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Technical Paper

Three Dimensional Calculations of DI Diesel Engine Combustion and Comparison whit In Cylinder Sampling Valve Data

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.
Technical Paper

Thermal Barriers Adoption in D.I. Diesel Engines: Effect on Smoke and Gaseous Emissions

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.
Technical Paper

The Role Of Mean Motion and Turbulence structure on Gaseous and Particulate Emissions of D. I. Diesel Combustion System

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.
Technical Paper

The Influence of Fuel Formulations on Pollutant of a Light Duty D.I. Diesel Engine

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.
Technical Paper

The Influence of Fuel Composition on Particulate Emissions of DI Diesel Engines

The effect of different fuel parameters on emissions is difficult to understand, the response depending upon different engine technologies. In addition the isolation of some of the fuel variables is often very hard. The present paper discusses the main results obtained testing a matrix of 14 fuels designed for obtain large variations of cetane number, sulphur and aromatic contents of Diesel oil. The aromatic structure of fuels and its effect on particulate emissions was also investigated. A linear regression analysis was performed in order to isolate the main controlling factors on particulate emissions. Finally the influence of aromatic contents of fuel on unregulated emissions was also assessed.
Technical Paper

Soot Formation and Oxidation in a DI Diesel Engine: A Comparison Between Measurements and Three Dimensional Computations

Three dimensional computations of Diesel combustion were performed using a modified version of Kiva II code. The autoignition and combustion model were tuned on a set of experimental conditions, changing the engine design, the operating conditions and the fuel characteristics. The sensitivity of the model to the different test cases is acceptable and the experimental trends are well reproduced. In addition the peak of pressure and temperature computed by the code are quite close to the experimental values, as well as the pressure derivatives. Once tuned the combustion model constants, different but simple formulations for the soot formation and oxidation processes were implemented in the code and compared with the experimental measurements obtained both with fast sampling technique and two colors method. These formulations were found unable to give good prediction in a large range of engine operating conditions, even if the model tuning may be very good for each test point.
Technical Paper

Some Insight on Premixed Combustion in Diesel Engine With Late Injection: The Influence of Air and Injection Parameters

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.
Technical Paper

Running Light-Duty DI Diesel Engines with Wood Pyrolysis Oil

This paper reports on the first successful tests performed on a production D.I. Diesel engine using wood pyrolysis oil (WPO). As reported in literature, any attempt to directly replace Diesel fuel with WPO required extensive modifications to the engine injection system, in order to overcome the intrinsic limits of the oil (poor self-ignition, high acidity and viscosity): new materials, additional pilot injection systems, careful procedures of start-up and shutdown were needed to obtain acceptable operation. Aim of the present work was to assess the limits of utilization of WPO in a strictly stock engine. Therefore, while no modifications at all were carried out on the engine, the efforts were addressed to make the WPO compatible with light-duty Diesel engines. Several long-running tests were performed on a single-cylinder engine, with: blends of WPO with different percentage of oxygenated compounds micro-emulsions of WPO in Diesel fuel standard (commercial) Diesel fuel.
Technical Paper

Potentiality of the Modern Engines Fed by New Diesel Fuels to Approach the Future European Emission Limits

This paper reports some results on the performance of an advanced common rail (CR) DI diesel engine burning 12 model diesel fuels. The experiments were carried out within a co-operative research program “NeDeNeF” (New Diesel Engines and New Diesel Fuels), partly sponsored by the Commission of European Communities. Partners of the project with Istituto Motori (IM) were: FEV (Germany), VTT (Finland), NTUA (Greece), Brunel University (UK), Fortum (Finland), LAT (Greece) under the coordination of the IFP (France). The matrix of twelve fuels was prepared by the fuel producer partner (Fortum). The research program of the Diesel Engines and Fuels Department of Istituto Motori aimed at assessing the effect of fuel quality on exhaust emissions. The engine employed in the tests was a Fiat four-cylinder DI CR diesel engine, EURO3 version, of 1.9 litre, installed on Fiat Group class C Cars (1350kg of mass).
Technical Paper

Potentiality of Oxygenated Synthetic Fuel and Reformulated Fuel on Emissions from a Modern DI Diesel Engine

This paper presents the performances of a modern DI diesel engine, equipped with a Common Rail injection system, fed on blends of an advanced diesel fuel (base fuel) and Diethylene-Glycol-Dimethyl-Ether (Diglyme - C6H14O3). The base fuel was a reformulated diesel fuel with low aromatic and sulfur content. Three blends with different volumetric percentage of Diglyme (10, 20 and 30%) in the base fuel were prepared and tested. The engine was a FIAT M724, installed in a Alfa Romeo 156 1.9 JTD, with a Bosch Common Rail injection system (EDC-15C). At the exhaust of the engine, soot, NOx, HC, CO, and CO2 were measured. The experiments represent the potential of diesel reformulation technology with synthetic fuels coupled with the new diesel technology generation.
Technical Paper

New Trends in Combustion System Design of Light Duty Diesel Engines Inferred by Threedimensional C.F.D. Computations

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.
Technical Paper

Multidimensional Modeling of Advanced Diesel Combustion System by Parallel Chemistry

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.
Technical Paper

Laser Diagnostic of Particles Exhaust Emission from Advanced Diesel Combustion Systems

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.
Technical Paper

Initial Results on the Impact of Automotive Diesel Oil on Unregulated Emissions of DI Light Diesel Engine

Cetane number, sulphur content and aromatic structure of Automotive Diesel Oil (ADO) were changed to assess their influence on emissions of light duty direct injection Diesel engine. The detailed chemical analysis of particulate soluble fraction allows to quantify the P.A.Hs emission. In addition also the aldehydes and volatile organic compounds were measured in the gaseous phase. The sulphur content of the fuel and its aromatic structure strongly influence particulate emission. The insoluble fraction of the particulate rises with an increase of the high sulphur content ADOs with about the same back end volatility. Unburned P.A.Hs control P.A.Hs emission at the part loads typical of normalized schedules for emission testing of light duty vehicles in Europe. Finally the level of emissions of benzene and 1-3 butadiene is comparable to the total P.A.Hs emission.
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.
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 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 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

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

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.