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The characterization of a turbulent diesel spray combustion process has been carried out in a divided chamber diesel system with optical accesses. Laser Doppler Anemometry, spectral extinction and flame intensity measurements have been performed from U.V., to visible from the start of injection to the end of combustion, at fixed air/fuel ratio and different engine speeds. Spatial distribution of fuel and vapor as well as the ignition location and soot distribution have been derived in order to study the mechanism of the air-fuel interaction and the combustion process. The analysis of results has shown that the high swirling motion transports the fuel towards the left part of the chamber and breaks up the jet into small droplets of different sizes and accelerates the fuel vaporization. Then, chemical and physical overlapped phases were observed during the ignition delay, contributing both to autoignition.

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=5.56. 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.

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.

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.

LDV measurements of the tangential component of the flow field velocity within the cylinder of a motored, real diesel engine are reported. A comparison of the fluid-dynamic behavior between toroidal and four-lobes square combustion chambers is shown. Tests were carried out over a range of engine speed of 500 and 1500 rpm. An ensemble-average data processing technique was used to analyze the velocity data recorded at 30 CAD BTDC and at TDC during compression stroke. The measurements were made at a depth of 3.0 mm from the piston head in two axial sections of the four-lobe combustion chamber. The results show that the four-lobe, square combustion chamber reduces the bulk swirl and increases the turbulence at the two engine speeds. The square cup transforms more of the kinetic energy of the bulk flows into turbulent kinetic energy than toroidal cup. At TDC the tangential velocity profile tends to solid body along the short section and to flat profile along the long section.

This paper illustrates the results of an experimental investigation on the liquid fuel spray from a multi-jet common rail injection system both under non evaporative and evaporative conditions. Tests have been taken using a 5 hole, 0.13 mm diameter, 150° spray angle, micro-sac nozzle having a flow rate of 270 cm3/30 sec@10 MPa exploring different injection strategies. Experiments have been taken, under non evaporative conditions, injecting the fuel within stagnant inert gas, at different density, in a high-pressure optically-accessible cylindrical vessel with three large quartz windows. Under evaporative conditions, the experiments have been taken within a crank-case scavenged single-cylinder 2-stroke direct injection Diesel engine provided of optical accesses to the combustion chamber. It allows to study the fuel injection process under thermodynamic conditions similar to those currently reached in modern direct injection diesel engines.

This paper illustrates a numerical and experimental analysis of performances and overall noise radiated from a common rail light duty diesel engine. The engine was equipped with two different injection systems: an under development low-cost fuel injector and a commercial Bosch one, employed for automotive applications. The injectors behaviour was compared throughout an experimental investigation that was carried out on a naturally aspirated, four strokes, two valves, single cylinder engine (225 cm3 displacement). Both engine performances, pollutant and noise emissions were measured at different operating conditions for two injection strategies. Concerning the acoustic analysis, both structure born and gasdynamic noise contributions were estimated using different experimental techniques.

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.

Experimental measurements and numerical computations were made to characterize a spray generated by a high-pressure swirl injector. The Phase Doppler technique was applied to get information on droplet sizes (d10) and axial velocities at defined distances from the injector tip. Global spray visualization was also made. Computations were carried out using a modified version of KIVA 3V. In particular, the break-up length of the sheet and its dimension were computed from a semi-empirical correlation related to the wave instability theory suggested by Dombrowski, including the modifications introduced by Han and Reitz. Two different approaches were used to describe the initial spray conditions. According to the first, discrete particles with a characteristic size equal to the thickness of the sheet are injected. The second approach assumes, that the particles having a SMD computed by a semi-empirical correlation are injected according to a statistical distribution.

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 atûP=300 and 500 mm of H2O.

The influence of fuel composition on mixture formation and first stage of combustion, occurring in a small high swirl combustion chamber of an IDI Diesel engine, was analyzed from measurements of spectral extinction and flame emissivity. Measurements were carried out in an optically accessible combustion chamber in which an air swirling flow is forced from the main chamber through a tangential passage. A conventional injection system was used to inject Tetradecane, N-heptane and Diesel fuel. The distribution of liquid and vapor and the interaction of the jet with air swirl were detected by UV-visible extinction measurements. The autoignition phase was characterized by UV-visible chemiluminescence measurements. For all fuels examined, it was observed that initially the liquid fuel penetrates almost linearly with time until reaching a maximum characteristic length, slightly dependent on the fuel.

Improvement of combustion system for low emissions of a single cylinder diesel engine is presented. In particular the effects of spray angle, holes diameter and number, compression ratio and combustion chamber geometry on engine performance and emissions are evaluated. The fluid-dynamic behaviour of combustion system is analyzed by LDA technique. Engine tests have been carried out at two engine speed and at different start of combustion. The particulate matter has been analyzed in terms of soluble organic fraction and dry soot.

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.

The optimization of combustion system of a single-cylinder d.i. diesel engine, representative of heavy-duty family, is discussed. The characterization of in-cylinder fluid motion of a conventional straight-sided and a re-entrant combustion chamber, carried out by LDA technique, is presented. Engine tests, using the same chambers and sacless nozzles with different holes diameter and appropriate spray angle, have been performed. Strong reduction of smoke and HC emissions has been obtained, remaining unchanged the engine performance.

The aim of the present paper is to provide an insight into the fluid dynamic processes that occur during the air/fuel mixture formation period in direct injection diesel engines. An experimental and numerical investigation has been performed to analyse the mixing process between an evaporating diesel spray and a swirl air flow under realistic engine conditions. Experimental tests have been carried out spraying the fuel within an optically accessible prototype 2-stroke Diesel engine equipped with an external combustion chamber having cylindrical shape. The intake air flow, coming from the engine cylinder, is forced within the combustion chamber by means of a tangential duct generating a well structured swirl flow similar to that developing in a real light duty diesel engine with a high swirl ratio. A micro-sac 5-hole, 0.13 mm diameter, 150° spray angle electro-hydraulic injector supplies the fuel by a common rail injection system able to manage multiple injection strategies.

The paper aims at providing information about the spray structure and its evolution within the combustion chamber of a heavy duty direct injection (HDDI) diesel engine. The spray penetration is investigated, firstly under quiescent conditions, injecting the fuel in a vessel under ambient temperature and controlled back pressure by both numerical and experimental analyses using the STAR-CD code and the imaging technique, respectively. Experimental results of fuel injection rate, fuel penetration, and spray cone angle are used as initial conditions to the code and for the comparison of predictions. The experimental investigation is carried out using a mechanical injection pump equipped by the heavy duty eight cylinder engine. Only one of its plungers has been activated and the fuel is discharged through a seven holes mechanical injector, 0.40 mm in diameter.

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.

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.