单项选择题
A.keep piston crown temperatures elevated for smoother combustion
B.reduce the possibility of overheating the top compression ring
C.help retain the heat of compression to prevent ignition delay
D.help retain the heat of compression to prevent combustion knock
单项选择题 The adverse effects of burning high sulfur fuel can be compensated for by using a cylinder oil having sufficient（）
单项选择题 Scuffed cylinder liner surfaces in a diesel engine can result form（）
单项选择题 When comparing different fuels for different engines, the ignition quality of diesel fuel oils becomes a less critical consideration as （）