Liquid Sheet Instability and Breakup in Primary Atomization for a Stirling Engine

Stirling engines use a pressure swirl nozzle and Combustion Gases Recirculation for fuel atomization and flammable mixture formation. Based on temporal linear stability analysis, an investigation of the liquid sheet instability and breakup in primary atomization is conducted, which reveals the liquid behavior and predicts the Sauter mean diameter (SMD). The effects of ejection ratio, back pressure, load, liquid sheet thickness, and liquid swirl intensity on primary atomization are studied. The results indicate that the ejected gas stabilizes the liquid sheet and holds back primary atomization. Increasing back pressure or load boosts primary atomization. The effect of liquid sheet thickness characterized by the liquid sheet inner radius to outer radius ratio h on instability is nonmonotonic. Above the thickness at h = 0.3, the liquid sheet instability is independent of liquid sheet thickness. Below that, the instability is related to thickness. The disturbance growth first decreases and then increases with decreasing thickness. The liquid swirl intensity has a slight destabilizing effect on the liquid sheet. Without a common rail system, the injection pressure is reduced under a low load, leading to poor atomization. To optimize the atomization under a low load, the common effects of ejection ratio, back pressure, and nozzle exit diameter are analyzed. SMD under the optimal condition decreases greatly. Additionally, the SMD does not decrease monotonically with the nozzle exit diameter.