustion initiation, thus incylinder temperature gets raised showing the increase in NOx emission. Yoon and Lee, 2011 proposed that the longer ignition delay of diesel fuel lead to the shifting and retardation of combustion towards the expansion stroke which helps in lowering the in-cylinder temperature and thus it reduces the exhaust gas temperature Thus, with increase in biodiesel percentage in a blend, the in-cylinder temperature increases.

Diesel

In-cylinder temperature (K)

2500

Algae B10 Algae B20

2000

Algae B100

1500 1000 500

-90

-70

-50

-30

0 -10 ° CA

10

30

50

70

90

Fig. 10. In-cylinder temperature of a diesel engine fuelled with different Spirulina algae biodiesel-diesel blends 3.4. Emission characteristics 3.4.1. Carbon monoxide The variation of carbon monoxide (CO) emission with load for algae biodiesel blends and diesel is represented in Fig. 11. CO is the product of partial oxidization of fuel combustion. The CO emission formation in exhaust emission are largely governed by factors such as fuel type, in-cylinder temperature and air: fuel ratio. The CO emission first shows the decline followed by an increase with the rise in load. The reason could be that when the engine is operating at lower loads, cylinder temperature is not satisfactory to convert carbon monoxide to carbon dioxide. This results in higher emission of CO at lower load than at partial loads. On the other hand, when the engine is operating at higher loads, CO shows an increase due to the poor air-fuel ratio leading to partial combustion yet again. There is the sudden rise of CO emission at 100% engine load. This could be due to the injection of greater amount of fuel at 100% load in order to retain the required constant engine speed, resulting in the formation of fuel-rich zone and thus oxygen

becomes less available for complete combustion, therefore CO emission showed the abrupt rise. When engine is operating at medium loads, the concentration of oxygen is adequate for complete fuel combustion. The CO emission for B100 blend of algae biodiesel reduced from 3.61 g/kWh to 0.53 g/kWh when the load was increased from 20% to 60% and thereafter rose to 1.2 g/kWh at full load. The CO emission increased suddenly at full load condition due to more quantity of fuel injected to maintain the constant engine speed which creates the fuel rich zone, creates the deficiency of available oxygen. The emission of carbon monoxide for biodiesel was less because of the extra oxygen present in biodiesel in ester form which aids in better combustion. The CO emission for algae biodiesel-diesel blends (B10, B20, B100) and base diesel at full load was 2.56 g/kWh, 2.33 g/kWh, 1.20 g/kWh and 3.10 g/kWh respectively. Similarly, with an increase in biodiesel quantity in blend, the CO emission reduced which is due inherent oxygen content and high cetane number of biodiesel. The high cetane number leads to shorter ignition delay which results in improved combustion. Longer the ignition delay period of a fuel, more time the fuel will take for evaporation which enhances the leaner local mixture region leading to increased CO emissions. Thus, B100 blend showed the lowest CO emission of CO in comparison to that with base diesel. Similar reasons are given by other researchers, Fattah et al., 2013 presented that the oxygen content present in biodiesel enhances the complete combustion of air- fuel mixture which reduces CO emissions. Wu et al., 2009 reported that high cetane number of biodiesel lowers the possibility of formation of fuel-rich zones and also lead to advancement of fuel injection and its combustion which justifies the lower CO emission with biodiesel. Rajak et al., 2019b reported the decrease in CO emissions by 3.6% by using Spirulina algae biodiesel in naturally aspirated compression ignition engine.

8.00 Diesel

CO (g/kWh)

7.00

Algae B10

6.00

Algae B20

5.00

Algae B100

4.00 3.00 2.00 1.00 0

20

40

60

80

100

Load (%) Fig. 11. CO emission in a diesel engine fuelled with different Spirulina algae biodiesel-diesel blends

3.4.2. Hydrocarbon Figure 12 shows the variation of emissions of hydrocarbon (HC) emission with change in load for blends and diesel. The HC likewise CO forms because of partial oxidation due to inadequacy of oxygen required for complete combustion. The in-cylinder temperature is also not enough to trigger fuel ignition. It can be noticed from the graph that HC emission was high at lower loads in comparison to intermediate and higher loads caused by the lower temperature conditions which makes complete combustion challenging. The HC emission with algae biodiesel (B100) showed the following trend: 0.13 g/kWh,0.08 g/kWh, 0.06 g/kWh, 0.05 g/kWh and 0.04 g/kWh at 20%, 40%, 60% 80% and 100% loads respectively. Hydrocarbon emission for blend was lesser than diesel due to the additional oxygen moiety present in biodiesel which helps in complete combustion. The other factor which causes the fall in HC was greater cetane number of biodiesel in comparison to diesel which resulted in the decrease of ignition delay. As the biodiesel percentage was improved in a blend, HC decreased consequently and therefore, engine fuelled with algae biodiesel (B100) resulted

in the formation of lowest HC (0.04-0.13 g/kWh) compared to B10, B20 and base diesel had the similar range of 0.06-0.13 g/kWh within the uncertainty limits. The results obtained were in line with the results reported by Ozcelik et al., 2015 and Ozener et al., 2014. According to them, the possible reason for lower emission with biodiesel fuelled engine in comparison to base diesel was the lower carbon and hydrogen content in biodiesel compared to diesel. Dhar and Aggarwal, 2014 reported the two possible sources of HC emission in the heterogeneous combustion environment of compression ignition engine i.e., (i) over-leaning of air-fuel mixture and (ii) fuel over-rich zones. Knothe et al., 2006, reported that the major reason which causes significant decrease in HC emission with biodiesel compared to base diesel is the presence of the methyl ester and the unsaturation in the structure of biodiesel. Ong et al., 2014 proposed that the length of carbon chain in biodiesel has a very pronounced effect on HC emissions. They reported that HC emissions from Cieba petandra biodiesel were lower than Jatropha biodiesel and Calophyllum biodiesel due to the presence of shorter carbon chain length in the former.

Diesel Algae B10 Algae B20 Algae B100

0.14

HC (g/kWh)

0.12 0.1 0.08 0.06 0.04 0.02 0 0

20

40

Load (%)

60

80

100

Fig. 12. HC emission in a diesel engine fuelled with different Spirulina algae biodiesel-diesel blends

3.4.3. Nitrogen oxides Even though nitrogen is considered as inert gas at atmospheric conditions, however when the temperature is very high, greater than 1100 °C, it becomes reactive towards oxygen to form oxides of nitrogen. There exist two major oxides of nitrogen viz. NO and NO2 which are usually designated together as NOx emission. They are largely produced by the three common chemical pathways and thus called as: thermal NOx, prompt NOx and fuel NOx. The mechanism called as Zeldovich mechanism (reactions 1-3) explains the steps involved in the formation of oxides of nitrogen at higher temperature above 1500°C which contributes to thermal NOx. O + N → NO + N 1 N + ! → NO + O 2 N + OH → NO + H 3 Prompt NOx is produced when the fragments of hydrocarbon (CH and CH2) react with nitrogen which results in generation of C-N species (reaction 4-5). These fragments are formed due to fuel combustion in the cylinder. The C-N moieties and oxygen react via series of reaction and form prompt NOx. The fuel NOx is a result of inherent nitrogen species present in the fuel. CH + &! → HCN + N 4 C(! + &! → HCN + NH 5 The formation of NOx is highly sensitive to in-cylinder temperature, concentration of oxygen and the residence time (Heywood, 1988). The greater bulk modulus of biodiesel in comparison to conventional diesel makes it less compressible and inevitably advances its injection timing (Hoekmon and Robbins 2012). The advancement of injection timing results in early start of combustion and this raises in-cylinder temperature. Thus, the longer residence time lead to increase in NOx emission. The inherent additional oxygen present in biodiesel brings the premixed phase closer to stoichiometric condition which lead to rise in in-cylinder temperature and as a result, NOx increases. The change in NOx with change in load for different algae biodiesel-diesel blends is shown in Fig. 13. The NOx emission shows the decreasing trend with an increase in the load. There is the sudden fall of NOx emission at 40% engine load. This could be due the fact that at lower load of 20% the combustion chamber is richer with air when compared with cylinder conditions at 40% load. The air rich zone at 20% lead to better combustion comparatively, which raises the temperature of cylinder and thus NOx is more at 20% load and drops suddenly at 40% load. With the increase of biodiesel percentage in blend, NOx showed an increase as well. This is because of oxygen atom biodiesel which lead to improved combustion, brings rise in the in-cylinder temperature resulting in higher NOx emission. The high cetane number of biodiesel raise timing of

injection that is also responsible for raising the NOx emission. Figure 13 also clarifies that NOx emission for fuels was at the maximum in lower loads and falls when load is increased. The high adiabatic flame temperature when biodiesel is combusted also contributes to high formation of the thermal NOx. The NOx emission with B10, B20 and B100 blends of algae biodiesel at full load was 13.36 g/kWh, 13.95 g/kWh and 16.19 g/kWh respectively which was higher in comparison to 13.13 g/kWh of base diesel. Benjumea et al., 2011 proposed that the presence of unsaturated fatty acids in biodiesel contribute to NOx emission via prompt mechanism as the percentage of hydrocarbon radicals increase substantially during combustion which is promoted by presence of unsaturation in fuel. 20 18 16 NOx (g/kWh)

14 12 10 8 Diesel

6

Algae B10

4

Algae B20 Algae B100

2 0 0

20

40

Load (%)

60

80

100

Fig. 13. NOx emission in a diesel engine fuelled with different Spirulina algae biodiesel-diesel blends

3.4.4. Smoke

Smoke opacity (%)

The variation of smoke opacity for algae biodiesel-diesel blends at varying engine loads is illustrated in Fig. 14. The formation of smoke is due to the incomplete combustion of fuel, specifically combustion of the aromatics hydrocarbon. The engine running with algae biodiesel-diesel blends emitted the lower smoke than that with base diesel because of the presence of lower sulphur and aromatic content in biodiesel and therefore, as the percentage of biodiesel is increased in the blend, the smoke opacity decreased accordingly. Smoke opacity with engine running on B100 blend of algae biodiesel was 0.70% compared to 0.60% with base diesel. Smoke opacity increased with a rise in the load as more quantity of fuel is introduced in cylinder as well as local amounts of oxygen concentration decrease leading to amplified smoke emission (Dhamodaran et al., 2017). Similarly, with the increase in load from 20% to 100% with B100 blend of algae biodiesel, the smoke opacity varied from 0.2% to 0.6% respectively. The smoke opacity shows a fall with an increase in the biodiesel percentage in blend. Furthermore, extra oxygen in biodiesel favors the further oxidation of residual carbon, thus lowers smoke. The similar results in the same line were reported in literature such as Ilkilic et al., 2011 and Ozener et al., 2014. Dhinesh et al., 2016 who assessed the emission characteristics of diesel engine fuelled with Cymbopogon flexuosus biodiesel reported that chemically biodiesel has lower C/H ratio, absence of aromatic compounds and presence of oxygen which results in lower smoke emissions when engine is powered by biodiesel compared to diesel. Silitonga et al., 2018 reported that the oxygen atom in the oxygenated fuels forms the very strong bond with carbon atoms which makes the bond difficult to break. This checks and prevents the formation of aromatic hydrocarbons and thus, smoke emissions are curbed. 0.8 0.7 0.6 0.5 0.4 0.3

Diesel Algae B10 Algae B20 Algae B100

0.2 0.1 0 0

20

40 Load (%) 60

80

100

Fig. 14. Smoke opacity in a diesel engine fuelled with different Spirulina algae biodiesel-diesel blends

4.

4. Limitations and perspectives Algae as a biodiesel feedstock gained popularity primarily due to their high lipid productivity and marginal land requirement. The oil production from algae usually range from 5.87 L/m2 to 13.69 L/m2 which is 10– 23 times higher than the highest oil producing crop. On the other hand, land required for cultivation is about 10–340 times smaller than their other counterparts (Nagarajan et al., 2013). The properties of biodiesel produced from algae are comparable with base diesel. However, it is expensive as compared to diesel due to high costs associated with algae cultivation and harvesting which creates the scaling up of algae biodiesel difficult. The U.S. Department of Energy (DOE) reported the limitations which caused the challenges in the commercialization of algae biodiesel (EERE, 2008). The published report stated that the cost of 1 litre of algae biodiesel was approximately $2.11 which is way higher as compared to soybean biodiesel ($1.05/L) (EERE, 2008). To overcome the problem of commercialization of algae biodiesel, detailed analysis on costs, technology alternatives and system integration are required. One of the effective strategies to lower the burden of overall processing cost is to directly convert algae biomass to biodiesel through simultaneous oil extraction and transesterification which significantly reduces chemicals, time and energy (Nagarajan et al., 2013). Drying of algae biomass is necessary for efficient extraction of lipid from it which again is energy intensive step. The latest development in this respect is to use the wet biomass for efficient lipid extraction (Dong et al., 2016). This approach can cut down the final price of biodiesel. The cost analysis by Nagarajan et al., 2013 suggested that instead of using pure CO2 for algae cultivation, the use of CO2 from flue gas can reduce the costs by 24.8– 26.8%. Moreover, the costs of biodiesel can also be reduced if the spent algae biomass is used for biogas generation which can result the cost drop by almost 36.9%. Doshi et al., 2016 reported that lipids which constitutes on an average around 30% by wt. of dry algae biomass, when extracted, the remainder biomass can be potentially used for production of various value-added products like as animal feed or other bio-energy alternatives such as ethanol, bio-gas or hydrogen that can be used as fuels. Algae has ability to grow in waste water and utilize the contaminants present in waste as the source of nutrients such nitrates and phosphates, thereby treating the wastewater too can reduce the cost. The contribution of algae for wastewater treatment, CO2 sequestration and biofuel production has potential to stimulate the algae biodiesel production system. Sharma and Singh, 2017 proposed the solutions to overcome the challenges with respect to high costs associated with algae biodiesel commercialization. One of them is to undertake the challenge of the development of cost-effective photo-bioreactor for algae cultivation and growth which should attain maximum biomass productivity with minimum operating costs. There is also the demand of an hour of skilled R& D in the field of genetic engineering which seems promising to develop a healthy algae strain with much higher lipid content and with high metabolic rate. In a nutshell, from the present study conducted it can be concluded that algae biomass has the immense potential to be the alternate feedstock for biodiesel production with its effective utilization in diesel engine, which is comparable to another established biodiesel and diesel. Some areas, such as algae cultivation and biomass availability, have received certain criticisms concerning with the financial viability of algae biodiesel. However, the literature survey

and current investigation have given a positive feedback about the potential of algae as a feedstock for biodiesel production. The factors questioning its sustainability can be reversed by focusing the research on utilizing the remainder carbon and hydrogen left in algae biomass for the generation of bioenergy and furthermore, by extracting the value-added products from remainder biomass, thus reducing largely the downstream processing expenses for biodiesel production and strengthening its economic sustainability. 5.

5. Conclusions In this study, biodiesel from Spirulina platensis algae was tested in compression ignition engine with an attempt to establish its potential as replacement for the existing fossil fuels. The fuel properties of biodiesel produced by simultaneous oil extraction and transesterification was found to meet the prescribed European and American standards. The results showed that HRR with biodiesel is lower in comparison to diesel through premixed combustion phase due to the shorter period of ignition delay for biodiesel. Brake thermal efficiency of the engine with biodiesel and its blend is almost same compared to base diesel. The maximum rate of pressure rise decreased with increase in concentration of biodiesel in the blend due to decrease in ignition delay period. The combustion duration for biodiesel blends is longer compared to diesel mainly because of rise in injection duration. The CO and HC emissions decreased significantly with biodiesel and its blends as compared to base diesel. Smoke opacity declined drastically with biodiesel owing to the oxygen content in biodiesel and less aromatic in its molecular structure. The NOx with biodiesel increased significantly attributable to the advancement in the timing of injection, oxygen embedded with fuel and higher adiabatic flame temperature. Acknowledgement Piyushi Nautiyal thanks Council of Scientific and Industrial Research, India for graduate fellowship.

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Highlights • • • •

Exploring the potential of third generation biodiesel feedstock, Spirulina platensis algae Brake thermal efficiency was very close to that obtained with base diesel Algae biodiesel showed lower heat release rate Emissions of CO, HC and smoke got drastically reduced

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Author’s name Dr. Piyushi Nautiyal

Dr. K.A. Subramanian Dr. M.G.Dastidar Dr. Ashok Kumar

Affiliation Indian Institute of Technology Delhi, India & New Horizon College of Engineering, Bengaluru, Karnataka, India Indian Institute of Technology Delhi, India Indian Institute of Technology Delhi, India Indian Institute of Technology Delhi, India& New Horizon College of Engineering, Bengaluru, Karnataka, India