Hamit Solmaz

A Comparison of Engine Performance and the Emission of Fusel Oil and Gasoline Mixtures at Different Ignition Timings

Alcohols have been used as a fuel for engines since 19th century. Among the various alcohols, ethanol is known as the most suited renewable, bio-based and ecofriendly fuel for spark-ignition (SI) engines. In addition, ethanol has higher evaporation heat, octane number, and flammability temperature therefore it has positive influence on engine performance and reduces exhaust emissions. In this study, engine performance and emission levels of unleaded gasoline and unleaded gasoline-fusel oil blends in a spark ignition engine, under variable ignition timings are investigated. Engine torque increased and brake specific fuel consumption (bsfc) decreased with the ignition timings. For F0 and F10 blends, hydrocarbon emissions changed by 22% on average and carbon monoxide (CO) emissions changed by 9.2%. It was also observed that nitrogen oxide (NOx) emissions were reduced.

A numerical study on the effects of EGR and spark timing to combustion characteristics and NOx emission of a GDI engine

ABSTRACT EGR is one of the most significant strategies for reducing especially nitrogen oxides (NOx) emissions from internal combustion engines. The thermal efficiency of spark ignition engines is lower than compression ignition engines because of its lower compression ratio. If the compression ratio is increased to obtain higher thermal efficiency, there may be a knocking tendency in spark ignition engines. EGR can be used in order to reduce NOx emissions and avoid knocking phenomena at higher compression ratios. In-cylinder temperature at the end of combustion is decreased and heat capacity of fresh charge is increased when EGR applied. Besides EGR, spark timing is another significant parameter for reducing exhaust emissions such as nitrogen oxides, and unburned hydrocarbon (UHC). In this study the effects of EGR and spark timing on spark ignition engine were investigated numerically. KIVA codes were used in order to model combustion process. The combustion process has been modeled for a single cylinder, four stroke and gasoline direct injection (GDI) spark ignition engine. The results showed that in-cylinder pressure and heat release rate decrease as EGR ratio increase. In-cylinder pressure increases with the advancing of spark timing. Advancing spark timing increases the heat release rate and in-cylinder temperature. The simulation results also showed that EGR reduced exhaust gas temperature and NOx emissions.

DÜŞÜK HIZLI BİR RÜZGAR TÜNELİNDE DEĞİŞİK OTOMOBİL MODELLERİNİN AERODİNAMİK DİRENÇ KATSAYILARININ BELİRLENMESİ

Tasit aerodinamik karakteristiklerinin belirlenmesi icin ruzgar tuneli testlerinden yararlanilmaktadir. Model veprototip arasinda Reynolds sayisi esligi saglanabilmesi icin ya cok yuksek hizli ruzgar tuneli kullanilmasi ya dadaha buyuk model kullanilmasi gerekmektedir. Bu maliyeti arttiran onemli bir faktordur. Daha kucuk olcekli vedaha dusuk ruzgar hizlarinda aerodinamik karakteristiklerin belirlenebilmesi icin Reynolds sayisibagimsizligindan faydalanilabilir. Bu calismada Reynolds sayisi bagimsizligindan faydalanilarak 1/24 olcekli ucotomobilin aerodinamik direnc katsayisi belirlenmeye calisilmistir. Testler maksimum serbest akis hizi 28 m/solan bir ruzgar tuneli ile gerceklestirilmistir. Test sonucunda butun modeller icin Reynolds sayisibagimsizligindan yararlanilamayacagi gorulmustur. BMW X5 E53, Alfa Romeo 156 ve Wolksvagen New Beetleotomobilleri ile yapilan testler sonucu aerodinamik direnc katsayilari sirasiyla % 14, % 12,5 ve % 7,8 hata oraniile bulunmustur.