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This paper refers to the experimental results obtained using two different 4 cylinder diesel engines, with total displacement respectively equal to 1.9l and 1.3l, both equipped with an advanced Common Rail system. An optically accessed prototype engine, having characteristics similar to the four cylinder engine, is used to visualize the in cylinder phenomena. Multidimensional simulations of the combustion and pollutants formation processes are performed, comparing the numerical predictions with the experimental data. By this way, integrating the 3D C.F.D. computations, the visualization techniques of the injection and combustion processes and the field measurements on the real engines, different settings of the multiple injection strategy have been analyzed.

This paper describes a characterisation of the combustion behaviour in an optical Common Rail diesel engine fed by different advanced fuels, via the application of the two-colour pyrometry technique. The acquired images were processed in order to calculate the instantaneous flame temperature and soot volume fraction. For the measurements, a single test point was chosen as representative of the reference four-cylinder engine performance in the European driven cycle ECE+EUDC. The test point was the 1500 rpm and 22 mm3/stroke of injected fuel volume, correspondent to the engine point of 1500rpm @ 5 bar of BMEP for the 4-cylinder engine of 1.9L of displacement. As general overview, the flame luminosity from combustion of the fuel injected during pilot injection was always below the threshold of sensitivity of the detection system.

In the present paper the KIVA3V code is used to model the behaviour of different combustion chambers, to be used in Common Rail engines with a single displacement lower than 0.5l. Some design parameters have been chosen to evaluate their influence on the combustion patterns. The optimum levels of turbulence and air mean motion have been selected with reference to some specific points of the engine map, managed by mean of multiple injection. Therefore the different combustion chambers geometries have been numerically investigated in terms of fluidynamic behaviour as well as in terms of combustion evolution. After that some chamber geometries, especially suitable for the second-generation common rail engines, have been selected.

This paper describes the project of a "small' single-cylinder direct injection diesel engine (300 cc). It is equipped with optical accesses to analyze the diesel combustion process employing the most recent optical diagnostic techniques. The injection system used is a second-generation common- rail system. The optical accesses are placed on the piston and on the cylinder wall.

This paper describes a preliminary characterization of in-cylinder spray and combustion behavior from a high-pressure common rail injection system. The engine used in the tests was a single-cylinder optical research diesel engine, adequately developed in a full-fired version, equipped with a common rail injection system. An elongated piston allows for the optical access to the combustion chamber for diagnostic applications. Characteristic of the optical engine is the availability to investigate different combustion system designs due to an interchangeable head-cylinder group. The system configuration tested in the present work corresponds to a four-cylinder engine of 1930 cc of displacement that is representative in the class of light duty d.i. diesel engine. Spray and combustion evolutions were visualized through a high-speed CCD camera synchronized with a copper vapor laser acting as light source.

In this paper results on in-cylinder pollutant concentration evolution during combustion of six different oxygenated fuels, in comparison with tetradecane and n-octane combustion, are presented. These four fuels are: Ethylene-Glygol-Dimethylether (monoglyme-C4H10O2), Diethylene-Glygol-Dimethylether (diglyme-C6H14O2), Diethylene-Glycol-Diethylether (diethyldiglycol-C8H18O3), butylether (C8H18O). Two techniques were adopted on a single cylinder direct injection diesel engine: two-color pyrometry for the measurement of in-cylinder soot loading and a fast sampling valve for the measurements of in-cylinder combustion products. In addition, the sampling line downstream of the fast sampling valve was adapted for the in-cylinder aldehyde measurements. The main results obtained provide information about the mechanisms that control soot evolution during diesel combustion.

This paper reports some results of a research carried out under part sponsorship of the Commission of the European Communities in the framework of the Joule II program. A twelve fuels matrix, derived from very different formulation techniques like hydrotreatment, Fisher Tropsch process, oligomerization and addition of oxygenated compounds to the straight run was tested. Istituto Motori performed tests on a turbocharged, after-cooled, direct injection diesel engine of two liter total displacement. It was equipped with an electronic E.G.R. system. Tests were performed in steady state conditions, representative of transient European schedules. Regulated and unregulated emissions was measured. Further tests were performed in cold conditions, the coolant temperature at the engine outlet was kept below 10°C in order to enhance the behavior of different fuels in producing regulated and unregulated emissions.

Selected measurements of the in-cylinder soot loading and the gaseous combustion products for ten different innovative fuels, burned in a D.I. diesel engine are presented and discussed. All the fuels which were tested have a very low sulfur content, so the insoluble fraction of the particulate is mainly composed of soot. Two different measure techniques are applied: the two-color pyrometry optical method and the fast sampling of gaseous products in the combustion chamber. A priori and experimental uncertainties relative to the reduction of the data obtained with the two-color measurements are preliminarily investigated.

A modified version of KIVA II code was used to perform three-dimensional calculations of combustion in a DI diesel engine. Both an ignition delay submodel and a different formulation of the fuel reaction rate were implemented and tested. The experiments were carried out on a single cylinder D.I. diesel of 0.75 I displacement equipped with sensors to detect injection characteristics and indicated pressure. A fast acting sampling valve was also installed in the combustion chamber to allow the measurement of main pollutants during the combustion cycle, by an ensemble average technique. Computational and experimental results are compared and the discrepancies are discussed. Today the demand for light duty engines that produce less emission and consume less fuel is increasing. Thus, if limits on CO2 emissions are established, the direct injection diesel engine for light duty applications will become an attractive option.

The fluid-mechanic behaviour of straight-sided and re-entrant chamber geometries has been studied using laser doppler anemometry (LDA) technique. Measurements have been carried out during the compression stroke in a direct injection diesel engine, representative of medium size family, operating at 1000 rpm under motored conditions. The mean motion and turbulence intensity have been computed using a filtering procedure on the LDA data. Using the second version of KIVA code, the air flow field evolution during the same crank angle period has been also computed. To perform proper comparisons between measured and computed values of mean velocity and turbulence intensity, a careful choice of the initial conditions for computations has been performed. Reasonable agreement has been found between computed and measured mean swirl velocities for both combustion chamber geometries tested. On the contrary, the computed turbulence intensities underestimate those measured.

A methodological analysis of combustion parameters and pollutant emissions measuring procedures during transient operation of a D.I. T.C. light duty diesel engine was performed. Combustion process was characterized by ignition delay time, combustion pressure peak value and heat release law measurements during the transient ECE 15 schedule on a dynamic test bed with electronic simulation of inertia. The particulate emission was measured every 0.05 s by an I.R. optical method. In addition some correlations, based on pressure cycle and injection law evolution, were implemented in order to calculate instantaneous fuel delivery and transient NOx emission. Some activities were carried out in order to asses the limits of engine configurations ranking performed with steady state measurements of performances and emissions. Strong differences were detected between carbon emission during transient operations and the value obtained by interpolation from a steady state map.

The status of the research carried out at the Istituto Motori aimed to optimize the direct injection light duty combustion system with regard to pollutant emissions is described. The influence of combustion chamber design on air flow field was investigated by means of a two colors LDA system as well as by engine test bed. Three-dimensional computer simulations of injection and in- cylinder air motion have been run in order to analyze some experimental results. In particular two configurations of axisymmetric combustion chambers were examined and, results were compared with those obtained from a four-lobe microturbulence combustion chamber. Tests showed that some improvement in the NOx-particulate trade off can be obtained at part load at both high and low speeds.

The behaviour of two combustion chambers, a toroidal and a turbulent one, has been compared. The engine performance in terms of imep and exhaust emissions were measured. Laser Doppler Anemometry technique was used to characterize the fluids dynamic aspect of combustion system. The axial asymmetry introduced in combustion chamber shape causes strong differences in the air flow field at the end of compression stroke. The tangential velocity profile is flattened to that obtained with toroidal chamber. Moreover the rms values of tangential velocity measured in turbulent combustion chamber are about three times higher than that measured in the toroidal chamber. At low engine speed the turbulent chamber allows to operate with low NOx levels without penalties of smoke emissions and fuel consumption as happens by using conventional toroidal chamber.

Two fuels having different aromatics content and different cetane numbers were tested in a direct injection diesel engine with thermally insulated pistons. Actually tests were carried out with a full aluminum piston, an aluminum piston modified to accept a stainless steel crown and a similar one coated with ceramic. Higher combustion noise and emissions were detected using the degraded fuel, having fixed the type of piston. Furthermore, the experiments showed that thermal barrier adoption has a positive effect on the combustion noise.

The paper describes some experiments carried out on two d.i. Diesel engines running with insulated pistons. Three different thermal barriers were tested; namely, a stainless steel cup, a Si3N4 cup and a stainless steel piston crown. The combustion process was characterized by heat release calculation and ignition delay measurements. The experiments showed that the indicated efficiency is not affected by thermal insulation adoption, Nox level increases while smoke level decreases consistently.