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A PC-programmable electronic control unit (PECU), able to manage both conventional and future electronic injection systems to make a fixed number of consecutive injections (1 to 5 or more) controlling the injection pressure and the injection pulses duration as well as the separation time or dwell in between was used to study the behaviour of a Bosch common rail injection system both on dynamic spray bench and on engine test bench. The PECU allowed a reduction in the dwell time between consecutive injection pulses from the current value of 1800 μs to 500 μs. Photographic sequences of a five holes mini-sac nozzle making five consecutive injections at 400 - 800 and 1200 bar respectively were taken at ambient pressure and temperature. They showed that both spray penetration and cone angle at all operative conditions are very uniform and stable.

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 C2 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.

In-cylinder combustion phenomena, performance and emissions of a new single cylinder (225 cm3) naturally aspirated DI Diesel engine, with an advanced low cost common rail system for multiple injections, were investigated. The main objective of the present work was the study of the combustion system in terms of combustion chamber geometry, spray angle and number, injection pressure as well as injections number per engine cycle to find the best compromise between smoke and NOx emissions. CFD simulations were made to optimise the combustion chamber shape and the spray angle of a 6 holes nozzle to control the in-cylinder soot formation. The common rail (CR) system consisted of an in-house modified low cost PF Bosch injection unit for pumping the fuel up to 60MPa, a high pressure accumulator (rail) equipped with a pressure regulator valve and sensor as well as improved fast electronic drivers to drive both the pressure regulator valve and a commercial solenoid injector.

A non-evaporating transient high pressure diesel spray operating under different ambient conditions was studied. Tip penetration and Sauter Mean Diameter (SMD) were measured using simultaneously the high speed photography and the laser light extinction techniques. Comparisons between experiments and computations were performed. The spray simulations were carried out by KIVA code version two with and without breakup submodel. The effect of the grid spacing on the numerical results was also evaluated. The KIVA simulations consistently underestimate the jet penetration. The computations of SMD are in disagreement with the experiments. These inaccuracies are probably caused by the inadeguate atomization model and, in part, by the limitation of the experimental techniques.

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 acceptable limits.

A high swirl divided-chamber Diesel engine system with longitudinal and lateral optical access was developed to study the air-fuel mixing and combustion processes using both conventional and optical techniques. In particular, the spatial and temporal spray evolution, the mixture formation and the combustion phenomena were visualized by a high speed camera. The spatial distribution of soot temperature and soot volume fraction were estimated by spectral flame emissivity measurements using a polychromator with an intensified CCD camera. A modified version of the KIVA-3 numerical code was used to compute the flow field and spray combustion. The code was coupled with a pre-processor to generate the grid of the divided-chamber system and included models of droplet deformation breakup (DDB), single step ignition delay and turbulent mixing-controlled combustion.

Non evaporating 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 ÷ 58.4 kg/m3. 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 (∼200÷800 μs) 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).