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The main objective of the present paper is the application of a detailed kinetic model to study diesel combustion in an optical accessible engine equipped with a common rail injection system. Three different injection schedules made of one to three consecutive injections are considered from both the numerical and the experimental point of view. The numerical model is assessed in such a way to assure its portability with respect to changing injection strategies. The employed detailed kinetic mechanism consists of 305 reactions involving 70 species and is included in the KIVA-3V code. The considered fuel has the liquid phase properties of the diesel oil, the vapor phase properties of C14H28. It is subsequently decomposed into n-heptane and toluene. The chemical solver is based on the use of the reference species technique and on the Partially Stirred Reactor (PaSR) hypothesis. These allow maintaining the computational cost within acceptablelimits. A comparison with experimental data is made regarding the in-cylinder pressure, the visualization of the spray evolution, the temperature and OH radical distribution during the combustion process, as well as the time history of the measurable soot amount within the combustion chamber. Tail pipe emissions are also compared with the values of the in-cylinder soot and NOx amount at the end of the expansion stroke.

The paper summarizes the activities related to the characterization of the noise sources and related sound emission levels emitted by a single-cylinder diesel engine. A deep analysis is carried out aiming to clearly define the various noise sources, through the employment of numerical and experimental techniques. In particular, an intensimetric analysis is carried out to define a bi-dimensional noise level map around the engine. In addition, the gas-dynamic noise, at the different engine speeds, is measured through a microphone mounted near the intake and exhaust mouth. Contemporarily to the experimental activity, a theoretical one-dimensional simulation of the whole engine is also carried out. The presented one-dimensional analysis is able to characterize the wave propagation phenomena in the external ducts and provide the estimation of both engine performance and gas-dynamic noise emission too. The presented techniques allow to fully describe the noise emission behavior of the tested engine.

This paper illustrates the results of an experimental characterization of a high-pressure diesel spray injected by a common- rail (CR) injection system both under non-evaporative and evaporative conditions. Tests have been made injecting the fuel with a single hole injector having a diameter of 0.18 mm with L/D\me5.56. The fuel has been sprayed at 60, 90 and 120 MPa, with an ambient pressure ranging between 1.2 to 5.0 MPa. The spray evolution has been investigated, by the Mie scattering technique, illuminating the fuel jet and acquiring single shot images by a CCD camera. Tests under non-evaporative conditions have been carried out in an optically accessible high-pressure vessel filled with inert gas (N2) at diesel-like density conditions. The instantaneous fuel injection rate, obtained with a time resolution of 10 microseconds, has been also evaluated by an AVL Fuel Meter working on the Bosch Tube principle. Tests for the evaporative conditions have been conducted on a crank- case-scavenged, single-cylinder, 2-stroke direct injection diesel engine at the rotational speed of 500 rpm. The engine provides a wide optical access and the gas velocity within the combustion chamber is low enough to assume that the fuel is injected under quiescent conditions as those reproduced for the experiments under high density gas chamber. Spray penetration and cone angle have been estimated at the same operative conditions as for the non-evaporative ones. Results have showed that the tip penetration, obtained by digital post-processing of the spray image sequence, increases with the injection time under non-evaporative conditions whereas, under evaporative conditions, it reaches a maximum early during the injection and remains constant or slightly decreases at later time up to the start of combustion. The cone angle, estimated under evaporative conditions, has given a decreasing profile along the injection interval. Applying the jet theory to a simplified model of fuel spray, the evaporated fuel mass has been estimated at the same gas density as that under nonevaporative tests.

Present paper couples the use of a modified version of the KIVA-3V code including a model for detailed chemistry to an experimental investigation performed on an optically accessible diesel engine. The engine is equipped with a commercial four valves cylinder head and a Common Rail injection system. Digital images and UV-visible flame emission measurements are compared with the visualization of the numerical results. The diesel fuel surrogate is considered within the numerical code, namely a blend consisting of n-heptane and toluene, approximating the physical and ignition properties of the diesel oil. Products, soot and NOx formation is described by a chain of 283 reactions involving 69 species. The Partially Stirred Reactor (PaSR) assumption is adopted to maintain the computational cost within acceptable limits. The collections of digital images of the spray evolution, the mixture formation and the combustion processes are undertaken by running the engine at 1000 rpm. Commercial diesel fuel is injected by using a single injection.

The Registry for Type 1 Diabetes Mellitus in Italy (RIDI) Study Group was established to coordinate the registries of type 1 diabetes in Italy. This report is based on 3,606 children younger than 15 years diagnosed with type 1 diabetes and prospectively registered during 1990-1999 by nine centers, covering35% of the Italian population.Registries were pooled in four geographic macro-areas: north, central, south, and insular. The completeness of registration was assessed by the capture-recapture method. Poisson regression analysis was used to evaluate temporal trend in incidence.Large variations in incidence were confirmed not only between Sardegna and the mainland but also among peninsular areas. In Sardegna, there was an excess of boys (the boy-to-girl incidence ratio was 1.4). The overall incidence showed average increases of 3.6% (P0.001) and 3.7% (P0.001) per year in peninsular Italy and in Sardegna, respectively. Significant increases in incidence rates were found in boys aged 10-14 years (6.7%, 95% CI 0.5-13.3) and in girls aged 5-9 years (6.6%, 0.5-13.1) living in the southern area. The incidence rate also increased in boys aged 10-14 years (5.0%, 0.3-10) and in girls aged 0-4 years (4.9%, 0.8-9.1) living in Sardegna.Italy is a country with large geographical variations in incidence rates of type 1 diabetes. However, the rates are evenly increasing both in the mainland and Sardegna, suggesting that similar environmental factors are operating over populations that have different genetic backgrounds.

Spectroscopic measurement and high-speed visualization were used in single-cylinder, four-stroke DI diesel engine, optically accessible. It was equipped with a four valves head and fully flexible electronic controlled "Common Rail" injection system. The effect of pilot and main injection on combustion process was evaluated. Mixing formation, autoignition and soot formation process were analyzed by broadband ultraviolet-visible flame emission spectroscopy and high-speed digital imaging. The autoignition phase occurred near the tip of the jet and was characterized by strong presence of OH radicals for both investigated conditions. The presence of C\d2 and OH radicals strongly characterized CR diesel combustion process during soot formation and evolution. In particular, high presence of OH concentration for the whole process from the autoignition to the soot formation and successive phases contributes to lower soot levels.

The paper illustrates an experimental and numerical investigation of the flow generated by an intake port model for a heavy-duty direct injection (HDDI) diesel engine. Tests were carried out on a steady-state air flow test rig to evaluate the global fluid-dynamic efficiency of the intake system, made by a swirled and a directed port, in terms of mass flow rate, flow coefficients and swirl number. In addition, because the global coefficients are not able to give flow details, the Laser Doppler Anemometry (LDA) technique was applied to obtain the local distribution of the air velocity within a test cylinder. The steady-state air flow rig, made by a blower and the intake port model mounted on a plexiglas cylinder with optical accesses, was assembled to supply the actual intake flow rate of the engine, setting the pressure drop across the intake ports at \gDP\me300 and 500 mm of H\d2O. The flow coefficients and the swirl number were computed measuring the flow rate by a turbine flow meter and a paddle wheel to evaluate the air vortex speed into the cylinder test. The LDA technique was used to obtain the tangential and axial components of the flow velocity on two planes and along three diameters within the test cylinder. The computation was carried out by the fluid-dynamic code STAR-CD that solves the ensemble averaged conservation equations for mass, momentum and energy in steady-state conditions with the turbulence model k-\ge. The grid, reproducing the geometry of the intake port and the real fluid system, was made using CAD data and the boundary conditions were the same as the experimental ones. Results of the computed mass flow rate, flow coefficients, and velocity profiles were compared to the experimental ones. The substantial agreement between experiments and computations suggests that an acceptable level of confidence may be assigned to calculations to design the intake port geometry of heavy-duty diesel engines.

Conventional methods to measure gas concentrations and, in particular, NO are typically based on sampling by valve, sample treatment and subsequent analysis. These methods suffer low spatial and temporal resolution. The introduction of high energy lasers in combination with fast detection systems allowed to detect the NO distribution inside optically accessible Diesel engines. In this paper, a high spatial and temporal resolution in-situ technique based on ultraviolet - visible absorption spectroscopy is proposed. The characterization of the combustion process by the detection of gaseous compounds from the start of combustion until the exhaust phase was performed. In particular, this technique allows the simultaneous detection of NO and OH absolute concentrations inside an optically accessible Diesel combustion chamber. Using a numerical procedure for retrieving of optical data, supported by the knowledge of local temperature, the temporal evolution and spatial distributions of OH radical and NO were evaluated.

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. It was observed that the high pressure had a considerable influence on the mixture formation and on the spray vaporization through the improvement of the jet atomization. Moreover, both liquid and vapor fuel were influenced by the high swirling flow moving the air-fuel mixture in the chamber region far from the tip of the jet. The autoignition occurred in the region at higher vapor concentration characterized by the chemiluminescence emission arisen from radical species like OH, CH and HCO.

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. The spectral features of broadband flame emission characterized soot formation and its evolution.

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Conventional methods for combustion gas concentration measurement are typically based on gas sampling, sample treatment and subsequent analysis. These procedures could affect the species concentrations in particular when temporal variations of process parameters are under study. Moreover, in these methods, the concentration measurements are usually performed at standard temperature and pressure. In order to overcome these limitations, in-situ and real-time concentration measurement techniques are needed. In this paper, an in-situ technique with high spatial and temporal resolution, based on ultraviolet-visible absorption spectroscopy, was proposed. This technique allowed the simultaneous determination of NO and OH absolute concentrations inside optically accessible diesel combustion chamber. Temporal and spatial distribution of OH and NO was evaluated.

Nonevaporating diesel sprays from an Electronic Common-Rail system are investigated by two different laser light techniques at room temperature within vessels at both ambient and high pressures. Injection is performed by using single-hole injectors of mini-sac type with nozzle orifices 0.18 and 0.22 mm, which operate at injection pressures in the range 40 to 120 MPa. The fuel used is the standard ISO 4113. The densities of ambient gas (nitrogen) are varied in the constant volume vessel within the range 1.2 \md 58.4 kg/m\u3. Two different laser diagnostics are used to infer quantitative information on jet properties. The first is the light Extinction Ratio (ER) method, which is applied at wavelengths 632.8 nm and 832 nm in correspondence of the early instants (\mA200\md800 \gms) after the end of the liquid injection to infer the average droplet diameter and the number concentration along the line-of-sight. The second experimental technique is the Laser Doppler Anemometry (LDA). The droplet 2D velocity fields are measured as function of the radial coordinate and distance from the nozzle. A methodology is proposed to precisely locate the spray contour from the measurements of the 2D velocity distributions on the spray periphery region.

The common-rail injection system has allowed achieving a more flexible fuel injection control in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection. All these benefits have been gained by installing this device in combustion chambers born to work with the conventional distributor and in-line-pump injection systems. Their design was aimed to improve air-fuel mixing and therefore they were characterized by the adoption of high-swirl ports and re-entrant bowls. Experiments have shown that the high injection velocities induced by common-rail systems determine an enhancement of the air fuel mixing. By contrast, they cause a strong wall impingement too. The present paper aims to exploit a new configuration of the combustion chamber more suited to CR injection systems and characterized by low- swirl ports and larger bowl diameter in order to reduce the wall impingement. The goal is to achieve a higher air flow rate during induction as well as to reduce the fuel vapor wall impingement without compromising air-fuel mixing efficiency. This new combustion chamber configuration has been tested numerically and its performances have been compared to those of a H.S.D.I four valve diesel engine conventional combustion chamber. The analysis has been carried out by using a customized version of the CFD code KIVA3. Experimental results of the conventional combustion chamber have been used to validate the numerical models. The influence of the injection system configuration (i.e, hole numbers, inclination of the spray axis with respect cylinder head) on pressure cycle and NO\dx and soot engine-out emissions has been analyzed too. Computational results seem to indicate that the new combustion system concept may provide relevant benefits with respect to engine-out emissions without reducing engine performance.

Spectral flame emissivity and absorption measurements with high temporal and spatial resolution were performed in an optically accessible high-swirl divided-chamber Diesel system. Simultaneous determination of soot temperature, soot volume fraction and the OH radical concentration were made from the start to the end of the combustion in 153 locations equally distributed in the chamber. The engine was run at 2,000 rpm and at fixed air-fuel ratio realizing 200 consecutive combustion cycles. To visualize the spatial and temporal spray and flame evolution, direct high-speed photographic sequences were taken at 8,000 frames/s. The photographic sequences showed that the spray is strongly distorted and mixed by very high swirl resulting in a well premixed region where the combustion starts. The OH radicals were detected in the fuel reaction zone. Moreover OH concentration and soot volume fraction are well correlated with soot temperature.

Tangential component of velocity and turbulence were measured in three locations in the re-entrant combustion chamber of a motored single-cylinder d.i. diesel engine (0.435 liter, 21:1 compression ratio) using a laser doppler velocimetry system. Moreover, a modified LDV system with two-probe volume was used to measure directly lateral integral length scales of the velocity tangential component at two engine speeds. The measurements were made on a horizontal plane at 5 mm below the engine head from 100 degrees before TDC to 60 degrees after TDC of both the compression and expansion strokes. The engine was motored at 1,000 and 1,500 rpm respectively. An ensemble-averaging technique was performed to analyze the instantaneous velocity information supplied by two burst spectrum analyzers. The lateral integral length scale was obtained from the integral of the spatial correlation coefficient of the velocity fluctuation for different separation. The results demonstrated, for all points investigated, that the turbulence increases during the last 30 degrees of the compression stroke deducting energy from the mean motion that consequently decreases. At the location closer to the combustion chamber wall the turbulence, after a first decrease at the beginning of the expansion stroke, reaches a relative maximum as consequence of the air coming out from the combustion bowl, then definitely decreases. The lateral integral length scale decreases during the compression stroke reaching a broad minimum (about 1 mm) near TDC and increases during the expansion. It shows a dependence on the clearance height but seems to be not sensitive to engine speed.