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Technical Paper

Hypersonic flow simulation towards space propulsion geometries

2019-09-16
2019-01-1873
With the actual tendency of space exploration, hypersonic flight have gain a significant relevance, taking the attention of many researchers over the world. This work aims to present a numerical tool to solve hypersonic gas dynamic flows for space propulsion geometries. This will be done by validating the code using two well-known hypersonic test cases, the double cone and the hollow cylinder flare. These test cases are part of NATO Research and Technology Organization Working Group 10 validation of hypersonic flight for laminar viscous-inviscid interactions. During the validation process several important flow features of hypersonic flow are captured and compared with available CFD and numerical data. Special attention is taken to the phenomenon of vibrational excitation of the molecules. Different vibrational non-equilibrium models are used and compared with the available data. The pressure and the heat flux along the surfaces are also analyzed.
Technical Paper

A New Positioning Device Designed for Aircraft Automated Alignment System

2019-09-16
2019-01-1883
Accurate and fast positioning of large aircraft component is of great importance for Automated Alignment System. The Ball joint is a widely-used mechanical device connecting the aircraft component and Automated Alignment System. However, there are some shortcomings for the device in man-machine engineering, such as the entry state of the ball-head still needs to be confirmed by the workers and then switched to the locking state manually. To solve above problems, a new positioning mechanism is present in this paper, which consists of a ball-head and a ball-socket. The new device is equipped with a monocular vision system, in which a calibrated industrial camera is used to collect the images of the ball-head. And then, the 3-D coordinate of the ball-head center is calculated by a designed algorithm, which combines the symmetry of the sphere and the principle of projection transformation, guiding the positioner to capture the ball-head.
Training / Education

Turbocharging Internal Combustion Engines

2019-09-16
The need to control emissions and maintain fuel economy is driving the use of advanced turbocharging technology in both diesel and gasoline engines. As the use of diesel engines in passenger car gasoline and diesel engines increases, a greater focus on advanced turbocharging technology is emerging in an effort to reap the benefits obtained from turbocharging and engine downsizing. This seminar covers the basic concepts of turbocharging of gasoline and diesel engines (light and heavy duty), including turbocharger matching and charge air and EGR cooling, as well as associated controls.
Technical Paper

Effects of Droplet Behaviors on Fuel Adhesion of Flat Wall Impinging Spray injected by a DISI Injector

2019-08-15
2019-24-0034
Owing to the short impingement distance and high injection pressure, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. For better understanding of the mechanisms behind the spray-wall impingement, the fuel spray and adhesion on a flat wall using a mini-sac injector with a single hole was examined. The microscopic characteristics of impinging spray were investigated through Particle Image Analysis (PIA). The droplet size and velocity were compared before and after impingement. The adhered fuel on the wall was measured by Refractive Index Match-ing (RIM). Time-resolved fuel adhesion evolution as well as adhesion mass, area, and thickness were discussed. Moreover, the relationships between droplets behaviors and fuel adhesion on the wall were discussed.
Technical Paper

One-way Coupling Methodology of Nozzle Flow and Spray for a Multi-Hole GDi Injector

2019-08-15
2019-24-0031
With future emission regulations, progressively tighter limitations on particulate number (PN) will be applied on GDi engines. The fuel spray plays an important role on PN formation as it directly affects the homogeneity of air fuel mixture. So detailed investigation of spray characteristics is required. To reduce high prototyping cost and time of making a new injector, a predictive spray model can be used to simulate nozzle flow and spray formation. However, those models are challenging due to the complex and multi-phase phenomena occurring in the combustion chamber, but also because of the different spatial and temporal scales in the different components of the injection systems. This work presents a methodology developed to accurately simulate the spray formation by Discrete Droplet Models (DDM) without experimentally measuring the injector mass flow rate and/or momentum flux. Transient nozzle flow simulations are used instead to define the injection conditions of the spray model.
Technical Paper

Experimental investigation on the use of Argon to improve FMEP determination through motoring method

2019-08-15
2019-24-0141
Mechanical friction is still one of the current topics in internal combustion engine research and development. In the ever increasing challenge of developing more efficient and less polluting engines, friction reduction is of significant importance; whose investigation needs an accurate and reliable measurement technique. The Pressurized Motoring method is one of the techniques used for both friction and heat transfer measurements in internal combustion engines. This method is able to simulate mechanical loading on the engine components similar to the fired conditions. It also allows measurement of friction mean effective pressure (FMEP) with a much smaller uncertainty as opposed to that achieved from a typical firing setup. Despite its advantages, this method of FMEP determination is usually criticized over the fact that the thermal conditions imposed in pressurized motoring are far detached from those seen in fired conditions, hence not able to simulate the complete effects on FMEP.
Technical Paper

Reduction of NOx in a Single Cylinder Diesel Engine Emissions Using Selective Non Catalytic Reduction (SNCR) with In-Cylinder Injection of Aqueous Urea

2019-08-15
2019-24-0144
The subject of this study was the effect of in-cylinder selective non-catalytic reduction (SNCR) of NOx emissions in diesel exhaust gas by means of direct injection of aqueous urea (NH2-CO-NH2) into the combustion chamber. A naturally aspirated single cylinder test engine was modified to accept an electronically controlled secondary common rail injection system to deliver the aqueous urea directly into the cylinder during engine operation. Direct in-cylinder injection was chosen to ensure precise delivery of the reducing agent without the risk of premature reactions. Aqueous urea also works as the primary reducing agent by breaking down into ammonia (NH3) and Cyanuric Acid ((HOCN)3). These compounds serve as the primary reducing agents in the NOx reduction mechanism explored here. The main reduction agent, aqueous urea, was mixed with glycerol (C3H8O3) in an 80-20 ratio by weight with the desire to function as a lubricant for the secondary injector.
Technical Paper

The effect of post injection coupled with extremely high injection pressure on combustion process and emission formation in an off-road diesel engine: a numerical and experimental investigation.

2019-08-15
2019-24-0092
In this paper, a numerical and experimental assessment of post injection potential for soot emissions mitigation in an off-road diesel engine is presented, with the aim of supporting hardware selection and engine calibration processes. As a case study, a prototype off-road 3.4 liters 4-cylinder diesel engine developed by Kohler Engines was selected. In order to comply with Stage V emission standards without a dedicated aftertreatment for NOx, the engine was equipped with a low pressure cooled EGR, allowing high EGR rates (above 30%) even at high load. To enable the exploitation of such high EGR rates with acceptable soot penalties, a two stage turbocharger and an extremely high pressure fuel injection system (up to 3000 bar) were adopted. Moreover, post injections events were also exploited to further mitigate soot emissions with acceptable Brake Specific Fuel Consumption (BSFC) penalties.
Technical Paper

Integrated CFD-Experimental Methodology for the Study of a Dual Fuel Heavy Duty Diesel Engine

2019-08-15
2019-24-0093
This paper deals with the experimental and numerical investigation of a 2.0 litre single cylinder Heavy Duty Diesel Engine fuelled by natural gas and diesel oil in Dual Fuel mode. Due to the gaseous nature of the main fuel and to the high compression ratio of the diesel engine, reduced emissions can be obtained. An experimental study has been carried out at three different load level (25%, 50% and 75% of full engine load). Basing on experimental data, the authors’ methodology is based on the use of one-dimensional and 3-dimensional models. The former is able to perform the whole engine with faster simulations while the latter can study deeply the even more complex phenomena (turbulence, combustion, etc.), due to the presence and to the interaction of the two fuels, which occur in the cylinder for the most interesting operating conditions.
Technical Paper

Development and validation of SI combustion models for natural-gas heavy-duty engines

2019-08-15
2019-24-0096
Flexible, reliable and consistent combustion models are necessary for the improvement of the next generation spark-ignition engines. Different approaches have been proposed and widely applied in the past. However, the complexity of the process involving ignition, laminar flame propagation and transition to turbulent combustion need further investigations. Purpose of this paper is to compare two different approaches describing turbulent flame propagation. The first approach is the one-equation flame wrinkling model by Weller, while the second is the Coherent Flamelet Model (CFM). Ignition is described by a simplified deposition model while the correlation from Herweg and Maly is used for the transition from the laminar to turbulent flame propagation. Validation of the proposed models was performed with experimental data of a natural-gas, heavy duty engine running at different operating conditions.
Technical Paper

PIV and DBI Experimental Characterization of Air flow-Spray Interaction and Soot Formation in a Single Cylinder Optical Diesel Engine using a Real Bowl Geometry Piston

2019-08-15
2019-24-0100
With demanding emissions legislations and the need for higher efficiency, new technologies for compression ignition engines are in development. One of them relies on reducing the heat losses of the engine during the combustion process as well as to devise injection strategies that reduce soot formation. Therefore, it is necessary a better comprehension about the turbulent kinetic energy (TKE) distribution inside the cylinder and how it is affected by the interaction between air flow motion and fuel spray. Furthermore, new diesel engines are characterized by massive decrease of NOx emissions. Therefore, considering the well-known NOx-soot trade-off, it is necessary a better comprehension and overall quantification of soot formation and how the different injection strategies can impact it.
Technical Paper

Ultra-Lean Pre-Chamber Gasoline Engine for Future Hybrid Powertrains

2019-08-15
2019-24-0104
Lean burn gasoline spark-ignition engines can support the reduction of CO2 emissions for future hybrid passenger cars. Very high efficiencies and very low NOx raw emissions can be achieved, if relative air/fuel ratios (lambda) of 2 and above can be reached. The biggest challenge here is to assure a reliable ignition process and to enhance the fuel oxidation in order to achieve a short burn duration and a good stability for the combustion. This article aims at introducing an innovative combustion system fully optimized for ultra-lean operation and very high efficiency. Thereto, a new cylinder head concept has been realized with high peak firing pressure capability and with a low surface-to-volume ratio at high compression ratios. 1D and 3D simulations have been performed to optimize the compression ratio, charge motion and intake valve lift. Numerical calculations also supported the development of the ignition system.
Technical Paper

A Study of Lean Burn Pre-chamber Concept in a Heavy Duty Engine

2019-08-15
2019-24-0107
Due to stringent emission standards, the demand for higher efficiency engines has been unprecedentedly high in recent years. Among several existing combustion modes, pre-chamber initiated combustion emerges to be a potential candidate for high-efficiency engines. Research on the pre-chamber concept exhibit higher indicated efficiency through lean limit extension while maintaining the combustion stability. In this study, different pre-chamber geometries were tested in a single-cylinder heavy-duty engine at different loads. The geometries were prepared with three different pre-chamber volumes and with three varying nozzle area to pre-chamber volume ratios. The pre-chambers were fueled with methane while two sets of experiments were conducted, the first with ethanol as main chamber fuel and the second with methane.
Technical Paper

Numerical and Experimental Investigation into Brake Thermal Efficiency Optimum Heat Release Rate for a Diesel Engine

2019-08-15
2019-24-0109
Although theoretical thermal efficiency is the best with ideal Otto cycle, brake thermal efficiency (BTE) with a diesel engine was projected to be higher with Sabathe (or Seilliger) like cycle than Otto or Diesel like cycle by a zero-dimensional calculation merged empirical energy loss models and mechanical constraints. To pursue the confirmation of the calculated result with the real engine, three injectors (center and two sides) were installed to a cylinder to achieve more degrees of freedom to control heat release rate (HRR) profile. The experimental result was well consistent with the calculated results, namely BTE with Sabathe like cycle was higher than other cycles even though its HRR had less peak and longer duration than ideal. On the other hand, several papers have concluded with a series of numerical simulation parameterized by the DoE technique that the simple delta-shaped HRR is the optimum for BTE under the realistic exhaust emissions’ and/or mechanical constraints.
Technical Paper

Experimental Investigation of Combustion Characteristics in a Heavy-Duty Compression-Ignition Engine Retrofitted to Natural-Gas Spark-Ignition Operation

2019-08-15
2019-24-0124
The conversion of existing diesel engines to natural gas operation can reduce U.S. dependence on petroleum imports and curtail engine-out emissions. Diesel compression ignition engines can be modified to NG spark ignition, by replacing the diesel injector with a NG spark plug and by fumigating NG in the intake manifold, to increase utilization of natural gas heavy-duty transportation sector. As the original diesel piston is maintained during conversion to decrease engine modification cost, the major of this study was to investigate the lean-burn characteristic of natural gas burning in this bowl-in-piston combustion chamber, which can accelerate the introduction of heavy-duty natural gas vehicles. Data analysis from engine experiments that changed spark timing indicated a two-stage combustion process in such retrofitted engines, which is different from traditional spark ignition engines.
Technical Paper

Development of a CFD Solver For Primary Diesel Jet Atomization in FOAM-Extend

2019-08-15
2019-24-0128
High fidelity CFD framework for the simulation of primary atomization of a high pressure diesel jet is presented in this work. The numerical model is based on a second order accurate, polyhedral Finite Volume method implemented in foam-extend, a community driven fork of the OpenFOAM software. A geometric VOF method isoAdvector is used for accurate interface advection, while the Ghost Fluid Method (GFM) is used to handle the discontinuity of the pressure and the pressure gradient at the interface between the two phases: n-dodecane and air in the combustion chamber. The discontinuities are a direct consequence of different densities and viscosities, and surface tension effects between the phases. In order to obtain highly resolved interface while minimizing computational time, an Adaptive Mesh Refinement (AMR) strategy for arbitrary polyhedral cells is employed in order to refine the parts of the mesh near the interface and within the nozzle.
Technical Paper

1D Modeling of Alternative Fuels Spray in a Compression Ignition Engine using Injection Rate Shaping Strategy

2019-08-15
2019-24-0132
The Injection Rate Shaping consists in a novel injection strategy to control air-fuel mixing quality via a suitable variation of injection timing that affects the injection rate profile. This strategy has already provided to be useful to increase combustion efficiency and reduce pollutant emissions in the modern compression ignition engines fed with fossil Diesel fuel. But today’s, the ever more rigorous emission targets are enhancing a search for alternative fuels and/or new blends to replace conventional ones, leading in turn a change in the air-fuel mixture formation. In this work a 1D model aims to investigate the combined effects of both Injection Rate Shaping and alternative fuels on the air-fuel mixture formation in a compression ignition engine. In a first step, a ready-made model for conventional injection strategies has been set up for the Injection Rate Shaping.
Technical Paper

Optical investigation of mixture formation in a small bore DISI engine by laser induced exciplex fluorescence (LIEF)

2019-08-15
2019-24-0133
Legislative and customer demands in terms of fuel consumption and emissions are an enormous challenge for the development of modern combustion engines. Downsizing in combination with turbocharging and direct injection is one way to increase efficiency and therefore meet the requirements. This results in a reduction of the displacement and thus the bore diameter. The application of direct injection with small cylinder dimensions increases the probability of the interaction of liquid fuel with the cylinder walls, which may result in disadvantages concerning especially particulate emissions. This leads to the question which bore diameter is feasible without drawbacks concerning emissions as a result of wall wetting. The emerging trends towards long-stroke engine design and hybridization make the use of small bore diameters in future gasoline engines a realistic scenario.
Technical Paper

Large Eddy Simulations and Tracer-LIF Diagnostics of wall film dynamics in an optically accessible GDI research engine

2019-08-15
2019-24-0131
Large Eddy Simulations (LES) and tracer-based Laser Induced Fluorescence (LIF) measurements have been performed to study the dynamics of fuel wall-films on the piston top of an optically accessible, four-valve pent-roof GDI research engine for a total of eight operating conditions. Starting from a reference point, the systematic variations include changes in engine speed (600; 1,200 and 2,000 RPM) and load (WOT and 500 mbar intake pressure); concerning the fuel path the Start Of Injection (SOI=360°, 390° and 420° CA after gas exchange TDC) as well as the injection pressure (10, 20 and 35 MPa) have been varied. For each condition, 40 experimental images were acquired phase-locked at 10° CA intervals after SOI, providing valuable insights with respect to the wall film dynamics in terms of spatial extent, thickness and temperature.
Technical Paper

CFD modeling and validation of the ECN Spray G experiment under a wide range of operating conditions

2019-08-15
2019-24-0130
The increasing diffusion of gasoline direct injection (GDI) engines requires a more detailed and reliable description of the phenomena occurring during the fuel injection process. Currently, one drawback of GDI engines is represented by the impingement on the piston wall, due to typically adopted hollow-cone fuel sprays, which can lead to high emissions of unburned hydrocarbons and soot formation. Within this context, the extensive validation of multi-dimensional models by means of experimental data represents a fundamental task to accurately predict the physical phenomena characterizing the injected spray. The aim of this work was to simulate with OpenFOAM different operating conditions of the 8-hole, ECN Spray G injector placed into a constant volume vessel. The resulting developments of the jet plumes were assessed, along with the physical effects of injection pressure and wall temperature on the wall impingement phenomenon.
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