單項(xiàng)選擇題The ratio of the brake horsepower to the indicate of a diesel engine is its （）

A.thermal efficiency
B.mechanical efficiency
C.brake thermal efficiency
D.volumetric efficiency


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1.單項(xiàng)選擇題In order to keep excess oil from the intake ports in two-stroke/cycle diesel engines, （）

A.wide compression rings are used
B.oil rings are located above the piston
C.chromium plating is used on all piston rings
D.oil rings are located near the bottom of the piston skirt

2.單項(xiàng)選擇題An over-speed trip stops a diesel engine when the engine （）

A.runs out of fuel
B.has low lubricating oil pressure
C.exceeds a set maximum speed
D.has high cooling water temperature

3.單項(xiàng)選擇題To function properly, oil control rings used on a diesel engine piston must distribute sufficient oil to all parts of the cylinder wall and must also（）.

A.prevent any lubricant from reaching
B.prevent excessive lubrication from reaching the combustion space
C.Provide metal-to-metal contact to seal the cylinder against blow-by
D.assure a positive means of scraping carbon accumulation from the cylinder

4.單項(xiàng)選擇題Which of the listed cylinder liner surface conditions indicates proper lubrication?（）

A.Dull black appearance
B.Bright appearance
C.Thin layer of lacquer
D.Thick oily film

5.單項(xiàng)選擇題In an operating diesel engine, which of the following condition is an indication of a leaking air starting valve?（）

A.noise coming from that air starting valve
B.continuous operation of the starting air compressor
C.zero air pressure in the air starting system
D.overheated starting air pipe to the cylinder head