What high condition leads to the formation of oxides of nitrogen in car engines?

The formation of oxides of nitrogen in car engines is primarily associated with high temperatures. In internal combustion engines, the combustion of fuel occurs at very high temperatures, often exceeding 2000°C. At these elevated temperatures, nitrogen from the air can react with oxygen to form various nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2). This reaction is facilitated because heat provides the necessary energy to break the strong bonds between nitrogen molecules, allowing them to react with oxygen.

High pressures also play a role in engine efficiency and combustion dynamics, but it is the high temperature that significantly promotes the chemical reaction leading to the formation of oxides of nitrogen. Low oxygen levels would typically lead to incomplete combustion, resulting in different products, while low humidity does not directly influence the formation of nitrogen oxides in the combustion process. Hence, high temperature is the key condition for the formation of nitrogen oxides in car engines.