الفهرس | Only 14 pages are availabe for public view |
Abstract Despite their initial successes, submarine pioneers were stilI eager to find some means to free their boats from the necessity of surfacing frequently for access to the atmospheric oxygen demanded by the gasoline or diesel engines that charged the batteries. Recently, growing demand for longer underwater endurance has generated increasing interest in promising AlP (Air-Independent Propulsion) technologies. Most of the studies encountered are for inter gases with synthetic air to enhance the deterioration in combustion performance due to synthetic air. In the present study a three dimensions, multi zone model is established using commercial Computational-Fluid Dynamic [CFD] code [Fluent 6.3] to model the combustion process in a direct injection diesel engine running under synthetic atmosphere operating conditions contaminated with different carbon dioxide concentrations. In addition, the beneficial effect of adding hydrogen gas to the working above-mentioned fluid with different concentrations is also investigated, meanwhile the effect of using the synthetic atmosphere with different composition on pollutants emissions is studied. The complexity of the combustion process either for conventional and non-air mixtures with its associated fuel atomization, delay period, kinetics of reactions, turbulent mixing, non equilibrium effects, heat release as well as heat transfer, etc, is taken into account. The gross indicated output is used to identify the impact of compression, combustion and expansion processes on engine performance and emissions. The engine performance as well as pollutants emissions due to the presence of carbon dioxide and hydrogen respectively in the working fluid containing constant 21 % oxygen by volume, as in normal air, have been investigated. The effects of carbon dioxide concentrations and different carbon dioxide - hydrogen concentrations on ignition delay period, specific fuel consumption, heat release, and soot formation and nitrogen oxide concentration have been determined. The engine model is validated against the normal diesel operation as well as closed cycle diesel operation. The results show that, increasing carbon dioxide concentrations deteriorate engine performance, increase soot formation and decrease nitrogen oxide concentrations due to in- cylinder temperature decrease. On the other hand, the effect of admitting hydrogen with different concentrations along with different carbon dioxide concentrations on the working fluid resulting in engine performance improve, however the rate of improvement is not significantly affected by increasing hydrogen concentrations, also the improvement is more |