This may be the author’s version of a work that was submitted/acceptedfor publication in the following source:

Hossain, Md Farhad, Nabi, Md Nurun, Rainey, Thomas, Bodisco, Timothy,Rahman, Md. Mostafizur, Suara, Kabir Adewale, Rahman, S M Ashrafur,Chu Van, Thuy, Ristovski, Zoran, & Brown, Richard(2017)Investigation of microalgae HTL fuel effects on diesel engine performanceand exhaust emissions using surrogate fuels.Energy Conversion and Management, 152, pp. 186-200.

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Licensed under the Creative Commons Attribution; Non-Commercial; No-Derivatives 4.0 International. DOI:10.1016/j.enconman.2017.09.016

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https://doi.org/10.1016/j.enconman.2017.09.016

Investigation of microalgae HTL fuel effects 1

on diesel engine performance and exhaust 2

emissions using surrogate fuels 3

4

Farhad M. Hossain1, 2*, Md. Nurun Nabi3,Thomas J. Rainey1, 2, Timothy Bodisco4, Md 5

Mostafizur Rahman5, Kabir Suara1, S, M. Ashrafur Rahman 1,2, Thuy Chu Van 1,2, Zoran 6

Ristovski1,2 and Richard J. Brown 1, 2, 7

8

1 Biofuel Engine Research Facility, Queensland University of Technology (QUT), Brisbane, Queensland 4001, 9 Australia 10 2 QUT, International Laboratory for Air Quality and Health 11 3 School of Engineering and Technology, Central Queensland University, Perth, WA 6000, Australia. 12 4 School of Engineering, Deakin University, Waurn Ponds, Victoria 3217, Australia 13 5 Rajshahi University of Engineering & Technology, Department of Mechanical Engineering, Bangladesh 14 15

* Corresponding author 16

Contact: Farhad M. Hossain 17

Email: mdfarhad.hossain@hdr.qut.edu.au; mfarhad03@yahoo.com 18

Postal address: Level-7, O-Block, Gardens Point Campus, QUT, 2 George St, Brisbane, QLD 19

4001, Australia 20

21

Highlights 22

Development of a microalgae HTL surrogate of biocrude fuel using chemical compounds. 23

Physiochemical properties of surrogate blends were analysed. 24

Experimentally investigated diesel engine performance and emissions using surrogate fuels. 25

No significant changes in engine performance were observed with HTL surrogate blends. 26

Major emissions including PM, PN and CO were reduced significantly with increasing of NOx 27

emission. 28

29

30

31

32

2

Abstract 33

This paper builds on previous work using surrogate fuel to investigate advanced internal 34

combustion engine fuels. To date, a surrogate fuel of this nature has not been used for 35

microalgae hydrothermal liquefaction (HTL) biocrude. This research used five different 36

chemical groups found in microalgae HTL biocrude to design a surrogate fuel. Those five 37

chemical groups constitute around 65% (by weight) of a microalgae biocrude produced by 38

HTL. Weight percentage of the microalgae HTL biocrude chemical compounds were used to 39

design the surrogate fuel, which was miscible with diesel at all percentages. The engine 40

experiments were conducted on a EURO IIIA turbocharged common-rail direct-injection six-41

cylinder diesel engine to test engine performance and emissions. Exhaust emissions, including 42

particulate matter and other gaseous emissions, were measured with the surrogate fuel and a 43

reference diesel fuel. Experimental results showed that without significantly deteriorating 44

engine performance, lower particulate mass, particulate number and CO emissions were 45

observed with a penalty in NOx emissions for all surrogate blends compared to those of the 46

reference diesel. 47

48

Keywords: Microalgae, surrogate fuel, diesel engine, emissions, particulate mass, particulate 49

number, PM, PN, NOx and CO. 50

51

52

53

54

55

56

57

58

59

60

3

1.0 Introduction 61

Alternative fuels have become a key issue in the modern world due to the depletion of 62

fossil fuel reserves, increasing fuel prices and issues relating to exhaust emissions. Compared 63

to petroleum diesel, biofuel has some advantages in relation to emissions, including low 64

emissions of carbon monoxide (CO), particulate matter and unburned hydrocarbons (HCs) [1]. 65

Hence, researchers have focused on the development of biofuel and associated upgrading to 66

meet fuel standards without compromising engine durability [2, 3]. Many groups have 67

investigated novel uses of biofuel in diesel engines [4-8]. Unfortunately, most biofuel are not 68

able to be produced at an industrial scale. This is chiefly due to high production costs and the 69

fact that fuel properties may not be suitable for use in current diesel engines due to their 70

physiochemical properties. However, microalgae has recently received a lot of attention as one 71

option for producing biofuel as a renewable energy source because it has minimal adverse 72

effects on food supply and other agricultural systems [9-12]. Microalgae may be a potential 73

feedstock for biofuel based on its lipids and HCs [13, 14]. Various conversion techniques have 74

been used to generate biofuel from microalgae including solvent extraction and hydrothermal 75

liquefaction (HTL) [10, 15-17]. 76

Hydrothermal liquefaction (HTL) methods are gaining interest for producing biocrude. 77

In liquefaction methods, biomass is changed into gas, liquid and solids in a similar manner to 78

pyrolysis [18]. HTL is the most energetically advantageous thermochemical biomass 79

conversion process and it has been investigated with a wide range of microalgae biomass 80

feedstocks, including laboratory and commercially grown strains Botryococcus braunii [19], 81

Spirulina and Tetraselmic sp. [10, 15]. Jena et al. [20] studied the production of biocrude from 82

Spirulina platensis. However, biocrude has a higher oxygen and nitrogen content compared to 83

reference diesel. In addition, HTL biocrude contains inorganic salts and metals which pose 84

challenges within the traditional refining process [10, 19, 21]. 85

Therefore, microalgae based biocrude requires further processing to improve quality by 86

reducing these undesired components. Chemical analysis of microalgae biocrude reveals the 87

presence of many chemical compounds in small quantities. However, five chemicals 88

contribute around 65% (wt.) of the total weight. In this study, those five chemicals were 89

blended to produce a surrogate fuel. 90

Surrogate fuels are not new. Many researchers have developed diesel surrogate fuels 91

using various techniques [22-26]. Surrogates of diesel fuels are useful design tools for 92

4

developing engines with cleaner and more efficient combustion [26]. A surrogate fuel is a 93

mixture of pure chemicals to mimic the physicochemical properties of a target fuel. Both 94

physical and chemical fuel properties should be matched to the surrogate fuel because those 95

properties are important for engine operation, performance and exhaust emissions. The 96

chemical characteristics of the fuel include molecular structure, flash point and C/H/O ration 97

whilst physical characteristics include HHV, density, viscosity and surface tension [22]. 98

Pitz and Mueller [22] reviewed recent progress in the development of diesel surrogate 99

fuels. They investigated the status of chemical kinetic models and experimental validation data 100

of surrogate fuel components. They concluded that the presence of higher molecular weight 101

components is needed in models and experimental investigations of surrogate fuel [22]. Dooley 102

et al. [27] formulated a jet surrogate fuel by real fuel properties. They used three chemical 103

compounds n-decane, iso-octane and toluene mixture of 42.67, 33.02 and 24.31 (mol %) to 104

obtain target surrogate properties [27]. Liu et al. [24] experimentally and numerically 105

investigated the combustion and emissions characteristics of diesel surrogate fuels in a diesel 106

engine. They investigated three different surrogates including 85% (vol.) n-heptane blended 107

with 15% toluene (T15), 81% n-heptane blended with 14% toluene and 5% c-hexane (T15 + 108

CH5), and 80% (vol.) n-heptane blended with 20% toluene (T20). They found the NOx and 109

soot emissions were reasonably predicted. From the modelling investigations, they inferred 110

that the effects of physical properties on the soot emission were larger than the effects of 111

chemical properties of the different fuel carbon-chain structures [24]. Das et al. [26] 112

investigated on sooting tendencies of diesel fuels, jet fuels, and their surrogates in a diesel 113

engine. They reported the opportunity for developing new surrogates, composed of HCs with 114

well-studied chemistry, which can be used to replicate the sooting behaviour of most fuels [26]. 115

Wu et al. [25] experimentally investigated the miscibility of hydrogenated biomass-pyrolysis-116

oil with diesel as surrogate-ethylene glycol and its applicability to diesel engines. They found 117

that only 10% volume ethylene glycol could be mixed with diesel. They also reported that there 118

was no significant difference in specific fuel consumption but found a reduction in soot 119

emissions [25]. Abboud et al. [28] tested the effect of the concentration of oxygenated 120

compounds on sooting propensities of surrogate diesel and biodiesel. They found different 121

behaviour for soot generation in both surrogate diesel and biodiesel. They also reported that 122

biodiesel-derived soot was smaller and less reactive than diesel-derived soots [28]. 123

The objectives of this study were to comparatively investigate the engine performance 124

and exhaust emissions of a series of microalgae HTL surrogate fuels on a common-rail, multi-125

5

cylinder, turbo-charged diesel engine. The significance of this research is to determine the 126

thermal efficiencies and exhaust emissions of a new surrogate fuel in a commercial diesel 127

engine and establish a non-conventional fuel application in a regular engine without 128

modification. The performance of the engine output is presented in terms of in-cylinder 129

pressure and volume, brake power (BP), brake mean effective pressure (BMEP), brake thermal 130

efficiency (BTE) and brake specific fuel consumption (BSFC). Gaseous emissions of nitrogen 131

dioxide (NO2), nitrogen oxide (NOx), CO, particulate matter (PM) and particulate number (PN) 132

were compared. 133

To the authors’ knowledge, no investigation has been performed using a microalgae HTL 134

biocrude surrogate fuel to investigate performance and exhaust emissions. This research will 135

also provide fundamental knowledge for developing microalgae biocrudes. 136

137

2.0 Concept of microalgae HTL surrogate 138

In earlier experimental work, microalgae biomass were used to produce biocrude using 139

a HTL method. . Two different variables were used as operating conditions: temperature and 140

slurry concentration. It was found that 25% slurry concentration and 350 ⁰C approved the best 141

operating conditions. Further detail of the microalgae biocrude operating conditions can be 142

found in Farhad et al. [29]. It was also found that microalgae HTL biocrude contains 13 main 143

chemical compounds, seven of which constitute 65% (wt.) of the total weight (i.e. under 144

operating conditions with 25% slurry concentration and 350 ⁰C ) [29]. Those seven chemical 145

compounds are ethylbenzene, 1, 4-dimethyl-benzene, 3-methyl-2-cyclopenten-1-one, 2, 3-146

dimethyl-2-cyclopenten-1-one, undecane, 4-hydroxy-4-methyl-2-pentanone and di(2-147

propylpentyl) ester. These chemical compounds also contain key functional groups present in 148

the biocrude including aromatics, cyclic ketones, alkanes, alcohols, and aromatic FAMEs as 149

shown in Figure 1 (results in duplicate). The horizontal red line drawn at 5% (wt.) is used for 150

illustrative purposes to elucidate which chemical compounds are present at levels above 5%. 151

Figure 2 shows the proportion of compounds in microalgae HTL biocrude by functional group. 152

6

153 154

Figure 1: Weight percentage of chemical compounds in microalgae HTL biocrude. 155

156

157 Figure 2: Major chemical compounds of microalgae HTL biocrude [29]. 158

2.1 Chemical compounds for surrogate fuel 159

Each section of the surrogate palette is referred to as a surrogate chemical compound. 160

The surrogate chemical compounds were selected based on five key functional groups: 161

aromatics, cyclic ketones, alkanes, alcohols, and aromatic FAMEs. Each are described in detail 162

below. 163

164

0

5

10

15%

of

HT

L b

io-c

ru

de c

om

po

un

ds

25% Slurry concentration @ 350 C_1

25% Slurry concentration@ 350 C_2

AlkaneCyclic ketone Aromatic FAMEAromatic Alcohol

Aromatics21%

Cyclic ketone17%

Alkane11%

Alcohel5%

Aromatic FAME11%

Others35%

7

Aromatics 165

Petroleum-based diesel contains around 25% of aromatic HCs [30]. They have an impact 166

on the cetane number and exhaust emissions of diesel engines, which means improved engine 167

performance. Aromatic HCs increase diesel engine particulate emissions, which has long been 168

of concern, due to the toxic composition of the emissions and the particle size distribution [31, 169

32]. Small fine particles are inhalable and penetrate deep into the lungs where they are able to 170

enter the bloodstream and even reach the brain [31, 33]. However, microalgae HTL biocrude 171

contained two aromatics in large quantities: 1, 4-dimethyl-benzene; and ethylbenzene. Their 172

chemical structures are shown in Figure 3 (a) and (b). Two methyl groups or an ethyl group are 173

attached to benzene. They are all colourless, flammable liquids. 174

175

176

(a) (b) 177

Figure 3: Chemical structure of (a)1,4 dimethyl, benzene and (b) Ethylbenzene. 178

179

Cyclic ketone 180

Two ketones (cyclic and straight chain) were found in microalgae HTL biocrude in 181

significant quantities. Figure 4 (a) and (b) shows cyclic ketone 3-methyl, 2-cyclopenten-1-one, 182

and 2, 3-dimethyl, 2-cyclopenten-1-one which is contained in microalgae HTL biocrude. 183

However, both cyclic ketones are very expensive for the purposes of engine testing, so 184

cyclopentone (shown in Figure 4 (c)) was used instead due to its functional similarity and low 185

cost. It is also a colourless liquid with a petrol like odour. Cyclopentene is produced industrially 186

in large amounts. It is used as a monomer for synthesis of plastics, and in several chemical 187

syntheses. 188

189

8

190

(a) (b) (c) 191

Figure 4: Chemical structure of (a) 3-methyl, 2-cyclopenten-1-one, (b) 2,3-dimethyl, 192

2-cyclopenten-1-one and (c ) Cyclopentene. 193

Alkane 194

The majority of diesel fuel is made up of alkanes. Alkanes are straight-chain and single 195

carbon-carbon bond HCs. Petroleum-based diesel is composed of 75% saturated HC, which 196

are alkanes [30]. They are stable chemical compounds compared to double or triple bond HC, 197

which is called alkene and alkaline respectively. Straight-chain alkanes are usually gaseous at 198

room temperature, those with 5 to 15 carbon atoms are usually liquids. The microalgae HTL 199

biocrude contain about 11% (wt.) undecane of the total biocrude weight. This chemical is low 200

cost and can readily be obtained. The chemical structure of undecane is shown in Figure 5. 201

202

Figure 5: Chemical structure of undecane. 203

Alcohol 204

The chemical compound 4-hydroxy-4-methyl-2-pentanone was found in the microalgae 205

HTL biocrude in significant quantities. This chemical contains both ketone and hydroxide 206

groups. It is also expensive. The chemical is structure shown in Figure 6 [34]. Butanol was 207

selected to represent the alcohol group which occurs on a number of biocrude compounds 208

including (4-hydroxy-4-methyl-2-pentanone and 1-acetate 1,2,3-propanetriol). Butanol is 209

readily available and at a suitable cost compared to 4-hydroxy-4-methyl-2-pentanone. 210

9

211

(a) (b) 212

Figure 6: Chemical structure of (a) 4-hydroxy-4-methyl and (b) butanol. 213

214

Aromatic FAME 215

The microalgae HTL biocrude contains a very irregular type of fatty acid methyl ester 216

(FAME): di-(2-propylpentyl) ester. This FAME contained aromatic ring in their chemical 217

structure which is shown in Figure 7. In general, these compounds have low toxicity. 218

219

Figure 7: Chemical structure of di-(2-propylpentyl) ester. 220

221

2.2 Design of microalgae HTL surrogate 222

There have been numerous engine studies using diesel surrogates [22-26, 28]. Most 223

previous studies have involved up to six components [23, 25, 26]. The current study provides 224

a methodology for creating microalgae HTL surrogate fuel. HTL microalgae biocrude contains 225

many different chemical compounds from different chemical groups. In addition, HTL 226

biocrude contains inorganic salts and metals, which bring challenges to the traditional refining 227

process [10, 19, 21]. Therefore, the biocrude requires further processing to improve quality by 228

reducing these undesired components. It is also noted that biocrude physicochemical properties 229

are not similar to regular diesel fuel, thereby preventing it being used directly in conventional 230

diesel engines (as a neat fuel). The approach for designing the target surrogate fuels with the 231

chemical groups is shown in Figure 8, while the final palette is shown in Figure 9. The 232

10

physicochemical properties of the target fuels were taken into account as design parameters 233

and the percentage of different chemical groups was decided according to literature [22, 23]. 234

The target fuel is a theoretical fuel with selected properties that are to be matched by a surrogate 235

fuel. Similarly, the design properties are the properties of the target fuel that are to be matched 236

by the surrogate fuel. The design properties included CN, HHV, density, and the chemical 237

composition of the fuel. The property target for CN was 45 and 0.82-0.84 (kg/L) for density. 238

However, the reference chemical groups were selected from the microalgae HTL biocrude list 239

which is shown in Figure 1. The surrogate fuel properties are shown in Table 3 and compared 240

to a reference diesel fuel. 241

Microalgae HTL biocrude contained about 4% (wt.) nitrogen based on a selected 242

operating condition [29]. However, there are two reasons that the nitrogen was not used in the 243

surrogate fuel: (i) the chemical compounds considered were those having above 5% weight 244

percentages in the biocrude; and (ii) in general, it is very uncommon for nitrogen to be in fuel. 245

However, nitrogenated components in the fuel could be another area for future research to 246

explore. The behaviour of multi-component fuels is more complicated than single component 247

fuels because of the potential for chemical interactions. Though, these chemical compounds 248

come from a relatively stable microalgae HTL biocrude so these interactions in the surrogate 249

fuel were presumed to be realistic. 250

251

11

Selected palette for design fuel

Blend selected palette base

on design properties

Measure design properties

of surrogate fuel

Achieved target fuel

properties?

Y

Surrogate

fuel complete

Change selected

chemicals proportion

N

Design fuel

Select the design properties

and target

Measure and analysis physicochemical

properties of palette: chemical

composition, density, viscosity and HHV

Stop 252

Figure 8: Proposed roadmap for development of microalgae HTL surrogate fuels. 253

254

255

Figure 9: Percentage of chemical compound of a new microalgae HTL surrogate. 256

Aromatics20%

Cyclic ketone15%

Alkane45%

Alcohol10%

Aromatics FAME10%

12

The microalgae HTL surrogate fuel (100%) was blended with the reference diesel to three 257

different percentages 10%, 20% and 50%. 258

Sur-10 Sur-20 Sur-50

259 260

Figure 10: Blended microalgae HTL surrogate for engine test. 261

262

3.0 Materials and methods 263

The experiments were conducted in the Biofuel Engine Research Facility (BERF) at QUT 264

with a EURO IIIA heavy duty diesel engine using surrogate blends and neat diesel fuel (100%). 265

The engine was operated at a constant speed of 1500 rpm (maximum torque speed), at four 266

different loads 25%, 50%, 75% and 100% of full load. Maximum load at any engine speed 267

depends on the type of fuel used, therefore the maximum load for each fuel was determined 268

when the engine was at 1500 rpm. 269

All experiments were conducted in a common-rail six-cylinder, turbo-charged and after-270

cooled diesel engine with the specifications listed in Table 1. The engine had a capacity of 5.9 271

L, maximum torque of 820 Nm at 1500 rpm and maximum power of 162 kW at 2000 rpm. This 272

engine was not fitted with any exhaust gas recirculation (EGR). Each cylinder has four valves, 273

two of them for inlet and two of them for exhaust. The engine was coupled with a water-based 274

dynamometer. Figure 11 shows the schematic of the experimental engine setup. Further detail 275

of the engine configuration and instruments can be found in Bodisco and Brown [35]. 276

Diesel

Surrogate

13

Table 1: Test engine specification. 277

278

Physicochemical properties of pure chemical compounds of surrogate fuel and its blends 279

is shown in Table 2 and Table 3 respectivey. The first row of Table 3 shows the name of the 280

four different fuels 100D, 90D10S, 80D20S, and 50D50S classified by the volume of each fuel. 281

The Microalgae HTL surrogate was in colour less with recognisable odour. The 282

physicochemical properties of the reference diesel and 100% surrogate fuel were 283

experimentally measured. The properties of the blends including 90D10S, 80D20S, and 284

50D50S were calculated proportionally based on the neat fuel properties shown in Table 3 [36, 285

37]. Conversely, CN of the surrogate chemical compound was found from published results, 286

which was shown in Table 2. CN for a few of the surrogate chemical compounds could not be 287

found in the literature. Therefore, an almost similar chemical compound for CN was used and 288

is described here. The CN for aromatic HC 1,2-dimethylbenzene is 8.3, which is part of the 289

xylene compound [38]. Xylene was used as a chemical compound of surrogate fuel, which is a 290

mixture of o-xylene, m-xylene, and p-xylene. The exact CN of xylene was unknown. Likewise, 291

the CN of cyclohexanone was unknown so the CN of cyclopentanone, which is 10 was used 292

instead. The CN for dihexyl phthalate was used instead of dioctyl phthalate (DOP) due to an 293

almost identical chemical structure [38]. 294

Figure 11 shows a schematic diagram of the experimental set up for diesel engine 295

performance and exhaust emissions measurement. The engine performance data including in-296

cylinder pressure, diesel injection timing and degrees of crank angle rotation, were recorded. 297

Indicated work (IW) was calculated by integrating a pressure vs volume diagram using the 298

trapezoid rule. Further detail of the engine performance measurements can be found in Bodisco 299

and Brown [35]. Different exhaust gas measuring instruments including DMS500, DustTrak 300

(Model 8530), SABLE (CA-10) and CAI 600 were used for emissions measurements. The 301

Model Cummins ISBe220 31

Cylinders 6 in-line

Capacity 5.9 L

Bore x stroke 102 x 120 (mm)

Maximum power 162 kW @ 2500 rpm

Maximum torque 820 Nm @ 1500 rpm

Compression ratio 17.3:1

Aspiration Turbocharged

Fuel injection High-pressure common rail

Dynamometer type Electronically controlled water brake dynamometer

Emission standard Euro IIIA

14

DMS500 (Cambustion Ltd.) is uniquely suited for a variety of diesel particulate filter 302

applications. CAI 600 series analysers were used to measure the raw exhaust gases CO, CO2, 303

NO and NOx, and Sable and DustTrak were used to measure diluted CO2 gas and particulate 304

mass respectively. Both DMS500 and DustTrak were used for measurement of PN and PM. 305

Further detail of the engine exhaust emission measurements can be found in Rahman et al. [36]. 306

All measurements were repeated three times, and the repeatability was quantify by calculating 307

the standard deviation and this is shown (Figure 21, 22, 24 26 and 28) as ±1σ standard 308

deviation. 309

Table 2: Properties of diesel and surrogate chemical compounds. 310

Properties

Methods

Diesel

Chemical Groups

Aromatic Cyclic

ketone

Alkane Alcohol Aromatic

FAME

Chemical compounds

Xylene

Cyclope-

ntanone

Undecane

Butanol

Dioctyl-

phthalate

CAS

1330-20-7

CAS

120-92-3

CAS

40-6701

CAS

71-36-1

CAS

117-81-7

Surrogate

composition (% wt.)

20 15 45 10 10

Density (kg/L)1 ASTM

D4052

0.84 0.84 0.92 0.77 0.81 0.96

K. Viscosity

(mm2/s)1

ASTM

D240

2.66 1.39 1.70 1.89 2.57 27.40

HHV (MJ/kg)1 ASTM

D240

45.64 42.41 34.09 46.24 36.2 35.7

LHV (MJ/kg) --- 43.95 40.48 32.14 43.09 33.43 33.70

Surface tension1 --- 26.77 27.44 29.89 25.17 25 30.55

Carbon (%wt.)2 --- 91.66 90.5 71.37 84.51 64.79 73.79

Hydrogen (%wt.)2 --- 8.34 9.5 9.59 15.49 13.61 9.81

Oxygen (%wt.)2 --- 0 0 19.04 0 21.59 16.4

C:H --- 10.99 9.52 7.44 5.45 4.76 7.52

Flash point (°C)3 ASTM

D93

67.5 25 30 70 35 207

Cetane index ASTM

D4737A

51.744 8.35 105 795 175 485

1- Measured at QUT, 2- Calculated, 3- Chemical certificate, 4- Caltex fuel certificate, 5- NREL report 311

(2004) - reference [40]. 312

313

314

315

316

15

Table 3: Properties of diesel, surrogate and surrogate blends [37]. 317

318

Properties Methods 100D 100S 90D10S 80D20S 50D50S Biodiesel

Standard

ASTM

6751-12

Density(Kg/L)1 ASTM D4052 0.84 0.83 0.84 0.84 0.84 0.86-0.9

HHV(MJ/kg)1 ASTM D240 45.64 42.34 45.2 44.83 43.62 --

LHV(MJ/kg)2 -- 43.95 39.77 42.45 42.07 40.93 --

K. viscosity

(mm2/s)2

ASTM D445 2.66 4.38

2.83 3.00 3.52

1.9 -6.0

Lubricity (mm)3 IP 450 0.412 -- -- -- --

Carbon (% wt.)2 -- 87 80.69 85.59 85.04 83.41 --

Hydrogen (%wt.)2 -- 13 12.65 13.75 13.62 13.26 --

Oxygen (%wt.)2 -- 0 6.65 0.67 1.33 3.33 --

C:H2 -- 6.69 6.38 6.23 6.24 6.29 --

Flashpoint (°C)2 ASTM D93 68.66 65.2 67.27 67.04 66.35 130

Cetane index3 ASTM

D4737A

51.74 45.212 51.092 50.432 48.472 7 min

1- Measured at QUT, 2- Calculated, 3- Caltex fuel certificate 319

Compressed Air

SABLE CA-10Dust Track

Diesel Engine Exhaust emissions flow Diluted exhaust flow

CAI gas analyser

Engine control roomEngine room

DMS500

320

Figure 11: Schematic diagram of the engine exhaust measurement system used for this study. 321

16

4.0 Results and discussion 322

This section describes the engine performance and exhaust emissions using microalgae 323

HTL surrogate blends, as well as comparisons of their individual measurements. The engine 324

performance parameters including BP, indicated power (IP), BSFC, indicated specific fuel 325

consumption (ISFC) and indicated thermal efficiency (ITE), BTE, and in-cylinder pressure and 326

volume, are presented in separate Figures. The properties of microalgae HTL surrogate fuels 327

were measured and calculated and were found to be close to those of diesel fuel. It is generally 328

accepted that the fuel properties influence the fuel spray characteristics, fuel evaporation, the 329

formation of fuel droplet size, distribution of fuel atoms, and, therefore, the exhaust emissions. 330

4.1 Engine performance 331

The IP of an engine is the power produced by the combustion products on the piston in 332

the cylinder. Conversely, the BP is the useful power at the output shaft. The IP and BP 333

variations with engine load are shown in Figure 12. It was observed that both IP and BP linearly 334

increased with increasing engine load for the reference diesel and surrogate blends. The 335

difference between the IP and BP reduced as the load increased, indicating a reduction in 336

friction power. This is consistent with other research findings [32, 34]. On this engine the 337

maximum IP for 100% of full load for reference diesel is 130 kW. No significant changes in 338

either IP or BP among the fuels were observed. This is most likely due to the close calorific 339

value of microalgae HTL surrogate blends compared to that of reference diesel. 340

17

341

Figure 12: IP and BP variation with engine loads for different fuels. 342

Figure 13 shows the BTE and BSFC, which are calculated using equations (1) and (2), 343

respectively. BTE can be defined as the BP of a heat engine as a function of the thermal input 344

from the fuel. BTE is used to measure how mechanically efficient an engine is at converting 345

the chemical power of fuel to useful mechanical power [39]. It was observed that BTE reached 346

a maximum (38%) at around 50% load for all fuels. This is consistent with other published 347

results [34, 35, 40]. Compared to diesel use of a surrogate blend results in a slight decrease in 348

BTE for all engine loads which is greatest for 50S50D. The reduction in BTE with surrogate 349

blends is due to the lower heating value of the surrogate blends. 350

BSFC is a measure of the fuel effectiveness of an engine that burns fuel and produces 351

power. It is typically used for comparing the efficiency of engines with output power and 352

represents the ratio between the rate of fuel consumption and the BP. Compared to diesel use 353

of a surrogate blend results in a slight increase in BSFC for all engine loads which is greatest 354

for 50S50D. The variation between BSFC for the reference diesel and for the blends was in the 355

range of 217 - 225 g/kWh across all loads. Zare et al. [41] reported similar results . It is revealed 356

from Figure 13 that BTE decreases with increasing engine load, BSFC increases with 357

increasing engine load for reference diesel and their blends. 358

18

𝐵𝑇𝐸 =𝐵𝑃∗100

Mf ∗ 𝐿𝐻𝑉 --------------------------------------- (1) 359

𝐵𝑆𝐹𝐶 =3600∗𝑀𝑓∗1000

BP ------------------------------- (2) 360

Where, BTE in % and BSFC in g/kWh, BP in kW, Mf is the mass flow rate of fuel in kg/s, and 361

LHV is the lower heating value of fuel in MJ/kg. 362

363

Figure 13: BTE and BSFC variation with engine load for different fuels. 364

19

365

Figure 14: ITE and ISEC variation with engine load for different fuels. 366

ISFC and ITE were calculated using equations (3) and (4). The ITE is a dimensionless 367

performance measuring parameter, which gives an idea of the power generated by the engine 368

with respect to the heat supplied. As illustrated in Figure 14, ITE was almost the same for all 369

tested fuels. The ITE reduced gradually with increase in engine load for both blended fuels, 370

which is consistent with other published results [42]. On the other hand, ISFC results indicate 371

that the fuel efficiency of the engine is affected with respect to thrust output. Figure 14 also 372

shows that ISFC slightly decreased with increasing engine load but stayed almost the same for 373

all tested blends. This indicates that there was no change in the fuel efficiency when using 374

microalgae HTL surrogate blends compare to reference diesel fuels. This could be due to the 375

fuel’s heating value, surface tension and density which are almost the same as the reference 376

diesel, as shown in Table 3. 377

𝐼𝑇𝐸 =𝐼𝑃∗100

𝑀𝑓∗𝐿𝐻𝑉 ---------------------------------------------------- (3) 378

𝐼𝑆𝐹𝐶 =3600∗𝑀𝑓∗1000

IP ------------------------------------ (4) 379

20

To avoid the effect of cycle-to-cycle variations, the in-cylinder pressure data was 380

recorded for 750 consecutive cycles and the mean was taken to plot the Figure 15 to Figure 18. 381

The peak in-cylinder pressure with the reference diesel was found to be 11 MPa, which is the 382

highest among the fuels, while 50D50S produced the lowest. Variation of in-cylinder pressure 383

(P) with respect to the crank angle (CA) for different fuels including 90D10S, 80D20S, 384

50D50S, and 100D are shown in Figure 15 and Figure 16 for 100% and 50% load respectively. 385

The lower in-cylinder pressure with surrogate blends is due to lower energy content (HHV) of 386

the fuel. Conversely, for both loads (100% and 50%), the surrogate fuels showed lower pressure 387

peaks than the reference diesel. Both loads in Figure 16 showed two pressure peaks, one near 388

the TDC and the other in the expansion stroke for all fuels, and is dominant for 50% load. The 389

dominant pressure peak for 50% load at the expansion stroke needs further investigation. 390

The in-cylinder volume is a function of the crank angle so that it is possible to relate the 391

cylinder pressure to cylinder volume, which depicted in the PV diagram shown in Figure 17 392

and Figure 18 for 100% and 50% of full load respectively. When the piston is at bottom dead 393

centre (BDC), the cylinder will have its largest volume. As the piston moves up to the top dead 394

centre (TDC), the volume is reduced to a minimum. No significant variation in pressure was 395

observed with respect to cylinder volume for all blends, which is consistent with the pressure 396

versus crank-angle curve. Combustion resonance with a frequency of ~ 6000 Hz was observed 397

in both Figure 17 and Figure 18. This resonance has been investigated in detail by Bodisco et 398

al [43]. 399

21

400

Figure 15: Variation of pressure with crank-angle for 100% load for different fuels. 401

402

403

404

Figure 16: Variation of pressure with crank-angle for 50% load for different fuels. 405

22

406

Figure 17: Variation of pressure with crank-angle for 100% load for different fuels. 407

408

Figure 18: Variation of pressure with crank-angle for 50% load for different fuels. 409

410

23

Figure 19 shows the peak pressure and rate of pressure rise versus engine load for the 411

four fuels. Although surrogate blends showed lower peak pressure, the reduction was small. In 412

regards to maximum pressure rise rate, compared to the reference diesel, all surrogate blends 413

showed a higher maximum pressure rise rate. This could be due to the lower CN in the surrogate 414

blends and warrants further investigation. The highest peak pressure and boost pressure were 415

found to be around 11,000 kPa and 245 kPa respectively for 50D50S which may pose a concern 416

for engine vibration and wear. 417

418

Figure 19: Effect of Microalgae HTL surrogate blended fuels on peak pressure and rate 419

of pressure rise. 420

24

421

Figure 20: Effect of Microalgae HTL surrogate blended fuels on boost pressure. 422

423

4.2 Engine performance 424

In this section, engine exhaust emissions including specific NO2, NOx, CO, PM and PN 425

are discussed. The engine was operated at a maximum torque speed condition (1500 rpm) with 426

four different loads. 427

428

Gaseous emissions 429

Figure 21 and Figure 22 show NO2 and NOx emissions with respect to engine load for 430

the reference diesel and three surrogate blends. At low load condition (25%), the formation of 431

NO2 emissions with surrogate blends was much higher than at high loads (50%, 75% and 432

100%), which could be due to pre-injection. This pre-injection works through an engine 433

management system (EMS) for low load conditions. Further research required to confirm the 434

reasons for higher NO2 emissions at low load conditions. However, compared to the reference 435

diesel, all surrogate blends produced higher NOx emissions at all engine loads. Figure 23 shows 436

the percentage of increase of NOx, which is approximately 15 - 20%, with respect to the 437

reference diesel. This is due to the oxygen percentage of surrogate blends, which is consistent 438

25

with the published literature [44-46]. Nabi et al. [34] reported that higher NOx emissions 439

resulted from fuel oxygen. The higher NOx emissions with surrogate blends are associated with 440

the higher maximum pressure rise rates (Figure 19) during the premixed combustion and lower 441

CN, which is shown in the Table 3. As shown in Figure 21 and Figure 22 that the percentage 442

of normalised NO2 compared to NOx is 4 - 5.5% for all tested fuels except for a 25% load of 443

surrogate fuel. 444

445

Figure 21: Brake specific nitrogen dioxide (NO2) emissions for four different load. 446

26

447

Figure 22: Brake specific nitrogen oxide (NOx) emissions for four different loads. 448

449

Figure 23: Percentage of increases of NOx emissions compare to reference diesel. 450

25 50 75 100

Load (% of full load)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

NO

x (

g/k

Wh)

100D 90D10S 80D20S 50D50S

EURO-III

27

451

Figure 24: Brake specific carbon monoxide (CO) emissions for four different loads. 452

453

Figure 25: Percentage of reduction of CO emissions compared to reference diesel. 454

28

The CO emission is one of the indications of the incomplete combustion of the air-fuel 455

mixture that takes part in the combustion chamber[47]. Diesel engines generally produce low 456

CO emission as they usually run on lean mixture [48]. It is important to note that all surrogate 457

blends reduced CO emissions compared to those of 100D at every loading condition revealed 458

in Figure 24. This is due to the oxygen content of in the fuel which helps to complete 459

combustion. [47]. A maximum of 45% reductions in CO emissions with surrogate blend was 460

observed compared to the reference diesel. Furthermore, the CO emissions among all fuels 461

were within EURO IIIA standard limit (5 g/kWh) [49]. 462

463

Particulate emissions 464

Figure 26 illustrates particulate matter (PM) emissions using three surrogate blends 465

(90D10S, 80D20S and 50D50S) and the reference diesel (100D). Reductions in PM emissions 466

with microalgae HTL surrogate blends were obtained compared to those with the reference 467

diesel which is shown Figure 27. Nabi et al. [34] and Zare et al. [41] reported that reduced PM 468

emissions with oxygenated fuels. The literature has revealed that the increases in surface 469

tension improve fuel combustion, while reducing NOx and PM emissions [49]. PM emissions 470

are significantly affected by the fuelling system, engine operating conditions and ambient 471

conditions [40, 50]. However, the relationship between PM and surface tension is not linear 472

and surface tension is possibly not the only factor to reduce PM emissions, there are other fuel 473

properties that could influence PM reductions [49]. The current investigations are consistent 474

with a number of previous studies [37, 39, 51]. It is interesting to note that the PM emissions 475

are significantly lower than the Euro IIIA standard for all tested fuels which is shown in Figure 476

27. Compared with the Euro IIIA standard, all three surrogate blends showed remarkable 477

reductions in PM emissions. Relative to the reference diesel, a maximum of 88% PM 478

reductions was observed with the surrogate blends. 479

Variations in the brake specific PN emissions across the four different fuels at four 480

loading conditions are shown in Figure 28. For all loading conditions, surrogate blends reduced 481

PN emissions compared to those of the reference diesel. At medium to high load conditions, 482

the reductions in PN emissions among the surrogate blends were low compared with low load 483

conditions. The percentage reduction of PN compared to the reference diesel is shown in Figure 484

29. The Literature showed that oxygenated fuels reduced PN emissions [36, 39, 52]. The 485

current investigation therefore supports the published literature [35, 38, 51]. 486

29

487

Figure 26: Variation of brake specific particulate mass emissions for different loads. 488

489

Figure 27: Percentage of reduction of particulate mass emissions compared to reference 490

diesel. 491

25 50 75 100

Load (% of full load)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

PM

(g

/kW

h)

100D 90D10S 80D20S 50D50S

EURO-III

30

492

Figure 28: Variation of brake specific PN for four different loads. 493

494

Figure 29: Percentage of reduction of PN emissions compared to reference diesel. 495

31

Based on the results discussed above, it can be concluded that microalgae HTL surrogate 496

blends performed well in terms of engine performance and exhaust emissions. Most of the 497

emissions using microalgae HTL surrogate blends were reduced due to the similarity in their 498

physical and chemical properties with biocrude. However, all engine performance parameters 499

showed no significant change with microalgae HTL surrogate blends due to the similarities in 500

energy content with that of the reference diesel. 501

502

503

504

505

506

507

508

509

510

511

512

513

514

515

516

517

518

519

32

5.0 Conclusions 520

The objective of this study was to develop a microalgae surrogate using pure chemical 521

compound of microalgae HTL biocrude that effectively approximated the chemical 522

composition, density, viscosity, HHV, and surface tension of the reference diesel. Engine 523

performance and exhaust emissions were also investigated with microalgae surrogate blends in 524

a six-cylinder fully instrumented turbo-charged diesel engine. 525

The aromatics, cyclic ketone, alkane, alcohol, and aromatic FAME chemical groups were 526

used to produce target surrogate fuel by HTL microalgae biocrude. Each chemical compound 527

of surrogate fuel had its physicochemical properties controlled by the target fuel. The 528

interaction between each chemical compound was already quantified because those chemical 529

compounds were part of the same microalgae biocrude. 530

No significant changes in engine performance were observed with HTL surrogate blends 531

when compared to those of the reference diesel. 532

All major emissions, including PM, PN and CO were reduced significantly with the 533

surrogate blends, with increasing of NOx emission. 534

When compared with the reference diesel, a maximum of approximately 88% and 58% 535

reductions in PM emissions were obtained with the surrogate blends at 25% and 100% of full 536

load. Maximum reductions in PN emissions with the surrogate blends were found at lower 537

loads, but minimum reductions were found at medium and higher loads. 538

NOx emissions with surrogate blends were higher compared to those of the reference 539

diesel. Exhaust after treatment including exhaust gas recirculation technique, or changing the 540

injection timing could also reduce NOx emissions with surrogate blends and thus needs more 541

investigation. 542

543

6.0 Acknowledgement 544

This research was supported by the Australian Research Council’s Linkage Projects 545

funding scheme (project number LP110200158). The authors would also like to acknowledge 546

Mr. Andrew Elder from DynoLog Dynamometer Pty Ltd and Mr. Noel Hartnett for their 547

laboratory assistance, Dr. Md Jahirul Islam and Dr. Svetlana Stevanovic for their guidance, and 548

Mohammad Jafari for assistance with measuring instruments. 549

33

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