الفهرس 
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Abstract
The aim of this work is to develop the injection system for natural gas engine
operated with lean mixture. In this work a proposed gas injector is designed
and constructed to operate with the same fuel pump attached to the original
Diesel engine. The gas injector is hydraulically operated by the fuel of the
Diesel fuel pump during the effective stroke. The hydraulic force opens the gas
valve and Jet the natural gas fuel to pass into the cylinder. The natural gas fuel
is introduced into the cylinder either by direct injection or by manifold
injection at two different speeds 1500 and 1750 rpm. The gaseous fuel flow
rate can be controlled either by varying Diesel pump rack position or by
increasing the inlet gas pressure. A control gate at inlet air manifold is used to
control the air fuel ratio to different lean limits. A one cylinder four stroke
Diesel engine of type USHA 5.5 hp at 1500 rpm was used and prepared in the
test rig. The engine is modified to suit the operation with natural gas. The
modification of the engine inc1udes the place of the gas injector, decreases the
compression ratio from 16.5 to 13, introducing electrical system for spark plug
and modification of the injection timing. The engine is tested on the original
Diesel engine at 1500-rpm speed and the modified natural gas engine tested at
two conditions; the first condition used direct gas injection of natural gas into
the cylinder, the second condition used the indirect gas injection into the inlet
air manifold. All tests for the modified natural gas engine are run at speeds
1500-rpm and I750-rpm.
A simulation study to calculate the gaseous fuel injection flow rate is
introduced. A mathematical simulation of the gas injector performance has
been made to calculate the Diesel oil pressure in the injector, the valve lift and
the rate of gas injected during the injection cyc1e as a part of the whole injection system and solved by finite difference methods with the
aid of computer program.
The experimental tests showed that the engine performance of the manifold
gas injection is nearly like the original Diesel results. The experimental results
showed that Operating with direct gas injection into the engine would produce
the same engine power but with 6% less in thermal efficiency and within the
emission pollution limits. In direct gas injection the mixture is operated lean at
part load and near stochiometric at full load. The excess air factor in direct gas
injection is equal to l.I at 65% of the engine load and 1500-rpm speed, willie in
the case of manifold injection A=1.24 at the same load and speed. The engine
performance with the manifold gas injection is better than with direct injection;
nearly the same as Diesel engine thermal efficiency and better pollution results
than direct gas injection. The pollution results for both direct and manifold
injection shows that the CO % is lower in case of manifold gas injection and
not more than 0.28% at full load. The NOx emission in manifold injection is
higher than direct injection.
A significant comparison between theoretical gas flow rate calculation and the
experimental gas flow rate is traced at different Diesel pump rack positions and
different inJet gaseous fuel pressure. As expected the rate of gaseous fuel
introducing the cylinder is increased by increase the pump rack position of the
Diesel pump and by increasing the inlet gaseous fuel pressure.