Auto Mechanics Paper 2,Nov/Dec 2012.  
Questions:   1 2 3 4 5   Main
General Comments

Question 4

(4)       The figure below is a sketch diagram of a diesel engine.

  1. Identify the:
  2. type of diesel engine;
  3. number of its cylinders.


  1. Name the parts labelled U, V and W.
  1. (i)        State one function of the part labelled U.

(ii)       State two functions of the part labelled V.

  1. State two merits of the engine.

A high percentage of the candidates who attempted this question did not perform well.   The required responses to the various parts of the question are:

(a) (i)  it is a two-stroke diesel engine or a horizontally-opposed engine.
     (ii)        it has one cylinder.
(b)  U    -   injector
      V    -  piston
      W   -   cylinder

(c)   (i)  One function of the part labelled U is to introduce fuel
           under pressure into the highly compressed, heated and
            turbulent charge of air in the combustion chamber.

      (ii)    The functions of the part labelled V are

        -   accommodates the rings;
        -   form a moveable gas light plunger in the cylinder;
        -    forms a guide and a bearing for the small end of the connecting rod;
        -    takes the side thrust caused by the angularity of the crankpin and connecting rod assembly;
        -   transmits the force caused by the expansion of gases in the cylinder through the connecting rod
             to the crankshaft during the power stroke.

(iii)       Merits of the engine are:

     -  it is very compact;
     -  it has very little vibration;
     -  it has better power-to-weight ratio.


Most of the candidate could not provide the required responses to part (a) and (b) of the question.  The required responses to parts (a) and (b) of the question are:

   (a)   U – Head.
          V – Neck.
          W – Stem.
           X – Tip.
          Y – Face.
(b)        The reasons for masking the inlet valve of some diesel engines is to help reduce swirl in the cylinder of the compression ignition engine.

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