Automobile Cooling Systems

An gasoline-powered automobile engine operates in a modified Otto cycle which may produce temperatures in the neighborhood of 2500°C. Approximately 70% of the energy from fuel combustion is converted into heat. This requires a high capacity cooling system to prevent the overheating of the engine. Most current automobile engines are water-cooled. Water has the advantage of a high heat capacity, but the disadvantages of a relatively high freezing point and relatively low boiling point for the purpose of auto cooling. Typically a mixture of ethylene glycol and water is used in a pressurized cooling system to transfer heat from the engine block.

一台燃油汽车发动机在修改后的奥托循环中运行，可能产生约2500°C的温度。燃料燃烧产生的约70%的能量转化为热量。这需要一个高容量的冷却系统以防止发动机过热。目前大多数汽车发动机都是水冷的。水的优点是具有较高的比热容，但缺点是凝固点相对较高，而沸点相对较低，不利于汽车冷却。通常在加压冷却系统中使用乙二醇和水的混合物来将热量从发动机块传递出去。

The effect of ethylene glycol on the freezing and boiling points is shown in the table.

乙二醇对冰点和沸点的影响如表所示。

The advantage of the lowered freezing point is obvious, but the raised boiling point is also significant and makes the antifreeze solution important in summer as well. The above boiling points are at atmospheric presure, but a higher maximum operating temperature can be achieved by pressurizing the cooling system. It is typical to have a spring-loaded pressure cap on the cooling system which permits the pressure to rise to about 14 to 15 lb/in² above atmosphere (i.e., an absolute pressure of about two atmospheres). For the coolant mixture, this can raise the boiling point another 25°C or 45°F.

降低的凝固点的好处是显而易见的，但升高的沸点也是显著的，这使得防冻液在夏季也变得重要。上述沸点是在大气压下测定的，但通过加压冷却系统可以实现更高的最大工作温度。典型的冷却系统会配备一个弹簧加载的压力盖，允许压力上升到大气压上方约14到15磅每平方英寸（即约两个大气压的绝对压力）。对于冷却剂混合物来说，这可以将沸点再提高25°C或45°F。