Analytical and experimental study of pressure dynamics in a pulsed water jet device

Pulsed high-velocity water jets are of interest for breaking rocks and other materials. This paper describes a straightforward way of generating single water pulse with a hammer impacting a piston that rests on top of a chamber filled with water. This impacting action pressurises the water, expelling it at high velocity through a nozzle. A theoretical investigation is outlined aimed at gaining a better understanding of this system for generating water pulses. A computational model is developed to simulate the pressure dynamics in the chamber based on continuity and momentum equations for a compressible viscous flow. This model is used to optimise the relative sizes of the hammer and piston as well as the height of the water column to produce the highest velocity water pulse. The model was validated by building an experimental apparatus. In these experiments maximum pressures of about 200 MPa were measured inside the chamber over a time period of about 560 μs. This produced a water pulse with maximum velocity of 600 m/s. Experiments were conducted with nozzle diameters between about 1 mm and 4 mm to study the effect of discharge volume on the pressure history. The results illustrate that although the peak attainable pressure decreases with an increase in nozzle diameter, the duration of the elevated pressure remains similar for all nozzles

Experimental Study of Ignition over Impact-Driven Supersonic Liquid Fuel Jet

This study experimentally investigates the mechanism of the ignition of the supersonic liquid fuel jet by the visualization. N-Hexadecane having the cetane number of 100 was used as a liquid for the jet in order to enhance the ignition potential of the liquid fuel jet. Moreover, the heat column and the high intensity CO2 laser were applied to initiate the ignition. The ignition over the liquid fuel jet was visualized by a high-speed digital video camera with a shadowgraph system. From the shadowgraph images, the autoignition or ignition of the supersonic liquid fuel jet, at the velocity of 1,186 m/s which is a Mach number relative to the air of 3.41, did not take place. The ignition still did not occur, even though the heat column or the high intensity CO2 laser was alone applied. The attempt to initiate the ignition over the liquid fuel jet was achieved by applying both the heat column and the high intensity CO2 laser. Observing the signs of luminous spots or flames in the shadowgraph would readily indicate the presence of ignitions. The mechanism of the ignition and combustion over the liquid fuel jet was clearly clarified. Moreover, it was found that the ignition over the supersonic liquid fuel jet in this study was rather the force ignition than being the auto-ignition induced by shock wave heating