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    A numerical study on the effects of EGR and spark timing to combustion characteristics and NOx emission of a GDI engine
    (Taylor and Francis Inc., 2016) Polat, Seyfi; Uyumaz, Ahmet; Solmaz, Hamit; Yılmaz, Emre; Topgül, Tolga; Yücesu, Hüseyin Serdar
    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. © 2015 © 2015 Taylor & Francis.
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    An experimental investigation on combustion and performance characteristics of supercharged HCCI operation in low compression ratio engine setting
    (Pergamon-Elsevier Science Ltd, 2020) Polat, Seyfi; Yucesu, H. Serdar; Uyumaz, Ahmet; Kannan, Kaushik; Shahbakhti, Mahdi
    This study investigates the effects of boost pressure on combustion and performance of an early direct injection homogenous charge compression ignition (HCCI) engine at a low compression ratio (CR). A 2.0 L, four-cylinder, four-stroke, gasoline direct injection engine was converted to operate in early direct injection HCCI mode. In addition, a supercharger unit was developed for engine boosting. The experiments were performed at different intake manifold absolute pressures (MAP) from 1.0 to 1.6 bar at different engine loads using n-heptane fuel. The effects of boost pressure were investigated on HCCI combustion and engine performance characteristics using volumetric efficiency, in-cylinder pressure, heat release rate (HRR), maximum in-cylinder pressure and gas temperature, CA50 (crank angle by which 50% of the fuel is burnt), combustion duration, apparent combustion efficiency, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), friction mean effective pressure (FMEP), indicated thermal efficiency (ITE), brake thermal efficiency (BTE), heat loss, exergy of heat loss, coefficient of variation of IMEP (COVIMEP), maximum pressure rise rate (MPRR) and ringing intensity (RI). The experimental results showed that high-efficiency HCCI operation is feasible at an engine compression ratio as low as 9.2 once the engine variables are properly optimized and an appropriate level of supercharging is utilized. An increase in indicated thermal efficiency was seen as boost pressure increased. In addition, combustion phasing advanced by increasing boost pressure or increasing air-fuel equivalence ratio values. Combustion events with CA50 2-3 degrees CA aTDC show the highest thermal efficiency especially at low boost pressure conditions. In addition, the pressure rise rate and ringing intensity increased by increasing air-fuel equivalence ratio and MAP. The test results also showed that HCCI operating range can be extended with the increase of intake manifold pressure especially at high load limits.
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    An Experimental Research on the Effects of Negative Valve Overlap on Performance and Operating Range in a Homogeneous Charge Compression Ignition Engine With RON40 and RON60 Fuels
    (Asme, 2020) Polat, Seyfi; Solmaz, Hamit; Uyumaz, Ahmet; Calam, Alper; Yilmaz, Emre; Yucesu, H. Serdar
    In this study, the effects of negative valve overlap (NVO) on homogenous charge compression ignition (HCCI) combustion and engine performance were experimentally investigated. A four stroke, single cylinder, port injection HCCI engine was operated at -16 deg crank angle (CA), -8 deg CA, and +8 deg CA valve overlap values and different lambda values and engine speeds at wide open throttle. RON40 and RON60 were used as test fuels in view of combustion and performance characteristics in HCCI mode. The variations of indicated mean effective pressure (IMEP), residual gas, CA50, indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), maximum pressure rise rate (MPRR) and ringing intensity (RI) were observed on HCCI combustion. The results showed that NVO caused to trap residual gases in the combustion chamber. Hot residual gases showed heating and dilution effect on HCCI combustion. Combustion was retarded with the presence of residual gas at -16 deg CA NVO. Test results showed that higher imep and maximum in-cylinder pressure were obtained with RON60 according to RON40. As expected, CA50 was obtained later with RON60 compared to RON40 due to more resistance of auto-ignition. RON60 residual gas prevented the rapid and sudden combustion due to higher heat capacity of charge mixture. RI decreased with the usage of RON60 compared to RON40. Significant decrease was seen on RI with RON60 especially at lower lambda values. It was seen that HCCI combustion can be controlled with NVO and operating range of HCCI engines can be extended.
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    An experimental study on the effects of diesel and jet-A1 fuel blends on combustion, engine performance and exhaust emissions in a direct injection diesel engine
    (Turkish Society for Thermal Science and Technology, 2016) Solmaz, Hamit; Yamık, Hasan; Uyumaz, Ahmet; Polat, Seyfi; Yılmaz, Emre
    In this study, an experimental investigation was performed in order to determine the effects of Jet-A1(A100), diesel fuel and Jet-A1/diesel fuel blends (A25, A50, A75) including 25% Jet-A1/75% diesel, 50% Jet-A1/50% diesel and 75% Jet- A1/25% diesel by volume respectively on combustion and engine performance in a single cylinder, direct injection diesel engine. For this purpose, the test engine was run at four different brake torques (7.5, 11.25, 15 and 18.75 Nm) at maximum brake torque engine speed (2200 rpm). The variation of cylinder pressure, heat release rate, ignition delay, combustion duration and exhaust emission were investigated in a naturally aspirated direct injection diesel engine fueled with diesel-Jet-A1 fuel blends. The test results showed that ignition delay time decreased with the increase of brake torque. Maximum in-cylinder pressure was retarded versus crank angle with the increase of brake torque. NO x emissions decreased with the increase of amount of Jet-A1 in the test fuels, but CO and soot emissions increased. It was also found that combustion duration increased when Jet-A1 (A100) fuel was used compared to A25, A50, A75 test fuels. In conclusion, Jet-A1 aviation fuel can be utilized via mixing with diesel fuel in diesel engines.
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    Bir dizel motorunun bilgisayar yardımı ile termodinamik ve performans analizi
    (Gazi Üniversitesi, 2013) Polat, Seyfi; Solmaz, Hamit; Yücesu, Hüseyin Serdar; Uyumaz, Ahmet
    Bu çalışmada, dört zamanlı, tek silindirli, normal emişli, direkt püskürtmeli bir dizel motorunun çevrim analizi için MATLAB programında bir simülasyon geliştirilmiştir. Simülasyon sonucunda; tam yükte krank mili açısına bağlı olarak farklı motor hızlarında (1000–4000 d/d), farklı sıkıştırma oranlarında (16,20,24) ve farklı hava fazlalık katsayılarında (1.3,1.5,1.7) silindir basıncı, sıcaklık ve motor performans eğrileri elde edilmiştir. 1.5 hava fazlalık katsayısı değerinde sıkıştırma oranı arttıkça silindir içi basıncın arttığı, ısı dağılımının azaldığı görülmüştür. Sıkıştırma oranı 20 değerinde hava fazlalık katsayısı arttıkça silindir içi basınç ve ısı dağılımının azaldığı görülmüştür. Sıkıştırma oranı ve hava fazlalık katsayısının silindir içi yanma işlemini ve motor performansını etkilediği görülmüştür. Sonuçta, sıkıştırma oranı arttıkçamotor performansının artmış, hava fazlalık katsayısı arttıkça azalmıştır.
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    Combustion and performance characteristics of an HCCI engine utilizing trapped residual gas via reduced valve lift
    (Elsevier Ltd, 2016) Çınar, Can; Uyumaz, Ahmet; Polat, Seyfi; Yılmaz, Emre; Can, Özer; Solmaz, Hamit
    In this study, the effects of residual gas fraction (RGF) on homogeneous charged compression ignition (HCCI) combustion were investigated experimentally. Experiments were performed at different lambda values and constant intake air temperature of 80 °C with the blend of 20% n-heptane and 80% isooctane (PRF80) test fuel. In order to obtain exhaust gas trapping and HCCI operation, two different cam mechanisms, having reduced valve lift, were used. Valve lift values of 5.5 mm (In5.5) and 3.5 mm (In3.5) were used in cam mechanisms. Exhaust valve lift values were 3.5 mm (Ex3.5) for both cam mechanisms. The experimental findings showed that in-cylinder pressure and heat release rate decreased using In5.5-Ex3.5 cam mechanism compared to In3.5-Ex3.5. More residual gases were trapped using In3.5-Ex3.5 cam mechanism. Combustion was also retarded with low lift cams due to more trapped residual gases. Indicated thermal efficiency was found 28.4% with In 3.5-Ex 3.5 whereas obtained 33.57% with In 5.5-Ex 3.5 cam mechanism at 1000 rpm. RGF was computed as 20.12% and 21.12% with In 5.5-Ex 3.5 and In 3.5-Ex 3.5 cam mechanisms, respectively, at 1000 rpm engine speed and stoichiometric air/fuel ratio. Moreover, indicated thermal efficiency was found to be higher about 17.91% with In 5.5-Ex 3.5 according to In 3.5-Ex 3.5 at 1200 rpm. Consequently, it was observed that HCCI combustion phasing can be controlled using low lift cams. It was seen that trapping exhaust gases in the cylinder is a feasible and practical method to control combustion phasing and spread out the HCCI operating range. In addition, stable HCCI combustion can be achieved trapping exhaust gases resulting in avoiding knocking especially at high engine loads. © 2016 Elsevier Ltd. All rights reserved.
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    Doğalgaz yakıtlı HCCI bir motorda hidrojen ilavesinin yanma karakteristikleri üzerindeki etkilerinin nümerik olarak incelenmesi
    (BİLEŞİM Yayıncılık, 2015) Polat, Seyfi; Uyumaz, Ahmet; İpci, Duygu; Yücesu, Hüseyin Serdar; Solmaz, Hamit; Yılmaz, Emre
    Homojen dolgulu sıkıştırma ile ateşlemeli motorlar konvansiyonel içten yanmalı motorlarla karşılaştırıldığında yüksek termik verim, NOx ve is emisyonlarındaki eş zamanlı azalma avantajlarından dolayı yeni bir araştırma alanı olmuştur. HCCI motorlarda kendi kendine tutuşma zamanlaması üzerinde direkt kontrol olmadığından çalışma ve yük aralığı sınırlı kalmaktadır. Yanma işlemini etkileyen en önemli parametrelerden bazıları karışımın kompozisyonu ve yakıtın kimyasal özellikleridir. Bu çalışmada sıkıştırma oranı 10:1 olan doğal emişli, tek silindirli, dört zamanlı, dört supaplı, doğal gaz ile çalışan bir HCCI motorunda hidrojen ilavesinin yanma işlemi üzerindeki etkileri açık kaynak kodlu KIVA-4 yazılımı ile nümerik olarak incelenmiştir. Bu amaçla doğalgaz yakıtının içerisine %0, %10, %20, %30,%40, oranlarında hidrojen ilave edilerek beş farklı yakıt karışımı hazırlanmıştır. Bununla birlikte yanma analizi üç farklı hava fazlalık katsayısı değerinde (?=1.5, ?=2, ?=2.5) gerçekleştirilmiştir. Sonuçta, hidrojen ilavesinin kendi kendine tutuşma zamanlaması, toplam yanma süresi, ısı dağılımı, silindir içi basınç ve silindir içi sıcaklık üzerindeki etkileri araştırılmıştır.
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    Effects of intake air temperature on combustion, performance and emission characteristics of a HCCI engine fueled with the blends of 20% n-heptane and 80% isooctane fuels
    (Elsevier, 2015) Cinar, Can; Uyumaz, Ahmet; Solmaz, Hamit; Sahin, Fatih; Polat, Seyfi; Yilmaz, Emre
    In this study, the effects of intake air temperature on the cylinder pressure, heat release rate, start of combustion, combustion duration, engine performance and exhaust emissions were investigated in a HCCI gasoline engine fueled with the blends of 20% n-heptane and 80% isooctane fuels. Intake air temperature was changed from 40 degrees C to 120 degrees C. The experiments were performed with a single-cylinder, four-stroke HCCI gasoline engine at two different excessive air coefficients at 1200 rpm. The results showed that in-cylinder pressure and heat release rate increased with the increase of intake air temperature. The increase of intake air temperature caused combustion to advance and the combustion duration to decrease. At 70 degrees C intake air temperature, brake torque decreased by 3.1% when the engine operated with lambda = 0.6 compared to lambda = 0.7. The specific fuel consumption and NO emissions tend to increase at higher intake air temperatures of 100 degrees C and 120 degrees C. It was also found that CO and HC emissions firstly increased and then started to decrease after the 90 degrees C intake air temperature. (C) 2014 Elsevier B.V. All rights reserved.
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    Experimental examination of the effects of military aviation fuel JP-8 and biodiesel fuel blends on the engine performance, exhaust emissions and combustion in a direct injection engine
    (Elsevier Science Bv, 2014) Uyumaz, Ahmet; Solmaz, Hamit; Yilmaz, Emre; Yamik, Hasan; Polat, Seyfi
    Biodiesels are the most popular fuels which can be used as an alternative fuel instead of diesel fuel in diesel engines. Low emission characteristics and high cetane numbers are the most significant advantages of biodiesels. However, JP-8 military aviation fuel which is a kerosene based fuel has a low viscosity, high lower heating value and very low freezing point. The usage of the fuel blends of biodiesel and JP-8 may be effective in improving the characteristics of biodiesel. In this study, JP-8 aviation fuel and sunflower methyl ester blends were tested at 7.5, 1125, 15 and 18.75 Nm engine loads and at maximum torque speed (2200 min(-1)) in a single cylinder, naturally aspirated, and direct injection diesel engine. In-cylinder pressure, ignition delay period, engine performance and exhaust emissions have been examined. As the engine load increases the specific fuel consumptions decrease for all test fuels. It was seen that NOx emissions increased with the increase of the amount of biodiesel in the test fuels. CO emissions decreased as the amount of biodiesel fuel increased in the test fuels. Consequently, it was observed that JP-8 and biodiesel fuel mixtures can easily and efficiently be used in diesel engine. (C) 2014 Elsevier B.V. All rights reserved.
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    Investigation of usability of the fusel oil in a single cylinder spark ignition engine
    (Elsevier B.V., 2015) Calam, Alper; Solmaz, Hamit; Uyumaz, Ahmet; Polat, Seyfi; Yılmaz, Emre; Içingür, Yakup
    In order to decrease the dependency on petrol-originated energy resources, the utilization of different energy resources in internal combustion engines has been the center of interest of researchers. The main renewable alternative combustible species are ethanol, methanol, hydrogen, biodiesel, and biogas. On the other hand, appearing as a by-product during alcohol production via fermentation, the fusel oil is another alternative energy resource which can be used in internal combustion engines. Containing high alcohols, fusel oil is dark brown colored alcohol mixture, and has a strong odor. The calorific value of fusel oil close to other alternative combustible types ones and the limited number of researches on utilization of fusel oil, an alcohol derivative, in internal combustion engines constitute the base of this research. In this study, the effects of the mixture of unleaded gasoline and fusel oil on engine torque, brake specific fuel consumption and exhaust emissions in a single cylinder, spark ignition engine having port-type fuel infection system at various engine speeds and loads have been investigated. As a result of research carried out, as the amount of fusel oil in mixture increased, the improvements have been observed in engine torque at all of engine speeds and loads compared to pure unleaded gasoline. It has been determined that the brake specific fuel consumption and carbon monoxide (CO) and hydro-carbon (HC) emissions have increased while nitrogen-oxide (NOx) emissions have decreased. © 2014 Energy Institute. Published by Elsevier Ltd. All rights reserved.
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    Mapping of an HCCI engine using negative valve overlap strategy
    (Taylor and Francis Inc., 2020) Polat, Seyfi; Solmaz, Hamit; Yılmaz, Emre; Calam, Alper; Uyumaz, Ahmet; Yücesu, Hüseyin Serdar
    In order to control combustion phasing and extend operation range of homogeneous charged compression ignition (HCCI) engines, several techniques such as controlling inlet air temperature and pressure, using alternative fuels, variable compression ratio, supercharging, etc. have been applied. Among them, variable valve mechanism received much attention to extend HCCI operating range and control autoignition. Mode switching between spark plug ignition (SI) to HCCI has been started to use widely because of limited operation range of the HCCI mode. To control of an engine switching combustion modes between SI and HCCI, embedded system needs parametrical control maps of the engine. In this study, operation range, air excess ratio, torque and thermal efficiency maps of an HCCI engine using negative valve overlap (NVO) strategy were obtained and additionally the effects of NVO on HCCI combustion in view of in-cylinder temperature, heat release rate, effective thermal efficiency, combustion phasing, and exhaust emissions were investigated. Also, variation of CO, HC, and NOx emissions were evaluated at different valve overlaps. Three different valve overlap including +8, ?8, and ?16 CA were used in the experiments. Test results showed that in-cylinder pressure and heat release decreased with NVO. The test engine could run without knocking by application of NVO. It was seen that operating range of HCCI extended with NVO. It was also found that effective thermal efficiency increased with ?16ºCA valve overlap compared to other valve timings.
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    Reaktif kontrollü sıkıştırma ile ateşlemeli (RCCI) bir motorda lamdanın yanma karakteristiklerine etkileri
    (Afyon Kocatepe Üniversitesi, 2017) Uyumaz, Ahmet; Solmaz, Hamit; Boz, Fahrettin; Yılmaz, Emre; Polat, Seyfi
    Bu çalışmada reaktif kontrollü sıkıştırma ile ateşlemeli (RCCI) bir motorda lamdanın (?) yanma karakteristikleri üzerindeki etkileri deneysel olarak incelenmiştir. Dört zamanlı, dört silindirli benzinli bir motor tam yük şartlarında referans yakıt PRF40 (Primary reference fuel, %40 porttan izooktan, %60 direkt n-heptan) kullanılarak ?=0.83, ?=0.88, ?=1, ?=1.24, ?=1.61 ve ?=2.65 lamda değerlerinde sabit 40°C emme giriş sıcaklığı ve 1000 d/d motor devrinde çalıştırılmıştır. RCCI yanma modunda yanma karakteristikleri, indike termik verim, net iş, kümülatif ısı yayılımı ve özgül yakıt tüketiminin değişimleri incelenmiştir. Deneysel çalışmalar sonucunda karışımın zenginleşmesi ile yanmanın rötara alındığı görülmüştür. Maksimum silindir içi basınç ?=0.83 ile elde edilmiştir. Lamda arttıkça indike termik verimin arttığı, özgül yakıt tüketiminin azaldığı görülmüştür. Maksimum indike termik verim ?=1.61'da %38.36 olarak belirlenmiştir. Karışımın daha da fakirleştirilmesi (?=2.65) termik verimin azalmasına neden olmuştur. Test sonuçları aynı zamanda karışım fakirleştikçe çevrimsel farklılıkların arttığını, maksimum çevrimsel farklılığın ?=2.65 değerinde %5.91 olduğunu göstermiştir. RCCI motorda lamdanın yanma karakteristikleri ve yanma süresi üzerinde kayda değer etkilerinin olduğu görülmüştür
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    The Effects of iso-propanol and n-heptane Fuel Blends on HCCI combustion characteristics and engine performance
    (2015) İpci, Duygu; Yılmaz, Emre; Aksoy, Fatih; Uyumaz, Ahmet; Polat, Seyfi; Solmaz, Hamit
    In this study, the effects of iso-propanol fuel blends were investigated on HCCI combustion and engine performance. The variations of cylinder pressure, heat release rate, start of combustion and engine performance were studied in a single cylinder, four stroke, gasoline HCCI engine. The experiments were conducted at different inlet air temperatures at constant air excessive coefficient (λ=2) and engine speed (1500 rpm). The test results showed that cylinder pressure and heat release rate delayed with the addition of iso-propanol in the test fuels. It was also found that the increase of inlet air temperature causes to advance the combustion. Iso-propanol has higher octane number compared to conventional fuels. However, calorific value of iso-propanol is lower than conventional fuels. The aim of this study is to research the usage of iso-propanol in HCCI engines. The experimental findings showed that the tendency of knocking combustion decreased with the increase of the amount of iso-propanol. The start of combustion was delayed with the increase of the amount of iso-propanol. In addition, combustion duration decreased with the addition of iso-propanol in HCCI combustion. As a result, knocking can be prevented using iso-propanol in HCCI engines. This effect also led to extend the HCCI operating range