The closed cycle diesel engine provides an economic solution to fill the strongly needed energy gap for naval submarine between the low performance conventional diesel electric system and the high performance nuclear reactor plant. The interrelationships between the non-air oxidants with moderate gases for synthetic atmosphere and engine performance, are either not well documented or understood. A theoretical model based on fuel/synthetic atmosphere cycle approximation for the diesel engine, is

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... developed. Model results show direct reflection of the intake gas mixture constituents effects without the uncertainties associated with the combustion process for actual cycle modeling under synthetic atmosphere. This necessitates the generation of temperature entropy charts for both synthetic atmosphere and corresponding combustion gases. The charts and engine cycles presentation are progranuned for PC with sufficient generality to represent any synthetic atmosphere constituents and under different excess synthetic atmosphere factors. An experimental rig, including single cylinder diesel engine, gas metering apparatus and instruments, is designed, constructed and employed to provide results for comparison. The performance deteriorating effects due to CO2 % increase by volume and the beneficial effects due to 02 % increase by volume, in the engine inlet mixture, are analyzed. The theoretical model results, show satisfactory correlation with the experimental results and/or previous works. Mr = total number of moles of combustion gases/kg of fuel Mt = molecular weight of the synthetic atmosphere Q = heat liberated / mole combustion gases T = absolute temperature X,y = the percentages in the mixture of CO 2 and 02 by volume respectively Y, = mole fraction of any given species Lc = molar synthetic atmosphere/fuel ratio 2 3 -5_ Proceedings of the sth ASAT Conference, 4-6 May 1999 Paper PR-04 118 vi = species moles of combustion products = excess synthetic atmosphere factor subscripts: th, act Denote theoretical and actual respectively i Specify any given species 1,2,3, m Denotes mixture s Denotes synthetic Introduction: The energy capacity of conventional electric powered submarine is only sufficient to allow undersea missions of about 48 hours, to be carried out before the storage batteries are to be recharged oversea or under snorkel mode [1,2,3]. On the other hand, the nuclear submarine can access almost limitless power. However, it is not available for all navies for economical or strategic reasons. It is also too large and noisy for shallow seas [4]. Thus, there is a strong need for a power system that can fill the energy gap between the low performance conventional diesel electric battery system and the high performance nuclear reactor base plant. The submerged endurance is of fatal importance in submarine effectiveness. Alternative systems have been proposed and the closed cycle diesel engine system provides the economical solution to fill this gap [1,5,6,7]. The engine, then, has to make use of synthetic atmosphere of oxygen and managed exhaust gases. The size of the exhaust gas management system is a direct reflection of the partial pressure of the CO2 in the working fluid. The higher the concentration of CO2 , the greater the possible separation and removal and hence the smaller the management system [8, 9] . The non-air breathing diesel may also be used in industrial applications where contamination of air supply is a practical possibility like in mines, industrial and chemical plants and nuclear power plants...etc. [10] Karim [10] analyzed experimentally the effect of unconventional atmosphere on diesel engine performance. He created the atmosphere by the addition of contamination gases such as CO2, N2 or 02 to the air intake change. The engine tolerated admission of CO2 concentration up to 16% by volume. However, the CO2 increase means, in effect, a reduction in the actual quantity of 0, inhaled by the engine. Zheng et al [11. 12, 13,14] made a theoretical and experimental work to study the effect of synthetic atmosphere on diesel engine performance. An imperical formula for the heat release was used in the actual cycle simulation program. The gravimetric concentration of 02 was maintained fixed at 23% while increasing the CO2 . The IDI diesel engine with compression ratio of 23, continued running untill CO2.% by mass of 45 % . At about 50 % CO2 . there was a sudden loss in performance. It is emphasized that maintaining the 02% concentration constant by mass in the studies means, in effect, that the 02 mass ingestion increases at the same engine speed and fueling rate. Hawley [15] used a 4-cylinder diesel engine with number one cylinder operating on non-air atmosphere. This provision enabled the extremes of engine performance to be observed. He reported achieving engine operation with up to 70% CO2 concentration by charge preheating to 150°C . He observed severe degradation in performance. Fowler [16] developed a complete closed cycle diesel engine. He reached only 4% CO2 by volume in the synthetic atmosphere with nitro-diesel system. The main restriction was the specific heat ratio of the inlet working fluid with the exhaust management system. The overall implication of the previous works indicates that the interrelationships between the non-air oxidants and engine's performance are not well documented nor understood.