Comparative Analysis of Performance and Emission of Diesel Engine by Varying Compression Ratio Using Different Fuels 86 Pavanendra Kumar Niraj Kumar Vineet Tirth ABSTRACT Presently lots of researches are being performed to evaluate biodiesel as alternative fuel for diesel engine due to associated problems with use of conventional diesel such as environmental degradation, petroleum depletion etc. However, the combustion behavior of biodiesel is different from diesel. To compensate the effects of utilization of biodiesel and maximize the performance, input parameters of the engine should be adjusted. This work investigates the influence of compression ratio (CR) on the performance and emissions of a DI diesel engine using biodiesel (50%) blended-diesel fuel, known as B50. Tests were carried out using three different CRs (14, 16 and 18:1) at 1500 rpm with varying load from 0 to 100%. The results showed that increasing compression ratio improves the burning characteristics of biodiesel. At higher compression ratio, brake specific fuel consumption (BSFC) increased while brake thermal efficiency decreased. However, slight increase in brake power is found especially at higher load. Steep decrease is recorded in smoke opacity (OP), carbon monoxide (CO), oxygen (O 2 ) and hydrocarbon (HC) emissions, while increase in CO 2 is also observed. Finally, it can be concluded that utilization of biodiesel as fuel in diesel engine required modifications in the input parameters. Keywords: Biodiesel, compression ratio, performance, emission. 1. INTRODUCTION Currently, The World is facing the problem of depletion of petroleum reserves, hike in petroleum prices, environmental degradation and global warming due to increasing number of petroleum fueled vehicles. The issues discussed above have triggered the attention of various researchers to replace the diesel fuel with biodiesel. The research conducted by various researchers on biodiesel showed that the diesel engine using biodiesel gives very close performance and less exhaust emission as compared to diesel fuels. Further biodiesel is also biodegradable and can significantly reduce the toxic emissions and the life cycle of CO 2 emission when used in diesel engine. Cheung et al. [1] carried out the experiment on naturally aspirated, water cooled, 4- cylinder, and direct injection diesel engine of 4334 cc engine capacity fueled with pure diesel, biodiesel with different quantities of fumigation methanol. The results showed that the diesel engine operating with biodiesel with fumigation methanol led to reduction of NO x and particulate emissions but increase in CO, HC, and NO x emissions, compared with operating on pure biodiesel. Some researchers showed that the operating parameters of engine (Compression Ratio, Injection Pressure and injection Timing) play an important role in reducing the exhaust emission to acceptable level. Sayin and Gumus [2] experimented with four stroke, naturally aspirated, single cylinder, DI diesel engine using diesel and different blends of biodiesel. The results showed that brake specific fuel consumption (BSFC), brake thermal efficiency (BTE) and brake specific energy consumption (BSEC) of engine increased with increase in compression ratio (CR). Further, exhaust emissions of hydrocarbon (HC), smoke opacity (OP) and carbon monoxide with biodiesel are less than that of diesel fuel. Muralidharan et al. [3] studied the effect of biodiesel blends on the performance and emission of diesel engine and concluded that brake thermal efficiency of biodiesel blends increases with increase in load, and hydrocarbon emission of various blends are higher at higher loads except B20. 2. EXPERIMENTAL SETUP AND PROCEDURES In the study, the variable compression ratio engine was run with JME (B50) at different compression ratios to evaluate the performance with emissions along with the standard settings (specified by manufacturer). The results were compared against the diesel fuel results as well as for different combinations of compression ratio.
87 2.1 Experimental Setup The study was carried out in the laboratory on an advanced fully computerized experimental engine test rig comprising of a single cylinder, water cooled, four stroke, VCR (variable compression ratio) diesel engine connected to eddy current type dynamometer for loading. The setup (Fig. 1) consists of single cylinder, four stroke, VCR diesel engine connected to eddy current type dynamometer for loading. The compression ratio can be changed without stopping the engine and without altering the combustion chamber geometry by specially designed tilting cylinder block arrangement. Setup is provided with necessary instruments for combustion pressure and crank-angle measurements. These signals are interfaced to computer through engine indicator for Pθ PV diagrams. Provision is also made for interfacing airflow, fuel flow, temperatures and load measurement. The set up has standalone panel box consisting of air box, two fuel tanks for duel fuel test, manometer, fuel measuring unit, transmitters for air and fuel flow measurements, process indicator and engine indicator. Rotameters are provided for cooling water and calorimeter water flow measurement. The setup enables study of VCR engine performance for brake power, indicated power, frictional power, BMEP, IMEP, brake thermal efficiency, indicated thermal efficiency, Mechanical efficiency, volumetric efficiency, specific fuel consumption, A/F ratio and heat balance. Engine Performance Analysis software package Enginesoft LV is used for line performance evaluation. The specifications of the engine and sensors used for study are given in Table 1. The exhaust gases were sampled from exhaust line through a specially designed arrangement for diverting the exhaust to sampling line without increasing the back pressure and was then analysed using a portable gas analyser (make AVL digas 444). It measures carbon monoxide (CO), carbon dioxide (CO 2 ), hydrocarbons (HC) and oxygen (O 2 ). For the measurement of smoke intensity of diesel engine s exhaust, a diesel smoke metre (model AVL437C) was used. 2.2 Fuel Used Jatropha ethyl ester was procured from University of Petroleum Dehradoon. The fuel used in the experiment was B50. The calorific value and viscosity were measured with bomb calorimeter and redwood viscometer respectively. The different properties of biodiesel are shown in the Table 2. 2.3 Experimental Procedures The performance test of the engine was conducted as per IS:10,000 [P: 5]:1980. Initially the engine was run on no load condition and its speed was adjusted to 1500 ± 10 rpm. The engine was then tested at no load and at 20%, 40%, 60%, 80% and 100% loads. The engine at the above mentioned loads was tested on both of the fuel types. For each load condition, the engine was run for at least 5 min after which data were collected. The compression ratios below 14 lead to poor power output and above 18 were not possible due to engine structural constraints. For all settings, the emission values were recorded. The performance of the engine at different loads and settings was evaluated in terms of BSFC, BTE and emissions of carbon monoxide, carbon dioxide, un-burnt hydrocarbon and oxygen with exhaust gas opacity and temperature. Engine specification Make Details Cooling Bore and stroke Cubic capacity Table 1: Engine specification Compression ratio 17.5 Rated power Modified ratio range Dynamometer Load cell compression Fuel flow measurement Kirloskar Single cylinder, four stroke diesel Water cooled 87.5 110 mm 661 cc(cubic centimeter) 3.5 kw at 1500 rpm 12-18 Type eddy current, water cooled, with loading unit Strain gauge, range 0-50 Kg DP transmitter, Range 0-500 mm WC Air flow transmitter Pressure transmitter, Range (-) 250 mm WC The BSFC is evaluated by the software on the basis of fuel flow and brake power. Similarly, BTE is also evaluated by software. Table 2: Properties of Biodiesel [4] Fuel properties Diesel Biodiesel Biodiesel standards (ASTM D6751) Specific gravity 0.838 0.88 0.87-0.89 Kinematic viscosity @ 40 0 C 3.2 5.8 1.9-6.0 Flash Point ( 0 C) 67 118 100-170 Cloud point ( 0 C) - -2-3 to 12 Calorific Value 44.14 39.19 Iodine value - 100 <125 3. RESULTS AND DISCUSSIONS 3.1 Performance 3.1.1 Brake power The brake power values for B50 at different loads and at different compression ratio are shown in Fig. 2. In general, the BP increases with increase in load. The Figure demonstrates
88 that both the fuel produced similar brake power. However, for higher compression ratio B50 produces more brake power especially at higher load. Due to shorter ignition delay the combustion starts earlier for biodiesel. This effect gets diminish with higher CR, as the temperature and pressure of the cylinder increases. Further, at higher load the inbuilt oxygen of biodiesel assists in complete combustion. It is also evident from the figure that the friction power of B50 is less than diesel. This factor also contributes in increasing BP for B50. 3.1.2 Brake thermal efficiency BTE is the ability of the combustion system to accept the experimental fuel, and it provides the comparable means of assessing how efficient the energy in the fuel was converted into mechanical output [8]. The variation of brake thermal efficiency with respect to load at different compression ratios for B50 is shown in Fig. 3. The Figure 3 depicts that the thermal efficiency increases with increase in load also it can be observed from the figure that Brake thermal efficiency improves at higher compression ratios. The reasons for this improvement of Brake thermal efficiency is better combustion and better lubricity of biodiesel. The maximum brake thermal efficiency is obtained at a compression ratio of 18, due to the superior combustion and better intermixing of the fuel. 3.1.3 Brake specific fuel consumption BSFC is an important parameter that reflects how good the engine performance is. The variation of BSFC with load at different compression ratio is shown in Figure 4. Figure 2: Brake power vs Load Figure 3: Brake thermal efficiency vs Load Figure 4: Brake specific fuel consumption vs load Generally the BSFC decreases with increase in load due to fact that the ratio of increase in brake power is more as compared to increase in fuel in fuel consumption. It is found the BSFC of B50 more as compared to diesel when experimented at different compression ratios. The reason for this increase in BSFC is low heat value of esters of vegetable oils compared to diesel so more BD is needed to maintain the power output. These findings were also reported by others researchers too [4-7]. 3.2 Emissions 3.2.1 HC emission The unburned fuel component present in exhaust of an engine consists hydrocarbon component is termed as HC emission. These hydrocarbons consist of small non-equilibrium molecules, which are formed when large fuel molecules breaks up by thermal cracking during combustion reactions. The major cause of HC emission is non-homogeneity of fuel- air mixture. Due to this non-homogeneity some local zones in combustion chamber will be too lean to combust properly and other zones may be too rich with not enough oxygen to burn all the fuel. The HC emission of CI engine with load at different compression ratio is shown in Figure 5. From figure it can be observed that HC emission decreases as the load increases. Generally HC emission from exhaust is measure of unburnt fuel in the exhaust of an engine. HC emission using biodiesel is lower than diesel. The test is performed at compression ratios 18, 16, and 14 and it is found that HC emission of B50 is minimum at CR 18. This is due to the fact that the cetane number of ester based fuel is higher than diesel and so results in better combustion leading to lower emission [5]. 3.2.2 CO Emission The presence of CO in the exhaust of an engine is a representation of the chemical energy of the fuel that is not fully utilized. Carbon monoxide is a colourless and odourless but a poisonous gas. Generally, the CO emission is affected by the equivalence ratio, fuel type, combustion chamber design, and atomization rate, start of injection timing, engine load,
89 that CO 2 emission increases with increase in compression ratio. This is due to better combustion and intermixing of fuel and air at higher compression ratio. Figure 5: HC emission vs Load Figure 7: CO 2 emission vs Load Figure 6: CO emission vs Load and speed. The most important among these parameters is the equivalence ratio [9]. The CO emission decreases as the load on an engine increases. This is a typical result for internal combustion engines because the combustion temperature increases with the engine load and CO emission reduces [10]. The CO emission variation with load is shown in Figure 6. The figure depicts that CO emission decreases as load increases and it has been observed that CO emission decreases as the compression ratio increases. This can be explained with the help of HC emission at higher compression ratio i.e. higher the HC emission, lower the CO emission. The temperature reached inside the cylinder is low at low compression ratio, so more CO is exhausted from the engine. 3.2.3 CO 2 Emission The higher CO 2 emission in the exhaust of internal combustion engine is indication of better combustion of fuel. The CO 2 emission increases as the load on an engine increases. This is due to the fact that at higher loads the combustion temperature increases which helps in complete combustion of the fuel. The CO 2 emission versus load graph shown in Figure 7. The graph showed that CO 2 emission increases as the load increases. Amount of CO 2 in the exhaust is an indication of the combustion of the fuel inside the cylinder. More amount of CO 2 in exhaust means better combustion. It has been observed 3.2.4 O 2 Emission The variation of oxygen emission in the exhaust is shown in Figure 8. The figure shows that the oxygen emission decreases with increase in load. This is due to better combustion at higher loads. Further it is observed that oxygen emission of biodiesel (B50) is more than diesel this is due to the fact that the biodiesel contains nearly 10% inbuilt oxygen. Similar trend is obtained on increasing the compression ratio this is again due to nearly complete combustion of fuel. 3.2.5 Smoke opacity Figure 8: O 2 emission vs Load Formation of smoke is basically a process of conversion of molecules of hydrocarbon fuels into particle of soot. The soot is an agglomeration of very large polybenzenoid free radicals. The soot formation takes place during early part of actual combustion but it is consumed during later part of combustion. Pyrolysis of fuel molecules themselves thought to be responsible for soot formation. The fuel heated with insufficient oxygen will give carbonaceous deposits. Among the particulate matter components, soot is recognized as the main substance which is responsible for the smoke opacity. Smoke opacity formation occurs at the extreme air deficiency.
90 The air or oxygen deficiency is locally present inside diesel engines. The variation of smoke emission at different loads for different fuels is shown in Figure 9. The significant reduction in smoke emission for the biodiesel (B50) may be due to the oxygenated blends. As discuss earlier the 10% inbuilt oxygen provides better and nearly complete combustion. Figure 9: Smoke opacity vs Load Smoke is mainly produced in the diffusive combustion phase; the oxygenated fuel blends lead to an improvement in diffusive combustion for biodiesel. Further, increasing compression ratio, in general, reduces smoke due to better combustion. For all loads, the smoke emission is lowest for B50 and at CR of 18. 4. CONCLUSION Following are the conclusions based on the experimental results obtained while experimented on single cylinder diesel engine fuelled with biodiesel (B50). The maximum brake power is obtained at compression ratio of 18:1 using B50 at full load. The maximum brake thermal efficiency is found using B50 at compression ratio of 18:1. It is found that the increase in compression ratio increases the brake thermal efficiency and reduces brake specific fuel consumption while having lower emissions. Finally it can be concluded that biodiesel (B50) could be used as alternative fuel for CI engine at compression ratio of 18:1, for better engine performance. The results of this study have been summarized. The performance of engine operating with B50 become better and approaches towards the performance of engine while operating with diesel. Further decrease in emission is also achieved with increasing CR and the best results are obtained at CR 18:1. Finally it can be concluded that increase in CR will help in utilization of higher percentage of BD in diesel fuel. REFERENCES [1] Cheung, C.S., Cheng, C., Chan, T.L., Lee, S.C., Yao, C., and Tsang, K.S. Emissions Characteristics of a Diesel Engine Fueled with Biodiesel and Fumigation Methanol. Energy & Fuels, 2008, 22, 906 914. [2] Sayin, C., Gumus, M., Impact of compression ratio and injection Parameters on the performance and emissions of a DI diesel engine furled with biodiesel blended diesel fuel. Applied Thermal Engineering, 31(2011) 3182-3188. [3] Muralidharan, K., Vasudevan, D., Sheeba, K.N., Performance, emission and combustion characteristics of biodiesel fueled variable compression ratio engine. Energy, 36 (2011) 5385-5393. [4] Jindal, S., Nandwana, B.P., Rathore, N.S., Vashistha, V. Experimental investigation of the effect of compression ratio and injection pressure in a direct injection diesel engine running on Jatropha methyl ester. Applied Thermal Engineering, 30 (2010) 442 448 [5] Sureshkumara, K., Velrajb R., Ganesan R. Performance and exhaust emission characteristics of a CI engine fueled with Pongamia pinnata methyl ester (PPME) and its blends with diesel. Renewable Energy, 33 (2008) 2294 2302 [6] Ramadhas, A.S., Muraleedharan, C., Jayaraj, S., Performance and emission evaluation of a diesel engine fueled with methyl esters of rubber seed oil, Renewable Energy, 30 (2005) 1789 1800. [7] Sahoo, P.K., Das, L.M., Babu, M.K.G, Naik, S.N., Biodiesel development from high acid value polanga seed oil and performance evaluation in a CI engine, Fuel, 86 (2007) 448 454. [8] Gerhard Knothe, Christopher, A. Sharp, and Thomas W. Ryan. 2006. Exhaust Emissions of Biodiesel, Petrodiesel, Neat Methyl Esters, and Alkanes in a New Technology Engine. Energy & Fuels, pp. 403-408. [9] Fuel Cenk Sayin, Metin Gumus and Mustafa Canakci. 2010. Effect of Fuel Injection Timing on the Emissions of a Direct- Injection (DI) Diesel Engine Fueled with Canola Oil Methyl Ester-Diesel Blends. Energy Fuels, 24, pp. 2675 2682. [10] Mustafa Canakci, Cenk Sayin, Ahmet Necati Ozsezen and Ali Turkcan. 2009. Effect of Injection Pressure on the Combustion, Performance, and Emission Characteristics of a Diesel Engine Fueled with Methanol-blended Diesel Fuel. Energy & Fuels, 23, pp. 2908 2920.