بررسي تاثير بازگشت گازهاي خروجي به داخل محفظه‌ي احتراق بر عملكرد موتور اشتعال تراكمي سوخت همگن

Investigation on the influence of exhaust gas recirculation on performanceof Homogeneous Charge Compression Ignition (HCCI) engine

در كار حاضر از يك مدل به‌منظور تجزيه و تحليل عملكرد موتور اشتعال تراكمي سوخت همگن ( ) استفاده شده است. در راستاي اعتباربخشي اين مدل، از نتايج تجربي حاصل از موتور نمونه‌ي با سوخت متان و تزريق سوخت ثانويه‌ي ديزل به داخل سيلندر در استفاده شده است. بررسي ها نشان مي دهد كه تطبيق قابل قبولي بين مدل و نتايج تجربي وجود دارد. نتايج تحقيقات حاكي از آن است كه با افزايش ميزان گازهاي برگشتي به داخل سيلندر، فشار و متوسط دماي داخل سيلندر كاهش مي يابد. با افزايش نيز ميزان توليد كاهش مي يابد. همچنين با افزايش درصد ميزان دوده‌ي توليدشده افزايش مي يابد كه اين عملكرد ناشي از توليد احتراق ناقص است. افزايش موجب كاهش ميزان توليد شده و در همين راستا با افزايش درصد ميزان افزايش مي يابد. در ادامه تغييرات دما، توليدي، و اكسيژن شركت‌كننده در واكنش هاي داخل سيلندر نيز مورد بررسي قرار مي‌گيرد.

Environmental pollution and energy constraints have made engineers research a new method of ignition in the internal combustion engines. Also, the automotive industries are searching to replace SI and CI engines due to the strict regulations of international organizations actives in the field of environment. (HCCI) is a suitable method for combustion in SI and CI engines. The HCCI engine uses a premixed air/fuel mixture that is pressed with high compression ratio. In the research, a CFD model has been used for the analysis of HCCI engine. In order to validate the model, we used the experimental results obtained from Dutez engines with Methane fuel and a secondary fuel injection diesel in 270oCAD position. Investigation showed that concordance between the model and experimental results is acceptable. Maximum cylinder pressure decreases with the increase of EGR. With an increase in EGR percentage, the rate of carbon black increases which it results from the incomplete combustion. Therefore, performance of EGR is acceptable within a certain range. Also, an increase of EGR reduces cylinder temperatures. Incomplete combustion causes a part of the air/fuel mixtures to leave the cylinder without participating in the combustion process. As a result, those parts of the air/fuel mixtures leave the cylinder without producing thermal energy. Increase of EGR rate reduces the amount of heat release due to incomplete combustion, but heat release increases even despite non-combustion. This performance is due to the increase of temperature which, in turn, causes the increase of cylinder density. As a result, heat release is produced even despite non-combustion. It is noteworthy that maximum heat releases occur under non-EGR condition. Change in the heat release rate regarding different EGR rates shows that the combustion occurs in different positions. The increase of EGR greatly reduces NOX emissions. So, EGR system can provide adequate effect on reducing NOX emissions.