The effect of using different Biodiesel fuels on jet development in a Diesel engine

The fuel properties and the injection rate-shape play an important role in the improvement of the combustion process of Diesel engines. In this work, the influences of using the forthcoming renewable biodiesel fuels on fuel jet development utilizing a computer simulation model created with the AVL Hydsim software were studied. Biodiesel fuels B20, B30 and B100 were considered and compared with the original pure Diesel fuel D100. The injection system behaviour under research was that one existing on a tractor engine equipped with Delphi DP200 pump and Delphi injectors. Two engine speeds of 1400 rpm and 2400 rpm were considered representative for the engine operation. For these speeds, the fuel jet characteristics as penetration, spray cone angle and Sauter mean diameter were analyzed. It can emphasize that in similar conditions of needle lift and injection rate-shape variation the usage of biodiesel fuels does not significantly alter the injection pressure and the Sauter mean diameter. However, the specific physical properties of biodiesel fuels affect substantially the spray penetration and its cone angle.

Comprehensive Knowledge-Driven AI System for Air Classification Process

Air classifier devices have a distinct advantage over other systems used to separate materials. They maximize the mill’s capacity and therefore constitute efficient methods of reducing the energy consumption of crushing and grinding operations. Since improvement in their performance is challenging, the development of an efficient modeling system is of great practical significance. The paper introduces a novel, knowledge-based classification (FLClass) system of bulk materials. A wide range of operating parameters are considered in the study: the mean mass and the Sauter mean diameter of the fed material, classifier rotor speed, working air pressure, and test conducting time. The output variables are the Sauter mean diameter and the cut size of the classification product, as well as the performance of the process. The model was successfully validated against experimental data. The maximum relative error between the measured and predicted data is lower than 9%. The presented fuzzy-logic-based approach allows an optimization study of the process to be conducted. For the considered range of input parameters, the highest performance of the classification process is equal to almost 362 g/min. To the best of our knowledge, this paper is the first one available in open literature dealing with the fuzzy logic approach in modeling the air classification process of bulk materials.

A Mathematical Model for Predicting the Sauter Mean Diameter of Liquid-Medium Ultrasonic Atomizing Nozzle Based on Orthogonal Design

As a new type of atomizing nozzle with superior atomizing performance, the liquid-medium ultrasonic atomization nozzle has been widely applied in the field of spray dust reduction. In this study, in order to establish a mathematical model for predicting the Sauter mean diameter (SMD) of such nozzles, the interaction between the SMD of the nozzle and the three influencing factors, i.e., air pressure, water pressure, and outlet diameter were investigated based on the custom-designed spraying experiment platform and orthogonal design methods. Through range analysis, it was obtained that the three parameters affecting the SMD of the nozzle are in the order of air pressure > water pressure > outlet diameter. On this basis, using the multivariate nonlinear regression method, the mathematical model for predicting the SMD of the nozzle was constructed. Comparison of the experimental results with the predicted values of the SMD of the nozzle by the multivariate nonlinear regression mathematical model, showed strong similarity with an average relative error of only about 5%. Therefore, the established mathematical model in this paper can be used to predict and calculate the droplet size for liquid-medium ultrasonic atomizing nozzles.

A Computational Fluid Dynamics-based Correlation to Predict Droplet Sauter Mean Diameter for Σ− Yliq Atomization Model in Pressure Swirl Atomizer

Liquid atomization is crucial to ensure efficient combustion as it is an inherent part of the injector system. The combustion of fuels relies on effective atomization to increase the surface area of the fuel and consequently achieve high rates of mixing and evaporation. Pressure swirl atomizers are inexpensive and reliable type of atomizer for fuel injection owing to its superior atomization characteristics and relatively simple geometry. The Sauter mean diameter (SMD) of atomizer contributes significantly to the combustion chamber performance. This paper presents a two-step strategy to predict droplet SMD for atomisation model in pressure swirl atomizer through the combination of experimentally validated Computation Fluid Dynamics (CFD) and Optimal Latin Hypercubes (OLHC) Design of Experiments (DoE) techniques. A three-dimensional Eulerian two-phase CFD model is developed to account for liquid and gas phases as a single continuum with high-density variation at large Reynolds and Weber numbers and validated against experimental measurements, before being employed to carry out a parametric study involving operating conditions and fluid properties of the pressure swirl atomizer. The atomizer is then represented in terms of four design variables, namely liquid viscosity, liquid velocity, surface tension and atomizer exit diameter. An 87-point OLHC DoE is constructed within the design variables space using a permutation genetic algorithm resulting in an accurate SMD prediction. Results show the newly developed SMD prediction is found to be superior compared with existing correlations and indicate significant improvement in the droplets SMD.

Interpreting Liquid Atomization Efficiency

Liquid atomization involves several mechanisms transforming a bulk of liquid into small droplets. The atomization efficiency usefulness is questionable considering its low values (0.01-1%). This work presents a general definition for atomization efficiency and explains why the Sauter mean diameter is the appropriate characteristic drop size (and no other mean diameter value). Finally, future directions are suggested for developing injector design tools from atomization efficiency.

Numerical Investigation of Droplet Properties of a Liquid Jet in Supersonic Crossflow

The atomization process of a liquid jet in supersonic crossflow with a Mach number of 1.94 was investigated numerically under the Eulerian-Lagrangian scheme. The droplet stripping process was calculated by the KH (Kelvin-Helmholtz) breakup model, and the secondary breakup due to the acceleration of shed droplets was calculated by the combination of the KH breakup model and the RT (Rayleigh-Taylor) breakup model. In our research, the existing KH-RT model was modified by optimizing the empirical constants incorporated in this model. Moreover, it was also found that the modified KH-RT breakup model is applied better to turbulent inflow of a liquid jet than laminar inflow concluded from the comparisons with experimental results. To validate the modified breakup model, three-dimensional spatial distribution and downstream distribution profiles of droplet properties of the liquid spray in the Ma = 1.94 airflow were successfully predicted in our simulations. Eventually, abundant numerical cases under different operational conditions were launched to investigate the correlations of SMD (Sauter Mean Diameter) with the nozzle diameter as well as the airflow Mach number, and at the same time, modified multivariate power functions were developed to describe the correlations.

Low-order modeling of high-altitude relight of jet engine combustors

A physics-based, low-order ignition model is used to assess the ignition performance of a kerosene-fueled gas-turbine combustor under high-altitude relight conditions. The ignition model used in this study is based on the motion of virtual flame particles and their extinction according to a Karlovitz number criterion, and a stochastic procedure is used to account for the effects of spray polydispersity on the flame’s extinction behavior. The effects of large droplets arising from poor fuel atomization at sub-idle conditions are then investigated in the context of the model parameters and the combustor’s ignition behavior. For that, a Reynolds-averaged Navier-Stokes simulation of the cold flow in the combustor was performed and used as an input for the ignition model. Ignition was possible with a Sauter mean diameter (SMD) of 50 μm, and was enhanced by increasing the spark volume. Although doubling the spark volume at larger SMDs (75 and 100 μm) resulted in the suppression of short-mode failure events, ignition was not achieved due to a reduction of the effective flammable volume in the combustor. Overall, a lower ignition probability is obtained when using the stochastic procedure for the spray, which is to be expected due to the additional detrimental effects associated with poor spray atomisation and high polydispersity.

Experimental Study of the Effect of the Expansion Segment Geometry on the Atomization of a Plain-Jet Airblast Atomizer

In this paper, the idea of adding an expansion segment over traditional airblast atomizer is proposed to improve the spray performance. According to the systematic experiments, the Sauter mean diameter, the droplet size distribution, and the droplet axial mean velocity were obtained to evaluate the spray performance. The correlations between spray performance and four geometrical parameters of the expansion segment which include the length, the angle, the throat area, and position of liquid jet are considered. The atomizer operates at atmospheric pressure and temperature, and the air liquid ratio range is from 0.48 to 2.85. The data of the results were measured by Phase Doppler Particle Analyzer. The results show that more uniform droplet size distribution can be achieved with the addition of expansion segment, and the droplet size distribution factor q of the case adding the expansion segment is 52.8% bigger than that of the case with no expansion segment. q increases as the length and angle of expansion segment increase. The Sauter mean diameter can be reduced by either reducing the length or angle of expansion segment. As for droplet velocity, it is determined that the droplet velocity increases along the radial direction, which is noteworthy because opposite trend is reported for traditional plain-jet atomizers. With an increase of the length, angle, and throat area of the expansion segment, the droplet axial velocity decays.

Effects of Discharge Area and Atomizing Gas Type in Full Cone Twin-Fluid Atomizer on Extinguishing Performance of Heptane Pool Fire under Two Heat Release Rate Conditions in an Enclosed Chamber

In this study, the effects of discharge area and atomizing gas type in a twin-fluid atomizer on heptane pool fire-extinguishing performance were investigated under the heat release rate conditions of 1.17 and 5.23 kW in an enclosed chamber. Large and small full cone twin-fluid atomizers were prepared. Nitrogen and air were used as atomizing gases. With respect to the droplet size of water mist, as the water and air flow rates decreased and increased, respectively, the Sauter mean diameter (SMD) of the water mist decreased. The SMD of large and small atomizers were in the range of approximately 12–60 and 12–49 μm, respectively. With respect to the discharge area effect, the small atomizer exhibited a shorter extinguishing time, lower peak surface temperature, and higher minimum oxygen concentration than the large atomizer. Furthermore, it was observed that the effect of the discharge area on fire-extinguishing performance is dominant under certain flow rate conditions. With respect to the atomizing gas type effect, nitrogen and air appeared to exhibit nearly similar extinguishing times, peak surface temperatures, and minimum oxygen concentrations under most flow rate conditions. Based on the present and previous studies, it was revealed that the effect of atomizing gas type on fire-extinguishing performance is dependent on the relative positions of the discharged flow and fire source.

Adsorption Kinetics of Various Frothers on Rising Bubbles of Different Sizes under Flotation Conditions

This paper studies the effect of the type and concentration of selected frothers, the gas flowrate, and the pore size of the porous frit on the bubble sizes (Sauter mean diameter, SMD) of bubbling flow produced in a micro-flotation cell, and the determination of bubble size distribution (BSD) in the presence of the frothers. The commercial frothers polypropylene glycols (PPG 200, 400, and 600), tri propylene glycol (BTPG), triethylene glycol (BTEG), dipropylene glycol (BDPG), and Methyl Isobutyl Carbinol (MIBC) were used in the present investigation. The frother concentration varied from 1 to 1000 ppm. The flow rate varied in the range of 25 to 100 cm3/min. The pore sizes of the frit were selected as 10–16 μm, 16–40 μm, and 40–100 μm. Each frother exhibited its own unique ability in preventing coalescence of the bubbles in the order of BTEG < BDPG < PPG 200 < MIBC < BTPG < PPG 400 < PPG 600. The factorial experiments established that the type of the frother and its concentration have a major effect on the size of the bubbles. The bubbles decreased twice their size when the frother concentration was increased from 1 ppm to 1000 ppm. The pore size of the frit is a significant factor as well. The size of the bubbles can be reduced from about 10% to about 40% by decreasing the pores from 40–100 μm to 10–16 μm but the level of this decrease depends on the type of the frother. The increase of the flowrate from 25 cm3/min to 100 cm3/min produced bubbles smaller by 25% to 50% for the case of BTEG, BDPG, PPG 200, MIBC, BTPG, while a minimum of the bubble sizes was reached for the case of PPG 400 and PPG 600, beyond which the bubbles enlarged their size. The BSD in the presence of PPG 600 varied around 0.3 mm, whereas BTEG gave a wider BSD which indicated that the type of frother affected the bubble production. Our analysis shows that the first group of frothers adsorbs instantly on the bubbles, once they leave the porous frit, thus reaching equilibrium. PPG 400 and PPG 600 adsorb significantly slower on the bubbles, possibly not reaching equilibrium during their resident time.