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In the cylinder head of a two-stroke/cycle diesel engine, valves are used for()
A . air intake
B . a fuel outlet
C . cooling water inlets
D . exhausting combustion ga
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Which of the following statements is true regarding the installation of piston rings on two-stroke/cycle, diesel engines as compared to four-stroke/cycle, diesel engines?()
A . In a two-stroke/cycle engine, the rings run hotter, requiring the end gap to be greater
B . Some provision must be made in a two-stroke/cycle engine to keep the rings from binding in the ports
C . No gap is required to exist between the ends of the ring when cold in a two-stroke/cycle engine, but a small gap is required in a four-stoke/cycle engine
D . The gaps should be staggered on either side of a piston in a two-stroke/cycle engine, while staggering is not necessary in a four-stroke/cycle engine
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What color exhaust will be exhibited when a slow speed two-stroke/cycle main propulsion diesel engine, designed to operate on light and heavy fuel oil, is operated on insufficiently preheated heavy fuel oil?()
A . White
B . Black
C . Blue
D . Clear
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A possible cause for an individual piston to knock when at TDC on a slow-speed, two-stroke/cycle main propulsion diesel engine could be due to ()
A . early fuel injection
B . excessive bearing play within the running gear
C . overloading of the cylinder
D . all of the above
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A six-cylinder, two-stroke/cycle diesel engine is fitted with a rotary distributing air starting systemThe speed of the rotating distributor disc is ()
A . one-half engine speed
B . the same as engine speed
C . twice engine speed
D . four times engine speed
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The process of scavenging a two-stroke/cycle diesel engine serves to()
A . improve fuel flow volume
B . cool the exhaust valves
C . reduce the intake air charge density
D . increase the temperature of exhaust gase
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The four-stroke cycle begins with the piston ().
A . coming up from the BDC
B . coming up from the TDC
C . coming down from the BDC
D . coming down from the TDC
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A two-stroke/cycle diesel engine requires less starting air than a four-stroke/cycle diesel engine, of equal displacement, because the two-stroke/cycle diesel engine()
A . has little or no internal friction
B . has a lower effective compression ratio
C . operates with scavenge air under a positive pressure
D . operates without energy absorbing intake and exhaust stroke
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Exhaust gases are generally removed from the cylinders of a two-stroke/cycle diesel engine by()
A . natural aspiration
B . masked intake valves
C . air cells
D . scavenging air
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Compared to four-stroke/cycle engines, two-stroke/cycle diesel engines have the disadvantage of ()
A . less even torque
B . higher cylinder head temperatures
C . fewer power strokes per revolution
D . greater weight/size requirement
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In a single acting, two-stroke/cycle, diesel generator engine, the power impulse in an individual cylinder occurs ()
A . once every crankshaft revolution
B . once every two crankshaft revolutions
C . once every piston stroke
D . twice every piston stoke
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The exhaust gases in a supercharged two-stroke/cycle diesel engine are expelled from the cylinder by ()
A . pumping action of the piston
B . pressure of the fuel charge
C . vacuum developed in the manifold
D . pressure of the fresh air charge
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A two-stroke diesel engine exhaust temperature will be lower than a four-stroke diesel engine of the same displacement because the () (1) scavenging air is cooling the exhaust gases (2) exhaust cycle time is longer
A . (1) only
B . (2) only
C . both (1) and (2)
D . neither (1) nor (2)
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The two strokes of a two-stroke/cycle diesel engine are ()
A . power and intake
B . intake and exhaust
C . exhaust and compression
D . compression and power
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If all other conditions such as bore, stroke, speed, and mean effective pressures are equal, a two-stroke/cycle diesel engine will develop approximately()
A . the same indicated horsepower as a four-stroke/cycle engine
B . twice the indicated horsepower as a four-stroke/cycle engine
C . one half indicated horsepower as a four-stroke/cycle engine
D . one power stroke for every two crankshaft revolutio
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Large, two-stroke/cycle, main propulsion, diesel engine cylinders can be successfully pressure charged during normal operation, by using the ().
A . exhaust gas temperature system
B . exhaust load system
C . constant or pulse pressure system
D . constant volume system
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Proper lubrication of the main bearing is more easily obtained in a single acting four-stroke/cycle diesel engine than in a single acting two-stroke/cycle diesel engine because ()
A、a circulating system; a total loss system
B、a total loss system; a circulating system
C、an opened system; a closed system
D、a closed system; an opened system
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When inspecting piston rings through the ports of a two-stroke/cycle diesel engine, black areas on the sealing surfaces are the result of ()
A . insufficient lubrication
B . improper piston cooling
C . blow-by
D . overload operatio
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A large two-stroke/cycle direct reversing diesel engine is to be reversedPrior to the admission of starting air you must ()
A . line up the engine fore restarting with light diesel oil
B . reposition the fuel injection cam
C . change the intake and exhaust valve cam positions
D . place the starting cam in the intermediate positio
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Which of the two events listed occurs simultaneously in a two-stroke/cycle diesel engine?()
A . Exhaust and scavenging
B . Scavenging and compression
C . Ignition and expansion
D . Exhaust and compressio
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In a two-stroke/cycle diesel engine, the exhaust gases are expelled from the cylinder by the()
A . exhaust manifold
B . valve bridge
C . pressure of the fresh air charge
D . valve adjusting gear
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In the _____phase of product life cycle, the total sales volume begins to fall and price war may often break out.
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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
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听力原文: Each night we alternate between two kinds of sleep: active sleep and passive sleep. The passive sleep gives our body the rest that is needed, and prepares us for active sleep, in which dreaming takes place. And we arc beginning to understand the importance of the dream period in our sleep cycles.
In passive sleep the body is at rest. We move very little. And the brain becomes very inactive, ff a person continues to sleep, she or he enters anew period, a more active period. The body goes through several changes: the brain temperature rises, blood in the brain increases, the body becomes very still and the brain goes into active state. And as the brain goes active, the eyes begin to move rapidly. And that is the sign of another change---the person is dreaming. Throughout the night, people alternate between passive and active sleep. Doctors have studied the sleep cycle and have found that everyone dreams---in fact, that everyone needs to dream in order to stay healthy. It appears we need both kind of sleep. We need passive sleep in order to rest our bodies. We need active sleep in order to dream. And dreaming helps us to rest our minds,
What does not happen in the brain in the active sleep?
A.The brain becomes very active.
B.The brain becomes very inactive.
C.The brain temperature rises.
D.The brain blood rises.