Search Results (75)

Post-combustion technology is a new kind of low-nitrogen combustion technology. To achieve the combined removal of nitrogen oxides (NO_x) and sulfur dioxide (SO₂) emissions, the post-combustion technology combined with the sorbent injection in the furnace and post-combustion chamber is proposed. Experiments investigating the effects of the sorbent addition in a post-combustion chamber and post-combustion air arrangement on NO_x and SO₂ emissions were conducted in a 0.1 MWth circulating fluidized bed test platform. In addition, a comparative analysis of the NO_x and SO₂ emissions under both combined removal methods was also performed. The results indicated that adding sorbent to the post-combustion chamber can reduce SO₂ emissions, but further increasing the amount of sorbent will not significantly improve the desulfurization effect. The injection position of the post-combustion air will affect the emissions of NO_x and SO₂ in the flue gas. When the three-stage distribution of post-combustion air is adopted, the further back the third nozzle is distributed, the lower the temperature in the post-combustion chamber, which is beneficial to the control of NO_x and SO₂ emissions. Compared with the conventional combined removal method, the NO_x emissions were significantly reduced under the new combined removal method. Through secondary desulfurization in the furnace and post-combustion chamber, oxygen-deficient combustion in the furnace can achieve the combined removal of NO_x and SO₂. Full article

Hydrogen is a promising fuel in the current transition to zero-net CO₂ emissions. However, most practical combustion equipment is not yet ready to burn pure hydrogen without adaptation. In the meantime, blending hydrogen with natural gas is an interesting option. This work reports a computational study of the performance of swirl-stabilized natural gas/hydrogen flames in a novel combustion chamber design. The combustor employs an air-staging strategy, introducing secondary air through a top-mounted plenum in a direction opposite to the fuel jet. The thermal load is fixed at 5 kW, and the effects of fuel composition (hydrogen molar fraction ranging from zero to one), excess air coefficient (λ = 1.3, 1.5 or 1.7), and primary air fraction (α = 50–100%) on the velocity, temperature, and emissions are analysed. The results show that secondary air changes the flow pattern, reducing the central recirculation zone and lowering the temperature in the primary reaction zone while increasing it further downstream. Secondary air improves the performance of the combustor for pure hydrogen flames, reducing NO emissions to less than 50 ppm for λ = 1.3 and 50% primary air. For natural gas/hydrogen blends, a sufficiently high excess air level is required to keep CO emissions within acceptable limits. Full article

Ammonia (NH₃) and hydrogen (H₂) are considered promising fuels for the power sector’s decarbonization. Their combustion is capable of producing energy with zero direct CO₂ emissions, and ammonia can act as a stable energy H₂ carrier. This study numerically investigates the design and implementation of staged combustion of a mixture of NH₃/H₂ by means of CFD simulations. The investigation employed the single-phase flow RANS governing equations and the eddy dissipation concept (EDC) combustion model, with the incorporation of a detailed kinetic mechanism. The combustion chamber operates under the RQL (rich–quench–lean) combustion regime. The first stage operates under rich conditions, firing mixtures of ammonia in air, enriched by hydrogen (H₂) to enhance combustion properties in a swirl and bluff-body stabilized burner. The secondary stage injects additional air and hydrogen to mitigate unburnt ammonia and NO_x emissions. Simulations of the first stage were performed for a thermal input ranging from 4 kW to 8 kW and flames with an equivalence ratio of 1.2. In the second stage, additional hydrogen is injected with a thermal input of either 1 kW or 2 KW, and air is added to adjust the global equivalence ratio to 0.6. Full article

High-frequency oscillations occur in the centrally staged combustor during operation. To effectively suppress them, real-time monitoring of the combustor exit temperature is critical. However, traditional contact temperature measurement methods are inadequate for accurately capturing temperature variations in the turbulent flow field. Tunable Diode Laser Absorption Spectroscopy (TDLAS) with a high acquisition frequency is employed to measure the temperature of the centrally staged combustor, utilizing a non-contact sensing method. The influence of various combustion parameters on the uniformity of combustion within the chamber and the capability of TDLAS to capture temperature data of the combustion chamber under different acquisition frequencies are studied. The results indicate that the staging ratio causes irregular oscillations in the combustion chamber outlet temperature. At an acquisition frequency of 1 kHz, an increase in the staging ratio raises the average temperature at the outlet and slows down the temperature oscillation when other parameters remain constant. At an acquisition frequency of 10 kHz, more small, high-frequency variations in the centrally staged combustor outlet temperature are observed. When the TDLAS system operates at 10 kHz, it can capture more details of the combustion chamber outlet temperature oscillation under the same working conditions and exhibits stronger noise immunity. However, compared with the acquisition frequency of 1 kHz, it cannot sustain long-term measurement. Full article

Compression via pressure waves is an effective but specific way of compressing gases. This paper presents a broad overview of work related to the use of unsteady processes in the construction of micro-engines. The main advantages of wave rotors, such as a low rotor speed, self-cooling channels, high compression in a single stage, and the possibility of operating at a very small geometric scale, are addressed, and their disadvantages, such as the requirement of the precise synchronization of wave processes and poor torque-generation properties, are also outlined. This review highlights the possibility of operating at a geometric scale, which conventional solutions have failed to achieve. In the thermodynamic cycle of a micro-engine, a compression process carried out in an unsteady manner is superior in efficiency to stationary solutions. On the contrary, in the expansion process, fluid inertia is an obstacle to the full utilization of the thermal energy transferred to the fluid in the combustion chamber. The best solution is, therefore, a favorable combination of both features, leading to unsteady compression and steady-state expansion in the heat engine cycle. This article presents an overview of the existing technical solutions and published research results devoted to the construction of pressure wave compression micro-engines: patents, scientific publications describing various research methods, numerical calculations, and the experimental results of unusual technical solutions. Characteristic solutions and problems arising in the development of these methods, which range from superchargers to autonomous engines, are presented and discussed. Directions for further research are suggested. Full article

The ignition and extinction performances of an engine’s combustion chamber are crucial for its overall performance, reliability, fuel efficiency, and environmental impact. This study focuses on a central staged dual-swirl direct mixing combustor’s ignition and extinction performances. The goal is to construct a network surrogate prediction model estimating the ignition and extinction boundaries in the central staged dual-swirl direct mixing combustor. The experimental results indicate that the minimum ignition fuel–air ratio of the combustor initially increases and then decreases with increasing inlet temperature. In contrast, the extinction fuel–air ratio decreases with increasing inlet temperature. The ignition fuel–air ratio decreases as the inlet pressure increases, while the extinction fuel–air ratio also decreases with increasing inlet pressure. The minimum ignition fuel–air ratio initially decreases and then increases as the inlet flow rate increases. Similarly, the extinction fuel–air ratio decreases with increasing inlet flow rate. Additionally, both the ignition and extinction fuel–air ratios decrease with increasing pilot and main stage swirl intensity. The constructed neural network model comprises an output layer representing the ignition and extinction fuel–air ratios and an input layer including variables such as inlet temperature, pressure, flow rate, and pilot and main swirl intensity. During training, the model achieved a final relative error of 0.4%, with a relative error of 0.3% for the ignition fuel–air ratio and 0.5% for the extinction fuel–air ratio. During validation, the relative error was 1.7%, with a relative error of 1.1% for the ignition fuel–air ratio and 2.1% for the extinction fuel–air ratio. The neural network model demonstrates its effectiveness in accurately predicting the numerical values of the ignition and extinction fuel–air ratios, indicating its potential for engineering predictions in the context of central staged dual-swirl direct mixing combustors. Full article

Currently, steady-state analysis predominates in combustion chamber design, while dynamic combustion characteristics remain underexplored, and there is a lack of a comprehensive index system to assess dynamic combustion behavior. This study conducts a numerical simulation of the dynamic characteristics of the combustion chamber, employing a method combining large eddy simulation (LES) and Flamelet Generated Manifold (FGM). The inlet air temperature, air flow rate, and fuel flow rate were varied by 1%, 2%, and 3%, respectively, with a pulsation period of 0.008 s. The effects of nine different inlet parameter pulsations on both time-averaged and instantaneous combustion performance were analyzed and compared to benchmark conditions. The results indicate that small pulsations in the inlet parameters have minimal impact on the steady-state time-averaged performance. In the region near the cyclone outlet, which corresponds to the flame root area, pronounced unsteady flame characteristics were observed. Fluctuations in inlet parameters led to an increase in temperature fluctuations near the flame root. Analysis of the outlet temperature results for each operating condition reveals that inlet parameter fluctuations can mitigate the inherent combustion instability of the combustion chamber and reduce temperature fluctuations at the outlet hot spot. Full article

In order to explore the influence of pilot structure on the lean ignition characteristics in a certain type of internally staged combustor, the current study was conducted on the effects of the auxiliary fuel nozzle diameter, the rotating direction of the pilot swirler, and the swirl number on the lean ignition fuel–gas ratio limit, combining numerical simulation and experimental validation. The optimization potential of the mixing structure of this type of internally staged combustor was further explored. It indicated that the lean ignition fuel–gas ratio limit was significantly influenced by the diameter of the auxiliary fuel nozzles the swirl number of the pilot swirler and the combination of the same rotating direction for both pilot swirlers, while the mass flow rate of air was constant. Increasing the diameter of the auxiliary fuel path nozzles (0.4~0.6 mm) and having excessively higher or lower swirl numbers of the pilot module primary swirlers are not conducive to broadening the lean ignition boundary. Compared with the two-stage pilot swirler with the same rotation combination, the fuel–gas ignition performance of the two-stage pilot swirler with the opposite rotation combination is better. Under the typical working conditions (the air mass flow rate is 46.7 g/s and the ignition energy is 4 J), for a pilot swirler with a rotating direction opposite to the main swirler, the diameter of the auxiliary fuel nozzles is 0.2 mm, the swirl number of first-stage of pilot swirler is 1.4, and the lean ignition fuel–air ratio was reduced to 0.0121, which is 32.78% lower than the baseline scheme, which further broadens the lean ignition boundary of the centrally staged combustion chamber. Full article

To investigate the combustion process and reduce Nitric Oxide (NO) emissions in the vertical heating flue of air-staged coke ovens, a three-dimensional computational fluid dynamics method was applied to simulate the combustion process. The model integrates the k-ε turbulence model with a multi-component transport combustion model. The impact of air staging on the flow field and NO emissions in the vertical fire chamber was assessed through comparative validation with experimental data. The impact of air staging on the flow field and NO emissions in the vertical fire chamber was assessed through comparative validation with experimental data. Based on this research, the effects of the excess air coefficient and air inlet distribution ratio on NO emission levels at the flue gas outlet were further investigated. Analysis of the flow field structure, temperature at the center cross-section, component concentration, and NO emission levels indicates that as the excess air coefficient increases, the NO emission levels at the flue gas outlet initially decrease and then increase, accompanied by corresponding changes in outlet temperature. At an air excess factor of 1.3 and an air inlet distribution ratio of 7:3, NO emission levels are at their lowest—53% lower than those in a conventional coke oven—and the temperature distribution in the riser channel is more uniform. These results provide a theoretical foundation for designing the air-staged coke oven standing fire channel structure. Full article

This study aimed to calculate the impact of inlet valve geometry and spray angle on the performance of internal combustion engines using computational fluid dynamics (CFD) analysis. CFD analysis was performed to explore the fuel flow dynamics within a combustion chamber at critical stages, considering factors such as swirl and tumble. This study investigated the role of the intake port’s geometry and spray angles in creating squish and swirl, which is crucial for enhancing combustion efficiency and overall engine performance. The analysis employed the Finite Volume Method (FVM), solved within ANSYS Fluent 2021 software, utilizing the standard k-ε turbulence model. Design Modeler was used for the geometry design and ANSYS Fluent facilitated the CFD analysis of the injection. Four distinct cases were explored to assess engine performance across various designs, examining parameters such as pressure, temperature, and velocity. These performance parameters were evaluated against the existing literature, enabling the identification of optimal configurations. This study identified optimal performance parameters based on the existing literature. The best design was further validated against existing designs under identical boundary conditions. This research demonstrates improved engine performance across all parameters compared to existing values in the literature. This suggests the efficacy of the proposed inlet valve geometry and spray angle configurations in increasing internal combustion engine efficiency. Full article

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 < 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. Full article

The development of modern reusable launchers, such as the Themis project with its LOX/LCH4 Prometheus engine, CALLISTO—a reusable VTVL-launcher first-stage demonstrator with a LOX/LH2 RSR2 engine, and SpaceX’s Falcon 9 with its Merlin 1D engine, underscores the need for advanced control algorithms to ensure reliable engine operation. The multi-restart capability of these engines imposes additional requirements for throttling, necessitating an extended controller-validity domain to safely achieve low thrust levels across various operating regimes. This capability also increases the risk of component failure, especially as engine parameters evolve with mission profiles. To address this, our study evaluates the dynamic reliability of reusable rocket engines (RREs) and their subcomponents under different failure modes using multi-physics system-level modelling and simulation, with a particular focus on turbopump components. Transient condition modelling and performance analysis, conducted using EcosimPro-ESPSS software (version 6.4.34), revealed that turbopump components maintain high reliability under nominal conditions, with turbine blades demonstrating significant fatigue life even under varying thermal and mechanical loads. Additionally, the proposed predictive model estimates the remaining useful life of critical components, offering valuable insights for improving the longevity and reliability of turbopumps in reusable rocket engines. This study employs deterministic, thermally dependent structural simulations, with key control objectives including end-state tracking of combustion chamber pressure and mixture ratios and the verification of operational constraints, exemplified by the LUMEN demonstrator engine and the LE-5B-2 engine class. Full article

This study focuses on the center-staged swirl model combustion chamber, conducting experiments and numerical simulations to investigate the unstable combustion characteristics of diffusion flames under different Reynolds numbers and air–fuel ratios. The results were analyzed using methods such as Empirical Mode Decomposition (EMD), Fast Fourier Transform (FFT), and Proper Orthogonal Decomposition (POD). The research found that the first three intrinsic mode functions (IMFs) of the combustion chamber pressure fluctuation signal (DP) correspond to different physical fluctuation characteristics. Specifically, the 1st IMF represents the fluctuation characteristics of the heat release rate, corresponding to the flame shear region in the heat release rate field; the 2nd IMF represents the fluctuation characteristics of airflow swirl, corresponding to the swirl vortex structure region in the vorticity field; the 3rd IMF represents the flame detachment fluctuation characteristics, corresponding to the flame detachment region in the heat release rate field. Using the same experimental and numerical calculation methods to study another swirl model combustion chamber, the results also showed the aforementioned correspondence, further demonstrating the accuracy of the experimental results and the universality of this conclusion. Full article

The control of powder aging during Selective Laser Sintering (SLS) processing is one of the challenges to be overcome for the implementation of this technique in serial production. Aging phenomena, because of the elevated temperatures and long processing times, need to be considered when a fraction of the polymer powders present in the build chamber and not used to manufacture the parts are reused at various times. The aim of this study was to investigate the influence of successive reuse of blends of pure Polyamide 12 and its blends with two types of flame retardants (FR): ammonium polyphosphate (APP) and zinc borate (ZB). The composition of the blends was 70/30 (wt/wt) PA 12/FR. Four successive processing stages have been carried out by collecting the remaining powder blend each time. The powders were re-used using the same processing parameters after sieving. DSC measurements showed that the incorporation of FRs entailed a reduction in the processing window up to 4 °C; nevertheless, no further reduction was noted after aging. The TGA curves of aged blends of powders were also similar for pure PA 12 and PA 12 with FR. In addition, initial and reused powders presented a higher degree of crystallinity than the specimens processed from the powders. The heterogeneous character of the PA 12 after LS processing or reprocessing was shown through Pyrolysis Combustion Flow Calorimetry (PCFC) and cone calorimeter (CC) tests. FTIR analysis also showed that post-condensation reactions have occurred. The mode of action of the flame retardants was clearly seen on HRR curves at both tests. The first reuses of PA 12 powders entailed a significant reduction in time to ignition at the cone calorimeter (150 for the initial material to around 90 s for the reused material), indicating the formation of short polymer chains. Only in the case of zinc borate was it noticed that re-used powder was detrimental to the fire performance because of a strong increase in the value of pHRR (between 163 and 220 kW/m² for reused material instead of 125 kW/m² for the initial one). Full article

The aim of the research was to determine the potential of hydrotreated vegetable oil (HVO) in reducing nitrogen oxides and particulate matter emissions from the Perkins 854E-E34TA compression ignition engine. The concentrations of these toxic exhaust gas components were measured using the following analyzers: AVL CEB II (for NOx concentration measurement) and Horiba Mexa 1230 PM (for PM measurement). The measurements were carried out in the ESC test on a compression ignition engine with direct fuel injection and a turbocharger. The engine had a common rail fuel supply system and met the Stage IIIB/Tier 4 exhaust emission standard. Two fuels were used in the tests: diesel fuel (DF) and hydrotreated vegetable oil (HVO). As part of the experiment, the basic indicators of engine operation were also determined (torque, effective power, and fuel consumption) and selected parameters of the combustion process, such as the instantaneous pressure of the working medium in the combustion chamber, maximum pressures and temperatures in the combustion chamber, and the heat release rate (HRR), were calculated. The tests were carried out in accordance with the ESC test because the authors wanted to determine how the new generation HVO fuel, powering a modern combustion engine with a common rail fuel system, would perform in a stationary emission test. Based on the obtained research results, the authors concluded that HVO fuel can replace diesel fuel in diesel engines even without major modifications or changes in engine settings. Full article