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Technical Paper

Effect of Gas Density and Temperature on Air Entrainment in a Transient Diesel Spray

1996-02-01
960862
The air entrainment in a transient diesel spray was studied using laser Doppler anemometry to provide information on the effect of gas density and temperature. The spray was injected vertically into a confined quiescent atmosphere and the entrained mass flow rate was evaluated by measuring the air velocity component normal to a cylindrical geometric surface surrounding the spray, and extending to about 200 nozzle diameters (50 mm). The experimental results, relative to a density range from 0.84 to 7.02 kg/m3 and a temperature range from 293 to 473 K, indicate that the non dimensional entrainment rate, averaged in time over the main injection period, depends on the distance from the nozzle and both gas density and temperature. A first analysis, based on the available data, allowed to quantify the dependence and provided a correlation with such variables.
Technical Paper

Reduction of NOx Emissions of D. I. Diesel Engines by Application of the Miller-System: An Experimental and Numerical Investigation

1996-02-01
960844
Emissions and performance parameters of a medium size, medium speed D.I. diesel engine with increased charge air pressure and reduced but fixed inlet valve opening period have been measured and compared to the standard engine. While power output and fuel consumption are slightly improved, nitric oxide emissions can be reduced by up to 20%. The measurements confirm the results of simulations for both performance and emissions, for which a quasidimensional model including detailed chemistry for nitric oxide prediction has been developed.
Technical Paper

Modeling and Assessment of Machine Tool Dynamics and Accuracy

1997-06-03
972219
Structural dynamics of machine tools causes deviations between the actual and NC programmed tool paths. These deviations, often negligible in traditional cutting, can become the major cause of errors in high speed machining. This paper presents new methods for: (1) model based assessment of the dynamic performance of machine tools, and (2) derivation of analytical models representing the structural dynamics. The assessment is accomplished by combining measurements obtained by means of the Heidenhain Cross Grid and multi-component, wide bandwidth accelerometers. The proposed performance assessment and modeling methods are illustrated by examples obtained for various machines at different feed speeds.
Technical Paper

Model Based Minimization of Dynamic Tool Path Errors

1998-06-02
981842
Minimization of tool path errors in high speed machining necessitates optimal design of machine tools and application of advanced control strategies. Analytical models that accurately represent interactions between the machine tool, workpiece and cutter prove necessary to accomplish these tasks. Two distinctive methods of modeling, suitable for the design of mechanical hardware and advanced control systems, are presented. One of these methods is highly intuitive and allows interactive model building [1]. The other method is more accurate and comprehensive but does not provide easy insight into the model development process and requires advanced software for performing symbolic computations [2]. Together, these methods form the basis of a systematic and stepwise modeling methodology and environment, and provide information needed for optimal design of a wide range of machine tools.
Technical Paper

Combustion Features and Emissions of a DI-Diesel Engine with Air Path Optimization and Common Rail Fuel Injection

1998-08-11
981931
Emission and performance parameters of a medium size, and medium speed D.I. diesel engine equipped with a Miller System, a new developed High Pressure Exhaust Gas Recirculation System (HPEGR), a Common Rail (CR) system and a Turbocharger with Variable Turbine Geometry (VTG) have been measured and compared to the standard engine. While power output, fuel consumption, soot and other emissions are kept constant, nitric oxide emissions could be reduced by 30 to 50% depending on load and for the optimal combination of methods. Heat release rate analysis provides the reasons for the optimised engine behaviour in terms of soot and NOx emissions: The variable Nozzle Turbocharger helps deliver more oxygen to the combustion process (less soot) and lower the peak gas temperature (less NOx).
Technical Paper

Near-Wall Unsteady Premixed Flame Propagation in S.I. Engines

1995-02-01
951001
A computational study of the near-wall premixed flame propagation in homogeneous charge spark ignited engines is presented on the basis of a spectral concept accounting for flow-chemistry interaction in the flamelet regime. Flame surface enhancement due to wrinkling and modification of the local laminar flame speed due to flame stretch are the main phenomena described by the model. A high pass filter in the turbulent kinetic energy spectrum associated with the distance between the ensemble-averaged flame front location and the solid surface has been also introduced. In addition a probability density function of instantaneous flamelet positions around the above mean flame front location allows to consider statistical effects in a simplified way. Issues of temperature distribution within the boundary layer and associated heat losses, except for the concept of a thermal quenching distance, are thereby not explicitly taken into account.
Technical Paper

An Initial Study of Variable Valve Timing Implemented with a Secondary Valve in the Intake Runner

1996-02-01
960590
This paper describes an investigation of implementing variable valve timing with the use of a secondary valve in the intake tract The secondary valve acts in series with the conventional poppet valve of the engine, which is actuated in the conventional manner and with fixed timing It is significantly easier to adjust the timing of the secondary valve than that of the main valve There are two possible modes of operation of this device One is to control valve overlap, improving low speed low load performance The other is to use it as a load control mechanism, replacing the conventional throttle and therefore reducing the ‘pumping losses’ associated with conventional throttling We have implemented such a system on a motored single-cylinder research engine using pneumatic actuation Our experiments have demonstrated successful load control, significant pumping loss reduction, and control of backflow from the exhaust to the intake manifold
Technical Paper

Duty Cycle Operation as a Possibility to Enhance the Fuel Economy of an SI Engine at Part Load

1996-02-01
960229
The potential of Duty Cycle Operation (DCO) of a Spark Ignited (SI) engine on part load has been investigated. DCO keeps an engine running at full throttle in a stop and go mode to speed up a flywheel as a short time energy storage device. So the actual power demand is covered by the flywheel instead of the convenient direct power transfer from the engine. This work includes the calculation of the theoretical potential and preliminary results of a test setup. The results show a clear advantage of fuel consumption at the engine's low power output. The potential of DCO has proved to be higher than that of variable intake valve timing.
Technical Paper

A Computational Investigation of Unsteady Heat Flux Through an I.C. Engine Wall Including Soot Layer Dynamics

1997-02-24
970063
This paper deals with the influence of a wall soot layer of varying thickness on the unsteady heat transfer between the fluid and the engine cylinder wall during a full cycle of a four-stroke Diesel engine operation. For that purpose a computational investigation has been carried out, using a one-dimensional model of a multi-layer solid wall for simulating the transient response within the confinement of the combustion chamber. The soot layer is thereby of varying thickness over time, depending on the relative rates of deposition and oxidation. Deposition is accounted for due to a thermophoretic mechanism, while oxidation is described by means of an Arrhenius type expression. Results of the computations obtained so far show that the substrate wall temperature has a significant effect on the soot layer dynamics and thus on the wall heat flux to the combustion chamber wall.
Technical Paper

Variable Valve Timing Implemented with a Secondary Valve on a Four Cylinder SI Engine

1997-02-24
970335
This paper describes an investigation of a method of implementing VVT with the use of a secondary valve in series with the conventional intake valve of the engine. The secondary valve is not required to withstand the temperatures and pressures of combustion, and therefore can be of relatively lightweight design, so that it is easier to adjust the timing of the secondary valve than that of the main valve. Experiments with such a valve installed in a production engine indicate that benefits of variable valve timing such as overlap optimisation and throttleless load control (4% Fuel benefits at 980 rpm and 1.5 bar IMEP) are attainable with this system.
Technical Paper

Investigation of Flame Speed Models for the Flame Growth Period During Premixed Engine Combustion

1994-03-01
940476
The premixed flame growth period of about 1% of the cylinder mass burned has been theoretically investigated under typical homogeneous charge engine conditions. For this purpose various flame kernel development models have been tested against measured values of flame radius vs. time after ignition in a research engine. The flame kernel growth has been computed on the basis of a zero-dimensional model incorporating spark-induced energy, heat loss to the electrodes and flame curvature effects. Subsequently the transition phase from laminar to fully turbulent flame propagation is shown to depend strongly on the relationship between the turbulent kinetic energy spectrum and characteristic scales of the flame. We thereby make use of recently reported results of fundamental experiments on vortex-flamelet interaction, that yield typical vortex sizes for flame wrinkling and quenching.
Technical Paper

Carbon-and Glass-Fiber Knits for Thermoplastic Composites in Cars

1994-03-01
940615
Knitted high performance fibers as reinforcement are interesting for loaded parts, due to their drapability and the possibility of waste free near net shape production methods. Additionally, a considerable advantage is seen in the coherence of the knit structure, which prevents uncontrolled fiber flow during thermoforming processes and allows strain hardening and strain stiffening during controlled drawing. Compared to common composite manufacturing processes, this may lower costs. The knit structure allows an adjustable anisotropy of the mechanical composite-properties due to its drawability. It has been shown that the rate of drawing and the mechanical anisotropy have a linear correlation. Specific weakening of the fiber-matrix interface revealed a dependence of fiber-matrix adhesion on the failure behavior.
Technical Paper

A New Diagnostic Tool for Fuel Spray Visualization in High Speed Passenger Car DI-Diesel Engines

1995-02-01
950459
Modern electronic engine control systems allow manipulation of many control parameters in order to meet the emissions standards at reasonable fuel consumption. The great number of engine variables lead to very time consuming and expensive studies to determine the optimal combination at each engine operating condition. Compared with the possibilities to control the injection, the quantitative effects of parameter variations on the real processes in a operating combustion chamber and its effects on emissions and fuel consumption are little known. The first part of this paper deals with the problem of optimization of a complex engine control system in a DI-diesel engine. In the second part of this paper a novel optical diagnostic technique is proposed to detect combustion-relevant and controllable parameters such as spray propagation, droplet size and density distribution during injection in a DI-diesel engine combustion chamber.
Technical Paper

Dynamic Tests of Racing Seats and Simulation with Vedyac Code

1998-11-16
983059
Dynamic tests have been performed on carbon fiber racing seats following the FIA regulations. The tests have shown, in rear impact tests, a relatively strong rebound leading to large forward bending of neck, and, in side impact tests, very large lateral displacement of the head, the latter protruding dangerously towards hard portions of the car structure. Stiffening the seat back by steel struts results in reducing strongly both the motion and the acceleration of the head. Simulations of the dynamics of the tests have been done with multi-body models, including the Hybrid III dummy and seat deflection, by means of the program VEDYAC. It has been found that computer simulation can predict very accurately the result of a test, provided the numerical models have been carefully calibrated to match the dummy tolerance bands. Once they have been calibrated and validated with a number of tests, the computer models can be very useful to extend the test results to different test conditions.
Technical Paper

Toothed Couplings for Diesel Engines: An Example of Steel Substitution With Fiber Reinforced Plastics

1996-04-01
91A100
The replacement with plastic of an important component, formerly in steel, in the timing drive of a heavily duty diesel engine has been studied and realized. The substituted part is the toothed coupling connecting the injection pump to the timing drive. Torque that stresses the coupling has been measured with laboratory tests. The tooth stresses have been calculated with FEM analysis. Finally, fatigue tests have been carried out directly on the engine at different loadings. The test results are consistent with the predicted behavior of this component.
Technical Paper

Considerations in Designing a Recovery Steam Generator for Incineration Plants

1992-08-03
929266
The design of recovery steam generators for incineration plants encounters certain specific problems, related to the nature of the exhausted gases, which, if not properly faced, can strongly condition the conduction of the whole system. Two problems, namely, demand for particular attention: the corrosion at high temperature and the formation of organochlorine compounds, in presence of ashes and/or deposits for definite temperature intervals. These phenomena can be controlled and minimized, whenever possible, by limiting to the greatest extent the regions where the temperatures of the metallic walls and of the ashes and/or deposits are within the critical interval.
Technical Paper

Effect of Spray-Wall Interaction on Air Entrainment in a Transient Diesel Spray

1993-03-01
930920
The influence of spray-wall interaction on air entrainment in an unsteady non-evaporating diesel spray was studied using laser Doppler anemometry. The spray was injected into confined quiescent air at ambient pressure and temperature and made to impact on a flat wall. The air velocity component normal to a cylindrical surface surrounding the spray was measured during the entire injection period, allowing to evaluate the time history of the entrained air mass flow rate. The influence of wall distance and spray impingement angle on air entrainment characteristics has been investigated and the results indicate that the presence of a wall increases the entrained mass flow rate in the region close to the surface, during the main injection period. Normal impingement appears to produce stronger effects than oblique incidence at 30 and 45 deg. A qualitative explanation of the results is also proposed, based on the drop-gas momentum exchange mechanism.
Technical Paper

Crash Performance of Rtm Composites for Automotive Applications

1996-04-01
91A120
This paper describes the experimental activity carried out at Aerospace Engineering Department of Politecnico di Milano about energy absorption capability of glass-epoxy RTM specimens, representative of automotive crash front structure sub-components. After the analysis of some automotive crashworthiness aspects, especially relevant to the structural adoption of composite materials, the specimen used and the technological route to produce them are described. Then experimental arrangements, test procedure and measurement technique, relevant to static and crash test are presented. Finally test results, reported in the form of numerical values, diagrams and high-velocity films are shown and critically commented.
Technical Paper

Solar Prototype for Shell-Eco Marathon Race

2017-03-28
2017-01-1260
Apollo is the name of a solar prototype vehicle of Politecnico di Milano (Technical University of Milan) that has been conceived and employed for the Shell Eco-marathon® Europe competition (SEM). The paper introduces the concept design, the detailed design, the construction, the indoor tests, the successful employment at SEM and the end-of-life of the prototype. Apollo is a three-wheeler with a single driving and steering wheel at the rear. A wing with solar cells provides part of the electric energy required for running. The conceptual design started from the accommodation of the driver inside the vehicle. A number of iterations focusing on CFD (computation fluid dynamics) and wind-tunnel tests allowed to refine the total drag to less than 2N at 35 km/h. The tyre characteristic was measured on a drum. The camber of front wheels was set to 4 deg which provided the least rolling resistance.
Technical Paper

Evolution of the Ride Comfort of Alfa Romeo Cars since 1955 until 2005

2017-03-28
2017-01-1484
The ride comfort of three Alfa Romeo cars, namely Giulietta (1955), Alfetta (1972) and 159 (2005) has been assessed both objectively and subjectively. The three cars belong to the same market segment. The aim is to let young engineers or graduate students understand how technology has evolved and eventually learn a lesson from the assessed trend. A number of cleats have been fixed at the ground and the three cars have traversed such uneven surface. The objective assessment of the ride comfort has been performed by means of accelerometers fixed at the seat rails, additionally a special dummy developed at Politecnico di Milano has been employed. The subjective assessment has been performed by a panel of passengers. The match between objective and subjective ratings is very good. Simple mathematical models have been employed to establish a (successful) comparison between experimental and computational results. The ride comfort differs substantially among the cars.
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