On engines having oil cooled pistons the lubricating oil pre-heater must be put into operation and the rate of heating so （） that the temperature of the piston cooling oil returns are 32℃ to 35℃ over a period of at least two hours.

Too much excess air is （）because the heat generated is ...

单项选择题Too much excess air is （）because the heat generated is being lost through the exhaust trunking instead of being made used of in heating the water to produce steam.

（） the oxygen content in the exhaust gas, （） the combus...

单项选择题（） the oxygen content in the exhaust gas, （） the combustion is.

Injectors on modern engines are cooled by a combination...

单项选择题Injectors on modern engines are cooled by a combination of the intensive bore cooling in the cylinder by a combination of the intensive bore pockets and by the fuel which is re-circulated through the injector when the follower is on the （）of the cam or when the engine is stopped.