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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 Rayleigh light scattering technique has been used to quantify the mean and fluctuating concentration of a passive scalar used to simulate fuel injection in a reciprocating, two-stroke model engine motored at 200 rpm in the absence of compression. The transient concentration field, which results from injection of Freon-12 vapour through the centre of an axisymmetrically located permanently open valve, has been investigated for injection timings of 40 deg. before and at top-dead-centre as a function of spatial position and crank angle. The purpose-built Rayleigh system, with gated digital data acquisition and software dust particle filtering, was first evaluated in a Freon-12 free jet by comparing results to those obtained with a sampling probe.