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GÜL, MEHMET ZAFER

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Mühendislik Fakültesi

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GÜL

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MEHMET ZAFER

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Now showing 1 - 9 of 9

Open Access
A validation methodology for urea spray on selective catalytic reduction systems
(2022-06-01) GÜL, MEHMET ZAFER; Savci I. H., GÜL M. Z., Sener R.
Selective catalytic reduction (SCR) is an emission control method that reduces the NOx emission using urea sprays as ammonia precursors for exhaust after-treatment systems. The urea injection system is an essential component of the SCR systems. A comprehensive SCR modeling approach is required to design compact after-treatment systems that meet the NOx emission legislation level. In this study, the characteristics of urea spray injectors of the SCR system were investigated using computational fluid dynamics (CFD) and the particle image velocimetry (PIV) technique. A validation strategy was developed to model the urea spray evaporation, liquid/wall contact, and formation of solid urea deposits. The sheet atomization model was modified to improve the performance of the CFD model. While the Rosin-rammler method predicted the results of 10% according to the experimental results, the proposed tabular method decreased the difference by 3%. In addition, 500 parcels were determined as an optimum number of parcels for urea spray according to the sensitivity study. Therefore, the validation methodology was proposed to predict more consistent results for urea spray modeling and the formation of solid urea deposits.
Open Access
Compressed Biogas-Diesel Dual-Fuel Engine Optimization Study for Ultralow Emission
(SAGE PUBLICATIONS LTD, 2014-01-01) GÜL, MEHMET ZAFER; Koten, Hasan; Yilmaz, Mustafa; Gul, M. Zafer
The aim of this study is to find out the optimum operating conditions in a diesel engine fueled with compressed biogas (CBG) and pilot diesel dual-fuel. One-dimensional (1D) and three-dimensional (3D) computational fluid dynamics (CFD) code and multiobjective optimization code were employed to investigate the influence of CBG-diesel dual-fuel combustion performance and exhaust emissions on a diesel engine. In this paper, 1D engine code and multiobjective optimization code were coupled and evaluated about 15000 cases to define the proper boundary conditions. In addition, selected single diesel fuel (dodecane) and dual-fuel (CBG-diesel) combustion modes were modeled to compare the engine performances and exhaust emission characteristics by using CFD code under various operating conditions. In optimization study, start of pilot diesel fuel injection, CBG-diesel flow rate, and engine speed were optimized and selected cases were compared using CFD code. CBG and diesel fuels were defined as leading reactants using user defined code. The results showed that significantly lower NOx emissions were emitted under dual-fuel operation for all cases compared to single-fuel mode at all engine load conditions.
Open Access
Effect of air pressure on nanofiber production in solution blowing method
(GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2020-07-21) EKİCİ, BÜLENT; Polat, Yusuf; Yangaz, Murat Umut; Calisir, Mehmet Durmus; Gul, Mehmet Zafer; Demir, Ali; Ekici, Bulent; Kilic, Ali
In this study, effect of air pressure on nanofiber diameter and morphology was studied for solution blowing technique. A computational fluid dynamics (CFD) analysis was realized via ANSYS (R) Fluent software, and the results were compared with experimental solutions. The results showed that an increase in air inlet pressure from 100 kPa to 300 kPa has significant effect on nanofiber diameter and morphology. In contrast, as the air inlet pressure increases above 300 kPa to 600 kPa, both nanofiber diameter increases, and the fiber agglomerations are observed due to high turbulence intensity. The droplets were observed at 100 kPa air inlet pressure due to low driving force applied to the polymer solution. The effects of air pressure on nanofiber diameter and morphology have been investigated by using finite volume method, and the results are compared with the experimental results.
Open Access
A methodology to assess mixer performance for selective catalyst reduction application in hot air gas burner
(2022-09-01) GÜL, MEHMET ZAFER; Savci I. H., Gul M. Z.
The active SCR aftertreatment system is one of the most crucial technology for the NOx reduction of diesel engines. One of the essential parameters of this technology is the urea spray performance on the catalyst.This study presents an experimental and numerical investigation of urea spray behavior used in the heavy-duty diesel engine\"s selective catalytic reduction (SCR) aftertreatment systems. The custom test rig is designed and built to simulate exhaust aftertreatment systems of heavyduty diesel vehicles. Urea injector parameters were observed in this test rig with optic windows for spray and flow visualization. This test rig is available to simulate diesel engines in the sense of exhaust mass flow rate, temperature and spray control unit. The discussion is made about the effects of droplet size of spray and velocity distribution upon flow characterization.A detailed assessment of the numerical model was presented, and validation was carried out for different interest measurement locations. The predicted droplet size distributions, breakup performance, and velocities are numerically and correlated with the experimental data. The validated model is subsequently used to study the urea-flow mixing dynamics to develop a urea mixer numerically. Test results show that smaller droplets enhance the mixing and thus catalyst efficiency. Mixer design performance can be assessed numerically in the droplet size break up based on the developed criteria called mixer performance criteria. Upstream and downstream of the mixer, droplet size can be extracted from the simulation, and different mixer designs can be compared in terms of the breakup performance.(c) 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
Open Access
ADVANCED NUMERICAL AND EXPERIMENTAL STUDIES ON CI ENGINE EMISSIONS
(YILDIZ TECHNICAL UNIV, 2018-06-14) GÜL, MEHMET ZAFER; Gul, M. Z.; Koten, H.; Yilmaz, M.; Savci, I. H.
In these studies, three important works examined to get ultra-low emission for a single cylinder diesel engine. The first study was performed for single fuel and compression ratio (CR), intake and exhaust valve timings, mass flow rate were optimized for a range of engine speed. Then for the same engine injection parameters such as start of injection (SOI), injector cone angle, and split injection structures were examined to get optimum parameters for the diesel engine. In CR studies, different combustion chambers were tested according to injector cone angles and fuel-wall interaction. In the second study, in addition to the above studies, dual fuel compressed biogas (CBG) and diesel combustion were analyzed under different engine loads both experimentally and computationally. Optimized single fuel diesel cases were compared with CBG + Diesel dual fuel cases which employed port injection for CBG fuel. In dual fuel engine applications, CBG fuel and air mixture is induced from intake port and this air-fuel mixture is ignited by pilot diesel fuel near top dead center (TDC). In dual fuel engine mode, exhaust emissions reduced considerably especially in NOx and particulate matter (PM) because of methane (CH4) rate and optimized engine parameters. The third study is focused on aftertreatment systems to minimize residual exhaust emissions. The emissions of the diesel engines consist of various harmful exhaust gases such as carbon monoxide (CO), particulate matter (PM), hydrocarbon (HC), and nitrogen oxides (NOx). Several technologies have been developed to reduce diesel emissions especially NOx reduction systems in last decades. The most promising NOx emission reduction technologies are exhaust gas recirculation (EGR) system to reduce peak cylinder temperature that reduces NOx form caused by combustion and active selective catalyst reduction (SCR) system using reducing agent such as urea-water-solution for exhaust aftertreatment system. In this study, computational fluid dynamic (CFD) methodology was developed with conjugate heat transfer, spray, deposit and chemical reaction modeling then emission prediction tool was developed based on the CFD results with deposit prediction mechanism. CFD and deposit results were correlated with image processing tool in flow test bench.
Open Access
Internal combustion engine heat release calculation using single-zone and CFD 3D numerical models
(SPRINGER HEIDELBERG, 2018-06) GÜL, MEHMET ZAFER; Mauro, S.; Sener, R.; Gul, M. Z.; Lanzafame, R.; Messina, M.; Brusca, S.
The present study deals with a comparative evaluation of a single-zone (SZ) thermodynamic model and a 3D computational fluid dynamics (CFD) model for heat release calculation in internal combustion engines. The first law, SZ, model is based on the first law of thermodynamics. This model is characterized by a very simplified modeling of the combustion phenomenon allowing for a great simplicity in the mathematical formulation and very low computational time. The CFD 3D models, instead, are able to solve the chemistry of the combustion process, the interaction between turbulence and flame propagation, the heat exchange with walls and the dissociation and re-association of chemical species. They provide a high spatial resolution of the combustion chamber as well. Nevertheless, the computation requirements of CFD models are enormously larger than the SZ techniques. However, the SZ model needs accurate experimental in-cylinder pressure data for initializing the heat release calculation. Therefore, the main objective of an SZ model is to evaluate the heat release, which is very difficult to measure in experiments, starting from the knowledge of the in-cylinder pressure data. Nevertheless, the great simplicity of the SZ numerical formulation has a margin of uncertainty which cannot be known a priori. The objective of this paper was, therefore, to evaluate the level of accuracy and reliability of the SZ model comparing the results with those obtained with a CFD 3D model. The CFD model was developed and validated using cooperative fuel research (CFR) engine experimental in-cylinder pressure data. The CFR engine was fueled with 2,2,4-trimethylpentane, at a rotational speed of 600 r/min, an equivalence ratio equal to 1 and a volumetric compression ratio of 5.8. The analysis demonstrates that, considering the simplicity and speed of the SZ model, the heat release calculation is sufficiently accurate and thus can be used for a first investigation of the combustion process.
Open Access
Zero-dimensional modelling of a four-cylinder turbocharged diesel engine with variable compression ratio and its effects on emissions
(SPRINGER INTERNATIONAL PUBLISHING AG, 2019-10) GÜL, MEHMET ZAFER; Khan, Daniyal; Gul, M. Zafer
With emission legislation becoming ever more stringent, declining fossil resources and an increase in greenhouse effect caused by CO2 emissions, manufacturers are exploring new ways to match the emissions regulations without compromising on the performance of the engine. This study included development of zero-dimensional model of a 2.0 L turbocharged diesel engine and then study the effects of changing its compression ratio in the numerical model. This paper gave a framework in determining the effect of compression ratios in different operational conditions of the engine. Implementation of variable compression ratio technology on a numerical model proved to be very cost-effective, time saving and validated the fact that numerical models can be used to study different parameters of the engines during the development stage. The main effect of an increase in compression ratio, was found to be as expected, a decrease in brake specific fuel consumption and an increase in thermal efficiency with a greater impact at low rpm-low load regions. Assuming, that the variable compression ratio technology can be utilized in the engine, this work found the best combination of compression ratios around the engine map, giving a best fit of trade-offs between the emissions and performance of the engine. This study also validates the fact that variable compression ratio technology, if implemented in the engine could not only reduce emissions of the engine but can be given as an option to the end-user to switch to more economic fuel consumption values during idling or cruising at long distant journeys.
Open Access
PERFORMANCE MAP MEASUREMENT, ZERO-DIMENSIONAL MODELLING & VIBRATION ANALYSIS OF A SINGLE CYLINDER DIESEL ENGINE
(YILDIZ TECHNICAL UNIV, 2017-07-21) GÜL, MEHMET ZAFER; Khan, D.; Gul, Z.
Single Cylinder Diesel Engines are simple and very economical in manufacturing. Their multipurpose usability and the capability to deliver the maximum power possible within a given envelope makes them very demanding engines in the market. Simulation tools are widely used nowadays to minimize the energy and time needed for a real engine design and development. Zero-dimensional models are very suitable and reliable to observe the engine operation under different conditions. Contrary to the previous studies, this paper presents a comparison between the practical and simulation model data of a single cylinder Diesel Engine. The purpose of this research was to investigate the fundamental variations between the simulation and experimental results with the help of characteristic engine performance maps. Experiments were conducted on a practical 1.16 L Diesel Engine under variable conditions which were then repeated on the simulation model to analyze and evaluate the differences between the obtained results. Zero-dimensional modelling was performed using GT-Power, a powerful commercial engine simulation software. This study also involved the prediction of optimum speed (RPM) of the engine by performing a vibration analysis using a wireless accelerometer. The maximum torque of the 1.16 L Erin Engine is given to be 80 Nm @ 1,800 RPM, while the simulation model indicated it to be 78 Nm at the same RPM value. Likewise, maximum power output was indicated to be 18 kW @ 2,400 RPM, while the experimental results showed it to be 15 kW @ 2,400 RPM. These results laid down a liable basis for the prediction of several operating parameters of the engine which could act as a solid rung for further studies on this subject.
Open Access
A Two-Time-Scale Turbulence Model and Its Application in Free Shear Flows
(2024-02-01) GÜL, MEHMET ZAFER; YANGAZ, MURAT UMUT; GÜL M. Z., YANGAZ M. U., Sen S.
A novel three-equation turbulence model has been proposed as a potential solution to overcome some of the issues related to the k–ε models of turbulence. A number of turbulence models found in the literature designed for compressed turbulence within internal combustion engine cylinders tend to exhibit limitations when applied to turbulent shear flows, such as those occurring through intake or exhaust valves of the engine. In the event that the flow is out of equilibrium where Pk deviates from ε, the turbulence models require a separate turbulence time-scale determiner along with the dissipation, ε. In the current research, this is accomplished by resolving an additional equation that accounts for turbulence time scale, τ. After presenting the rationale behind the model, its application to three types of free shear flows were given. It has been shown that the three-equation k–ε–τ model outperforms the standard k–ε model as well as a number of two-equation models in these flows. Initially, the k–ε–τ model handles the issue of the plane jet/round jet anomaly in an effective manner. Secondly, it outperforms the two-equation models in predicting the flow behavior in the case of plane wake, one that is distinguished by its weak shear form.