What is meant by the combustion occurs with a lean mixture?

Combustion with a lean mixture occurs when the air-fuel ratio is higher than the stoichiometric ratio, which is the ideal ratio of air to fuel for complete combustion. In other words, there is more air than the fuel requires for complete combustion.

When combustion occurs with a lean mixture, the mixture burns hotter than with a rich mixture (more fuel than air). This can cause higher engine temperatures and increased wear on engine components. Additionally, lean mixtures can lead to increased emissions of nitrogen oxides (NOx) and carbon monoxide (CO).

Lean mixtures are often used in internal combustion engines to improve fuel efficiency. However, the engine must be carefully designed and calibrated to operate safely with a lean mixture.