Performance, emission and combustion characteristics of a variable compression ratio engine using methyl esters of waste cooking oil and diesel blends

Applied Energy 88 (2011) 3959–3968

Contents lists available at ScienceDirect

Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Performance, emission and combustion characteristics of a variable compression ratio engine using methyl esters of waste cooking oil and diesel blends K. Muralidharan ⇑, D. Vasudevan Department of Mechanical Engineering, PSNA College of Engineering & Technology, Dindigul 624 622, India

a r t i c l e

i n f o

Article history: Received 13 October 2010 Received in revised form 28 February 2011 Accepted 2 April 2011 Available online 22 April 2011 Keywords: Bio diesel Methyl esters of waste cooking oil Compression ratio Variable compression ratio multi fuel engine

a b s t r a c t The performance, emission and combustion characteristics of a single cylinder four stroke variable compression ratio multi fuel engine when fueled with waste cooking oil methyl ester and its 20%, 40%, 60% and 80% blends with diesel (on a volume basis) are investigated and compared with standard diesel. The suitability of waste cooking oil methyl ester as a biofuel has been established in this study. Bio diesel produced from waste sun flower oil by transesterification process has been used in this study. Experiment has been conducted at a fixed engine speed of 1500 rpm, 50% load and at compression ratios of 18:1, 19:1, 20:1, 21:1 and 22:1. The impact of compression ratio on fuel consumption, combustion pressures and exhaust gas emissions has been investigated and presented. Optimum compression ratio which gives best performance has been identified. The results indicate longer ignition delay, maximum rate of pressure rise, lower heat release rate and higher mass fraction burnt at higher compression ratio for waste cooking oil methyl ester when compared to that of diesel. The brake thermal efficiency at 50% load for waste cooking oil methyl ester blends and diesel has been calculated and the blend B40 is found to give maximum thermal efficiency. The blends when used as fuel results in reduction of carbon monoxide, hydrocarbon and increase in nitrogen oxides emissions. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The progress of bio fuels can be traced back to early 19th century. In fact, the development of diesel engines and bio fuels has simultaneous history of technological advancements and economic struggle. Bio fuels offer enhanced employment opportunities and livelihood generation, leading to regional as well as national self sufficiency [1]. Vegetable oils present a very hopeful alternative fuel to diesel oil, since they are renewable, biodegradable and clean burning, having properties analogous to that of diesel. They offer similar power output with slightly lesser thermal efficiency due to their lesser energy content compared to diesel [2]. Bio diesel, produced from different vegetable oils (soybean, rapeseed and sunflower etc.), have been used in internal combustion engines without major modifications, with only slightly decreased performance [3]. Various researchers have conducted experiments to study the performance and emission characteristics of diesel engine when vegetable oils, blends of vegetable oil and its derivatives are used as fuel and it has been found to be economical and competitive compared to standard diesel [4–7]. Research works on such studies show that different kinds of vegetable oils such as cottonseed oil, soybean oil, sunflower oil ⇑ Corresponding author. Mobile: +91 9443775518. E-mail address: [email protected] (K. Muralidharan). 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.04.014

and their corresponding methyl esters, rapeseed oil methyl ester, palm oil methyl ester, corn oil, olive kernel oil, deccan hemp oil, jojoba oil, paradise oil, eucalyptus oil, poon oil, pongamia pinnata methyl ester, coconut oil based hybrid fuels and pre heated waste frying oil has been used as an alternative fuel for diesel engine. In these entire cases, engine showed an improved performance with reduction in smoke, hydrocarbon and CO emissions and increase in NOx emission. In this way, a lucid image has been formed viewing the relative performance and emission characteristics of these fuels [8–15]. In 2009, Arul Mozhi Selvan et al. [16] compared the combustion characteristics of single-cylinder four stroke direct injection variable compression ratio engine under compression ratios of 15:1, l7:1, and 19:1 when using diesel and bio diesel–ethanol blends as fuel. It has been observed that the cylinder gas pressure, maximum rate of pressure rise and heat release rate increase with higher ethanol concentration due to longer ignition delay. The exhaust gas temperature was found to be less. The study also examined the fuel burning characteristics of the diesel–bio diesel–ethanol blends under various compression ratios and loading conditions. The performance and emission tests have been carried out by using the stable fuel blends on a computerized variable compression ratio engine and compared with neat diesel [17]. In 2010, Panwar et al. [18] investigated the engine performance of Castor Methyl Ester (CME) and Potassium Hydroxide (KOH) catalyst used in four stroke, single cylinder variable compression ratio

3960

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

Nomenclature B20 B40 B60 B80 BP BTE CA CO CO2

20% bio diesel + 80% diesel 40% bio diesel + 60% diesel 60% bio diesel + 40% diesel 80% bio diesel + 20% diesel brake power brake thermal efficiency crank angle carbon monoxide carbon dioxide

type diesel engine at different loads and concluded that the lower blends of bio diesel increased the break thermal efficiency and reduced the fuel consumption. The exhaust gas temperature increased with increasing bio diesel concentration. Gumus and Kasifoglu [19] studied the performance and emissions of a compression ignition diesel engine without any modification, using neat apricot seed kernel oil methyl ester and its blends with diesel fuel and found that lower concentration of apricot seed kernel oil methyl ester in blends give a better improvement in the engine performance and exhaust emissions. Prem Anand et al. [20] evaluated the combustion performance and exhaust emission characteristics of turpentine oil fuel blended with conventional diesel fuel in a diesel engine. Saravanan et al. [21] analyzed the combustion characteristics of crude rice bran oil methyl ester blend in a direct injection compression ignition engine and found that the cylinder pressure was comparable whereas the delay period and the maximum rate of pressure rise were lower than that of diesel. Ismet Celikten et al. [22] compared the performance and emissions of diesel fuel from rapeseed and soybean oil methyl esters injected at different pressures (250, 300 and 350 bar). It has been found that the torque and power of diesel fuel engine reduced with increasing injection pressure. Smoke level (%) and CO emission also reduced while NOx emission increased as the injection pressure is increased. Jindal et al. [23] studied the effects of the engine design parameters such as compression ratio, fuel injection pressure and the performance parameters such as fuel consumption, brake thermal efficiency, emissions of CO, CO2, HC, NOx, smoke opacity with Jatropha methyl ester as fuel. A comparison of performance and emission for different compression ratios along with injection pressure and the best possible combination for operating engine with Jatropha methyl ester has been found. It is found that the combined increase in compression ratio and injection pressure increases the brake thermal efficiency and reduces the brake specific fuel consumption while lowering the emissions. Raheman and Ghadge [24] studied the performance of Ricardo E6 engine using bio diesel obtained from mahua oil (B100) and its blend with high speed diesel at varying compression ratio, injection timing and engine loading. The brake specific fuel consumption and exhaust gas temperature increased, whereas brake thermal efficiency decreased with increase in the proportion of bio diesel in the blends for all compression ratios (18:1–20:1) and injection timings (35–45° before TDC). The authors concluded that, bio diesel could be safely blended with HSD up to 20% at any of the compression ratio and injection timing tested for getting fairly accurate performance as that of diesel. Most of the studies are conducted in different types of engines with bio diesel prepared from different oils. The effect of parameters on the performance of the engine with emission characteristics and combustion characteristics of the bio diesel has been emphasized in many studies [24–27]. However, it has to be noted that the study on variable compression ratio engine using

CR HC IMEP NOx O2 SFC VCR WCO

compression ratio hydro carbon indicated mean effective pressure nitrogen oxides oxygen specific fuel consumption variable compression ratio waste cooking oil

bio diesel is limited [16,22,24]. The effect of compression ratio on engine parameters, emission and combustion characteristics have not been studied extensively. Hence this study has been devoted to find suitable compression ratio which gives optimum performance. In this study, waste cooking oil (methyl esters of waste cooking oil) and its blends with diesel is chosen as a fuel for variable compression ratio multi fuel engine. The various blends of waste cooking oil (WCO) and standard diesel fuel are prepared and the following investigations are carried out.  The performance and emission characteristics of variable compression ratio engine using various blends at compression ratios 18:1, 19:1, 20:1, 21:1 and 22:1 for 50% load and its comparison with the results of standard diesel fuel.  The combustion parameters such as variation of cylinder pressure, maximum rate of pressure rise, heat release rate and mass fraction burnt are discussed with reference to the crank angle for different compression ratios. 2. Experimental set up Fig. 1 shows the schematic diagram of the experimental set up. The test engine used is a variable compression ratio multi fuel engine coupled with eddy current dynamometer. The specification of the engine is shown in Table 1. Engine performance analysis software package ‘‘Engine Test Express V5.76’’ have been employed for online performance analysis. The Kistler piezoelectric pressure transducer and a crank angle encoder which measures the combustion pressure and the corresponding crank angle respectively are mounted into the engine head. The pressure transmitter Type 6613CA contains a piezoelectric sensor and an integrated charge amplifier. The output shaft of the eddy current dynamometer is fixed to a strain gauge type load cell for measuring applied load to the engine. Type K–Chromel (Nickel–Chromium Alloy)/ Alumel (Nickel– Aluminum Alloy) thermocouples are used to measure gas temperature at the engine exhaust, calorimeter exhaust, water inlet of calorimeter and water outlet of calorimeter, engine cooling water outlet and ambient temperature. Mass air flow sensor is used to measure the airflow rate. A shell and tube gas to liquid heat exchanger is used as a calorimeter for conducting the heat balance. The fuel flow is measured by the use of 20 cc burette and stopwatch with level sensors. A computerized data acquisition system is used to collect, store and analyze the data during the experiment by using various sensors. 2.1. Experimental methodology The variable compression ratio engine is started by using standard diesel and when the engine reaches the operating

3961

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

Bio diesel

Petrol

Multi fuel VCR Engine Exhaust gas Analyzer

Computer

Data Acquisition System

Air plenum

Coupling

Eddy current Dynamometer

VCR Engine

Measuring Burette

Encoder

BED

BED

Fig. 1. Schematic diagram of the experimental set up.

Table 1 Specification of the variable compression ratio engine. General details Rated power Speed Number of cylinder Compression ratio Bore Stroke Ignition Loading Load sensor Starting Cooling

4-Stroke, water cooled, variable compression ratio engine, compression ignition 3 .7 kW 1500 rpm (constant) Single cylinder 5:1–22:1 (variable) 80 mm 110 mm Compression ignition Eddy current dynamometer Strain gauge load cell Manual crank start Water

temperature, 50% load is applied. The warm up period ends when cooling water temperature is stabilized at 60 °C. The tests are conducted at the rated speed of 1500 rpm. In every test, volumetric fuel consumption and exhaust gas emissions such as carbon monoxide (CO), hydrocarbon (HC), nitrogen oxides (NOx), carbon dioxide (CO2) and oxygen (O2) are measured. From the initial measurement, brake thermal efficiency (BTE), specific fuel consumption (SFC), brake power (BP), indicated mean effective pressure (IMEP) mechanical efficiency and exhaust gas temperature with respect to compression ratios 18:1, 19:1, 20:1, 21:1 and 22:1 for different blends are calculated and recorded. At each operating conditions, the combustion characteristics and exhaust emission levels are also processed and stored in personal computer (PC) for further processing of results. The same procedure is repeated for different blends of waste cooking oil methyl esters. Table 2 shows the accuracy of the measurements and the uncertainty of the calculated results of the various parameters. The properties of the diesel fuel and the bio diesel blends are summarized in Table 3. The typical values taken from the different references men-

Table 2 The accuracies of the measurements and the uncertainty of the calculated results. Measurements

Accuracy

Engine speed Temperatures Carbon monoxide Hydrocarbon Carbon dioxide Nitrogen oxides Time Calculated results Power Specific fuel consumption Crank angle encoder

±2 rpm ±1 °C ±0.02 % ±10 ppm ±0.5% ±15 ppm ±0.5% Uncertainty ±1% ±2% ±0.5° CA

tioned. The actual density, viscosity, fire point, flash point and gross calorific value were measured in the laboratory. The values are provided to comprehend the relative performance and emission activities of the different fuel blends. 3. Results and discussions 3.1. Brake thermal efficiency and Specific fuel consumption The variation of brake thermal efficiency (BTE) for different compression ratios and for different blends is given in Fig. 2. It has been observed that the brake thermal efficiency of the blend B40 is slightly higher than that of the standard diesel at higher compression ratios. It appears that the brake thermal efficiency of the blend B40 is higher for the compression ratio 21. The brake thermal efficiency of the standard diesel and blend B40 for compression ratio 21 is 26.08% and 31.48% respectively. By increasing the compression ratio of the engine, the brake thermal efficiency

3962

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

Table 3 Fuel properties of diesel and bio diesel blends.

c

Diesel

B20

B40

B60

B80

B100

Density (kg/m3) Viscosity at 40 °C(mm2/s) Flash point Fire point Calculated cetane index Gross calorific value (kJ/kg)

0.835 1.382 42 °C 68 °C 45–50a 45240a

0.84 1.407 43 °C 65 °C 52 40606

0.845 1.44 53 °C 76 °C 48 38895

0.85 1.464 82 °C 104 °C 46 37267

0.87 1.556 84 °C 124 °C 44 36246

0.89 2.72 186 °C 208 °C 41 35401

Bio diesel standardsb,c ASTM D 6751–02

DIN EN 14214

– 1.9–6.0 >130 – 41 min –

0.86–0.90 3.5–5.0 >120 – 51 min –

Ref. [26]. Ref. [33]. Ref. [24].

3.2. Brake power and indicated mean effective pressure

Brake thermal efficiency (%)

40 36 32 28 24 Diesel

20 18

B20

19

B40

B60

20

B80

21

22

Compression ratio Fig. 2. Variation of brake thermal efficiency with compression ratio for different blends.

also gets increased for all the fuel types tested. Brake thermal efficiency is directly proportionate to the compression ratio [28]. The result indicates a significant improvement in brake thermal efficiency for blend B40 at compression ratio 21. The specific fuel consumption of B40 blend is lower than that of all other blends at compression ratio 20 and 21 and is shown in Fig 3. This may be due to fuel density, viscosity and heating value of the fuels. B40 has higher energy content than B60 and B80, but lower than B20 and diesel. It appears that the specific fuel consumption (SFC) for blend B40 is lower at compression ratio 21. The specific energy consumption decreases with the increase in compression ratio [16]. The specific fuel consumption of the blend B40 at the compression ratio of 21 is 0.259 kg/kwh whereas for diesel it is 0.314 kg/Kwh. At higher percentage of blends, the specific fuel consumption increases. This is due to the decrease in calorific value for the higher blends. Low values of specific fuel consumption are obviously desirable [29].

The brake power values for different blends of different compression ratios are shown in Fig. 4. The figure shows that the blends B20, B40, B60 and B80 with standard diesel have a reduction in brake power. Thermal efficiency is defined as the ratio of the power output to the energy introduced through fuel injection; the later is the product of the injected mass flow rate and the lower heating value [31]. Brake power decreases at higher compression ratio due to the conversion from the chemical energy to mechanical energy. Due to the lower heating value of the blends and unstable combustion the brake power decreases. The maximum brake power obtained for B40 and diesel at a compression ratio 21 is 2.07 KW and 2.12 KW respectively. The other blends are also indicated at a reduction in brake power, with higher compression ratios due to lower heating value of fuel. The indicated mean effective pressure for blend B40 is higher at lower compression ratios 2.2

Brake power (KW)

a b

Properties

2.1

2

1.9 Diesel

1.8 18

B20

19

B40

B60

20

B80

21

22

Compression ratio Fig. 4. Variation of brake power with compression ratios for different blends.

0.4 6.5

6

0.32

IMEP (bar)

SFC (kg/KWh)

0.36

0.28

5.5

0.24 5 Diesel

0.2 18

19

B20

B40

B60

20

B80

21

Diesel

22

Compression ratio

4.5 18

19

B20

B40

B60

20

B80

21

Compression ratio Fig. 3. Variation of specific fuel consumption with compression ratio for different blends.

Fig. 5. Variation of IMEP with compression ratio for different blends.

22

3963

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

and lower at higher compression ratio than standard diesel. The variation of indicated mean effective pressure with compression ratio for different blends is shown in Fig. 5. The blend B40 closely follows the diesel at higher compression ratios. The indicated mean effective pressure for blend B40 and diesel at compression ratio 21 is 5.583 bar and 5.774 bar. 3.3. Mechanical efficiency

due to the lower calorific value of blended fuel as compared to the standard diesel and lower temperature, at the end of compression [16]. Lower exhaust loss may be the possible reason for higher performance [11].

4. Emission analysis 4.1. Procedure

The variations of mechanical efficiency with compression ratio for various blends are shown in Fig. 6. It has been observed that the mechanical efficiency of the blends is lesser in lower compression ratio and higher in higher compression ratio. The mechanical efficiency of the blend B40 increases with the increase in compression ratio, when compared to that of standard diesel. The maximum mechanical efficiency obtained from blend B40 for compression ratio 21 is 52.53%. Mechanical efficiency increases with increasing compression ratio for all the blends. 3.4. Exhaust gas temperature The variations of exhaust gas temperature for different compression ratio and for different blends are shown in Fig. 7. The result indicates that exhaust gas temperature decreases for different blends when compared to that of diesel. At lower compression ratio 18 the exhaust gas temperature of the blends are higher compared to that of standard diesel. As the compression ratio increases, the exhaust gas temperature of the various blends is lesser than that of diesel. The highest temperature obtained is 233.48 C for standard diesel for a compression ratio of 21, whereas the temperature is only 200.61 °C for the blend B40. The reason for the reduction in exhaust gas temperature at increased compression ratio is

A MN–05 model, MARS portable gas analyzer was used for measuring the exhaust gas emissions. The probe of the analyzer is inserted into the exhaust pipe of the engine before taking the measurements. After the engine has stabilized in working condition, the exhaust emissions were measured. By using this analyzer Carbon monoxide (CO), Hydrocarbon (HC), Nitrogen oxides (NOx), Carbon dioxide (CO2) and Oxygen (O2) were measured for different blends of methyl ester of waste cooking oil with standard diesel and analyzed for different compression ratios. The various Indian standards used for emission analysis are given in Table 4 [32]. The results of waste cooking oil methyl ester and blends of bio diesel are within the acceptable limits.

Table 4 Indian standards used for emission analysis [34]. Elements

Standard

Carbon dioxide Carbon monoxide Nitrogen oxides Hydrocarbon

IS 13270:1992 (reaffirmed 1999) IS 11293:1992 IS 11255 – (PART 7) – 2005 –

80 70

56

60

HC (g/kWhr)

Mechanical efficiency (%)

60

52 48 44 Diesel

40 18

B20

B40

B60

50 40 30 20

B80

10

19

20

21

Diesel

22

0 18

Compression ratio

B20%

B40%

19

B60%

20

B80%

21

22

Compression ratio Fig. 6. Variation of mechanical efficiency with compression ratio for different blends.

Fig. 8. Variation of hydro carbon with compression ratio for different blends.

1200 1100

ο

Exhaust gas temperature ( C)

260 240

NOx (PPM)

1000

220 200 180

900 800 700 600

Diesel

B20

B40

B60

B80

500 160 18

19

20

21

22

Compression ratio

400 18

Diesel

19

B20

B40

B60

20

B80

21

Compression ratio Fig. 7. Variation of exhaust gas temperature with compression ratio for different blends.

Fig. 9. Variation of NOx with compression ratio for different blends.

22

3964

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

fuels [13]. In this research, it shows that the increase in compression ratio increases the HC emission for Blend B40. The other blends B20, B60 and B80 produce lesser hydrocarbon emissions at higher compression ratio than the standard diesel. Due to the longer ignition delay, the accumulation of fuel in the combustion chamber may cause the higher hydro carbon emission.

0.5

CO (%)

0.4 0.3 0.2 0.1 Diesel

0 18

B20

B40

19

20

B60

B80

21

22

Compression ratio Fig. 10. Variation of carbon monoxide with compression ratio for different blends.

5

4.2.2. Nitrogen oxides (NOx) emission The variations of nitrogen oxides (NOx) emission with respect to different compression ratio for different blends are shown in Fig. 9. As observed from the figure, the NOx emission for diesel and other blends increase with the increase of compression ratio. From the figure, it is obvious that for compression ratio 21, NOx emission from the waste cooking oil blend B40 is higher than that of diesel. The other blend closely follows the standard diesel. The reason for higher NOx emission for blends is due to higher peak temperature. The reduction of NOx is the prime aim of the engine researchers. The NOx emission for diesel and blend B40 for compression ratio 21 is 621 ppm and 640 ppm respectively.

CO2 (%)

4.5 4 3.5 3

Diesel

B20%

B40%

B60%

B80%

2.5 18

19

20

21

22

Compression ratio Fig. 11. Variation of CO2 with compression ratio for different blends.

4.2. Result and discussions 4.2.1. Hydro carbon emission The variation of hydrocarbon emission with different compression ratios for different blends is given in Fig. 8. It shows that the hydrocarbon emission of various blends is higher at higher compression ratios. The effects of fuel viscosity, on the fuel spray quality, are expected to produce some HC increase with vegetable oil

4.2.3. Carbon monoxide emission Fig. 10 shows the variation of carbon monoxide emission of the blends and diesel with various compression ratios. The CO emission of the blend B40 is close to the standard diesel and it is found to be higher for compression ratio 21. The other blends B20, B60 and B80 have slightly lesser CO emission for compression ratio 21. The percentage of CO increases due to rising temperature in the combustion chamber, physical and chemical properties of the fuel, air–fuel ratio, shortage of oxygen at high speed, and lesser amount of time available for complete combustion [32]. The effects of fuel viscosity on fuel spray quality would be expected to make some CO increase with vegetable oil fuels. [30]. 4.2.4. Carbon dioxide emission The variation of carbon dioxide emission with different compression ratios are shown in Fig 11. The blend emits higher percentage of CO2 than diesel at lower compression ratios and vice versa. More amount of CO2 is an indication of complete combustion of fuel in the combustion chamber. It also relates to the exhaust gas temperature. CO2 emission of the blend B40 for compression ratio 21 is lesser due to incomplete combustion and inadequate supply of oxygen. The accumulation of CO2 in the

100

Combustion pressure (bar)

80

60

40

20

Diesel 0 325

335

345

355

B20% 365

B40% 375

B60% 385

B80% 395

405

415

Crank angle (deg) Fig. 12. Variation of combustion pressure with crank angle for compression ratio 18.

425

3965

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

atmosphere leads to many environmental problems like ozone depletion and global warming. The CO2 emission from the combustion of bio fuels can be absorbed by the plants and the carbon dioxide level and is kept constant in the atmosphere. 5. Combustion analysis 5.1. Result and analysis 5.1.1. Combustion pressure The variation of combustion pressure with respect to crank angle for different compression ratios and for different blends are shown in Figs. 12–16. It has been observed from the variation of cylinder pressure for various compression ratios 18:1, 19:1, 20:1, 21:1 and 22:1 that the waste cooking oil blends give high combustion pressure compared to that of standard diesel due to longer ignition delay of WCO and may be due to the lower cetane number

of the blend. The fuel absorbs more amount of heat from the cylinder immediately after injection and resulting in longer ignition delay [30]. It is observed that 63.53 bar, 62.35 bar, 64.06 bar, 64.61 bar and 64.71 bar for standard diesel and waste cooking oil blends B20, B40, B60 and B80. The combustion pressure for diesel is higher for lower compression ratios and the combustion pressure for blends are higher for higher compression ratios. The maximum rate of increase in pressure is increasing with increase in the compression ratio. The oxygen fortification in the blend due to the addition of bio diesel is the reason for the increased pressure rise [16]. At a compression ratio 19:1, maximum pressure rise of the blend B80 is very different from B20. This is due to the faster and complete combustion of fuel inside the combustion chamber. At lower compression ratios, the maximum combustion pressure for diesel is higher than that of diesel–bio diesel blends. The maximum rate of increase in pressure is increasing with increase in compression ratio for different blends.

100

Combustion pressure (bar)

80

60

40

20

Diesel 0 325

335

345

355

B20% 365

B40% 375

B60%

385

395

B80% 405

415

425

Crank angle (deg) Fig. 13. Variation of combustion pressure with crank angle for compression ratio 19.

100

Combustion pressure (bar)

80

60

40

20

Diesel 0 325

335

345

355

B20% 365

B40% 375

B60% 385

395

B80% 405

415

Crank angle (deg) Fig. 14. Variation of combustion pressure with crank angle for compression ratio 20.

425

3966

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

100

Comustion pressure (bar)

80

60

40

20

Diesel 0 325

335

345

B20% 355

365

B40% 375

B60% 385

B80% 395

405

415

425

Crank angle (deg) Fig. 15. Variation of combustion pressure with crank angle for compression ratio 21.

100

Combustion pressure (bar)

80

60

40

20

Diesel 0 325

335

345

355

B20% 365

B40% 375

B60% 385

395

B80% 405

415

425

Crank angle (deg) Fig. 16. Variation of combustion pressure with crank angle for compression ratio 22.

20 25

15

15 10 5 0 325 -5

345

365

385

405

425

Crank angle (deg) Diesel

B20

B40

B60

Heat release rate (J/CA)

Heat release rate(J/CA)

20

10 5 0 325

Fig. 17. Variation of heat release rate with crank angle for different blends at compression ratio 18.

365

385

405

425

Crank angle (deg)

-5 Diesel

B80

-10

345

B20

B40

B60

B80

-10 Fig. 18. Variation of heat release rate with crank angle for different blends at compression ratio 19.

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

5.1.2. Heat release rate The variation of heat release rate with respect to crank angle for different waste cooking oil blends and different compression ratios 18:1, 19:1, 20:1, 21:1 and 22:1 is given in Fig. 17–21 respectively. The heat release is analyzed based on the changes in crank angle variation of the cylinder. It has been observed that the heat release rate increases with the lower compression ratios and slightly decreases at higher compression ratios. This may be due to the air entrainment and lower air/fuel mixing rate and effect of viscosity of the blends. The heat release rate of standard diesel is higher than oil blend due to its reduced viscosity and better spray formation

3967

[13]. The heat release rate of waste cooking oil blends decreases compared to diesel for increase in compression ratios. This may be due to the reduction in viscosity and good spray formation with increase in compression ratio in the engine cylinder. The mass fraction burnt of blends is slightly higher at lower compression ratio and closely follows the standard diesel at higher compression ratio. Due to the oxygen content of the blend, combustion is sustained in the diffusive combustion phase. The engine operates in rich mixture and it reaches stoichiometric region at higher compression ratio. More fuel is accumulated in the combustion phase and it causes rapid heat release [16]. The waste cooking oil blends causes longer duration for combustion at lower compression ratio and lesser duration for combustion at higher compression ratio.

Heat release rate (J/CA)

20 15

6. Conclusion

10

The performance, emission and combustion characteristics of a multi fuel variable compression ratio engine fueled with waste cooking oil bio diesel and diesel blends have been investigated and compared with that of standard diesel. The experimental results confirm that the BTE, SFC, BP, exhaust gas temperature and mechanical efficiency of variable compression ratio engine, are a function of bio diesel blend, load and compression ratio. For the similar operating conditions, engine performance reduced with increase in bio diesel percentage in the blend. However by increasing the compression ratio the engine performance varied and it becomes comparable with that of standard diesel. The following conclusions are drawn from this investigation:

5 0 325

345

365

385

405

425

Crank angle (deg)

-5 Diesel

B20

B40

B60

B80

-10 Fig. 19. Variation of heat release rate with crank angle for different blends at compression ratio 20.

20

Heat release rate (J/CA)

15 10 5 0 325

345

365

385

405

425

Crank angle (deg)

-5 Diesel

B20

B40

B60

B80

-10 Fig. 20. Variation of heat release rate with crank angle for different blends at compression ratio 21.

20

Heat release rate (J/CA)

15 10 5 0 325

345

365

385

405

425

Crank angle (deg)

-5 Diesel

B20

B40

B60

B80

-10 Fig. 21. Variation of heat release rate with crank angle for different blends at compression ratio 22.

 The brake thermal efficiency of the blend B40 is slightly higher than that of standard diesel at higher compression ratios. The specific fuel consumption of blend B40 is lower than that of all other blends and diesel. This may be due to better combustion, and increase in the energy content of the blend. The maximum brake power obtained for B40 and diesel at the compression ratio 21 is 2.07 kW and 2.12 kW respectively. The indicates that mean effective pressure for the blend B40 is higher at lower compression ratios and lower at higher compression ratios than for standard diesel.  The exhaust gas temperature decreases at higher compression ratio. The reason is the lower calorific value of blended fuel as compared to that of standard diesel and lower temperature at the end of compression. The exhaust gas temperature for the blends is higher compared to that of standard diesel at lower compression ratios. At higher compression ratios the exhaust gas temperature for the blends are lower compared to that of standard diesel. These variations can be attributed to the increase in thermal efficiency.  The hydrocarbon emission of various blends is higher at higher compression ratios. The increase in compression ratio increases the HC emission for blend B40. The emission of oxides of nitrogen (NOx) from the waste cooking oil blend B40 is higher than that of diesel. The CO emission of the blend B40 is closer to the standard diesel and it is very higher at compression ratio 21. The CO2 emission is also lesser at the same conditions.  Waste cooking oil blends give higher combustion pressure at high compression ratio due to longer ignition delay, maximum rate of pressure rise and lower heat release rate when compared to diesel. From the above observations, it has been found that the performance of the B40 blend is superior when compared with the conventional standard diesel at compression ratio 21. There is slight increase in NOx emission, but it is still comparable with that of standard diesel fuel and is also in the acceptable range. The

3968

K. Muralidharan, D. Vasudevan / Applied Energy 88 (2011) 3959–3968

experimental result also proves that lower and medium percentages of waste cooking oil methyl ester can be substituted for diesel fuel. Acknowledgments The authors are thankful to the All India Council for Technical Education (AICTE), Government of India for providing Grant (No. 8024 / RID / BOR / MOD / 70 / 08 / 09) under Modernization and Removal of Obsolescence (MODROB) Scheme and the Management of PSNA college of Engineering and Technology for providing matching grant for the purchase of variable compression ratio multi fuel engine test rig. The research work has been carried out in this test rig. References [1] Kishore VVN. Renewable energy engineering and technology principles and practice. TERI 2008. [2] Banapurmath NR, Tewari PG, Yaliwal VS, Kambalimath Satish, Basavarajappa YH. Combustion characteristics of a 4-stroke CI engine operated on Honge oil, Neem and Rice bran oils when directly injected and dual fuelled with producer gas induction. Renew Energy 2009;34:1884–7. [3] Carraretto C, Macor A, Mirandola A, Stoppato A, Tonon S. Biodiesel as alternative fuel: Experimental analysis and energetic evaluations. Energy 2004;29:2195–211. [4] Pramanik K. Properties and use of jatropha curcas oil and diesel fuel blends in compression ignition engine. Renew Energy 2003;28:239–48. [5] Senthil Kumar M, Ramesh A, Nagalingam B. An experimental comparison of methods to use methanol and Jatropha oil in compression ignition engine. Biomass Bio Energy 2003;25:309–18. [6] Forson FK, Oduro EK, Hammond-Donkoh E. Performance of jatropha oil blends in a diesel engine. Renew Energy 2004;29:1135–45. [7] Ramdhas AS, Jeyaraj S, Muraleedharan C. Use of vegetable oils as IC engines fuels – a review. Renew Energy 2004;29:727–42. [8] Huzayyin AS, Bawady AH, Rady MA, Dawood A. Experimental evaluation of diesel engine performance and emission using blends of jojoba oil and diesel fuel. Energy Convers Manage 2004;45:2093–112. [9] Pugazhvadivu M, Jeyachandran K. Investigations on the performance and exhaust emissions of a diesel engine using preheated waste frying oil as fuel. Renew Energy 2005;30:2189–202. [10] Rakopoulos CD, Antonopoulos KA, Rakopoulos DC, Hountalas DT, Giakoumis EG. Comparative performance and emissions study of a direct injection diesel engine using blends of diesel fuel with vegetable oils or bio – diesels of various origins. Energy Convers Manage 2006;47:3272–87. [11] Hebbal OD, Vijayakumar Reddy K, Rajagopal K. Performance characteristics of a diesel engine with deccan hemp oil. Fuel 2006;85:2187–94. [12] Sureshkumar K, Velraj R, Ganesan R. Performance and exhaust emission characteristics of a CI engine fueled with Pongamia pinnata methyl ester (PPME) and its blends with diesel. Renew Energy 2008;33:2294–302. [13] Devan PK, Mahalakshmi NV. A study of Performance, emission and combustion characteristics of a compression ignition engine using methyl ester of paradise oil – eucalyptus oil blends. Appl Energy 2009;86:675–80. [14] Pranil J, Singh, Jagjit Khurma, Anirudh Singh. Preparation, characterization, engine performance and emission characteristics of coconut oil based hybrid fuels. Renew Energy 2010;35:2065–70.

[15] Huseyin Aydin, Hasan Bayindir. Performance and emission analysis of cottonseed oil methyl ester in a diesel engine. Renew Energy 2010;35:588–92. [16] Arul Mozhi Selvan V, Anand RB, Udayakumar M. Combustion characteristics of diesohol using bio diesel as an additive in a direct injection ignition engine under various compression ratios. Energy & Fuels 2009;23:5413–22. [17] Arul Mozhi Selvan V, Anand RB, Udayakumar M. Stability, performance and emission characteristics of diesel – ethanol blend with castor oil as additive in variable compression ratio engine. Proceedings of the international conference of Fascinating Advances in Mechanical Engineering – FAME’08. India. 2008. [18] Panwar NL, Hemant Y, Shrirame Rathore NS, Sudhakar Jindal, Kurchania AK. Performance evaluation of a diesel engine fueled with methyl ester of castor seed oil. Appl Therm Eng 2010;30:245–9. [19] Gumus M, Kasifoglu S. Performance and emission evaluation of a compression ignition engine using a biodiesel (apricot seed kernel oil methyl ester) and its blends with diesel fuel. Biomass Bioenergy 2010;34:134–9. [20] Prem Anand B, Saravanan CG, Ananda Srinivasan C. Performance and exhaust emission of turpentine oil powered direct injection diesel engine. Renew Energy 2010;35:1179–84. [21] Saravanan S, Nagarajan G, Lakshmi Narayana Rao G, Sampath S. Combustion Characteristics of a stationary diesel engine fuelled with a blend of crude rice bran oil methyl ester and diesel. Energy 2010;35:94–100. [22] Ismet Celikten, Atilla Koca, Mehmet Ali Arslan. Comparison of performance and emissions of diesel fuel, rapeseed and soybean oil methyl esters injected at different pressures. Renew Energy 2010;35:814–20. [23] Jindal S, Nandwana BP, Rathore NS, Vashistha V. Experimental investigation of the effect of compression ratio and injection pressure in a direct injection diesel engine running on Jatropha methyl ester. Appl Therm Eng 2010;30:442–8. [24] Raheman H, Ghadge SV. Performance of diesel engine with biodiesel at varying compression ratio and ignition timing. Fuel 2008;87:2659–66. [25] Xue Jinlin, Grift Tony E, Hansen Alan C. Effect of biodiesel on engine performances and emissions. Renew Sust Energy Rev 2011;15:1098–116. [26] Murugesan A, Umarani C, Subramanian R, Nedunchezhian N. Bio-diesel as an alternative fuel for diesel engines-a review. Renew Sust Energy Rev 2009;13:653–62. [27] Enweremadu CC, Rutto HL. Combustion, emission and engine performance characteristics of used cooking oil biodiesel-a review. Renew Sust Energy Rev 2010;14:2863–73. [28] Ramadhas AS, Jayaraj S, Muraleedharan C. Theoretical modeling and experimental studies on biodiesel–fueled engine. Renew Energy 2006;31:1813–26. [29] Heywood JB. Internal combustion engine fundamentals. McGraw Hill Book Co; 1988. [30] Devan PK, Mahalakshmi NV. Performance, emission and combustion characteristics of poon oil and its diesel blends in a DI diesel engine. Fuel 2009;88:861–7. [31] Devan PK, Mahalakshmi NV. Study of the performance, emission and combustion characteristics of a diesel engine using poon oil – based fuels. Fuel Process Technol 2009;90:513–9. [32] Arpa Orhan, Yumrutas Recep, Argunhan Zeki. Experimental investigation of the effects of diesel – like fuel obtained from waste lubrication oil on engine performance and exhaust emission. Fuel Process Technol 2010;91:1241–9. [33] Gumus M. A comprehensive experimental investigation of combustion and heat release characteristics of a biodiesel (hazelnut kernel oil methyl ester) fuelled direct injection compression ignition engine. Fuel 2010;89:2802–14. [34] Hirkude Jagannath Balasaheb, Padalkar Atul S. Performance and emission analysis of a compression ignition engine operated on waste frie oil methyl esters. Appl Energy 2010. doi:10.1016/ j.apenergy.2010.11.02.