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This article presents an experimental analysis investigating the impact of swirl number (S) and annular passage area (B) on the stability limits of the premixed flames in a 20-kW tangential swirl burner. Three nozzles with different diameters (DN = 20, 25, and 30 mm) were used to achieve variable geometric swirl numbers (Sg = 0.918, 1.148, and 1.377). Three central fuel injectors (as a bluff-body) with different diameters (Dinj = 6, 8, and 12 mm) were used to obtain different annular passage areas. In the first part of the study, the results revealed that as swirl number (S) increased, flashback limits (FB) decreased (i.e., worsened), and the flame resistance to blowoff (BLO) improved. Thus, the best flame stability map was obtained with increasing S. In the second part of the study, changing the central fuel injector diameter (bluff-body) led to a change in the annular passage area (B) and had an important role in resisting and preventing flashback from combustion-induced vortex breakdown (CIVB). When B was increased (increasing fuel injector diameter), a significant improvement in flashback resistance was observed due to an increase in the momentum of the unburned mixture, while with a decrease in B (reducing fuel injector diameter), the limits of the flashback decreased and moved towards lean regions. However, it was found that the burner operation map increases with increasing B; the best operation map was found at S = 1.377 and B = 0.4, and it was (ϕFB = 1.18 - ϕBLO = 0.42) in the inlet tangential velocity range (Winlet= 0.58 to 2.84 m/s). Also, tests were carried out without the use of a bluff-body (central fuel injector), and it was found that there is a great impact on the flow field and the location and shape of the central recirculation zone (CRZ); thus, the stability map was narrower than that using the bluffbody. Consequently, adding bluff-bodies to swirling flows improves the mixing properties, increases the intensity of the CRZ, thus enhances the stable operation map. In addition, the bluff-body's presence greatly helps in eliminating CIVB flashback. [ABSTRACT FROM AUTHOR]

Diesel engines are considered one of the main sources of air pollution because of the gases emissions and particulate matter (PM), so, must be searched for a fuel helps to reduction from these harmful emissions. The aim of this research is to study the effect of using diesel-water emulsion as a fuel on diesel engine emissions. In this study, an experimental test was conducted on a single cylinder four-stroke diesel engine at constant speed (1500 rpm) and various loads (0% to 100% load) fueled with different ratios of dieselwater emulsions and compared it with the pure diesel fuel. Emulsion was prepared with proportions at 5%, 10%, 15% and 20% of the volume of water in diesel fuel; the Tween 20 and Oleic Acid were used as a surfactant to maintain the stability of emulsion fuel for long periods of time. The tests were conducted on the engine and NOX, HC, CO, and CO2 emissions were measured by using an exhaust gas analyzer of type (AVL DIGAS 444), and smoke opacity by using a smoke meter device of type (AVL 437C). Experimental results showed that the using of diesel-water emulsion significantly reduces from the NOX and smoke emissions. From the results, it was found that the highest of reduction ratio in NOX and smoke emissions were at fuel of WD-20, where they decreased by 32.3% and 38.8% respectively, compared with pure diesel fuel. [ABSTRACT FROM AUTHOR]