Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

Atomization and Sprays

Scalar profiles and NO formation in laminar opposed-flow partially premixed methane/air flames

Concentrating solar power (CSP) has received significant attention among researchers, power-producing companies and state policymakers for its bulk electricity generation capability, overcoming the intermittency of solar resources. The parabolic trough collector (PTC) and solar power tower (SPT) are the two dominant CSP systems that are either operational or in the construction stage. The USA and Spain are global leaders in CSP electricity generation, whereas developing countries such as China and India are emerging by aggressive investment. Each year, hundreds of articles have been published on CSP. However, there is a need to observe the overall research development of this field which is missing in the current body of literature. To bridge this gap, this study 1) provides a most up-to-date overview of the CSP technologies implemented across the globe, 2) reviews previously published review articles on this issue to highlight major findings and 3) analyzes future research trends in the CSP research. Text mining approach is utilized to analyze and visualize the scientific landscape of the research. Thermal energy storage, solar collector and policy-level analysis are found as core topics of discussion in the previous studies. With a holistic analysis, it is found that direct steam generation (DSG) is a promising innovation which is reviewed in this study. This paper provides a comprehensive outlook on the CSP technologies and its research which offers practical help to the future researchers who start to research on this topic.

A comprehensive review of state-of-the-art concentrating solar power (CSP) technologies: current status and research trends

Flow physics plays a key role in nearly every facet of the COVID-19 pandemic. This includes the generation and aerosolization of virus-laden respiratory droplets from a host, its airborne dispersion and deposition on surfaces, as well as the subsequent inhalation of these bioaerosols by unsuspecting recipients. Fluid dynamics is also key to preventative measures such as the use of face masks, hand washing, ventilation of indoor environments and even social distancing. This article summarizes what we know and, more importantly, what we need to learn about the science underlying these issues so that we are better prepared to tackle the next outbreak of COVID-19 or a similar disease.

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The flow physics of COVID-19

Numerical models of surface tension play an increasingly important role in our capacity to understand and predict a wide range of multiphase flow problems The accuracy and robustness of these models have improved markedly in the past 20 years, so that they are now applicable to complex, three-dimensional configurations of great theoretical and practical interest In this review, I attempt to summarize the most significant recent developments in Eulerian surface tension models, with an emphasis on well-balanced estimation, curvature estimation, stability, and implicit time stepping, as well as test cases and applications The advantages and limitations of various models are discussed, with a focus on common features rather than differences Several avenues for further progress are suggested

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Numerical Models of Surface Tension

In the present study, the spray characteristics of Jatropha methyl ester (JME), diesel, and two surrogate fuels, n-dodecane and n-hexadecane, are investigated under evaporating ambient conditions. A high-pressure chamber with optical access is used for the study. Nitrogen gas filled in the chamber is heated to reach a final pressure of 50 bar and a final temperature of 900 K. A single-hole nozzle with a hole size of 190 mu m has been used for fuel injection. The results showed that the liquid length of JME is longer by 19%, 17%, and 11% compared to that of diesel at injection pressures of 500 bar, 1000 bar, and 1500 bar, respectively. At a given operating condition, the vapor penetration of JME and diesel are observed to be similar. Two surrogate fuels, n-dodecane and n-hexadecane, with similar property differences as those between diesel and a typical biodiesel, have been studied. The results show that the liquid length of n-hexadecane is about 20% longer than that of n-dodecane whereas both fuels have similar vapor penetration. Thus, the surrogate fuels exhibit differences between spray characteristics similar to those of diesel and biodiesel. A separate comparison of spray characteristics of diesel and n-hexadecane showed that it is an acceptable spray surrogate for diesel. An analytical model for vapor penetration has been verified against the experimental data and found to match well with the data. A parametric variation of fuel density showed that the effect of fuel density variation is compensated by the corresponding variation in injection velocity at a given injection pressure, which explains the experimentally observed trend of similar vapor penetration of all the fuels

A comparison of evaporating spray structure of jatrophamethyl ester and diesel, and surrogate fuels

This paper presents computational work on the biogas early phase combustion in spark ignition (SI) engines using detailed chemical kinetics. Specifically, the early phase combustion is studied to assess the effect of various ignition parameters such as spark plug location, spark energy, and number of spark plugs. An integrated version of the KIVA-3V and CHEMKIN codes was developed and used for the simulations utilizing detailed kinetics involving 325 reactions and 53 species The results show that location of the spark plug and local flow field play an important role. A central plug configuration, which is associated with higher local flow velocities in the vicinity of the spark plug, showed faster initial combustion. Although a dual plug
configuration shows the highest rate of fuel consumption, it is comparable to the rate exhibited by the central plug case. The radical species important in the initiation of combustion are identified, and their concentrations are monitored during the early phase of combustion. The concentration of these radicals is also observed to correlate very well with the above-mentioned trend.Thus, the role of these radicals in promoting faster combustion has been clearly established. It is also observed that the minimum ignition energy required to initiate a self-sustained flame depends on the flow field condition in the vicinity of the spark plug.Increasing the methane content in the biogas has shown improved combustion.

Full Chemical Kinetic Simulation of Biogas Early Phase Combustion in SI Engines

A new air-assisted injection system-based two-stroke engine has been developed at the Indian Institute of Science, Bangalore over the past few years and shows the potential to meet emission norms such as Euro II and Euro III and yet deliver satisfactory performance. The 70 cc engine works on the direct mixture injection principle with scavenging performed by air alone instead of an air-fuel mixture. A small 20 cc pump driven off the engine is used for mixture preparation prior to in-cylinder injection of the mixture. In the present study, the mixture injection and subsequent charge stratification process inside the engine cylinder is modelled. A three-dimensional compressible flow code with a standard k-e turbulence model with wall functions is developed and used for this modelling. To account for the moving boundary or piston in the engine cylinder domain, a non-stationary and deforming grid is used in this region with stationary cells in the ports and connecting ducts. A flux conservation scheme is used in the domain interface to allow the in-cylinder moving mesh to slide past the fixed port meshes. The initial conditions for flow parameters are taken from the output of a three-dimensional scavenging simulation. The state of the inlet charge is obtained from a separate modelling of the air-assisted injection system of this engine. The simulation results show that a large, near-stoichiometric region is present at most operating conditions in the cylinder head plane. The state of the in-cylinder charge at the onset of ignition is studied, leading to a good understanding of the mixing process. In addition, the sensitivity of two critical parameters in the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted pressure-crank angle history from a combustion simulation supports this recommendation.

In-cylinder charge stratification and fuel-air mixing in a new, low-emission two-stroke engine

Quantitative vapour concentration measurements in n-dodecane and n-hexadecane sprays

The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulations (LES). The modeling efforts are supported by experiments which are used both to provide accurate boundary and initial conditions and to evaluate droplet shapes in the near nozzle region. The droplets are modeled as Lagrangian parcels in an Eulerian continuum. Droplets in such configuration have been found to be distorted and not in perfect spherical shape from experimental results of our previous study. Droplet distortion is computed by Taylor-Analogy Breakup (TAB) distortion model. Each droplet is modelled as damped spring-mass system, where surface tension acts as a spring on the mass of the droplet and viscous dissipation provides the damping effect. The effort is to examine the effect of drag law used and the effect of this distortion on the droplet sizes produced in the flow field. Spray wind-ward trajectory and droplet sizes obtained from simulations are compared with the experimental results available. Although computational spray trajectory shows a reasonable match with experimental values, droplet sizes using the standard TAB model are found to be larger than that from experimental observation. To account for this distortion and its role in early breakup of droplets, constants of the TAB model are modified and the droplet sizes are found to be in good agreement with the experimental data.

https://journals.sagepub.com/doi/pdf/10.1177/1756827716652511

RV Ravikrishna

Papers

A comparison of evaporating spray structure of jatrophamethyl ester and diesel, and surrogate fuels

Full Chemical Kinetic Simulation of Biogas Early Phase Combustion in SI Engines

In-cylinder charge stratification and fuel-air mixing in a new, low-emission two-stroke engine

Quantitative vapour concentration measurements in n-dodecane and n-hexadecane sprays

LES of spray in crossflow - Effect of droplet distortion