how are combustion and cellular respiration similar to each other
Both combustion and cellular respiration involve the oxidation of substances. While in respiration, food is oxidised and energy is released in a stepwise manner, in combustion the combustible substance is oxidised with the release of large amount of energy. Also, in both the processes energy is liberated.
Engines need energy to move. This is true whether you are talking about the internal combustion engines that power most cars or the processes that power organic life forms. Internal combustion engines get their energy through the process of combustion, while organisms get their energy through a process called cellular respiration. The two processes are very similar in nature.