INTERNATIONAL JOURNAL OF APPLIED ENGINEERING RESEARCH, DINDIGUL Volume 2, No 1, 2011

Transcription

1 Performance of copper coated two stroke spark ignition engine with Gasohol with Catalytic converter with different catalysts Narasimha Kumar.S 1, Murali Krishna M.V.S. 2, Murthy P.V.K. 3, Reddy D.N. 4, Kishor K 5 1,2,5 Mechanical Engineering Department, Chaitanya Bharathi Institute of Technology, Gandipet, Hyderabad ABSTRACT 3 Vivekananda Institute of Science and Information Technology, Shadnagar, Mahabubnagar J.N.T. University, Hyderabad Krishnamurthy_venkata@yahoo.co.in Investigations are conducted on two stroke, single cylinder spark ignition (SI) engine with gasohol (80% gasoline, 20% ethanol, by vol) having copper coated engine [CCE, copper (thickness, 300 μ) coated on piston crown, inner side of liner and cylinder head] provided with catalytic converter with different catalysts such as sponge iron and mangane and compared with conventional SI engine (CE) with gasoline operation. Brake thermal efficiency and volumetric efficiency increased with gasohol with both versions of the engine. CCE showed improved performance and decreased pollution levels when compared to CE with both test fuels. Catalytic converter with air injection significantly reduced pollutants with both test fuels on both configurations of the engine. The catalyst, sponge iron reduced emissions effectively when compared with mangane in both versions of the engine with both test fuels. Keywords: SI engine, CCE, Copper coating, Performance, Pollutants, Catalytic converter, Air injection 1. Introduction Gasohol improved engine performance and decreased pollution levels when compared to pure gasoline on conventional engine (1 3). Carbon monoxide (CO) and un burnt hydrocarbons (UBHC), major exhaust pollutants formed due to incomplete combustion of fuel, cause many human health disorders 4 9. Such pollutants also cause detrimental effects 9 on animal and plant life, besides environmental disorders. Engine modification with copper coating on piston crown and inner side of cylinder head improves engine performance as copper is a good conductor of heat and combustion is improved with copper coating. Catalytic converter is effective in reduction of pollutants in SI engine. The present paper reports the performance evaluation of CCE, which consists of determining the performance parameters and recording pollution levels with gasohol and compared with CE with pure gasoline operation. The pollutants of carbon monoxide (CO) and un burnt hydro carbons (UBHC) are controlled by catalytic converter with different catalysts such as sponge iron and manganese ore and compared the performance of one over the other. 2. Materials and Methods Fig.1 shows experimental set up used for investigations. A two stroke, single cylinder, water cooled, SI engine (brake power 2.2 kw at the rated speed of 3000 rpm) is coupled to an 205

2 rope brake dynamometer for measuring brake power. Compression ratio of engine is 7.5:1 Exhaust gas temperature, torque, speed fuel consumption and air flow rate of engine are measured with electronic sensors. In catalytic coated engine, piston crown and inner surface of cylinder head are coated with copper by plasma spraying. A bond coating of NiCoCr alloy is applied (thickness, 100 μ) using a 80 kw METCO plasma spray gun. Over bond coating, copper (89.5%), aluminium (9.5%) and iron (1.0%) are coated (thickness 300 μ). The coating has very high bond strength and does not wear off even after 50 h of operation 12. Performance parameters of brake thermal efficiency (BTE), exhaust gas temperature (EGT) and volumetric efficiency (VE) are evaluated at different magnitudes of brake mean effective pressure (BMEP) of the engine. CO and UBHC emissions in engine exhaust are measured with Netel Chromatograph analyzer. A catalytic converter 13 (Fig.2) is fitted to exhaust pipe of engine. Provision is also made to inject a definite quantity of air into catalytic converter. Air quantity drawn from compressor and injected into converter is kept constant so that backpressure does not increase. Experiments are carried out on CE and CCE with different test fuels [pure gasoline and gasoline blended with ethanol (20% by vol)] under different operating conditions of catalytic converter like set A, without catalytic converter and without air injection; set B, with catalytic converter and without air injection; and set C, with catalytic converter and with air injection. Air fuel ratio is varied so as to obtain different equivalence ratios. 3. Results and Discussion Fig. 3 shows the variation of BTE with BMEP in different versions of the engine with pure gasoline and gasohol at a compression ratio of 7.5:1 and at a speed of 3000 rpm, which indicated that BTE increased with an increase of BMEP. Higher BTE is observed with gasohol over pure gasoline at all loads due to lower stoichiometric air requirement of ethanol blended gasoline over pure gasoline operation. CCE showed higher thermal efficiency when compared to CE with both test fuels at loads, particularly at near full load operation, due to efficient combustion with catalytic activity, which is more pronounced at peak load, as catalytic activity increases with prevailing high temperatures at peak load. The ratio of moles of products to the reactants for gasoline and alcohol is as follows C 8 H O N 2 8 CO H 2 O +47 N 2 (60.5 moles) (64.0 moles) C 2 H 5 OH + 3 O N 2 2CO 2 +3 H 2 O N 2 (15.3 moles) (16.3 moles) Assuming all the fuel enter the engine completely evaporated, the fuel giving largest number of moles of product per mole of reactant should produce the greatest pressure in the cylinder after the combustion, all other factors being equal (which incidentally are not) The greater pressure taken alone would results in an increase in engine power. But an engine may not ingest its mixture with the fuel already evaporated. Under such conditions the number of moles of products should be examined on the basis of number of moles of air inducted since fuel occupies very little volume. Table 1 shows the comparative moles of products per moles of air at chemically correct mixture ratio neglecting dissociation. Consider the fuel to enter the cylinder in liquid state points to a somewhat enhanced power output from ethanol on this rather simple basis. 206

3 1. Engine, 2.Electrical swinging field dynamometer, 3. Loading arrangement, 4.Fuel tank, 5.Torque indicator/controller sensor, 6. Fuel rate indicator sensor, 7. Hot wire gas flow indicator, 8. Multi channel temperature indicator, 9. Speed indicator, 10. Air flow indicator, 11. Exhaust gas temperature indicator, 12. Mains ON, 13. Engine ON/OFF switch, 14. Mains OFF, 15. Motor/Generator option switch, 16. Heater controller, 17. Speed indicator, 18. Directional valve, 19. Air compressor, 20. Rotometer, 21. Heater, 22. Air chamber, 23. Catalytic chamber, 24. CO/HC analyzer Figure 1: Experimental set up for two stroke SI engine 207

4 Note: All dimensions are in mm. 1.Air chamber, 2.Inlet for air chamber from the engine, 3.Inlet for air chamber from compressor, 4.Outlet for air chamber, 5.Catalyst chamber, 6. Outer cylinder, 7. Intermediate cylinder, 8.Inner cylinder, 9. Outlet for exhaust gases, 10.Provision to deposit the catalyst and 11.Insulation Figure 2: Details of Catalytic converter CE conventional engine: CCE Copper coated engine: BTE brake thermal efficiency BMEP Brake mean effective pressure Figure 3: Variation of BTE with BMEP in different versions of the engine with pure gasoline and gasohol at a compression ratio of 7.5:1 and speed of 3000 rpm 208

5 35 30 CE GASOLINE CE ETHANOL BLENDED GASOLINE CCE GASOLINE CCE ETHANOL BLENDED GASOLINE 25 BTE (%) Equivalence ratio Figure 4: Variation of BTE with Equivalence ratio in both versions of the engine with different test fuels with a compression ratio of 7.5:1 at a speed of 3000 rpm CE, conventional engine; CCE, Copper coated engine; EGT Exhaust gas temperature: Figure 5: Variation of EGT with BMEP in different versions of the engine with pure gasoline and gasohol at a compression ratio of 7.5:1 and speed of 3000 rpm 209

6 CE GASOLINE CCE GASOLINE CE ETHANOL BLENDED GASOLINE CCE ETHANOL BLENDED GASOLINE EGT ( o C) Equivalance ratio Figure 6: Variation of EGT with Equivalence ratio in both versions of the engine with different test fuels with a compression ratio of 7.5:1 at a speed of 3000 rpm CE Conventional engine; CCE Copper coated engine; BMEP brake mean effective pressure; VE Volumetric efficiency Figure 7: Variation of Volumetric efficiency (VE) with BMEP in different versions of the engine with pure gasoline and gasohol at a compression ratio of 7.5:1 and speed of 3000 rpm 210

7 CE GASOLINE CE ETHANOL BLENDED GASOLINE CCE GASOLINE CCE ETHANOL BLENDED GASOLINE Volumetric efficiency (%) Equivalence ratio Figure 8 : Variation of Volumetric efficiency (VE) with Equivalence ratio in both versions of the engine with different test fuels with a compression ratio of 7.5:1 at a speed of 3000 rpm CE Conventional engine; CCE Copper coated engine; BMEP brake mean effective pressure; CO Carbon monoxide emissions Figure 9: Variation of Carbon monoxide emissions with BMEP in different versions of the engine with pure gasoline and gasohol at a compression ratio of 7.5:1 and speed of 3000 rpm 211

8 CE GASOLINE CE ETHANOL BLENDED GASOLINE CCE GASOLINE CCE ET HANOL BLENDED GASOLINE CO (%) Equivalence raio Figure 10: Variation of CO emissions with Equivalence ratio in both versions of the engine with different test fuels with a compression ratio of 7.5:1 at a speed of 3000 rpm CE GASOLINE CE ETHANOL BLENDED GASOLINE CCE GASOLINE CCE ETHANOL BLENDED GASOLINE UBHC, ppm BMEP (bar) CE Conventional engine: CCE Copper coated engine: BMEP brake mean effective pressure: UHC Un burnt hydro carbon emissions: 212

9 Figure 11: Variation of Un burnt hydro carbon emissions (UBHC) with BMEP in different versions of the engine with pure gasoline and gasohol at a compression ratio of 7.5:1 and speed of 3000 rpm CE GASOLINE CE ET HANOL BLENDED GASOLINE CCE GASOLINE CCE ET HANOL BLENDED GASOLINE UBHC, ppm Equivalence ratio Figure 12: Variation of UBHC emissions with Equivalence ratio in both versions of the engine with different test fuels with a compression ratio of 7.5:1 at a speed of 3000 rpm Table 1: Comparative moles of products per moles of air at chemically correct mixture ratio neglecting dissociation Dry basis Fuel Ratio Compared to gasoline Wet basis Ratio Copmpared to gasoline Gasoline Ethanol Table 2: Data of co emissions (%) with different test fuels with different configurations of the engine at different operating conditions of the catalytic converter with different catalysts Conventional Engine (CE) Copper Coated Engine (CCE) Pure Gasoline Gasohol Pure Gasoline Gasohol Set Spong e iron Spong e iron Spong e iron Sponge iron Set A Set B Set C Set A Without catalyst, Set B With catalyst, Set C With catalyst and with air injection 213

10 Table 3: Data of UBHC emissions ( ppm) with different test fuels with different configurations of the engine at different operating conditions of the catalytic converter with different catalysts Conventional Engine (CE) Copper Coated Engine (CCE) Pure Gasoline Gasohol Pure Gasoline Gasohol Set Spong e iron Spong e iron Spong e iron Sponge iron Set A Set B Set C Set A Without catalyst, Set B With catalyst, Set C With catalyst and with air injection Fig. 4 shows the variation of BTE with equivalence ratio, φ with both test fuels in both configurations of the engine. Efficiency is observed to be higher for both fuels at leaner mixture. When φ is equal to 0.9, gasoline fuel with both versions of the engine attains maximum value. It should be noted that it is necessary to use a lean mixture to eliminate fuel waste, while rich mixture is required to utilize all oxygen. Slightly leaner mixture would give maximum efficiency but too lean a mixture will burn slowly, increasing the time losses or will not burn at all causing total waste. In the rich mixture some of the fuel will not get oxygen and will be completely wasted. Also the flame speed in the rich mixture is low thereby increasing the time losses and lowering the efficiency. The composition of the working mixture influences the rate of combustion and the amount of heat evolved. With hydro carbon fuels the maximum flame velocities occur when the mixture strength is 110 % stoichiometric. When the mixture is made leaner or enriched and still more the velocity of flame diminishes. Lean mixture release less thermal energy resulting in lower flame temperature and flame speed. Very rich mixtures have incomplete combustion (Some carbon only burns to CO and not to CO 2, which results in production of less thermal energy and hence again flame speed is again low. Fuel air analysis suggests that thermal efficiency will deteriorate as the mixture supplied to the engine is enriched. That is explained by increasing losses due to variable specific heat and dissociation, is as the engine temperatures are raised by enrichment towards the chemically correct ratio. Enrichment beyond the chemically correct ratio results in the supply of unusable excess fuel and the thermal efficiency drops very rapidly. It would therefore appear that thermal efficiency would increase as the mixture is weakened. However, beyond a certain weakening the combustion becomes erratic with loss of efficiency. Thus the maximum efficiency is within the weak zone bear chemically correct ratio. As the mixture is made lean due to less energy input the temperature rise during the combustion will be less. The low temperature will result in lower specific heat. It will also mean lower chemical equilibrium losses ( ie., larger fraction of fuel energy is in the form of sensible energy ). The efficiency is therefore higher in fact approaches the air cycle efficiency as the fuel ratio is reduced. As the mixture becomes richer the efficiency falls rapidly. This is because in addition to higher specific heats and chemical equilibrium losses there is insufficient air which will result in the formation of CO and H 2 in the combustibles, which represents the direct wastage of fuel. At chemically correct ratio there is still some 214

11 oxygen present at the maximum temperature point because of the chemical equilibrium effects and hence rich mixture will cause more fuel to combine with oxygen at maximum temperature point raising the temperature further. However, at rich mixtures more formation of CO overcomes the effect of more combustion and maximum temperature becomes less. However, maximum efficiency is attained for gasohol fuel when φ =0.8 as stoichiometric air requirement of gasohol is less, compared to hydro carbon fuel. There is no effect of copper coating on the variation of BTE with fuel air equivalence ratio. However, copper coating improves the efficiency of the engine with both test fuels. Fig. 5 shows the variation of EGT with BMEP in different versions of the engine with both test fuels. EGT is lower with gasohol when compared to pure gasoline at all loads in CE and CCE because, with gasohol, work transfer from piston to gases in cylinder at the end of compression stroke is too large, leading to reduction in the magnitude of EGT. This is also due to high latent heat of evaporation of ethanol. CCE registered lower EGT when compared to CE for both test fuels, which confirm efficient combustion with the CCE than CE. Fig.6 shows the variation of EGT with equivalence ratio φ in different versions of the engine with both test fuels. EGT increases up to the value of φ =1 and later decreases for both test fuels with both configurations of the engine. The exhaust temperature is higher at the chemical correct mixture. At this point, the fuel and oxygen are completely used up as the effect of chemical equilibrium is not significant. At the lean mixtures because of less fuel, maximum temperature is less and hence exhaust gas temperature is less. At rich mixtures the formation of CO and UBHC emissions increases the fuel wastage and decreases the exhaust gas temperature. Fig.7 shows the variation of volumetric efficiency (VE) with BMEP with both test fuels and different configurations of the engine. VE decreased with increase of BMEP. CCE showed higher VE at all loads in comparison with CE with different test fuels, due to reduction of residual charge and deposits in the combustion chamber of CCE when compared to CE, which shows the same trend as reported earlier 13. Gasohol showed higher VE than pure gasoline operation in both versions of the engine at all loads, due to increase of mass and density of air with reduction of temperature of air due to high latent heat of evaporation of ethanol. Fig. 8 shows the variation of VE with equivalence ratio, φ in both versions of the engine with different test fuels. Volumetric efficiency is more at leaner mixtures and rich mixtures with both test fuels and with different configurations of the engine. At leaner mixtures, fuel intake is less and air intake is more leading to produce higher volumetric efficiency. At richer mixtures, charge cooling takes place due to latent heat of evaporation of fuel gives higher density of air and hence higher volumetric efficiency. Fig. 9 shows the variation of CO emissions with BMEP in different versions of the engine wit both test fuels. Gasohol decreased CO emissions at all loads when compared to pure gasoline operation on CCE and CE, as fuel cracking reactions 1 are eliminated with ethanol. The combustion of alcohol produces more water vapor than free carbon atoms as ethanol has lower C/H ratio of 0.33 against 0.5 of gasoline. Ethanol has oxygen in its structure and hence 215

12 its blends have lower stoichiometric air requirements compared to gasoline. Therefore more oxygen that is available for combustion with the blends of ethanol and gasoline, leads to reduction of CO emissions. Ethanol dissociates in the combustion chamber of the engine forming hydrogen, which helps the fuel air mixture to burn quickly and thus increases combustion velocity, which brings about complete combustion of carbon present in the fuel to CO 2 and also CO to CO 2 thus makes leaner mixture more combustible, causing reduction of CO emissions. CCE reduces CO emissions in comparison with CE. Copper or its alloys acts as catalyst in combustion chamber, whereby facilitates effective combustion of fuel leading to formation of CO 2 instead of CO. Similar trends are observed with Reference 10 with pure gasoline operation on CCE. Fig.10 shows the variation of CO emissions with equivalence ratio, φ in both configurations of the engine with both test fuels. At leaner mixtures marginal increase in CO emissions, and at rich mixtures drastic increase in CO emissions are observed with both test fuels in different configurations of the engine. With gasohol operations minimum CO emissions are observed at φ = 0.85 and with pure gasoline operations minimum CO emissions are observed at φ = 0.9 with both configurations of the engine. This is due to lower value of stoichiometric air requirement of gasohol when compared with gasoline. Very rich mixtures have incomplete combustion. Some carbon only burns to CO and not to CO 2. Table 2 shows the data of CO emissions with different test fuels with different configurations of the engine at different operating conditions of the catalytic converter with different catalysts. From the table, it can be observed that CO emissions deceased considerably with catalytic operation in set B with gasohol and further decrease in CO is pronounced with air injection with the same fuel. The effective combustion of the gasohol itself decreased CO emissions in both configurations of the engine. Sponge iron decreased CO emissions effectively when compared with the mangane in both versions of the engine with both test fuels. Fig.11 shows the variation of un burnt hydro carbon emissions (UBHC) with BMEP in different versions of the engine with both test fuels. UBHC emissions followed the same trend as CO emissions in CCE and CE with both test fuels, due to increase of flame speed with catalytic activity and reduction of quenching effect with CCE. Catalytic converter reduced pollutants considerably with CE and CCE and air injection into catalytic converter further reduced pollutants. In presence of catalyst, pollutants get further oxidised to give less harmful emissions like CO 2. Sponge iron decreased CO emissions considerably when compared with mangane in both versions of the engine with different configurations of the engine. Similar trends are observed with Reference 10 with pure gasoline operation on CCE. Fig. 12 shows the variation of UBHC emissions with equivalence ratio, φ with both test fuels in both configurations of the engine. The trends followed by UBHC emissions are similar to those of CO emissions. Drastic increase of UBHC emissions is observed at rich mixtures with both test duels in different configurations of the engine. In the rich mixture some of the fuel will not get oxygen and will be completely wasted. During starting from the cold, rich mixture is supplied to the engine, hence marginal increase of UBHC emissions is observed at lower value of equivalence ratio. 216

13 Table 3 shows the data of UBHC emissions with different test fuels with different configurations of the engine at different operating conditions of the catalytic converter with different catalyst. The trends observed with UBHC emissions are similar to those of CO emissions in both versions of the engine with both test fuels. Sponge iron is more effective in reducing UBHC emissions in both versions of the engine with different test fuels. 4. Conclusions Thermal efficiency and volumetric efficiency increased by 22% and 3% respectively with gasohol with copper coated engine in comparison with pure gasoline operation with conventional engine at a compression ratio of 7.5:1 and speed of 3000 rpm of the engine. CO and UHC in exhaust decreased by 30% and 25% respectively in conventional engine with gasohol when compared to pure gasoline operation. These pollutants decreased by 20% with catalytic coated engine when compared to conventional engine with both test fuels. Set B operation decreased CO and UBHC emissions by 40%, while Set C operation decreased these emissions by 60% with test fuels when compared to Set A operation. Sponge iron is more effective in reducing CO and UHC emissions in both versions of the engine with different test fuels. Acknowledgements Authors thank authorities of Chaitanya Bharathi Institute of Technology, Hyderabad for facilities provided. Financial assistance from Andhra Pradesh Council of Science and Technology (APCOST), Hyderabad, is greatly acknowledged. 5. References 1. M.V.S.Murali Krishna, K.Kishor, A.Sahithy and B.Kavya, (2006), Control of pollutants from copper coated spark ignition engine with gasohol, Indian Journal of Environmental Projection, 26(8)8, pp M.V.S. Murali Krishna, K.Kishor, P.V.K.Murthy, A.V.S.S.K.S. Gupta and S.Narasimha Kumar, (2010), Performance evaluation of copper coated four stroke spark ignition engine with gasohol with catalytic converter, International Journal of Engineering Studies,,2(4), pp P.V.K.Murthy, M.V.S.Murali Krishna, S.Narasimha Kumar, K.Kishor and P. Giridhar Reddy, (2011), Performance of copper coated two stroke spark ignition engine with alternate fuels with catalytic converter, International Journal of Engineering & Techno science, 2(2), pp Khopkar.S.M (2004), Environmental Pollution Analysis, edited by New Age International (P) Ltd, Publishers, New Delhi, Fulekar M H, (1999), Chemical pollution a threat to human life, Indian Journal of Environmental Protection, 1, pp

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