A phenomenological model for near-nozzle fluid processes: Identification and qualitative characterisations. (15th February 2022)

• Record Type: Journal Article
• Authors: Sykes, Dan; Stetsyuk, Viacheslav; Turner, Jack; de Sercey, Guillaume; Gold, Martin; Pearson, Richard; Crua, Cyril
• Is Part Of: Fuel. Volume 310:Part A(2022)
• Publication Date: 2022-02-15
• Subjects: High-speed microscopy -- Dribble -- Split injections -- Cavitation -- Rarefaction -- Fuel discharge -- Gas ingestion -- Surface films -- Low load -- Idling -- Near-nozzle region -- Injector deposits -- Spray wetting; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2021.122208
• Languages: English
• ISSNs: 0016-2361

Abstract

Abstract: It is well established that emissions and inefficiencies primarily arise from localised fuel rich regions, which do not undergo complete combustion. In order to achieve significant reductions in NOx and soot, modern engines employ multiple injection and flow rate profiling strategies. However, during the end of each injection event, the needle restricts the internal flow of fuel, rapidly reducing the inertia of the emerging spray. Atomisation is inhibited and large fluid structures are released into the cylinder. Once the flow subsides, fuel films remain on the nozzle surface well into the cycle. Fuel residing in the nozzle cavities emerges as the cycles progresses, amalgamating with the spray deposited films. The surface-bound fuel presents an ideal environment for deposit forming reactions and a medium for precursors to adhere onto. In order to better understand these processes we performed measurements of injection transients inside an optical reciprocating rapid compression machine, using high-speed long-distance microscopy to obtain detailed characterisations of fuel films on the surface of an injector. We summarise our observations into a new phenomenological model which describes the uncontrolled release of fuel over an entire engine cycle. This model identifies the micro-scale processes that lead to the ejection, accumulation and vaporisation of fuel in-between injection events. Characterisation of these critical, transient processes can support mitigation strategies that inhibit pollutants and the formation of injector deposits. Graphical abstract: Highlights: We observed nozzle-bound film behaviour after an injection event. A conceptual model is proposed for full-cycle, near-nozzle fluid processes. Splashback, expansion overspill and late-cycle overspill contribute to nozzle wetting. The frequency and magnitude of nozzle tip wetting is governed by injection pressure. Film morphology and transitional timings are driven by in-cylinder pressure cycling.