The energy sector today continues to witness great advancements, with energy production engineers taping into electric and green energies to drive the economies of the world (Senft, 56). In the current age where people are using electric vehicles, biodiesel, and fuel cells, energy productions techniques such as locomotive engines, steam engines cannot escape being referred to archaic technologies (Senft, 56). For thousands of years, human beings have trained themselves to use engines to increase their productivity (Senft, 56). As a result, one can see that even the oldest forms of energy engines that were steam driven were indeed massive discoveries. Today, people are overwhelmingly dependent on engines and technology to the point that they cannot go without them (Senft, 56). Among the most used engines in the world are the heat engines. Heat engines work primarily by converting fuel energy into force and motion. Naturally occurring coals lack importance to human being in its raw form, but when burnt, it produces energy that is used in factories and other machines.
First and Second Laws of Thermodynamics in Heat Engines
Typically, any heat engine uses heat energy to move machines and do work (Reeve, 473). By revisiting thermodynamics, the first and the second principles or laws, one can have a better understanding of the working of heat engines (Reeve, 472). The first law relates to conservation of heat energy. This law states that in any system, the change in internal energy is equal to added heat less the work done by the system (Reeve, 471). Mathematically, the first thermodynamic principle can be summed up as follows:
Change in Internal energy = heat into the system – work done, (Reeve, 472).
This is one of the fundamental laws and principles that heat engines follow along their working together with the second principle of thermodynamic (Reeve, 472). The second law states that between two regions, heat will always from high temperature areas to low temperature regions. The second law of thermodynamics however, is not always applied, as sometimes, heat can made to move from regions of lower temperatures to regions of higher temperatures (Reeve, 65). This violation of the second law occurs in systems such as the air conditioners. In a heat engine, the first law of thermodynamics is applied in the energy conversion stage (Reeve, 471). The energy is then used in running the engine and doing work, while the second law is used in the determination of the direction to which the energy flows (Reeve, 471). In real world, heat engines are used in running automobiles. PV diagram below are refined representations of the working of heat engines. The diagram shows how heat engines employ both the first and the second laws or principles of thermodynamics to produce energy that is later used to run among many other things such as automobile engines (Reeve, 471).
Working of a Heat Engine
Heat engines use gas fuel as the main products of energy, which is burnt to produce energy by employing the first and the second laws of thermodynamics. Typically, heat engines are composed of gas fuel confined or enclosed in a piston. The working on the engines depends on the heat produced by burning the gas fuel. When the gas fuel is burnt, several processes or things occur. The gas fuel expands upon heating, pushing the piston outward. Practically however, a heat engines works by following cycles. Within the cycles, the engine move back and forward in cycles unwanted stops.
In a complete cycle, three major things occur in a heat engine. First, heat is added into the system, second, energy produced by the heat is used to perform work in the engine, and three, the excess heat is removed from the engine through a cooling mechanism.
The diagram below show the three cycles of a heat engine
To achieve its maximum efficiency, the heat engine works by employing the reversible process (Bryant, 23). This is the process where the system and its surrounding can be restored to their initial conditions; the states in which they were before the engine started running (Bryant, 156). Heat in the engine system can be lost when two things happen; first when it is through friction and second, when it moves from hot to cool regions in the system, in such a case, the process cannot be revised (Bryant, 158). Therefore, it follows that heat engines working through the reversible process are more efficient than systems working through the irreversible process.
Heat engines also work in machines such as refrigerators and air conditioners (Bryant, 23). Here, they work through the third law of dynamics. Then third law states that it is impossible to attain absolute zero in heat engines, this is because the efficiency will always be less one (Bryant, 157). Devices such as the air conditioners and refrigerators work by moving heat from high temperature areas to areas with low temperatures (Bryant, 157).
Figure 3: a sketch showing the working of a refrigerator and an air conditioner.
Therefore, from the above, it follows that heat engines work in two major processes, first, by moving heat from high temperature areas to cool temperature zones, and second by moving heat from low temperature areas to high temperature zones. In its working, a heat engine employs the first three laws or principles of thermodynamics.
- Bryant, Lynwood. “The Role of Thermodynamics in the Evolution of Heat Engines.” Technology and Culture, vol. 14, no. 2, 2013, pp. 152–165.,
- Lumley, John L. Engines: An Introduction. Cambridge [u.a.: Cambridge Univ. Press, 2014. Print.
Reeve, Sidney A. “Thermodynamics of Heat-Engines.” Science, vol. 17, no. 429, 2014, pp. 470–471.,
- Senft, J R. Mechanical Efficiency of Heat Engines. New York, NY: Cambridge University Press, 2016. Print.