Injection characteristics and fuel-air mixing process of ammonia jets in a constant volume vessel

Fuel ◽  
2021 ◽  
Vol 304 ◽  
pp. 121408
Author(s):  
Zhifei Zhang ◽  
Tie Li ◽  
Run Chen ◽  
Ning Wang ◽  
Yijie Wei ◽  
...  
Keyword(s):  
Constant Volume ◽  
Mixing Process ◽  
Air Mixing

Analysis of the Mixing and Emission Characteristics in a Model Combustor

2018 ◽  
Author(s):  
Shan Li ◽  
Shanshan Zhang ◽  
Lingyun Hou ◽  
Zhuyin Ren
Keyword(s):  
Gas Turbines ◽  
Schmidt Number ◽  
Numerical Study ◽  
Flame Temperature ◽  
Scalar Dissipation ◽  
Mixing Process ◽  
Nox Formation ◽  
Turbulent Schmidt Number ◽  
Wide Range ◽  
Air Mixing

Modern gas turbines in power systems employ lean premixed combustion to lower flame temperature and thus achieve low NOx emissions. The fuel/air mixing process and its impacts on emissions are of paramount importance to combustor performance. In this study, the mixing process in a methane-fired model combustor was studied through an integrated experimental and numerical study. The experimental results show that at the dump location, the time-averaged fuel/air unmixedness is less than 10% over a wide range of testing conditions, demonstrating the good mixing performance of the specific premixer on the time-averaged level. A study of the effects of turbulent Schmidt number on the unmixedness prediction shows that for the complex flow field involved, it is challenging for Reynolds-Averaged Navier-Stokes (RANS) simulations with constant turbulent Schmidt number to accurately predict the mixing process throughout the combustor. Further analysis reveals that the production and scalar dissipation are the key physical processes controlling the fuel/air mixing. Finally, the NOx formation in this model combustor was analyzed and modelled through a flamelet-based approach, in which NOx formation is characterized through flame-front NOx and its post-flame formation rate obtained from one-dimensional laminar premixed flames. The effect of fuel/air unmixedness on NOx formation is accounted for through the presumed probability density functions (PDF) of mixture fraction. Results show that the measured NOx in the model combustor are bounded by the model predictions with the fuel/air unmixedness being 3% and 5% of the maximum unmixedness. In the context of RANS, the accuracy in NOx prediction depends on the unmixedness prediction which is sensitive to turbulent Schmidt number.

Mixing Field Analysis of a Gas Turbine Burner

2002 ◽  
Author(s):  
Peter Flohr ◽  
Patrick Schmitt ◽  
Christian Oliver Paschereit
Keyword(s):  
Gas Turbine ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Turbulence Models ◽  
Design Tool ◽  
Field Analysis ◽  
Mixing Process ◽  
Fuel Injector ◽  
Air Mixing ◽  
Gas Turbine Burner

An analytical and numerical study has been carried out with the view on the understanding of the physical mechanisms of the mixing process in a gas turbine burner. To this end, three methods at various levels of approximation have been used: At the simplest level an analytical model of the burner flow and the mixing process has been developed. It is demonstrated how this approach can be used to understand basic issues of the fuel-air mixing and how it can be applied as a design tool which guides the optimisation of a fuel injector device. At an intermediate level of approximation, steady-state CFD simulations, based on the k–ε- and RSM-turbulence models are used to describe the mixing process. All steady simulations fail to either predict the recirculation zone or the turbulence level correctly, and can therefore not be expected to capture the mixing correctly. At the most involved level of modelling time-accurate CFD based on unsteady RSM and LES-turbulence models are performed. The simulations show good agreement with experiments (and in the case of LES excellent agreement) for both, velocity and turbulence fields. Mixing predictions close to the fuel injectors suffer from a simplification used in the numerical setup, but the mixing field is predicted very well towards the exit of the burner. The contribution of the asymmetric coherent flow structure (which is associated with the internal recirculation zone) to the mixing process is quantified through a triple decomposition technique.

Computational Studies on Charge Stratification and Fuel-Air Mixing in a New Two-Stroke Engine

2005 ◽  
Author(s):  
Shamit Bakshi ◽  
T. N. C. Anand ◽  
R. V. Ravikrishna
Keyword(s):  
Initial Conditions ◽  
Computational Study ◽  
Three Dimensional ◽  
The State ◽  
Operating Conditions ◽  
Injection System ◽  
Critical Parameters ◽  
Mixing Process ◽  
Air Mixing ◽  
Stroke Engine

In this paper, detailed computational study is presented which helps to understand and improve the fuel-air mixing in a new direct-mixture-injection two-stroke engine. This new air-assisted injection system-based two-stroke engine is being developed at the Indian Institute of Science, Bangalore over the past few years. It shows the potential to meet emission norms such as EURO-II and EURO-III and also deliver satisfactory performance. This work proposes a comprehensive strategy to study the air-fuel mixing process in this engine and shows that this strategy can be potentially used to improve the engine performance. A three-dimensional compressible flow code with standard k–ε turbulence model with wall functions is developed and used for this modeling. 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 modeling 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, sensitivity of two critical parameters on the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted P–θ from a combustion simulation supports this recommendation.

Prediction of the Autoignition of a Fuel Jet in a Confined Turbulent Hot Coflow Using Machine Learning Methods

2020 ◽  
Author(s):  
Suhui Li ◽  
Wenkai Qian ◽  
Haoyang Liu ◽  
Min Zhu ◽  
Christos N. Markides
Keyword(s):  
Machine Learning ◽  
Quartz Tube ◽  
Support Vector ◽  
Model Parameters ◽  
Mixing Process ◽  
Learning Methods ◽  
Machine Learning Methods ◽  
Fuel Jet ◽  
Lean Premixed ◽  
Air Mixing

Abstract For advanced lean premixed gas turbine combustors that have high inlet air temperatures, autoignition may occur during the fuel/air mixing process, which can cause flame-holing inside the premixing device and burn the hardware. An experimental study was performed using a setup that mimics the fuel/air mixing process of lean-premixed combustors. In the present experiment, the preheated air was injected into a quartz tube, and a fuel jet was injected concentrically into the hot turbulent air coflow. The quartz tube allows for direct observation of the autoignition behavior, which develops when the fuel and air mix as they flow inside the tube. This paper presents a study combining machine learning methods and physical analysis that is aimed at predicting autoignition in such flows. A model for the prediction of autoignition of a fuel jet in a flow configuration referred to as a ‘confined turbulent hot coflow’ (CTHC) is developed using machine learning techniques based on binary logistic regression and support vector machine. Key factors that impact the autoignition phenomenon are identified by analyzing the underlying physics and are used to form the feature vector of the model. The model is trained using data from experiments and is validated by an additional set of data, which are selected randomly. The results show that the model predicts the autoignition event with satisfactory accuracy and quick turnaround. The trained model parameters in turn provide insights into the quantitative contribution of different factors that impact the autoignition event. Thus, the machine-learning based method can form an alternative to CFD modeling in some cases.

Analysis on the Mixing Process in a Heavy-Duty Diesel Engine under Different Conditions of Spray Position

2013 ◽  
Vol 732-733 ◽  
pp. 387-391
Author(s):  
Ye Yuan ◽  
Guo Xiu Li ◽  
Yu Song Yu ◽  
Yang Jie Xu
Keyword(s):  
Combustion Chamber ◽  
Three Dimensional ◽  
Mixing Process ◽  
Heavy Duty ◽  
Power Performance ◽  
Position Change ◽  
Heavy Duty Diesel Engine ◽  
Air Mixing ◽  
Circumferential Distribution ◽  
Heavy Duty Diesel

In order to investigate the influence of spray position on fuel air mixing quality, three-dimensional numerical simulation of the working process of a heavy-duty diesel was conducted. To quantitatively study the mechanism of the effect of spray position on fuel air mixing process, the deviation of spray centroid was introduced to describe the spray position change in combustion chamber. The results show that the gas intake swirl can affect the spatial distribution of spray in combustion chamber under three directions in cylindrical coordinate, in which the circumferential distribution is affected most. It then can be concluded that the spray can be limited to the vicinity of the combustion chamber axis. Better spray position, which is more helpful for the process of fuel air mixing and combustion, can be achieved by using optimal swirl, so that the power performance will be improved.

scholarly journals Air Mixing in Firn and the Age of the Air at Pore Close-Off

1988 ◽  
Vol 10 ◽  
pp. 141-145 ◽  
Author(s):  
J. Schwander ◽  
B. Stauffer ◽  
A. Sigg
Keyword(s):  
Molecular Diffusion ◽  
Age Distribution ◽  
Ice Cores ◽  
Age Difference ◽  
Mixing Process ◽  
One Dimensional ◽  
Dimensional Diffusion ◽  
Air Mixing ◽  
Age Relation ◽  
Diffusive Mixing

The air trapped in the bubbles of natural ice is not the same age as the surrounding ice. This is due to the fact that the air is enclosed in isolated bubbles only at the depth of the firn–ice transition. Within the overlying porous firn layer the air is able to mix and to exchange to a certain degree with the atmosphere. The age difference between ice and air is given by the age of the ice at pore close-off, less the mixing delay. Also, there is an age distribution due to diffusive smoothing and due to the gradual enclosure of the air at the firn–ice transition. Knowledge of this age relation is necessary for the interpretation of climatic parameters measured on ice cores. This work concentrates on the effect of diffusive mixing. We report on measurements of the diffusivity of CO2 and O2 (in N2) in firn samples from Siple Station, Antarctica. It is shown that the dominant mixing process is molecular diffusion. The diffusion coefficient depends approximately linearly on the porosity. A one-dimensional diffusion model has been used to calculate the air mixing in firn at Siple Station (Antarctica), at the South Pole, and at Station Crête (Greenland). An exchange time of between 10 and 50 years is obtained.

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