Why is the piston head in 2 stroke engines shaped like, as shown in Figure below? [2] (b) What causes turbulence in an I

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Why is the piston head in 2 stroke engines shaped like, as shown
in Figure below? [2]
(b) What causes turbulence in an IC engine and how does it
impact the engine performance, if it is too high? [2]
(c) Which power is improved by using lubricants? Justify with
reason [2]
(d) What type of engine (SI or Cl) is preferred for fuels with a
low octane number value? Give a clear reason for this [2]
(e) Which device is used to start the engine under cold
conditions? How does it help to do so? [2]