diesel blends on performance, combustion and emissions characteristics of compression ignition engine

Journal Pre-proof Effect of cracked naphtha/biodiesel/diesel blends on performance, combustion and emissions characteristics of compression ignition engine Mahmoud K. Ashour, Yehia A. Eldrainy, Ahmed E. Elwardany PII:

S0360-5442(19)32285-6

DOI:

https://doi.org/10.1016/j.energy.2019.116590

Reference:

EGY 116590

To appear in:

Energy

Received Date: 15 June 2019 Revised Date:

12 October 2019

Accepted Date: 21 November 2019

Please cite this article as: Ashour MK, Eldrainy YA, Elwardany AE, Effect of cracked naphtha/biodiesel/ diesel blends on performance, combustion and emissions characteristics of compression ignition engine, Energy (2019), doi: https://doi.org/10.1016/j.energy.2019.116590. 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.

Effect of cracked naphtha/biodiesel/diesel blends on performance, combustion and emissions characteristics of compression ignition engine Mahmoud K. Ashoura, Yehia A. Eldrainya, Ahmed E. Elwardanya,b,* Mechanical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt b Department of Energy Resources Engineering, Egypt-Japan University of Science and Technology (E-JUST), 21934-Alexandria, Egypt * Corresponding Author: [email protected]; [email protected] a

Abstract Utilization of biofuels has drawn attention of researchers for many years to face depletion of fossil fuels. The high viscosity and low heating value of biodiesel are main drawbacks of using it along with high NOx emissions. Addition of ternary component to relax these drawbacks are widely considered. The focus of this study is to illustrate the effect of a novel ternary component to diesel-biodiesel blend on combustion characteristics, engine performance and emissions. This third component is cracked naphtha which is a low cetane/low octane fuel. Engine experiments were performed using a single cylinder, 4-stroke, air-cooled compression ignition (CI) engine. Different naphtha concentrations were considered. This included 5%, 10% and 15%. The engine performance results revealed that 10% and 5% are the maximum allowable percentages of naphtha to D100 and B30, respectively. A reduction in brake specific fuel consumption (bsfc) of 6.28% and 11.7% was achieved for 5% and 10% naphtha addition to diesel, respectively. Negligible effect was observed for naphtha on bsfc for B30-N5. Naphtha has decreased NOx emissions for B30-N5 at all considered loads and for diesel-naphtha blends at high and medium loads. CO emissions have been reduced for diesel-naphtha blends, while for B30-N5, CO emissions was increased.

Keywords: naphtha; diesel; ternary blends; compression ignition; NOx; engine performance

Nomenclature ASTM

American Society for Testing and Materials

AMOC

Alexandria Mineral Oils Company

B100

Neat Biodiesel (100%)

B30

Diesel (70%) + Biodiesel (30%) (on volume basis)

B30-N5

Diesel (65%) + Biodiesel (30%) + Naphtha (5%) (on volume basis)

B30-N10

Diesel (60%) + Biodiesel (30%) + Naphtha (10%) (on volume basis)

B30-N15

Diesel (55%) + Biodiesel (30%) + Naphtha (15%) (on volume basis)

Bsfc

Brake specific fuel consumption

CA

Crank angle

CI

Compression ignition

CO

Carbon monoxide

1

CO2

Carbon dioxide

COV

Coefficient of variation

D100

Neat Diesel (100%)

D85-N15

Diesel (85%) + Naphtha (15%)

D90-N10

Diesel (90%) + Naphtha (10%)

D95-N5

Diesel (95%) + Naphtha (5%)

DAQ

Data acquisition system

FAMEs

Fatty acid methyl esters

FT-IR

Fourier transform infrared spectroscopy

GC-FID

Gas chromatography- flame ionization detector

GCI

Gasoline compression ignition

GC-MS

Gas chromatography- mass spectroscopy

HSRN

Haltermann straight-run naphtha

IDT

Ignition delay time

Imep

Indicated mean effective pressure

LPL

Liquid penetration length

MON

Motor octane number

N100

Neat naphtha (100%)

NOx

Nitrogen oxides

NTC

Negative temperature coefficient

RON

Research octane number

SD

Standard deviation

SI

Spark ignition

TTW

Tank-to-wheel

T

Student’s statistic

TDC

Top dead center

U

Uncertainty

Us

Systematic uncertainty

Ur

Random uncertainty

WTT

Well-to-tank

1. Introduction

2

Restrict regulations are created to cut off the high rates of greenhouse gas emissions as carbon dioxide CO2. There are three main approaches to reduce CO2 emissions. The first one is by targeting fuels that produced through low-emitting CO2 distillation processes. This means improving well-to-tank (WTT) CO2 emissions compared to other fuels [1]. The second approach is by using fuels with relatively low carbon content as methane. The third path way is by using carbon neutral energy sources and biofuels. Biofuels have short carbon life cycle in contrast to fossil fuels that produce CO2 emissions that were absorbed millions of years ago by plants from which fossil fuels had been formed. The second and third approaches are lying under low tank-to-wheel (TTW) CO2 emissions. Many research efforts have been carried out to find fuels that can achieve one of the previous approaches. Naphtha, a low octane gasoline, is one of the promising hydrocarbons produced by light distillation of crude oil with a boiling range of 30-200℃ [2]. Naphtha and gasoline have nearly the same carbon content and boiling range. Naphtha refinery has a low WTT CO2 emissions and low cost of production. Naphtha has been introduced to run gasoline compression ignition (GCI) engines which works in the low-temperature combustion region [3]. Hence, naphtha is considered as an encouraging alternative for diesel fuels with less NOx and CO2 emissions [4]. Even though, low cetane number and low lubricity of naphtha have hindered its usage in conventional compression ignition (CI) engines. This motivates the research in upgrading naphtha by additives or through chemical processing (isomerization) to enhance performance and emissions characteristics of CI and spark ignition (SI) engines [5, 6]. The use of naphtha without isomerization introduces a fuel with less refinery-cost and less CO2 emissions compared to conventional fuels. Many fundamental and applied combustion studies have been conducted on naphtha. This includes ignition delay measurements in shock tubes and rapid compression machine [7-9] and spray characteristics [10-14]. Engine-based studies include the efforts carried out by [1, 2, 4, 15-19]. Ignition delay time of Haltermann straight-run naphtha (HSRN) and light naphtha was measured in shock tubes and rapid compression machine by Alabbad et al. [7] and Javed et al. [8], respectively. Alabbad et al. [7] claimed that long ignition time of straight-run naphtha ,relative to tested surrogates, is due to the high content of cyclo-alkanes such as naphthene and aromatics (25% for both). By conducting engine experiments, Akihama et al. [1] found that long ignition delay time of naphtha increases the effect of premixed combustion phase leading to higher peak in-cylinder pressure and hence higher noise that limits the maximum power obtained from the engine. To improve its ignition quality, Vallinayagam et al. [5] blended light-naphtha that having derived-cetane number (DCN) of 31 with diethyl ether (DCN = 139) as a cetane enhancer. By using ignition quality tester, it was found that a blend of 30% diethyl ether and 70% naphtha approximately matched measured ignition delay of US NO.2 diesel fuel. Naphtha has a strong potential to decrease soot and NOx emissions in CI engines because of its low ignition quality [3]. Furthermore, low research octane number (RON = 60 - 68) of naphtha promotes its usage in GCI engines [20]. In GCI engines, low soot and NOx emissions can be achieved by improving combustion homogeneity using fuels with high autoignition resistance as naphtha. Combustion homogeneity and its effect on soot formation for dieseline (a mixture of diesel and gasoline) and naphtha fuels in CI and partially premixed combustion (PPC) modes were investigated by Vallinayagam et al. [17]. Stratification analysis revealed that naphtha improves combustion homogeneity, leading to lower soot emissions in CI mode than dieseline and nearly zero-soot emissions in PPC mode. Akihama et al.[1] introduced naphtha engine that works on variable modes of combustion according to the load; SI on low load, homogeneous charge compression ignition (HCCI) on intermediate load and CI on high load. Experiments showed good performance for low speed at high and medium loads.

3

However, at high speed, increasing the load led to severe noise resulting in minimizing the maximum power produced by this engine. To increase the limited power for naphtha engine, splitting combustion was utilized at high loads. Chang et al. [2] investigated naphtha applicability by modifying injector flow rate, compression ratio and piston bowl shape in modern diesel engines to fit Euro 6 regulations for NOx emissions. The main drawbacks of naphtha as a fuel for conventional CI engines are its low ignition quality (DCN) and low flash temperature that represents fire hazards during storage and handling. Naphtha also has low kinematic viscosity and lubricity that is why lubricity additives are necessary for the lubrication of fuel pump [2]. Fortunately, on the opposite side biodiesel has a good lubricity and higher cetane number with higher flash temperature than those of naphtha. Literature is rich of such ternary blends of diesel-biodiesel and third additive. Oxygenated fuels, mainly alcohols and ethers, were used as a third constitute of the ternary mixture. Table 1 illustrates a brief review of ternary blends. The advantage of naphtha/biodiesel/diesel blend is combining the usage of renewable energy represented in the biodiesel with using this low-cost refinery product naphtha that has little carbon footprint during refinery and combustion. Table 1 Brief literature review of diesel-biodiesel ternary blends. Zaglinskis et al.

Pradelle et al.

Li et al.

Nanthagopal et al.

[21]

[22]

[23]

[24]

Methanol

Ethanol

Pentanol

Diethyl ether

diesel

60

65

40

50

Composition

biodiesel

30

15

30

47.5

(%)

Third additive

10

20

30

12.5

30% biodiesel + 70% diesel

15% biodiesel + 85% diesel

30% biodiesel + 70% diesel

50% biodiesel + 50% diesel

Reference Third additive

Reference Fuel

Lower Bsfc

Higher

Higher

(Indicated specific fuel consumption)

Higher

CO

Lower (mediumhigh load)

N/A

Approximately no effect

Approximately no effect

Higher (low load) NOx

Higher

N/A

Lower

Lower

In-cylinder peak Pressure

N/A

Lower

Lower

Lower

Maximum heat release rate

Higher

N/A

Higher

Lower

Ignition delay time

Higher

Higher

Higher

Higher

Combustion temperature

Lower

Lower

Lower

Lower

Combustion duration

N/A

Shorter

Shorter

N/A

4

One could conclude that the naphtha-based research in literature is mainly focused on straight-run naphtha not the cracked one. The straight-run naphtha is produced from atmospheric distillation of crude oil while cracked naphtha is produced from vacuum distillation of residue waxes. Hence, the focus of the current study is to investigate the effect of running CI engine with different blends of cracked naphtha/biodiesel/diesel on engine performance and emissions characteristics. To the best of authors knowledge, this effect of using cracked naphtha directly in a blend with diesel/biodiesel has not been studied before. Also, the utilization of naphtha in high compression ratio engine was not considered before in a blend or solely. The optimal blends of three base fuels (diesel, biodiesel and cracked naphtha) are to be defined experimentally. These blends achieve the minimum fuel consumption and reasonable emissions while meeting acceptable fuel standards of density, viscosity, flash and fire temperatures. 2. Materials and Method 2.1. Test fuels The three fuels that were considered in the current study are diesel, biodiesel and cracked naphtha. Diesel fuel was supplied from local fuel station while biodiesel was supplied from Biodiesel-Misr company for producing biodiesel from waste cooking oil. The cracked naphtha was supplied by Alexandria for Minerals and Oils Company (AMOC) located in Alexandria, Egypt. The AMOC cracked naphtha used in this study differs from straight-run naphtha that is produced by light distillation of crude oil. Cracked naphtha is manufactured by mild hydrocracking of vacuum distillate for heavy residue waxes. These waxes are resulted from lubrication oil which is the main product of AMOC. Long aliphatic chains in residue waxes are cracked and hydrogenated in mild catalytic reactor with pressure of 50 bar to produce three AMOC products which are gas oil, liquified petroleum gas and cracked naphtha. The pathways for three base fuels are shown in Fig. 1.

Fig. 1. Base fuels pathway to blend. Table 2 illustrates a comparison between AMOC cracked naphtha and other naphthas that produced from distillation of crude oil from literature. It is shown that AMOC naphtha has the lowest percentage of n-paraffins and highest percentage of iso-paraffins compared to other ones. Therefore, it has low ignition quality [25] and high RON and motor octane number (MON). The compositional analysis of cracked naphtha showed less aromatics and naphthene which lower its sooting tendency [26-28]. This proves the significance of blending cracked

5

naphtha with straight-run naphtha in refineries to increase gasoline yield. The key point in this work is using AMOC cracked naphtha with a blend of diesel-biodiesel in conventional CI engine without any modification. Naphtha properties in this research were measured following the ASTM standards. Table 2 Comparison between AMOC cracked naphtha and other naphthas in literature. Cracked naphtha

Straight-run naphtha

Light Naphtha

Heavy Naphtha

Supplier

AMOC

Haltermann Solutions

Saudi Aramco

Saudi Aramco

Reference

Current study

[7]

[8, 15]

[15]

MON

63.5

58.3

62-63.5

58

RON

66.8

60

66-64.5

62

Derived cetane number

N/A

N/A

34

41

Sensitivity (RON - MON)

3.3

1.7

4-1

4

Specific gravity

0.671

N/A

0.66

0.73

Average molecular weight 88.1763

92.4

78.4

N/A

H/C ratio

2.27

2.147

2.34

N/A

n-Paraffins (mol%)

29.14

36.7

53.3-55.4

34.8

i-Paraffins (mol%)

60.45

37.8

35.9-39.6

35.3

Aromatics (mol%)

2.34

10.5

0.9-1.32

11.5

Naphthenes (mol%)

7.53

15

6.2-6.7

17.9

Olefins (mol%)

0.54

0

0

0.5

Sulfur (ppm)

<100

N/A

<20

<20

2.2. FT-IR and GC analyses for basic fuel elements To identify the chemical structure and functional groups in naphtha, biodiesel and diesel, FT-IR and GC tests were held for the three base fuels of the considered blends. Shimadzu 8400S FT-IR spectrometer was utilized to investigate the functional groups in naphtha, diesel and biodiesel with wavenumber span of 400- 4000 cm-1. GC-MS system was employed to investigate the hydrocarbon compounds in diesel and biodiesel. The system consisted of Thermo Ultra (2009) gas chromatograph provided with Thermo ISQ-mass spectrometric detector. The sample was analyzed at TG5-MS capillary column. Due to its high volatility, cracked naphtha was analyzed using a new technique that combines GC Shimadzu 2014 and flame ionization detector (FID) to measure the concentrations of compounds separated in the capillary column Rtx-100 DHA. 2.3. Experimental setup Experiments were conducted on HATZ-1B30-2 4-stroke, single cylinder, direct injection, air-cooled, CI diesel engine facility in Egypt-Japan university of science and technology (EJUST) [29, 30]. Engine experiments were carried out at different loads and constant speed of 6

2000 rpm. El-seesy et al.[31] has examined the effect of different engine speed on combustion and performance characteristics for the same engine test rig with different fuels. The considered speeds were 1500, 2000 and 2500 rpm. It was concluded that the speed has limited effect on trend while its effect appeared in the values of the corresponding parameters. The maximum rated power of 5 kW at 3600 rpm rated speed was defined by Heywood [25] as the maximum power that an engine could developed for short operating periods. Hence, following the performance characteristic curve [32], the operating speed of 2000 rpm was chosen to ensure optimal performance with lowest bsfc. Engine specifications are represented in Table 3. In-cylinder pressure was measured by Kistler piezoelectric pressure sensor model 6052C. Engine speed measurement was carried out by Wachendorff proximity sensor. Top dead center (TDC) location was determined by using Wachendorff proximity switch. Braking load was subjected on the engine by asynchronous motor type Partelli TFCP 132 SB-2. Torque was measured using beam load cell sensor type Flintec ZLB-200kg. A schematic diagram of experiment layout is presented in Fig. 2. The engine test bench GUNT-CT-110 is equipped with fuel and intake air flow measurement devices in addition to K-Type thermocouples to measure fuel, exhaust and intake air temperatures. Fuel consumption was calculated from the rate of change of the fuel column weight in the measurement fuel glass. This weight is measured by a pressure transducer at the bottom in the glass as illustrated in Fig. 2. CO and NOx emissions were measured using Bacharach exhaust analyzer type ECA 450. All measurements were taken under steady-state condition and warming up for 20 minutes were carried out after each cold start. Each single experiment was repeated 5 times and the average values were reported. Table 3 Test engine specifications. Parameter

Value

Rated power/speed

5.4 kW/3600 rpm

Bore diameter

80 mm

Stroke length

69 mm

Connecting rod length

114.5 mm

Compression ratio

21.5:1

Displacement volume

120 °CA bTDC

Intake valve closure (IVC) Exhaust valve opening (EVO) Start of injection (SOI)

347 cm

125 °CA aTDC 15 °CA bTDC

7

Fig. 2. A schematic diagram for experimental setup of GUNT-CT-110 test bench. 2.4. Cycle-to-cycle variation A cycle-to-cycle variation plays a vital rule in engine stability. Cycle-to-cycle variation can be expressed in terms of in-cylinder pressure, flame front characteristics and burning rate parameters [25]. By utilizing in-cylinder pressure data, coefficient of variation (COV) is employed in this study to express the effect of naphtha on cycle-to-cycle variation and thus the engine stability. The COV was calculated using indicated mean effective pressure (imep) following [25]: COV = (σ /ımep ) × 100

(1)

where σ and ımep  is the standard deviation and arithmetic mean of imep calculated for n consecutive cycles as shown in Eqs. (2-3). In this study, 100 cycle is utilized in the analysis.  = ∑ ımep

σ

! " imep(i) /n

 !

= $1/(n − 1) ∗ '(imep − ımep )(  "

(2)

(3)

8

2.5. Uncertainty analysis To estimate the error percentage for performance parameters, uncertainty analysis is performed using root sum square (RSS) law following: !

( ∂R U* = ±$' , U0 1 3 2 ∂x

(4)

 "

where UR is the uncertainty of dependent parameter R which is affected by n number of independent variables x. Each independent variable has total uncertainty U0 1 . The 2 independent variables in this study are the experimentally measured parameters such as pressure, engine speed and torque, crank angle, and fuel flow rate, while the dependent parameters are brake power and brake specific fuel consumption. The uncertainties of independent parameters were estimated by using measuring devices that have specific range and accuracy that are determined by the manufacturer as shown in Table 4. In addition to instrument accuracy which can be defined as systematic uncertainty U4 , there is also, random uncertainty U5 , which is the experimental uncertainty obtained from Eq. (5), Mofatt [33]: U5 (%) = ±(t × SD/√N)/X × 100

(5)

where t is the Student’s t statistics. For 95% confidence level t = 1.96 and SD is the standard deviation of N repeated measurements. By applying Eq. (6) , The total uncertainty of independent variables was calculated from systematic Us and random Ur uncertainties, [33]. U0 = =U4( + U5(

(6)

The uncertainty of brake power and brake specific fuel consumption were found to be ± 1.36% and ± 3.47%, respectively.

Table 4 Range, resolution, accuracy, experimental and total uncertainty for measured parameters.

Range

Resolution

Exhaust gas analyzer CO (ppm)

0-4000 ppm

1 ppm

NOx (ppm)

0-4000 ppm

1 ppm

Pressure transducer (bar)

0-250

-

Crank angle encoder (degree)

0-720

0.5

Instrument uncertainty (Us)

±10 ppm or ±5% of the reading

Random Uncertainty (Ur)

Total uncertainty

± 1.52%

± 5.23%

(Ut)

±5 ppm or ±5% of the reading

± 0.68%

± 5.05%

±0.5 degree

±0.3

± 0.583

±1% of the reading

±1%

± 1.41%

9

Torque indicator (Nm)

0-50

0.1

Fuel burette (cm3)

153

-

Speed sensor (rpm)

0-10000

1 rpm

±1% of the reading

±0.88%

± 1.33%

±5 rpm

± 0.1%

± 0.27%

±0.2 cm3

±2.4%

±2.5%

3. Results and discussion 3.1. Fuel Characterization 3.1.1. Fuel blends properties Three different naphtha percentages of 5%, 10% and 15 % are added either to neat diesel (D100) or B30. A mixture of diesel and 5% naphtha is referred to as D95-N5 while a mixture of B30 and 5% naphtha is referred to as B30-N5. The different blends abbreviations are shown in Table 5. The physical properties were set as a first criteria to evaluate the applicability of fuel blends. Adding naphtha to D100 and B30 has significant effects on physical characteristics of the blends as illustrated in Table 5. Due to its high volatility, naphtha has low flash and fire temperatures. This highlights the importance of using it in blends with different base fuel not in a neat form as in GCI cases. As illustrated in Table 5, the addition of 5% of naphtha to neat diesel led to 35% and 30% reduction in flash and fire temperatures, respectively. Increase naphtha concentration to 10% resulted in severe reduction in flash and fire temperatures that would increase fire hazards during storage. In contrast to naphtha, biodiesel has high flash and fire temperatures due to its low volatility and high boiling point. High flash temperature of biodiesel compensates the low flash point of naphtha, leading to acceptable flash and fire temperatures for B30-N5. Increasing naphtha percentage over 5% in B30, led to dramatic reduction in flash temperature that hinders the applicability of the blend. Considering flash temperature as a criterion in evaluating diesel-naphtha and diesel-biodiesel-naphtha blends promotes D95-N5 and B30-N5 as optimum blending ratios achieving flash, fire temperature and viscosity that meets ASTM D-975 standards for diesel fuel. Table 5 Tested fuel blends properties. Sample number

Fuel

Density kg/m

Kinematic viscosity

Flash temperature

Fire temperature

Lower heating value

(40℃)

(℃)

(℃)

(MJ/kg)

mm/s (

1

D100

853.0

4.230

82

108

44.8[34]

2

B100

885.2

4.418

180

198

40.5[34]

3

N100

671.0

0.690

< 20

< 20

42.2[15]

4

D95-N5

843.6

4.031

54

74

44.7

5

D90-N10

835.7

2.910

26

29

44.59

6

D85-N15

828.5

2.689

< 20

< 20

44.48

7

B30

862.0

4.290

92

122

43.48

8

B30-N5

853.3

4.069

56

94

43.36

10

9

B30-N10

844.6

2.970

28

50

43.24

10

B30-N15

836.8

2.563

22

22

43.12

3.1.2. FT-IR and GC-MS results for basic fuel elements Figs. 3 (a-c) represent FT-IR spectrum for diesel, biodiesel and naphtha for wavenumber range from 400 cm-1 to 4000 cm-1. Diesel FT-IR spectrum shown in Fig. 3(a), represents a typical spectrum for long linear aliphatic compound. The strong peaks at 2924 cm-1 and 2855 cm-1 corresponds to asymmetric and symmetric stretching vibration respectively of C-H bond in methylene group CH2. The peak at 2955 cm-1 is attributed to asymmetric stretching vibration of C-H in methyl group CH3 [35]. Bending vibration of C-H band for methyl (asymmetric bending) and methylene has overlapped peaks at 1465-1458 cm-1. The peak at 1377 cm-1 is due to symmetric C-H bending vibration in methyl group. Peaks at the region 718-725 cm-1 is attributed to methylene rocking vibration [35]. The difference in intensity between strong peaks of methyl and methylene band (1465 – 1458 cm-1) and the weaker peak for methyl group (1377 cm-1) refers to the long chain structure of diesel aliphatic compounds. The same difference in intensity is noted for n-heptane in contrast to iso-octane which has stronger peak at 1377 cm-1 as shown in Fig. 3(a), [36]. This similarity between n-heptane and diesel spectrums corresponds to higher percentage of n-paraffins than iso-paraffins in diesel. Indeed, moderate splitting at the region 1465-1458 cm-1 and 718-725 cm-1 in diesel spectrum emphasizes the crystalline structure and regular linear backbone structure that's achieved for n-paraffins [35]. Fig. 3(b) shows the FT-IR results for biodiesel with peak at 3439 cm-1 corresponds to OH stretching vibration that indicates water existence in the biodiesel [37, 38]. The main characteristic peaks distinguished for biodiesel are the esters absorption bands such as 1732 cm-1 and 1194 cm-1 attributed to stretching of C=O in carbonyl group and C-O in esters respectively. The stretching vibration for C-H in methylene group is indicated by the peak at 2914 cm-1 while the peak at 1433 cm-1 indicates the bending vibration for C-H in methyl group [35]. The C-H bending out of the plane is identified through the peak at 702 cm1 . FT-IR spectrum for naphtha is shown in Fig. 3(c). It includes peaks at 2938 cm-1 that corresponds to C-H asymmetric stretching vibration in methyl group and a peak at 1668 cm-1 that indicates C=C stretching vibration for alkenyl group. The peak at 1530 cm-1 corresponds to bending vibration of C=C band in aromatics. A comparison between FT-IR spectrum of diesel, biodiesel and naphtha is depicted at Fig. 3(d). The band 1740- 1190 cm-1 contains characteristic peaks through which each fuel can be distinguished. For biodiesel the peaks at 1732 cm-1 and 1194 cm-1 corresponding to C=O and C-O in esters. These peaks are specific for oxygenated fuels such as biodiesel and disappear in oxygen-free fuels such as naphtha and diesel. Naphtha also has distinctive peaks at 1668 cm-1 and 1530 cm-1 corresponds to C=C band in aromatics.

11

Fig. 3. FT-IR spectrum for (a) diesel (b) biodiesel (c) naphtha (d) diesel, biodiesel and naphtha. The compositional analysis of biodiesel (fatty acid methyl esters (FAMEs)) is shown in Table 6. It is noticed that biodiesel mainly consists of long chain C16-C18 methyl esters that have molecular weights of 270 to 296 kg/kmol. This is in agreement with the GC-MS results of ElSeesy et al. [37]. Table 6. GC-MS results of the biodiesel sample including most important FAMEs. FAME

Acid number

Formula

Molar Percentage

Hexadecanoic acid

C16:0

C17H34O2

35.26

Methyl 9-cis,11-transoctadecadienoate

C18:2

C19H34O2

6.99

9,12-Octadecadienoic acid methyl ester

C18:2

C19H34O2

26.78

9-Octadecenoic acid methyl ester

C18:1

C19H36O2

15.67

Methyl stearate

C18:0

C19H38O2

8.97

Methyl ester

Others

6.33

12

The results of compositional analysis of cracked naphtha revealed that it mainly consists of short hydrocarbon chains (C5-C10) with rich paraffinic content mainly iso-paraffins (60.45%) and lower percentage of n-paraffins (29.15%) as given in Table 7. Also, it is found that naphtha has about 9.87% content of cycloalkanes (naphthenes) and aromatics. A comparison between main hydrocarbon groups existed in naphtha and commercial diesel is presented in Table 8. The results showed that diesel mainly consists of normal long chain alkanes (C16C27), the same conclusion obtained from FT-IR analysis of diesel Fig. 3(a). Table 8 shows top five branched and normal paraffinic compounds in both naphtha and diesel with the percentage of each compound relative to the total detected compounds. It is obvious that naphtha has higher ratio of branched alkanes to normal alkanes (2.07) than this of diesel (0.06). Hence, AMOC cracked naphtha has higher anti-knock quality and longer ignition delay time than this of diesel [39]. This long ignition time is to produce severe radicals scavenging during oxidation which will result in inhibiting auto-ignition for the fuel [39]. Table 7 Naphtha composition on molar basis as obtained from GC-FID results. (mol%)

C5

C6

C7

C8

C9

C10

C11

Total

n-Paraffins

14.8

8.99

3.48

1.52

0.27

0.07

0.02

29.15

i-Paraffins

19.1

20.02

11.89

7.01

2.21

0.22

0

60.45

Olefins

0.2

0.03

0.05

0.19

0.06

0

0

0.53

Naphthenes

0.33

2.42

3.26

1.33

0.12

0.07

0

7.53

Aromatics

0

0.42

0.81

0.81

0.3

0

0

2.34

Table 8 Comparison between branched and normal paraffinic compounds in naphtha and diesel. Naphtha Alkane

Diesel Formula

Molar Percentage

Alkane

Formula

Molar Percentage

i-pentane

C5H12

19.1

Octadecane, 6-methyl

C19H40

1.23

2-methylpentane

C6H14

9.79

Pentadecane,2,6,10,14tetramethyl

C19H40

1.15

3-methylpentane

C6H14

7.87

Heptadecane,2,6,10,15tetramethyl

C21H44

0.81

3-methylhexane

C7H16

4.99

Pentadecane,2,6,10trimethyl

C18H38

0.75

2-methylhexane

C7H16

3.81

Heptadecane,2,3dimethyl-

C19H40

0.52

C5H12

14.8

Heptacosane

C27H56

8.74

Main Iso-Paraffins

Main n-Paraffins n-pentane

13

n-hexane

C6H14

8.99

Hexadecane

C16H34

8.56

n-heptane

C7H16

3.48

Heptadecane

C17H36

8.45

n-octane

C8H18

1.52

Octadecane

C18H38

7.88

n-nonane

C9H20

0.27

Heneicosane

C21H44

7.81

3.2. Engine performance Eight different test fuels were examined on the CI engine out of the ten shown in Table 5 excluding B100 and N100. The experiments were performed at constant engine speed of 2000 rpm and five different loads (0% (0 Nm) - 20% (3 Nm) - 40% (6 Nm) - 60% (9 Nm) - 80% full load (12Nm)). It was shown that the maximum allowable percentage of naphtha addition to D100 and B30 are 10% and 5%, respectively. Adding more naphtha (e.g. D85-N15 or B30N10) leads to unstable performance and misfire at high loads. Hence, only two concentrations of 5% and 10% of naphtha could be used with neat diesel while only one concentration of 5% of naphtha could be added to B30. Fig. 4 illustrates the brake specific fuel consumption (bsfc) for tested fuels at different engine loads. As shown in Fig. 4, bsfc decreases with increasing load for all fuels owing to the higher thermal efficiency achieved by high combustion temperature at high loads. For entire load range, B30 has higher bsfc than diesel due to the lower calorific value of biodiesel [34, 40] that decreases the overall heating value of B30. As shown in Fig. 5(a), for B30-N5 about 2.67% increase and 2.84% reduction in bsfc relative to B30 are achieved at 6 Nm and 12 Nm respectively. Since it doesn’t exceed the uncertainty limit, naphtha effect on bsfc of B30 is considered negligible. Interestingly, adding naphtha to diesel has achieved average reduction in bsfc of 4.4% for D95-N5 and 6.5% for D90-N10 as illustrated in Fig. 5(b). Lower bsfc for diesel-naphtha blends could be attributed to the enhancement in atomization, evaporation and fuel-air mixing quality due to high volatility and low viscosity of naphtha, leading to improve the combustion process. Fig. 5(b) shows also that enhancement in bsfc in diesel-naphtha blends is higher in high load than low load. This may be attributed to the cooling effect of naphtha whose effect at low temperature for low loads is more pronounced since the temperature is already low. Kabil et al.[14] has shown that the effect of heating and evaporation processes is of interest at low temperatures. Cooling effect deteriorates premixed combustion and lower thermal efficiency leading to lower enhancement in bsfc at low loads than at high loads. Enhancement in fuel consumption was not achieved for B30-N5 because biodiesel has higher viscosity than this of diesel. This makes the impact of adding naphtha to biodiesel is less than this to diesel. High viscous liquids have low tendency to break-up compared to less-viscous one as drawn from Taylor analogy break-up model [41]. This leads to increasing droplet momentum and therefor, increasing liquid penetration length. Also, the addition of naphtha which is high volatile compared to B30, this means most of it will evaporate and be wellmixed with air in the whole chamber that could cause over leaning the mixture and then misfire for higher naphtha percentages in B30. Thus, it was required to add more naphtha to B30 than what was added to diesel to achieve a notable effect on atomization, evaporation and fuel-air mixing quality and hence on bsfc. However, misfire occurs when increasing naphtha percentage over 5% in B30. It can also be attributed to the increase in liquid penetration length (LPL) of B30-N5 as a result of increasing latent heat of evaporation of the blend by naphtha addition [42]. Hence, more wall impingement will be achieved for B30-N5 than B30

14

leading to incomplete combustion and deterioration effect on engine performance. This deterioration can be equalized with the enhancement in atomization in naphtha leading to nearly same bsfc for B30 and B30-N5. Wall impingement may haven’t been occurred in D95N5 and D90-N10 since diesel has already shorter LPL than B30 due to its low viscosity and bulk modulus of elasticity and thus low injection pressure relative to B30 [43].The results of bsfc promotes D90-N10 as the most economic blend in this study.

Fig. 4. Variation in bsfc for tested fuels at different loads with constant speed 2000 rpm.

15

Fig. 5. (a) bsfc reduction percentage for B30-N5 relative to B30. (b) bsfc reduction percentage for D95-N5 and D90-N10 relative to D100. 3.3. Combustion characteristics Investigating combustion characteristics is an essential step to understand the effect of fuel additives on engine performance and emissions. In-cylinder pressure is the main raw data by which combustion analysis was carried out. 3.3.1. Coefficient of variation Heywood [25] claimed that COV more than 10% represents unstable operation with high level of torque variation during engine operation. Fig. 6 shows COV for tested fuels. For most of the considered fuels, COV at idling has the highest value along the load range which agrees well with the findings of [25, 44, 45]. The high values of COV at idling indicates less stable engine performance at this condition. This may be attributed to the high percentage of residual gases relative to the fresh air-fuel mixture in idling. This would result in consequences as using high percentage of exhaust gas recirculation including more incomplete combustion regions and lower combustion temperature leading to less stability at idling [25, 45, 46]. It is observed that for B30-N5 and D95-N5, engine stability at idling was enhanced relative to B30 and D100 which have COV more than 10% at idling. This may be attributed for lowering

16

autoignition temperature of the blends and better atomization and mixing by addition of naphtha. For other loads, it’s noted that COV is less than 10% for all test blends indicating that engine had stable performance at that loads. It is noted also for D90-N10 that stability at idling was deteriorated (COV greater than 10%) relative to D95-N5. This may be attributed to the over-enhancement in mixing process between air and D90-N10 at lean conditions of idling. This leads to more air penetration and forming too-lean zones where air-to-fuel ratio is out of the flammability limit. Thus, more blow-off regions occur and stability of D90-N10 is deteriorated. It worth to refer that un-stability in idling did not reach misfire limit, it was just like high variation in combustion chamber pressure but still steady-state condition can be obtained and results are recorded. That is opposite to un-stability in high loads for B30N10,B30-N15 and D85-N15 in which misfire occurs and steady-state condition are not achievable as will be illustrated in the next subsection.

Fig. 6. COV for tested fuels along the load span. 3.3.2. In-cylinder pressure and heat release rate analyses Figs. 7(a-b) represent the in-cylinder pressure and net heat release rate (calculated following the procedure suggested by [25]), respectively versus crank angle (CA) degrees. Five blends of D100, B30, D95-N5, D90-N10 and B30-N5 were tested at constant speed of 2000 rpm and load of 12 Nm. A 100 consecutive cycle of in-cylinder pressure was recorded and averaged. It could be seen from Fig. 7(a) that B30 has the highest peak pressure among tested fuels, the same results were obtained in literature [23, 47, 48]. This could be attributed to the high oxygen content of biodiesel that promotes the combustion reactions and leads to higher peak pressure [47]. It was shown also, that naphtha has slightly reduced the peak pressure for B30N5 relative to B30 and for D95-N5 and D90-N10 relative to D100. This modest reduction in peak pressure is attributed to the slight retarding of the peak pressure position or CA50 (crank angle at 50% of heat release) about 1° - 0.5° far away from TDC in the expansion stroke. This is owing to longer ignition delay time of naphtha, furthermore the high latent evaporation heat of naphtha that decrease the pre-combustion temperature that may results in lower pressure [12, 22, 49]. That retardation led to increase the volume at which peak pressure occurs.

17

. Fig. 7.(a) In-cylinder pressure (b) Net heat release rate versus crank angle for tested fuel blends at 12 Nm and 2000 rpm. In order to justify misfire occurred for D85-15, B30-N10 and B30-N15 at high loads, Figs. 8(a-b) depict peak pressure and combustion phasing (CA50) at different engine loads starting from no load condition up to 12 Nm at constant speed of 2000 rpm. Results illustrated in Figs. 8(a-b) include all test blends even blends experienced misfire. As shown in Figs. 8(a-b) misfire occurs for D90-N10 and B30-N10 at 12 Nm while for B30-N15 at lower load of 9 Nm. Results for misfired cases couldn’t be recorded since steady state condition was not achievable with misfire. It is shown that for diesel-naphtha blends (D100, D95-N5, D90-N10 and D85-N15), pure diesel D100 has the highest peak pressure for all loads and minimum CA50 while D95-N5 and D90-N10 has nearly the same peak pressure and approximately the same CA50. It is found also that D85-N15 has nearly same peak pressure while it has the highest CA50 between all other diesel-naphtha blends. For diesel-biodiesel-naphtha blends (B30, B30-N5, B30-N10 and B30-N15), it is observed that peak pressure for B30-N5 is slightly higher than B30 for all loads except at 12 Nm. However, B30-N10 has lower peak pressure than B30-N5 while B30-N15 has the lowest peak pressure between B30-naphtha blends. It is obvious from Fig. 7(b) and Fig. 8(b) that at 12 Nm, naphtha has retarding effect

18

on combustion phasing for both D100-naphtha and B30-naphtha blends. Retarding in combustion phasing due to naphtha addition led to misfire at high loads for B30-N10, B30N15 and D85-N15 [50]. Misfire occurs when pressure/temperature rise resulting from hot zones in the combustion chamber becomes insufficient to initiate/sustain combustion in cold zones, then partial burning starts and ends with misfire. According to Sjöberg et al.[50] retarding combustion phasing (increasing CA50) leads to lower pressure rise from combustion of hot zones in combustion chamber. Consequently, the effect of expansion on reducing pressure during expansion stroke becomes more pronounced than the effect of hot zones on increasing pressure. Thus, cold zones won’t reach the autoignition temperature leading to partial burning or misfire. Sjöberg et al.[50] stated that misfire and partial burning start when CA50 exceeds 376°CA. This value differs according to the fuel/air mixture ignitability. One could conclude that the CA50 for D90-N10 that has low firing temperature did not reach its misfire-threshold value in contrast to B30-N10 with high fire temperature. This could be attributed to easier initiation of combustion in cold zones for D90-N10 than that for B30-N10 because of high reactivity to diesel compared to biodiesel. Hence, engine operation with D90-N10 (fire temperature of 29°C) is stable; while engine operation with B30-N10 (fire temperature of 50°C) is unstable. It is also noted that despite the higher fire temperature of B30-N5 than B30-N10 and B30-N15, misfire occurs at B30-N10 and B30-N15 but not in B30-N5. This is due to the excessive increase in CA50 for B30-N10 and B30-N15 leading to exceeding the misfire-threshold value at high loads. The retarding in combustion phasing may be attributed to cooling effect of naphtha and its longer chemical ignition delay due to high content of isoparaffins relative to n-paraffins. It could be noted also from Figs.8(a-b) that there is an inverse proportion relationship between CA50 and peak pressure. Fig.8(b) indicates that the slight increase in peak pressures of B30 over B30-N5 at low and intermediate loads was just within uncertainty limits and can be negligible. This indicates that impact of 5% naphtha on B30 is weaker than D100 since the effect on peak pressure was not obvious. However, when increasing naphtha over 5% to B30 (B30-N10 and B30-N15), the reduction in peak pressure became more. Consequently, naphtha in both diesel-naphtha and diesel-biodiesel-naphtha decreases peak pressure and increases CA50 as a general trend.

19

Fig. 8. (a) In-cylinder peak pressure versus load conditions. (b) CA50 versus load for tested fuel blends. 3.3.3. Ignition delay time To investigate the prominence area of physical and chemical specifications of tested fuel blends at different loads, ignition delay time is calculated as the time between start of injection and the first positive value of net heat release curve [51, 52]. Fig. 9 shows the ignition delay time for each fuel at different loads. For AMOC naphtha, longer ignition delay time is attributed to the high content of iso-paraffins and the lower content of n-paraffins, that leading to inhibiting fuel reactivity [25, 39]. On the other side, the low viscosity and high volatility of naphtha leads to shorter evaporation time referring to shorter physical ignition delay time. As shown in Fig. 9, for diesel-naphtha blends ignition delay time increases with increasing naphtha percentage and D90-N10 has the highest ignition delay time (IDT) due to the dominance of naphtha chemical delay. But it is found that as the load increases, the effect of naphtha on ignition delay become weaker until it disappears in 12 Nm since the chemical

20

delay effect is reducing as the temperature increases. The same result was found by Wang et al.[12] who studied autoignition of light naphtha spray in different ambient temperatures. They found that the effect of octane number on autoignition is effective at low temperatures rather than high temperatures. At high temperatures, it was found that ignition delay time is similar for all tested fuel having different octane number. Consequently, at high loads effect of chemical delay became less dominant and so that the physical delay [14] leading to same ignition delay of D100. For diesel-biodiesel-naphtha blends, naphtha doesn’t affect the ignition delay time of the mixture because of high cetane number and viscosity of biodiesel. This leads to decrease naphtha impact on B30 relative to its impact on diesel which supports the explanation given for the neutral effect of naphtha on bsfc and peak pressure for B30-N5. Thus, ignition delay time of B30 doesn’t change with just 5% of naphtha addition. The only point that is out of the trend is at 9 Nm. It is obvious from Fig. 5 that ignition delay time for loads 0,3,6 Nm for B30 and B30-N5 ranges between 11°CA to 12°CA. However, ignition delay at 9 Nm dropped rapidly to 8°CA for B30 and 6.5°CA for B30-N5. This indicates that 9 Nm represents the transition state from low and intermediate load to high load or in other meaning the transition from low temperature to high temperature. This indicates generation of more OH radicals that control high temperature oxidation process of fuel [53]. rather than HO2 radical that control low temperature oxidations. The rate constant of reaction OH + fuel is higher than this of HO2 + fuel [53].

Fig. 9. Ignition delay time for tested fuels over the load span. 3.3.4. Exhaust gas temperature Fig. 10 illustrates the variation in exhaust gas temperature for test fuels. Generally, as the load increases the exhaust temperature increases due to the higher combustion temperature as a result of higher fuel consumption. For diesel-naphtha blends, it’s noted that D95-N5 and D90-N10 have slightly higher exhaust gas temperature than diesel that reach up to 2.5% increase at 12 Nm for D90-N10. This can be attributed to the retardation in combustion phasing due to naphtha. That retardation leads to higher gas temperature in the latecombustion phase that results in higher exhaust temperature. However, for B30-N5 naphtha effect on exhaust temperature is marginal since B30-N5 and B30 have nearly the same exhaust temperature.

21

Fig. 10. Exhaust gas temperature for test blends at different loads 3.4. Emission characteristics 3.4.1. NOx emissions Fig. 11 shows NOx emissions for tested fuel blends versus load. NOx increases with engine load for all tested fuels. The increase of NOx with load is attributed to the increase of incylinder temperature at higher loads which means richer mixtures than low loads, leading to higher NOx formation.

Fig. 11. Variation of NOx emissions for all tested fuels under load range from 0 Nm up to 12 Nm at constant speed of 2000 rpm.

22

Fig. 12. (a) NOx reduction percentage for B30-N5 relative to B30. (b) NOx reduction percentage for D95-N5 and D90-N10 relative to D100. Due to the high oxygen content in biodiesel, NOx emissions are higher for B30 and B30N5 than that for diesel-naphtha blends over the entire load span. It is found also that addition of naphtha has a positive effect on NOx emissions for diesel-biodiesel-naphtha blends. NOx reduction by naphtha addition to B30 reaches up to 11.7% at 6 Nm and 18% at no load condition as shown in Fig. 12(a). B30-N5 has lower NOx emissions due to lower combustion temperature and pressure achieved by naphtha as shown in Fig. 7(a). For diesel-naphtha blends, naphtha addition increases NOx at low loads 0-3 Nm, and decreases NOx for medium and high loads 6-12 Nm as shown in Fig. 12(b). Reduction of NOx by naphtha addition to B30, promotes naphtha as an additive to B30 over methanol whose cooling effect did not affect NOx emissions in the work of Zaglinskis et al. [21] despite the high evaporative enthalpy of methanol. NOx emissions are affected by the amount of oxygen mixed with fuel and combustion temperature [54]. Naphtha addition leads to quick atomization and evaporation. However, due to its high RON, diesel-naphtha blends have long ignition delay time Fig. 9. Because of quick atomization and evaporation of diesel-naphtha blends, most of ignition delay time is consumed by the mixing process. This leads to higher oxygen content in the premixed mixture formed during delay period and thus higher NOx emissions [54]. This occurs significantly for very lean mixtures with higher ignition delay time during low loads as shown in Fig. 9. At medium and high loads effect of mixing becomes marginal because of shorter ignition delay time and higher equivalence ratio. Hence NOx formation will mainly be 23

affected by the combustion temperature. Due to high enthalpy of evaporative of naphtha, combustion temperature of diesel-naphtha is lower than diesel [55].Therefore less NOx emissions are achieved at medium and high loads as shown in Fig. 12(b) for diesel-naphtha blends. 3.4.2. CO emissions Fig. 13 represents CO emissions versus load for different tested fuels. It could be observed that CO emissions decreases with load for all tested fuels except at high load 12 Nm. This trend agrees with the literature [37, 56]. The reduction of CO emissions with load increase is due to the increase in combustion temperature that increases the reaction rates of oxidation reactions for CO emissions. While sudden increase in CO emissions at high loads is attributed to using richer air-fuel mixture which leads to more incomplete combustion regions in combustion chamber. The same trend of CO emissions was found by Bayındır et al.[57] who explained it as a result of using richer mixtures at high loads. Due to higher oxygen content in biodiesel, CO emissions in B30 has the lowest amount among tested fuels except at 12 Nm. B30-N5 has higher CO emissions than this for B30 due to high latent heat of evaporation of naphtha. This leads to stronger evaporating cooling effect that cause a reduction in mean gas temperature, leading to incomplete combustion [56]. Furthermore, naphtha high latent heat of evaporation increases liquid penetration length (LPL) of B30-N5 relative to B30 [42]. Then B30-N5 experiences more wall impingement leading to incomplete combustion and more CO emissions than B30. For diesel-naphtha blends, adding naphtha to diesel has showed promising results of CO reduction. About 9.73% and 14.07% decrease in CO emission is achieved for D95-N5 and D90-N10 relative to D100. This is attributed to higher oxygen amount entrained in combustion process because of enhancing mixing process and combustion homogeneity through increasing blends volatility due to naphtha. It is important to explain the opposite effect of naphtha of CO emissions for diesel-naphtha blends and for diesel-biodiesel-naphtha blends as follow: 1. B30 has longer LPL than D100 because of high viscosity of B30 leading to higher injection pressure and thus longer LPL [43, 58]. Due to high latent heat of evaporation, naphtha addition already increases LPL hence B30-N5 has longer penetration length than D95-N5 and D90-N10. Consequently, B30-N5 has more wall impingement and thus more incomplete combustion and CO emissions than B30. On the opposite side, effect of wall-impingement was marginal due to short LPL of diesel while effect of enhancement in atomization and mixing is more effective because of low viscosity of diesel relative to B30. 2. According to sensitivity analysis carried out by Cheng et al.[59] of biodiesel thermophysical properties effect on spray characteristics. Sensitivity analysis revealed that biodiesel spray characteristics is mostly sensitive to latent heat of evaporation which had the most dominant effect on LPL between other thermophysical parameters including liquid viscosity, vapor pressure, surface tension and liquid heat capacity. Therefore, effect of latent heat of vaporization of naphtha has stronger effect on LPL of B30 than viscosity in contrast to diesel which is affected mainly by viscosity than latent heat of evaporation.

24

Fig. 13. CO emissions for tested fuels at different load conditions at 2000 rpm. 4. Summary The effects of using cracked naphtha as an additive in ternary blends of diesel/biodiesel and binary blends with diesel are summarized in Table 8. Engine experimental results illustrated in Table 8 are obtained at constant speed of 2000 rpm along the load span of the engine. Also, characterization of the three main components diesel, biodiesel and naphtha was carried out using FTIR, GC-MS and GC-FID systems. It was found that cracked naphtha has higher isoparaffins to n-paraffins ratio than diesel. Hence, mixing naphtha with diesel in binary blends, has led to longer ignition delay time than this of neat diesel. For diesel-naphtha, due to high volatility and low viscosity of naphtha enhancement in atomization, evaporation and mixing processes is achieved. This enhancement leads to advantages like decreasing bsfc and CO emissions and disadvantages like increasing NOx emissions and deterioration engine stability at idling for D90-N10. For B30-N5, due to low percentage of naphtha and low sensitivity of B30 to naphtha, neither certain change appears in combustion characteristics nor in bsfc for B30-N5. However, due to high latent heat of evaporation of naphtha NOx emissions decreased while CO emissions increased. Table 8 Summary of the experimental results obtained from this work. Parameter

Effect of naphtha Diesel-biodiesel-naphtha (relative to B30) Physical properties

Density Viscosity Flash/Fire temperature Bsfc Stability

Diesel-Naphtha (relative to D100)

Decrease Decrease

Decrease Decrease

Decrease

Decrease

Engine performance No effect Decrease Stable for B30-N5 Stable for D95-N5 & D90-N10 Misfire for B30-N10 & B30Misfire for D85-N15 N15 Combustion characteristics 25

(For B30-N5, D95-N5 and /D90-N10) Peak pressure Heat release rate Ignition delay time CA50 Exhaust temperature Emissions CO NOx

No effect

Decrease

No effect

Decrease

No effect

Increase

No effect

Increase

No effect

Increase

Increase

Decrease Increase at low load & idling Decrease at medium and high loads

Decrease

5. Conclusion and future work This paper investigates the effect of adding AMOC cracked naphtha to diesel (D100) and B30 on combustion characteristics, engine performance and harmful emissions percentage in exhaust like NOx and CO emissions. The findings of the study can be summarized in the following points: 1. AMOC cracked naphtha has rich content of iso-paraffins relative to normal-paraffins in contrast to straight-run naphtha. Hence, AMOC naphtha has higher RON than other naphthas in literature. 2. Maximum percentage that could be added to D100 was 10%. Further increase in naphtha percentage to 15% led to unstable performance of engine and misfire at high loads. 3. Maximum naphtha percentage added to B30 was lower than for that of D100. Adding more than 5% of naphtha to B30, led to instability and misfire at high loads. 4. D90-N10 was the most economic fuel in the study. D90-N10 showed significant reduction in bsfc that reached 11.7% at 12 Nm in comparison to D100. 5. For diesel-biodiesel-naphtha blends, B30-N5 achieved 12% reduction in NOx emissions in comparison with B30. While, for diesel-naphtha blends at idling and low load conditions, naphtha increased NOx emissions by 15.88% and 18.87% for D95-N5 and D90-N10 relative to D100, respectively. However, at medium and high loads, NOx emissions were decreased by 12.13% and 9.48% in case of D95-N5 and D90-N10, respectively. 6. CO emission was reduced by 9.73% and 14.07% for D95-N5 and D90-N10 relative to D100, respectively. For diesel-biodiesel-naphtha blends, CO emission was increased by 13.22% for B30-N5 relative to B30. There are plenty of experimental work that is out of the scope of the paper that can improve the understanding of using naphtha in a blend with diesel and biodiesel in CI engine. This includes studying the effect of advancing injection timing which may increase the allowable percentage of naphtha addition to D100 and B30 by advancing CA50. It is also recommended to investigate ignition delay time and spray characteristics of ternary blends of dieselbiodiesel-naphtha and binary blends of diesel-naphtha in shock tube and rapid compression machine, and spray chamber, respectively. Acknowledgement

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Highlights •

Effect of addition of cracked naphtha to diesel-biodiesel blend was investigated.

•

Optimum ratio of naphtha to D100 and B30 were found 10% and 5%, respectively.

•

Adding 5% and 10% naphtha to D100 decreased bsfc by 6.28% and 11.7%, respectively.

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NOx emissions were decreased by 12% for B30-N5.

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CO emission was reduced by 14.1% for D90-N10 compared to D100.

Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.