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3.
  • Aghaali, Habib, 1981-, et al. (författare)
  • Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines
  • 2013
  • Ingår i: SAE Technical Papers.
  • Konferensbidrag (refereegranskat)abstract
    • A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity.The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine.  λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.In this study, the effects of different λ values and exhaust back-pressure have been investigated on the efficiency of a heavy-duty Diesel engine equipped with a single-stage electric turbocompounding. A one-dimensional gas dynamics model of a turbocharged engine was utilized that was validated against measurements at different load points. Two configurations of turbocompound engine were made. In one configuration an electric turbocharger was used and the amount of fuel was varied with constant intake air pressure. In another configuration the turbocharger turbine and compressor were disconnected to be able to control the turbine speed and the compressor speed independently; then the compressor pressure ratio was varied with constant engine fuelling and the exhaust back-pressure was optimized for each compressor pressure ratio.At each constant turbine efficiency there is a linear relation between the optimum exhaust back-pressure and ideally expanded cylinder pressure until bottom dead center with closed exhaust valves. There is an optimum λ for the turbocharged engine with regard to the fuel consumption. In the turbocompound engine, this will be moved to a richer λ that gives the best total specific fuel consumption; however, the results of this study indicates that turbocompound engine efficiency is relatively insensitive to the air-fuel ratio.
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  • Hadadpour, Ahmad (författare)
  • Spray combustion with multiple-injection in modern engine conditions
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Combustion of fuel in diesel engines emits substances harmful to the environment such as soot. These emissions can be reduced by either in-cylinder treatments or after-treatments. One of the common in-cylinder treatments is multiple-injection, which divides a single fuel injection to multiple smaller injections. There are many open questions on the physical processes of the ignition, combustion and emissions of diesel spray flame with multiple injections. The current PhD project aims at studying these processes using large-eddy simulations (LES) and strives to answer some of the open questions. To develop a fast and robust LES tool for this study, a new method is formulated for spray combustion simulation. This method is developed based on the flamelet-generated manifold (FGM) method and the Eulerian stochastic fields (ESF) method. The new ESF/FGM method relaxes some of the substantial assumptions in conventional FGM, while it still keeps the computational costs at a reasonable level for engineering applications. Additionally in this work, a new reaction progress variable for FGM models is proposed by using local oxygen consumption, and the advantages and limitations of this progress variable are explored. Spray-A from Engine Combustion Network (ECN) which is designed to mimic modern engine conditions is chosen as the baseline case for simulations. In this case, liquid n-dodecane, which is a diesel surrogate, is injected into a high-pressure constant-volume vessel. The comparison of simulation results with experimental measurements shows that the ESF/FGM method with the new progress variable can predict the spray combustion characteristics such as ignition delay time, ignition location, lift-off length, pressure rise and thermochemical structure of the spray flame, accurately. After validation of simulation results against experimental measurements, the new ESF/FGM and other available turbulence-combustion simulation tools are applied to simulate multiple-injection spray combustion. Different multiple-injection strategies are investigated by systematically changing the injection timing. The effects of applying each strategy on the ignition, combustion, mixing and emissions are investigated. The results show that in split-injection and post-injection strategies the major physical reason for reduction of soot is better air entrainment and lower local equivalence ratio. It is shown that increasing the dwell time and retarding it toward the end of injection can enhance this effect. On the contrary, for the pre-injection strategies, shortening the ignition delay time of the main injection reduces its pre-mixing and increases its soot formation. In these strategies, the high-temperature region from the pre-injection combustion can increase soot oxidation of the main injection fuel, only if this region is not cooled down as a result of air entrainment during dwell time. Therefore, in such cases shortening the dwell time decreases net soot emissions.
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6.
  • Munjulury, Raghu Chaitanya, et al. (författare)
  • Knowledge-based future combat aircraft optimization
  • 2016
  • Ingår i: NFFP5/NFFP6. - Bonn : International Council of Aeronautical Sciences (ICAS). ; , s. 273-280
  • Konferensbidrag (refereegranskat)abstract
    • Future combat aircraft inherently conceal all the components internally essentially for stealth reasons. The geometry is optimized for subsonic and supersonic flight area distribution and the components and payload to be fitted inside the aircraft. The basic requirements to accomplish are fuel consumption, mission profile, and military performance. Analytical methods comprise of a quick aerodynamic and structural optimization. The result obtained is then compared with multi-fidelity aero-structural analysis
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7.
  • Gantasala, Sudhakar, et al. (författare)
  • Aeroelastic simulations of wind turbine using 13 DOF rigid beam model
  • 2016
  • Ingår i: Open archives of the 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery. - : Symposia on Rotating Machinery.
  • Konferensbidrag (refereegranskat)abstract
    • The vibration behavior of wind turbine substructures is mainly dominated by their first few vibration modes because wind turbines operate at low rotational speeds. In this study, 13 degrees of freedom (DOF) model of a wind turbine is derived considering fundamental vibration modes of the tower and blades which are modelled as rigid beams with torsional springs attached at their root. Linear equations of motion (EOM) governing the structural behavior of wind turbines are derived by assuming small amplitude vibrations. This model is used to study the coupling between the structural and aerodynamic behavior of NREL 5 MWmodel wind turbine. Aeroelastic natural frequencies of the current model are compared with the results obtained from the finite element model of this wind turbine. Quasi-steady aerodynamic loads are calculated considering wind velocity changes due to height and tower shadow effects. In this study, vibration responses are simulated at various wind velocities. The derived 13 DOF simplified model of the wind turbine enables to simulate the influence ofchange in parameters and operating conditions on vibration behavior with less computational effort. Besides that, the results of the simplified models can be interpreted with much ease.
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8.
  • Shetty, Sandeep (författare)
  • Optimization of Vehicle Structures under Uncertainties
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Advancements in simulation tools and computer power have made it possible to incorporate simulation-based structural optimization in the automotive product development process. However, deterministic optimization without considering uncertainties such as variations in material properties, geometry or loading conditions might result in unreliable optimum designs. In this thesis, the capability of some established approaches to perform design optimization under uncertainties is assessed, and new improved methods are developed. In particular, vehicle structural problems which involve computationally expensive Finite Element (FE) simulations, are addressed.The first paper focuses on the evaluation of robustness, given some variation in input parameters, the capabilities of three well-known metamodels are evaluated. In the second paper, a comparative study of deterministic, reliability-based and robust design optimization approaches is performed. It is found that the overall accuracy of the single-stage (global) metamodels, which are used in the above study, is acceptable for deterministic optimization. However, the accuracy of performance variation prediction (local sensitivity) must be improved. In the third paper, a decoupled reliability-based design optimization (RBDO) approach is presented. In this approach, metamodels are employed for the deterministic optimization only while the uncertainty analysis is performed using FE simulations in order to ensure its accuracy.In the fifth paper, two new sequential sampling strategies are introduced that aim to improve the accuracy of the metamodels efficiently in critical regions. The capabilities of the methods presented are illustrated using analytical examples and a vehicle structural application.It is important to accurately represent physical variations in material properties since these might exert a major influence on the results. In previous work these variations have been treated in a simplified manner and the consequences of these simplifications have been poorly understood. In the fourth paper, the accuracy of several simple methods in representing the real material variation has been studied. It is shown that a scaling of the nominal stress-strain curve based on the Rm scatter is the best choice of the evaluated choices, when limited material data is available.In this thesis work, new pragmatic methods for non-deterministic optimization of large scale vehicle structural problems have been developed. The RBDO methods developed are shown to be flexible, more efficient and reasonably accurate, which enables their implementation in the current automotive product development process.
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9.
  • Hellman, Pasi, et al. (författare)
  • Development of Quality Management Systems : How Have Disruptive Technological Innovations in Quality Management Affected Organizations?
  • 2013
  • Ingår i: Quality Innovation Prosperity. - : Quality Innovation Prosperity. - 1335-1745 .- 1338-984X. ; 17:1, s. 104-119
  • Tidskriftsartikel (refereegranskat)abstract
    • This research investigates the history of quality and development of quality management systems. History of quality is investigated from Hammurabi’s law all the way to today’s reigning quality initiatives including ISO, Six Sigma and Lean manufacturing. In the last chapters the current state of quality management is being examined. The foresight method is also opened up and examined. The Innovator’s dilemma concept, originally presented by Clayton Christensen, is used to analyse how quality management systems have been evolved in the last 100 years. Special emphasis is placed on the US manufacturing in the 1970s and 1980s. Based on the literature, the concept of Innovator’s dilemma and the fall of US manufacturing are merged. The result is a prime example that the Innovator’s Dilemma is a universal phenomenon. The industry leader is trying to maintain its position and do everything right but still it is destined to fail. The causes and effects are being discussed in later chapters.
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10.
  • Hermans, Johanna, et al. (författare)
  • Quality management in the new product development : A PPAP approach
  • 2013
  • Ingår i: Quality Innovation Prosperity. - : Quality Innovation Prosperity. - 1335-1745 .- 1338-984X. ; 17:2, s. 37-51
  • Tidskriftsartikel (refereegranskat)abstract
    • The purpose of this paper is to test Production Part Approval Process (PPAP) as a tool to build quality into the new product and processes and ensure that it meets the customer expectations. Research method is qualitative method using so called case-study to study the suitability of PPAP as a tool for quality management by building quality right into the new product and process. The case studies have been made with three different kinds of companies. PPAP is suitable tool for quality management in NPD processes when taking into account many requirements about personnel, processes, documentation etc. The paper has some limitations such as limited sample size. The results are encouraging managers to use PPAP as a tool for managing their company’s product development processes, quality work and supply chain partnerships. The manner in which the stakeholders could use to facilitate a sense of partnerships or co-workers aiming the same goals rather than have a traditional customer-seller relationship was valued in this study.
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