If the flame from combustion in the cylinder of a four-strok

第一组： The Wartsila 50DF operates on the lean-bum principle: the mixture of air and gas in the cylinder has more air than is needed for complete combustion. Lean combustion reduces peak temperatures and therefore NOx emissions. Efficiency is increased and higher output is reached while avoiding knocking. Combustion of the lean air-fuel mixture is initiated by injecting a small amount of LFO (pilot fuel) into the cylinder. The pilot fuel is ignited in a conventional diesel process, providing a high-energy ignition source for the main engine. To obtain the best efficiency and lowest emissions, every cylinder is individually controlled to ensure operation at the correct air-fuel ratio and with the correct amount and timing of pilot fuel rejection. Wartsila has developed a special electronic control system to cope with the demanding task of controlling the combustion in each cylinder, and to ensure optimal performance in terms of efficiency and emissions under all conditions by keeping each cylinder within the operating window. Stable and well-controlled combustion also contributes to less mechanical and thermal load on the engine components. Current stringent emission regulations demand the reduction of NOx emissions. In an internal combustion engine this means controlling peak temperature and residence time, which are the main parameters governing NOx formations. In the Wartsila 50DF engine, the air-fuel ratio is very high (typically 2.2). Since the same specific heat quantity released by combustion is used to heat up a larger mass of air, the maximum temperature and consequently NOx formation are lower. The mixture is uniform. throughout the cylinder since the fuel and air are premixed before introduction into the cylinders, which helps to avoid local NOx formation points within the cylinder. Benefiting from this unique feature, NOx emissions from the Wartsila 50DF are extremely and comply with the most stringent existing legislation.

What is the combustion feature of the Wartsila 50DF?

A.Lean air in the cylinder

B.Excessive fuel in the cylinder

C.Excessive air in the cylinder

D.Spark ignition

If the flame from combustion in the cylinder of a four-stroke engine past the piston into the space below, the accumulation of flammable mixture would be ignited, thus resulting in _____.

A.the crankcase explosion

B.lifting of the cylinder safety valve

C.a scavenge fire

D.opening of the manhole

Which of the following statements represents the function of the compression rings installed at the top of a diesel Engine piston?

A.Control the amount of lube oil burned in the combustion chamber

B.Transmit heat from the piston to the cylinder liner

C.Prevent damage to ring groove inserts by acting as a heat dam

D.Dissipate combustion chamber gas pressure by channeling it through the ring gap

Flame screens are used to ______.

A.contain flammable fumes

B.protect firefightiers from flames

C.prevent flames from entering tanks

D.keep flame and sparks from getting out of an engine’s exhaust system

For the Wartsila 50DF, the complete combustion compared with the lean-combustion can decrease the following results ____ .①Exhaust temperatures ②NOx emissions ③Propeller efficiency ④Output ⑤Cylinder knocking ⑥Fuel supply

A.①②

B.③⑥

C.④

D.④⑤

How does combustion air enter the cylinder of a two-cycle diesel engine ? Through _______．

A.Cylinder head valves

B.Ports

C.Turbo chargers

D.Bleeder valves

Diesel engine blow-by is the leakage of combustion gases past the( ).

A.oil rings only

B.compression and scraper rings

C.cylinder liner sealing

D.cylinder liner ring grooves