Read about  the transition from engines running with excess air to the adoption of Stoichiometric and Lean-Burn strategies to address exhaust emissions concerns and achieve better efficiency. Two strategies emerged to reduce NOx while containing CO and unburned hydrocarbons: Stoichiometric (Rich-Burn Combustion) and Lean-Burn Combustion. The former involves operating engines at a stoichiometric fuel mixture using oxygen sensors to maintain precise oxygen levels for catalytic converter reactions. The latter employs excess air to lower combustion temperatures and reduce NOx levels, often not requiring catalytic converters.