单选题Scavenging in a four-stroke/cycle diesel engine occurs during the （）.A last part of the exhaust stroke, and the first part of the intake strokeB last part of the intake stroke onlyC early part of the injection stroke onlyD early part of the power strok

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 the indicated horsepower as a four-stroke/cycle engine

D.one power stroke for every two crankshaft revolutions

Proper lubrication of the main bearings is more easily obtained in a single acting, four-stroke/cycle diesel engine than in a tow-stroke/cycle diesel engine because________.

A.The direction of pressure on the journal in four-stroke engine is continuously

B.positive feed lubricators are installed on all bearings of four-stroke engine, whereas as a splash feed system is used on tow-stroke engine

C.four-stroke engines usually utilize a heavier grade of oil than tow-stroke engines

D.Low-stroke engines usually consume less lube oil than four-stroke engines

During the valve overlap period, the exhaust pressure of a turbocharged four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure ______.

A.effective cylinder scavenging and cooling

B.constant pressure from the turbochargers

C.cooler operation of the exhaust system

D.effective constant pressure for turbocharger operation

Any increase in the exhaust back pressure of a four-stroke/cycle diesel enginewill( ).

A.reduce engine horsepower output

B.aid in silencing the exhaust noise

C.increase the mean effective pressure

D.contribute to effective cylinder scavenging