
Fuel control
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8.2 Engine fuelling and exhaust emissions
8.2.1 Operating conditions
The ideal air–fuel ratio is about 14.7 : 1. This is the theoretical amount of air
required to burn the fuel completely. It is given a ‘lambda (λ)’ value of 1.
λ = actual air quantity ÷ theoretical air quantity
The air–fuel ratio is altered during the following operating conditions of an
engine to improve its performance, drivability, consumption and emissions.
• Cold starting – a richer mixture is needed to compensate for fuel
condensation and improves drivability.
• Load or acceleration – a richer mixture to improve performance.
• Cruise or light loads – a weaker ...