轮机英语【轮机长】

考试试题

[问答题]Governing prime movers, particularly diesel engines, require careful consideration. The cyclic variations of a diesel cycle can be passed into the governor drive if it is too "stiff". That is, the cyclic vibrations will be imposed on the internal gearing etc. inside the governor housing. To prevent this, some form of damper should be used on the drive into the governor. The mounting point for the governor should be rigid; a vibration mounting would soon downgrade even the best of governors. Chain or belt drives should be avoided as far as possible, as slapping of the belt or chain produces speed variations causing malfunction of the governor. Similarly the drive from the end of the camshaft is subject to torsional vibrations, and governors should not be located at that point. They should be located as close as practicable to the fuel pumps, thereby limiting the mass/inertia of operating linkage. In all cases, the governor should be matched to the engine requirements in terms of droop, load limiting, response time etc. On large engines there is an inertial resistance to acceleration within the masses of reciprocating and rotating elements of the engine, so that during acceleration fuel could be released to the cylinders at a faster rate than efficient combustion can burn it. In an attempt to compensate for this, and to maintain acceptable combustion during acceleration, a tapping from the scavenge space may be taken and the pressure used to regulate the rate of fuel released to the engine. This process is incorporated into the governor operating system so that the governor releases a quantity of fuel commensurate with the increase in air pressure in the scavenge space. (during deceleration the problem is not so great, as excess air can be tolerated far more easily than can the incomplete combustion associated with insufficient air.) (The following questions are based on the passage above)