Dynamics of spray impingement wall film under cold start conditions

Abstract

Fuel film that adhered on engine walls from spray impingement is considered a primary source of harmful combustion emissions. However, the physics of the wall film formation, propagation, and breakup is not fully understood yet because of its multiphase nature. Existing literature has revealed that the mass transportation within the fuel film takes a wave propagation form. This article aims to identify the dynamics of the wall film during spray impingement via high-speed laser diagnostics. In this work, a single-hole injector was used and the spray impinged onto a stage made of sapphire glass for diagnostics purposes. Iso-octane was used as the fuel and 10% ethanol was blended to dope rhodamine 6G as the fluorescent species for laser excitation. Simultaneous optical measurements, such as laser-induced fluorescence and Mie scattering, are performed to obtain the characteristics of the wall film quantitatively. Various aspects of the wall film, including the frequency of the wave, wave speed, and wave height, are inspected. The impact of fuel temperature and wall temperature under typical cold-start conditions are also studied to investigate the temperature dependence of the wall film dynamics. The research is also intended to provide quantitative experimental data for numerical models for impingement prediction and thus help the process of emission reduction and combustion optimization of internal combustion engines.

Optical investigation of flash boiling and its effect on in-cylinder combustion for butanol isomers and iso-octane

“…To the best of author's knowledge, such a link between flash boiling spray and in-cylinder combustion is relatively rare in open literature. [52][53][54][55][56][57] Soot emission in terms of natural flame luminosity was estimated using high-speed imaging inside an optically accessible engine.…”

Spray-wall interactions in direct-injection engines: An introductory overview

“…Li et al 5 report high-speed Mie scattering and calibrated LIF imaging to study the dynamics of relatively thick fuel films (∼100 µm) in a spray chamber under cold-start conditions. The impinging spray drives the formation of a few waves along the thick surface film, whose frequency, propagation speed, height, and dependence on plate temperature (–30 °C to 20 °C) are characterized in detail.…”

“…For the relatively thick films (typically at least a few tens of µm) that are prevalent under cold conditions, applications of LIF continue to advance, as illustrated by four papers in the present collection. 5,6,8,9 Successful application, especially in-cylinder, requires careful attention to calibration and to fluorescent-tracer selection and characterization (e.g. linear response, spectral and temperature dependence, and co-evaporation with the base fuel).…”

“…This special issue of International Journal of Engine Research (IJER) presents 11 papers that investigate spray-wall interactions (SWIs) and their effects at both fundamental and practical levels. These studies include numerical simulations 1–3 and measurements 4–8 of SWIs and fuel-film formation and dynamics, as well as measurements of fuel-film combustion and emissions processes. 9–11…”

Tip-Wetting Film Analysis Using Laser-Induced Fluorescence for Multihole Gasoline Direct Injectors under Flash Boiling Conditions

“…Liquid fuel usually stays in the combustor in the form of liquid films due to spray–wall interactions during fuel injection. Such interactions include direct spray–wall interactions, for instance, spray impingements where the fuel spray plumes directly hit the combustor wall or combustor piston. − Such issues can be addressed to some extent by spray or combustor heating methods. , Another category of spray–wall interactions is indirect spray interference, for example, wall wetting by entrained spray droplets or injector tip wetting during fuel injections. With more stringent emission regulation standards (e.g., Euro 6) implemented, soot emission from tip-wetting film combustions has been considered a significant source.…”