Performance, Combustion, and Emission Analysis of Neat Palm Oil


Performance, Combustion, and Emission Analysis of Neat Palm Oil...

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Performance, combustion and emission analysis of neat palm oil bio-diesel and higher alcohol blends in diesel engine Yuvarajan Devarajan, Dinesh Babu Munuswamy, Arulprakasajothi Mahalingam, and Beemkumar Nagappan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02939 • Publication Date (Web): 17 Nov 2017 Downloaded from http://pubs.acs.org on November 18, 2017

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Performance, combustion and emission analysis of neat palm oil bio-diesel and higher alcohol blends in diesel engine Yuvarajan Devarajan1, †, Dinesh Babu Munuswamy2, Arulprakasajothi Mahalingam3, Beemkumar Nagappan4

1, 3

Department of Mechanical Engineering, Vel Tech Dr.RR & Dr.SR University, Chennai, India. 2

Department of Mechanical Engineering, Panimalar Engineering College, Chennai, India.. 4

Department of Mechanical Engineering, Sathyabama University, Chennai, India.

1,

[email protected]

Abstract: In this work, palm oil biodiesel (POBD100) with cyclo-octanol additive was employed in a constant speed diesel engine and its effects on engine combustion, emission and performance were studied. The biodiesel produced from palm oil by conventional transesterification process, sodium hydroxide and methanol were involved in the conversion of oil into biodiesel. The five fuels evaluated were neat palm oil biodiesel (POBD100), octanol blended with palm oil biodiesel by10% volume (POBD90O10), octanol blended with palm oil biodiesel by20% volume (POBD80O20), octanol blended with palm oil biodiesel by30% volume (POBD70O30) and petroleum diesel. The experimental results revealed that with the increased octanol fraction, the 1 ACS Paragon Plus Environment

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combustion was smooth. All the octanol and biodiesel blends provide earlier combustion when compared to neat palm oil biodiesel which leads to higher thermal efficiency, lower fuel consumption, lower peak pressure, and shorter ignition delay. All the emissions are reduced by the addition of cyclo-octanol in palm oil biodiesel in all loads owing to the higher oxygen concentration of air/fuel mixtures and improved atomization. Based on the outcome of this study palm oil biodiesel and cyclo-octanol blends can be employed as a potential alternative fuel for existing unmodified diesel engines owing to its improved combustion, emission and performance characteristics. Keywords: cyclo-octanol; Combustion; Performance; ignition delay; Palm oil 1. Introduction The fuel and energy crisis in recent times and depletion of the world’s non-renewable resources provided the incentives to look for alternatives to conventional fossil fuels. Biodiesel continues to gain its reputation as a promising alternative fuel owing to its renewable nature. Biodiesel can be used as dual or bi-fueling but is generally blended with petroleum diesel 1. Biodiesel is a renewable, biodegradable, cleaner burning alternative to petroleum fuels. With tax incentives and the rising petroleum prices, biodiesel is becoming more economically competitive. It has a higher cetane rating, which promotes easier cold starting and lowers idle noise 2. Biodiesel is produced from different raw materials and processes as a result of which there is a minor deviation in its properties 3. Further, the lubricating properties of biodiesel are superior to diesel. Drawbacks of biodiesel are high kinematic viscosity, volatility, density, lower calorific value; longer delay period and higher NOx emission 4. Hence, there is a necessity to improve the

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drawbacks for the effective implementation of biodiesel in diesel engine applications. Much research had been carried out in biodiesel operation by changing the injection parameters, engine modifications, exhaust gas recirculation, preheating, and by adding additives in fuel formulation 5, 6

. Formulation method is the effective technique to reduce the drawback of biodiesel. In the

fuel formulation method, the emulsion process is an effective technique to reduce exhaust emission in CI engine. Many works have been carried out by doping alcohols with biodiesel and diesel blends

6-13

. From the outcome of the many studies available in the technical literature,

there exists a gap in implementing 100% neat biodiesel and higher alcohol blends as a replacement for diesel for practical applications. Therefore intensive study on the effect of higher alcohols on combustion, performance, and emission on neat biodiesel is to be carried. Furthermore, the blending of alcohol to fuels has been limited to 20% by volume in available technical literature. This work also investigates the effect of higher alcohols at higher blending ratios (30% volume). In this work, cyclo-octanol is chosen as oxygenated additive owing to its improved blend stability, higher energy density and lower energy requirement during production process than from other alcohols

11, 12

. Neat palm oil biodiesel (POBD100) and cyclo-octanol blends at

different concentrations are fueled by a stationary diesel engine to evaluate its combustion, emission and performance characteristics and compared with diesel. 2. Experimental materials and Procedure Physicochemical properties of all the fuel samples were measured according to the ASTM standards. Acid based transesterification process was employed for conversion of raw oil to biodiesel. Table 1 presents the fuel properties of fuels employed in this study. Table 2 presents the fatty acid composition of palm oil. A four-stroke, direct-injection air-cooled, multi-cylinder, 3 ACS Paragon Plus Environment

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2100 rpm constant speed diesel engine was employed in this study. Mechanical type fuel injection system was employed. Layout of engine is illustrated in figure 1. Table 3 presents the basic properties of alcohol employed in this work. In this experiment, Dynomax-2000 software was used to measure the performance of the engine. A portable BOSCH were used to analyze the exhaust emission. To measure the fuel consumption, a kobold ZOD positive displacement-type fuel flow meter is employed and Exhaust gas temperature was measured by the K-type thermocouple. AVL GH12D pressure transducer was used to sense the pressure exerted in the chamber. AVL3066A02 piezo charge amplifier was used as an analogue to digital converter. Table 4 illustrates the specification of the experimental setup. Before starting the test, diesel fuel was used to run the engine for a few minutes to warm up and after each test, the engine was made to run by fuelling with diesel in order to flush out the biodiesel and octanol blends from the fuel injection system. Table 5 shows the details of gas analyzer range, accuracy and uncertainties details of quantities measured.

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Figure 1. Experimental Engine Layout Table 1. Properties of fuels PROPERTIES

POBD100

POBD90O10

POBD80O20

POBD70O30

Diesel

METHOD

Density @ 18OC (gm/cc)

0.778

0.769

0.771

0.774

0.8200

ASTM D4052

Kinematic viscosity @35°C (mm2/s)

4.60

4.7

4.8

4.9

2.5

ASTM D445

Calorific Value (kJ/kg)

38807

38924

39122

39335

42500

ASTM D240

Cetane Index (CI)

52

52

52

52

47

ASTM D976

Flash point in O C

143

140

139

140

50

ASTM D93

Pour point in OC

-18

-19

-21

-22

-5.6

ASTM 5853

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Cloud point in O C C (% wt) H(% wt) O(% wt)

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ASTM -6.3

-8.4

-9.1

-9.4

-24 2500

77.4

77.1

76.4

75.6

-

ASTM D5291

11.3

11.6

12.2

10.8

-

ASTM D5291

11.3

10.7

11.4

13.6

-

-

Table 2. Fatty acid compositions of palm oil biodiesel Fatty acids Palmitic C16:0 Stearic Oleic Linoleic C18:2 Linoleic C18:3

POBD100 10.3 8.8 24.7 39.7 16.5

POBD90O10 10.7 9.1 26.4 41.2 12.6

Table 3. Properties of cyclo-octanol Chemical formula

C8H18O

Density (kg/m3)

Two

Melting point (K)

257

Boiling point (K)

467

Table 4 . Specification of Experimental Setup Make

Kirloskar

Cylinder

Two

Power ( Rated)

4.2 kW

Speed ( Rated)

2100 rpm

Bore (D)

87.5 mm 6

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POBD80O20 11.1 9.4 27.1 42.3 10.1

POBD70O30 11.2 9.5 27.2 42.4 10.1

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Stroke(L)

110mm

Injection

Direct

Fuel Injection

Mechanical Type

Compression Ratio

18

Injection pressure

210 bar

Table 5. Gas analyzer range, accuracy and uncertainties details Model of gas analyzer

AVL gas analyzer

Measured Quantity

Range

Accuracy

Uncertainties

CO

0-5000 ppm

0.02%

±0.5 (%)

HC

0-20000

± 10 ppm

±0.1 (%)

NOx

0-5000 ppm

± 10 ppm

±0.3 (%)

Cylinder pressure

0-250 bar

±0.1 bar

±0.1 ±0.2

Crank angle

0-360°

±1°

Performance BTE

-

-

Absolute

Relative

±0.01 %

±1

3. Results and discussion 3.1. Pressure Vs crank angle The variation of pressure with crank angle at peak conditions for tested fuels is shown in Figure 2. Peak pressure of diesel is lower than biofuels. The peak pressure of POBD100 is the highest among all other tested fuels. The kinematic viscosity of biodiesel is higher than other fuels, atomization and mixing of fuel with air is not in uniform rate causing longer breakup 7 ACS Paragon Plus Environment

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length, lower dispersion rate, and increased ignition delay 15, 16. As a result of longer delay period more quantity of fuel is accumulated in the combustion chamber and result in a rapid increase in peak pressure

13-15

. This result supplements the observation of higher NOX emissions for

POBD100 than from other test fuels.

60 100% LOAD Cylinder Pressure (bar)

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50 40 30 POBD100 DIESEL POBD90O10 POBD70O30 POBD80O20

20 10 0 -20

-10

0 10 Crank angle (deg CA)

20

30

Figure 2. Variations in-cylinder pressure with crank angle Fuel injection is delayed for biodiesel- octanol blends than neat biodiesel (POBD100). Viscosity decreases with increase in octanol for biodiesel- octanol blends. Fuel with lower viscosity requires additional time to reach the combustion chamber owing to its lower compressibility 15. Leakage losses (biodiesel- octanol blends) for low viscous fuel are higher causing lower injection pressure of fuel during combustion 12, 13. Further, fuel with higher viscosity (POBD100) takes additional time for atomization process which increases the delay period 16. Hence the time period between the fuel injection and ignition is higher for POBD100 and result in higher

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pressure (peak) and NOx emissions. This result is inline the results obtained from NOx emissions. The beginning of combustion for POBD100 is deferred by 3°CA than POBD70O30 though it had been admitted late. The viscosity of biodiesel- octanol blends are lower and hence less amount of fuel is injected (Confirmation from BSEC) leading to shorter delay period (better fuel spray, better vaporization and atomization, and complete mixing) 11, 15. 3.2. Heat release rate (HRR) HRR with crank angle at peak conditions for test fuels is shown in Figure 3. The peak value of heat release rate normally occurs for all fuels only at peak conditions. This is due to the fact that in peak load, the quantity of fuel admitted is more. HRR for diesel is the least among the fuels. The maximum heat release rate of POBD100, POBD90O10, POBD80O20, POBD70O30 and diesel are 70.2, 66.1, 65.5, 64.6 and 64.5 J/°CA, respectively. Since the calorific value of diesel and its BTE is higher than biofuels, the quantity of diesel combusted are less and Hence, resulting in lower HRR. Fuel with longer ignition delay (POBD100 in our case) accumulates more quantity of fuel causing rapid burning in the premixed combustion chamber, resulting in higher heat release rate 12, 15

. The addition of cyclo-octanol to POBD100 reduces the delay period and promotes earlier

commencement of combustion. Hence, the HRR for POBD90O10, POBD80O20 and POBD70O30 is lower than for POBD100. POBD70O30 resulted in enhancement of its combustion characteristics. This facilitated improvement in BTE, and reduced ignition lag. Hence, the HRR of POBD100 is higher than POBD70O30

11-13

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. The consolidation of the

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combustion parameters of tested fuels - at constant-speed and peak condition - is presented in Table 5. 80

POBD70O30 POBD80O20

100% LOAD Heat release rate(J/deg CA)

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POBD90O10

60

POBD100 DIESEL

40

20

0 -20

-10

-20

0

10

20

Crank angle (deg CA)

Figure 3. Variations in heat release rate with crank angle

Table 5 Combustion parameters of test fuels (2100 rpm and at peak conditions)

Fuel type

Maximum Pressure (bar)

Peak pressure occurrence (°aTDC)

Maximum heat release rate (J/°CA)

POBD100

63.2

8

70.2

POBD90O10

62.3

3

66.1

POBD80O20

60.0

5

65.5

POBD70O30

58.2

6

64.6

Diesel

55.8

3

64.5

3.3. Brake Thermal Efficiency (BTE) 10 ACS Paragon Plus Environment

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Variations in BTE with Load for Diesel, POBD100, and POBD100 blended with cyclooctanol in different proportions are shown in Figure 4. For all the fuels tested, the BTE tends to increase for the corresponding increment in engine load. The increment in BTE is due to the attainment of the higher load for a corresponding increase in fuel rate

15

. When compared to

POBD100, all the emulsion samples which contain cyclo-octanol show an increase in brake thermal efficiency 12. In addition, cyclo-octanol inclusion lowers the viscosity of POBD100 and improves vaporization and result in improvement in thermal efficiency 13. From the results, an improvement of 1.17% is observed in BTE for POBD70O30 fuel compared to the POBD100 at full load. This result is in line with most of the other research works carried for higher alcohols with biodiesel 8, 11-13.

30 Brake Thermal Efficiency (%)

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POBD100 POBD90O10

25

POBD80O20 POBD70O30

20

DIESEL 15 10 5 0

25

50 Load (%)

75

Figure 4. Variations in BTE with Load 3.4. Brake Specific Energy Consumption (BSEC)

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Variation in BSEC with a load for Diesel, POBD100, and POBD100 blended with cyclooctanol in different proportions is shown in Figure 5. POBD100 and its cyclo-octanol blend show a higher BSEC compared to the diesel fuel at all conditions. POBD100 and its cyclooctanol blend are more viscous which leads to the poor atomization of fuel leading to higher BSEC

12, 13

. From the figure, it is clear that addition of cyclo-octanol to POBD100 result in an

improvement in BSEC owing to the improved oxidation reaction

17

. Additional oxygen

molecules supplied by cyclo-octanol promotes the combustion reaction. In addition, there is a reduction in ignition delay for the cyclo-octanol blends owing to its better heat transfer and momentum exchange among fresh charge and burnt products inside the combustion chamber. Further, cyclo-octanol higher energy improves the combustion rate and end up with lower BSEC 11, 12

. Fuel with more viscosity as in the case of CB90P10, CB80P20, and CB70P30 reduces the

residue time to mix with air and causing a reduction in ignition delay which helps to complete the combustion process in the early stage

15

. This provides more work per amount of fuel

injected. From the results, a reduction of 0.5 MJ/kWh is observed in BSEC for POBD70O30 fuel compared to the POBD100 at full load.

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14 Brake Specific Energy Consumption (MJ/kW-hr)

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POBD100 POBD90O10

13

POBD80O20 POBD70O30

12

DIESEL 11

10

9 0

25

50 Load (%)

75

100

Figure 5. Variations in BSEC with Load 3.5 Brake specific hydrocarbon emission (BSHC) Figure 6 shows the variations in BSHC with a load for Diesel, POBD100, and POBD100 blended with cyclo-octanol in different proportions. HC increases with load due to the presence of more fuel inside the combustion chamber. POBD100 and cyclo-octanol blends have lower HC emission than diesel. It contains extra oxygen molecules which are taking part in the combustion and leads to lower HC emission

18

. It is found that addition of cyclo-octanol to

POBD100 further decreases the HC. Cyclo-octanol promotes the complete combustion and acts as an additional oxygen buffer which supplies surplus oxygen to smooth the progress of proper combustion of fuel

11

. The maximum reduction in HC emission was observed for POBD70O30

and this is owing to the complete combustion with an aid surplus oxygen content of cyclo-

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octanol12, 13. From the results, a reduction of 0.09 g/kWh is observed in BSHC for POBD70O30 fuel compared to the POBD100 at high load.

0.5 Brake Specific HC Emission (g/KWh)

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POBD100 POBD90O10 0.4

POBD80O20 POBD70O30

0.3

DIESEL

0.2

0.1 0

25

50 Load (%)

75

100

Figure 6. Variations in BSHC emissions with Load 3.6. Brake specific carbon dioxide emissions (BSCO2) Figure 7 shows the variations in BSCO2 with a load for diesel, POBD100, and POBD100 blended with cyclo-octanol in different proportions. CO2 increases with a load for all fuels tested due to the presence of more fuel inside the combustion chamber causing complete combustion and to converts the CO into CO2 emissions 17, 18. The result shows that carbon dioxide emission for POBD100 & cyclo-octanol blends is more than that of diesel. Since diesel constitutes of the pure hydrocarbon chain, lower CO2 is obvious. It is found that addition of cyclo-octanol to POBD100 decreases the BSCO2 emissions

15

. Cyclo-octanal enhances the combustion rate and

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also supplies more oxygen which reduces CO2 emissions. The maximum reduction in CO2 emission for cyclo-octanol blends was observed for POBD70O30 and this is owing to the 11, 12

complete combustion with aid surplus oxygen molecules present in cyclo-octanol

. Further,

reduction in viscosity of mixtures also played a key role in a reduction in BSCO2 emission 15, 18. From the results, a reduction of 1.3 g/kWh is observed in CO2 for POBD70O30 fuel compared to the POBD100 at peak load. Blending 30 % of cyclo-octanol on volume basis reduces significant CO2 emissions of POBD100. However, BSCO2 emissions of diesel fuel are lower than for other fuels.

Brake Specific CO2 Emissions (g/kWh)

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8 7 6 5 POBD100 4

POBD90O10

3

POBD80O20 POBD70O30

2

DIESEL 1 0

25

50 Load (%)

75

100

Figure 7. Variations in BSCO2 emission with Load 3.7. Brake specific oxides of nitrogen emission (BSNOx) Variations in BSNOx emission with a load for Diesel, POBD100, and POBD100 blended with cyclo-octanol in different proportions is shown in Figure 8. NOx emission for the

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POBD100 is found to be more compared to the diesel fuel as a result of the higher oxygen content of the fuel and high temperature inside the chamber during combustion

19, 20

. NOx

emission is highest for pure POBD100 and lowest for POBD70O30. A reduced value for NOx emission is due to reduced ignition delay due to oxidization effect of cyclo-octanol 13. POBD100 blended with the cyclo-octanol result in reduced in-cylinder pressure and temperature which reduces NOx emission. Fuel with lower viscosity increases the atomization process and thus 19

reducing the delay period and NOx emission

. From the results, a reduction of 1.19 g/kWh is

observed in BSNOx for POBD70O30 fuel compared to the POBD100 at peak load. NOx emission reduces the inclusion of cyclo-octanol to POBD100. The maximum reduction in NOx emission is observed by doping 30% of cyclo-octanol on volume basis to POBD100. This result is in accordance with other research 17, 19, 20.

Brake Specific NOx Emission (g/KWh)

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POBD100 13

POBD90O10 POBD80O20

11

POBD70O30 DIESEL

9

7 0

25

50 Load (%)

75

Figure 8. Variations in BSNOX emission with Load 3.8. Exhaust Gas Temperature (EGT)

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Figure 9 shows the variations in exhaust gas temperature with a load for diesel, POBD100, and POBD100 blended with cyclo-octanol in different proportions. Biodiesel with cyclo-octanol blends have lower EGT than from diesel due to the presence of cyclo-octanol leading to better evaporation rate and enhance the oxidation property of the fuel

11

. Oxidative

property of POBD100 blended with cyclo-octanol stimulates the enhanced combustion by reducing ignition delay period

12, 13

. Reduced ignition delay accelerates the flame propagation

and reduces carbon activation temperature and reduces EGT 20. From the results, a reduction of 2.1 % is observed in EGT for POBD70O30 fuel compared to the POBD100 at peak load. Blending 30 % by volume of cyclo-octanol reduces significant EGT.

400 POBD100 Exhaust gas temperature (deg C)

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350

POBD90O10 POBD80O20

300

POBD70O30 250

DIESEL

200 150 100 0

25

50 Load (%)

75

Figure 9. Variations of EGT with Load

3.6. Brake specific carbon monoxide emissions (BSCO) 17 ACS Paragon Plus Environment

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Energy & Fuels

Figure 10 shows the variations in BSCO with a load for diesel, POBD100, and POBD100 blended with cyclo-octanol in different proportions. CO increases with a load for all fuels tested due to the presence of more fuel inside the combustion chamber causing complete combustion and to converts the CO into CO2 emissions

15

. It was observed that the carbon monoxide

emission for POBD100 and POBD100 blended with cyclo-octanol is less than diesel owing to the presence of inbuilt surplus oxygen molecules in the biodiesel. CO emission reduces with increase in cyclo-octanol content. The lowest value of CO emissions was observed for POBD70O30. Complete combustion of POBD100 and cyclo-octanol blends result in lower CO emissions owing to surplus oxygen molecules present in cyclo-octanol

14, 15

.

In addition,

POBD100 and cyclo-octanol blends have a lower kinematic viscosity than from POBD100. Fuel with lower viscosity improves the atomization and vaporization of fuel with air and reduces CO emissions 18, 21. From the results, a reduction of 1.8 g/kWh is observed in CO2 for POBD70O30 fuel compared to the POBD100 at peak load. Blending 30 % of cyclo-octanol on volume basis reduces significant CO2 emissions of POBD100. 4 Brake Specific CO Emission (g/kWh)

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POBD100 POBD90O10 POBD80O20 POBD70O30 DIESEL

3.5 3 2.5 2 1.5 1 0

25

50 Load (%)

75

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Figure 10. Variations in BSCO emission with Load Conclusion Stationery diesel engine is made to run on diesel, POBD100, POBD90O10, POBD80O20 and POBD70O30 to study the effect of cyclo-octanol on combustion, emission and performance characteristics of the palm oil biodiesel. Following are the key observations made during this study. •

Peak pressure and ignition delay are reduced by doping cyclo-octanol in the biodiesel.



Heat Release Rate is least for POBD70O30 owing to the improved oxidation stability of cyclo-octanol in alcohol and biodiesel blends.

• POBD100 and cyclo-octanol blends have better brake thermal efficiency than from POBD100. However, better brake thermal efficiency of POBD100 and its cyclo-octanol blends is lower than for petroleum diesel at all loads. • Brake specific energy consumption is lower for diesel among all the fuels owing to its higher calorific value. Doping cyclo-octanol in the biodiesel reduces the energy consumption and exhaust gas temperature as the oxidation effect reduces the amount of fuel required. • The oxidation effect of cyclo-octanol contributes to enhancing oxidation capability of fuel which reduces the HC, CO, CO2, and, NOX emissions of palm oil biodiesel.

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