What are the chemical reactions in internal combustion engine?

Answer 1

Internal combustion engines usually use some kind of hydrocarbon fuel (gasoline for example). The fuel is burned together with the oxidizer (atmospheric air in most cases with the exception of rocket engines). The result of the chemical reaction between the hydrocarbon fuel and air is H2O, CO2 and, in smaller quantities (depending on the proportions in which the fuel and air are mixed into the combustion chamber), some radicals like CO, OH, O, H maybe even C solid particles (also known as soot). The process is not as simple as it is taught in high school chemistry as there's no single reaction leading from reactants to final products. There are many reactions leading from the decomposition of the gasoline and air molecules to the formation of the final products (all of this reactions form the reaction mechanism). You can read more about reaction mechanisms in the related link.

Answer 2

In an internal combustion engine, the main chemical reaction is the combustion of a fuel (such as gasoline or diesel) with oxygen to produce carbon dioxide, water vapor, and heat. This process is typically carried out through a series of combustion reactions in the combustion chamber of the engine, resulting in the generation of mechanical energy used to power the vehicle.