الفهرس 
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Abstract
The design, development and optimization of an internal combustion engine require the
application of a modem sophisticated analysis tool. In addition to experimental work,
numerical calculations are now necessary to provide an insight into the complex in-cylinder
process. A commercial Computational Fluid Dynamic code Fluent 6.3 is used as a modeling
platform for investigating the effect of hydrogen direct injection in direct injection compressed
natural gas spark ignited engine on engine performance. The simulation is conducted in a
single cylinder, four stroke direct injection engine running at wide open throttle mode. The
engine incorporated a centrally positioned direct injector in close proximity to the spark plug.
The engine main fuel is natural gas and for the matter of simplification the fuel is reduced to
methane only. Different hydrogen ratios (3%, 4 %, and 5 %) by mass are directly injected in
the combustion chamber using a side mounted secondary injector. The engine speed is varying
from 1000 to 2500 RPM with increment of 500 RPM. The engine is configured with no swirl
and low tumble motion. The numerical calculations is carried out during crank angle period
that starts after intake valve closure (137° before top dead center) to exhaust valve opening
(133° after top dead center) with different hydrogen injection timing (100°, 110°, 120°, 130°,
and 136°) before top dead centre while retarding and advancing the ignition timings in the
range of (3° to 14°) before top dead centre. The results shows that a loss in in-cylinder pressure
by 27% when hydrogen is directly injected in the combustion chamber. Also it is noticed an
improvement by 4% in the in-cylinder pressure with retarding the hydrogen injection timing.
Ignition timing has a significant influence on engine performance and the performance
parameters increases with advancing the ignition timing also the engine speed improves the
engine performance by 35%.
Also the study revealed that the lean limit in the combustion chamber for different driving
conditions can be controlled by control the hydrogen injection flow rate for different driving
conditions and loads.