FUEL INJECTION CONTROL OPERATION[MZ-CD 1.6 (Y6)]

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Pilot Injection

•  As pressure generation and injection in common rail systems are separate, it is possible to considerably enhance the range for pilot injection (up to approx. 3,000 rpm). This leads to a decisive improvement in the running characteristics of the engine. Pilot injection injects a small quantity of fuel into the cylinder before the main injection process.
This type of pre‐injection reduces the pressure in the combustion chamber, which results in an increase in the combustion quality.
The small, pre‐injected quantity of fuel is ignited and heats up the upper part of the cylinder, thereby bringing it into an optimum temperature range.
This means that the main injection mixture will ignite more quickly and the rise in temperature will be less abrupt as a result.
Because there is a smaller rise in temperature, combustion pressure is also reduced, which in turn substantially reduces combustion noise.
•  Advantage:
―  continuous build‐up of combustion pressure, resulting in reduced combustion noise.
―  reduction of nitrogen oxides in the exhaust gas.

Main injection

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1
Combustion pressure in the cylinder
2
Needle lift
3
Needle lift for main injection
4
Crank angle

Pilot injection

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1
Combustion pressure in the cylinder
2
Needle lift
3
Needle lift for pilot injection
4
Needle lift for main injection
5
Crank angle


Post Injection


High power-Euro 4

•  For vehicles with a diesel particulate filter system two post injections are employed during the regeneration process, in addition to pilot and main injections, depending on the requirements.
•  Advanced post injection is initiated in certain load/speed ranges immediately after main injection.
Fuel is then injected during the ongoing combustion.
•  The main purpose of this advanced post injection is to raise the exhaust gas temperature during the regeneration process of the diesel particulate filter. In addition, some of the diesel particulates produced during regeneration are after‐burned.
•  Retarded post injection only occurs shortly before bottom dead centre and also serves to raise the exhaust gas temperature.
•  In contrast to the previous injections, during retarded post injection the fuel is not burnt, but evaporates due to the residual heat in the exhaust gas. This exhaust/fuel mixture is delivered to the exhaust system by the exhaust stroke.
•  In the oxidation catalytic converter, the fuel vapor reacts with the residual oxygen (above a certain temperature) and burns. This provides sustained heating of the oxidation catalytic converter, which supports the regeneration of the diesel particulate filter.
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1
Needle lift
2
Pilot injection
3
Crank angle
4
Main injection
5
Advanced post injection
6
Retarded post injection