Principal, Sri Ganesh college of engineering and Technology, Pondicherry. Abstract- This paper ... However, Diesel engines are the major sources ... automotive industry the reduction of NOx and PM emission is the most important task. Indian.
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Performance, Emission and Combustion Characteristics of a Biodiesel Fuelled Diesel Engine with the Effect of Different Compression ratios 1
Prabhu L1, S.Satish Kumar2, K. Rajan3 and R.Ramadoss4
Research Scholar, Department of Mechanical Engineering, Sathyabama University, Chennai-109, India. 2 Professor , Department of Mechanical Engineering, Velammal Engineering College, Chennai-66. 3 Professor, Department of Mechanical Engineering, Dr.M.G.R. Educational & Research Institute, Chennai-95. 4 Principal, Sri Ganesh college of engineering and Technology, Pondicherry.
Abstract- This paper investigates the performance, emission and combustion characteristics of biodiesel (Neem oil methyl ester: NOME) blend in a single-cylinder water-cooled diesel engine at a constant speed of 1500 rpm. The experiments were carried out at in a diesel engine with 20% biodiesel-diesel blend and neat biodiesel with different compression ratios such as 17.5:1, 18.5:1 and 19.5:1 under different load conditions. The measured values are analyzed are compared with diesel fuel. The results showed that the higher brake thermal efficiency and lower brake specific fuel consumptions for B20 with CR 19.5 and have lower carbon monoxide, unburned hydrocarbon at full load. The nitrogen oxide (NOx) emission was increased and smoke emissions were decreased for B20 compared with diesel fuel. The peak pressure and heat release rate were higher for B20 blend with compression ratio 19.5 compared to diesel fuel at full load. It is concluded that the 20% biodiesel blend with 19.5 compression ratio gave better performance, emission reduction and combustion of biodiesel without any other hardware modifications of the engine. Keywords - Emission, combustion, neem oil methyl ester, performance, compression ratio, biodiesel. 1. INTRODUCTION Diesel engines are dominant in the field of power plant and road transportation, ships, railway locomotives, equipment used for farming, construction, and in almost every type of industry due to its fuel efficiency and durability. However, Diesel engines are the major sources of NOx and particulate matter (PM) emissions which are environmental concerns. For automotive industry the reduction of NOx and PM emission is the most important task. Indian governments are imposing stringent emissions on automotive sector to reduce NOx and PM emissions. The rising cost of petroleum diesel fuel, stringent emission regulations and depletion
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of petroleum reserves are forcing us to search alternative fuels like biomass and biodiesel for diesel engines. Vegetable oils are considered as good alternatives to diesel as their properties are close to diesel. Thus, they offer the advantage to be used in existing diesel engine without any engine hardware modifications [1-2]. Use of vegetable oils can be used directly or blended with diesel to operate compression ignition engines. Use of blends of vegetable oils with diesel has been carried out successfully by various researchers in several countries [3-5].It has been reported that the use of 100 percent vegetable oil also possible with minor modification of fuel system. Short-term engine performance tests have indicated good potential for most vegetable oils as fuel. The use of vegetable oil in diesel engine resulting in increased volumetric fuel consumption and brake specific fuel consumption (BSFC). The carbon monoxide (CO) and hydrocarbons (HC) were found to be higher, whereas nitrogen oxides (NOx) and particulate emission were lower than diesel [6, 7]. This was attributed to the lower heating value, high viscosity, poor atomization, low volatility and polyunsaturated characteristic of neat vegetable oils. Undoubtedly, transesterification is the well accepted method of utilizing vegetable oils in a compression ignition engine without significant long-term operational and durability issues. However it adds extra cost of processing because of transesterification reaction involving chemicals and process heat inputs. Tranesterification is the process of converting vegetable oil into methyl ester, known as biodiesel. Biodiesel may be used in existing diesel engines without necessitating engine modifications, and its use does not result in a shortening of engine life [8, 9]. Even though biodiesel has many advantages, because of engine problems its use is restricted to maximum 20% only [10, 11]. Also when biodiesel is used as fuel in existing engines, there is decrease in power, drop in thermal efficiency, increase in specific fuel consumption, and higher nitrogen oxide (NOx) emissions [12, 13] compared to diesel fuel. In order to overcome these problems various modifications in engine operating parameters are suggested. The various modifications suggested are varying the compression ratio [14, 15], injection pressures and injection timings [16, 17]. Table 1 presents the comparison of properties of diesel and neem biodiesel. The objectives of the present study are to investigate the performance and emission characteristics of a diesel engine with neem oil biodiesel with different compression ratios at various operating conditions. The measured values are analyzed and compared with the diesel fuel. 2. BIODIESEL PREPARATION The raw neem oil was extracted by mechanical expeller in which small traces of organic matter, water and other impurities were present. Transesterification is a most common and well established chemical reaction in which alcohol reacts with triglycerides of fatty acids (vegetable oil) in presence of catalyst to form glycerol and esters [1-3]. The chemical reaction is shown in Figure.1. The biodiesel prepared in a laboratory setup consisting of heating mantle, reaction flask, separating funnel and mechanical stirrer. A round bottom flask of two litres was used as laboratory scale reactor for the present analysis. It consisted of three necks. One for stirrer, the others for condenser and inlet of reactants, as well as for placing the thermocouple to observe the reaction temperature. The flask has a stopcock at the bottom for collection of the final product. The progress of the reaction was observed by measuring the acid value. During the test, it was observed that the appropriate quality of biodiesel could be produced from neem oil in both acid catalyst esterification and alkaline catalyst esterification. The properties of diesel and neem biodiesel are listed in Table.1
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Fig.1 Transesterification reaction Table 1 Properties of diesel, Neem oil and its methyl ester Properties Specific gravity Kinematic Viscosity at 40°C (cSt) Flash point (°C) Fire point (°C) Calorific value (kJ/ kg) Cetane No
Diesel 0.830 3.720 62 64 42500 48
Neem oil 0.920 38 350 365 39500 38
NOME 0.860 4.5 152 180 38500 51
3. EXPERIMENTAL SET UP A single cylinder, direct injection, four-stroke, vertical, water-cooled, naturally aspirated variable compression ratio diesel engine, with a bore of 80 mm and a stroke of 110 mm was selected for the present study. This test engine is manufactured by Legion Brothers, Bangalore (India) and having rated output of 7.5 HP. The nozzle opening pressure recommended by the manufacturer is 200 bars. The view of the experimental setup and instrumentation are depicted in the Fig. 2. The detailed technical specifications of engine are given in Table.2. Table 2 Test engine specifications Make Engine Type Bore Diameter Stroke Length Brake Power Compression Ratio Speed Fuel injection
Kirloskar, Single cylinder Four stroke, diesel engine Vertical, Aspirated engine 87.5 mm 110 mm 4.44 kW 17.5:1 1500 rpm 23o before TDC
4. RESULTS AND DISCUSSIONS Present research work has been focused to investigate the effect of compression ratio on the performance, emissions, and combustion characteristics of a diesel engine with neem biodiesel blend and diesel fuel. All the experiments were carried out on a single-
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cylinder diesel engine used for agriculture purposes and at a constant speed of 1500 rpm. The experimental results of thermal efficiency, HC, CO, NOx, smoke opacity, were analyzed at various loads such as 25%, 50%, 75%, and 100% and compare d with diesel fuel.
Fig. 2 Schematic of the experimental setup a) Cylinder pressure Figure 3 shows the variation of cylinder pressure with crank angle for all the fuels at full load condition. In a compression ignition engine, peak pressure depends on the combustion rate in initial stages, which in turn is influenced by the amount of fuel taking part in the uncontrolled combustion phase. The premixed or uncontrolled combustion phase is generated by the ignition delay period and by the mixture preparation during the delay period. The maximum cylinder pressure increases with the increase in compression ratios at all loads with 20% NOME fuel. It is observed that the cylinder peak pressure for the B20 with CR 19.5 is higher than other compression ratios with the same blend. This may be due to increase in pressure and temperature of biodiesel before combustion at higher compression ratio and the presence of oxygen in the bio-diesel resulting in complete combustion of fuel leading to increase in peak pressure at full load. The maximum cylinder pressure for 20% NOME with CR 19.5, CR 18.5 and CR 17.5 are 69 bar, 67.5 bar and 66 bar respectively, whereas for diesel it is 71 bar at full load. 80 Diesel-Base-CR 17.5:1 B20-Base-CR 17.5:1
Cylinder pressure (bar)
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60 50 40 30 20 10 0 -60
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Fig. 3 Variation of Cylinder pressure with CA at full load
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o
Heat release rate (J/ CA)
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B20-CR 18.5:1
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10 30 50 Crank angle (deg.)
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Fig. 4 Variation of Heat release rate with CA at full load b) Heat release rate Figure 4 shows the variation of heat release rate (HRR) with crank angle for the fuels for different compression ratios at full load. The premixed burning phase associated with a high heat release rate is significant with bio-diesel operation. The higher peak heat release rate of 108 J/deg. (19.5:1 CR), 106 J/deg. (18.5:1 CR) and 104 J/deg. (17.5:1 CR) were obtained for 20% NOME, whereas for diesel it is 112 J/deg under full load conditions. Increase in HRR is an indication of better premixed combustion and is probably the reason for shorter ignition delay due to higher compression ratios. Higher heat release rate for bio-diesel blends is probably due to excess oxygen present in its structure and dynamic injection advance apart from static injection advance. Higher boiling point of bio-diesel can also result in higher heat release rate. c) Brake thermal efficiency The variation of brake thermal efficiency with load for diesel and 20% biodiesel blends ratios are represented in Figure 5. It is observed that the brake thermal efficiency increases with increase in load. This can be attributed to reduction in heat loss and increase in power with increase in load. The maximum brake thermal efficiencies obtained for B20 is 27.12% at 17.5:1 CR , 28.32% at 18.5:1 CR and 29.45% at 19.5:1 CR ,whereas for diesel it is 30.53 at 17.5 CR at full load. The mixing of bio-diesel in diesel oil yields good thermal efficiency at full load. The brake thermal efficiency of the engine is improved for the B20 blend may be due to the additional lubricity provided by bio-diesel. The higher amount of (12% by weight) oxygen molecules is present in the bio-diesel which takes part in the combustion process. The BTE of B20 blend at 19.5 CR is 8.59 % higher than at 17.5 CR, 4% higher than 18.5 CR and 3.5 lesser than diesel fuel at full load. d) Brake specific fuel consumption Figure 6 illustrates the variation of brake specific fuel consumption (BSFC) with load for diesel and 20% biodiesel blend at different compression ratios. For all fuels tested, The brake specific fuel consumption (BSFC) decreased with increase in load at all compression ratios. This may be due to higher percentage of increase in brake power with load compared to fuel consumption. The BSFC of diesel at 17.5 CR is about 0.312 kg/kW-hr was obtained at full load. The BSFC obtained for B20 is 0.379 kg/kW-hr at 17.5 CR, 0.364 kg/kW-hr at 18.5 CR and 0.32 kg/kW-hr at 19.5 CR at full load. The BSFC is almost same as diesel fuel for B20 at 19.5 CR at full load. The BSFC for B20 at 17.5 CR is 22% and 12.9% higher than diesel fuel at full load. This may be due to lower
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Brake thermal efficiency (%)
calorific value fuel and poor volatility of biodiesel blend. The higher BSFC shows that the more amount of fuel is burned to develop the same amount of power. 35 30 25 20
Diesel
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Fig.5 Variation of brake thermal efficiency with BP Brake specific fuel consumption (kg/kW-hr)
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Fig.6 Variation of brake specific fuel consumption with BP e) Exhaust gas temperature Figure 7 shows the variation of exhaust gas temperature with brake power for different compression ratio for diesel and biodiesel blend. The exhaust gas temperatures were found to be increasing with the increase in load and compression ratio. The maximum exhaust gas temperature was recorded for the compression ratio 19.5 for B20 blend and it is lower for B20 blend for the CR at 17.5 at full load. The exhaust temperature for B20 at CR 19.5 is 348oC and at CR 17.5 is 328oC, whereas for diesel it is 317oC at CR 17.5 at full load. f) Carbon monoxide emissions (CO) Figure 8 depicts the variation of carbon monoxide (CO) emissions with brake power for different compression ratios for diesel and biodiesel blend. It is observed that the CO emissions are decreased at maximum load for B20 at increasing compression ratios from 17.5: 1 to 19.5:1. The CO emission for B20 at CR 17.5, CR 18.5 and CR 19.5 are 0.05%Vol, 0.045%Vol and 0.04%Vol at full load, whereas for diesel it is 0.065%Vol. The decrease in CO emissions may be due to more oxygen present in biodiesel and better atomization of fuel particle at higher compression ratios.
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300
(oC)
Exhaust gas temperature
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Diesel B20-17.5
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B20-18.5 B20-19.5
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Fig.7 Variation of Exhaust gas temperature with BP
Carbon monoxide (% Vol)
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Fig. 8 Variation of CO emission with BP g) Hydrocarbons emission (HC) The variation of hydrocarbons emission (HC) for different compression ratios with brake power for diesel and biodiesel blend is shown in Figure 9. The hydro carbon emission for B20 operation showed very low throughout the load range for all compression ratios. It is observed that the HC emissions are reduced at maximum load for B20 at increasing compression ratios from 17.5: 1 to 19.5:1. The diesel fuel operation produced the highest HC emissions at high load and when the engine load reaches a maximum power of 4.4 kW, the HC emissions start to increase more rapidly for both diesel and B20 blend. The HC emission for B20 at CR 17.5, CR 18.5 and CR 19.5 are 22ppm, 23ppm, and 19ppm at full load, whereas for diesel it is 26ppm. The decrease in HC emissions may be due to more oxygen present in biodiesel and better atomization of fuel particle at higher compression ratios. h) Nitrogen Oxide emission (NO) The variation of nitrogen oxide emission for different compression ratios with brake power for diesel and biodiesel blend is shown in Figure 10. The nitrogen oxide emissions (NOx) increases with increase in load for all the fuels. The NO emissions are formed in the combustion chamber at higher peak combustion temperature in the presence of free nitrogen available in the atmospheric air, which take part in the combustion process. The NO emissions for B20 at CR 17.5, CR18.5 and CR 19.5 are 661ppm, 717ppm and 776 ppm respectively and for the diesel it is 575 ppm at full load.
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Hydrocarbon emission (ppm)
The increase in NO emission may be due to more oxygen present in the biodiesel and higher combustion temperature at high load for high compression ratios. However, NOx emissions in case of biodiesel blends are higher than diesel due to higher temperatures prevalent in the combustion chamber. 35 28 21 Diesel
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B20- C.R 17.5 B20-C.R 18.5
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Nitrogen oxide emission (ppm)
Fig. 9 Variation of HC emission with BP 800 Diesel B20- C.R 17.5 600
B20-C.R 18.5 B20-C.R 19.5
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Fig. 10 Variation of NO emission with BP j) Smoke emission Figure 11 shows the variation of smoke opacity with brake power for different compression ratios for diesel and B20 blend. One can observe that soot emitted by all bio-diesel blends is lower than neat diesel at all compression ratios. This is attributed to the combustion being controlled for the B20 blend with the presence of excess oxygen present in the biodiesel and more atomization of blend at higher compression ratio resulting in complete combustion of biodiesel blend. The maximum value of smoke for B20 at CR 17.5, CR18.5 and CR 19.5 are 3.3BSU, 3.1 BSU and 2.8 BSU respectively, whereas for diesel it is 3.2 BSU at full load.
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Smoke emission (BSU)
4 Diesel B20-17.5
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B20-18.5 B20-19.5
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2 3 Brake power (kW)
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Fig. 11 Variation of Smoke emission with BP Figure 11 shows the variation of smoke opacity with brake power for different compression ratios for diesel and B20 blend. One can observe that soot emitted by all bio-diesel blends is lower than neat diesel at all compression ratios. This is attributed to the combustion being controlled for the B20 blend with the presence of excess oxygen present in the biodiesel and more atomization of blend at higher compression ratio resulting in complete combustion of biodiesel blend. The maximum value of smoke for B20 at CR 17.5, CR18.5 and CR 19.5 are 3.3BSU, 3.1 BSU and 2.8 BSU respectively, whereas for diesel it is 3.2 BSU at full load. CONCLUSIONS From the experimental investigations the following conclusions were made, 1. Peak pressure increases with increase in compression ratio for the biodiesel blend. The peak cylinder pressure for 20% NOME with CR 19.5 is higher than 3 bar compared with 20% NOME with CR 17.5 at full load. 2. Heat release rate increases with increase in compression ratio for the biodiesel blend. The heat release rate for 20% NOME with CR 19.5 is higher than 4 J/ o CA compared with 20% NOME with CR 17.5 at full load 3. The brake thermal efficiency was found to increase with increase in compression ratio and there is no large difference in the brake thermal efficiency B20 blend and neat diesel. The maximum brake thermal efficiency is achieved for B20 at CR 19.5 and it is followed by CR 18.5 and CR 17.5 at full load. 4. The Brake specific fuel consumption was found to have minimum for neat diesel as compared to biodiesel blend at all loads for all compression ratios. For the blend B20 at CR 19.5 has least specific fuel consumption when compared to neat diesel. 5. The CO and HC emissions are decreased for B20 with increase in compression ratios compared to diesel fuel. 6. The NO emissions are higher and smoke emissions are lower for B20 blend at CR 19.5 and it is followed by CR 18.5 and CR17.5, were lower when compared to diesel fuel at full load. 7. On the whole, it is concluded that the 20% biodiesel blend with CR19.5 gave better performance, emission reduction and better combustion of biodiesel without any modifications of the engine.
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