Abstract

Swirl stabilized combustion is one of the most successful technologies for flame and nitrogen oxides control in gas turbines. However, complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Although there is active research on the topic, there are still various gaps in the understanding of how interaction of large coherent structures during the process affect flame stabilization and related phenomena. Thus, this paper approaches the phenomenon of lean premixed swirl combustion of CH4/H2/CO blends to understand the impacts of these fuels on flame blowoff. An atmospheric pressure generic swirl burner was operated at ambient inlet conditions. Different exhaust nozzles were used to alter the Central Recirculation Zone and observe the impacts caused by various fuel blends on the structure and the blowoff phenomenon. Methane content in the fuel was decreased from 50% to 10% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Experimental trials were performed using Phase Locked PIV. The Central Recirculation Zone and its velocity profiles were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the fuel blend, changing stability based on the carbon-hydrogen ratios. Nozzle effects on the shear flow and Re numbers were also observed. Modelling was carried out using the k-ω SST CFD model which provided more information about the impact of the CRZ and the flame nature close to blowoff limit. It was observed that the model under-predicts coherent structure interactions at high methane fuel content, with an over-prediction of pressure decay at low methane content when correlated to the experimental results. Thus, complex interactions between structures need to be included for adequate power prediction when using very fast/slow syngas blends under lean conditions. 

Using natural gas as a fuel for internal combustion engine (spark ignition) results in reduction of pollutant emission such as NOx, HC, CO and SOOT if compared with conventional hydrocarbon fuel in addition the high-octane number of natural gas allows an increase of compression ratio in spark ignition engine and consequently improves their efficiency.

In this paper an extension of the model presented by Ferguson [1], is applied using FORTRAN language. A comprehensive performance data is presented for equivalence ratios, compression ratios, and engine speed. The contributions were to develop and validate a computer code simulation for 4-stroke cycle SI engine by using different fuel and compare the results with previous experimental studies. The results of the computer code are in very good agreement with the experimental studies under various conditions.

Experiments showed that a compression ratio of 12:1 is a reasonable value for a compressed-natural-gas direct-injection engine to obtain a better thermal efficiency without a large penalty of emissions.

لقد تزايد الاهتمام المحلي والدولي بمكافحة الفساد المالي والإداري وخاصة في ظل التطورات المتلاحقة للحياة الإقتصادية والتي تُحتم على منظمات الأعمال ضرورة مكافحة الفساد المالي والإداري حتى يتسنى لها البقاء الأمن في بيئة الأعمال. وتعد المحاسبة القضائية من الآليات الحديثة في مجال منع واكتشاف الغش والفساد المالي والإداري، لذا فقد هدفت هذه الدراسة إلى التعرف المفاهيم الأساسية للمحاسبة القضائية و توضيح السمات الشخصية التي يجب أن يتميز بها و التعرف على المعايير المهنية الصادرة عن جمعية ممتحني الاحتيال المعتمدين بخصوص ممارسة مهنة المحاسبة القضائية، ولتحقيق هذه الاهداف تم تقسيم الدراسة إلى ثلاثة اجزاء، تناول الجزء الاول الاطار العام للدراسة وتناول الجزء الثاني الإطار النظري للمحاسبة القضائية في حين خصص الجزء الثالث للدراسة الميدانية والذي تم فيه اختبار مدى توفر تلك المعايير الدولية في ممارسي مهنة المحاسب القضائي في ليبيا، وقد خلصت الدراسة إلى عدم توفر تلك المعايير مما يستوجب ضرورة العمل على تطوير القدرات والمهارات لدى المحاسب القضائي حتى يتسنى له أداء مهامه بكل كفاءة واقتدار.