Experimental investigation on Zirconia coated high compression spark ignition engine with ethanol as fuel

Transcription

1 Journal LAWRENCE of Scientific et & al: Industrial ZIRCONIA Research COATED HIGH COMPRESSION SPARK IGNITION ENGINE WITH ETHANOL AS FUEL Vol. 70, September 2011, pp Experimental investigation on Zirconia coated high compression spark ignition engine with ethanol as fuel P Lawrence 1 *, P Koshy Mathews 2 and B. Deepanraj 3 1 Department of Mechanical Engineering, Priyadarshini Engineering College, Vaniyambadi , India 2 Principal, Kalaivani College of Technology, Coimbatore , Tamilnadu, India 3 Department of Mechanical Engineering, Adhiparasakthi Engineering College, Melmaruvathur , India Received 18 October 2010; revised 07 July 2011; accepted 12 July 2011 This study presents effect of coating on piston, cylinder head, and valves on the performance of a modified four stroke diesel engine using wet ethanol (5% water) as a fuel and emission characteristics of exhaust gas. Zirconia, which has low thermal conductivity, high temperature resistance, chemical inertness, high resistance to erosion, corrosion and high strength, was selected as a coating material for engine components. Ethanol was sprayed in inlet manifold and spark plug was erected on engine head to facilitate ignition. Engine s performance was studied for both wet ethanol and diesel with and without Zirconia coating. Also, emissions values were recorded to study the engine s behavior on emissions. Keywords: Diesel engine, Ethanol, Zirconia Introduction Thermal efficiency of diesel engines can be increased by reducing heat loss to the surroundings by means of coolant and exhaust gases. In low heat rejection (LHR) engines, heat is transferred from combustion chamber to piston, to combustion chamber walls and finally to cooling water circulated in cooling water jacket around the cylinder, leading to insulating piston and cylinder walls. This can be realized by coating pistons, and cylinder walls with ceramics, which can withstand high thermal stresses 1-4. When cylinder cooling losses are reduced, more of the heat is delivered to exhaust system. Thus, efficient recovery of energy of exhaust improves thermal efficiency of a LHR engine. However, installing in engine configuration even without heat recovery systems, some of the heat is converted to piston work and increases thermal efficiency. Therefore, LHR engines without exhaust heat recovery systems are worth studying 5,6. Peak burned gas temperature in cylinder of an internal combustion (IC) engine is 1200 K. Regions of combustion chamber that are contacted by rapidly moving high temperature burned gases generally experience highest fluxes. Heat transfer affects engine performance, efficiency and emissions. For a given mass of fuel within *Author for correspondence lawphd2008@gmail.com the cylinder, higher heat transfer to combustion chamber walls will lower the average combustion gas temperature and reduce the work per cycle transferred to piston. Thus, power and efficiency are affected by the magnitude of engine heat transfer During combustion, gas temperature increases substantially and this is the period when heat transfer rates are highest. During expansion, gas temperature decreases and hence heat transfer rates also decrease. Substantial heat transfer from exhausting gases to the valves and ports occurs during exhaust process. This study presents effect of Zirconia coating on piston, cylinder head, and valves on the performance of a modified four stroke diesel engine using wet ethanol (5% water) as a fuel and emission characteristics of exhaust gas. Experimental Section Coating Materials Where conventional metals and lubricants fail to perform at elevated temperatures, advanced ceramic materials [nitrides and carbides of silicon (Si 2 N 4 and SiC); oxides of chromium, aluminum, and iron (Cr 2 O 3, Al 2 O 3 and FeO 2 ); and partially stabilized oxide of zirconium (ZrO 2 or PSZ)] provide an alternative. Low ductility, low tensile strength, and low bending strength have impeded the direct replacement of metals with ceramics in

2 790 J SCI IND RES VOL 70 SEPTEMBER 2011 conventional engine designs. A high temperature resistant coating has recently been developed with main objective to provide thermal insulation to metallic components at elevated temperature especially for diesel, gas turbine and aero-engine applications. Partially Stabilized Zirconia (PSZ) PSZ, also called as tetragonal zirconia polycrystalline (TZP), consists of: MgO, 2.77; CaO, 3.81; Y 2 O 3, ; and ZrO 2, 87.17%. A smaller addition of stabilizer to pure zirconia will bring its structure into a tetragonal phase at a temperature higher than 1000 C, and a mixture of cubic phase and monoclinic (or tetragonal)-phase at a lower temperature. Therefore, PSZ is a transformationtoughened material. Micro crack depends upon difference in thermal expansion between cubic phase particle and monoclinic (or tetragonal)-phase particles in PSZ. Coefficient of thermal expansion for monoclinic form is / C up to 1200 C, and / C for cubic form. This defference creates micro cracks. Induced stress depends upon tetragonal-to-monoclinic transformation, once the application temperature over pass transformation temperature at 1000 C. Pure zirconia particles in PSZ can metastably retain high-temperature tetragonal phase. Cubic matrix provides a compressive force that maintains tetragonal phase. Stress energies from propagating cracks cause transition from Meta stable tetragonal to stable monoclinic zirconia. Energy used by this transformation is sufficient to slow or stop propagation of cracks. Low thermal conductivity (8 Btu/ft 2 /in/ F at 1800 F) ensures low heat losses, and high melting point permits stabilized zirconia refractory s to be used continuously or intermittently at 2200 C (4000 F) in neutral or oxidizing atmospheres. Above 1650 C (3000 F), in contact with carbon, zirconia is converted in to zirconium carbide. PSZ refractory s are rapidly finding application as setter plates for ferrite and titillate manufacture, and as matrix elements and wing tunnel liners for aerospace industry. PSZ is also used experimentally as heat engine components, such as cylinder liners, piston caps and valve seats. Engine Modifications Under engine modifications, components added include Bajaj make contact breaker, Fiat make condenser, ignition coil & car spark plug, and a 12 V Exide battery. Fuel injector is replaced by spark plug. A throttle valve is introduced for air adjustment in inlet manifold. As a spark plug is introduced in the system, there is need of ignition system, which requires fixing of cam profile in the shaft. A circular plate is clamped to engine housing. Cam profile is tightened by using key along with the shaft. Then contact breaker is fixed so that it touches cam edge at the required stage. When cam touches contact breaker, current is passed to ignition coil and hence spark is produced in spark plug. A 12Volts battery is used to charge ignition coil. When ignition switch is switched ON, current from battery passes through ignition switch to ignition coil. When contact breaker switch comes in contact with cam profile, current is passed to spark plug and thus spark is produced. Timing is fixed by making fuel injection at the end of compression stroke and at the same time contact breaker comes in contact with cam profile. Hence a spark is produced at the end of compression stroke. Properties of Ethanol Important properties of ethanol used are as follows: latent heat, 855 kj/kg; octane number, 106; lower calorific value, 2600 KJ/kg; boiling point, 78 C; and self ignition temperature, 420 C. Experimental Setup Experimental work was conducted on four stroke, single cylinder, water cooled, manifold injection ethanol engine and direct injection diesel engine coupled on an eddy current dynamometer (Fig. 1). Specifications of test engine are as follows: stroke, 110 mm; bore, 95 mm; power, 5.9 kw; and rated speed, 1500 rpm. Exhaust temperature of engine was measured using digital chromel-alumel thermocouple. Nitrogen oxides (NOx) level was measured using NOx analyzer. Carbon mono oxide (CO) and unburned HC were measured by using IR analyzer. Fuel consumption was measured with the help of burette and digital stop watch. Experiments were conducted at various loads from no load to full load with uncoated piston and coated piston with different fuel (wet ethanol, diesel). Experimental Procedure Various steps involved in setting up of experiments are as follows: i) Initially fuel tank and auxiliary fuel tanks are filled with right amount of required fuel; ii) Water pump is switched ON to cool stator coils of eddy current dynamometer; iii) Instruments such as NOx meter and CO/HC analyzer are connected to exhaust pipe; iv) Eddy current dynamometer is switched ON and set to constant

3 LAWRENCE et al: ZIRCONIA COATED HIGH COMPRESSION SPARK IGNITION ENGINE WITH ETHANOL AS FUEL 791 Fig. 1 Experimental setup Brake thermal efficiency, % Total fuel consumption, kg/h Fig. 2 Variation of brake thermal efficiency with brake power Fig. 3 Variation of total fuel consumption with brake power torque mode; v) Engine is started and allowed to run for 20 min to attain steady state condition; vi) Time taken for 25 cc normal ethanol fuel consumption is noted using stop watch; vii) NOx, CO and HC emissions are noted using IR Analyzer and NOX meter; viii) Exhaust gas temperature is noted; ix) Procedures vi, vii, viii are repeated for diesel fuel also; x) Experiment is repeated for various loads and respective readings are taken; and xi) After taking above readings, engine parts are dismantled. Coated cylinder head, piston head and walls are assembled. Same procedure was repeated to predict the performance of the engine with zirconia coating. Results and Discussion Engine Performance Parameters Brake Thermal Efficiency (BTE) Zirconia acts as barrier for heat transfer to surroundings from engine s combustion chamber and reduces heat loss from engine. Also, as per first law of thermodynamics, heat reduction in heat loss will ultimately increase power output and thermal efficiency of engine. BTE of engine is found slightly increased after coating (Fig. 2) for both diesel (3.26%) and ethanol (1.64%). Total Fuel Consumption (TFC) TFC of engine after coating is found reduced (Fig. 3). This will increase BTE of engine due to reduction

4 792 J SCI IND RES VOL 70 SEPTEMBER 2011 Specific fuel consumption, kg/h/kwh a) Fig. 5 Variation of NOx emissions with brake power Specific fuel consumption, kg/h/kwh Oxides of Nitrogen, ppm coating coating Unburned hydrocarbon, ppm b) Fig. 4 Variation of brake power with SFC using: a) ethanol; b) diesel of heat loss to surroundings from engine. Also, TFC is reduced up to some extent and increased for higher power requirement. For ethanol, it is low up to 4kW, after that, it starts increasing. But in the case of diesel, this problem won t happen. Specific Fuel Consumption (SFC) SFC is found decreasing after coating (Fig. 4). There is slight variation in ethanol s SFC before and after coating. Reduction in SFC is kg/kwh after coating for ethanol. But in the case of diesel, there is a very small variation (0.033 kg/kwh) in SFC reduction. Emission Parameters NOx An increased reduction of NOx was observed due to coating (Fig. 5) because nitrogen is absorbed by zirconia. Generally, oxygen (O 2 ) availability in diesel is high, so at high temperatures, nitrogen (N) easily combines Fig. 6 Variation of unburned HC emissions with brake power with O 2 but availability of N is very less due to coating and therefore forms less NOx. It is observed that at part load (up to 2 kw), NOx emissions are slightly increased for engine with and without coating, but there is considerable reduction in NOx after coating compared to without coating. There is rapid increase of NOx above 2 kw load and more reduction of NOx with coating. For ethanol, there is a slight reduction of NOx due to coating; at part load (up to 2 KW). There is slight increases of NOx above 2 kw load for both cases and considerable reduction of NOx with coating. Unburned HC Unburned HC are found reduced (Fig. 6) when engine runs with coating. Unburned HC are slightly higher for both fuels when engine runs without zirconia coating, because at high temperatures, engine will have sufficient amount of oxygen, which mixes with HC emissions. As

5 LAWRENCE et al: ZIRCONIA COATED HIGH COMPRESSION SPARK IGNITION ENGINE WITH ETHANOL AS FUEL 793 a) Fig. 8 Variation of exhaust temperature with brake powe Carbon monoxide, volume Carbon monoxide, volume Exhaust gas temperature, o C b) Fig. 7 Variation of brake power with CO using: a) ethanol; b) diesel a result, HC will split into H and C, which mixes with O 2, thereby reducing HC emissions. CO CO is found decreased (Fig. 7) after coating due to complete combustion. Generally, oxygen availability in diesel is high, so at high temperatures, C easily combines with O 2 and reduces CO emission. At part load (up to 3 KW), CO emissions are same for engine with and without coating. There is a slight increase of CO at full load without coating. But in the case of engine with coating, CO emission is reduced. For ethanol also, the same process as that of diesel occurs. Exhaust Gas Temperature (EGT) EGT is found increased (Fig. 8) when engine runs with coating, due to more amount of heat generated inside the engine casing, in which all amount of heat cannot be Fig. 9 Corroded piston using wet ethanol converted into useful work. EGT increase under this condition because of its heat is mixed with exhaust gas. Corrosions Due to wet ethanol (5% water), piston top surface and cylinder head bottom surface gets corroded. But this can be completely eliminated by applying zirconia coating on piston top surface and cylinder head bottom surface ((Fig. 9). Conclusions As a low thermal conductivity material, zirconia is capable of reducing heat loss from cylinder to surroundings; this increases life of piston & piston rings.

6 794 J SCI IND RES VOL 70 SEPTEMBER 2011 Due to reduction in heat loss to surroundings, power output and BTE of engine is increased. Since zirconia is a corrosion resistant material, it will completely eliminate corrosion problem, which occurs when engine runs with ethanol fuel. In case of emissions, CO and unburned HC are reduced. But greater reduction of NOx due to coating because of nitrogen is absorbed by zirconia. References 1 Subramanian K A, Singal S K, Saxena M & Singhal S, Utilization of liquid biofuels in automotive diesel engines: An Indian perspective, Biomass Bioenergy, 29 (2005) Kass M D, Thomas J F, Storey J M, Domingo N, Wade J et al, Emissions from a 5.9 liter diesel engine fuelled with ethanol diesel blends, SAE Tech Pap, (2001) SP Hejwowski T & Weronski A, The effect of thermal barrier coatings on diesel engine performance. Vacuum, 65, (2002) Srinivasan A C & Saravanan C G, Emission reduction in SI engine using ethanol gasoline blends on thermal barrier coated pistons. Int J Energy Environ, 1 (2010) Chan S H, Performance and emission characteristics of a partially insulated gasoline engine, J Therm Sci, 40 (2001) Hardenberg H O & Schaefer A J, The use of ethanol as a fuel for compression ignition engines, SAE Tech Pap, (1981). 7 Bekal S & Babu A, Bio-fuel variants for use in CI engine at design and off-design regimes: An experimental analysis, Fuel, 87 (2008) Al Hasan M, Effect of ethanol unleaded gasoline blends on engine performance and exhaust Emission, J Energy Convers Mgmt, 44 (2003) Miyamoto N, Ogawa H, Nurun N, Obata K & Arima T, Smokeless, low NOx, high thermal efficiency, and low noise diesel combustion with oxygenated agents as main fuel, SAE Tech Pap, (1998). 10 He B Q, Wang J X, Hao J M & Xiao J H, A study on emission characteristics of an EFI engine with ethanol blended gasoline fuels, J Atmos Environ, 37 (2003) Nithyanandan N, Sendilvelan S, Bhaskar K, Balaji N & Mohanamurugan S, Exposed area influence for light off of catalyst to reducing hc/co emission from automobile SI engine exhaust by using low mass electrically heated metal catalyst, Int J Appl Engg Res, 5 (2010) Zhao F, Lai M C & Harrington D L, Automotive spark-ignited direct-injection gasoline engines, Progr Energy Combust Sci, 25 (1999) Durgun O, Alternative engine fuels, J Engg Mech, 33 (1988)