الفهرس 
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Abstract
The world has been concerned and worried about the depletion of the liquid oil fuel, besides new environmental rules are to be followed to reduce pollution hazards and global warming. The utilization of natural gas (as a near term fuel) and hydrogen (as long term fuel) are receiving great attention, because they have less pollution effects. Since the aviation has a great de,1! in environmental pollution effects due to the cruise flight in the upper troposphere (supersonic aircraft) or in the lower stratosphere (subsonic aircraft) where most or the ozone concentrate which helps in protecting the earth form ultra violet radiation, So the use of alternate fuel has a great attention in aviation ,USA 8-57 bomber was the first aircraft to use the liquid hydrogen as a fuel. While in the former USSR was the leader of using liquid natural gas in their aircraft’s as well as liquid hydrogen; some of these aircraft TLi-156 which first flew in ]9Xl) and Tu 206 and Tu 338. The use of liquid natural gas became more popular than liquid hydrogen because or some problems in storing liquid hydrogen, since it is stored under -235oC and 21.43 MPa, while liquid natural gas stored at -163oC: and 0.1 MPa.
In the present study, the thrust specific fuel consumption, specific thrust and the emissions from the aircraft during aircraft flight profile are predicted, when using aviation fuel and natural gas.
The present work presents a comprehensive. study on the use of natural gas as an alternative fuel for aircraft propulsion including the latest research work in this area.
The P&W JT9D -7R-turbofanjet engine is taken as a base line engine propelling the Boeing 747-200 aircraft as a base line aircraft with lour engine nacelles mounted on wings.
The study introduces the temperature-entropy charts for both aviation fuel and natural gas, while computerized with sufficient generality to include any excess air factor and temperature variations, The model engine fuel-air cycle representation is carried out for design point calculations based on sea level static conditions and variable specific heats along engine components, The predicted engine performance results compared very well with the reported values by the manufacture. Predictions carried out using aviation fuel and natural gas show an increase in the specific thrust by 3% and decrease in the thrust specific fuel consumption by 14% and fuel to air ratio by 11% when using natural gas. Pollutant emissions are therefore reduced by 23% for CO2 emissions
And 16% for NoX emissions due to better conversion efficiency or natural gas.
The two spool turbofan jet engine simulation and matching between the gas generator and nozzles based on sea level static conditions as reference values, taking an average gas