Interaction of Intake-Induced Flow and Injection Jet in a Direct-Injection Hydrogen-Fueled Engine Measured by PIV 2011-01-0673

The in-cylinder charge motion during the compression stroke of an optically accessible engine equipped with direct injection of hydrogen fuel is measured via particle image velocimetry (PIV). The evolution of the mean flow field and the tumble ratio are examined with and without injection, each with the unmodified 4-valve pent-roof engine head and with the intake ports modified to yield higher tumble. The measurements in the vertical symmetry plane of the cylinder show that intake modification produces the desired drastic increase in tumble flow, changing the tumble ratio at BDC from 0.22 to 0.70. Either intake-induced flow is completely disrupted by the high-pressure hydrogen injection from an angled, centrally located single-hole nozzle. The injection event leads to sudden reversal of the tumble. Hence the tumble ratio is negative after injection. However, the two intake configurations still differ in tumble ratio by about the same magnitude as before injection. Cyclic variability of the tumble ratio is similar for high and low-tumble cases, and in each case injection increases variability from about 0.4 units to 1 unit, remaining roughly constant throughout the compression stroke. Through its counter-flowing action, high pre-injection tumble modifies the spatial structure of the post-injection flow and reduces the peak mean velocities near the end of the compression stroke. Without injection, the magnitude of the velocity field's ensemble root-mean-square (RMS) is generally greater for high tumble, while with injection the low-tumble case exhibits higher RMS towards the end of the compression stroke.