Experimental investigation on the conversion of fuel-N to NOx of quasi-particle in flue gas recirculation sintering process

Flue gas recirculation sintering process is a potential technology to decrease fuel consumption and NOx emissions compared with conventional sintering process. In present work, a vertical quartz tube reactor was used to investigate the combustion characteristics and conversion of fuel-N to NOx of quasi-particle. The mass conversion rate of quasi-particle increases with higher temperature. It was found that D₁ model is more appropriate than other models to describe quasi-particle combustion process through comparing correlation coefficients calculated by different mechanism models. Effects of temperature, coke size and proportion, circulating flue gas components on the conversion of fuel-N to NOx of quasi-particle were studied. The conversion rate of fuel-N to NOx of quasi-particle increases with higher temperature. With increasing coke size and proportion, the conversion rate of fuel-N to NOx decreases obviously. O₂ has a positive impact on the conversion of fuel-N to NOx of quasi-particle. CO could decrease the conversion rate of fuel-N to NOx by reducing NO directly or reacting with char to decrease NOx indirectly. CO₂ has an obviously inhibitory effect on the conversion of fuel-N to NOx of quasi-particle because it reacts with char to generate CO. The results were conducive to further understanding the combustion behavior and NOx formation mechanism of quasi-particle during flue gas recirculation sintering.     

Diluted Air Combustion and NOx Emission in a HiTAC Furnace

CFD modeling of NOx emission via N₂O-intermediate mechanism was developed to predict the NOx formation in an experimental furnace equipped with high temperature air combustion (HiTAC) system. The good agreement between the predicted and measured results illustrates the superiority of using a N₂O-intermediate model in prediction of NOx emission during low peak temperature, which happens in HiTAC systems. Moreover, the CFD and measured results show that the flame volume as well as NOx emission significantly depends on temperature and oxygen concentration. Lower NOx emission was experimentally and numerically obtained at lower input oxygen concentration conditions.     

Separate and combined effects of hydrogen and nitrogen additions on diesel engine combustion

Shortage of non-renewable energies, increase in fossil fuel prices and stricter emissions regulations due to high NOx and soot emissions emitted from combustion of heavy diesel fuels by compression ignition engines, has led consumers to use renewable, cleaner and cheap fuels. An investigation has been computationally carried out to explore the influences of hydrogen and nitrogen addition on engine performance such as indicated power and indicated specific energy consumption and amounts of pollutant emissions like NOx, soot, and CO in an HSDI (High-Speed Direct Injection) diesel engine. Optimized sub-models, such as turbulence model, spray model, combustion model and emissions models have selected for the main CFD code. Meanwhile, HF (Homogeneity Factor) has been employed for analysing in-cylinder air-fuel mixing quality under various addition conditions. After validations with experimental data of diesel combustion with a single addition of 4% hydrogen and combined addition of 6% hydrogen + 6% nitrogen, investigations have conducted for modeling mixing and combustion processes with additions of hydrogen and nitrogen by ranges of 2–8% (v/v). Results showed that a single addition of H₂ increased NOx and decreased CO and soot and improved ISEC and IP. In the case of nitrogen addition, NOx decreased, both CO and soot emission increased and ISEC and IP considerably ruined compared with NDC operation. Based on the results obtained for simultaneous addition of N₂ (8% of v/v) and H₂ (8% of v/v), NOx and soot emissions decreased by 11.5% and 42.5% respectively, and ISEC and IP improved 25.7% and 13%, respectively. But amount of CO emissions had an increase of 52% should be paid necessary attention as a main disadvantage.     

A chemical reactor network for oxides of nitrogen emission prediction in gas turbine combustor

This study presents the use of a new chemical reactor network （CRN） model and non-uniform injectors to predict the NOx emission pollutant in gas turbine combustor. The CRN uses information from Computational Fluid Dy- namics （CFD） combustion analysis with two injectors of CH4-air mixture. The injectors of CH4-air mixture have different lean equivalence ratio, and they control fuel flow to stabilize combustion and adjust combustor＇s equiva- lence ratio, Non-uniform injector is applied to improve the burning process of the turbine combustor. The results of the new CRN for NOx prediction in the gas turbine combustor show very good agreement with the experimen- tal data from Korea Electric Power Research Institute.     

Bayesian inference and uncertainty quantification for hydrogen-enriched and lean-premixed combustion systems

Development of probabilistic modelling tools to perform Bayesian inference and uncertainty quantification (UQ) is a challenging task for practical hydrogen-enriched and low-emission combustion systems due to the need to take into account simultaneously simulated fluid dynamics and detailed combustion chemistry. A large number of evaluations is required to calibrate models and estimate parameters using experimental data within the framework of Bayesian inference. This task is computationally prohibitive in high-fidelity and deterministic approaches such as large eddy simulation (LES) to design and optimize combustion systems. Therefore, there is a need to develop methods that: (a) are suitable for Bayesian inference studies and (b) characterize a range of solutions based on the uncertainty of modelling parameters and input conditions. This paper aims to develop a computationally-efficient toolchain to address these issues for probabilistic modelling of NOx emission in hydrogen-enriched and lean-premixed combustion systems. A novel method is implemented into the toolchain using a chemical reactor network (CRN) model, non-intrusive polynomial chaos expansion based on the point collocation method (NIPCE-PCM), and the Markov Chain Monte Carlo (MCMC) method. First, a CRN model is generated for a combustion system burning hydrogen-enriched methane/air mixtures at high-pressure lean-premixed conditions to compute NOx emission. A set of metamodels is then developed using NIPCE-PCM as a computationally efficient alternative to the physics-based CRN model. These surrogate models and experimental data are then implemented in the MCMC method to perform a two-step Bayesian calibration to maximize the agreement between model predictions and measurements. The average standard deviations for the prediction of exit temperature and NOx emission are reduced by almost 90% using this method. The calibrated model then used with confidence for global sensitivity and reliability analysis studies, which show that the volume of the main-flame zone is the most important parameter for NOx emission. The results show satisfactory performance for the developed toolchain to perform Bayesian inference and UQ studies, enabling a robust and consistent process for designing and optimising low-emission combustion systems.     

Progress on the studies about NOx emission in PFI-H2ICE

Owing to its brilliant combustion performance and cleanest combustion products, hydrogen has been widely considered as one best alternative fuel for internal combustion engines. However, in the cylinder of hydrogen internal combustion engines, high combustion temperature and oxygen enrichment make NOx is still one but the only combustion pollutant. Therefore, it is particularly important to control NOx emission for hydrogen fuelled engines. Since PFI-H₂ICE (port-fuel-injection hydrogen internal combustion engine) is the normal type of hydrogen fuelled engines, the present article will focus on the studies about NOx emission in PFI-H₂ICE researches. First, the present article reviews the mechanism of NOx generation in PFI-H₂ICE; upon chemical kinetics, the generation of NOx will be summarized and discussed into three major paths which including thermal NO path, NNH–NO path and N₂O–NO path. Then, the researches on the control methods of NOx for PFI-H₂ICE in recent years will be systematically reviewed, the influencing factors to reduce NOx emission will be summarized in some aspects which including combustion component control strategy, injection control strategy, ignition control strategy and engine compression ratio control strategy. To the PFI-H₂ICE operated at lean fuel conditions (like equivalence ratio is less than 0.5) or rich fuel conditions (like equivalence ratio is higher than 1), the technologies and the strategies of EGR (exhaust gas re-circulation) will be reviewed and discussed. It is hoped this literature review would enable researchers to systematically understand the progress of NOx emissions research in PFI-H₂ICE and explore further research directions.     

Experimental analysis of the effects of hydrogen addition on methane combustion

This paper presents gas emissions from turbulent chemical flow inside a model combustor, for different blending ratios of hydrogen–methane composite fuels. Gas emissions such as CO and O₂ from the combustion reaction were obtained using a gas analyzer. NOx emissions were measured with a NOx analyzer. The previously obtained flame temperature distributions were also presented. As the amount of hydrogen in the mixture increases, more hydrogen is involved in the combustion reaction, and more heat is released, and the higher temperature levels are resulted. The results have shown that the combustion efficiency increases and CO emission decreases when the hydrogen content is increased in blending fuel. It is also shown that the hydrogen–methane blending fuels are efficiently used without any important modification in the natural gas burner. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparison of combustion characteristics of petroleum coke and coal in one-dimensional furnace

The effect of primary air fraction ƒ ₁, outer secondary air swirl strength and excess oxygen coefficient on the combustion characteristics of petroleum coke, Hejin lean coal and Shenmu soft coal are researched on a one-dimensional furnace using a dual channel swirl burner. The results show that with the increase in primary air fraction ƒ ₁, the NO _x emission concentrations of both Hejin lean coal and petroleum coke increase, and the combustion worsens in the earlier stage, but the burn-out rate of Shenmu soft coal is improved. The NO _x emission concentration obtains a minimum value with an increase in ƒ ₁. The ignition and burn-out rate of petroleum coke and Shenmu soft coal are optimal when Ω_dl is minimum and Ω_dl= 0.87, respectively. However, both the NO _x emission concentration of petroleum coke and Shenmu soft coal are minimum when Ω_dl= 1.08. The increase in excess oxygen coefficient delays the ignition of petroleum coke, worsens the combustion condition and increases the NO _x emission concentration, but it greatly decreases the NO _x emission concentration of Shenmu soft coal.     

小缸径柴油机采用浅ω型燃烧系统的研究──燃烧率与NO_x排放

在两台采用浅ω型燃烧系统的高速柴油机上，对延迟供油的燃油消耗率、最高燃烧压力、NOx排放与排气烟度的影响进行了试验研究，并依据实测示功图采用现象学燃烧模型推求燃烧率与NOx生成，据此对试验结果作出理论解释。     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

超超临界锅炉炉内燃烧过程的数值模拟

采用计算流体力学软件PHOENICS，选择合理的数学模型，对1台1000 MW超超临界单炉膛双切圆煤粉炉内的燃烧过程进行数值模拟．着重研究了单炉膛双切圆燃烧特性、炉内焦炭燃烧特性及NO生成特性。结果表明：燃烧器前后墙布置导致炉内气流呈椭圆形，NO生成总体水平较低，焦炭燃尽效果较好，但在炉膛高度方向40m以上的区域，烟气高温区及大量未燃尽焦炭偏向前墙附近，且未燃尽焦炭在辐射屏区逐渐燃尽。针对这一问题提出了解决方案，结果表明：改进后的工况明显提高了焦炭的燃烧速度．使其在屏区以下基本燃尽，NO2排放量也有所降低。     

The decreasing effect of ammonia enrichment on the combustion emission of hydrogen,methane, and propane fuels

In the present study, non-premixed combustion and NOx emission of H₂, NH₃, C₃H₈, and CH₄ fuels have been studied in a combustion test unit under lean mixture conditions (λ = 4) at 8.6 kW thermal capacity. Furthermore, the combustion and NOx emission of the H₂, C₃H₈, and CH₄ fuels have been investigated for various NH₃ enrichment ratios (5, 10, 20, and 50%) and excess air coefficients (λ = 1.1, 2, 3, and 4) at the same thermal capacity. The obtained results have been compared for each fuel. Numerical simulation results show that H₂ emits intense energy through the reaction zone despite the lowest fuel consumption in mass, among others, due to its high calorific value. Therefore, it has a higher flame temperature than others. At the same time, C₃H₈ has the lowest flame temperature. Besides, NH₃ has the shortest flame length among others, while C₃H₈ has the most extended flame form. The highest level of NOx is released from the NH₃ flame in the combustion chamber, while the lowest NOx is released from the CH₄. However, the lowest NOx emission at the combustion chamber exit is obtained in NH₃ combustion, while the highest NOx emission is obtained with H₂ combustion. It results from the shortest flame length of NH₃, short residence time, and backward NOx reduction to N₂ for NH₃. As for H₂, high flame temperature and relatively long flame, and high residence time of the products trigger NOx formation and keep the NOx level high. On the other hand, excess air coefficient from 1.1 to 2 increases NOx for H₂, CH₄, and NH₃ due to their large flame diameters, unlike propane. Then, NOx emission levels decrease sharply as the excess air coefficient increases to 4 for each fuel. NH₃ fuel also emits minimum NOx in other excess air coefficients at the exit, while H₂ emits too much emission. With NH₃ enrichment, the NOx emissions of H₂, CH₄, and C₃H₈ fuels at the combustion chamber exit decrease gradually almost every excess air coefficient apart from λ = 1.1. As a general conclusion, like renewable fuels, H₂ appears to be a source of pollution in terms of NOx emissions in combustion applications. In contrast, NH₃ appears to be a relatively modest fuel with a low NOx level. In addition, the high amount of NOx emission released from H₂ and other fuels during the combustion can be remarkably reduced by NH₃ enrichment with an excess air combustion.     

基于SVM的对冲燃煤锅炉NOx排放特性

提出了一种基于支持向量机理论在燃煤锅炉NOx排放预测的方法．对某台300 MW旋流对冲燃煤电站锅炉进行了多工况热态试验,考虑温度对NOx生成的影响,利用火焰诊断系统对炉膛温度场进行了测量．应用支持向量机理论建立了NOx排放特性模型并进行了校验．通过同神经网络模型比较,证实了该模型泛化能力强、预测精度高的优点．该模型可为电厂锅炉通过燃烧调整降低NOx排放提供参考．     

污泥焚烧NOx排放特性预测的径向基网络模型

随着环保要求的不断提高,循环流化床的污泥焚烧以其较高的燃烧效率和较低的NO1x排放而日益受到关注.文中在循环流化床污泥焚烧试验研究的基础上,建立了基于径向基网络的NOx排放特性预测神经网络模型,并对此模型进行校验.结果表明,在不同污泥成分和运行参数下,径向基网络较反向传播网络能更好地预测污泥焚烧排放特性.     

船用柴油机EGR技术仿真研究

采用某船用中速单缸柴油机进行了EGR对性能及排放影响的仿真研究,并进行了试验验证。研究结果表明,采用EGR技术后,NOx加权排放下降到1.94(g.(kW.h)-1),但加权燃油消耗率上升至9.93(g.(kW.h)-1);通过提前喷油和增加EGR率相结合进行优化,虽然NOx加权排放上升到2.09(g.(kW.h)-1),但加权燃油消耗率下降至4.36(g.(kW.h)-1),柴油机燃油经济性得到明显优化。试验验证显示:仿真和试验结果吻合较好,表明经标定的DI-jet燃烧模型精度满足要求,能较准确预测柴油机性能及排放。     

The regulation effect of methane and hydrogen on the emission characteristics of ammonia/air combustion in a model combustor

Ammonia, made up of 17.8% hydrogen, has attracted a lot of attention in combustion community due to its zero carbon emission as a fuel in gas turbines. However, ammonia combustion still faces some challenges including the weak combustion and sharp NOx emissions which discourage its application. It was demonstrated that the combustion intensity of ammonia/air flame can be enhanced through adding active fuels like methane and hydrogen, while the NOx emission issue will emerge in the meantime. This study investigates regulation effect of methane and hydrogen on the emission characteristics of ammonia/air flame in a gas turbine combustor. The instantaneous OH profile and global emissions at the combustion chamber outlet are measured with Planar Laser Induced Fluorescence (PLIF) technique and the Fourier Transform Infrared (FTIR), respectively. The flames are also simulated by large eddy simulation to further reveal physical and chemical processes of the emissions formation. Results show that for NH₃/air flames, the emissions behavior of the gas turbine combustor is similar to the calculated one-dimensional flames. Moreover, the NOx emissions and the unburned NH₃ can be simultaneously controlled to a proper value at the equivalence ratio (φ) of approximate 1.1. The variation of NO and NO₂ with φ for NH₃/H₂/air flames and NH₃/CH₄/air flames at blending ratio (Z_f) of 0.1 are similar to the NH₃/air flames, with the peak moving towards rich condition. This indicates that the NH₃/air flame can be regulated through adding a small amount of active fuels without increasing the NOx emission level. However, when Z_f = 0.3, we observe a clear large NOx emission and CO for NH₃/CH₄/air flames, indicating H₂ is a better choice on the emission control. The LES results show that NO and OH radicals exhibit a general positive correlation. And the temperature plays a secondary role in promoting NOx formation comparing with CH₄/air flame.     

Characterization and challenge of development of producer gas fuel combustor: A review

Producer gas, which derived from a biomass gasification process, is considered as one of the alternative fuels, which is suitable for the heating process and power generation. Due to low heating density and impurities, combustion in an external combustion chamber constitutes an obvious option for the utilization of producer gas via the combustion process. This paper reviews the technical challenges and the development of the producer gas combustor. Various combustion techniques are reviewed. A stable flame combustion with low emissions (both CO and NO_x) constitutes a main requirement of the producer gas combustion. Flame stabilization techniques such as swirl-vane coupled with bluff-body, swirl flow configuration, and staging combustion were successfully employed to enhance the stability and performance of the producer gas combustion. As shown in the results of the studies, the combustion process can operate in a wide range of equivalence ratios with the exhaust gas temperature >600 °C. This temperature is sufficiently hot for the power generation and heating applications. Overall, NOx and CO emissions were below 700 ppm and 1.3%, respectively. In the flameless combustion mode, ultra-low emission for both CO and NOx were recorded. However, higher emission can be found when operated at a higher thermal load combustor. Homogeneity of the thermal field and low polluting emissions make flameless combustion a promising lean and clean combustion technology. Integration of the benefits of flameless combustion and producer gas fuel is an outstanding contribution in reducing emissions and enhancing the efficiency of the combustion systems.     

汽车排放物中NOx、HC和CO的预测模型研究

为更深入细致的研究汽车有害排放物的排放规律,提出了用以计算机仿真计算的柴油机排放物的数学模型。该预测模型是以现象学燃烧模型为基础的,NOx的数学模型用广义Zeldoich不平衡原理建立,HC和CO的数学模型采用化学平衡和反应动力学原理建立。用该模型计算了某型号柴油机的排放物,得到了这3种排放物在缸内的生成过程,并从它们的生成机理出发,分析了不同喷油定时对排放规律的影响,讨论了推迟喷油措施对降低排放物的效果。实机实验结果表明计算值与测量值吻合较好,并且都反映出相同的规律:NOx和CO的生成量随喷油提前角的增大而增大,而HC排放量随喷油提前角的增大而减少。     

Experimental parametric investigation of platinum catalysts using hydrogen fuel

The aviation organization is creating awareness for the overall reduction of NOx emissions by up to 80% in the near future. This motivates to conduct research on the current state of art, catalytic stabilized combustion chamber using hydrogen. This was achieved by performing an experimental parametric investigation of Platinum catalysts in two phases. Firstly, the design of three diverse configurations of mixers and was investigated experimentally and numerically. The chosen mixer was implemented in the parametric study of five different Pt catalysts varying in geometric and material properties. This was executed at unpressurized and NOx emission solely due to the catalytic reaction was examined for varying thermal power and air/fuel ratios. Furthermore, temperatures were recorded. Additionally, CFD simulation was accomplished and compared with the measurement data. The overall least NOx achieved was 7.5  ppm at 5 kW for the metal catalyst. The result of this work proposed suitable catalyst for the development of a combined combustor configuration (including catalyst and combustion chamber) which will be intended for small aircraft engine applications.     

Experimental research on a blended hydrogen-fuel engine

An experimental study on the performance of a single cylinder engine fueled with hydrogen/gas fule blends was carried out. The performance of engine with different fuel components under the load characteristics of the engine was analyzed. The experimental results showed that with the increase of hydrogen blending ratio, the combustion speed was accelerated, and the maximum torque and maximum pressure in the cylinder were increased; The maximum torque of blended fuel with 40% CO₂ was 68.3% of that without CO₂; The maximum pressure in cylinder of blended fuel with 40% H₂ was 1.6 times higher than that without hydrogen; When the proportion of hydrogen was more than 30%, the torque decreased; When the mixture was blended with 30% N₂, the engine torque reached the maximum at the hydrogen ratio of 15%; With the increase of hydrogen blending ratio, the emission of CO increased and the emission of HC and NOx decreased; When the hydrogen blending ratio remained unchanged, the CO emission was the largest at medium load, the HC emission was the largest at small load, and the NOx emission was the largest at high load; When the mixture was blended with 15% H₂, with the increase of the proportion of nitrogen, emission of CO decreased, emissions of HC and NOx increased. The research of this paper provided an experimental basis for the design and development of gas fuel engines.