單項選擇題

In a diesel engine, exhaust valves open before the intake ports are uncovered to （）
Ⅰ.reduce pumping losses
Ⅱ.reduce back pressure

A.Ⅰonly
B.Ⅱonly
C.bothⅠand Ⅱ
D.neitherⅠnor Ⅱ


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1.單項選擇題Which of the engine components listed increases air charge density and helps to improve engine operating efficiency?（）

A.Intake manifold
B.Water-cooled exhaust system
C.After-cooler
D.Exhaust diffuser

2.單項選擇題A diesel engine will lose power if fuel injection occurs too early because the （）

A.fuel will not be properly atomized in the cylinder
B.ignition will be delayed due to low ignition temperature
C.maximum fuel expansion will occur on the compression stroke
D.fuel will ignite before top dead center

3.單項選擇題The air supplied to the cylinders by a turbocharger is often reduced in volume by a/an （）

A.air compressor
B.diffuser
C.after-cooler
D.ventilator

4.單項選擇題Which of the listed set of conditions indicates early fuel injection timing?（）

A.Loss of engine power and high exhaust temperatures
B.Higher than normal firing pressure and low exhaust temperatures
C.High fuel consumption and high exhaust temperatures
D.Lower than normal compression pressure and high exhaust temperature

5.單項選擇題When fuel is injected in a diesel engine cylinder too early, （）

A.ignition may be delayed
B.fuel economy is not affected
C.exhaust gas temperature will be unchanged
D.the exhaust will be clear