Diesel engines play a major role in power generation, agriculture,
mass transportation etc. India, one of the fast developing
countries, is known as diesel driven economy as the consumption
of diesel to gasoline is about 5:1. This is mainly due to diesel engine
operation at higher compression ratio and leaner air fuel ratio
than SI engine resulting in higher thermal efficiency. Even though
the levels of HC and CO are very lower in the diesel engines than
gasoline engine, however, it emits high levels of NOx and smoke
emission. The stringent emission norms pose to a big challenge
to the researchers for controlling these emissions.
The main causes of formation of particulate emission from diesel
engines are heterogeneous air–fuel mixture, poor mixing of fuel
with air, high diffusion combustion phase, fuel containing sulfur
content, high fuel density, etc. Particulate emission could be reduced
by improving mixing rate of fuel with air, enhancing premixed
combustion phase by increasing ignition delay, etc.
However, it would lead to high in-cylinder temperature resulting
in high NOx formation as it is mainly a function of temperature.
This conflict nature leads to difficulty in simultaneous control of
NOx and particulate emissions from diesel engines.
Several methods have been tried and reported in literatures to
control the emissions. Most in-cylinder control techniques do not
simultaneously reduce NOx and smoke emissions. For example,
EGR technique can reduce NOx significantly but it would increase
particulate emissions where as oxygen enrichment technique