All of the diesel engine cylinder firing pressures are normal, yet all of the exhaust temperatures are lowWhich of the following situations is responsible for this condition?（）

单项选择题Which statement about diesel engine combustion is true?（）

A.Combustion does not begin until the piston starts down on the power stroke
B.Maximum combustion pressure is reached before TDC
C.Turbulence in the cylinder causes a delay in ignition
D.Maximum cylinder firing pressure is not developed until the piston passes TDC

单项选择题Diesel engine exhaust gas temperatures can be used to determine individual cylinder （）.

A.performance
B.horsepower output
C.fuel consumption
D.scavenge effect

单项选择题Improper cooling of a diesel engine cylinder liner due to the accumulation of scale deposits may cause （）.

A.low compression pressure
B.increased piston wear
C.increased cylinder lube oil consumption
D.poor contact between compression rings and liner

单项选择题In describing engine operation, what does the term “cycle” mean?（）

A.The sequence of events that produce a power pulse
B.One rotation of the engine crankshaft
C.One stroke of a piston
D.All of the above

单项选择题An advantage of aluminum pistons, when compared to cast iron pistons is （）.

A.greater high temperature strength
B.better heat conductivity
C.greater weight per cubic inch
D.increased resistance to wear