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Öğe CFD-based investigation of the effectiveness of a novel longitudinal ventilation concept in tunnels(Avestia Publishing, 2017) Altay, Merve; Sürmen, Ali[No abstract available]Öğe Combustion characteristics and performance of a Wankel engine for unmanned aerial vehicles at various altitudes(Elsevier Ltd, 2024) Kucuk, Merve; Sürmen, Ali; Şener, RamazanThis study investigates the effects of altitude on the combustion, emissions, and performance of a Wankel engine for unmanned aerial vehicles (UAVs). The main motivation behind the presented study is to contribute to the Wankel engine designs used as a power source in UAVs by revealing the operating conditions at various altitudes. For these purposes, a gasoline fueled Wankel engine was simulated at sea level conditions for different equivalence ratios and results were validated with their experimental counterparts. Then, CFD simulations were carried out at various altitudes (6000 ft, 10,000 ft, and 15,000 ft). The simulation results show that decreasing ambient air temperature, and pressure at higher altitudes reduces the fresh charge density, hence combustion efficiency and heat release rate (HRR). As a result, the performance characteristics such as the indicated mean effective pressure (IMEP), the indicated torque, and indicated power decrease and exhaust emissions increase. For 6000 rpm, IMEP decreases by 39.11%, 53.79%, and 69.22%, and the indicated power reduces by 35.51%, 52.47%, and 65.05% at the altitudes of 6000 ft, 10,000 ft, and 15,000 ft, respectively, compared to those obtained at the sea level conditions. As for exhaust emissions, CO and CO2 are lowest at sea level conditions and increase with altitude. © 2023 Elsevier LtdÖğe Development of a variable-profile cam to enhance the volumetric efficiency of IC engines(INDERSCIENCE ENTERPRISES LTD, 2017) Sürmen, Ali; Arslan, Ridvan; Kopmaz, Osman; Avci, Atakan; Karagoz, Irfan; Karamangil, M. IhsanIn this study, it is aimed to develop a new concept camshaft for continuously variable valve timing (CVVT). The concept is based on obtaining a curvilinear cam surface by integrating a number of conventional cam contours. Thirteen unworked camshafts, with arbitrary different contours, i. e., valve opening and closing times, were machined and tested on a fourstroke single-cylinder diesel engine to determine their volumetric efficiency at varied engine speeds. Then with suitable axial arrangement of these individual contours on a camshaft and integration of them, a single curvilinear cam surface was obtained. It is expected to get the same volumetric efficiency, with a ball contact follower when it follows a specific contour, as obtained when the specific cam of the same contour individually yielded. By giving an axial motion to the camshaft, allowing the follower to follow different contours, continuous variation of valve timing will be achieved.Öğe Effect of the relative positions of vehicular blockage on the smoke flow behaviour in a scaled tunnel(Elsevier Sci Ltd, 2019) Altay, Merve; Sürmen, AliVentilation is an efficient method to keep the fire induced smoke dispersion under control in tunnel fires. Critical ventilation velocity (Uc), defined as the minimum longitudinal velocity to prevent smoke back flow from the fire source in tunnels, plays a vital role to provide safe conditions in the event of a tunnel fire. Although, it is one of the most remarkable and well-studied parameters for tunnel fire ventilation system design, there are some conflicts about the changing pattern of Uc and the ventilation flow characteristics in the presence of a vehicular blockage in tunnel fires between researchers. The main purposes of this study are to investigate numerically the effects of vehicular blockages, located in the upstream and downstream of the fire source, on the smoke spread and the back layering length and also to estimate the critical ventilation velocity in the presence of a vehicular blockage in tunnel fires. In addition, the review of the related studies and the elimination of the conflicts between the researchers on this issue are some important objectives of this study. Simulations of this study show that the presence of a vehicular blockage in tunnel fire cases make considerable changes on smoke flow pattern and critical ventilation velocity. Current knowledge in the related literature and this study have been assessed and some estimates have been made about the parameters leading these changes on the ventilation conditions.Öğe Effectiveness of hydrogen enrichment strategy for Wankel engines in unmanned aerial vehicle applications at various altitudes(Elsevier Ltd, 2024) Kucuk, Merve; Şener, Ramazan; Sürmen, AliThis study investigates the effectiveness of the hydrogen-enrichment strategy on a Wankel engine for unmanned aerial vehicles (UAVs). The primary motivation behind this study is to contribute to the Wankel-type rotary engine designs by revealing the influences of the hydrogen enrichment method on the Wankel engine performance at various altitudes. To achieve these objectives, CFD simulations were conducted by applying a hydrogen enrichment method to a neat gasoline Wankel engine model at sea level, 5000 ft and 15,000 ft altitudes. The hydrogen energy fraction at the intake was gradually increased from 0% to 10%. The decrease in ambient air temperature, pressure, density, and insufficient fresh charge with the increase in altitude leads to the reduced reference chamber temperature and pressure of the Wankel engine. Thus, the combustion worsens, the heat release rate (HRR) and performance decrease, also emissions deteriorate in these colder operating conditions. On the other hand, the unique physicochemical properties of hydrogen such as wide flammability limits, high homogeneity, relatively small quenching distance and high flame speed allow hydrogen-enriched mixture flames to propagate toward the narrower gaps in the combustion chamber and make up for some drawbacks of Wankel engines. As a result, flame propagation is accelerated and fuel burning rate, peak pressure and temperature values in the reference chamber are increased by hydrogen addition. For the cases at sea level with 5% and 10% hydrogen energy fraction, IMEP is increased by 6.59%, 8.50%, and the indicated power is increased by 35.51% and 52.47%. In the cases with the same energy fraction at 15,000 ft, IMEP is increased by 26.61% and 48.75%, and the indicated power is reduced by 26.61% and 48.75%, respectively. It has been proven that a small amount of hydrogen by energy fraction improves combustion efficiency and performance. The findings show that hydrogen has excellent compatibility with Wankel engines and hydrogen enrichment is a very practical concept for the improvement of the performance of these engines for UAVs. Thus, Wankel engines, which are already a very favorable power source for UAVs, become even more favorable by the hydrogen-blending strategy. © 2023 Hydrogen Energy Publications LLCÖğe Enhancing the heavy load performance of a gasoline engine converted for LPG use by modifying the ignition timings(PERGAMON-ELSEVIER SCIENCE LTD, 2015) Erkus, Baris; Karamangil, M. Ihsan; Sürmen, AliThis paper presents the results of the experiments conducted on a spark-ignition (SI) engine fuelled with liquefied petroleum gas (LPG) by varying the ignition timing at the excess air coefficients of 1.0 and 1.3. Experiments were carried out at wide open throttle (WOT) position and at engine speed of 4300 rpm aiming to determine the lean operation performance of an engine when fuelled with LPG at full load. Performance parameters, namely brake power, brake-specific fuel consumption (BSFC), brake thermal efficiency and exhaust emissions such as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx), were studied. It was shown that advancing the ignition timing improved the performance of LPG-fuelled SI engine for excess air coefficients higher than 0.8. The highest brake power and the lowest BSFC were obtained with modified ignition timing at an excess air coefficient of 1.0. The lowest exhaust emissions were obtained with an excess air coefficient of 1.3. In general, advancing the ignition timings caused increase in HC and NO emissions, while the effect of ignition timing on CO emissions was negligible.Öğe Experimental investigation of performance and emission improvement by altering ignition timing with use of E10 ethanol blend in SI engine(Elsevier, 2013) Karamangil, Mehmet İhsan; Turkoz, N.; Erkus, B.; Sürmen, AliIn this study, the best ignition timing for an SI engine with the use of E10 ethanol blend was experimentally investigated. Ignition timing was retarded successively by 2 degrees up to 6 degrees at most (denoted as -2, -4 and -6 respectively) and then advanced by 2 degrees successively up to 6 degrees (denoted as +2, +4 and +6 respectively) with respect to the advance values realised with gasoline (termed as 'original advance values') at full load operation. It was generally observed that overall efficiency increases with advanced ignitions. The best performance and emissions were obtained with +4. This increase amounts to 6% for 4 degrees advanced ignition at 3000 rev min(-1). Advanced ignition timing resulted with increase in NOx emissions, while CO and CO2 remained relatively unaffected. Increasing retard in ignition timing caused poorer combustion and hence more fuel consumption but less hydrocarbon emissions.Öğe Experimental investigation of the effect of E85 on engine performance and emissions under various ignition timings(Elsevier Ltd, 2014) Türköz, Necati; Erkuş, Bariş; Karamangil, M. Ihsan; Sürmen, Ali; Arslanoǧlu, NurullahIn this study, we experimentally investigated the best ignition timing in an SI engine using an E85 ethanol blend by altering the timing angle with respect to gasoline use regarding the output performance parameters such as power and efficiency. We also determined the energy distribution of the engine. The experiments were carried out on a 4-stroke, 4-cylinder spark ignition engine, and the excess air coefficients were almost all maintained at approximately unity. To achieve this, the fuel orifice holes of the carburettor were suitably enlarged for the E85 ethanol blend. The ignition timing was successively delayed in 2° increments up to 6° (denoted as -2, -4, -6, respectively) and then successively advanced by 2° up to 6° (denoted as +2, +4, +6, respectively) with respect to the advance values used with gasoline (called the "original advance values") at full load operation. The best performance and emissions were obtained with +4. Advanced ignition timing resulted in an increase in NOx emissions, while CO and CO2 remained relatively unaffected. Increasing the delay in ignition timing caused poorer combustion and hence more HC emissions and fuel consumption.Öğe MATHEMATICAL MODELING OF HC EMISSIONS RELEASED by OIL FILM for GASOLINE and GASEOUS FUELS(Gazi Universitesi, 2014) Karamangil, M. Ihsan; Yenice, Seckin; Kaynakli, Omer; Sürmen, AliOil film on cylinder liner has been suggested as a major source of engine-out hydrocarbon emissions. In this study, a mathematical modeling for the rate of absorption/desorption of the fuel in the oil film has been developed for gasoline, LPG and methane. It was seen that the absorption/desorption mechanism of LPG and methane into the oil film were lower than gasoline. It was determined that the most dominant parameter of this difference was Henry's constant, which was related to solubility. As interaction time of oil film-fuel vapor was longer at low engine speeds, the quantities of HC absorbed/desorbed increased. The quantities of HC absorbed/desorbed increased with increasing inlet pressure and compression ratio.Öğe Mathematical modeling of hydrocarbon emissions from oil film for different fuels(Elsevier, 2014) Karamangil, M. Ihsan; Sürmen, Ali; Yenice, SeckinOil film on the inner surface of the cylinder liner is one of the major sources of the vehicle-out HC emissions as fuel vapor is absorbed by the oil film under high pressure and then released after late expansion stroke when the pressure is low. This process is extensively affected by type of the fuel and lubricating oil. In this theoretical study, the effect of different engine parameters on oil film HC emissions for various fuels, such as iso-octane, methanol, ethanol, LPG and methane, is investigated. The results show that fewer HCs are released from the oil film when using gaseous fuels, such as LPG and methane, than when using liquid fuels. The fuels can be ranked according to their effect (from greatest to least) on HC emissions as follows: iso-octane, methanol, ethanol, LPG and methane. The most important parameters affecting the HC absorption/release mechanism are found to be Henry's coefficient and the diffusion coefficient. As interaction time of oil film-fuel vapor was longer at low engine speeds, the quantities of HC absorbed/desorbed increased. The quantities of HC absorbed/desorbed increased with increasing inlet pressure and compression ratio.Öğe Modelling and Performance Analysis of an Electric Vehicle Powered by a PEM Fuel Cell on New European Driving Cycle (NEDC)(Springer Science and Business Media Deutschland GmbH, 2021) Işıklı, Fırat; Sürmen, Ali; Gelen, AyetülModelling of a complete polymer electrolyte membrane fuel cell (PEMFC) power systems and performance of the models when subjected to common driving cycle are important research issues. In this study a complete PEMFC system, including air and hydrogen supply equipment, fuel cell stack, electrical system and a 75 kW car, is modelled. An efficiency map of a brand new electric motor is directly imported into the model for it. MATLAB & Simulink tools, based on this mathematical model of PEMFC, are used to establish a dynamic model for a vehicle which is electrically supplied by the fuel cell according to cruise characteristics of New European Driving Cycle (NEDC). Model results show significant instabilities during transient operation regarding the late response of the air supply system. Obtained stack characteristics are similar to those obtained in similar studies conducted previously. Performance results of the car based on energy consumption shows perfect agreement with the results of another model developed for an electric vehicle of the same weight and run also on NEDC.Öğe THE EFFECT OF PRESSURE INCREASE ON DROPLET EVAPORATION IN TWO-PHASE COMBUSTION ENVIRONMENT(Begell House Inc., 2022) Kucuk, Merve; Sürmen, AliThe effects of pressure increase on combustion quality due to the droplet evaporation in dropletladen mixtures have been analyzed with the emphasis on the importance of detailed chemistry. A one-dimensional (1D) code with detailed chemistry and transport has been utilized in order to investigate the evaporation process of fuel droplets of different diameters at a high ambient pressure. Steady-state parametric analyses are performed using n-heptane fuel droplets. It has been found that the initial droplet diameter and the stoichiometry have significant effects on droplet evaporation, thus on flame propagation and combustion quality under high-pressure conditions. The findings regarding the effects of droplet diameter on combustion indicate that evaporation rate of the droplets is directly related to the gaseous fuel mass fraction. Small droplets evaporate before the flame front, but larger droplets cannot complete their evaporation before they reach the flame front, causing a lower gaseous fuel mass fraction. Findings regarding the stoichiometry effects are that the gaseous fuel mass fraction reaches its highest value after the flame front under rich mixture conditions. While the droplets in the lean mixture evaporate completely before the flame front, the droplets in the rich mixture can penetrate towards the flame. Increase in the equivalence ratio and decrease in the droplet diameter increase the evaporation rate and flame spread. It should be noted that this is only a theoretical study on combustion phenomena using detailed chemistry. However, pressure levels used in the analyses are similar to operating pressure of various combustors. For this reason, findings are believed to give researchers insight into the design of many combustors with spray combustion. © 2022 Begell House Inc.. All rights reserved.Öğe WANKEL MOTORUNUN PERFORMANSININ NUMERİK OLARAK İNCELENMESİ(Hakan Serhad SOYHAN, 2021) Altıparmak, Bekir; Altay, Merve; Sürmen, AliKüçük motor hacminden yüksek güç üretimine imkân sağlayan Wankel tipi döner pistonlu motorlar; düşük titreşim, hafiflik, daha az parça sayısı, atalet kuvvetlerinin kolay dengelenebilir olması, gazların geçiş kesitlerinin daha geniş yapılabilmesi gibi özelliklere sahiptirler. Böylece daha yüksek volumetrik verim, vuruntuya daha az bağımlılık ve güç/ağırlık oranının yüksek olması gibi pek çok avantajları sayesinde başta insansız hava araçları, hibrit araç uygulamaları, binek araçlar olmak üzere pek çok uygulama alanında tercih edilmektedir. Bu çalışmada, ilk olarak dört zamanlı Wankel motorunun geometrik hesaplamaları yapılarak motorun katı modeli oluşturulmuştur. Daha sonra, bu veriler kullanılarak GT SUITE yazılımı yardımıyla 1 boyutlu performans analiz yapılmış ve raporlanmıştır. 1 boyutlu performans analizi verilerinin sınır koşulu olarak kullanıldığı Hesaplamalı Akışkanlar Dinamiği (HAD) analizleri ise devam etmektedir. Çalışma tamamlandığında tam yük koşulunda farklı hızlar için moment ve volumetrik verim yönünden karşılaştırılarak çevrim sürecine etki eden parametreler incelenmiş olacaktır.
