Page 231 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 215

Figure 2.278 Operating modes. (Source: Bosch Media)

Stratified mode Homogeneous mode

Torque 0
pedal position

Open

Throttle valve position closed

λ = 1
Air/Fuel ratio 0

Figure 2.279 Switching between operating modes depending on engine load. (Source: Bosch
Media)

With increasing engine load, and therefore increasing injection quantities,
Defi nition
the stratifi ed charge cloud becomes even richer and emission characteristics
become worse. As in diesel engine combustion, soot may form. In order to Homogeneous
prevent this, the DI-Motronic engine control converts to a homogeneous cylinder Of uniform composition throughout.
charge at a predefi ned engine load ( Fig. 2.279 ). The system injects very early
during the intake process to achieve a good mixture of fuel and air at a ratio of
λ 1.
As is the case for conventional manifold injection systems, the amount of
air drawn in for all operating modes is adjusted through the throttle valve
according to the desired torque specifi ed by the driver. The Motronic ECU
calculates the amount of fuel to be injected from the drawn-in air mass
and performs an additional correction via lambda control. In this mode of
operation, a torque increase of up to 5% is possible. Both the thermodynamic
cooling effect of the fuel vaporizing directly in the combustion chamber and
the higher compression of the engine with gasoline direct injection play a role
in this ( Fig. 2.280 ).