Evaluation of orifice inlet geometries on single liquid injectors through cold-flow experiments

An experimental investigation was conducted to evaluate the inlet geometry effects of single, circular orifices on liquid injector pressure drop and exiting jet breakup length. Experiments were performed using distilled water as a hydrazine fuel simulant flowing through passageways simulating rocket engine injectors at the same Reynolds numbers and temperature conditions. Multiple orifice internal diameters and length-to-diameter ratios were evaluated with chamfered or sharp-edge orifice inlet geometries. Results showed that an increase in orifice diameter or decrease in length-to-diameter ratio led to decreased pressure drop across the injector. A sharp-edge orifice inlet geometry experienced cavitation under turbulent flow conditions at small length-to-diameter ratios and small orifice diameters, but was unaffected by cavitation at large orifice diameters for the same flow conditions. While a sharp-edge orifice inlet geometry was observed to have a greater pressure drop and longer jet breakup length for small orifices and length-to-diameter ratios, the chamfered orifice inlet geometry was not greatly influenced by length-to-diameter ratio at smaller orifices and had longer jet breakup lengths at higher orifices; meaning a larger percentage of liquid spray would reach an impingement point in a hypergolic liquid engine, increasing mixing and combustion.