الفهرس 
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Abstract
This present research work was carried out in the biogas laboratory of the Agricultural Engineering Department in order to study the possibility of utilizing biogas energy as a fuel for operating small electric generator. The main objectives of this research work were to modify a small electric generator engine to operate on biogas and investigate the effect of biogas fuel on the mechanical performance and efficiency of engine and generator using six different nozzle diameters 4, 5, 6, 7, 8, and 9 mm with seven different electric loads 0, 0.29, 0.58, 0.87, 1.16, 1.43 and 1.62 kW. The results indicated that the biogas can be used as a new fuel for operating the enginegenerator unit at the maximum output of generator (1.62 kW) and rated power (1.43 kW) under the following optimum conditions: 1 The best nozzles diameter for biogas supply were 4 and 5 mm, at the operating biogas pressure ranged from 19 to 21 mbar 2 The specific biogas consumption was 0.488 and 0.491 m3/kWh at the average engine speed of 3080 rpm and the brake power was 2.106 kW. 3 The brake thermal efficiency was 28.2 and 28%, while the mechanical efficiency was 82.4 and 81.9%. Moreover, the generator thermal efficiency was 21.67 and 21.56% but the electric generation efficiency was constant for all experiments (76.9%). 4 The CO value in exhaust gas was 594 and 571 ppm with reduction ratio of 70.81 and 71.94% as compared with kerosene. While the combustion efficiency was 79.7 and 81.3% as compared with 75.4% for kerosene fuel. 5 The cost of mechanical energy unit was 0.079 E.L./kWh with reduction ratio of 45.52% as compared with kerosene. While it was 0.158 E.L./kWh for electrical energy unit, the reduction value was 46.4%.