Draw and explain the turning moment diagram of 4-stroke I.C. Engine.

A turning moment diagram for a four stroke cycle internal combustion engine is shown. We know
that in a four stroke cycle internal combustion engine, there is one working stroke after the crank
has turned through two revolutions, i.e. 720° (or 4 ð radians). Turning moment diagram for a four
stroke cycle internal combustion engine.
Since the pressure inside the engine cylinder is less than the atmospheric pressure during
the suction stroke, therefore a negative loop is formed as shown in Fig. During the compression
stroke, the work is done on the gases, therefore a higher negative loop is obtained. During the
expansion or working stroke, the fuel burns and the gases expand, therefore a large positive loop
is obtained. In this stroke, the work is done by the gases. During exhaust stroke, the work is done
on the gases, therefore a negative loop is formed. It may be noted that the effect of the inertia
forces on the piston is taken into account in Fig