Abstract:
Diesel engine emission levels are strictly regulated over the year. Meeting these
emission regulations has always been a challenging job for diesel engine developers.
Considering the cost problems and complexities of diesel engine aftertreatment systems,
in order to meet the soot and NOx levels, engineers had to come up with alternative
design solutions. Since changing the combustion chamber design has always been a
more cost effective and easily applicable solution compared to complex diesel engine
aftertreatment devies, various chamber designs have been researched and tested by
engineers. The geometrical shape of the combustion chamber is particularly significant
in order to improve the turbulent flow structures and in-cylinder flow velocities that
would affect combustion efficiency and engine-out emissions. Two of the most widely
used designs are mexican hat and stepped-lip chambers. The stepped lip design in
particular, has been widely investigated due to their fuction of promoting recirculating
flow structures which enhances fuel-air mixing and resulting with lower soot emission
levels. The main objective of this thesis is to investigate the effect of stepped-lip
combustion chamber design and compare the in-cylinder vortex structures with a
conventional mexican hat chamber. A 3D CFD model has been carried out in order to
understand the in-cylinder flow structures and vortex formations. Then an experimental
study has been conducted with a single cylinder diesel engine with an in-line pump
injection system and soot emission levels of both mexican hat and stepped lip
combustion chambers have been compared.
