Quantitative characterization on cyclic variation of mixture formation for flash boiling sprays

Abstract

The cyclic variation characteristics of the fuel-air mixture formation are essential for the fuel economy and the operating stability of engines. In this work, the cyclic variations of flash boiling and non-flash sprays were investigated experimentally by ultraviolet–visible laser absorption-scattering (UV-LAS) and high-speed Mie scattering optical diagnostics. The cyclic variations in the spray morphology and the mass distributions of liquid/vapor phase of acetone were characterized, and the effects of fuel temperature (Tf, 55–200 °C) and injection pressure (Pinj, 5–35 MPa) on the cyclic variations were analyzed. It was found that variations in morphology (penetration varies ± 10%) and fuel concentration distributions are more significant for the flash boiling sprays than those for the non-flash sprays, and the variations increase with the spray development, especially after end of injection. The cyclic variations of vapor mass distribution (Mv) increases by 22% when superheat degree varies from −47.8 to 97.2 °C and is reduced by 61% when increasing Pinj from 5 MPa to 35 MPa for the flash boiling spray. This study can provide insightful analysis and quantitative data for evaluating the issues caused by cyclic variations of spray such as spray impingement, ignition unreliability and combustion instability.