(a) Carefully draw a P-V diagram for a 4-stroke cycle SI, premix charged engine. Label the following points on the diagram: Exhaust valve opening and closing, intake valve opening and closing, top dead centre, bottom dead centre, and likely time for a sparking event. Show a horizontal line parallel to the x-axis (the V axis) which indicates atmospheric pressure. (b) Under the P-V diagram sketch a piston in a cylinder with the axial direction of the piston parallel to the x-axis. Sketch the piston when it is half way through the expansion stroke. Also, show the direction of the sliding piston and the positions of intake and exhaust valve for this time