Q.12 Gudgeon pin bearing are difficult to lubricate because of their oscillating motion and
Ans. (d) their position in the lubricating system.
As the gudgeon pin is fitted between the piston and connecting rod, it is difficult to convey oil to it. Also by the time oil reaches this bearing after passing through the main bearing and bottom end bearing, there is a large amount of pressure drop as well as loss of quantity of the lubricating oil. Thus this bearing is starved of the oil. Also load on this bearing is acting downwards. Also the area of the bearing is less. All these factors contributes to the difficulty in the lubricating the gudgeon pin bearing.
Q.13 The camshaft drive is designed to maintain the proper camshaft speed relative to the crankshaft speed. In maintaining this relationship the camshaft drive causes camshaft to rotate at
Ans. (b) crankshaft speed in a two-stroke diesel engine i.e. camshaft and crankshaft speeds for two stroke engines are same.
In a two stroke engines for every revolution there is one power stroke. For every power stroke, there is one fuel injection movement and one exhaust valve opening movement. This fuel injection and exhaust valve opening is controlled by the camshaft rotation. Hence it is necessary for camshaft to rotate at the same speed as the crankshaft, so as to have fuel injection and exhaust to be carried out for every revolution of the crankshaft.
Q.14 Engine having bore exceeding 250 mm, but not exceeding 300 mm, are to have at least
Ans. (c) one explosion relief door or one explosion relief valve in the way of each alternate crank throw with a minimum of two valves.
This is a minimum requirement under the classification society rules. When arriving to this requirement figures, the calculation of the crankcase volume and the rate at which the explosive gases are released, in order to avoid the building of pressure and explosion of the crankcase, atleast two safety valves are needed; in case one valve fails to open atleast the second one will respond.
Q.15 The opening of an exhaust valve on a modern large two-stroke slow-speed main propulsion diesel engine may be actuated by
Ans. (c) hydraulic “pushrods”.
The opening of exhaust valve on a modern engine of a large slow-speed main propulsion diesel engine may be actuated by hydraulic pushrods as it eliminates the need of mechanical pushrods and the rocker arms. Also it eliminates the problem encountered due to the thermal expansion of the valve spindle. There is no need for checking and adjustment of the tappet clearance. Also, closing and opening timing of the valve can be adjusted depending upon the load, and the closing and opening action can be made smooth with less hammering of the valve on the seat and hence less noisy. Thus hydraulic pushrod is most convenient method for opening of exhaust valve. In modern engines, closing is carried out by mechanical or air springs.
Q.16 Shaker/circulation and spray are the three general methods used in
Ans. (d) piston cooling.
