1996-10-01

Measurement of Fuel Droplet Dynamics in the Inlet Port of an S.I. Engine Under Firing Conditions 961924

Cycle resolved fuel droplet dynamics measurements in the inlet port of an S.I. engine were performed under firing conditions in order to study real dynamic effects in the fuel flow to the engine.
A Phase Doppler Particle Analyzer (PDPA) was used to detect the droplet size and velocity. The optical access was through a glass window in the bottom of the intake channel. The PDPA was synchronised with the engine combustion cycle in order to study the results in the engine frequency domain. The measurements were performed over the cross section of the channel. Different injection timing and engine running conditions were investigated, using standard unleaded gasoline.
The results show that, during the camshaft's overlap period, there exists a “push-back” droplets effect, due to the pressure difference between the inlet manifold and the cylinder, that transports droplets far back in the inlet manifold. This “push-back” is immediately followed by a forward flow induced by the piston movement. The droplet flow is asymmetrically distributed over the height of the channel's cross section, with more droplets flowing backwards in the lower part of the channel. During a throttle opening, fewer droplets are detected and no pronounced push-back effects can be seen, compared to steady state conditions, however, during a throttle closing the opposite was not observed.
The study also shows that a refractive index of 1.44 in this type of PDPA measurement may be used as a fairly good approximation for all gasoline types. It is preferable to use the PDPA set-up for first order refraction mode since the second order refraction mode is not able to correctly measure some of the droplet diameters.

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