Air Preheat Temperature Research Articles

Interplay Between Unburned Emissions and NOx Emissions From a Dual Swirl Hydrogen Air Injector

Abstract OH planar laser induced fluorescence (OH-PLIF) and particle image velocimetry (PIV) are employed to analyze the structure of hydrogen/air flames stabilized by a dual swirl injection system under globally lean and atmospheric conditions with preheat air temperature varied from ambient up to 673 K. The flames exhibit two distinct reaction branches. The first, located in the central recirculation zone (CRZ), is a diffusion-controlled reaction layer characterized by a relatively large thickness associated with low strain rates. The second branch, stabilized in the shear layer of the swirling jet, is strongly influenced by large coherent structures. Depending on operating conditions, this front may adopt either the form of a fully diffusive strained reaction layer anchored to the hydrogen injector lip or a lifted diffusion front with a leading-edge flame evolving into a partially premixed flame at high air injection velocities. Flue gas analysis indicates NOx emission levels, typically below 10 ppm at 15% O2, for sufficiently large air injection velocities. Air preheating barely increases NOx emissions at lean operating conditions. The injector operational range is constrained only by the ultralean blowout limit reached for global equivalence ratios below 0.02. Furthermore, it demonstrates remarkable resilience to large and rapid drop in fuel flow rate. However, combustion efficiency drops close to the lean blowout (LBO) limit due to intermittent fragmentation of the flame wings that progresses further upstream as the equivalence ratio drops. The results demonstrate that fragmentation arises from the combined effects of a temperature drop in the central recirculation zone and the flame wings being exposed to high shear stress. Additionally, it is shown that combustion efficiency under ultralean conditions improves significantly with an increase in air preheat temperature.

Soot volume fraction measurements in aero-engine model combustor outlet using two-color laser-induced incandescence

Quantitative measurement of Soot Volume Fraction (SVF) is an essential prerequisite for controlling soot particle emissions from aero-engine combustors. As an in-situ and non-intrusive optical diagnostic technique, Laser-Induced Incandescence (LII) has been increasingly applied for soot concentration quantification in various combustion environments such as laminar flame, vehicle exhaust, internal combustion chamber as well as aero-engine combustor. In this work, we experimentally measured the spatial and temporal distribution of SVF using two-color LII technique at the outlet of a single-sector dual-swirl aero-engine model combustor. The effect of inlet pressure and air preheat temperature on the SVF distribution was separately investigated within a pressure range of 241–425 kPa and a temperature range of 292–500 K. The results show that soot production increases with the inlet pressure but generally decreases with the air preheat temperature. Qualitative analysis was provided to explain the above results of parametric studies. The LII experiments were also conducted under 3 designed conditions to evaluate soot emission under practical operations. Particularly, weak soot emission was detected at the outlet under the idle condition. Our experimental results provide a valuable benchmark for evaluating soot emission in the exhaust plume of this aero-engine combustor during practical operations.

Comprehensive pollutant emission prediction models from hydrogen-enriched methane combustion in a gas-fired boiler based on box-behnken design method

Hydrogen-enriched methane (HEM) combustion is an effective method for reducing the consumption of carbonaceous fuels. However, high adiabatic flame temperature of H2 can cause large NO emissions. To reduce the NO and CO2 emissions from HEM combustion, the Box-Behnken design (BBD) method combining response surface experimental design, analysis of variance, and multi-nonlinear regression models was adopted. The effects of the H2 doping ratio (XH2), preheated air temperature (Tair), excess air coefficient of burners arranged at the bottom (Ex,b), and their interactions on the NO, N2O, and CO2 emissions of a gas-fired boiler were investigated. According to the BBD method, the NO, N2O, and CO2 emissions prediction models with R2 exceeding 0.98 were proposed, respectively. The results showed that the increase of Tair had a positive effect on reducing NO emissions, as the NO exhausted from HEM combustion is mainly thermal NO. Compared with Tair and Ex,b, XH2 was the most significant factor affecting N2O and CO2 emissions, indicating that an increase in XH2 can significantly reduce greenhouse gas emissions. Additionally, the formation and consumption of N2O emissions presented a competitive mechanism at XH2 increased from 0 to 0.8, and CO2 emissions reduced with the increase of XH2, Tair, and Ex,b. Furthermore, a comprehensive emission prediction model with NO, N2O, and CO2 emissions was proposed. With the target of minimizing total NO, N2O and CO2 emissions, three groups of combinations for XH2, Tair, and Ex,b were obtained from the equal weight, entropy weight method, and criteria importance through the inter-criteria correlation method as 1:1:1, 24:9:17, and 21:11:18. The results showed that for minimize emissions, there is not much difference in the results calculated based on the optimal boundary conditions under different weights. For various reduction targets for nitrogen, carbon, and greenhouse gases, three groups of optimal combinations of XH2, Tair, and Ex,b were obtained and their accuracies were verified based on numerical calculations with relative errors below 6%. The proposed comprehensive pollutant emission prediction models are conducive to calculating the pollutant emissions of HEM combustion and guiding the investigation of prediction models considering other operating conditions.

Topology characteristics of liquid ammonia swirl spray flame

The utilization of liquid ammonia in gas turbines can reduce energy loss and start-up time. However, the flash boiling phenomenon and the high latent heat of liquid ammonia make the spray flame difficult to stabilize. Increasing the preheated air temperature or adding a small amount of hydrogen as a piloted fuel are considered as effective methods to enhance the stability. To understand the flame topological structure, simultaneous Mie scattering and planar laser-induced fluorescence of OH (OH-PLIF) techniques were used to visualize the liquid ammonia spray structure and flame region information. Results show that the liquid ammonia swirl spray flame exhibits the flame topological structure of distinct zoning characteristics, including the droplet zone, the mixing zone, and the flame zone. Increasing the preheated air temperature accelerates the evaporation of liquid ammonia, leading to an increase in the local equivalence ratio and radial flame splitting. At lower air temperature conditions, increasing the hydrogen blending ratio has minimal impact on the flame topological structure. However, at higher temperature conditions, hydrogen blending significantly promotes reaction intensity upstream and reduces the flame lift-off height, which makes the mixing zone smaller. In general, to achieve a better flame stability effect, the two factors need to be reasonably matched, which has important reference value for the development of liquid ammonia fueled gas turbine combustors.

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

Exergoeconomic Evaluation of a Cogeneration System Driven by a Natural Gas and Biomass Co-Firing Gas Turbine Combined with a Steam Rankine Cycle, Organic Rankine Cycle, and Absorption Chiller

Considering energy conversion efficiency, pollution emissions, and economic benefits, combining biomass with fossil fuels in power generation facilities is a viable approach to address prevailing energy deficits and environmental challenges. This research aimed to investigate the thermodynamic and exergoeconomic performance of a novel power and cooling cogeneration system based on a natural gas–biomass dual fuel gas turbine (DFGT). In this system, a steam Rankine cycle (SRC), a single-effect absorption chiller (SEAC), and an organic Rankine cycle (ORC) are employed as bottoming cycles for the waste heat cascade utilization of the DFGT. The effects of main operating parameters on the performance criteria are examined, and multi-objective optimization is accomplished with a genetic algorithm using exergy efficiency and the sum unit cost of the product (SUCP) as the objective functions. The results demonstrate the higher energy utilization efficiency of the proposed system with the thermal and exergy efficiencies of 75.69% and 41.76%, respectively, while the SUCP is 13.37 $/GJ. The exergy analysis reveals that the combustion chamber takes the largest proportion of the exergy destruction rate. The parametric analysis shows that the thermal and exergy efficiencies, as well as the SUCP, rise with the increase in the gas turbine inlet temperature or with the decrease in the preheated air temperature. Higher exergy efficiency and lower SUCP could be obtained by increasing the SRC turbine inlet pressure or decreasing the SRC condensation temperature. Finally, optimization results indicate that the system with an optimum solution yields 0.3% higher exergy efficiency and 2.8% lower SUCP compared with the base case.

Numerical study of inlet air conditions on methane flameless combustion characteristics

The current study investigates the influence of inlet air momentum and temperature for flameless characteristics. Three-dimensional computations were implemented by ANSYS FLUENT. A small-scale experimental combustor geometry was used for validation study. Turbulence modelling was performed by RNG k- ε model and the GRI-Eddy Dissipation Concept (GRI-EDC) model was used for the combustion modelling. The influence of inlet air velocity was investigated through using different air jet diameters at constant flow rate. Five different air jet diameters (4,6,8,10 and 12 mm) were studied. It was found that decreasing air jet diameter leads to an increase in the exhaust gas recirculation which reserve in mixture dilution (low O2 content mixture) subsequently, the reaction rate decreases which support the flameless mode creation. Also, this recirculated gas participates in heating up of fresh reactants which make the mixture tends to complete combustion. The influence of combustion air preheating temperature on NO and CO emissions were studied. CO and NO concentration were decreased with reducing the temperature of inlet preheated combustion air.

Spray Flame Characterization of a Dual Injector for Compact Combustion Systems

ABSTRACT The scalability of liquid fuel operated jet stabilized combustion system toward scales and mixing timescales relevant for corresponding micro gas turbine systems is impeded by the lack of suitable injection concepts. The high momentum of the combustion air jet can deteriorate the spray quality of conventional injection systems. In combustors with reduced mixing timescales (e.g. MGT and compact aero-engines) this results in elevated emissions and a prompt primary atomization is essential. For this purpose, a canonical confined jet spray burner is developed and equipped with a novel in-house dual-pressure swirl/airblast injection concept. An extensive parameter variation on the jet bulk velocity (80 , equivalence ratio (0.6 , combustion air preheat temperature (500 (K) 800) and premixing length (0.0 (mm) ≤ 48) is conducted to delineate the operational range. The spray process originating a partially premixed and a direct injection case is characterized by means of phase Doppler interferometry and shadowgraphy. The combustion process is described via OH*-chemiluminescence, flame photographs and exhaust gas measurements. The results show that the developed injection system yields Sauter mean diameters predominantly below 25 μm over the entire parameter range due to robust and prompt primary atomization. Moreover, the primary atomization process of the dual injector is sufficient under all conditions to confine secondary atomization close-to the combustor nozzle exit. The flame stabilization and reaction progress are more sensitive to the air preheat temperature than the bulk jet velocity variation as the mixture homogenization is limited by the vaporization process. Moreover, with decreasing reactivity (i.e. equivalence ratio and preheat temperature) the flame stabilization is increasingly dominated by the recirculated hot exhaust gas, indicating a transition from conventional turbulent flame propagation to auto-ignition influenced reaction progress. The resulting NOx and CO emissions approximate the values measured previously in related methane powered combustion systems. Consequently, the developed injection system is promising to expand the flexibility of compact gas turbines to liquid fuels while maintaining low emissions.

Development of an innovative high-performance poly-generation plant for efficient multi-level heat recovery of a biogas-powered micro gas turbine: Environmental and Multi-criteria analysis

Nowadays, the biogas-powered gas turbine cycles in poly-generation systems play a crucial role due to increasing fuel prices, declining renewable energy sources, and environmental concerns associated with fossil fuels. Concerning the high temperature of expanded gas, a novel high-performance poly-generation plant is achievable by intelligently selecting different subsystems. This paper presents a novel biogas-fueled poly-generation plant for producing electricity, refrigeration load, distilled water, and hydrogen simultaneously using multi-level heat recovery. An extended assessment of the devised plant output is performed based on energy-exergy, environmental, and exergoeconomic criteria, in which the plant’s gas turbine inlet temperature, preheated air temperature, air compressor pressure ratio, as well as turbine inlet pressure, are considered as variables. In the following, to demonstrate the advantages of using a Stirling engine, this study investigates two scenarios to reveal its superiority, and a bi-objective optimization is performed, where the objective functions comprise minimizing the poly-generation unit products cost and maximizing the sustainability index. When the plant is operated with a Stirling engine, the plant produces 986 kW of electricity, 137.5 kW of refrigeration load, 8.39 m3/h of distilled water, and 2.96 kg/h of hydrogen. In this case, the energetic and exergetic efficiencies of the proposed system are enhanced by 2.96% and 7.89%, respectively compared to non-Stirling engine mode. Also, the carbon dioxide emissions and sustainability index are ameliorated from 606.2 kg/MWh to 588.6 kg/MWh and from 1.47 to 1.5, respectively. In addition, the sensitivity analysis indicates that in a certain ratio of PRAC, the plant's performance reaches its optimal mode. Moreover, the unit cost of products and sustainability index are improved by 9.9% and 8%, respectively, compared to the base design case with the SE.

Stability and structure of lean swirling spray flames with various degrees of prevaporization

Achieving full premixing and complete evaporation in lean prevaporized premixed combustors is challenging as it depends on the spray injector characteristics, prevaporisation strategy, and flow conditions. This article experimentally explores the stability and structure of a turbulent swirling n-heptane spray flame under various degrees of prevaporization. The results show that preheating the air to 343 K and 393 K has little effect on the lean blow-off velocity, while recessing the fuel injection significantly decreases the lean stability limit. To correlate these limits, various attempts to define a Damköhler number were made, but unlike previous studies with no prevaporisation, the difficulty in defining laminar flame speed in the present case does not allow a single correlation to work for all degrees of prevaporization. Four stable cases that differ in equivalence ratio, air preheat temperature, and fuel injection recess are investigated using one-dimensional PDA, OH* chemiluminescence and CH[Formula: see text]O-planar laser-induced fluorescence (PLIF). Cases without fuel injection recess or air preheat exhibit a conical-shaped heat release zone near the shear layers. Preheating the air to 393 K reduced the Sauter mean diameter, increased prevaporization, and enabled a second heat release zone downstream of the fuel injection. Recessing the fuel injection by 25 mm reduced droplet velocities and led to a semi-spherical instead of a conical heat release zone. The CH[Formula: see text]O-PLIF signal without injection recess was high along the central axis and its distribution resembled that observed for spray jet flames. In contrast, with recessed spray injection, CH[Formula: see text]O was mainly found outside the central recirculation zone and only appeared inside during lean blow-off; similar to previous work with premixed flames. These findings show that different methods of prevaporization, which only differ by subtle changes in droplet characteristics, strongly impact flame stability. The present data can be used for turbulent flame modelling focusing on sprays and finite-rate kinetics.

Thermodynamic, exergoeconomic, and exergoenvironmental analysis of a combined cooling and power system for natural gas-biomass dual fuel gas turbine waste heat recovery

Integrating biomass energy into existing fossil fuel power plants is a practical way to solve the current energy shortages and environmental problems considering system feasibility and economic benefits. In this work, a novel combined cooling and power (CCP) system is proposed for waste heat recovery of a natural gas-biomass dual fuel gas turbine (DFGT) based on the organic Rankine cycle (ORC) and absorption refrigeration cycle (ARC). Comprehensive thermodynamic, exergoeconomic, and exergoenvironmental performance and parametric analysis of this system are performed. Results show that under the design condition, thermal efficiency, exergy efficiency, levelized cost of exergy (LCOE), and levelized environmental impact of exergy (LEIOE) of the system are 68.88%, 42.10%, and 21.16 $/GJ, and 5208.82 mPts/GJ, respectively. Among all the components, combustion chamber has the highest exergy destruction rate. The parametric analysis indicates that the thermal and exergy efficiencies rise by increasing the gas turbine inlet temperature (GTIT) and ORC turbine inlet pressure or by decreasing the preheated air temperature (PAT) and exhaust gas outlet temperature at high-temperature vapor generator. The LCOE and LEIOE present similar trends in most cases, which are most affected by the PAT and GTIT. Finally, a tri-objective optimization is conducted using exergy efficiency, LCOE, and LEIOE as objective functions. Pareto frontier is obtained and the final optimum solution is recommended for engineering practice.

Numerical simulation and operation optimization for billet heating in disc reheating furnace based on grey correlation

To further promote the equipment improvement of reheating furnaces in iron and steel production, considering heating movement and oxidation loss for the billet in 40 tons/hour self-designed disc reheating furnace, a comprehensive CFD model is established through the dynamic mesh technology with UDF subroutines. The billet heating process in the disc reheating furnace is numerically simulated to explore the dynamic heating characteristics of the billet in the disc reheating furnace. According to the orthogonal design, the grey correlation method is used to optimize the operation parameters such as the oxygen concentration, the charging temperature, the air preheated temperature, and the rotation speed. The results show the discharging temperature increases as the charging temperature, the oxygen concentration, or the air preheated temperature, and yet reduces with the rotation speed, which is opposite to the temperature difference. The important order is successively the oxygen concentration, the rotation speed, the air preheated temperature, and the charging temperature. The charging temperature has little effect on oxidation weight, while the oxygen concentration is obvious. It is of great significance for the current heat treatment of steel to increase efficiency, save cost, lower energy consumption, reduce pollutant emissions, and improve the automation application.

Investigation of jet A-1 and waste cooking oil biodiesel fuel blend flame characteristics stabilized by radial swirler in lean pre-vaporized premixed combustor

Energy crisis and the new environmental legislations have motivated researchers worldwide to come up with new solutions to these emerging problems. One of the proposed solutions is to biodiesel from vegetable and waste oils to substitute the conventional fuels. The current study aims to investigate the flame characteristics of waste cooking oil biodiesel fuel blend stabilized by radial swirler in Lean Pre-vaporized Premixed (LPP) combustor. In this scope following tasks were performed (i) preparing Waste Cooking Oil Methyl (WCOME) via an ultrasonic assisted transesterification process, (ii) designing and constructing radial swirler (with swirl number SN = 0.55), and (iii) investigating the flame structures of base Jet A-1 fuel and a blend of WCOME and Jet A-1 containing 10% of WCOME (symbolized as B10). Experiments were performed at equivalence ratio Φ = 0.75 and air preheat temperature of 310 °C. Measurements revealed more temperature distribution with lower maximum value for B10 than those for base fuel. CO was higher for B10 at exit level in the range of 14,000 ppm. On the other hand, it was on average of 230 ppm for Jet A-1. NOx emissions recorded was slightly lower for B10 than Jet A-1, but both were about 10 ppm. It could be concluded that, B10 can replace Jet A-1 to reduce NOx emissions with uniform temperature distribution. Use of LPP combustion reduces gas turbine emissions and use of radial swirler to stabilize the lean premixed mixture is confirmed.

Parametric study of the ceramic roller hearth kiln combustion chamber with pre-heated air from the kiln flue gases

The energy demand for the heating process of ceramic tiles is very high and plays a significant role in environmental pollution with a higher rate of release of CO2. The energy consumption of ceramic tiles can be optimized with an efficient or complete combustion possibility with less fuel input. This is achieved with the optimum design of the burner and its combustion air. In this research, an attempt has been made to optimize the combustion process of the ceramic kiln section with the utilization of waste heat recovery from the exhaust gases released from the kiln section. This exhaust air consists of high internal energy; hence, its effect has been studied with different temperature and pressure inlet conditions to optimize the combustion process. The whole project has been executed numerically by considering the cross-sectional domain of the kiln module. It is equipped with two burners on either side of the domain and accomplishes combustion of natural gas. The internal flow physics with chemical reaction has been analyzed by solving the Reynolds averaged Navier-Stokes equations, energy, and species transport conservation equations. From the analysis of different operating conditions of the kiln, it is found that the reaction rate increases with an increase in pre-heated air temperature, which is heated by the kiln exhaust gases. The desired operating temperature of 1100–1300 °C of the kiln has been achieved even with decreased fuel intake of 0.02 g/s by considering the increased waste heat recovery from the kiln flue gases. Among the different working conditions, case-4 is the optimum operating condition for reducing the fuel usage of 103.67 kg per day without compromising the desired output.

Autoignition of isolated n-heptane droplets in air and hot combustion products at microturbine conditions

Spontaneous ignition of isolated n-heptane droplets with initial diameters of 20–100 is simulated using air at 4 atm and 700–1200 K, which includes the typical operating conditions of recuperated microturbines. Because some fuel droplets in a combustor may be sprayed or carried to near the recirculation zone, the simulations use a mixture of pure air and hot combustion products as the oxidiser. The flame structures, evaporation times, and autoignition times in both physical and mixture fraction spaces for the different conditions are presented and compared. The variables examined include the air preheat temperature, amount of dilution with hot products, initial fuel droplet diameter, oxidiser temperature, and oxygen concentration. The results show that droplets in pure air at microturbine conditions fully evaporate before ignition, suggesting that a prevaporised concept is suitable for microturbines. The dilution with hot combustion products decreases the ignition delay time mainly by raising the oxidiser temperature. Low-temperature chemistry does not have a significant effect on droplet ignition because adding even a small amount of hot combustion products can increase the oxidiser temperature to higher than the temperatures favourable for low-temperature kinetics. The cool flame is only observed for 100 droplets at low temperatures, but two-stage ignition is not observed.

Effect of air humidity and natural gas composition on swirl burner combustion under unstable conditions

Combustion instabilities are an undesired phenomenon in premix burners, leading to vibrations and potential flame problems such as lift-off or flashback. The combustion stability in a premix burner is highly sensitive to fuel composition and local environmental conditions. Consequently, this work presents the effect of air humidity and fuel composition on the degree of combustion instability in a swirl stabilized premix burner at atmospheric pressure, initiating in both unstable and stable states. The experimental setup consists of a swirl stabilized 20 kW burner with a square combustion section of 100 mm × 100 mm, with optical access to the reaction zone on three sides. Three types of fuel were evaluated: methane (CH4), CUSIANA (85% CH4; 10% C2H6; 5% C3H8), and propane (C3H8). Atmospheric humidity was emulated over a range from 0% to 5%, molar basis, the high point corresponding to the greatest atmospheric humidity. The degree of burner instability was characterized by the standard deviation of the pressure signal. It was found that atmospheric humidity can reduce combustion instability, affecting methane more significantly than propane at low air preheat temperature (315 K); at high preheat temperature, the water content was found to have no effect on combustion instability. The flame structure, i.e. shape and size, was similar for all fuel types at the same adiabatic flame and air preheat temperatures. Under unstable operating conditions, a similar flame shape and area of oscillation were found with the same resonant frequencies. This indicates that the variables characterizing thermoacoustic instability maintain similar values or proportions, regardless of the fuel type.

Experimental Investigation of the Combustion Behavior of Single-Nozzle Liquid-FLOX®-Based Burners on an Atmospheric Test Rig

Abstract As an alternative to the commonly used swirl burners in microgas turbines (MGT), the FLOX®-based combustion concept promises great potential for the nitric oxide emission reduction and increased fuel flexibility. Despite having to deal with a new set of challenges while utilizing liquid fuel in the burner, first steps are taken to gain more information on the influencing operational parameters. In this regard, a FLOX®-based liquid fuel burner is developed to fit into a newly designed combustor for the Capstone C30 MGT. The C30 combustor operates with three burners arranged tangentially to an annular combustion chamber and provides a total thermal power of 115 kW. In this work, operational properties of merely one of the three C30 liquid fuel burners are investigated and the rest of the two burners are emulated in form of hot cross-flow. As for the liquid burners, the experiments are conducted with three geometrically different single-nozzle burners at atmospheric pressure. The cross-flow is realized by utilizing a 20–nozzle FLOX®-based natural gas combustor. Measurements include visualization of the reaction zone and analysis of the exhaust gas emissions. By detecting the hydroxyl radical chemiluminescence (OH*-CL) emissions, the position of the heat release zone within the combustion chamber is attained. Correspondingly, the flame height above burner and the flame length are calculated. The investigated design parameters include air preheat temperature up to 733 K, equivalence ratio, burner geometry, and thermal power. Through variation of thermal power, the effect of liquid fuel preparation, i.e., atomization, evaporation, and mixing on combustion properties and exhaust gas emissions are examined. The results show that the burners with the medium diameter consistently performed remarkably at different flame temperatures and thermal powers. The lowest NOx and CO emissions for the medium diameter burner lied between 5 to 7 ppm and 8 to 10 ppm, respectively.

Experimental Study on the Influence of Preheated Air and Air-fuel Ratio on the Combustion Temperature of Natural Gas Cupola

In order to improve the combustion temperature, this paper took 2t/h natural gas cupola as an example, designed the performance experimental systems, discussed and analyzed the influence of critical factors such as air-fuel ratio and preheated air temperature on the combustion temperature in the furnace. The results showed that the combustion temperature can reach the highest value by controlling the air-fuel ratio around 9. 8. The increase or decrease of air-fuel ratio can reduce the temperature, increasing the amount of air decreased the amount of smoke and taking away a lot of the heat, and decreasing the amount of air resulted in incomplete combustion. The combustion temperature can be increased by increasing the temperature of preheated air. The temperature rise rate is about 35°C for every 100°C increase below 200°C, and 55°C for every 100°C increase after 200°C.

Performance Characterization of a Natural Gas–Air Rotating Detonation Engine

An experimental study of a rotating detonation engine (RDE) operating with natural gas and air at elevated chamber pressures and air preheat temperatures was conducted to quantify its performance at conditions representative of land-based power generation gas turbine engines. The thrust produced by the combustor was measured to characterize its work output potential. High-frequency pressure transducers and broadband chemiluminescence measurements of the flame provided information about the wave structure and dynamics. Analysis of common performance metrics demonstrated the necessity of normalizing any RDE performance parameter by the driving system potential, typically the reactant manifold pressure. Application of a thermodynamic performance model to a generic RDE identified the area ratio between the RDE exhaust and injection throats as the primary parameter affecting delivered pressure gain. The model was further applied to draw comparison with experimental measurements of net pressure gain for identical flow conditions. Only one of the two tested injector configurations followed the predicted trends, suggesting that performance of the second was governed by physical processes other than the reactant thermodynamics. Although an absolute pressure gain was not demonstrated, it is promising that the natural gas–air RDE delivered up to 90% of the theoretical performance.

Operability of a Natural Gas–Air Rotating Detonation Engine

A combustor was developed to operate with natural gas and air as the primary propellants at elevated chamber pressures and air preheat temperatures representative of land-based power generation gas turbine engines. Detonation dynamics were studied to characterize the operability of rotating detonation-based pressure gain combustion systems for this application. Measurements of chamber wave dynamics were performed using high-frequency pressure transducers and high-speed imaging of broadband combustion chemiluminescence. The rotating detonation engine was tested with two injector configurations across a broad range of mass flux (), equivalence ratio (0.85–1.2), and oxygen mass fraction (23.2–35%) conditions to determine the effect of operating parameters on the propagation of detonation waves in the combustor. Wave propagation speeds of up to 70% of the mixture Chapman–Jouguet detonation velocity and chamber pressure fluctuations greater than 4 times the mean chamber pressure were observed. Supplementing the air with additional oxygen, varying the equivalence ratio, and enriching the fuel with hydrogen revealed that combustor operability is sensitive to the chemical kinetics of the propellant mixture. Comparing the operational trends of the two injector configurations suggests that one design mixes the incoming propellants more effectively. Although most test conditions exhibited counter-rotating detonation waves within the chamber, the injector design with superior mixing characteristics was able to support single-wave propagation.