Page 340 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

Over the years, lots of developments in electronics have taken place. Therefore, in gasoline engines control of the
following parameters is easily monitored by using sensors and actuators linked to an electronic control module.
The important parameters that can be controlled are:
i Air-fuel ratio
ii Mixture distribution between cylinders
iii Ignition timing
iv Injection timing of the fuel
v Idle speed

As known a diesel engine uses a heterogeneous fuel air mixture. The load is controlled by varying the amount
of fuel injected. The fuel that is injected has to be atomized and mixed with air without leaving rich pockets so
that combustion can take place properly. Too much mixing may lead to very lean mixtures. Again the fuel will
not burn completely and this will result in hydrocarbon emission. Insufficient mixing will lead to high smoke, HC,
CO emissions and fuel consumption. Proper timing of the ignition can lead to low combustion temperatures and
smooth engine operation. This will also reduce NO x emissions.
Modern emission standards and performance requirements cannot be met by conventional fuel injection systems
operated mechanically. Injection timing, pressure, duration etc. can be easily controlled electronically to minimize
fuel consumption and emissions. Here again a set of sensors determines the engine operating conditions and
this data is fed to the electronic control module to take suitable steps in order to control the engine operation via
actuators. Electronic controls can also be used for engine speed governing. These systems can give very close
control over the engine speed under transients and wide load fluctuations. In both SI and CI engines the electronic
control module works on software specially developed which uses sensor inputs and previously stored data about
the engine. Using this information, it controls various parameters. The control is achieved through actuators.
The data about the engine is stored as a table that is analyzed to take appropriate decisions. In most cases the
electronic control module has to work in conjunctions with mechanical systems. In this chapter we will introduce
different instrumentation and sensors that can be used in practice.
Typical engine management systems

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CITS : Automotive - Mechanic Diesel - Lesson 104 - 107