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【单选题】

Reducing combustion engine exhaust emissions is a continued object of research and development, driven both by awareness of environmental effects and increased government regulation. Some of the most effective and cost-efficient emissions controls involve the use of downstream chemical catalysts(化学催化剂) that further oxygenate incompletely combusted compounds. Sometimes exhaust is directed sequentially through multiple catalyst beds. It is generally understood that higher catalyst temperatures provide more effective emissions control. Much exhaust catalysis development has been focused on developing catalytic converters for automotive applications, in which engine speed varies substantially with vehicle speed and gear selection.Marine engines and generators are subjected to specific regulations, both for emissions and for safety concerns. For example, exposed engine suce temperatures (including exhaust system suce temperatures) must be kept low to avoid increased risk of fire hazard. Seawater is injected into many marine engine exhaust flows so as to cool exiting exhaust gases, and seawater is also frequently circulated through exhaust system components so as to maintain low suce temperatures.Further improvements in exhaust emissions controls for constant and variable speed engine applications are desired, particularly improvements suitable for marine use.

The engine speed changes mainly with_____.

A.
the type of the main engine
B.
the condition of the engine
C.
the load of the marine engine
D.
the gear selection
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参考答案:
参考解析:
.
刷刷题刷刷变学霸
举一反三

【单选题】酶和一般化学催化剂相比具有下列特点,例外的是

A.
具有更强的催化效能
B.
具有更强的专一性
C.
催化的反应无副反应
D.
可在高温下进行
E.
其活性可以受调控的

【单选题】酶与化学催化剂的主要区别是?

A.
都是低分子化合物
B.
都是人工合成的物质
C.
都耐热,不耐低温
D.
在催化反应中质和量的方面,都不发生变化
E.
酶的特异性,催化效率极高