Interaction of two in-line bubbles with different size in a viscous liquid is studied using volume-of-fluid method. Simulations are performed on initially spherical bubbles starting from rest. The influences of size ratio 0.5 ≤ R ≥ 1 and initial distance ratio 1.7 ≤ S ≥ 3 are investigated with fixed Eötvös number Eo = 50, Galilei number Ga = 100, density ratio η = 1,000, and viscosity ratio λ = 100. Two arrangement patterns are considered, the small-big arrangement (SBA) and big-small arrangement (BSA). Two distinct evolution regimes are defined: coalescence and penetration. The bubble-bubble interaction is intensified by increasing R and decreasing S, promoting the possibility of coalescence. Penetration is more prone to occur in BSA than in SBA, and it is absent in BSA when R ≤ 0.625 regardless of S. The ascending velocity of the leading bubble (LB) is nearly independent of size ratio, initial distance ratio, and arrangement pattern, since the motion of the LB is little influenced by the trailing bubble (TB). Meanwhile, the ascending velocity of the TB increases with increasing R and decreasing S. The LB usually plays a dominant role in the interaction, especially in BSA.KEYWORDS arrangement pattern, bubble-bubble interaction, initial distance ratio, size ratio, VOF
Fuel formulation with particular selection of fuel components is a promising approach that offer the reduction of harmful emissions without altering the combustion system performance. Each fuel component has their own combustion characteristics and hence contribution in emissions. Aromatic is one of the main component of fossil based fuels and have a strong correlation with the formation of PM emissions. Besides aromatics presence in fuel is essential for compatibility of fuel with combustion system and maintaining the energy density of the fuel. In this regard, a Rolls Royce combustor rig was used to test 16 aromatics blended with jet fuels in three different proportions. Moreover, a novel approach of flame luminosity imaging is employed to measure the PM emissions through the soot propensity profile. The results show that PM emissions increase with the proportional increase of aromatics. The di- and cyclo-aromatics produced significantly higher PM emissions compared to alkyl-benzenes. 3-isopropylcumene has the tendency to lowest PM formation and thus is a consideration as a selection of aromatic type in future fuels for lower PM emissions. Furthermore, it was also observed that PM number concentration measured by extractive method with DMS500 instrument correlates well with imaging methods for all the tested fuels. The present study provides an information of particular selection of aromatic for future fuel development.
Flow interference between an upstream stationary cylinder and an inline oscillating cylinder is studied with the lattice Boltzmann method. With a fixed Reynolds number Re=100 and pitch ratio L/D=4, the effects of oscillation amplitude A/D=[0.25, 1] and frequency f e /f s =[0.5, 2] are investigated. The wake response state is categorized into lock-in and non-lock-in. The lockin zone in the bifurcation diagram of amplitude versus frequency is discontinuous. Response states of upstream and downstream wakes are similar under the conditions of small amplitude or low frequency. However, with large oscillating parameters, the two wakes are prone to be in different states as the flow field becomes irregular. Two distinct flow regimes have been identified, i.e., single-cylinder and two-cylinder shedding regimes. The presence of single-cylinder shedding regime is attributed to the low shedding frequency of the downstream cylinder at large amplitude. Hydrodynamic forces of the oscillating tandem system are discussed. The results reveal that forces on the two cylinders behave differently and that the absence of vortices in the gap flow significantly reduces the forces exerting on the tandem system.
This work investigates the effect of blending biodiesel with diesel on the combustion of an isolated fuel droplet. Biodiesel blends substituting diesel oil in different concentrations on volumetric basis, in addition to neat diesel and biodiesel were studied. High speed schlieren and backlighting imaging techniques have been used to track droplet combustion. The results showed that partial substitution of diesel oil by biodiesel at the test conditions led to increasing secondary atomization from the droplet, compared to neat diesel or biodiesel fuel droplets. This in turn enhances evaporation, mixing, and then combustion. Additionally, the results showed that biodiesel has a higher burning rate compared to diesel, and that increasing biodiesel in the blend increases the burning rate of the blend. Nucleation has also been traced to take place inside the droplets of the blends. Moreover, flame size (height and width) has been reduced by increasing biodiesel concentration in the blend.
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