One of the greatest challenges humans faced in ancient times, has become in recent years, an almost trivial matter – that is the need to travel to faraway places as fast as possible. For many years, humans have relied solely on their feet or the feet of horses and other pack animals to travel on the ground. All of this has fundamentally changed with the invention of the engine. 

Nowadays, it is difficult for us to imagine a world without engines helping us move faster. In our world there are over a billion cars, and many more means to move fast, even very fast, such as with trains, airplanes and even spaceships. You probably have not given this subject much thought the last time you traveled to the Golan Heights, but while you were complaining that the trip was very long and took two whole hours, you should keep in mind that in a world without engines, a similar trip from the center of the country to the Golan Heights would take between four days and a full week.

This great revolution began with the first prototype of a motorized vehicle, which was created as early as 1770. It continued with the construction of the first production lines of commercial cars in the early 1900’s, and is still advancing to this day. All of this was enabled due to technological breakthroughs and by using two basic chemical principles. The first is, of course, finding the means to create energy and translate it into the motion of a vehicle. The second, and just as important, is the utilization of the properties of different materials in order to dispose of excess energy and heat, and thus enable the engine to function well over time. 

The burn that makes the wheels move
The gasoline and diesel engines that propel most cars these days work on a similar principle. These engines compress air and fuel fumes together, and then, at a specific point, sometimes with the help of an electrical spark, a combustion reaction is produced. This combustion is actually a controlled explosion. The gas produced in the reaction, together with the large amount of energy released, combine to push a piston. A contraption called a crankshaft translates the linear motion of the piston into the rotational motion of the wheels.

The mechanism of action of the four-stroke cycle engine
 

Cooling system
One of the challenges of utilizing this combustion energy to create a force that will enable motion, is how to deal with the side-effects of this reaction, which includes gas and a large amount of heat. Without an appropriate cooling mechanism, the large amount of heat will accumulate in the engine. The temperature in the engine will rise until its metal components distort from the heat, eventually ruining the engine.

An appropriate cooling system should easily reach all parts of the engine, absorb large amounts of heat, and transfer the heat outside. A system such as this should also be as efficient as possible, and thus should be closed and recurrent.

Here, a second chemical principle comes into play. The cooling system needs to use a material that enables it to go in and out of the engine. The property that measures the ability of a material to carry heat is its volumetric heat capacity, which translates into the amount of energy that will cause the temperature of one gram of a material to rise by one degree. 

Luckily, the most common liquid on earth is also one of those with the highest volumetric heat capacities. We are talking about water, of course. However, water turns into gas at a relatively low temperature of one hundred degrees, and freezes and expands at zero degrees. Therefore, on a very cold day, when the temperature drops below zero, the water will freeze and inflict damage to the cooling system and the engine.

Hence, we should use water for cooling, but we want its boiling point to be higher and its freezing point to be lower. The solution lies within a deep understanding of the different states of matter and the transition points between them.

As water transforms from liquid to ice, the molecules need to come closer to one another, and organize in a recurrent and condensed manner. If we make it more difficult for the molecules to crystalize, the transition to a solid state will occur at a lower temperature. In the transition from liquid water to gas, the molecules need to acquire enough energy in order to completely spread away from each other. In addition, in order for the gas bubbles to disperse in the air, the vapor pressure should exceed the atmospheric pressure pushing the gas to stay inside the liquid. Thus, if we manage to lower the vapor pressure of the water, the boiling temperature will rise.

In order to meet these two requirements we can make a solution from the appropriate substances. In our case, if we dissolve ethylene glycol in water at an equal ratio, we will achieve a solution that has a freezing point of -37˚C and a boiling point of 106˚C. These types of solutions have different properties than each of their components. Mixing different ratios of solute and solvent will give rise to different boiling and freezing points.   

Movie produced for TEDed

The chemistry of coolants is one example of many for our ability to utilize our understanding of the laws of nature and the properties of materials, in order to create a new compound with better qualities, which are more fitting for a specific application than those of the substances that comprise it. Exploiting our knowledge in chemistry and physics for new applications stands at the heart of applied chemistry and industrial chemistry, which are two schools of thought that have changed the world. Thanks to them, we know how to build airplanes from very complex, strong, and light materials, develop fertilizers that enable us to feed the world population, and travel from place to place without having our engine overheat.

So the next time you take a long drive, with cars moving around you at high speed, give a moment of thought to the chemistry and physics that allows you to get to your destination.

 

Eitan Oksenberg
PhD student, Department of Materials and Interfaces
Weizmann Institute of Science


Article translated from Hebrew by Elee Shimshoni, PhD student at the Weizmann Institute of Science.
 
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