تحلیل اکسرژی حاصل از احتراق سوخت‌های دیزل و بیودیزل در یک موتور دیزل

شبیه‌سازی مدل موتور احتراق داخلی یک ابزار موفق برای مطالعه عملکرد موتور و کمک به ارزیابی و پیشرفت‌های جدید می‌باشد. مدل‌های ترمودینامیکی چرخه واقعی موتور ابزاری مناسب برای تجزیه و تحلیل کامل عملکرد موتور و حساسیت پارامترهای عملیاتی مختلف می‌باشد. در این تحقیق به تحلیل اکسرژی حاصل از احتراق موتور چهار سیلندر، دیزل om 924 پرداخته شد و همچنین تاثیر پارامترهای عملکردی موتور بر روی بازده اکسرژی برای اختلاط سوختی دیزل– بیودیزل پرداخته شد. با افزایش بار موتور و میزان بیودیزل در سوخت اختلاطی بازده اکسرژی به‌ترتیب کاهش و افزایش می‌یابد. همچنین با افزایش سرعت موتور تحت تمام شرایط کاری موتور این دو مشخصه ابتدا افزایش و در سرعت‌های میانی به بیشترین مقدار خود رسیدند و سپس کاهش پیدا کردند. بیشترین مقدار بازده اکسرژی (37.72 درصد) در سرعت دورانی 2036 دور بر دقیقه در بار اعمالی 95 درصد و برای سوخت دیزل خالص (d100b0) رخ داد. نتایج حاصل از تحلیل اکسرژی نشان داد که 44.65 درصد اکسرژی سوخت به‌طور کامل از بین می‌رود و قابل تبدیل به‌کار نیست و بازده اکسرژی برابر با 32.62 درصد می‌باشد.

Analysis of the Exergy of Combustion the Diesel and Biodiesel Fuel in a DI Diesel Engine

<p > <strong >Introduction </strong > </p > <p >In recent years, the exergy analysis method has been widely used in the design, simulation and performance assessment of various thermal systems. In this regard, this method may be applied to various types of engines for identifying losses and efficiencies. This analysis is based on the second law of thermodynamic. Exergy is a potential or quality of energy. It is possible to make sustainable quality assessment of energy.   In this study, the second law of thermodynamics is employed to analyze the quantity and quality of exergy in a fourstroke, fourcylinder, diesel engine using diesel fuel and biodiesel fuel. </p > <p > <strong >Materials and Methods </strong > </p > <p >Four experiment variables in the present study including the operating parameters, load and speed, and the added volume of biodiesel of diesel fuel were considered as effective factors on the Break   exergy efficiency. Designs that can fit model must have at least three different levels in each variable. This is satisfied by Central Composite Rotatable Designs (CCRD). Similar to the case of the energy analysis, the same assumptions were valid for exergy analysis; the whole engine was considered to be a steadystate open system. For exergy analyses, the entire engine was considered to be a control volume and a steadystate open system. Fuel and air enter, and mechanical work, heat loss and exhaust gases leave the control volume at a constant rate. The exergy balance for the control volume can be stated as. </p > <p >                                                                                                                             </p > <p >where  is the exergy transfer rate associated with the heat loss from the control volume to the environment, assumed to be through cooling water;  is the exergy work rate, which is equal to the energetic work rate;  is the mass flow rate;  is specific flow exergy; and  is the exergy destruction (irreversibility) rate. </p > <p > <strong >   </strong > </p > <p > <strong >Results and Discussion </strong > </p > <p >exergy efficiency increased with increasing engine load. This relationship could be attributed to the reason that brake power increased with increasing engine load, and the other side, there was a positive direct relationship between brake power and exergy efficiency, resulting in an increase of exergy efficiency. Although fuel consumption increased along with increasing engine load, increase in the brake power was much greater than increase in the fuel consumption. On the other hand, an increase in the engine load enhanced combustor temperature which was provided an appropriate condition for combustion and caused an increase in cylinder pressure. At all engine operating conditions, with increasing engine speed, the thermal efficiency at first increased, at moderate speed reached to a maximum amount and finally with more increase in engine speed, the thermal efficiency decreased. The initial increase in thermal efficiency could be attributed to the increase in air to fuel ratio and engine torque which caused an increase in the brake power. Decreasing thermal efficiency in high levels of engine speed could be caused by a decrease in volumetric efficiency of the combustion chamber, because of the time limit on filling cylinder. With increasing biodiesel concentration in the fuel blend, exergy efficiency decreased. The reason could be due to the lower calorific value and the higher viscosity of biodiesel compared to diesel fuel. </p > <p > <strong >Conclusions </strong > </p > <p >At all engine operating conditions, the exergy efficiency of the engine increased with increasing engine load also with increasing percentages of biodiesel into synthetic fuel, exergy efficiency increased. 43.09% of the fuel exergy was completely destructed and was not convertible to work. The results of optimization indicated that the most exergy efficiency (37.72%) was occurred for the pure diesel at 2036 rpm and 95% load. </p >