Fuel-Air Mixture

Fuel-Air Mixture
A gasoline engine requires a certain air-fuel ratio (lambda) in order to operate effectively. The theoretical air-fuel ratio is 14.7 :1.

Different operating conditions (cold, warm, acceleration, etc.), however, render necessary an air-fuel mixture that deviates from the ideal value. Mixture correction must take place with the aid of various facilities.

A rich mixture is necessary during full throttle operation in order to develop the

There is insufficient air if lambda is < 1. The fuel-air mixture is rich. The engine develops its maximum power output at lambda = 0.85 to 0.95.

There is surplus air if lambda is > 1. The air-fuel mixture is lean. As a result, fuel consumption and power output are reduced.

If lambda is > 1.3, the air-fuel mixture no longer readily ignites, the engine no longer runs, the operating limit is exceeded.

A lambda value of 0.9 to 1.1 has proven to be the most favorable in practical
applications. If, however, it is necessary to operate the engine about a lambda value = 1, a fuel injection with emission (lambda) control will be necessary for the purpose of mixture preparation.

The electronic fuel injection system measures the air drawn in by the engine and converts the measured value into an electrical signal that is evaluated by the DME control unit. The control unit calculates the fuel requirement on the basis of the electronic signal and other parameters. The control unit correspondingly activates electromagnetic fuel injectors. These fuel injectors intermittently inject fuel ahead of the inlet valves of the cylinders.