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The effect of inlet port design on swirl generation has been investigated for four helical ports from production, prototype and research Dl diesel engines by analyzing experimentally measured steady flow velocity distributions at the inlet valve curtain area and comparing their swirl characteristics in terms of the calculated in-cylinder angular momentum components and swirl ratio under operating conditions.

The effect of fuel injection on the flow and the spray/swirl and spray/piston interactions in direct-injection diesel engines have been investigated by simulating diesel sprays with gaseous jet(s) injected through centrally located, single- and multi-hole nozzles into the quiescent and swirling air of a motored engine running at 200rpm and incorporating a flat piston and a re-entrant piston-bowl. The axisymmetric velocity field with and without ‘fuel’ injection was characterised by laser velocimetry near TDC of compression in terms of spatially-resolved ensemble-averaged axial and swirl velocities, the ‘fuel’ concentration field was quantified by laser Rayleigh scattering and the two-dimensional flow was visualised by gated still photography using hollow microballoons as light scatterers.

Multidimensional calculations and laser Doppler anemometry measurements are presented of the air flow in a research diesel engine motored at 900 rpm with a compression ratio of ∼8.5. The engine comprised the cylinder head of a Ford 2.5L high speed direct-injection diesel mounted on a single cylinder Fetter engine modified to provide optical access for LDA measurements in a toroidal piston-bowl. The accuracy of the predictions is assessed against ensemble-averaged velocity data and found to be sufficient to allow better understanding of the flow in production engine geometries under realistic operating conditions.

The origin and development of swirl center precession in engine flows has been investigated in a steady flow rig, with and without a porous plate simulating a stationary piston, and in a model engine motored at 200rpm; swirl, in all cases, was generated by means of 60° vanes located in the axisymmetric inlet port. The swirl center performs a helical motion that originates as an instability in the forced-vortex core from its interaction with the axial flow at a free stagnation point and develops in the engine from the piston towards the cylinder head; an opposite trend has been observed in the steady flow case with the open-ended cylinder. In the ensemble-averaged measurements, swirl center precession has been identified by the increased tangential velocity fluctuations around the off-centre zero swirl velocity.

An optical single-cylinder four-valve high speed DI Diesel engine equipped with a high-pressure electronic fuel injection system has been used to obtain information about the spray development, combustion and exhaust emissions (NOx and smoke levels) for a range of operating conditions corresponding to engine speeds between 600 and 1800 rpm, injection pressures up to 1200 bars and fuel injection quantities from idle to full load. Two six-hole vertical mini-sac type injection nozzles with different hole sizes have been employed in order to investigate the effect of nozzle hole diameter on spray formation, combustion and exhaust emissions. Parallel to the experimental programme, a computational investigation of the fuel flow distribution inside the injection system and of the subsequent spray characteristics has been performed in order to assist in the interpretation of the results.

A new simulation approach to the modeling of the whole fuel injection process within a common-rail fuel injection system for direct-injection gasoline engines, including the pressure-swirl atomizer and the conical hollow-cone spray formed at the nozzle exit, is presented. The flow development in the common-rail fuel injection system is simulated using an 1-D model which accounts for the wave dynamics within the system and predicts the actual injection pressure and injection rate throughout the nozzle. The details of the flow inside its various flow passages and the discharge hole of the pressure-swirl atomizer are investigated using a two-phase CFD model which calculates the location of the liquid-gas interface using the VOF method and estimates the transient formation of the liquid film developing on the walls of the discharge hole due to the centrifugal forces acting on the swirling fluid.

An enlarged transparent model of a six-hole vertical diesel injector has been used to allow visualization of the flow at Reynolds and cavitation numbers matching those of real size injectors operating under normal Diesel engine conditions. The visualization system comprised a CCD camera, high-magnification lenses and a spark light source which allowed high-resolution images to be obtained. The flow conditions examined in terms of flow rates and pressures covered the range from low to full load of the real size injector while the needle lift position corresponded to that of full lift of the first- and second- stage in two-stage injectors. In addition, different values of needle eccentricity were tested in order to examine its effect on the cavitation structures within the injection holes.

A production six-hole conical sac-type nozzle incorporating a quartz window in one of the injection holes has been used in order to visualize the flow under cavitating flow conditions. Simultaneous variation of both the injection and the back chamber pressures allowed images to be obtained at various cavitation and Reynolds numbers for two different fixed needle lifts corresponding to the first- and the second-stage lift of two-stage injectors. The flow visualization system was based on a fast and high resolution CCD camera equipped with high magnification lenses which allowed details of the various flow regimes formed inside the injection hole to be identified. From the obtained images both hole cavitation initiated at the top inlet corner of the hole as well as string cavitation formed inside the sac volume and entering into the hole from the bottom corner, were identified to occur at different cavitation and Reynolds numbers.