Search Results

Cycle resolved LDA measurements of the tangential velocity component, made along a diameter of two combustion chambers (toroidal and square) during the compression stroke of a diesel engine operating at 600 and 1000 rpm, are discussed. Indirect measurements of lateral integral length scales determined by single point autocorrelation technique are presented. Finally direct measurements of lateral integral length scales made by a new laser doppler velocimeter system based on two probe volume technique are reported.

The present paper reports the results of an experimental investigation carried out on a four-stroke single- cylinder D.I. diesel engine (100 x 95mm bore x stroke) with the aim to evaluate the effects of a four-lobe square combustion chamber on the gaseous and particulate emissions. Fluid-dynamic behaviour of the axisymmetric toroidal and four-lobe square chambers was investigated by Laser Doppler Anemometry. Engine tests at 2000 and 3000 rpm for different start of combustion (SOC) and A/F ratio are reported. Particulate, HC and NOx emission index measured under different operating conditions are given. In addition, the volatile content of the particulates produced from the two chambers at various engine operative conditions was measured by thermogravimetric analysis (TGA). Finally, the catalytic activity of a metal-oxide-based catalyst in the combustion of particulate was also evaluated by TGA.

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.

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.

The present paper aims at investigating the flow field behavior within a reciprocating engine under motoring conditions. Simultaneous two velocity components of the air velocity were acquired at different engine speeds within the cylinder at different radii from the cylinder axis. Mean motion, integral time scales and Reynolds shear stresses, for the radial and tangential components, were estimated from the instantaneous velocity data by applying an ensemble averaging technique. The integral time scale was obtained from the single point time autocorrelation function whereas, the Reynolds shear stresses were computed through the estimate of the degree of the fluctuations correlation. Tests, carried out at 1,000, 1,500, and 2,000 rpm, showed that the tangential mean motion scales approximately with engine speed whereas a radial inward motion can be observed during the last part of compression.

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 the last years, there has been an increasing concern on the emission of ultrafine particles in the atmosphere. A detailed study of formation and oxidation of these particles in the environment of the diesel cylinder presents many experimental difficulties due to the high temperatures, pressures and extremely reactive intermediate species. In this paper, in order to follow the different phases of diesel combustion process, high temporal and spatial resolution optical techniques were applied in the optically accessible chamber of diesel engine, at 2000 rpm and A/F=80:1 and 60:1. Simultaneous extinction, scattering and flame chemiluminescence measurements from UV to visible were carried out, in order to study the diesel combustion process from the droplet ignition to the formation of soot, through the growth of its precursors.

Ignition delay in diesel engine combustion comprehends both a chemical and a physical amount, the first depending on fuel composition and charge temperature and pressure, the last resulting of time needed for the fuel to atomize, vaporize and mix with air. Control of this parameter, which is mandatory to weight the relative amount of premixed to diffusive stage of the hydrocarbon combustion, is here considered. Experimental measurements of flame intensity spectra obtained by in situ measurements on an optically accessible test device show the presence of peaks corresponding to radicals as OH and CH appearing at the pressure start of combustion. Since OH radicals result from chain branching reactions, a numerical simulation is performed based on a reduced kinetic scheme which allows to measure the branching agent concentration, and whose approximate nature is adequate to the proportion chemical aspects contribute to the overall delay.

A second generation of Common-Rail injection systems is coming into production making feasible multiple injection strategies. This paper aims to assess the capability of multiple injection in reducing NOx and soot emissions of HSDI Diesel engines. The analysis has been carried out at a characteristic point of the EUDC emission test cycle by using a customized version of the CFD code Kiva3, with updated sub-models developed by University of Bologna and University of Wisconsin. In particular, a recent modification has been introduced in the fuel conversion rate calculation in order to account for turbulence non-equilibrium effects. Different multiple injection profiles and combustion chamber configurations have been simulated and their effects on mixture formation, heat release rate and NOx and soot formation have been analyzed. The main target was to comply with emission standards without significant loss in engine performance.

An experimental investigation, using the Laser Doppler Anemometry (LDA) technique, was carried out to investigate the complex structure of the intake flow in a commercial four-cylinder automotive Diesel engine. The attention was focused on the evaluation of the mean motion and turbulence intensity by using a steady state test rig with dynamic valve flow arrangements, supplying a flow rate of 17.4m3/h, that corresponds to the actual flow rate of the engine running at 2,000 rpm. The LDA tests were performed with the engine head mounted on a plexiglas cylinder, having the same diameter as that of the real engine, equipped with optical accesses. The intake manifold was connected to a flow bench tester to simulate the actual flow rates of the engine. Measurement points were located within the cylinder at different distances from the cylinder axis, on two orthogonal diameters, and at different depths from the engine head.

Polychromatic extinction and chemiluminescence techniques, from ultraviolet to visible, were applied in an optical diesel engine, in order to analyze the temporal and spatial evolution of a high pressure fuel jet interacting with a swirling air motion. A fully flexible Common Rail fuel injection system equipped with a single hole nozzle was used. The experiments were performed at fixed engine speed and air/fuel ratio for three injection strategies. The first one consisted of a main injection to compare with those operating at low pressure injection. The other ones were based on a pilot and main injections, typical of current direct injection diesel engines, with different dwell time. A detailed investigation of the mixture formation process inside the combustion chamber during the ignition delay time was performed. The liquid and vapor fuel distribution in the combustion chamber was obtained analyzing the polychromatic extinction spectra.

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.

An experimental and numerical investigation, using the Laser Doppler Anemometry (LDA) technique and a 3D fluid-dynamic code (KIVA 3V), was carried out in a prototype engine under steady-state conditions. The aim of the present activity was the flow field characterization and the effect of the intake geometry on the in-cylinder tumble flow. A new steady flow test rig designed for capturing the tumble motion within a test cylinder, made by a blower and an engine head, was assembled to simulate the intake flow. The engine head was mounted on an aluminum cylinder, having the same bore as the real engine. The cylinder was provided with optical accesses on the periphery and a flat optical window located at the bottom to a depth equal to the stroke of the engine. The cylinder was also equipped with two cylindrical ducts, used as air outflow ports.

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.

The optimization of diesel engine performance and emissions can be achieved through a better understanding of the in-cylinder combustion process. Advanced non-intrusive optical techniques are providing new tools for investigating the thermo-fluid dynamics processes as well as they are contributing to develop predictive models for DI diesel combustion. High-speed images of spray and flame evolution as well as UV-visible chemiluminescence measurements were carried out in an optical 0.5-liter, single-cylinder, four-stroke, direct- injection diesel engine equipped with a prototype four valves cylinder head and a fully flexible CR injection system. In order to evaluate the effect of different injection strategies on the combustion process, measurements were performed varying injection parameters. The ignition location and time were individuated by combustion visualization and detection of radical species, obtained by chemiluminescence measurements.

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.

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.

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.