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Technical Paper

An Assessment of Predictivity of CFD Computations of Combustion and Pollutants Formation in D.I. Diesel Engines

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.
Technical Paper

Combustion Behavior Analysis in a Transparent Research Engine Equipped with a Common Rail Diesel Injection System

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.
Technical Paper

Combustion Chamber Design Effects on D.I. Common Rail Diesel Engine Performance

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.
Technical Paper

Combustion Process Management in Common Rail DI Diesel Engines by Multiple Injection

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.
Technical Paper

Design of a small displacement transparent research engine equipped with a common-rail diesel injection system

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.
Technical Paper

Diesel Combustion Improvements by the Use of Oxygenated Synthetic Fuels

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.
Technical Paper

Diesel Engines Fueled by Wood Pyrolysis Oil: Feasibility and Perspectives

Aim of this paper was to assess the feasibility of the application of wood pyrolysis oil (WPO) as a fuel for medium-duty Diesel engines. The experimental activity was carried out both on a diesel injection system and on a DI Diesel engine. High-speed visualization was used to highlight the spray characteristics and an instrumented test bench to evaluate engine performance and emissions. No modification was carried out on the engine and the efforts were addressed to make the WPO compatible with engine operation. Accordingly, WPO was not tested as a pure fuel, but in blends with diglyme and in emulsions with Diesel fuel.
Technical Paper

Downsizing of Common Rail D.I. Engines: Influence Of Different Injection Strategies on Combustion Evolution

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.
Technical Paper

Dynamic Testing of Light Duty Diesel Engine: Characterization of Combustion Parameters Evolution

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.
Technical Paper

Effect of Combustion Chamber Shape on Air Flow Field in a D.I. Diesel Engine

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.
Technical Paper

Effect of Fuel Quality on the Performance of High-Speed Direct Injection Diesel Engines

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.
Technical Paper

Evaluation of Combustion Behavior and Pollutants Emission of Advanced Fuel Formulations by Single Cylinder Engine Experiments

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.
Technical Paper

Experimental Investigation on High-Quality Diesel Fuels Effects in a Light Duty CR Diesel Engine

In this paper some preliminary results on the emission performance of a modern CR DI diesel engine running on reformulated diesel fuels are discussed. The engine employed in the tests was a Fiat M724 1910cc, installed on Alfa Romeo 156 1.9 JTD. Modern injection systems can modify the spray structure with respect to a spray of a classical rotary injection pump so the well-consolidated knowledge on the correlation between fuel parameters and pollutant emissions may not be valid for the new generation of DI diesel engines. Two high quality fossil fuels and a synthetic fuel were selected for the tests. Tests were directed to analyze the relative influence on exhaust emissions between injection parameters and fuel quality. One engine test point (2000 rpm × 2 bar of b.m.e.p.) was chosen, with different setting of injection pressure, EGR ratio and pilot injection activation.
Technical Paper

Experimental and Numerical Investigation of Air Flow Field in an Open Chamber Diesel Engine

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.
Technical Paper

Fuel Jet Models for Multidimensional Diesel Combustion Calculation: An Update

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.
Technical Paper

Further knowledge on effects of fuels quality changes on emission potential of common-rail D.I. diesel engine

This paper reports some results on the emission performance of a CR DI diesel engine burning five model diesel fuels. The fuels were prepared by Agip Petroli S.p.A within the PNRA research program, sponsored by Italian Ministry of Environment and were a base fuel, a synthetic fuel and three oxygenated fuels. The engine employed in the tests was a prototype derived from Fiat M724 1910 cc, installed on Fiat Group class C Cars (1350 kg of mass). The prototype complies with EURO3 regulations. Two test points representative of two zones of ECE15+EUDC test cycle were chosen. Thermodynamic variables, emissions and injection systems parameters were recorded. Tests show the further potential of advanced fuels, obtained by blends of reformulated and oxygenated components, in reducing pollutants emissions.
Technical Paper

In-Cylinder Flow Measurements by LDA and Numerical Simulation by KIVA-II Code

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.
Technical Paper

In-Cylinder Sampling of High Molecular weight Hydrocarbons From a D.I. Light Duty Diesel Engine

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.
Technical Paper

In-Cylinder Soot and NOx Concentration Measurements in D.I. Diesel Engine Fed by Fuels of Varying Quality

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.
Technical Paper

In-cylinder Soot Evolution Analysis in a Transparent Research DI Diesel Engine Fed by Oxygenated Fuels

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.