me318_03-04 by zhangsshaohui123


									                                               s                                      ME318 1 / 7

                                  SCHOOL OF ENGINEERING

                              MODULAR HONOURS DEGREE

                                            LEVEL 3

                                         SEMESTER 2



                                                    Examiners: Dr J. J. Leary / Dr P.A. Howson

Attempt FIVE questions only                                          Time allowed : 3 hours.

                                                               Total number of questions = 8

All questions carry equal marks

The figures in brackets indicate the relative weightings
of parts of a questions

Special requirements : None
                                                                                              ME318 2 /7

1) The majority of spark ignition internal combustion engines utilise an inductive discharge
      ignition system rather than a or capacitor discharge spark ignition system.

     a) Sketch the voltage and current characteristic of a typical spark produced by a inductive
          discharge system.                                                                          (5)

     b) Indicate on a sketch of the voltage characteristic in (a) where you would expect to find
          the “Arc Phase” of the spark.                                                              (7)

     c)   Discuss what are the causes of radio frequency emission produced by a spark ignition
          System.                                                                                   (8)


      a) Describe briefly the phenomena of “pre ignition” and “detonation”, in particular the
          causes of each and the differences.                                                        (5)

      b) Figure 1 shows the electrical representation of a typical ignition coil at the point of
          ignition, where ;

          Ip=Primary Peak Current, Io=Secondary Current, Cp=Primary winding capacitance,
          Rp=Primary winding resistance, Lp=Primary Winding Inductance, Ls=Secondary
          Winding inductance, Rs=Secondary Winding Resistance and Cs=Secondary Winding
              Ip                                           Io

                               Rp                     Rs

                                                                     Cs              Vo
                                Lp               Ls

 Derive an approximate expression to obtain the peak value of Vo in terms of Ip, Lp and Cs.         (10)
                                                                                              ME318 3 /7

       c) Sketch the electrical representation of a spark plug explaining what each component
          represents. Assume that the spark plug does not contain any internal noise suppression
          resistor.                                                                                       (5)


        a) Explain the principal advantages and disadvantages of single point fuel injection
           compared to sequential fuel injection systems.                                               (4)

        b) Why is it considered essential that after treatment exhaust emission control systems, that
           contain a three way catalytic converter, should operate at lambda = 1.                 (6)

        c) What are the application differences between a “hot” differences between a running

           spark plug compared to “cold” running spark plug.                                            (6)

        d) What are the potential consequences of using a “hot” running spark plug in a engine

           that requires a “cold” type spark plug.                                                      (4)

4) An industrial twin cylinder four stroke engine is under test on a engine test bed,
       utilising a electrical dynamometer as the load. The engine is fuel injected on each
       revolution and running at a fixed speed, but a slight misfire was observed.

      The following data were recorded by the engine monitoring system;

Torque ( Nm )         Engine speed       Average Inlet Air     Lambda (sensor)   Injector open Time
                      (r.p.m)            mass flow (kg / hr)                     per cycle (ms)

4.5                      1600            2.0                   1.2               0.51

       a) Calculate the power produced by the engine at the crankshaft.                                   (2)

       b) Calculate the efficiency of the engine.                                .                        (6)

       c) Calculate what the true value of lambda should be.                                              (4)

       d) Explain why there is a difference between the calculated value of lambda and the
          measured value.                                                                                 (5)
       e) If the ignition is switched off and the engine speed maintained by the dynamometer
          what would you expect the air mass to do.                                                       (3)
                                                                                             ME318 4 /7

Take the injector flow rate to be 1.86 grams per second.
Energy value of the fuel to be 41 MJ per kg.
Relative density of fuel to be 0.79.
     a) Given the following flow chart for an interrupt loop within an engine management
         system, derive the discrete time equation y(i) in terms of x(i), y(i-1) etc.               (5)


                                  1. y      0            Initialize running total to zero

                                  2. x      ADC          Read the ADC value and store in x

                                  3. y      y+x          Calcu late the new running total

                                  4. DA C       y        Send the running total to the ADC

                                  5. WAIT T              Delay until T seconds has elapsed

                                   6. Goto step 2        Do it all over again

     b) The above flow chart actually represents one form of integration (the backward rule)
         where the sample interval is 1 second. Rewrite the backward rule equation to include a
         sample interval of T seconds in terms of a z transform.                                    (2)

     c) Describe the other two rules for integration that are commonly used and their
         corresponding discrete time equation and z transforms.                                     (3)

     d) Using the backward rule derive the difference equation for a discrete time
         approximation to the phase lead compensator for a sample time of 1 second:                (10)

                                                    U ( s ) 1  as
                                                    E (s)    1  s
                                                                                          ME318 5 /7

6) The following controller transfer function is used to control the motor torque which drives
    the fuel pressure pump in a CDI (common rail direct injection) diesel engine.

                                                bz  1
                                     Gz   a 1 
                                                   z  1 

                                                           U z 
                                         where G  z  
                                                           E z 

   a) Derive the discrete time equation for motor torque u(i) in terms of e(i), e(i-1), u(i-1) and
       so on.                                                                                        (10)

   b) Given a=b=1, show how you would construct an Excel spreadsheet to model the system
       response to an arbitrary input.                                                                (5)

   c) Calculate in tabular form the system output response to a unit step input over the range
       0 - 5 seconds for a sample time interval of 1 second.                                          (5)
                                                                                         ME318 6 /7

7) Given the following block diagram of an internal combustion engine:

                                                    A           V
          U                 TI     - T                 1                     C
                     K1           + N                                  K3
     0-100%                        -       J         S
                                                           
                                                                            Engine
     Acceleration                                                            Speed
     position                         TF                                     (rev/min)


                       Figure Q7 A dynamometer control system model

   U       Engine throttle (%)
   TI      Gross torque from combustion or indicated torque (Nm)
   TN      Net torque (Nm)
   TF      Frictional torque (Nm)
   TL      Torque Load (Nm) (external load)
   A       Angular acceleration (rad/s2)
   V       Angular velocity (rad/s)
   C       Engine speed (rev/min)

   K1     0.3
   K2     0.3/
   K3     60/2 (to convert from rad/s to rev/min)
   J      0.1 kg m2 (rotational inertial)

   a) Describe in detail the function and contents of all the blocks shown in the diagram, and
       explain the reasons why each of the connections are made as shown, as if you were
       writing a tutorial for someone who is seeing it for the first time.                       (10)

    Using either Excel or Visual Basic, show how you would create a mathematical model of
    the above block diagram on a computer to model the time response.                            (10)
                                                                                           ME318 7 /7

8) A digital traction control system for a modern sports car needs to be implemented for
  engine torque control during acceleration, using a digital equivalent of the analogue three
  term controller shown here:

                                              1           de 
                                   u c  K e   e.dt  Td 
                                            Tr            dt 

   a) Explain the function of each of the terms K, Tr and Td                                  (5)

   b) Explain in detail the individual steps needed to convert the above analogue controller
       equation to the following digital controller, stating any assumptions made:           (10)

                                                   T z  1 z  1Td 
                                   Gc z   K 1 
                                   ˆ                                   
                                                2z  1Tr      T .z 

   c) Given that u(i) = up(i) + ui(i) + ud(i) where each term is either proportional, integral or

       derivative, determine the discrete time equation for ud(i) only in terms of e(i).      (5)

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