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|Title:||Spatio-temporal Evolution of Diesel Sprays at the Early Start of Injection|
|Keywords:||Diesel sprays;Used injectors;Deposits;Transients;Start of injection anomalies;Hole-to-hole spray variation|
|Citation:||Applied Energy, 2018, 205 pp. 391 - 398 (8)|
|Abstract:||The impact of injector life on the spatio-temporal evolution of fuel spray quality was optically investigated using high speed imaging techniques. Both new and used injectors, which had been used in intense operation for up to 90,000 miles, were considered in this investigation. Used injectors are prone to wear, deposit formation, and altered internal nozzle ﬂow. High resolution SEM images clearly portray the presence of carbonaceous deposits both at the injector tip as well as within the holes of used injectors. Investigations revealed that used injectors tend to produce a chaotic hole-to-hole variation at the start of each injection, resulting in an asymmetric early fuel spraypenetration pattern in the ﬁrst 500μs. Often those sprays thatsuﬀereda reduced spray tippenetration rate at the start of injection also showed oﬀ-axis transient expansions, and those sprays appeared to be bulky compared to other sprays. Following the early asymmetric spray penetration phase of injection the retarded sprays undergo rapid acceleration with time, and this transformed the early asymmetric spray pattern into a nearly uniform spray pattern from all the oriﬁces in the quasi-steady state regime. The hole-to-hole penetration variations and the resultant asymmetric spray structure at the early start are therefore short lived transient phenomena. However if the radial expansion of the spray is large during the early phase, the radially expanded plume remains almost at the same radial location due to lack of local axial momentum, even after diﬀerent time instants of spray tip propagation. This appears as a bulge to the spray and can eventually end up as a stationary local pocket of fuel vapor close to the nozzle for the entire duration of injection. This may alter the ignition, ﬂame lift-oﬀ and entrainment characteristics of sprays injected from used or deposit rich injectors.|
|Appears in Collections:||Dept of Mechanical Aerospace and Civil Engineering Research Papers|
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