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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

Large eddy simulation of an ignition wave front in a heavy duty partially premixed combustion engine

2019-08-15
2019-24-0010
In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in an ignition wave-front dominated combustion mode. 3D-CFD modeling of such a combustion mode is challenging as the reaction speed is dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of energetic turbulence scale on the fuel/air mixing and on the propagation of reaction wave. The results are compared with optical experiments to validate both pressure trace and ignition location. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane).
Technical Paper

Intake manifold primary trumpet tuning options for fuel flow limited high performance ICEs

2019-08-15
2019-24-0005
The 2014 change in Formula 1 power units, from naturally aspirated to highly-downsized and heavily-boosted hybridized power units led to a relevant increase of the internal combustion engine brake specific power output in comparison with former V-8 units. The newly designed “down-sized” engines are characterized by a fuel flow limitation and relevant increase in the thermal loads acting on the engine components, in particular on those facing the combustion chamber. Furthermore, efficiency becomes an equivalent paradigm as performance. In the power unit layout, the air path is defined by the compressor, the intercooler and the piping from the intake plenum to the cylinder. Intake duct length is defined from intake plenum to valve seat and it is a key parameter for engine performance.
Technical Paper

CFD analysis and knock prediction within the crevices of piston to liner fireland of a high performance I.C.E.

2019-08-15
2019-24-0006
The paper aims at defining a methodology for the prediction and understanding of knock tendency in internal combustion engine piston crevices by means of CFD simulations. The motivation for the analysis comes from a real design requirement which appeared during the development of a new high performance SI unit: it is in fact widely known that, in high performance engines (especially the turbocharged ones), the high values of pressure and temperature inside the combustion chamber during the engine cycle may cause knocking phenomena. “Standard” knock can be easily recognized by direct observation of the in-cylinder measured pressure trace; it is then possible to undertake proper actions and implement design and control improvements to prevent it with relatively standard 3D-CFD analyses.
Technical Paper

Valve Flow Coefficients under Engine Operation Conditions: Piston Influence and Flow Pulsation

2019-08-15
2019-24-0003
Engine valve flow coefficients are used to describe the flow throughput performance of engine valve/port designs, and to model gas exchange in 0D/1D engine simulation. Valve flow coefficients are normally estimated at a stationary flow test bench, separately for intake and exhaust side, in the absence of the piston. However, engine operation differs from this setup; i. a. the piston might interact with valve flow around scavenging top dead center, and instead of steady boundary conditions, valve flow is nearly always subjected to pressure pulsations, due to pressure wave reflections within the gas exchange ports. In this work the influences of piston position and pressure pulsation on valve flow coefficients are investigated for different SI engine geometries by means of 3D CFD and measurements at an enhanced flow test bench.
Technical Paper

Heavy-Duty Compression-Ignition Engines Retrofitted to Spark-Ignition Operation Fueled with Natural Gas

2019-08-15
2019-24-0030
Natural gas is a promising alternative gaseous fuel due to its availability, economic, and environmental benefits. A solution to increase its use in the heavy-duty transportation sector is to convert existing heavy-duty compression ignition engines to spark-ignition operation by replacing the fuel injector with a spark plug and injecting the natural gas inside the intake manifold. The use of numerical simulations to design and optimize the natural gas combustion in such retrofitted engines can benefit both engine efficiency and emission. However, experimental data of natural gas combustion inside a bowl-in-piston chamber is limited. Consequently, the goal of this study was to provide high-quality experimental data from such a converted engine fueled with methane and operated at steady-state conditions, exploring variations in spark timing, engine speed and equivalence ratio.
Technical Paper

Optimization of Multi Stage Direct Injection-PSCCI Engines

2019-08-15
2019-24-0029
The more stringent regulations on emissions induce the automotive companies to develop new solutions for engine design, including the use of advanced combustion strategies and the employment of mixture of fuels with different thermochemical properties. The HCCI combustion coupled with the partial direct injection of the charge, in order to control the performance and emissions and to extend the operating range, is a promising technique. In this work an in-house developed multi-dimensional CFD software package was used to analyse the behaviour of a multi stage direct injection (DI)-partially stratified charge compression ignition engine fueled with PRF. A skeletal kinetic mechanism for PRF oxidation was employed, with a dynamic adaptive chemistry technique to reduce the computational cost and a model based on the partially stirred reactor model to couple turbulence and chemistry.
Technical Paper

A Review of Spark-Assisted Compression Ignition (SACI) Research in the Context of Realizing a Production SACI Strategy

2019-08-15
2019-24-0027
Low temperature combustion (LTC) strategies have been a keen interest in the automotive industry for over four decades since they offer improved fuel efficiency compared to conventional spark-ignition (SI) engines. LTC strategies use high dilution to keep combustion temperatures below about 2000 K to reduce heat transfer losses while avoiding locally rich in-cylinder regions that produce high soot. High dilution also enables an efficiency improvement from reduced pumping work and improved thermodynamic properties, though it requires high ignition energy. Combustion can be achieved by triggering autoignition from compression energy. High compression ratios are typically required to produce this level of ignition energy, which further improves fuel efficiency. The timing of the autoignition event is influenced by fuel properties and mixture composition, and is exponentially sensitive to temperature.
Technical Paper

HCCI with Wet Ethanol: Investigating the Charge Cooling Effect of a High Latent Heat of Vaporization Fuel.

2019-08-15
2019-24-0024
The combustion phasing of Homogeneous Charge Compression Ignition combustion is incredibly sensitive to intake temperature. Controlling the intake temperature on a cycle-to-cycle basis is one-way control combustion phasing, however accomplishing this with an intake air heater/intercooler is unfeasible. One possible way to control the intake temperature is through the direct injection of fuel. The direct injection of fuel during the intake stroke cools the charge via evaporative cooling. Some heat is absorbed from the incoming air, lowering the in-cylinder temperature, while some heat is absorbed from the piston/cylinder walls if the spray reaches the walls. The amount of heat that is absorbed from the air vs. the walls depends on the injection timing during the intake. Therefore, if a high latent heat of vaporization fuel is used, the intake temperature will become very sensitive to injection timing, allowing for cycle-to-cycle control of combustion phasing.
Technical Paper

Experimental and numerical analysis of a pre-chamber turbulent jet ignition combustion system

2019-08-15
2019-24-0018
The growing demand for more efficient and less polluting internal combustion engine has pushed the development of non-conventional ignition systems. One of the most promising techniques appears to be the so-called Pre-Chamber initiated Turbulent Jet Ignition Combustion system in which a jet of hot combusting gasses is employed to initiate the combustion in the main chamber. In the present study, the combustion process related to this ignition system has been experimentally investigated in an optically accessible single cylinder Spark-Ignition engine. The pre-chamber was composed of a gas injector and a miniaturized spark-plug, embedded in a small annular chamber connected to the cylinder through a 4 holes pipette. A small amount of methane is injected within the pre-chamber for initiating the combustion. The flame reaches the combustion chamber through the four narrow orifices and rapidly consumes a homogeneous mixture of port injected gasoline and air.
Technical Paper

Design and development of a new piston for an off-road Diesel engine with special focus on improvements of the piston cooling jet. Part I: root cause analysis of initial design failure.

2019-08-15
2019-24-0043
Similarly to passenger car engine manufacturers, it is increasingly common for off-road engine manufactures to extend the array of their products increasing the engine BMEP or, in other words, downsizing the engine. This strategy leads to increase the thermos-mechanical stress of the engine components, which therefore need often to be re-designed. Pistons, in particular, are among the most critical components, because high local temperatures strongly reduce their mechanical properties. Therefore, relevant design efforts to ensure increased piston cooling are demanded. This paper, based on a real case occurred during the early development stage of a new Diesel unit, focuses on the criticalities of piston cooling design.
Technical Paper

Biogenous Ethanol: CO2 Savings and Operation in a Dual-Fuel Designed Diesel Engine

2019-08-15
2019-24-0040
The usage of ethanol and two different mixtures of ethanol and gasoline (E85 and E65) was investigated on a modified diesel engine designed to work in a dual-fuel combustion mode with intake manifold alcohol injection. The maximum ratio of alcohol to diesel fuel was limited by irregular combustion phenomena like degrading combustion quality and poor process controllability at low load and knock as well as auto-ignition at high load. With rising alcohol amount, a significant reduction of soot mass and particle number was observed. At some testing points, substituting diesel with ethanol, E65 or E85 led to a reduction of NOx emissions; however, the real benefit concerning the nitrogen oxides was introduced by the mitigation of the soot-NOx trade-off. With regard to the engine efficiency aspect, the results show bidirectional behaviour: at low load points engine efficiency degrades, whereas the process becomes by up to 6 % (rel.) more effective at higher engine loads.
Technical Paper

Design and Development of a new piston for an off-road Diesel engine with special focus on improvements of the piston cooling jet. Part II: design improvements and final validation.

2019-08-15
2019-24-0041
This paper is the conclusion of a joint experimental/simulation effort to improve the effectiveness of piston cooling for a new generation engine for off-road applications. Motivations for the activity were described in the preceding part I of the paper. This part II describes a design improvement process aimed at increasing the effectiveness of piston cooling In particular, steady-state CFD simulations of several piston cooling jet solutions are initially carried out to select the most promising variants, which are then prototyped using 3D printing. Prototypes are tested using a specific hydraulic bench to compare and to validate the CFD analyses. Three design variants are then selected and analysed using a more complex CFD approach involving fully transient Volume of Fluid simulations of the piston gallery.
Technical Paper

Experimental High Temperature Analysis of a Low-Pressure Diesel Spray for DPF Regeneration

2019-08-15
2019-24-0035
In the current automotive scenario, particulate filter technology is mandatory in order to attain emission limits in terms of particulate matter for Diesel engines. Despite DPF is often considered a mature technology, significant issues can derive from the use of the engine fuel injectors to introduce in the exhaust pipe the fuel needed to light on the particulate matter in the filter during its regeneration, primarily the lubricant oil dilution with fuel a consequence of significant spray impact on the cylinder liner. As an alternative, the fuel required to start regeneration can be introduced in the exhaust pipe by an auxiliary low pressure injector spraying in the hot exhaust gas stream. In this conditions, the spray evolution and its possible interaction with the surrounding gas stream are relevant in order to better identify the overall layout of the system, so to have the fuel vaporized at the DPF inlet section.
Technical Paper

Driving Cycle and Elasticity Manoeuvre Simulation of a Small SUV Featuring an Electrically Boosted 1.0 L Gasoline Engine

2019-08-15
2019-24-0070
Nowadays, the increasing trend in low voltage electrification promotes the introduction of electrified powertrain. In this context, electric boosting systems are a promising solution to improve the driveability of heavily downsized gasoline engines. The aim of this work is therefore to evaluate, through numerical simulation, the impact of different (12 V or 48 V) electric superchargers (eSC) on an extremely downsized 1.0 L engine in terms of vehicle performance and fuel consumption over different driving cycles. The virtual test rig developed for the analysis integrates a vehicle model representative of a B-SUV segment car with a 1-D CFD fast-running engine model representative of a 1.0 L state-of-the-art gasoline engine, equipped with a dual boost charging system, featuring an eSC in series with the main turbocharger. Vehicle performances were evaluated in terms of vehicle elasticity manoeuvers and in terms of CO2 emissions for type approval and RDE driving cycles.
Technical Paper

Smart cylinder deactivation strategies to improve fuel economy and pollutant emissions for Diesel-powered applications

2019-08-15
2019-24-0055
Further improvement of the trade-off between CO2- and pollutant emissions is the main motivating factor for the development of new diesel engine concepts, from light-duty car applications via medium-duty commercial vehicles up to large long-haul trucks. The deactivation of one or more cylinders of a light-duty diesel engine during low load operation can be a sophisticated method to improve fuel economy and reduce especially NOx emissions at the same time. Dynamic Skip Fire (DSF) is and advanced cylinder deactivation technology, where the decision to fire or skip singular units of a multi-cylinder engine architecture is taken just prior to each firing opportunity, based on a balanced rankling of multiple input parameters.
Technical Paper

Study of Friction Optimization Potential for Lubrication Circuits of Light-duty Diesel Engines

2019-08-15
2019-24-0056
Over the last two decades, engine research has been mainly focused on reducing fuel consumption in view of compliance with stringent homologation targets and customer expectations. As it is well known, the objective of overall engine efficiency optimization can be achieved only through the improvement of each element of the efficiency chain, of which mechanical constitutes one of the two key pillars (together with thermodynamics). In this framework, the friction reduction for each mechanical subsystems has been one of the most important topics of modern diesel engine development. In particular, the present paper analyzes the lubrication circuit potential as contributor to the mechanical efficiency improvement, by investigating the synergistic impact of oil circuit design, oil viscosity characteristics (including new ultra-low formulations) and thermal management. For this purpose, a combination of theoretical and experimental tools were used.
Technical Paper

Inverted Brayton cycle as an option for waste energy recovery in turbocharged diesel engine

2019-08-15
2019-24-0060
Energy recovery in reciprocating internal combustion engines (ICE) is one of the most investigated options for the reduction of fuel consumption and GHG emissions saving in the transportation sector. In fact, the energy wasted in ICE is greater than that converted in mechanical form. The contribution associated to the exhaust gases is almost one third of the fuel energy, calling for an urgent need to be recovered into mechanical form. An extensive literature is oriented toward this opportunity, strongly oriented to ORC (Organic Rankine Cycle)-based power units. From a thermodynamic point of view, one option, not extensively explored, is certainly represented by the Inverted Brayton Cycle (IBC) concept and by the corresponding components which make possible this recovery.
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