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Aim of the present paper was an evaluation of the importance of some engine parameters (intake gas flow and injection parameters) on the approach of Premixed Low Temperature Combustion (PLTC) conditions with the same efficiency of a conventional diesel cycle and ultra-low pollutant emissions. The results have demonstrated that the control of PLTC mode is very difficult and the engine parameters play a critical role on the exhaust pollutant emissions, indicating that further massive research activities are needed to reach reliable practical applications.

In the present paper the combustion process in a modern second generation Common Rail Diesel engine for light duty application is experimentally and numerically investigated. An improved version of the KIVA3V-Release 2 code was used for the simulations. To model the combustion process, a detailed kinetic scheme involving 57 species and 290 equations, based on the n-heptane combustion, was used, interfacing the KIVA3V code with the CHEMKIN-II chemistry package. The full set of equations is concurrently solved in each computational cell by different solvers with the final aim of obtaining a locally adaptative code: local choices are undertaken in terms of time steps as well as in terms of the employed solvers. To reduce computational time, the code was parallelized: this parallelization is mainly focused on the chemical subroutines, considering that they are responsible for more than the 95% of the computing.

The effect of fuel injection strategy and charge dilution on NOx and soot emissions has been investigated with a modern DI diesel engine. Particulate mass has been measured by a standard smoke meter and soot particles have been characterized by means of time-resolved Laser Induced Incandescence (LII) at the exhaust of the engine. Two steady-state test points have been selected, representative of low and medium load conditions. The influence of the different engine management strategies has been assessed, highlighting the potential of unconventional operating modes to meet forthcoming emission limits.

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.

The improvements of the solenoid injector and of the Electronic Control Unit of the present Common Rail injection system (C.R.) allow the use of multiple sequential injections. Thanks to this feature this advanced Common Rail system is capable to perform up to five consecutive injections in one engine cycle thus improving control of the combustion process. In particular, in some operating conditions, the activation of a small injection after the main one allows the oxidation of the soot produced in the previous stages of the combustion process, without increasing nitrogen oxide emissions. This paper describes the experimental results obtained with the application of a prototype of this advanced Common Rail system both to a Fiat L4 1.9 JTD 8 valve engine and to a single-cylinder prototype, having the same combustion system and large optical access allowing investigation of the injection and combustion processes.

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.

According to the results of several studies concerning the influence of fuel formulation on exhaust emissions from diesel engines, a new matrix of twelve fuels was tested in a single cylinder DI diesel engine of conventional technology. The matrix was designed by the partners of the FLOLEV research project, partly founded by the E.U., in the framework JOULE III program. The aim of the project is to study the influence on pollutants emission reduction of modern refining process and fuel additivation with some alternative fuels and cetane improvers. The fuel matrix is structured into three sub-matrices. The first sub-matrix is constituted by six fuels which represent different products obtainable with the modern refinery technology. The second and third sub-matrices were designed to test the influence of cetane improver additives and high-oxygenated fuels respectively.

In the present paper some results, obtained by the use of modern numerical C.F.D tools, are presented. In particular, starting from the experimental characterization of a conventional design D.I. diesel engine, the empirical constants of the different submodels were tuned to obtain satisfactory results in some key test conditions. After that, in the same points of the engine performance map, the following parameters were systematically varied: Fuel injection system design and operating conditions Intake swirl level Exhaust gas recirculation level. The influence of each parameter on combustion evolution is discussed and the most promising trend for the engine optimization is presented. Taking into account the model formulations limits, the results obtained suggest, from a theoretical point of view, that “common rail” equipped light duty diesel engines are suitable to meet the future European emission regulations.

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.

In the present paper the status of development of diesel combustion and pollutants formation modelling at Diesel Engines and Fuels Research Division of Istituto Motori is pointed out. The main features and performances of the model are discussed comparing the numerical results with some experimental data. For the experiments a single cylinder direct injection diesel engine was used. In the head of the engine two small quartz windows have been mounted, in order to obtain pictures of the injection and combustion processes by high speed cinematography, and to apply the two colour technique for soot temperature and soot loading measurements. The soot loading was measured by the two colour technique and the a priori and the experimental uncertainties of the measurement technique were carefully evaluated. In addition, the engine may be also equipped with a second head, in which a fast acting valve allows the direct sampling of the combustion products.

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.

The multidimensional simulation methods, today available for spray motion predictions, solve the spray equations including the mass, momentum and energy changes due to the interaction between the drops and the gas, considering also the collision and coalescence phenomena. As concerns break up, two models are the most commonly used: the TAB one, proposed by O'Rourke and Amsden and based on the Taylor analogy, and the WAVE model; developed by Reitz and Diwakar. Both models need the tuning of some empirical constants. Considering also that the mechanism, that controls atomisation, is not yet well understood, it seems that further calculations and experimental comparisons over a range of injection conditions may be useful to improve the prediction capability of these models. Therefore the present paper concerns a sensitivity analysis of the TAB and WAVE models to changes of the empirical constants.

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.

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 formation and oxidation of soot, light and heavy hydrocarbons, CO, CO2 and NOx in a D.I. diesel engine have been studied by means of direct fast sampling and chemical analysis of the combustion products collected during the combustion cycle. Particular attention has been paid to the histories of each fuel hydrocarbon class analyzing the chemical transformations that the paraffins, and monoaromatic and polyaromatic compounds, contained in a diesel fuel oil, undergo during the combustion cycle. This approach is able to give information on the origin of soot and heavy hydrocarbon emission from a diesel engine. The concentration of the heavy hydrocarbons decreases during the early stages of the combustion cycle and their profile corresponds roughly to the fuel disappearance rate because of the chemical similarity with the fuel compounds.

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.

Comparisons are presented of computed and measured air flow fields in an open chamber diesel engine running at 1,000 and 2,000 rpm without combustion. Both Conchas spray and KIVA codes were tested. The effect of turbulence is represented using both K-ε and SGSD (Sub-grid Scale Differential) submodels. A Laser Doppler Velocimeter (LDV) was used to make velocity and turbulence measurements during the compression stroke. Reasonable agreement between numerical and experimental results for the engine examined was observed.