After adapting fire in antiquity for one’s needs, a person was constantly searching for some new options for using fire and new types of fuel. Different types of combustible substances were used as fuel: solid, liquid, gaseous. And with all this specific heat of combustion?
By definition, the amount of heat obtained by burning 1 kg of solid or 1 cubic meter. meters of a gaseous substance - this is the specific heat of combustion. To measure it, use the Joule per kilogram (or per cubic meter) or calorie per kilogram.
Already from the very definition it becomes clear that such a concept as specific heat of combustion allows you to compare different types of fuel with each other. In essence, this means how much energy in the form of heat can be obtained from a unit of fuel. For each substance, this value will be different. For a clearer understanding, we turn to the directories.
It turns out that for wood the specific heat of combustion is 8.4-11 MJ / kg, but for coal it will be 15-16 MJ / kg. What does this mean?
And here everything is very simple. One kilogram of coal during combustion gives almost twice as much heat as it does when a kilogram of firewood is burned, and here we are talking about wood with a certain humidity. Because if the humidity of the wood is high, then part of the thermal energy will be spent on evaporation and vaporization of the water contained in the wood, and the final result will be even worse.
You can still consider the practical application of this concept to technology. Let's go back a little, in the era of steam locomotives and steamboats. Already from what we see, the specific heat of combustion of the fuel (for coal and firewood) is different, from this it becomes clear that on the same path a steam locomotive or steamer will need more firewood than coal. Of course, based on the fact that they spend energy on the road the same way, regardless of the type of fuel.
And another conclusion suggests itself from the above example. Knowing the specific heat of combustion, it is possible to determine how many kilometers a steam locomotive can travel or a steamer can sail, having a fuel supply of coal or firewood. If you make a mistake with the fuel supply, then all movement along the route will end.
There is already a practical application at first glance of an incomprehensible and unnecessary parameter. You can compare different substances and determine the possibility of their use in a particular situation as fuel, as well as evaluate the consequences of this use.
Recently, there has been a lot of talk about switching to other energy sources instead of gasoline. If you look at this problem from the point of view of the energy potential of the fuel, then, without touching any other aspects of this issue, the situation becomes clear and transparent. So, for example and further reasoning, the specific heat of combustion of gasoline is 44-47 MJ / kg, ethyl alcohol - 27 MJ / kg. And although ethyl alcohol is suitable for use as a fuel for internal combustion engines, when comparing the above data, the situation is similar to that described above with wood and coal. Ethyl alcohol is needed more, the car will pass at one gas station less, and engine power will drop when using alcohol.
True, this applies to ethyl or methyl alcohol. If, however , butyl alcohol is used as fuel , whose specific heat of combustion is the same as that of gasoline, then the practical experiments of car manufacturers confirm the possibility of its use as motor fuel instead of gasoline, but this does not concern the issue at hand.
So, it becomes clear that the specific heat of combustion is the energy characteristic of a substance, in particular fuel. This value allows you to compare the capabilities of different substances and materials, evaluate their advantages and disadvantages.