Characterization of Fuel Vapor Concentration Inside a Flash Boiling Spray

For current passenger vehicles, multi-point injection (MPI) systems are extensively employed for gasoline engines due to ease of control and rapid response. In these systems, the pressure within the intake manifold to which the injectors are installed can fall below the saturated vapor pressure of some hydrocarbon components present in the fuel. Such a condition leads to an atomization process in which flash boiling occurs. In the present work, the atomization process under flash boiling conditions has been characterized both experimentally and theoretically. The experimental investigation has been carried out with a spray test facility consisting of a variable pressure chamber equipped with a pintle type fuel nozzle. Infrared Extinction/Scattering (IRES) is utilized to provide temporal and spatially resolved distribution of the fuel vapor concentration within the spray. Imaging of elastic light scattering from a laser sheet is utilized to characterize the spatial and temporal distribution of the liquid. A theoretical model has been developed for the atomization process taking place for the present spray and compared with the experimental results. The results show that (1) IRES is suitable for application to transient sprays, (2) a correlation exists between vapor concentration and droplet distribution, (3) the amount of vapor increases and becomes uniform over a large volume when the chamber pressure is reduced to cause the flash boiling effect, and (4) the measured vapor mass flux correlate with the modeled mass flux.