單項選擇題Combustion knock can occur in the cylinders of a diesel engine under any condition permitting （）.

A.a shortened ignition delay period
B.a lean fuel/air mixture
C.excess fuel in the combustion chamber
D.rapid vaporization of injected fuel droplets


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1.單項選擇題Which of the following may cause that an engine doesnt turn on starting air?（）

A.too low starting air pressure
B.main starting valve closed
C.neither A nor B
D.A and B

2.單項選擇題Poor combustion in a diesel engine can be caused by （）.

A.high compression pressure
B.low intake air temperature
C.low exhaust pressure
D.high scavenge air temperature

3.單項選擇題A built-up exhaust valve is one in which （）.

A.the stem and heads are made of different material
B.low-alloy steel is used throughout
C.a replaceable valve disk is welded to the head
D.the self-centering action comes from motion of the valve stem in the guide

4.單項選擇題If scavenge box should be hot, （）would occur.

A.seized piston
B.defective atomizer
C.scavenge fire
D.too much LO

5.單項選擇題If exhaust temperatures are too high, you should check （）.

A.air cooler
B.turbocharger
C.charge air
D.A+B+C