The foundation of second law of thermodynamics was laid by the inventions made by Sadi Carnot, a young French scientist considered to be the father of thermodynamics.. Before the findings of Carnot it was considered that the efficiency of heat engine was dependent on the type of working fluid used in the engine. In his book “Reflections on the Motive Power of Fire” published in the year 1824, Carnot said that the efficiency of the heat engine was independent on the type of fluid used in the engine. As per him efficiency of the heat engine is dependent just on two temperatures: the temperature of the source (hot body) from where the engine absorbs heat and the temperature of the sink (atmosphere) where the engine gives up the exhaust heat.
It was a remarkable discovery, but people found it absurd that the efficiency of the engine was dependent only on the high and low temperatures of the source and sink respectively. Sadi Carnot’s findings were ignored and many of his papers went unpublished. Fortunately his book did get published. The future scientists like Kelvin studied Carnot’s findings in more details and made further advancements.
The concept of the second law of thermodynamics applied to heat engine is equally applicable on the internal combustion engines used in our cars, motorcycles, ships, airplanes, etc. In the internal combustion engines the heat is generated by combustion of fuel inside the engine. The combustion of fuel takes place due to generation of the spark (Spark Ignition or SI engines) as in case of the gasoline engines or due to compression of the fuel (Compression Ignition or CI engines) as in case of the diesel engines.