Page 233 - 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 217

Figure 2.282 Diesel fuel injection components. (Source: Bosch Media)

The capacity of the NO accumulator catalytic converter is limited. As soon
x
as it is exhausted, the catalytic converter must be regenerated. To remove the
deposited nitrates, the DI-Motronic briefl y changes over to its third operating
mode (rich homogeneous operation with lambda values of about 0.8). The nitrate
together with the carbon monoxide is reduced in the exhaust to non-harmful
nitrogen and oxygen. When the engine operates in this range, the engine torque
is adjusted according to the accelerator pedal position via the throttle valve
opening. Engine management has the diffi cult task of changing between the two
different operating modes, in a fraction of a second, in a way not noticeable to
the driver.
The continuing challenge, set by legislation, is to reduce vehicle emissions to
very low levels. Bosch is a key player in the development of engine management
systems. The DI-Motronic system, which is now used by many manufacturers,
continues to refl ect the good name of the company.

2.5.3 Diesel fuel injection systems

Diesel engines have the fuel injected into the combustion chamber where it
Key fact
is ignited by heat in the air charge. This is known as compression ignition (CI)
because no spark is required. The high temperature needed to ignite the fuel is The high temperature needed
to ignite fuel in a diesel engine is
obtained by a high compression of the air charge. Diesel fuel is injected under
obtained by high compression of the
high pressure from an injector nozzle, into the combustion chambers. The fuel
air charge.
is pressurized in a diesel injection pump. It is supplied and distributed to the
injectors through high-pressure fuel pipes or directly from a rail and/or an injector.
The high pressure is generated from a direct acting cam or a separate pump.
The air fl ow into a diesel engine is usually unobstructed by a throttle plate so
a large air charge is always provided. Throttle plates may be used to provide
control for emission devices. Engine speed is controlled by the amount of fuel
injected. The engine is stopped by cutting off the fuel delivery. For all engine
operating conditions a surplus amount of air is needed for complete combustion
of the fuel.

Diesel engines used to be considered as indirect and direct injection. Nowadays,
almost all are direct and a number of methods are used, as shown in Figs 2.282
and 2.283 . The rotary pumped direct injection and common rail systems will be
discussed further in this section.