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A computer model simulating the flow in fuel injection systems has been used in order to investigate the fuel injection processes in an in-line pump-based fuel injection system for direct-injection diesel engines. The model is one-dimensional and it is based on the mass and momentum conservation equations for the simulation of the fuel flow and on the equilibrium of forces for the simulation of the mechanical movements of the valves present in the system. The fuel injection system tested comprised an in-line pump whose characteristics were examined by using as input the measured line pressure signal and by modeling the pump operation itself as well as the fuel flow through single- and two-stage injectors. For the validation of the model, extensive comparison with experimental data has been performed for a wide range of pump operating conditions.

The flow structure in a four-stroke model engine motored at 200 rpm with a compression ratio of 3.5 has been investigated. Ensemble-averaged axial and swirl mean and rms velocities have been obtained by laser-Doppler anemometry downstream of an axisymmetrically located single valve with 30 and 60 degree seat angles and various lifts, with and without induction swirl. In all cases, the intake-generated flow structure in the axial plane disappears by the time the inlet valve closes and results in nearly homogeneous turbulence during compression with levels of 0.5–0.7 times the mean piston speed. The swirling flow, however, which is induced by means of vanes, persists through the compression stroke, evolving from a spiralling motion early during intake into solid body type of rotation near TDC of compression, with associated swirl ratios increasing with valve lift.

Measurements of flow, spray, combustion and performance characteristics are reported for a Hydra direct-injection diesel, based on the Ford 2.5 L, engine and equipped with a variable-swirl port, a unit fuel injector and optical access through the liner and piston. The results provide links between the pre-combustion and combustion flow and, at the same time, between purpose-built single-cylinder optical engines and multi-cylinder production engines of nearly identical combustion chamber geometry. In particular, the spray penetration was found to depend on engine speed, rather than load, with velocities up to around 260 m/s at atmospheric pressure and temperature which are reduced by a factor of 2.5 under operating conditions and seem to be unaffected by swirl. The duration of combustion was reduced with increasing swirl and ignition delay increased linearly with engine speed.

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.

Ensemble-averaged and in-cycle axial and swirl velocities have been measured by laser Doppler anemometry in the three-dimensional flow field of a four-stroke model engine motored at 200 rpm with a compression ratio of 6.7 and various cylinder head and piston geometries. The inlet configurations comprised an axisymmetric port with a shrouded valve and an off-centre port with two valve and swirl generating vane geometries. The piston configurations comprised flat, cylindrical and re-entrant axisymmetric piston-bowls. The results indicate that with the off-centre port a complex vortical flow pattern is generated during induction, which later either collapses in the absence of induction swirl or is transformed into a single rotating vortex in the transverse plane when swirl is present. The axisymmetric port with the shrouded valve gives rise to a double vortex structure and higher turbulence levels at TDC of compression compared to the off-centre port.