Theoritical investigations of injection pressure in a four stroke di diesel engine


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Theoritical investigations of injection pressure in a four stroke di diesel engine

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME209THEORITICAL INVESTIGATIONS OF INJECTION PRESSURE IN AFOUR STROKE DI DIESEL ENGINE WITH ALCOHOL AS FUELS.Sunil Kumar Reddy1and Dr. V. Pandurangadu21Associate Professor, Mechanical Department, N.B.K.R.I.S.T, Vidyanagar, Nellore, A.P2Professor, Mechanical Department, Jawaharlal Nehru Technological University, Anantapur.A.PABSTRACTAn intensive search for alternate fuels is going on due to the stringent emissionlegislation all over the world for diesel engines which produce more environmental pollution.The major pollutants from these engines are oxides of nitrogen (NOx), smoke and particulatematter. The difficulty in meeting the increasingly stringent limitations on emissions hasstimulated interest in alcohol -fueled diesel engines because it is a renewable bio-basedresource and it is oxygenated, thereby providing the potential to reduce particulate emissionsin compression–ignition engines and ethanol diffusion flames produce virtually no soot. Withthe high latent heat of vaporization, alcohol absorbs heat from the combustion chamber andmakes it cools. This reduces the efficiency of the engine. So, more amount of fuel cannot beinjected in to combustion chamber. But due to the low viscosity of alcohol more fuel will beinjected in to the combustion chamber with the available fuel injection pump, which normallyoperates at 180 bar pressure. This makes the starting of the engine difficult.In order to compensate this, the fuel injection pressure is to be reduced. So an attempt ismade to find an injection pressure for the suitability of using alcohol in diesel engines. In thepresent theoretical investigation, the performance parameters for normal diesel engines areobtained by using a computer program. Then the performance of the diesel engine is comparedwith alcohol at different injection pressures. The injection pressure of alcohol fuel is selectedfor the further experimental work in such a way that the injection pressure at which theperformance of alcohol and diesel fuel are in close agreement. So to study the effect ofinjector opening pressures, five injector opening pressures (180, 175, 170, 165 and 160 bar)are considered. From the theoretical results, it is observed that the injector opening pressureof 165 bar results in higher brake thermal efficiency and is in close agreement with dieselfuel.INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGAND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4, Issue 2, March - April (2013), pp. 209-216© IAEME: Impact Factor (2013): 5.7731 (Calculated by GISI)www.jifactor.comIJMET© I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME210KeyWords: alcohols, fuel pump, injection pressures and emissionsINTRODUCTIONDuring recent years INDIA imported 75% of crude oil from other countries to meetenergy requirements. This intensified the research for discovering the new type of enginedesign and alternative fuels for better control over pollution, and further leads to the stringentemission norms. Alcohols are being considered to be supplementary fuels to the petroleumfuels in India because these are derived from indigenous sources and are renewable. Due tothe high self-ignition temperature and latent heat of alcohols, it requires abnormally highcompression ratios to use them in conventional diesel engines [2].J P Subrahmanyam [6] developed a computer simulation model for the single cylinderDI diesel engine with diesel and alcohol as fuel. This model illustrates the simulation ofoverall cycle consisting of compression, combustion, expansion and exhaust processes andpredicts various combustion and performance parameters. Further, this model is validatedwith available experimental results. Nadir Yilmaz et al [3] identified some of the practicalproblems encountered during the usage of alcohol in the diesel engines due to itscharacteristics (high latent heat of vaporization, high auto ignition temperature) in which thereaction transport mechanism is absent. He developed a model which measures the chemicalreactions in the combustion, which further models cylinder pressure and attendant extent ofreaction. Saeed et al [5] conducted experiments with alcohol in single cylinder diesel engineto find effect of alcohol to diesel fuel on the ignition delay period and concluded that withincreasing the alcohol content ignition delays are prolonged and this can be reduced by airpreheating and/or supercharging.For the complete combustion in the diesel engine very short time is available. So theliquid fuel should be injected in droplets of smallest size to obtain largest surface-volumeratio. But the rate of burning depends primarily upon the rate at which the products ofcombustion can be removed from the combustion chamber and replaced by fresh oxygen. Soin diesel engines for the efficient combustion, fuel injection pump plays an important role [7].An attempt is made for theoretical investigations with different injection pressures forsuitability of using alcohol in diesel engines.The diesel engine performance is obtained with a computer programming. In suchanalysis, if all the variables are taken into account, the computer capability and time requiredwill be beyond those available for this work. Hence the aim of this theoretical analysis isrestricted only to identify the important variables affecting the performance of the insulatedengine and to know the trends.The general assumptions that are made in developing this model for the diesel enginesare as follows [4]:(a) The charge inside the cylinder at any instant consists of a non-reacting mixtureof air and residual gases.(b) The fuel is assumed to mix homogeneously with air.(c) The pressure and temperature are spatially uniform.The performance equations used for the development of computer program for thediesel engine at various stages is explained below briefly
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME211)(P)(Pθθθ d+COMPRESSION PERIODDuring the compression period the charge consists of air and residual gas.The general equation for the work can be written as followsWCOMP = NA CVR (T2-T 1)Assumed wall temperature is the temperature at the end of the compression stroke.With this value of P (θ +dθ ) and knowing the value of index and pressure P (θ ) and thetemperature T (θ +dθ ) can be computed.T (θ +dθ ) = [ ]( r/1r − )* T (θ )COMBUSTION PERIODThe combustion model for the simulation is based on the following assumptions andsimplifications.i) The ideal gas law is applicable.ii) The cylinder content consists of a homogeneous mixture of air and combustionproducts at all times.Work done is calculated using the equation.WCOMB = Σ ((P + ∆P)/2) ∆VEXPANSION PERIODDuring this process the computations carried out are all similar to the computationscarried out earlier during the compression period.HEAT TRANSFER MODELThe heat transfer (hc) in the engine can be calculated with the HOHENBERG RELATIONhc = 0.13 * V-0.06* [P(W+1.4)]0.8T-0.4( KW / m2K)HEAT RELEASE MODELThe rate of heat release (Hr) is calculated using an empirical relationHr = WC * C1 (m+1) exp (-WC (θ /θ C) mIGNITION DELAY MODELIgnition delay is understood as being the period of time elapsing between the start ofinjection nozzle needle lift and the rise in cylinder pressure which is indicated by a markeddeviation of the cylinder pressure from the compression pressure.ID (CA) = [0.044 exp (45 / T) / P 1.1] * RPM
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME212FRICTION MODELBecause of various parameters like gas pressure, wall tension of rings, blow by loss,pumping losses, throttling loss etc;, the frictional mean effective pressure varies in thecombustion chamber and is given by the GOSCH equation.FMEP = 0.6 (CR-4) + RPM / 200 +1.1x10 6V2COMPUTER PROGRAMThe computer program for this model is written in C language. The computerGraphics has been developed to plot various output parameters on the monitor theoretically[1]. The various engine geometry parameters such as bore, stroke, connecting rod length andcombustion chamber geometry are given as inputs to the program. The engine variables suchas compression ratio, intake temperature, intake pressure, injection advance, calorific valueand combustion duration are also given as inputs.For the practical results experiments are conducted on 4-stroke 3.68 KW Kirloskarwater cooled DI Diesel engine at various loads with an injection pressure of 180 bar. Airsuction rate and exhaust air flow rates were measured with the help of an air box method.Temperatures at the inlet and exhaust valves are monitored using Nickel-Nickel Chromiumthermocouple thermocouples. Time taken to consume 20 cc of fuel was noted using a digitalstop watch.Figure1. Experimental set up of Engine Test RigEngine RPM is measured using an electro-magnetic pick up in conjunction with a digitalindicator of AQUTAH make. The experimental set up used is as shown the followingFigure.1.
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME213RESULTSPressureThe computed values of the engine parameters for the normal engine are evaluated. Thecomputed values of pressure during compression and expansion at various crank angles for020406080100120-120 -60 0 60 120Pressure(bar)Crank Angle (degree)Practi…Theo…Exhibit 1 Variation of Pressure with Crank angletheoretical and practical normal engine are shown in Exhibit 1 and are observed that the peakpressure is higher for the theoretical engine than for the practical normal engine and increasessubstantially with increase of crank angle. The cycle peak pressure for a normal practicalengine is 72.76 bar and for theoretical engine it is 79.34 bar.TemperatureExhibit 2 shows the cycle peak temperature for theoretical and practical normalengines. The cycle peak temperature for a normal practical engine is 1156 K and fortheoretical engine it is 1375 K. The rise is about 219K at the peak value. At the end of theexpansion the cycle temperature for the practical engine is 719 K and for theoretical engine itis 790 K. The rise is about 69 K for the theoretical engine.040080012001600-120 -60 0 60 120Temperature(K)Crank Angle (degree)PracticalExhibit 2 Variation of Temperature with Crank angle
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME214This concludes that both the theoretical and experimental values are in closeagreement. So this program can be used to verify at which injection pressure the diesel enginehas better performance characteristics when Alcohol is used as fuel. In the computer programinstead of diesel fuel properties, alcohol properties are introduced with different injectionpressures to know at which injection pressure the alcohol performance will be in closeagreement with diesel fuel. Injection pressures are varied from 180 bar to 160 bar to test theperformance ofthe engine. The optimum alcohol pressure obtained is used in diesel engines for the furtherexperimental investigations.Brake Thermal EfficiencyThe variation of Brake Thermal Efficiency with power output using alcohol as fuel isshown in exhibit.3 with different injection pressures and the same is compared with dieselfuel performance. It is evident from the graph that diesel has the highest Brake ThermalEfficiency. Brake Thermal Efficiency depends on combustion process which is very complexphenomenon that depends on chamber design, viscosity of the fuel, latent heat ofvaporization and the fuel injection pressure. It is observed that at 165 bar injection pressure,the brake thermal efficiency is slightly better than the other and is in close agreement with051015202530350 1 2 3 4BrakeThermalEfficiency(%)Power (KW)Pure dieselAlcohol-180Alcohol-175Alcohol-170Alcohol-165Alcohol-160Exhibit 3 Comparison of Brake Thermal Efficiency with PowerOutput with Different Injection Pressuresdiesel fuel. The remaining values of Brake Thermal Efficiency of alcohol are in between 180bar and 165 bar pressure.Indicated Thermal EfficiencyIt is evident from the graph that diesel has the highest Indicated Thermal efficiency.From the graph shown in exhibit 4, it is observed that at 165 bar injection pressure, theindicated thermal efficiency is maximum compared to other injection pressures. This is due tothe amount of alcohol entered in to the combustion chamber is reduced with the reduction of
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME215fuel injection pressure. This further reduces the amount of heat absorbed by the alcohol forthe evaporation from the combustion chamber. At 160 bar fuel injection pressure, the amountof alcohol injected is less and this reduces the power output. So at 165 bar fuel injectionpressure, optimum amount of fuel is injected in such way that the indicated thermal0510152025303540450 1 2 3 4IndicatedThermalEfficiency(%)Power (KW)Pure dieselAlcohol-180Alcohol-175Alcohol-170Alcohol-165Alcohol-160Exhibit 4 Comparison of Indicated Thermal Efficiency with PowerOutput with Different Injection Pressuresefficiency is higher. The remaining values of Indicated Thermal Efficiency of alcohol are inbetween 180 bar and 165 bar pressure.CONCLUSIONS• The pure Alcohol at 165 bar pressure has higher Brake Thermal Efficiency andindicated thermal efficiency than all other. This is due to the entering of optimumamount of alcohol in to the combustion chamber and at the remaining pressures moreamount of alcohol is entered and made the combustion chamber cool.• It is concluded that Alcohol can be used in diesel engines with 165 bar pressure atwhich the performance of alcohol is in close agreement with diesel fuel. At thispressure the low viscosity of the alcohol is compensated. So the same fuel injectionpump can be used for the experiments by reducing the injection pressure to 165 bar.REFERENCES1. Y.Miyairi,” Computer Simulation of an LHR DI diesel engine”, SAE Paper No.880187.2. Dr.V.Ganesan., “Internal Combustion Engines”3. Nadir Yilmaz, A. Burl Donaldson “Modeling of Chemical Processes in a Diesel Enginewith Alcohol Fuels”, Journal of Energy Resources Technology, December 2007,Volume 129, Issue 4, pp 355-359.4. Dr.V. Ganeshan, “ C.I. Engine Simulation”5. Saee, M.N, Henein, N.A “Combustion phenomenon of alcohols in C.I. Engines”,Journal of Engineering for Gas Turbines and Power, Vol/Issue 111:3, 1999.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME2166. J P Subrahmanyam, Rafiqul Islam “ computer simulation studies of an alcohol-fueled,Low hear Rejection, Direct- Injection diesel engine”, SAE 9729767. Roy Kamo, Nagesh S “ Injection characteristics that improve performance of ceramiccoated diesel engines”, SAE 1999-01-09728. Ram Chandra, T.K. Bhattachary, “Performance Characteristics of a Stationary ConstantSpeed Compression Ignition Engine on Alcohol-diesel Micro emulsions”, AgriculturalEngineering International: the CIGR E Journal, Vol VIII, June 2006.9. Shri. N.V. Hargude and Dr. S.M. Sawant, “Experimental Investigation of Four StrokeS.I. Engine Using Fuel Energizer for Improved Performance and Reduced Emissions”,International Journal of Mechanical Engineering & Technology (IJMET), Volume 3,Issue 1, 2012, pp. 244 – 257, ISSN Print : 0976 – 6340, ISSN Online: 0976 - 6359.10. A. P. Patil and H.M.Dange, “Experimental Investigations of Performance Evaluation ofSingle Cylinder, Four Stroke, Diesel Engine, using Diesel, Blended with Maize Oil”,International Journal of Mechanical Engineering & Technology (IJMET), Volume 3,Issue 2, 2012, pp. 653 - 664, ISSN Print : 0976 – 6340, ISSN Online: 0976 - 6359.11. N.V. Hargude, “An Experimental Investigation for Performance Analysis of FourStroke S.I. Engine using Oxyrich Air”, International Journal of Mechanical Engineering& Technology (IJMET), Volume 3, Issue 2, 2012, pp. 532 - 542, ISSN Print : 0976 -6340, ISSN Online: 0976 - 6359.NOMENCLATUREV = Cylinder volume, m3P = Cylinder pressure, atm.W = Mean piston speed, ms-1T = Cylinder temperature, KWC = Wibe’s constant (6.908)m = constant (0-2)θ = crank angle under consideration (CAD)θ C = combustion duration (CAD)C1 = FKG* HV/COMDURCA = Crank angleT = Temperature in the combustion chamberP = Pressure in the combustion chamberRPM = Speed of the engineFMEP = frictional Mean Effective pressureCR = Compression ratio