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 Powered By Docstoc
					 International Journal of JOURNAL OF MECHANICAL ENGINEERING
INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 –
 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
                         AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)                                                        IJMET
Volume 4, Issue 2, March - April (2013), pp. 209-216
© IAEME: www.iaeme.com/ijmet.asp
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      THEORITICAL INVESTIGATIONS OF INJECTION PRESSURE IN A
       FOUR STROKE DI DIESEL ENGINE WITH ALCOHOL AS FUEL

                           S.Sunil Kumar Reddy1 and Dr. V. Pandurangadu2
      1
        Associate Professor, Mechanical Department, N.B.K.R.I.S.T, Vidyanagar, Nellore, A.P
  2
      Professor, Mechanical Department, Jawaharlal Nehru Technological University, Anantapur.
                                               A.P


  ABSTRACT

          An intensive search for alternate fuels is going on due to the stringent emission
  legislation 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 particulate
  matter. The difficulty in meeting the increasingly stringent limitations on emissions has
  stimulated interest in alcohol -fueled diesel engines because it is a renewable bio-based
  resource and it is oxygenated, thereby providing the potential to reduce particulate emissions
  in compression–ignition engines and ethanol diffusion flames produce virtually no soot. With
  the high latent heat of vaporization, alcohol absorbs heat from the combustion chamber and
  makes it cools. This reduces the efficiency of the engine. So, more amount of fuel cannot be
  injected in to combustion chamber. But due to the low viscosity of alcohol more fuel will be
  injected in to the combustion chamber with the available fuel injection pump, which normally
  operates 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 is
  made to find an injection pressure for the suitability of using alcohol in diesel engines. In the
  present theoretical investigation, the performance parameters for normal diesel engines are
  obtained by using a computer program. Then the performance of the diesel engine is compared
  with alcohol at different injection pressures. The injection pressure of alcohol fuel is selected
  for the further experimental work in such a way that the injection pressure at which the
  performance of alcohol and diesel fuel are in close agreement. So to study the effect of
  injector 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 pressure
  of 165 bar results in higher brake thermal efficiency and is in close agreement with diesel
  fuel.

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

KeyWords: alcohols, fuel pump, injection pressures and emissions

INTRODUCTION

        During recent years INDIA imported 75% of crude oil from other countries to meet
energy requirements. This intensified the research for discovering the new type of engine
design and alternative fuels for better control over pollution, and further leads to the stringent
emission norms. Alcohols are being considered to be supplementary fuels to the petroleum
fuels in India because these are derived from indigenous sources and are renewable. Due to
the high self-ignition temperature and latent heat of alcohols, it requires abnormally high
compression ratios to use them in conventional diesel engines [2].
        J P Subrahmanyam [6] developed a computer simulation model for the single cylinder
DI diesel engine with diesel and alcohol as fuel. This model illustrates the simulation of
overall cycle consisting of compression, combustion, expansion and exhaust processes and
predicts various combustion and performance parameters. Further, this model is validated
with available experimental results. Nadir Yilmaz et al [3] identified some of the practical
problems encountered during the usage of alcohol in the diesel engines due to its
characteristics (high latent heat of vaporization, high auto ignition temperature) in which the
reaction transport mechanism is absent. He developed a model which measures the chemical
reactions in the combustion, which further models cylinder pressure and attendant extent of
reaction. Saeed et al [5] conducted experiments with alcohol in single cylinder diesel engine
to find effect of alcohol to diesel fuel on the ignition delay period and concluded that with
increasing the alcohol content ignition delays are prolonged and this can be reduced by air
preheating and/or supercharging.
        For the complete combustion in the diesel engine very short time is available. So the
liquid fuel should be injected in droplets of smallest size to obtain largest surface-volume
ratio. But the rate of burning depends primarily upon the rate at which the products of
combustion can be removed from the combustion chamber and replaced by fresh oxygen. So
in 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 for
suitability of using alcohol in diesel engines.
        The diesel engine performance is obtained with a computer programming. In such
analysis, if all the variables are taken into account, the computer capability and time required
will be beyond those available for this work. Hence the aim of this theoretical analysis is
restricted only to identify the important variables affecting the performance of the insulated
engine and to know the trends.
        The general assumptions that are made in developing this model for the diesel engines
are as follows [4]:
         (a)     The charge inside the cylinder at any instant consists of a non-reacting mixture
                 of 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 the
diesel engine at various stages is explained below briefly




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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

COMPRESSION PERIOD

       During the compression period the charge consists of air and residual gas.
       The general equation for the work can be written as follows
       WCOMP = NA CVR (T2-T 1)
       Assumed wall temperature is the temperature at the end of the compression stroke.
With this value of P ( θ +d θ ) and knowing the value of index and pressure P ( θ ) and the
temperature T ( θ +d θ ) can be computed.

       T ( θ +d θ ) = [ P(θ + dθ ) ]( r − 1 / r ) * T ( θ )
                          P (θ )

COMBUSTION PERIOD

        The combustion model for the simulation is based on the following assumptions and
simplifications.
        i)     The ideal gas law is applicable.
        ii)    The cylinder content consists of a homogeneous mixture of air and combustion
               products at all times.
        Work done is calculated using the equation.
             WCOMB = Σ ((P + ∆P)/2) ∆V

EXPANSION PERIOD

        During this process the computations carried out are all similar to the computations
carried out earlier during the compression period.

HEAT TRANSFER MODEL

The heat transfer (hc) in the engine can be calculated with the HOHENBERG RELATION
       hc = 0.13 * V-0.06 * [P(W+1.4)]0.8 T-0.4 ( KW / m2 K)

HEAT RELEASE MODEL

       The rate of heat release (Hr) is calculated using an empirical relation
       Hr = WC * C1 (m+1) exp (-WC ( θ / θ C) m

IGNITION DELAY MODEL

        Ignition delay is understood as being the period of time elapsing between the start of
injection nozzle needle lift and the rise in cylinder pressure which is indicated by a marked
deviation of the cylinder pressure from the compression pressure.
        ID (CA) = [0.044 exp (45 / T) / P 1.1] * RPM




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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

FRICTION MODEL

      Because 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 the
combustion chamber and is given by the GOSCH equation.
      FMEP = 0.6 (CR-4) + RPM / 200 +1.1x10 6 V2

COMPUTER PROGRAM

       The computer program for this model is written in C language. The computer
Graphics 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 and
combustion chamber geometry are given as inputs to the program. The engine variables such
as compression ratio, intake temperature, intake pressure, injection advance, calorific value
and combustion duration are also given as inputs.
       For the practical results experiments are conducted on 4-stroke 3.68 KW Kirloskar
water cooled DI Diesel engine at various loads with an injection pressure of 180 bar. Air
suction 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 Chromium
thermocouple thermocouples. Time taken to consume 20 cc of fuel was noted using a digital
stop watch.




                      Figure1. Experimental set up of Engine Test Rig

Engine RPM is measured using an electro-magnetic pick up in conjunction with a digital
indicator of AQUTAH make. The experimental set up used is as shown the following
Figure.1.




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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

RESULTS

Pressure
The computed values of the engine parameters for the normal engine are evaluated. The
computed values of pressure during compression and expansion at various crank angles for

                              120
                              100                     Practi…
                                                      Theo…
                                          80
                         Pressure (bar)



                                          60
                                          40
                                          20
                                              0
                                               -120   -60         0     60       120
                                                         Crank Angle (degree)
                      Exhibit 1 Variation of Pressure with Crank angle

theoretical and practical normal engine are shown in Exhibit 1 and are observed that the peak
pressure is higher for the theoretical engine than for the practical normal engine and increases
substantially with increase of crank angle. The cycle peak pressure for a normal practical
engine is 72.76 bar and for theoretical engine it is 79.34 bar.

Temperature

        Exhibit 2 shows the cycle peak temperature for theoretical and practical normal
engines. The cycle peak temperature for a normal practical engine is 1156 K and for
theoretical engine it is 1375 K. The rise is about 219K at the peak value. At the end of the
expansion the cycle temperature for the practical engine is 719 K and for theoretical engine it
is 790 K. The rise is about 69 K for the theoretical engine.

                               1600
                                                      Practic
                                                      al
                               1200
                            Temperature (K)




                                          800

                                          400

                                              0
                                               -120    -60      0        60      120
                                                          Crank Angle (degree)

                    Exhibit 2 Variation of Temperature with Crank angle


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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

        This concludes that both the theoretical and experimental values are in close
agreement. So this program can be used to verify at which injection pressure the diesel engine
has better performance characteristics when Alcohol is used as fuel. In the computer program
instead of diesel fuel properties, alcohol properties are introduced with different injection
pressures to know at which injection pressure the alcohol performance will be in close
agreement with diesel fuel. Injection pressures are varied from 180 bar to 160 bar to test the
performance of
the engine. The optimum alcohol pressure obtained is used in diesel engines for the further
experimental investigations.

Brake Thermal Efficiency

        The variation of Brake Thermal Efficiency with power output using alcohol as fuel is
shown in exhibit.3 with different injection pressures and the same is compared with diesel
fuel performance. It is evident from the graph that diesel has the highest Brake Thermal
Efficiency. Brake Thermal Efficiency depends on combustion process which is very complex
phenomenon that depends on chamber design, viscosity of the fuel, latent heat of
vaporization 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 with


                                                35
                 Brake Thermal Efficiency (%)




                                                30                                 Pure diesel

                                                25                                 Alcohol-180

                                                20                                 Alcohol-175
                                                                                   Alcohol-170
                                                15
                                                                                   Alcohol-165
                                                10
                                                                                   Alcohol-160
                                                5
                                                0
                                                     0   1       2         3   4
                                                             Power (KW)

              Exhibit 3 Comparison of Brake Thermal Efficiency with Power
                           Output with Different Injection Pressures

diesel fuel. The remaining values of Brake Thermal Efficiency of alcohol are in between 180
bar and 165 bar pressure.

Indicated Thermal Efficiency

        It 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, the
indicated thermal efficiency is maximum compared to other injection pressures. This is due to
the amount of alcohol entered in to the combustion chamber is reduced with the reduction of

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

fuel injection pressure. This further reduces the amount of heat absorbed by the alcohol for
the evaporation from the combustion chamber. At 160 bar fuel injection pressure, the amount
of alcohol injected is less and this reduces the power output. So at 165 bar fuel injection
pressure, optimum amount of fuel is injected in such way that the indicated thermal



                                                     45
                                                     40
                  Indicated Thermal Efficiency (%)




                                                                                         Pure diesel
                                                     35
                                                                                         Alcohol-180
                                                     30
                                                                                         Alcohol-175
                                                     25
                                                     20                                  Alcohol-170

                                                     15                                  Alcohol-165
                                                     10                                  Alcohol-160
                                                     5
                                                     0
                                                          0   1       2          3   4
                                                                  Power (KW)
                Exhibit 4 Comparison of Indicated Thermal Efficiency with Power
                   Output with Different Injection Pressures

efficiency is higher. The remaining values of Indicated Thermal Efficiency of alcohol are in
between 180 bar and 165 bar pressure.

CONCLUSIONS

     •    The pure Alcohol at 165 bar pressure has higher Brake Thermal Efficiency and
          indicated thermal efficiency than all other. This is due to the entering of optimum
          amount of alcohol in to the combustion chamber and at the remaining pressures more
          amount 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 at
          which the performance of alcohol is in close agreement with diesel fuel. At this
          pressure the low viscosity of the alcohol is compensated. So the same fuel injection
          pump can be used for the experiments by reducing the injection pressure to 165 bar.

REFERENCES

1.       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 Engine
         with 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.

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME

6.    J P Subrahmanyam, Rafiqul Islam “ computer simulation studies of an alcohol-fueled,
      Low hear Rejection, Direct- Injection diesel engine”, SAE 972976
7.    Roy Kamo, Nagesh S “ Injection characteristics that improve performance of ceramic
      coated diesel engines”, SAE 1999-01-0972
8.    Ram Chandra, T.K. Bhattachary, “Performance Characteristics of a Stationary Constant
      Speed Compression Ignition Engine on Alcohol-diesel Micro emulsions”, Agricultural
      Engineering International: the CIGR E Journal, Vol VIII, June 2006.
9.    Shri. N.V. Hargude and Dr. S.M. Sawant, “Experimental Investigation of Four Stroke
      S.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 of
      Single 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 Four
      Stroke 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.


NOMENCLATURE

             V    = Cylinder volume, m3
              P    = Cylinder pressure, atm.
              W    = Mean piston speed, ms-1
              T    = Cylinder temperature, K
              WC = Wibe’s constant (6.908)
              m    = constant (0-2)
               θ   = crank angle under consideration (CAD)
              θ C = combustion duration (CAD)
              C1 = FKG* HV/COMDUR
             CA = Crank angle
              T    = Temperature in the combustion chamber
              P    = Pressure in the combustion chamber
             RPM = Speed of the engine
             FMEP = frictional Mean Effective pressure
              CR = Compression ratio




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