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The paper presents a study of the influence of fuel pressure supply fluctuations on the upstream side of the fuel injector atomizer. The study is performed over a wide range of pressures (70 to 130 Mpa) with two different common-rail (CR) high-pressure fuel injectors. The common atomizer is a VCO-type equipped with conically shaped atomizer bores. With the injector tip (nozzle) mounted in a counter-pressure vessel the pressure fluctuations in the fuel-rail and in the injector body are recorded simultaneously with stroboscopic Schlieren-visualization of the time-resolved spray behavior. It is demonstrated that not only the instantaneous mass flow is affected. As a function of rail-pressure, pulse-width and injection strategy the pressure fluctuations change the spray hard-core structure and its break-up behavior.

In the present paper the impact of three different geometrical layouts of the discharge nozzle of a high-pressure diesel injector designed is examined for a common rail second generation direct injection system. The paper presents a comparative study of the spray behavior of the three different nozzle layouts connected to a 150 MPa rail-pressure when mounted on a 1.6 liter European passenger car engine. To evaluate experimentally the differences in the fundamental physical spray parameters several specially developed optical visualization techniques are used, which enable phase-Doppler, Laser-sheet and high-speed recordings of dense high pressure sprays. The change in basic spray parameters (time-resolved droplet distribution and spray momentum) caused by the nozzle geometry variation is examined. The impact on the in-cylinder penetration and mixing characteristics is studied with a 3D-numerical simulation code NCF-3D.

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.

In the present paper are examined the consequences of a substantial rise in the injection pressure for Gasoline Direct Injection (GDI) injector assemblies. The paper presents a comparative study of the spray behavior of two different injector nozzle layouts submitted to current 10 Mpa rail-pressure as well as to a 30 Mpa injection pressure. To evaluate the differences in the fundamental physical spray parameters are used several specially developed optical visualization techniques, which enable phase-Doppler, PIV, Laser-sheet and high-speed recordings of dense high pressure fuel sprays. A recently developed injector actuator and the necessary modifications to existing high-pressure pumps to reach a 30 MPa pressure level in the fuel system are presented. The change in basic spray parameters (time-resolved droplet distribution and spray momentum) caused by the rail-pressure rise is examined.

The paper presents a study of a key-element in the mixture preparation process. A typical common-rail (CR) high-pressure fuel injector was fitted with a prototype injector nozzle with atomizer bores of a particular conical layout. It is demonstrated within certain layout limits, that a considerable enhancement can be obtained for the secondary break-up of the hard-core fluid sprays produced by the nozzle. The impact on the combustion process is examined in terms of pressure and heat release as well as of the engine-out pollutant emission. The results are compared to those of an earlier developed CR high-pressure injector nozzle. The atomization behavior of the prototype nozzle is illustrated through experimental results in terms of engine-out emissions from a 1.3-liter turbo-charged passenger car diesel engine. The detailed spray behavior is visualized on a component test rig by use of specially developed optical visualization techniques.

In order to improve the atomization capability of a standard port fuel injector, an optimized suggestion for an air shrouded injector is presented. The fluid dynamic part of the retained solution is composed of a special flat seat design for the fuel metering function combined with a post atomization adapter enabling both mono- and multi-spray modes. The concept works equally well in natural manifold gradient mode and with an external pressure pump. The realized concept is tested in both free jet experiments and on two different 2 litre engines, one operated in stoechiometric conditions the other in lean-burn conditions. The experimental work confirms a potential of the concept to increase torque stability and thereby lean-burn limits, decrease required spark advance and enable open inlet valve injection and consequently decrease wall wetting phenomena.

In the future generation of low consumption SI-engine layouts, it has become necessary to reduce costs as well as the complexity level and, increase the system reliability by the latter. To avoid driving the GDI-system in the critical, very lean stratified operation mode without losing the fuel consumption benefit, a solution is suggested, which combines a fully variable valve control system with a low level, robust GDI combustion layout. The first part of the present paper presents the latest development in the field of high precision multi-hole GDI injector spray nozzles. The basic aspects of mixture preparation with multi-hole gasoline atomizers are highlighted and their spray behavior compared to that of the current swirl atomizer nozzle. The second part of the paper presents primary optimization of a largely homogeneous GDI combustion layout combined with a fully variable valve timing control system including complete cylinder de-activation.

The first part of the paper outlines the main potential advantages of the direct fuel injection concept and describes the overall layout of a system in which the keystones are a piston rotary fuel delivery pump with integrated pressure regulation and electromechanical fast responding fuel injectors. Three different nozzle designs are discussed, a divergent pintle solid cone, a pintle hollow cone swirl layout and a closed cap multijet design. In the second part of the paper the used experimental high pressure dynamic test equipment is discussed. Then the results obtained by the use of phase illuminated visualisation techniques and phase Doppler analysis as well as by a 3D CFD approach are presented. The paper concludes by relating the spray patterns and the associated droplet penetration velocities, produced by the different nozzle types, to the combustion chamber layout and to the possible manufacturing precision requirements for each nozzle type.

The present paper describes a study of the basic parameters, which govern particulate (soot) formation within the combustion chamber of a small displacement (1.3 liter) turbocharged European CR-diesel engine. The main tools used for the study are a real fired engine, a numerical virtual engine and a special high ambient pressure vessel for injector spray visualization. The paper describes an improved soot formation model implemented in the virtual engine setup. A comparison is presented between measured and computed combustion data at 8 different load points. The paper concludes with a discussion of the means, which can be used to minimize the particulate matter formation in the design phase of both the combustion layout and the fuel injector atomizer as well as in the design of the injection control strategies.