问题
单项选择题
在提高柴油机压缩比中的主要限制是（）。
A．限制机械负荷
B．限制热负荷
C．限制曲轴上的最大扭矩
D．A＋B
答案
参考答案：D
解析：机械负荷限制了ε的上限。同时随着压缩比ε的升高，柴油机的最高爆发压力PZ提高的同时最高燃烧温度也提高，使柴油机的热负荷也增加，燃烧室部件的工作条件恶化。因此热负荷成为了限制ε的另一因素。
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在提高柴油机压缩比中的主要限制是（）。
A．限制机械负荷
B．限制热负荷
C．限制曲轴上的最大扭矩
D．A＋B
参考答案：D
解析：机械负荷限制了ε的上限。同时随着压缩比ε的升高，柴油机的最高爆发压力PZ提高的同时最高燃烧温度也提高，使柴油机的热负荷也增加，燃烧室部件的工作条件恶化。因此热负荷成为了限制ε的另一因素。
| 阅读理解。 | ||||||||||||
| All living things on the earth need other living things to live. Nothing lives alone. Most animals must live in a group, and even a plant grows close together with others of the same kind. Sometimes one living thing kills another, one eats and the other is eaten. Each kind of life eats another kind of life in order to live, and together they form a food chain (链条). Some food chains are simple, while others are not. But all food chains begin with the sun, and all food chains become broken up if one of the links disappears. All life needs sunlight to live on. But only plants can use sunlight directly. Plants are "factories". They make food from sunlight, water and things in the soil and air. Plants feed all other living things. Animals can only use the sun's energy after it has been changed into food by plants. Some animals feed directly on plants, others eat smaller animals. Meat-eating animals are only eating plants indirectly. What about human beings? We are members of many food chains. We eat rice, vegetables, and fruits and so on. We also eat meat and drink milk. But men often break up the food chains. They kill wild animals. They also make rivers, lakes and seas polluted, when these rivers, lakes and seas are polluted, the fish in them can not be eaten. If men eat the fish, they will get strange diseases. Each form of life is linked to all others. Breaking the links puts all life in danger.
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