High pressure gas -liquid flow inside an effervescent diesel injector and its effect on spray characteristics

A study of effervescent Diesel injector (EDI) internal flow structure and spray characteristics was conducted to: (1) understand overall EDI internal flow structure and identify fundamental flow phenomena occurring at various locations; (2) establish the effect of internal flow structure on spray characteristics; (3) develop physical understanding of gas injection into a high-pressure, confined liquid cross-flow; (4) develop guidelines for commercial EDI design. Experiments were conducted using a specially developed optically accessible, variable geometry EDI (maximum operating pressure, p = 40 MPa). Effects of pressure, atomizing-gas-to-liquid ratio (GLR), injector exit orifice diameter, gas injection orifice diameter (do), and mixing chamber width (w c) on the internal flow structure and spray characteristics are assessed. A regime plot is provided for predicting the mixing chamber flow structure. Bubbly flow in the injector exit orifice, due to its low sonic speed, is anticipated to lead to the finest and most energy efficient atomization. Spray SMD lies between 5 and 10 μm for GLR \u3c 1% and p \u3e 10 MPa. Under these conditions the atomizing gas carries much greater energy than is needed for atomization and injector internal geometry has negligible effect on spray SMD. The gas injection into a high pressure (up to 40 MPa), confined liquid cross-flow study particularly focused on gas jet disintegration regimes and bubble size. Effects of gas injection and liquid cross-flow momentum fluxes, p, wc, and do were considered. Seven gas stream disintegration regimes were observed: single bubbling, pulse bubbling, pulse-to-jet-transition, jet varicose breakup, jet sinuous breakup, jet atomization, and severe effect of far wall. The regimes are classified based on gas and liquid momentum fluxes. Gas and liquid velocities and operating pressure have relatively little effect on bubble size. Gas injection orifice diameter has the strongest effect. A simple force balance based bubble size prediction model is developed. It is accurate within 20%. Future EDIs should be designed with smallest possible aerator holes in order to have bubbly flow in the exit orifice. Liquid cross-flow velocity should be high to avoid gas hold-up. EDIs should be operated around p = 30 MPa to minimize pulsation