In certain operation conditions , the fuel requirement differs greatly from the basic injection-fuel quantity so that corrective is required in mixture formation .

1.Cold Start

During a cold start , the air-fuel mixture drawn in by the engine leans off . This is due to the low turbulence at cranking speeds causing poor mixture of the fuel particles with the air , and to the minimal evaporation of the fuel and wetting of the cylinder walls and intake ports with fuel at low temperature . In order to compensate for these phenomena , and thus facilitate staring of the cold engine , additional fuel must be injected during cranking .

2.Post-start Phase

After staring at low temperatures , it is necessary to enrich the mixture for a short period in order to compensate for poor mixture formation and wetting of the cylinder and intake walls with fuel . In addition , the rich mixture results in higher torque and therefore better throttle response when accelerating from idle .

3.Warm-up

The warm=up phase follows the cold-start and the post-start phase . The engine needs extra fuel during the warm-up phase because some of the fuel condenses on the still cold cylinder walls . At low temperatures , mixture formation is poor due to the large fuel droplets concerned , and due to the inefficient mixing of the fuel with the air drawn in by the engine , The result is that fuel condenses on the intake valves and in the intake manifold , and only evaporates at higher temperatures .

The above factors all necessitate an increasing enrichment of the mixture along with decreasing temperature .

4.Acceleration

If the throttle is opened abruptly , the air-fuel mixture is momentarily leaned-off , and a short period of mixture enrichment is needed to ensure good transitional response .

5 . Part Load

During part-load operation , achieving maximum air-fuel economy and observing the emission values are the crucial factors .

6.Full Load

The engine delivers maximum power at full load , when the air-fuel mixture must be enriched compared to that at part load .

This enrichment depends on engine speed and provide maximum possible torque over the entire engine-speed range . This also ensure optimum fuel-economy figures during full-load operation .

7.Idling

In addition to the efficiency of the engine , the engine idle speed principally determines the fuel filter at idle .

The higher frictional resistances in the cold engine must be overcome by increasing the air-fuel mixture input . In order to achieve smoother running at idle , the idle-speed control increases the idle speed . This also leads to more rapid warm-up of the engine . Close-loop idle-speed control prevents too high an idle speed . The mixture quantity corresponds to the quantity required for maintaining the idle speed at the relevant load ( e.g.. cold engine and increased friction ) . It also permits constant exhaust-gas emission values for a long period without idle adjustment . Closed-loop idler arm control also partially compensates for charges in the engine resulting from aging and ensures stable engine idling throughout the service life .

8.Overrun

Cutting off the fuel during deceleration reduces fuel consumption not merely on long downhill runs and during braking , but also in town traffic . Because no fuel is burnt , there are no emission .

9.Engine-speed Limiting

When a presser engine speed is reached , the ECU suppresses the fuel-injection pulses .

10.Adaptation of the Air-fuel Mixture at High Altitudes

The low density of air at high altitudes necessitates a leaner air-fuel mixture . At high altitudes , due to the lower air density , the volumetric floe measured by the air-fuel sensor corresponds to a lower air-mass floe . This error can compensated for by correcting the fuel quantity . Over-enrichment is avoided and , therefore , excessive fuel consumption .

Adaptation to Operating Condition

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