Abstract    In the present study, a computational fluid dynamics (CFD) method have been utilized to investigate the effects of exhaust gas recirculation (EGR) and initial charge pressure by means of using a supercharger on the emissions and performance of a SI engine. This engine is fueled separately by gasoline and two potential alternative fuels, hydrogen and ethanol. The results of simulation are compared to the experimental data. There is a good agreement among the results. The calculations are carried out for EGR ratios between 0% and 20% and four cases of initial pressure have been mentioned: Pin= 1, 1.2, 1.4, 1.6 bar. The effect of EGR on NOx emission of hydrogen is more than others while its effect on IMEP of hydrogen is less than others. From the viewpoints of emission and power, 10% of EGR seems to be the most desirable amount. The most noticeable effect of supercharging is on gasoline unlike hydrogen that seems to be affected the least. The comparison of results shows that hydrogen due to its high heating value and burning without producing any carbon-based compounds such as HC, CO and CO2 is an ideal alternative fuel compared to the other fuels.

Keywords    SI engine, hydrogen, alternative fuels, EGR, supercharging, emission

چکیده    در این مطالعه از یک کد دینامیک سیالات محاسباتی برای تحلیل اثر بازخورانی گازهای خروجی (EGR) و همچنین تغییر فشار اولیه ورودی به سیلندر توسط یک سوپرشارژر بر روی عملکرد و آلایندگی یک موتور اشتعال جرقه­ای استفاده شده است. این موتور به طور جداگانه با بنزین و دو سوخت جایگزین بالقوه یعنی هیدروژن و اتانول سوختگیری شده است. به منظور اعتبار سنجی مدل نتایج بدست آمده برای فشار داخل سیلندر و آلایندگی_ها با داده_های تجربی مقایسه شده که تطبیق مناسبی را نشان می_دهد. محاسبات برای دامنه EGR از 0% تا 20% انجام شده است و چهار حالت برای فشار اولیه در نظر گرفته شده است: Pin= 1, 1.2, 1.4, 1.6 bar. اثر EGR بر آلاینده NOx هیدروژن بیش از بقیه سوخت­ها بوده در حالی که اثر آن بر IMEP هیدروژن کمتر از بقیه است. از دیدگاه آلایندگی و قدرت، 10% EGR مطلوب­ترین مقدار می­باشد. بیشترین اثر قابل توجه سوپرشارژ کردن بر روی بنزین می­باشد برخلاف هیدروژن که کمترین اثر را برداشته است. مقایسه نتایج نشان می_دهد که هیدروژن به عنوان یک حامل انرژی پاک با ارزش حرارتی بالا و احتراق بدون تولید محصولاتی از منشا کربن مانند CO2 ، CO و HC توانایی جایگزین شدن با سوخت_های متداول را دارد.

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