AFR is context dependent
A single number is not universally rich, lean, safe or powerful across petrol, diesel and alternative fuels. Lambda is often the clearer normalized reference because it compares the operating mixture with the stoichiometric requirement of the fuel.
Measurement and control
Wideband oxygen sensors, modeled air charge, injection quantity and fuel pressure all affect interpretation. Sensor placement, exhaust leaks and calibration state can invalidate a reading.
Related terminology
LambdaA normalized mixture value comparing the operating air-fuel ratio with the stoichiometric requirement of the fuel. Lambda 1 is stoichiometric; interpretation above or below depends on combustion type and operating state.Ignition timingThe commanded spark event relative to piston position in a spark-ignition engine. Knock, fuel octane, charge temperature, combustion speed and component protection constrain the safe target.Injection timingThe timing of one or more fuel-injection events. It affects combustion phasing, pressure rise, noise, efficiency, temperature and emissions.Knock correctionAn ECU response that reduces ignition advance when knock-related signals exceed modeled thresholds. Interpretation requires cylinder, load, fuel and sensor context.