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The use of particulate filters (DPF) has become in recent years the state of the art technology for the reduction of soot aerosol emissions for light, medium and heavy duty Diesel vehicles. However, the effect of the system location on engine performance is a key aspect that should be studied. In the present work a numerical study has been carried out with the objective to analyze the effect on the engine performance of an innovative DPF placement upstream of the turbine. This study has been performed by means of the gas dynamic simulation of a two-stage turbocharged heavy duty Diesel engine, which has been previously modeled from experimental data obtained under steady state conditions. The original DPF has been divided into two monoliths for the case of the pre-turbo DPF configuration. Three cylinders discharge in each of these monoliths and after the filtration the flow is driven towards the high-pressure turbine and the EGR system.

The onset and development of the inner cavitating flow in Diesel injectors is analyzed in relation with the needle movement, using Computational Fluid Dynamics studies realized with moving mesh. Two real six-hole injector geometries have been considered, one with cylindrical nozzles, the other with conical nozzles. A full analysis of the flow results is presented, including a dynamic picture of the developing pattern. Results show that depending on the needle lift, the cavitation pattern varies strongly throughout the nozzle, and affects the characteristics of the flow at the nozzle exit. A kind of hysteresis in the development of the flow has also been observed between needle opening and closing.

An experimental study of real multi-hole diesel nozzles with different geometry in terms of conicity factor has been performed under current DI Diesel engines operating conditions. A complete characterization of the internal nozzle flow and the sprays injected under non-evaporative conditions has been performed. The results of that study are applied in order to assist the analysis of spray in evaporative conditions. In this case, results of liquid-phase fuel penetration were obtained from a wide optical access engine operating under non-reacting conditions. From these measurements, a comparison of the results with a theoretical Diesel spray model in evaporative conditions has been carried out. This comparison has allowed the determination of the dependence of stabilized liquid length on injection pressure, ambient conditions and nozzle geometry.

Although in combustion diagnosis models the uncertainty in the trapped mass is not critical, different authors have reported non negligible effects on the rate of heat release. Usually, an emptying-and-filling model is used to estimate the residual mass, whence the trapped mass is obtained. Generally, the instantaneous pressure at the intake and exhaust ports are not measured for combustion diagnosis applications and hence, it is difficult to estimate accurate values of the residual mass. The objective of this work is to propose a simple physical model to estimate the residual mass in a DI Diesel engine for a combustion diagnosis model. The proposed model specially focuses on the exhaust port conditions, because they appear to be the most important factor affecting the residual mass estimation.

Diesel injector nozzles with different geometries have been investigated, firstly to study the effect of cavitation on the flow at the exit of the nozzle, and secondly to see its effect on the spray and the consequent flame formation. The flow at the exit of the nozzle was characterized by measuring both the injection rate and the momentum flux for a wide range of typical engine's rail and cylinder pressures. The injection rate is directly affected by cavitation and it will become choked when this phenomenon appears. The measurement of the momentum flux can be combined with the injection rate to derive the velocity at the nozzle exit. The momentum flux does not seem to be influenced by the appearance of cavitation. Apart from this hydraulic characterization, the different nozzles have also been mounted on an engine with optical access to the combustion chamber. During these tests, the spray, its vaporization and combustion were visualized and recorded with a high resolution camera.

Modern DI Diesel engines are widely used in automotive applications. Improvements in performance and emissions have been produced in the last ten years on these engines, so that they are now very competitive in comparison with petrol engines. However, cold startability is one of the main challenges of Diesel engines, since great differences with petrol engines still can be noticed. Today, in small engines glow plugs are universally used as an aid system for cold start. In large engines, where the cold start is less critical, intake air heating technology is employed. In this paper the application of this technology to small engines is evaluated in terms of its viability for cold starting and HC/CO emissions and combustion noise reduction during the warm-up phase of the engine.

In order to study differences between Diesel nozzle holes, four methodologies have been tested. The techniques compared in this paper are: the internal geometry determination, hole to hole mass flow measurement, spray momentum flux and macroscopic spray visualization. The first one is capable of obtaining the internal geometry of each of the orifice of the nozzle; the second one is capable of measuring the mass flow of each nozzle hole in both, continuous and real injections. The third one gives the momentum flux of each orifice, and finally, with the macroscopic spray visualization, the spray penetration and spray cone angle of each hole, are obtained. Generally, all these techniques can be used in order to determine the hole to hole dispersion due to different angle inclination of the holes, different internal geometry of orifices, deposits, nozzle needle off-center, needle deflection, etc.

This paper reports the results obtained in the ECOBUS Project. This project has been supported by the LIFE Program, one of the spearheads of European Union's environmental policy. The main aim for this project was to convert used cooking oil into biodiesel and then use this biodiesel in urban buses, contributing to reducing in one hand waste cooking oil that can create problems in the drainage city system and water contamination and on the other hand reducing engine polluting emissions. Departamento de Máquinas y Motores Térmicos (DMMT) facilities at the Universidad Politécnica de Valencia (Spain) were used to conduct detailed performance and emission measurements in a Diesel engine similar to those used by the urban transport operator in Valencia (Empresa Municipal de Transporte, EMT). The test engines were operated with conventional Diesel fuel (EN 590) and three different biodiesel blends: 30, 50 and 70%, using the pure biodiesel obtained from used cooking oil (EN 14214).

In this paper the heat transfer of the hot gases to the cylinder walls of DI Diesel engines is analyzed using Computational Fluid Dynamics (CFD) and compared to the predictions obtained with a zero-dimensional thermodynamic model based on a variant of the Woschni equation. The final objective is to improve the simple model by modifying the original equations to better take into account the influence of important parameters, such as swirl, on the heat transfer. CFD calculations of the compression and expansion strokes have been made for two real DI Diesel engine geometries, a small one with a displacement of 0.4 l. and a heavy duty one of 2.0 l., and for different working points. The total heat transfer rate to the cylinder surfaces is highly dependent on the mean flow behavior and turbulence levels.

This paper summarizes the optimisation work of the air-assisted direct fuel injection 50 cc. 2-stroke spark ignition DERBI TSI engine. The methodology employed is based on the use of mathematical models to assist to the design procedure. The models used are a 1D wave action model and a 3D CFD model. In the paper is described the modelling procedure for some of the engine systems: exhaust, injection, scavenging and mixture processes. The existing 1D model has been improved to simulate 2-stroke engines. Some studies have been devoted to the calculation of tapered pipes, exhaust system, reed valves and injection system. The study of the exhaust shows that only the exhaust parts closest to the cylinder have influence on the exhaust response in terms of performance. The study of the injection system shows that the injection pressure and duration will depend on the discharge duct diameter and compressor clearance.

The objective of this work is to make an analysis of the behaviour of the venturi in real working conditions. The modelling of the venturi, as well as the experimental and modelled results obtained, will be described. Modelled and measured techniques have been used to realize this work. A new model of the venturi was developed and using this, it is possible to find important instantaneous variables of the venturi. In order to adjust the calculated model, it was necessary to characterise the steady flow test rig of the venturi. In addition, the information obtained from the engine tests has been essential to correctly adjust the model. Therefore, a combination of the information obtained from both the venturi test and from modelled work was necessary in order to understand the behaviour of the venturi installed in an engine. Different tests have been performed on each venturi.

This paper is related to the load transient modelling of heavy-duty (HD) turbocharged diesel engines with a wave action model. The control variables of this transient are analysed and the modelling alternatives reviewed. Afterwards, the developed computer model is described as well as the novel sub-models. The model predictions are compared with the experimental results for validation in a six-cylinder HD turbocharged engine at different engine speeds. The evolution of engine variables, difficult to measure experimentally during the transient, as the instantaneous relative fuel to air ratio, FR, are computed with the model and analysed. These parameters provide very meaningful information of the transient evolution. As an example of the model application, the influence of the intake manifold tuning on the transient evolution is evaluated.

The characteristic parameters and the evolution of continuous Diesel sprays injected against a high density gas have been investigated using high speed photography and phase Doppler anemometry. The injector used for these tests was a two-spring one providing different injection conditions. Three test sections were analyzed at 10, 20 and 30 mm from the injector with several radial measurements for each one. The obtained results provided qualitative and quantitative information about the macroscopic evolution of the spray, but also about the drop velocity distribution and drop size evolution.

The present paper deals with the valve lift curves that can be obtained by the use of a variable valve timing system (early valve closure type), and with the performance that can be expected from an engine with such a system. In the first stage of the work, the hydraulic mechanism which controls the anticipated closure, has been designed by means of a mathematical model, adjusted with empirical data obtained from laboratory tests about the hydraulic behaviour of the main components: flow coefficients and time dependent behaviour of the electrical-hydraulic ports. A computational study of realistic variable valve timing engine performance was carried out by means of a wave action model based on the method of characteristics. These results were compared with the ones corresponding to a conventional throttled engine and with those that can be obtained by the use of an ideal variable valve timing system in which the closure of the valve occurs instantaneously.

The paper describes the theoretical and experimental development of the intake manifold for a 12-liter, 6-cylinder supercharged Diesel engine with intercooling. The objective has been to obtain a torque diagram optimum for traction, i.e. with the maximum torque at a low engine rpm without penalizing the peak power, in addition the design has to keep a reduced fuel consumption and low smoke level. To meet these requirements, the solution adopted has been to obtain the cylinder filling by means of the combined effect of the turbocharger and the geometry of the intake manifold. The design of the manifold is based on the use of lengths and diameters for the pipes appropriate to obtain the desired volumetric efficiency diagrams, avoiding the use of intermediate reservoires. This solution has some advantages for the case of big automotive engines with intercooling, since usually long pipe lengths among turbocharger, intercooler and cylinders are needed.

It exists the possibility of adopting variable valve timings to reduce pump-losses in spark-ignition engines. With this method, engine load regulation can be achieved mainly by acting over the total time that the inlet valve remains open, and eliminating the throttle valve in an ideal case. The timing diagram (total opening valve and angular phase) should depend on the engine speed and load desired in each moment. The mechanical system for the proposed regulation system is a four-bar mechanism which is now in a stage of final adjustment for a monocylinder engine. In order to get the valve timing, a calculation model for the inlet and exhaust processes has been developed and is presented in this article, as well as the results obtained.