In-Cylinder Fuel Transport During the First Cranking Cycles in a Port Injected 4-Valve Engine

Fuel transport was visualized within the cylinder of a port injected four-valve SI engine having a transparent cylinder liner. Measurements were made while motoring at 250 rpm to simulate cranking conditions prior to the first firing cycle, and at 750 rpm to examine the effects of engine speed. A production GM Quad-4 cylinder head was used, and the stock single-jet port fuel injector was used to inject indolene. A digital camera was used to capture back-lighted images of cylinder wall wetting for open and closed intake valve injection. In addition, two-dimensional planar imaging of Mie scattering from the indolene fuel droplets was used to characterize the fuel droplet distribution as a function of crank angle for open and closed intake valve injection. LDV was used to measure the droplet and air velocities near the intake valves during fuel induction.

It was found that with open-valve injection a large fraction of the fuel impinged on the cylinder wall opposite the intake valves. This fuel did not completely vaporize over the engine cycle and built up over successive motored cycles. The small droplets that impinged upon the cylinder wall coalesced quickly due to surface tension forces, which impeded fuel vaporization from the cylinder wall. For closed-valve injection the fuel was stripped from the intake valves and ports very shortly after intake valve opening by the incoming air. There was very little impingement of fuel on the cylinder walls with closed-valve injection, but some fuel droplets apparently impinged on the piston top. It was observed that the droplets from closed-valve injection tend to be larger than those from open-valve injection, although this was not quantified. With closed valve injection, droplets entering the cylinder had lower velocities than the incoming air. With open valve injection, the early droplets entering the cylinder had higher velocities than the incoming air, but the droplet and air velocities were very close for most of the injection period.