CO Emission Index Research Articles

Performance seeking control method for minimum pollutant emission mode for turbofan engine

The research shows that the impact of aero-engine pollutant emission on the environment cannot be ignored. In addition to fuel type and combustor structure, aero-engine exhaust pollutants are also related to engine operating conditions and control systems. In this context, taking CO and NOx as the main exhaust pollutants of the engine as the research object, a performance optimization control method of the minimum pollutant emission mode of the engine is proposed. Firstly, the CO and NOx emission characteristics of the engine under different operating conditions at sea level are calculated by CFD numerical simulation method, and the engine component-level model applicable to all flight envelope and all conditions is established according to the characteristic data. Secondly, in order to improve computational efficiency, an airborne model with high accuracy and real-time performance is established through the deep neural network. Compared to the component-level model, the average relative error of each performance parameter is less than 0.5 %, and the real-time performance is improved by about 12 times. Finally, the optimization principle of the minimum pollutant emission mode is discussed. The feasible sequential quadratic programming (FSQP) algorithm is selected, and the fuel quantity and throat area of the tail nozzle are taken as control variables. Numerical simulations are performed in the typical mission envelope. Simulation results show that the CO emission index decreases by 5 % and the NOx emission index decreases by more than 6.5 % through performance optimization control of the minimum pollutant emission mode under the premise of ensuring constant engine thrust and meeting other constraints.

Effect of hydrogen addition on combustion and thermal characteristics of impinging non-premixed jet flames for various heating value gases

This study experimentally investigates the effect of hydrogen addition on combustion and thermal characteristics of impinging non-premixed jet flames for low-heating values gases (LHVGs). We evaluate the flame morphology and stability using a concentric non-premixed combustor with an impingement plate. OH radicals are visualized using the OH* chemiluminescence and OH-planar laser-induced fluorescence (OH-PLIF) system. Emission characteristics are investigated by calculating CO and NOx emission indices. The results show that the flame stability region narrows as the heating value decreases but expands as hydrogen has been added. The low-OH radical intensity of LHVGs increases with the hydrogen addition. EICO and EINOx decrease with the reduction of heating values. EICO rapidly declines near the lifted flame limit due to the premixing of fuel and air downstream of the flame region. The effect of the hydrogen addition on EINOx is insignificant and shows very low emissions. The heat transfer rate into cooling water indicates a linear tendency with thermal power regardless of the fuel type. These findings show that LHVGs can be employed in existing-impinging flame systems so long as they remain within flame stability regions. Furthermore, hydrogen addition positively affects the expansion of flame stability, enhancing the utility of LHVGs.

Machine learning based approach for forecasting emission parameters of mixed flow turbofan engine at high power modes

To predict aircraft emissions from their own features has become more important as the usage field of aviation engines is extended to different sectors for different purposes. In the present study, thanks to by-pass ratio, pressure ratio and rated thrust of the one hundred sixty Mixed-Flow Turbofan (MFT) engines, NOx and CO emission indices as well as fuel flow for take-off and climb-out phases are predicted by using conventional Long-Short Term Memory (LSTM) at initial stage. After that, to improve the obtained estimations, hybrid Convolutional Neural Network (CNN-LSTM) model is employed to these engine dataset. The differences between two methods are presented by several types of error for each parameter. When considering the correlations, the relation between three variables and CO emission index is opposite whereas it is positively for NOx index. Moreover, NOx emission index of the MFT engines is predicted with 0.8166 of R2 by LSTM whereas its R2 increases to 0.8991 by means of hybrid CNN-LSTM approach. Amongst the models, the fuel flow is predicted the highest more than 0.95 of R2 whereas hybrid model makes it predictable with the higher accuracy, which has more than 0.99 of R2 for both phases. Moreover, these enhancements are observed in predicting of the other parameters regarding MFTs. It is thought that the proposed CNN-LSTM model could help in estimation of important parameters of gas turbine engines with higher level of accuracy.

Effects of flame-flame interaction on emission characteristics in gas turbine combustors

AbstractIn real gas turbines, multiple nozzles are used instead of a single-nozzle; therefore, interactions between flames are inevitable. In this study, the effects of flame-flame interaction on the emission characteristics and lean blowout limit were analysed in a CH4-fueled single- and dual-nozzle combustor. OH* chemiluminescence imaging showed that a flame-interacting region, where the two flames from the nozzles were merged, was present in the dual-nozzle combustor, unlike the single-nozzle combustor. Flow-field measurements using particle image velocimetry confirmed that a faster velocity region was formed at the flame merging region, thereby hindering flame stabilisation. In addition, we compared the emission indices of NOx and CO between the two combustors. The emission indices of CO were not significantly different; however, a distinct effect of flame-flame interaction was indicated in NOx. To understand the effect of flame-flame interaction on NOx emissions, we measured temperature distribution using a multi-point thermocouple. Results showed that a wider high-temperature region was formed in the dual-nozzle combustor compared to the single-nozzle combustor; this was attributable to the high OH* chemiluminescence intensity in the flame-interacting region. Furthermore, it was confirmed that the size of this interacting region caused the deformation of the temperature distribution in the combustor, which can induce a difference in the increase ratio of NOx emission between high and low equivalence ratio ranges. In conclusion, we confirmed that flame-flame interaction significantly affected temperature distribution in the downstream of the flame, and the change in temperature distribution contributed primarily to the varying concentration of the emission gas.

Experimental Investigation on the Heat Flux Distribution and Pollutant Emissions of Slot LPG/Air Premixed Impinging Flame Array

Experiments were carried out to investigate the heat transfer and pollutants emission characteristics of a slot LPG premixed flame array impinging normally onto a flat plate. The effects of jet-to-jet spacing (S/de), nozzle-to-plate distance (H/de), and jet Reynolds number (Re) on the heat flux and emission index of CO, CO2, and NOx/NO2 were examined. In addition, the thermal and emission characteristics between slot jets and circular jets were compared under identical experimental conditions. The results show that the more uniform heat flux distribution and higher total heat flux can be obtained at moderate jet-to-jet spacing, large jet-to-plate distance, and higher Reynolds number. EICO emissions can be influenced by the combined effects of jet-to-jet spacing, jet-to-plate distance, and higher Reynolds number. For the sake of the better combustion efficiency and lower EICO emission, the moderate jet-to-jet spacing (S/de = 2.5), larger jet-to-plate distance (H/de = 4), and relatively higher Reynolds number (Re = 1500) are preferred for the slot jet flame array. Furthermore, it is found that there exists a trade-off between the EICO and EINOx of the slot LPG flame array. Compared with multiple circular flame jets, multiple slot flames jets have the higher area-averaged heat flux due to the larger heating area and more uniform heat flux distribution, while the higher EICO emission and lower EINOx emission are due to the greater jet interaction suppressing the air entrainment. Thus, it is known that the slot flame array has a better heating performance but relatively higher pollutant emissions than the circular flame array.

Flow field characteristics, mixing and emissions performance of a lab-scale rich-quench-lean trapped-vortex combustor utilizing a quench orifice plate combined with a bluff-body

In this study, the low emission combustion technology of Rich-Quench-Lean (RQL) has been applied in Trapped-Vortex Combustor (TVC), and the combinative RQL-TVC shows a promising low emissions performance. By utilizing a quench orifice plate combined with a bluff-body, a lab-scale RQL-TVC was designed. The flow fields of RQL-TVC were measured by 2-D PIV and predicted by 3-D numerical simulation. Flow structures, radial profiles of normalized mean axial velocity, turbulence intensity and mixing level of the quench zone were analyzed. Results reveal that the dual-vortex and the single-vortex flow patterns both exist in cavities and quench zone of RQL-TVC, and the turbulence intensity is strong in the quench zone with some reverse flows. The spiral vortex was discussed by 3-D streamlines and the detail flow structures of the quench zone were analyzed based on the numerical results. The mixing level of the quench zone was determined, and results show that the quench device enhances the mixing level compared with TVC. Combustion efficiency and emissions performance were investigated experimentally, and results demonstrate that RQL-TVC has relatively higher combustion efficiency and lower emission index of CO, UHC and NOx than the same size lab-scale TVC in present work.

Research on Combustion Characteristics of Air–Light Hydrocarbon Mixing Gas

Air–light hydrocarbon mixing gas is a new type of city gas which is composed of light hydrocarbon with the main component of n-pentane and air mixed in a certain proportion. To explore the dominant reactions for CO production of air–light hydrocarbon mixing gas with different mixing degrees at the critical equivalence ratios, a computational study was conducted on the combustion characteristics, including the ignition delay time, laminar flame speed, extinction residence time, and emission of air–light hydrocarbon mixing gas at atmospheric pressure and room temperature in the present study. The calculated results indicate that the ignition delay time of air–light hydrocarbon mixing gas at temperatures of 1000–1118 K is greater than that of n-pentane, while the opposite at temperatures of 1118–1600 K. From the study of the laminar flame speed and ignition delay time, it was found that the essence of air–light hydrocarbon mixing gas is that its attribute parameter is determined by the ratio of n-pentane to the total amount of air at the moment of combustion. The changes in the extinction residence time and the CO emission index of air–light hydrocarbon mixing gas are not synchronized, that is the CO emission index is not necessarily small for air–light hydrocarbon mixing gas with excellent extinction residence time. CO sensitivity analysis and CO rate of production identified key species and reactions that are primarily responsible for CO formation and annihilation. The mixing degree plays a key role in the CO emission index of air–light hydrocarbon mixing gas, which has a constructive opinion on the future experiment and application of air–light hydrocarbon mixing gas.

Numerical Study of the Effect of Hydrogen or Syngas Additions to n-Decane on the Harmful Substance Emission from a Homogeneous Combustion Chamber

In this paper, we perform a comparative numerical analysis of turbulent combustion and harmful substance emission from a homogeneous combustion chamber operating on pure n-decane and mixed n-decane/hydrogen or n-decane/syngas fuels. The calculations were performed using the ANSYS Fluent program, and a reduced kinetic mechanism describing the oxidation of the fuels under consideration was developed. The hydrogen or syngas addition to n-decane in a 50/50 volume ratio is shown to lead to a decrease in temperature both inside the combustion chamber and in its outlet section. There is a simultaneous decrease in the carbon oxides and nitrogen emission. The depletion of the air–fuel mixture with an excess air coefficient of α = 2.3–2.5 sharply reduces the nitric oxide emission and simultaneously increases significantly the carbon monoxide emission. In this depletion, total NO and CO emission index increases more than twofold.

Effect of waste cooking oil methyl ester – Jet A-1 fuel blends on emissions and combustion characteristics of a swirl-stabilized lean pre-vaporized premixed flame

In the current work, Lean Pre-vaporized Premixed (LPP) combustion concept was used to investigate the flame characteristics of blended fuels using 5, 10, 15, and 20% blending ratios of Waste Cooking Oil Methyl Ester (WCOME) with Jet A-1 (symbolized as B5, B10, B15, and B20). Here, WCOME was produced from raw waste cooking oil by transesterification process with the help of ultrasonicator to reduce the production time. The flame was stabilized using a swirl burner characterized by the formation of central recirculation zone with Swirl Number (SN) equal 0.55; commonly called High Swirl Burner (HSB). The incoming air was preheated to a constant temperature of 250 °C and mixed with air at equivalence ratio φ of 0.75 for all tested fuel blends. Comparing to neat Jet A-1 fuel flame, flames of WCOME/Jet A-1 fuel blend revealed great effect of adding biodiesel to Jet A-1 on local and global emission characteristics of LPP combustion with comparable temperature distributions. Results showed a significant reduction in CO and NOx emissions indices for B20 at combustor exit by 41% and 30%, respectively, compared to those for pure Jet A-1 fuel. Aiming to increase the share of biofuel in fuel combustion, it can be concluded that, Jet A-1 fuel can be replaced by B20 without any modifications in the combustor design as they have similar temperature distribution with potential to remarkably reduce emissions.

Experimental Characterization of Circumferentially Arranged Fuel Port Inverse Jet Diffusion Flame Burner

ABSTRACT This paper presents experimental studies on flame height, thermal and emission characteristics of Inverse Jet Diffusion Flame (IJDF) using a circumferentially arranged fuel port (CAFP) burner by following two different protocols, namely, Protocol I and Protocol II. Experiments are carried out to investigate the effect of momentum flux ratio (MFR) on flame height and base flame height characteristics for a fixed air jet velocity, by varying fuel jet velocity (Protocol I) and by varying air jet velocity for a fixed fuel jet velocity (Protocol II). For both Protocols, there is a decrease in flame height with MFR due to the deterioration of fuel-air mixing process. Two separate semi-empirical correlations between normalized flame height and MFR are proposed for Protocol I and II, respectively. The center-line temperature characteristics indicate a faster air-fuel mixing at higher MFR for both Protocols. Moreover, Froude number is used to delineate the buoyancy and momentum-controlled regimes in IJDF. A constant temperature plateau is defined to identify the suitability of burner for industrial heating applications and is found to be higher for 32-port burner than that of the 12- port inverse jet diffusion flame burner due to enhanced air-fuel mixing along the jet central axis. Moreover, at lower MFR, emission index (EI) of NO remains independent of both the Protocols, whereas at higher MFR, the variation depends on the type of Protocol due to a larger variation of Froude number. On the other hand, the variation of CO emission index is almost independent of Protocol I and II. The experimental results show that the present 32 port burner design outperforms the emission characteristics of 12-port burner for an overall equivalence ratio less than 1.63. Two semi-empirical correlations for EINO and EICO, respectively, are developed as a function of overall equivalence ratio and MFR, which can be used for design and development of CAFP IJDF burner.

Experimental correlation of laminar flame pollutant emission indices with methyl ester fuel degree of unsaturation and equivalence ratio

Fuel unsaturation has been widely cited as a reason for the increased nitric oxide emissions from compression ignition engines when fueled with methyl esters (biodiesels) and their blends with petroleum counterparts. In an earlier study, a parameter called degree of unsaturation (DOU) was established to serve as a common platform across different fuel families (esters/alkanes/aromatics) to quantify the effects of fuel unsaturation, particularly with petroleum/biodiesel blends. DOU can be evaluated based on the average molecular formula of the fuel alone without involving complex and expensive experimental procedures such as those involved in the measurement of iodine number and bromine number. In this article, the fuel unsaturation effects on the emission characteristics from the laminar flames of blends of various pre-vaporized methyl esters, such as methyl oleate, neat biodiesels (from methyl esters of soy, canola, palm and rapeseed feedstock) and biodiesel blends were investigated at four burner-exit equivalence ratios of 0.9, 1.0, 1.2 and 1.5. The selection of these fuels for this study was an attempt to isolate the fuel unsaturation effect of biodiesels, and their blending effect with petroleum fuels. Experimental correlations were developed between DOU (over a range of 1.7–2.5) and global NO and CO emission indices as a function of equivalence ratio. The effects of DOU on EINO were significantly influenced by the equivalence ratio, with the maximum influence at an equivalence ratio of 1.2.

Numerical simulation of plasma-assisted combustion of methane-air mixtures in combustion chamber

A two-dimensional mathematical model was developed to investigate the effects of dielectric barrier discharge (DBD) plasma on CH4-air mixtures combustion at atmospheric pressure. Considering the physical and chemical processes of plasma-assisted combustion (PAC), plasma discharge, heat transfer and turbulent were simultaneously coupled into simulation of PAC. This coupling model consists of DBD kinetic model and methane combustion model. By comparing simulations and the original reference’s results, a high-accuracy of this model was validated. In addition, the effects of PAC actuation parameters on combustion characteristics were studied. Numerical simulations show that with an inlet airflow velocity of 10 m s−1, a CH4-air mixtures’ equivalence ratio of 0.5, an applied voltage of 10 kV, a frequency of 1200 kHz, compared to conventional combustion (CC), the highest flame temperature rises by 32 K; outlet temperature distribution coefficient drops by 2.3%; the maximum net reaction rate of CH4 and H2O increase by 11.22% and 12.80% respectively; the maximum CO emission index decreases by 14.61%; the mixing region turbulence mixing time reduces by 89 ms.

An Experimental Investigation on the NO and CO Emission Characteristics of a Swirl Convergent-Divergent Nozzle at Elevated Pressure

The behavior of the pollutants NO and CO at elevated combustor pressure are of special importance due to the continuing trend toward developing engines operating at higher pressure ratios to yield higher thermal efficiency. An experiment was performed to examine the NO and CO emissions for a swirl convergent-divergent nozzle at elevated pressure. The NO and CO correlations were obtained. Meanwhile, the flame length, exhaust gas oxygen concentration, exit temperature and global flame residence time were also determined to analyze the NO and CO emission characteristics. The results showed that, with the increase in combustor pressure P, flame length decreased proportionally to P−0.49; exit O2 volume fraction increased and exit temperature was reduced. The global flame residence time decreased proportionally to P−0.43. As pressure increased, The NO and Emission Index of NO (EINO) levels decreased proportionally to P−0.53 and P−0.6 respectively, which is mainly attributed to the influence of global flame residence time; the NO and EINO increased almost proportionally with the increase in global flame residence time. The EINO scaling EINO (ρue/d) was proportional to Fr0.42, which indicated that compared with pure fuel, the fuel diluted with primary air can cause a decrease in the exponent of the Fr power function. At higher pressure, the CO and Emission Index of CO (EICO) decreased proportionally to P−0.35 and P−0.4, respectively, due to the increased unburned methane and high pressure which accelerated chemical reaction kinetics to promote the conversion of CO to CO2.

Thermal performance evaluation of production technologies for non-centrifuged sugar for improvement in energy utilization

Non-centrifuged sugar (NCS) is produced through the evaporation of water from sugarcane juice, using the thermal energy released from the combustion of sugarcane bagasse. The energy efficiency of the process varies significantly according to the technology implemented in evaporation and combustion operations. Therefore, energy optimization usage becomes essential for the improvement of the equipment, as well as the appropriate development of the manufacturing process. The aim of this study was to evaluate seven groups of technologies related to bagasse combustion and heat exchange systems, used in the production of NCS. The evaluation was performed based on five parameters: overall thermal efficiency (η), energy consumption (MJ)/NCS (kg), O2, CO2 and CO emission indices at the exit of the process, flue gases/NCS (kg/kg), and air-fuel ratio (AFR). Each group of technologies evaluated had a significant effect on the parameters considered. However, the best results were shown by the technologies where steam was used in closed systems, obtaining an overall thermal efficiency of 63.63 ± 5.17%, with a significant decrease in fuel consumption and lower gas emissions.

Empirical analysis of the effect of descent flight path angle on primary gaseous emissions of commercial aircraft.

In this study, the effects of descent flight path angle (between 1.25° and 4.25°) on aircraft gaseous emissions (carbon monoxide, total hydrocarbons and nitrogen oxides) are explored using actual flight data from aircraft flight data recording system and emissions indices from the International Civil Aviation Organization. All emissions parameters are corrected to flight conditions using Boeing Fuel Flow Method2, where the ambient air pressure, temperature and humidity data are obtained from long-term radiosonde data measured close to the arrival airport. The main findings highlight that the higher the flight path angle, the higher the emission indices of CO and HC, whereas the lower the emissions index of NOx and fuel consumption. Furthermore, during a descent, a heavier aircraft tends to emit less CO and HC, and more NOx. For a five-tonne aircraft mass increase, the average change in emissions indices are found to be-4.1% and-5.7% (CO),-5.4% and-8.2% (HC), and+1.1% and+1.6% (NOx) for high and low flight path angle groups, respectively. The average emissions indices for CO, HC and NOx during descent are calculated to be 24.5, 1.7 and 5.6 g/kg of fuel, whereas the average emissions for descending from 32,000 ft (9.7 km) and 24,000 ft (7.3 km) are calculated to be 7-8 kg (CO), ∼0.5 kg (HC) and ∼3 kg (NOx).

Modeling study of hydrogen or syngas addition on combustion and emission characteristics of HCCI engine operating on iso-octane

Numerical study of energetic and emission characteristics of HCCI engine operating on iso-octane based fuel blends comprising hydrogen or syngas as additives is conducted on the basis of 2D CFD simulation for two values of fuel-to-air equivalence ratio ϕ = 0.4 and 0.2. The features of combustion are analyzed for the case when the maximal mass-average temperature (Tev)max during the combustion of different fuels is realized at an identical crank angle, which can be implemented at adequate intake temperature for every fuel blend. It is shown that the addition of H2 or syngas retards the ignition and decreases the combustion duration. This effect is more pronounced for leaner mixture with ϕ = 0.2. The admixture of H2 to iso-octane leads to the increase of the specific indicated work both for ϕ = 0.2 and ϕ = 0.4. The opposite tendency is detected when syngas H2/CO = 2/1 is added to iso-octane. The total emission index EINOx + EICO is determined mostly by the emission of NOx at ϕ = 0.4 and by the emission of CO at ϕ = 0.2. At ϕ = 0.4, the replacement of iso-octane by iso-octane/hydrogen(syngas) blend increases the NOx emission index (by 86% for iso-C8H18/H2 = 20/80 blend), which occurs due to the growth of maximal temperature in the cylinder. At ϕ = 0.2, the addition of H2 or syngas decreases the emission indices of CO, unburned hydrocarbons, and organics. The higher is the H2 amount in the blend, the more significant is the effect. The emission indices of NO2 and N2O, in this case, are essentially higher than that of NO. As N2O is a very harmful gas, its emission should be taken into consideration when evaluating the total emission of the engine at low load regimes.

Combustion Characteristics of Partially Premixed Prevaporized Palm Methyl Ester and Jet A Fuel Blends

Palm methyl ester (PME) is an attractive alternate biofuel produced by the transesterification of palm oil with methanol. This paper is a sequel to our earlier papers on the comparison of the flame structure and emission characteristics of neat PME with those of petroleum-derived fuels (No. 2 diesel and neat Jet A). Blends of prevaporized Jet A fuel and PME (25%, 50%, and 75% by volume) were studied in a laminar flame environment at burner-exit equivalence ratios of 2, 3, and 7. The global combustion characteristics including flame length, CO and NO emission indices, radiative heat fraction, and in-flame profiles of species concentration (CO, CO2, NO, and O2), temperature, and soot volume concentration were measured. The global CO emission index decreased significantly with the PME content in the blend at an equivalence ratio of 7; a 30% reduction was observed with the addition of 25% PME by volume, and a further reduction of 25% was observed with the addition of another 25% PME. The global NO emission index of the neat PME flame was 35% lower than that of the Jet A flame at an equivalence ratio of 2. The near-burner homogeneous gas-phase reaction zone increased in length with the addition of PME at all equivalence ratios. The concentration measurements highlighted the nonmonotonic variation of properties with the volume concentration of PME in the fuel blend. The fuel-bound oxygen and hydrogen of PME affected the combustion properties significantly.

배기가스 재순환을 적용한 희박-과농 연소시스템의 공해물질 배출특성 연구

In this study, the CH4/air lean-rich combustion system with exhaust gas recirculation (EGR) was investigated to explore the potential for lowering pollutant emissions. To achieve this purpose, experiments of lean-rich combustion system with EGR were conducted to measure the changes in the characteristics of the pollutant emission and flame shape with various equivalence ratios and EGR rates. Here, this study was applied to the fuel distribution ratio of 3:1 for the formation of the lean and rich flames. Additionally, the results were compared with CH4/air lean premixed combustion system. The results show that flame shape of lean-rich combustion system was determined by lean and rich equivalence ratios (ΦL and ΦR) and stratified flame was formed with increasing ΦR. According to the pollutant emission characteristics based on experimental results, the NOx and CO emission index (EINOx and EICO) decreased with increasing EGR rate. Especially, in the range needed to form a stable flame, the reduction rates of EINOx and EICO were approximately 47% and 48% for an EGR rate of 25%, global equivalence ratio of 0.85 and ΦL of 0.80 compared with lean premixed combustion system (Φ = 0.78).

Experimental and numerical study on NOx and CO emission characteristics of dimethyl ether/air jet diffusion flame

Abstract Dimethyl ether (DME) is one of the most promising alternative fuels emerging in the past few decades. At present, DME is mainly applied to the compression ignition (CI) engines, and numerous studies showed its superior performances in CI engines versus the traditional fuels. More recently, DME was also introduced into the field of industrial boiler to solve the pollution problem raised by coal usage. But the emission behavior of DME in this type of combustion system was not studied as thoroughly. In this paper, experiments and simulations are conducted to study the NOx and CO emission characteristics of the DME/air jet diffusion flame, which may be valuable for design and operation of the DME-fueled industrial boilers. During the measurements, a series of fuel jet velocities (uf) and air co-flow velocities (uco) were designed for the experiments to investigate their effects on NOx and CO emission indices systematically. Additionally, the CFD–CRN method was also employed to analyze NOx formation characteristics in different regions of the flame. The conversion relationship between the nitrogenous species (including NO, NO2, HCN, etc.), NOx formation and consumption pathways, and NOx and CO emission indices of the DME/air jet diffusion flame were analyzed by reaction rate and sensitivity analyses.

Global characteristics of non-premixed jet flames of hydrogen–hydrocarbon blended fuels

Blending hydrogen into hydrocarbon fuels can reduce the carbon-intensity of the fuel and extend the lean flammability limit. However, limited information is available of the global performance of attached, non-piloted hydrogen–hydrocarbon jet flames under well-defined boundary conditions. Three groups of blended fuels were investigated in the current study: Natural gas +H2 (with H2 volume fraction varying from 18.6% to 100%), C2H4+H2 (with H2 volume fraction varying from 0% to 100%), and 40% C2H4+41% H2+19% N2. Measurements were performed of flame dimensions, radiant fraction, and emission indices of NOx and CO. For flames with constant exit strain rate, the increase of hydrogen volume fraction was found to decrease the radiant fraction, decrease the global residence time and increase the NOx emission index. For flames of the same fuel composition, a higher strain rate results in a lower radiant fraction. The NOx production rate scales with the reciprocal of non-adiabatic flame temperature, consistent with the thermal NOx mechanism. The CO/CO2 ratio is determined by the competing influences of flame residence time, carbon input rate and mixing rate of the fuel and air.