Air Ratio Research Articles

ANALYSIS OF THE EFFECT OF SWIRL FLAME SHAPING ON EMISSIONS FROM THE CO-FIRING OF AMMONIA AND METHANE

This paper presents experimental and numerical insights into the behaviour of lean swirl flames with co-combustion of ammonia and methane. In order to evaluate the accuracy of the emissions modelling for CH4/NH3/air preheated (473K) mixtures with an increasing share of ammonia, experimental investigations were performed, varying the share of ammonia up to 25% in the fuel and the equivalence ratio of air to fuel of 0.71. A burner featuring swirl outflow blades with a 30-degree angle of outflow and a convergent-divergent nozzle was employed in the experimental setup. In order to determine the size of the reaction zone, the concentrations of NO and CO along the probing radius inside the combustion chamber were measured. A complete geometry of the combustion chamber and burner was modelled with RSM and EDC models. The outcomes of the Okafor, Xiao, and San Diego mechanisms were compared to the test data. A further DES simulation was conducted to assess the potential applicability of the models. For the flames tested with 3D RSM, a good agreement was achieved for NO emissions. In the case of a fuel containing between 10% and 25% ammonia, the Okafor mechanism demonstrated the most favourable qualitative and quantitative agreement. The reactor volume, residence time and heat transfer conditions for the CRN reactor network were calculated using numerical CFD methods. A satisfactory correlation was observed between the calculated and experimental NO emissions, with a discrepancy of only 10%. In view of the considerable computational expense associated with the models employed and the high degree of accuracy demonstrated in the emission predictions, the 3D RSM simulation was deemed to be an appropriate means of modelling small-scale applications.

3-D full-field reconstruction of chemically reacting flow towards high-dimension conditions through machine learning

Monitoring chemically reacting flow is crucial for optimizing and controlling the conversion processes in various chemical engineering scenarios. These processes are often influenced by multiple factors, creating a high-dimensional condition space that imposes intensive computational cost to computational fluid dynamics (CFD) methods. We present a machine learning (ML) framework to reconstruct the 3-D scalar field preserving the accuracy and resolution of CFD modeling. We demonstrate the framework’s effectiveness through a case study on biomass combustion in an industrial-scale grate furnace, which exemplifies the challenges of modeling chemically reacting flow in complex geometric domains influenced non-linearly by multiple parameters. The framework implements three core principles: (1) a Reactor-Structure-Resembled Network (RSRNet) reflecting the operational logics of the reactor, (2) an incremental learning strategy based on random Latin Hypercube Sampling, and (3) the incorporation of self-extracted high-level features from data as soft constraints in the loss function. Ground truth data were calculated through a CFD model, with all cases sampled from a 11-variable condition space. Using only 240 randomly sampled cases (around 1 % total cases in the discretized condition space), RSRNet precisely replicated 1-D and 2-D scalar distributions through incremental training. Further reconstruction of 3-D temperature field only used 40 3-D CFD cases, resulting in the training and testing errors decreased to 7.94 × 10-4 and 1.55 × 10-3, respectively, approaching the level of the 2-D reconstruction, with the average error in temperature field predictions not exceeding 50 K. The generalization ability was validated using a separate test dataset with continuously changing excess air ratio and capacity ratio in wide ranges, including some extreme values, and the model successfully captured complex phenomena under unseen conditions.

Hydrogen-fueled PFI SI engine investigation for near-zero NOx emissions in de-throttled and supercharged ultra-lean burn conditions

This study investigates the efficiency and combustion characteristics of a hydrogen port fuel injection (PFI) spark ignition (SI) engine under various load levels, excess air ratios and intake pressures. Experiments were conducted on a single-cylinder research engine to evaluate the effects of throttle opening and supercharging on pumping work and combustion parameters. The key findings indicate that abnormal combustion events are more closely related to the relative air-fuel ratio (λ) than to load, further limiting load increases during de-throttled operation. Additionally, combustion variability compromised mixture enleanment in both naturally aspirated and supercharged conditions. The gross indicated efficiency was approximately 40.7% across the range of 2.2 < λ < 3.5 with minimal variation. Efficiency gains were linked to reduced heat transfer losses in lean conditions, as validated by computational heat transfer, thermodynamic and fluid dynamic models on Gamma Technologies GT-ISE software. Moreover, nitrogen oxides (NOx) emissions were nearly zero for all test conditions when λ was above 2.2. These findings provide crucial insights into optimizing hydrogen engine performance under various intake pressures, highlighting the potential for achieving high efficiency and low emissions.

Simulation of Dynamic Characteristics of Supercritical Boiler Based on Coupling Model of Combustion and Hydrodynamics

To accommodate the integration of renewable energy, coal-fired power plants must take on the task of peak regulation, making the low-load operation of boilers increasingly routine. Under low-load conditions, the phase transition point (PTP) of the working fluid fluctuates, leading to potential flow instability, which can compromise boiler safety. In this paper, a one-dimensional coupled dynamic model of the combustion and hydrodynamics of a supercritical boiler is developed on the Modelica/Dymola 2022 platform. The spatial distribution of key thermal parameters in the furnace and the PTP position in the water-cooled wall (WCW) are analyzed in a 660 MW supercritical boiler when parameters on the combustion side change under full-load and low-load conditions. The dynamic response characteristics of the temperature, mass flow rate, and the PTP position are investigated. The results show that the over-fire air (OFA) ratio significantly influences the flue gas temperature distribution. A lower OFA ratio increases the flue gas temperature in the burner zone but reduces it at the furnace exit. The lower OFA ratio leads to a higher fluid temperature and shortens the length of the evaporation section. The temperature difference in the WCW outlet fluid between the 20% and 60% OFA ratios is 11.7 °C under BMCR conditions and 7.4 °C under 50% THA conditions. Under the BMCR and 50% THA conditions, a 5% increase in the coal caloric value raises the flue gas outlet temperature by 32.7 °C and 35.4 °C and the fluid outlet temperature by 6.5 °C and 9.9 °C, respectively. An increase in the coal calorific value reduces the length of the evaporation section. The changes in the length of the evaporation section are −2.95 m, 2.95 m, −2.62 m, and 0.54 m when the coal feeding rate, feedwater flow rate, feedwater temperature, and air supply rate are increased by 5%, respectively.

Математична модель камери згоряння газотурбінного двигуна, який працює на етанолі

Ethanol is one of the most promising alternative fuels for Ukraine. To convert existing projects of power and cogeneration plants based on gas turbine engines (GTEs) operating on petroleum products and natural gas to ethanol, as well as for their design and performance calculation, it is necessary to have a mathematical model of the working process of GTE combustor. The object of the study is the working process of the GTE combustor fueling on ethanol. The subject of the study is a mathematical model of the working process of GTE combustor fueling on ethanol. The work aims to improve a mathematical model of the working process of a GTE combustor fueling on ethanol by changing the algorithm for calculation of the fuel air ratio, considering thermal dissociation, and a correctly formulated equivalent chemical reaction path of the combustion process. To achieve the aim, the following tasks were solved: based on the use of experimental values of specific isobaric heat capacities of combustion products, which are a function of temperature and pressure, a mathematical model of the working process of the GTE combustor was improved ("simplified" mathematical model); based on the solution of the system of equations of chemical thermodynamics, a mathematical model of the working process of the GTE combustor was developed ("complex" mathematical model); the results of calculation by "simplified" mathematical model of the working process of the GTE combustor were compared with the "complex" one. The following results were obtained: the difference in the calculation of the combustion products' thermodynamic parameters between the developed mathematical models was less than 1.2% for the three modes of the General Electric CF6-80A engine. Conclusion: the "simplified" mathematical model of the working process of the GTE combustor fueling on ethanol was improved. A feature of the model is the implicit consideration of the effect of thermal dissociation and correctly formulated equivalent chemical reaction path of the combustion process by using experimental values of specific isobaric heat capacities of combustion products. This will improve the accuracy of fuel air ratio calculation and other thermodynamic parameters of GTE combustor mathematical models fueling on ethanol, without significantly complicating the model algorithm.

Numerical Investigation on the Effect of Air Humidification and Oxygen Enrichment on Combustion and Emission Characteristics of Gas Boiler

Gas boilers exhibit thermal inefficiency and unsatisfying pollutant emissions. In this study, numerical simulations were conducted to examine the effect of humidified oxygen-enriched air on methane combustion in a furnace and the effects of different premixed ratios of air on the temperature field inside the furnace, intermediate product OH groups, component concentration distribution, and pollutants. Although humidification of ambient air effectively reduced the flame center temperature and mass concentration of the NOx generated during combustion in the furnace, the highest growth rate of CO concentration at the furnace outlet was 18.6%. Humidification of oxygen-enriched air increased the center temperature and outlet NO concentration of the furnace compared with those during no oxygen enrichment, but the outlet CO concentration showed a decreasing trend, with the highest decrease rate of 34.6%. This study determined an optimal CO–air premix ratio with a moisture concentration of 50 g/kg dry air and an oxygen concentration of 23%. The air humidification and oxygen enrichment technology proposed in this article provides a technical reference for low nitrogen transformation of existing gas boilers.

Effects of different gas energy shares on combustion and emission characteristics of compression ignition engine fueled with dual-fossil fuel and dual-biofuel

This study systematically investigates the energetic and environmental performance of a four-cylinder compression ignition (CI) engine fueled by gaseous and liquid dual-fuel (D-F), utilising various combinations of fossil fuels and biofuels. Fossil diesel or pure hydrotreated vegetable oil (HVO) – new generation biodiesel was used as the pilot fuel to initiate ignition of the gaseous fuel. The gaseous fuels used were natural gas (NG) and simulated biogas (BG) composed of 60 % NG and 40 % CO2 by volume, injected into the intake manifold at varying gas energy shares (GES) of 40 %, 60 %, and 80 %. Reference values were provided from conventional combustion of diesel fuel and HVO. This study used numerical simulations to examine indicators of combustion, such as ignition delay, premixed combustion phase, diffusion combustion phase, and subsequent combustion phases, across diverse fuel combinations. Within lean dual-fuel mixtures, when the gaseous fuel remained below the flammability threshold, the peak pressure was diminished, the rate of pressure rise was lowered, and the combustion process decelerated, facilitating a faster transition to the diffusion phase. As the engine load and GES increased, the excess air ratio decreased, bringing the air-fuel mixture closer to the flammability limit, which in turn altered the combustion characteristics and engine performance trends. Combustion with increasing BG content showed partial similarities to that of NG, though the high CO2 content in biogas was found to suppress combustion, functioning similarly to an exhaust gas recirculation. The study also compared brake thermal efficiency (BTE), as well as specific emissions of CO, HC, NOX, CO2, and smoke for the D-F engine operation against pure diesel and HVO at different loads and GES levels. Additionally, an overlimit function was used to assess the emission levels of D-F engines with reference to emission limits.

Control of Liquid Hydrocarbon Combustion Parameters in Burners with Superheated Steam Supply

A numerical simulation of reacting mixture flow in a full-scale combustion chamber of a prototype burner with a fuel-sprayed jet of superheated steam and a controlled excess air ratio was performed based on a verified model. The influence of steam jets on the combustion parameters of the created prototype device was analyzed based on the results, and a comparison with data from various atmospheric burners, including evaporative and spray types, direct-flow and vortex types, and those with natural and forced (regulated) air supply, was made. Various schemes for supplying steam to burner devices were discussed. It was shown that the relative steam consumption is a parameter for controlling the emission of toxic combustion products, such as NOx and CO, for all designs. A high burner performance is achieved when superheated steam is supplied at more than 250 °C with a relative steam flow rate of &gt;0.6. The design features of the burner systems and operational parameters that ensure high thermal and environmental efficiency when burning various types of fuel and waste are identified.

Optimization of operational parameters of marine methanol dual-fuel engine based on RSM-MOPSO

Methanol and natural gas, as green fuels for environmental protection, have shown great potential in the field of maritime transportation. This study explores how the methanol energy fraction (MEF), exhaust gas recirculation (EGR), excess air ratio (λ), and engine injection timing (EIT) influence combustion and emission traits in marine dual-fuel (DF) engine. Initially, a DF engine model was formulated through experiments using CONVERGE software, while the CHEMKIN program devised a chemical mechanism involving 100 compounds and 512 reactions. The response surface methodology (RSM) was subsequently utilized to design the experiment and develop the regression model. The improved multi-objective particle swarm optimization (MOPSO) algorithm was applied to optimize three critical variables: brake thermal efficiency (BTE), carbon monoxide (CO), and nitrogen oxide (NOx) emissions. Ultimately, feature-optimized scenarios from the Pareto front were chosen for comparative evaluation to derive the optimal configuration. The results show that when the decision variables MEF, EGR, λ and EIT are 22.33 %, 10 %, 1.81 and 11°CA BTDC respectively, there is a better trade-off between the three target variables. Compared with the original case, the change of ITE, NOx and CO emissions in the optimal case are +0.97 %, −39.53 % and −14.51 %, respectively. Overall, based on the intelligent optimization approach, the rational selection of DF engine parameters improved the ITE and most NOx and CO emissions were effectively suppressed.

Impact of the hopper-air and overfire-air distribution on the low-NOx combustion performance within a 600 MWe staged arch-firing furnace

Within a 600 MWe staged arch-firing furnace (SAF) having the staged hopper air (HA) and overfire air (OFA) as its last two air-staging layers, the present attention was focused on evaluating the impact of the HA:OFA distribution and determining an appropriate HA:OFA ratio used to improve the hopper environment and low-NO x performance. Accordingly, by varying the HA:OFA distribution at a total air ratio of 31%, four HA:OFA ratio settings of 11:20, 13.5:17.5, 16:15, and 18.5:12.5 were formed to compare the in-furnace flow, coal combustion, and NO x emissions. With increasing the HA flux to raise the HA:OFA ratio, all of combustion symmetry, the downward flame penetration, and the HA's combustion-aided effect on char firstly improved and then weakened, the OFA penetration became shallower, and the high-temperature flame in the upper furnace extended. Final performance indexes showed that both NO x emissions and burnout loss first declined and then ascended, meaning a rise-to-drop trend in the low-NO x performance as deepening the HA:OFA ratio. Among the four settings, the moderate HA:OFA = 13.5:17.5 achieved the optimal indexes with NO x emission of 543 mg/m3 (6% O2) and carbon in fly ash of 4.89%. Compared with its previous reference furnace (holding levels of 905 mg/m3 and 5.1% respectively in the two index aspects), the SAF furnace using such a HA:OFA distribution mode reduced significantly NO x by 40%, improved a little burnout, and dropped apparently the hopper temperatures by 500 K to eliminate its high overheating risk.

The Influence of Helium Addition on the Combustion Process in a Hydrogen-Fueled Turbulent Jet Ignition Engine

There are considerably fewer requirements for the quality of hydrogen combusted in an engine than its quality for fuel cells. Therefore, the analysis was carried out on the combustion of hydrogen–helium mixtures in an engine with a two-stage combustion system (TJI—Turbulent Jet Ignition). A single-cylinder research engine with a passive and active prechamber was used. A hydrogen–helium mixture was supplied to the main chamber in proportions of 100:0, 90:10, 80:20, 30:70, and 60:40 volume fractions. The prechamber was fueled only with pure hydrogen. Combustion was carried out in the lean charge range (λ = 1.5–3) and at a constant value of the Center of Combustion (CoC = 8–10 deg aTDC). It was found that the helium concentration in the mixture affected the changes in combustion pressure, heat release rate and the amount of heat release. It was observed that increasing the proportion of helium in the mixture by 10% also reduces the IMEP by approximately 10% and reduces the rate of heat release by approximately 20%. In addition, helium influences knock combustion. Limits of MAPO = 1 bar mean assumed that knock combustion occurs in the main chamber at values of λ &lt; 1.9. Increasing the excess air ratio results in a gradual reduction in the temperature of the exhaust gas, which has a very rapid effect on changes in the concentration of nitrogen oxides. Studies carried out on the helium addition in hydrogen fuel indicate that it is possible to use such blends with a partial deterioration of the thermodynamic properties of the two-stage combustion process.

Combustion and emissions of an ammonia heavy-duty engine with a hydrogen-fueled active pre-chamber ignition system

Combustion and emission characteristics of a heavy-duty single-cylinder ammonia engine with a hydrogen-fueled active pre-chamber ignition system are investigated experimentally at the condition of IMEP 10 bar, 1000 rpm, where effects of spark timing, excess air ratio (λ), and hydrogen energy ratio are tested. Three distinguishable combustion phases are observed, including pre-chamber combustion, turbulent-jet-controlled combustion, and ammonia-chemical-kinetics-controlled combustion. Advancing spark timing makes combustion phases earlier, increasing pressure rise rate, combustion pressure, and NOx emissions. The optimal spark timing for the highest indicated thermal efficiency (ITE) is −12°CA ATDC in the experiment. λ range for stable combustion is 1.1–1.5 and ITE peaks at λ = 1.3. The hydrogen energy ratio, 7.9%∼10.5%, has little influence on the engine performance. However, a low hydrogen energy ratio could increase the risk of misfire. The optimal hydrogen energy ratio is about 9∼10%.

Performance analysis of a conventional two-stage indirect evaporative cooler

With the aim of saving a portion of the high-quality energy consumed in mechanical vapor compression systems for air conditioning applications, the present work focuses on utilization of low-quality energy conversion processes due to fluid evaporation. The conventional indirect evaporative cooler is selected based on its preference for further modification compared to a regenerative indirect evaporative cooler. It is configured to be operated with two identical stages in series. This task is achieved by developing a thermodynamic model to analyze the performance of the cooling unit and to indicate the extent of its development compared to the cooler in one stage. Preliminary results show that the best operating condition is when the ratio of primary air to secondary air is 1. The cooling unit produces fairly comfortable air within limited climatic conditions. It delivers air at 26 °C and lower even at climatic temperatures as high as 48 °C, but within a very low relative humidity range. The relative humidity range extends to less than 58% as the outdoor air temperature decreases. At high humidity levels (64 to 80% depending on climate temperature), cool air cannot be obtained at 26 °C, and the cooling unit performance is limited only by what the first stage produces. The average performance of the cooling unit exceeds that of the first stage by 42.6%. Increasing air flow rate leads to an increase in cooling capacity, but it also has a negative impact on supply temperature and effectiveness.

Upper mantle scale enrichment of Cenozoic intraplate magmatism in Northeast Asia: He-Sr-Nd-Pb-O isotope geochemistry of the basalts around the Korean peninsula

The Earth’s mantle is considered to be geochemically heterogeneous, which is reflected by the diverse composition of oceanic island basalts (OIB). The mantle enrichment resulting in this is attributed primarily to the influx of recycled crustal materials into the mantle through subduction. Additionally, the sub-continental lithospheric mantle (SCLM) complicates the elucidation of mantle heterogeneity. From this perspective, Northeast Asia, where the Pacific stagnant slab in the mantle transition zone and the SCLM distribution are presented, is the suitable site for examining the upper mantle scale enrichment. Here we report He-Sr-Nd-Pb-O isotope values of basalts that erupted around the Korean Peninsula to illustrate the source lithology and components that led to mantle heterogeneity. Our measured helium isotope ratios ranging from 5.7 to 7.3 Ra (3He/4He ratio of air, Ra = 1.39 x 10-6) are mostly within the SCLM range (6.1 ± 0.9 Ra) but lower than the mid-ocean ridge basalt range (MORB; 8 ± 1 Ra). The Sr-Nd-Pb isotope compositions of the basalts generally display a mixture of depleted MORB mantle (DMM), enriched mantle 1 (EM1), and enriched mantle 2 (EM2) components. In addition, the basalts have δ18Oolivine (vs. V-SMOW) values ranging from 4.7 to 5.7 ‰ that deviate from the DMM range (δ18Oolivine = 5.1 ± 0.2 ‰). Our isotopic analysis results highlight the role of the pyroxenite source in the metasomatized SCLM in the genesis of basalts. The low 3He/4He range of the basalts indicates a significant role in the SCLM. Moreover, the delaminated cratonic SCLM and asthenosphere-lithosphere interaction are candidate scenarios for the low 3He/4He ratios. Therefore, we propose that mixing of DMM (high 3He/4He ratio; 7 to 9 Ra) and the metasomatized SCLM (low 3He/4He ratio; 5 to 7 Ra) allowed enrichment within the upper mantle scale for the Cenozoic intraplate magmatism in Northeast Asia.

Assisting denitrification and strengthening combustion by using ammonia/coal binary fuel gasification-combustion: Effects of injecting position and air distribution

The direct co-firing of ammonia (NH3) with coal is an effective approach for reducing carbon emissions from coal-fired plants. However, the limitations of NH3 combustion, such as its high ignition energy requirement and high NOx emissions, restrict its large-scale co-combustion in coal-fired units. In this study, a self-sustaining gasification–combustion experimental system was employed, and its denitrification performance and combustion strengthening capability for NH3/coal binary fuel under different NH3 injection positions and air distribution methods were evaluated. The results of co-firing 20% NH3 in the gasifier revealed that its operating temperature can be flexibly controlled within the optimal reaction temperature window of SNCR by adjusting the primary air ratio (λ1). Increasing λ1 was beneficial for NH3 and coal conversion and denitrification in the gasifier; at λ1 = 0.53, the conversion rate of NH3 and N2 reached 86.37% and 83.59%, respectively, with no NOx being detected at the gasifier outlet. Furthermore, increasing λ1 promoted the development of gasified char pore structure, thereby improving reactivity. After entering the down-fired combustor (DFC), increasing λ1 promoted NH3 and coal burnout and effectively controlled NOx emissions, reaching a level similar with that of pure coal under λ1 = 0.53. Co-firing 20% NH3 in the DFC also demonstrated that the introduction of inner secondary air was conducive to char burnout, however, increased NH3 slip. The outer secondary air promoted NH3 combustion, however, exacerbated NOx emissions and inhibited gasified char combustion. The uniform air distribution method balanced the combustion of NH3 and gasified char, and effectively controlled NOx emissions. When the same air distribution method was used, co-firing NH3 in the gasifier was more favourable for NOx control, whereas co-firing NH3 in the DFC benefited coal burnout. This study provides innovative ideas and serves as a reference for developing enhanced combustion and low NOx emission technologies for large-scale NH3 co-firing in coal-fired units.

Investigation of the optimal timing and amount of fuel injection on the efficiency and emissions of a diesel engine through experimentation and numerical analysis

The purpose of this study is to investigate the performance, in-cylinder combustion, and emissions of the MTE660E heavy-duty diesel engine using 3D CFD simulation. The CFD simulation model based on AVL FIRE software was developed to numerically investigate the performance, in-cylinder combustion, and emissions of the MTE660E engine. The AVL model was validated against empirical data. The 6-cylinder MTE660E engine was operated under a constant excess air ratio of 1.75 and at 1600 rpm engine speed. The geometry and lattice design of the MTE660E engine were simulated to provide a computationally efficient approach. The AVL model was validated against experimental data and the error between the measured and calculated value of combustion characteristics and emissions was acceptable (R2> 90 %), error <5.6 %). Design Expert software was used to optimize the dependent variables (peak chamber temperature, brake mean effective pressure, engine torque, engine thermal efficiency and emissions of NOx) according to the studied variables (injection time and fuel injection quantity) based on response surface methodology. The results show that the recommended injecting time of 342 °C and the specific amount of fuel lead to better combustion efficiency, resulting in high engine performance and low emissions. The specific fuel consumption was highest at 2200 rpm with a 50 % load, while the lowest SFC level was observed at 1750 rpm with a 100 % load. The maximum value of NOx emissions was observed at full load. The findings show that the optimization of the injection timing and fuel injection quantity can effectively enhance the performance of the MTE660E engine. The study provides valuable insights into improving combustion efficiency, resulting in greater performance and reduced emissions without requiring expensive overhaul. It has potential applications in automotive and commercial transportation industries, thereby reducing fuel consumption and emissions.

Experimental study on spray ignition and blow out performances in a centrally staged annular combustor: Low pressure conditions

The ignition and flame propagation process within the centrally staged annular combustor is considerably intricate, particularly under low pressure conditions. Experiments with kerosene as fuel were conducted under varying pressures ranging from 30 to 90 kPa. A high-speed camera was employed to capture images of the ignition process. The experiments illustrate that the fuel–air ratio at the ignition boundary initially decreases and then increases with increasing pressure drop at different inlet pressures. The ratio increases as the pressure decreases at a constant pressure drop, exhibiting a more pronounced effect, particularly at lower pressures. The flame propagation time of annular combustion is shortened by the increase in the fuel–air ratio. Moreover, an increase in pressure drop enhances flame propagation speed and reduces flame propagation time. Under identical working conditions and parameters, lower inlet pressures result in longer flame propagation time. Additionally, asymmetry is observed in circumferential flame propagation within the annular combustor. Since the swirl flow direction exhibits faster propagation speeds, the ratio of propagation speeds remains nearly constant across different directions. Furthermore, distinct flame propagation paths are identified in various directions. Three different flame propagation patterns were observed, including “archlike-axial,” “entrainment-rotation,” and “sweep-transverse.” Fuel–air ratio and pressure drop serve as primary parameters governing flame propagation patterns. The flame propagation pattern exhibits similarities to that of atmospheric conditions, with the exception of the inhibition observed in the entrainment-rotation pattern. Notably, compared to the ignition between two adjacent burners, ignition in the middle of a certain burner shows a higher probability of successful ignition.

Impacts of MTBE in gasoline on the tailpipe ammonia emissions from China-6 certified passenger vehicles

Postcatalyst ammonia emissions from gasoline vehicles recently received attentions because of their contribution to the formation of urban secondary aerosols. To better understand whether fuel formulation would curb ammonia, the influence of methyl tertiary-butyl ether (MTBE) additive in gasoline on the tailpipe ammonia emissions from six China-6 compliant vehicles was investigated over the World Harmonized Light-duty Test Cycle (WLTC) at −7 ℃ and 23℃. Ammonia emissions were measured with MTBE-free and 10% MTBE-containing China-6 compliant gasoline fuels on the test vehicles. At – 7 ℃, the ammonia emissions with and without MTBE addition ranged from 0.15-17.07mg/km and 0.81−25.13mg/km, respectively. At 23 ℃, ammonia emissions were 0−7.4mg/km for MTBE-containing fuel and 0−8.76mg/km for MTBE-free fuel. More ammonia emissions were often observed as a result of maneuvering of enriched air-fuel mixtures to improve the combustion inability after cold-start and for de-NOx purpose, called as “λ sweep” (λ is excess air ratio). Due to the oxygen-containing nature of MTBE, its addition favors ammonia reduction. It is noted that “λ sweep”, an engine control strategy injecting extra fuel to deplete stored oxygen in the catalyst and suppress transient NOx formation during reacceleration after prolonged deceleration, may contribute to ammonia emissions due to the use of enriched air-fuel mixtures.

Transient dynamic cycle evolution and thermodynamic performance analysis of a free-piston engine generator

The free-piston engine generator (FPEG) is a promising hybrid power system. Eliminating the crankshaft mechanism, it features a variable piston dynamic cycle distinct from traditional engines. This paper investigates transient dynamic evolutions, identifies the stable operation zone, and further analyzes thermodynamic performance under various key design parameters. First, a coupled dynamic-thermodynamic model is developed for FPEG. Second, transient dynamic evolutions from start-up to combustion-generation stage are analyzed. The boundaries of operating parameters are identified to ensure the presence of limit cycles for stable operation. Subsequently, the thermodynamic performance is comprehensively evaluated. The indicated power and thermal efficiency improve as load resistance and excess air ratio decrease. The maximum and minimum performance points consistently occur on the overshooting and damping lines, respectively. A lower piston assembly mass and higher design compression ratio are recommended to achieve higher indicated power and thermal efficiency. A lower stroke-to-bore ratio leads to higher indicated power with a slight decrease in thermal efficiency. Additionally, the load coefficient should be adjusted to ensure stable operation according to the design parameters. This paper enhances the understanding of transient dynamic evolutions of the FPEG and provides guidance for prototype design aimed at achieving stable operation and improved output performance.

Comprehensive Assessment and Optimization of a Middle-Arch Dual-Channel Municipal Solid Waste Incinerator Using Numerical Simulation Methods.

The present study focuses on a middle-arch dual-channel municipal solid waste (MSW) incinerator facing issues of high NO x emission and overheating. To address these problems and optimize the incinerator, an advanced numerical simulation method was employed to comprehensively assess its bed combustion, freeboard combustion, and NO x emission characteristics. A multiphase fuel bed model considering large-particle characteristics of MSW was developed, coupled with a three-dimensional (3D) model for combustion in freeboard. The analysis revealed that the observed issues stem from multiple factors, including primary-to-secondary air ratio, flame propagation in bed, release of volatiles from bed, and distribution and mixing of components in freeboard. Reducing the proportion of primary air and correspondingly increasing secondary air effectively alleviated the localized overheating in the furnace and reduced NO x emission. Further adjustments to the distribution of primary air in three stages delaying air supply toward the burnout stage, together with the decrease in the grate movement speed, can better control the amount and speciation of N released from the bed. Implementing a counterflow mixing strategy with NH3 in the front channel and NO in the rear channel can greatly reduce the original NO x emission concentration to 95.94 mg/(N·m3), as predicted by a numerical simulation. Subsequent practical adjustments to an actual incinerator led to notable improvements, clearly optimizing the localized high-temperature issues at various locations, especially the front channel suffering severe slagging problems, with the temperature reduced from 1118 to 957 °C. Meanwhile, NO x emission concentration decreased from 200 mg/(N·m3) to around 50 mg/(N·m3), with no negative effect on the boiler load.