Formation Of Nitrogen Oxides Research Articles

Machine learning based spray process quantification

Droplet size distribution and liquid loading are two of the most important properties to characterise spray processes. For example, nitrogen oxide (NOx) formation of liquid fuel-operated combustion systems is dominated by mixture homogenisation that is heavily dependent on atomization. While phase Doppler interferometry (PDI) is the technique of choice to measure droplet size distribution, shadowgraphy enables the detection of liquid bodies of arbitrary shape, e.g. ligaments, and thus can be used to delineate primary atomization. For this purpose, a data analysis tool is developed that enables a quantitative description of droplet size and the primary break-up process simultaneously. In this context, machine learning-based (ML) object detection provides a generally applicable approach that is used here to characterise a pressure swirl water spray. The deep neural networks are trained using synthetic training data with physics-informed domain randomisation. Two different network architectures (namely Mask R-CNN and SparseInst), backbones (ResNet50 and ResNet101) and several different training approaches are evaluated. The inference accuracy of the ML models is validated against PDI measurements in terms of droplet size distribution. The best-performing ML model provides a robust detection method for a wide range of measurement conditions. The validated ML model is used to characterise the primary break-up to delineate the effect of aerodynamic forces on the atomization of a hollow cone pressure swirl spray in high momentum gaseous co-flow. The results show the largest and most deformed liquid bodies away from the centre line in regions of high co-flow velocity.

Palladium Catalysts for Methane Oxidation: Old Materials, New Challenges.

ConspectusMethane complete oxidation is an important reaction that is part of the general scheme used for removing pollutants contained in emissions from internal combustion engines and, more generally, combustion processes. It has also recently attracted interest as an option for the removal of atmospheric methane in the context of negative emission technologies. Methane, a powerful greenhouse gas, can be converted to carbon dioxide and water via its complete oxidation. Despite burning methane being facile because the combustion sustains its complete oxidation after ignition, methane strong C-H bonds require a catalyst to perform the oxidation at low temperatures and in the absence of a flame so as to avoid the formation of nitrogen oxides, such as those produced in flares. This process allows methane removal to be obtained under conditions that usually lead to higher emissions, such as under cold start conditions in the case of internal combustion engines. Among several options that include homo- and heterogeneous catalysts, supported palladium-based catalysts are the most active heterogeneous systems for this reaction. Finely divided palladium can activate C-H bonds at temperatures as low as 150 °C, although complete conversion is usually not reached until 400-500 °C in practical applications. Major goals are to achieve catalytic methane oxidation at as low as possible temperature and to utilize this expensive metal more efficiently.Compared to any other transition metal, palladium and its oxides are orders of magnitude more reactive for methane oxidation in the absence of water. During the last few decades, much research has been devoted to unveiling the origin of the high activity of supported palladium catalysts, their active phase, the effect of support, promoters, and defects, and the effect of reaction conditions with the goal of further improving their reactivity. There is an overall agreement in trends, yet there are noticeable differences in some details of the catalytic performance of palladium, including the active phase under reaction conditions and the reasons for catalyst deactivation and poisoning. In this Account we summarize our work in this space using well-defined catalysts, especially model palladium surfaces and those prepared using colloidal nanocrystals as precursors, and spectroscopic tools to unveil important details about the chemistry of supported palladium catalysts. We describe advanced techniques aimed at elucidating the role of several parameters in the performance of palladium catalysts for methane oxidation as well as in engineering catalysts through advancing fundamental understanding and synthesis methods. We report the state of research on active phases and sites, then move to the role of supports and promoters, and finally discuss stability in catalytic performance and the role of water in the palladium active phase. Overall, we want to emphasize the importance of a fundamental understanding in designing and realizing active and stable palladium-based catalysts for methane oxidation as an example for a variety of energy and environmental applications of nanomaterials in catalysis.

Effects of dual injection strategies on combustion, heat-work conversion process and emissions of a spark ignition engine fuelled with E20 blends

In this paper, the combustion, heat-work conversion process and emission characteristic at high compression ratio for the spark ignition engine fuelled with E20 (20 % ethanol, 80 % gasoline) fuel were investigated under ultra-lean burn conditions. Specifically, the direct injection (DI) mode combined with port fuel injection (PFI) mode strategy was used in the experiments. In addition, the dual injection strategies were comprehensively investigated by using different fuel injection masses and injection timing. The results indicated that using optimal injection timing and reasonable injection masses can improve heat-work conversion efficiency and combustion efficiency, combustion stability in the test engine. Furthermore, under the lean combustion model, using earlier injection timing could not only inhibit the soot production, but also decrease the nitrogen oxides formation. Compared to the equivalence ratio at 0.82 and DI injection timing at 120 °CA bTDC, soot and NOX emissions were respectively reduced by 14.93 %–26.6 % and 39.84 %–73.56 % under the equivalence ratio at 0.685 and DI injection timing at 180 °CA bTDC. This study provides an optimization direction for the application of ethanol-gasoline blends in the internal combustion engine (ICE) engines for high efficiency and clean combustion.

Analysis of the Vibrational Behavior of dual-fuel RCCI combustion in a Heavy-Duty Compression Ignited Engine fueled with Diesel-NG at Low Load

In the field of internal combustion engines, the Low Temperature Combustions (LTC) appear to have the potential to reduce the formation of both soot and nitrogen oxides. One of the most promising LTC is Reactivity Controlled Compression Ignition (RCCI) which is based on the combustion of a lean low reactivity fuel-air mixture generated in the intake manifold and autoignited by small injections of high reactivity fuel introduced at high pressure in the combustion chamber. By the combination of net-zero natural gas and biodiesel, such LTC methodology might represent a suitable solution moving toward zero-emissions in transportation sector.Despite the potential to reduce pollutant emissions, Low Temperature Combustion strategies face a challenge in controlling the angular position where the combustion takes place which can be overcome by a proper management of the high-pressure injections.One potentially interesting application is related to trucks, mainly because they have long periods of idling, since emissions can be drastically reduced by means LTC. A single cylinder research engine for heavy duty application is operated under steady state conditions at low load and speed to analyze the possibility of controlling the engine behavior in dual fuel RCCI mode. The results indicate that the combustion mode switches from the dual-stage to gaussian within a narrow angular range. A further advance of the start of injection can generate misfires and significant variations in typical combustion indexes, while a delayed start of injection can cause impulsive combustion that rises the cylinder temperature and results in high-frequency pressure oscillations inside the combustion chamber. These oscillations are related to the combustion chamber typical resonance frequency, and if relevant in amplitude and persist for a long time, they might generate a potential source of failures.

The impact of hydrogen addition and OH concentration on NO emissions in high-pressure NH3/air combustion

The addition of hydrogen to ammonia enhances combustion stability and widens the flame limits. However, it also brings the drawback of increased nitrogen oxide (NO) emissions. Therefore, this study employs a chemical kinetics simulation system to investigate the effects of OH concentration and hydrogen addition on NO emissions in a laminar premixed hydrogen/ammonia/air swirling flame at high pressures. The research reveals a distinct positive linear correlation between NO emissions and the peak mole fraction of OH radicals. Within the range of 1.0≤φ ≤ 1.1 and 0≤XH2≤0.5, as hydrogen content (0≤XH2≤0.5) increases, the promoting effect of max(OH) on NO emissions continuously intensifies. Pressure, on the other hand, has virtually no impact on their correlation.Furthermore,the analysis of production rates, sensitivity, and reaction pathways indicates that NH3 primarily transforms into NO through three pathways: NH3→NH2(NH)→HNO→NO, NH3→NH2→NH→NO, and NH3→NH2→NH→N→NO. The HNO intermediate pathway is the major route for NO generation, with OH radicals significantly promoting NO production via the NH→HNO intermediate pathway. This theoretically validates the correlation between max(OH) and NO emissions. Data analysis using MATLAB yields the relationship between max(OH) and NO emissions, providing a theoretical basis for the practical application of OH chemiluminescence detection. Additionally, NNH proves to be a crucial radical in ammonia oxidation chemistry and is involved in the NO formation process in reaction R69 NNH + ONH + NO. This study sheds light on the complex interplay between OH, hydrogen content, and NO emissions, providing valuable insights into combustion dynamics and emissions control.

Efficiency of limiting nitrogen oxides emissions by exhaust gas recirculation systems of marine internal combustion engines

The subject of this study is systems for ensuring environmental safety of marine internal combustion engines, in particular, technologies for limiting emissions of nitrogen oxides (NOx). The regulatory requirements for reducing emissions are presented in the paper. The main theoretical aspects of the problem of nitrogen oxides formation during combustion in a diesel engine are considered. On the basis of these theoretical aspects the effectiveness of using various methods to achieve the requirements for the permissible level of NOx concentration in the exhaust gases is assessed. Exhaust gas recirculation (EGR) systems and selective catalytic reduction (SCR) systems are considered as the main technologies; they allow achieving the highest indicators of nitrogen oxide emissions control in accordance with the requirements of the Tier 3 standard. Taking into account the peculiarities of the requirements for the design and layout of systems as part of a ship power plant, as well as operational and investment costs, the main attention in the work is paid to systems of indirect influence on the engine in-cylinder processes, which include exhaust gas recirculation systems. Based on the comparison of high and low pressure EGR, the advantages and disadvantages of the designs are determined. It is noted that high-pressure exhaust gas recirculation systems have a number of advantages, which primarily include the compactness and high speed of the system response to changes in operational conditions. On the example of the leading manufacturers developments, the potential capabilities of the high-pressure EGR system and the engine characteristics confirming the effectiveness of its use are demonstrated. Based on the results of the work, a conclusion about the high efficiency and expediency of using exhaust gas recirculation systems to meet the requirements of the current environmental safety standards of ship power plants is made.

Performance of fuel reactor in chemical looping combustion system with mixed metal oxides

The Chemical Looping Combustion (CLC) technique shows great potential as an innovative technology to enhance thermal efficiency of system. It has a capability to achieve complete carbon capture (up to 100 %) and prevent the formation of nitrogen oxides (NOx). The current study focuses on the computational analysis of bubble behavior within fuel reactor of CH4-fueled Chemical Looping Combustion (CLC) setup. During numerical examination, a user-defined function (UDF) was utilized to integrate a reaction kinetics into active environment of fuel reactor. In the current research, CuO and NiO are employed as mixed oxygen carrier substances, while CH4 is utilized as fuel within the combustion procedures. The preparation, growing, rising, and bursting of bubbles' hydrodynamics has been observed; additionally, it has been evaluated in addition to examining the solidus-gaseous molar fraction within a fuel reactor. The current simulation opted for a gaseous fuel composed of natural gas (CH4), a hydrocarbon, alongside mixed metal oxides as CuO and NiO in varying ratios. A mixed metal oxide has been chosen in the proportion of CuO as 0.3 and NiO as 0.7, CuO as 0.5 and NiO as 0.5, and CuO as 0.7 and NiO as 0.3 by weightage. The fuel conversion rate has been observed 20 %, 25 %, and 30 % respectively for the different metal oxide mixture proportions. It has been clearly noticed that in the mixture of NiO and CuO; if the CuO amount is more, then the fuel conversion rate is high due to highly reactivity of CuO at high temperatures.

Study on Mechanisms of NOx Formation and Inhibition during the Combustion of NH3/CH4 and NH3/CO Mixtures

Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NOx) emissions. Co-firing ammonia with an industrial by-product gas (with CH4 and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NOx generation. Currently, the research on NOx formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NOx formation and inhibition mechanisms during the combustion of NH3/CH4 and NH3/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (α), temperature, residence time, and fuel concentration, the key factors influencing NOx generation and inhibition were further analyzed. The results showed that when α was no less than 1, the production of NOx initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 °C to 1500 °C, the amount of NOx generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH3/CH4 and NH3/CO, the emissions of NOx were higher than those during pure ammonia combustion.

Numerical Study on the Combustion Properties of Ammonia/DME and Ammonia/DMM Mixtures

Ammonia (NH3) is considered a promising zero-carbon fuel and was extensively studied recently. Mixing high-reactivity oxygenated fuels such as dimethyl ether (DME) or dimethoxymethane (DMM) with ammonia is a realistic approach to overcome the low reactivity of NH3. To study the combustion characteristics of NH3/DMM and NH3/DME mixtures, we constructed a NH3/DMM chemical mechanism and tested its accuracy using measured laminar burning velocity (LBV) and ignition delay time (IDT) of both NH3/DMM and NH3/DME mixtures from the literature. The kinetic analysis of NH3/DMM flames using this mechanism reveals that the CH3 radicals generated from the oxidation of DMM substantially affects the oxidation pathway of NH3 at an early stage of flame propagation. We investigated the formation of nitrogen oxides (NOx) in NH3/DMM and NH3/DME flames and little difference can be found in the NOx emissions. Using NH3/DMM flames as an example, the peak NOx emissions are located at an equivalence ratio (φ) of 0.9 and a DMM fraction of 40% in the conditions studied. Kinetic analysis shows that NOx emission is dominated by NO, which primarily comes from fuel nitrogen of NH3. The addition of DMM at 40% significantly promotes the reactive radical pool (e.g., H, O, and OH) while the maintaining a high concentration of NO precursors (e.g., HNO, NO2, and N2O), which results in a high reaction rate of NO formation reaction and subsequently generates the highest NO emissions.

The methodology of decoupling fuel and thermal nitrogen oxides in multi-dimensional computational fluid dynamics combustion simulation of ammonia-hydrogen spark ignition engines

Under the paradigm of carbon neutrality, ammonia-hydrogen (NH3–H2) blended fuel presents itself as a zero-carbon alternative to petroleum-based fuels, effectively reducing carbon emissions originating from internal combustion engines. In the combustion process of conventional hydrocarbon fuels, the production of nitrogen oxides (NOX) predominantly arises from nitrogen present in the atmosphere, which occurs through the Zeldovich mechanism under high-temperature conditions. These NOX species, commonly referred to as thermal NOX, rely on inert nitrogen. However, the utilization of ammonia fuel activates the reactivity of nitrogen element, leading to the nitrogen-containing species formation, including NOX, termed as fuel NOX. Consequently, the combustion of ammonia-hydrogen fuel entails the coupling of thermally formed nitrogen oxides and fuel-derived nitrogen oxides. The generation of NOX is significantly influenced by the physicochemical environment, while the transient combustion conditions within the engine combustion chamber further complicate the process of NH3–H2 combustion and NOX formation. As a consequence, comprehensively investigating the NOX emission characteristics in NH3–H2 engines presents a considerable challenge. By decoupling fuel NOX and thermal NOX, a more profound understanding of NOX emission control strategies for ammonia-hydrogen engines can be attained. This research paper accomplishes the decoupling of fuel nitrogen elements and atmospheric nitrogen elements in three dimensional computational fluid dynamics engine combustion simulations. The results indicate that this decoupling methodology disregards the differentiation between the fuel NOX pool and the thermal NOX pool, resulting in a slight modification in NOX concentration. Nevertheless, this approach has minimal impact on the combustion process, ensuring that the NOX formation environment remains largely unchanged. Furthermore, it successfully demonstrates the spatial and temporal distribution characteristics of thermal NOX and fuel NOX, thereby furnishing an effective analytical tool for the comprehensive study of NOX emission characteristics in NH3–H2 engines.

Investigation into the Influence of Temperature on the Formation of Nitrogen Oxides during the Staged Combustion of Low-Reactive Coal with the Use of Direct-Flow Burners

Investigation into the Influence of Temperature on the Formation of Nitrogen Oxides during the Staged Combustion of Low-Reactive Coal with the Use of Direct-Flow Burners

Study of the aerodynamics of air flow in burners using the Comsol Multiphysics software

The article presents the processes of modeling the aerodynamic flow of air in two burner microflame devices: 1. The burner device of the combustion chamber of a gas turbine plant; 2. The micromodular gas burner. The aerodynamic flow is modeled in the Comsol Multiphysics software package, which is reasonable in terms of availability and quality. The performed analysis of microflame fuel-burning devices revealed that the dynamic and geometric characteristics affect the aerodynamics and velocity profiles. Different airflow rates significantly affected the intensity of the formation of recirculation zones, which also led to an increase in pressure in the circuit. Accordingly, the flow at different heights of the cylindrical nozzle showed that the dimensions will affect the combustion processes and, as a result, the stabilization and formation of nitrogen oxides.

A surface mechanism for O3 production with N2 addition in dielectric barrier discharges

Ozone, O3, is a strong oxidizing agent often used for water purification. O3 is typically produced in dielectric barrier discharges (DBDs) by electron-impact dissociation of O2, followed by three-body association reactions between O and O2. Previous studies on O3 formation in low-temperature plasma DBDs have shown that O3 concentrations can drop to nearly zero after continued operation, termed the ozone-zero phenomenon (OZP). Including small (<4%) admixtures of N2 can suppress this phenomenon and increase the O3 production relative to using pure O2 in spite of power deposition being diverted from O2 to N2 and the production of nitrogen oxides, N x O y . The OZP is hypothesized to occur because O3 is destroyed on the surfaces in contact with the plasma. Including N2 in the gas mixture enables N atoms to occupy surface sites that would otherwise participate in O3 destruction. The effect of N2 in ozone-producing DBDs was computationally investigated using a global plasma chemistry model. A general surface reaction mechanism is proposed to explain the increase in O3 production with N2 admixtures. The mechanism includes O3 formation and destruction on the surfaces, adsorption and recombination of O and N, desorption of O2 and N2, and NO x reactions. Without these reactions on the surface, the density of O3 monotonically decreases with increasing N2 admixture due to power absorption by N2 leading to the formation of nitrogen oxides. With N-based surface chemistry, the concentrations of O3 are maximum with a few tenths of percent of N2 depending on the O3 destruction probability on the surface. The consequences of the surface chemistry on ozone production are less than the effect of gas temperature without surface processes. An increase in the O3 density with N-based surface chemistry occurs when the surface destruction probability of O3 or the surface roughness was decreased.

Two-dimensional calculation model for hazardous substances formation in combustion products of a spark-ignition engine

Introduction (problem statement and relevance). Improvement of environmental parameters of internal combustion engines is one of the most relevant tasks of the domestic transport engineering. Calculation support allows reducing the time and raising the efficiency of works for refining of the bench work process in order to meet the required parameters. The paper is devoted to development of a two-dimensional calculation model for hazardous substances formation in combustion products of spark-ignition engines based on the non-equilibrium kinetic models of formation of nitrogen oxides and carbon monoxide.Methodology and research methods. Computational methods for differential equations (ordinary and partial ones) are applied. Non-equilibrium kinetics of hazardous substances formation in combustion products is considered. The work process is calculated based on a combination of the mesh control-volume method and determination of the observable flame rate based on the experimental data (taking into account the development stage of the flame source).Scientific novelty and results. The new calculation method for flame propagation in the spark-ignition engine is suggested. The developed model combines such advantages as good predictability and short time of calculation.Practical significance. The model can be applied, in particular, to preliminary planning of three-dimensional calculations of the work process or their check in the absence of experimental data (at the stage of preliminary/concept design). The calculation results can be used as initial data for modeling of the exhaust gas aftertreatment (additional purification) system.

An Experimental Study of Operating Range, Combustion and Emission Characteristics in an RCCI Engine Fueled with Iso-Propanol/n-Heptane

Recently, studies have been carried out using environmentally sustainable technologies with more efficient energy conversion to fulfill emission requirements. One of these technologies, reactivity controlled compression ignition (RCCI), is a low-temperature combustion mode and has a dual fuel strategy. The controllability of combustion, high thermal efficiency and low nitrogen oxide (NOx) and soot emissions are some of the most prominent advantages of this combustion mode. In this study, the effects of the premixed ratio (PR) and intake air temperature (IAT) on the operating range, combustion characteristics and emissions were investigated experimentally. In the experiments, iso-propanol and n-heptane were used as fuels. The experiments were carried out for two different case studies. In the first case, the experiments were performed at a 50 °C intake air temperature and three different premix ratios (PR25, PR50, PR75). The minimum brake-specific fuel consumption (BSFC) was 268 g/kWh and the widest operating range was obtained with PR25. In addition, the lowest emission values in NOx, hydrocarbon (HC) and carbon monoxide (CO) emission formation were recorded with the use of PR25 fuel. In the other case, experiments were conducted at three different intake air temperatures (30 °C, 50 °C, 70 °C) with PR50. The minimum BSFC was measured as 268 g/kWh and the widest operating range was observed at a 70 °C intake air temperature. At the same time, the lowest NOx emission values were obtained at a 30 °C intake air temperature. The maximum HC emission was determined as 586 ppm at a 30 °C intake air temperature. In addition, the minimum CO emission was measured as 0.142% by volume at a 70 °C intake air temperature.

Reduced Mechanism for Combustion of Ammonia and Natural Gas Mixtures

A fuel mixture of ammonia and natural gas as a low-carbon alternative for future power generation and transportation is an attractive option. In this work, a 50-species reduced mechanism, NH3NG, suitable for computational fluid dynamics simulations (CFD), is developed for ammonia–natural gas cofiring while addressing important emission issues, such as the formation of nitrogen oxides (NOx), soot, carbon monoxide, and unburnt methane/ammonia. The adoption of reduced mechanisms is imperative not only for saving computer storage and running time but also for numerical convergence for practical applications. The NH3NG reduced mechanism can predict soot emission because it includes soot precursor species. Further, it can handle heavier components in natural gas, such as ethane and propane. The absolute error is 5% for predicting NOx and CO emissions compared to the full Modified Konnov mechanism. Validation with key performance parameters (ignition delay, laminar flame speed, adiabatic temperature, and NOx and CO emissions) indicates that the predictions of the reduced mechanism NH3NG are in good agreement with published experimental data. The average prediction error of 13% for ignition delay is within typical experimental data uncertainties of 10–20%. The predicted adiabatic temperatures are within 1 °C. For laminar flame speed, the R2 between prediction and data is 0.985. NH3NG over-predicts NOx and CO emissions, similar to all other literature methods, but the NOx predictions are closer to the experimental data.

Prediction of nitrogen oxide emissions from diesel exhaust gases when using composite fuel

BACKGROUND: The problem of using composite fuel (CF) in diesel engines consists in a wide variation of their physicochemical properties, which affect the emission of nitrogen oxides (NOx) with ex-haust gases (EG). Therefore, the predictive assessment of the formation of NOx with EG when using CF is very relevant.&#x0D; AIMS: Predictive assessment of quantitative NOx emission with diesel EG when using various types and compositions of CF. Scientific novelty lies in development of the method of prediction of NOx emission by a diesel engine when using CF.&#x0D; METHODS: The method of prediction of quantitative NOx emissions with diesel EG regarding the use of various CF kinds and compositions has been developed. Predictive indicators of NOx emissions have been defined. Multi-parameter characteristics of NOx emission with EG of the D-245.582 diesel engine of 4ChN 11.0/12.5 size have been obtained experimentally. Degree of convergence of the experimental data with the calculated values is assessed.&#x0D; RESULTS: As a result of the carried-out studies, it was theoretically established that the load (pe) increase from 0.2 to 1.0 MPa, the engine speed (n) decrease from 1800 to 1400 min-1 and decrease of mass fraction of rapeseed oil (RO) and ethanol (E) in CF from 40 to 20% lead to increased NOx emissions with diesel EG from 131 to 2225 ppm and from 75 to 1450 ppm respectively. The increase in NOx emissions with the EG from 152 to 2125 ppm for CF consisting of DF and RO and from 175 to 1550 ppm for CF consisting of DF and E in the above mentioned operating modes experimentally confirmed. The degree of convergence of the experimental data with the calculated values is 90.14%, which in turn indicates the possibility of using the developed methodology as a predictive indicator.&#x0D; CONCLUSIONS: As a result of the studies, it was established that the developed method of prediction of quantitative NOx emissions with diesel EG is highly likely to use for preliminary assessment when various CF kinds and compositions are considered, as the degree of convergence of the experimental data with the calculated values, assessed with a statistical processing method and experimental error calculation, is 90.14%.

Physical and Chemical Features of Hydrogen Combustion and Their Influence on the Characteristics of Gas Turbine Combustion Chambers

Hydrogen plays a key role in the transition to a carbon-free economy. Substitution of hydrocarbon fuel with hydrogen in gas turbine engines and power plants is an area of growing interest. This review discusses the combustion features of adding hydrogen as well as its influence on the characteristics of gas turbine combustion chambers as compared with methane. The paper presents the studies into pure hydrogen or methane and methane–hydrogen mixtures with various hydrogen contents. Hydrogen combustion shows a smaller ignition delay time and higher laminar flame speed with a shift in its maximum value to a rich mixture, which has a significant effect on the flashback inside the burner premixer, especially at elevated air temperatures. Another feature is an increased temperature of the flame, which can lead to an increased rate of nitrogen oxide formation. However, wider combustion concentration ranges contribute to the stable combustion of hydrogen at temperatures lower than those of methane. Along with this, it has been shown that even at the same adiabatic temperature, more nitrogen oxides are formed in a hydrogen flame than in a methane flame, which indicates another mechanism for NOx formation in addition to the Zeldovich mechanism. The article also summarizes some of the results of the studies into the effects of hydrogen on thermoacoustic instability, which depends on the inherent nature of pulsations during methane combustion. The presented data will be useful both to engineers who are engaged in solving the problems of designing hydrogen combustion devices and to scientists in this field of study.

Emissions and efficiency of pure CO and H2-rich simulated gases combustion with peach and rice biomasses syngas characteristics: A renewable energy pathway for the agroindustrial sector in Rio Grande do Sul, Brazil

The possibility of using renewable energy generated in the industrial sector for the combined generation of electricity and heat is becoming one of the most efficient energy generation methods, without the need for sophisticated systems of biogas compression for its use. Different fuels are able to extend the lean threshold of spark ignition engines (SI). Although synthesis gas (syngas) lean combustion raises combustion efficiency, its use can result in high carbon monoxide (CO) emissions, making it urgent to investigate the CO combustion process in SI engines. Currently, only data referring to the combustion of pure hydrogen are found. Also, studies on the emissions from the use of syngas generated from peach kernels and rice husks are scarce. Therefore, the innovation and goal of this paper were to investigate the emissions resulting from lean combustion in SI engines fueled with both pure CO and hydrogen-rich gas with close characteristics of syngas generated from rice husk and peach kernel, two highly produced biomasses in Brazil. As the main results, regarding nitrogen oxide (NOx) emissions, the combustion of pure CO was quite high when compared to syngas. The syngas H2/CO ∼ 1 was also responsible for the largest emission of hydrocarbons (HC), a little less than twice that of H2/CO ∼ 0.38. Furthermore, by allowing lean combustion, the temperatures of the flared gas can be kept below the NOx formation limit. Moreover, the combustion of pure CO resulted in reduced efficiency and increased COV of IMEP. Besides emissions reduction, the use of waste for biofuel production is essential for the overall strategy for a transition to a circular economy.

Advanced combustion strategies for improving ic engine efficiency and emissions

The growing need for higher fuel efficiency and compliance with increasingly stringent emission regulations has prompted significant advancements in internal combustion (IC) engine technology. Traditional combustion methods, while widely utilized, face inherent challenges such as limited thermal efficiency and the production of harmful emissions like nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), and unburned hydrocarbons (HC). To address these concerns, researchers and engineers have developed a range of advanced combustion strategies that offer the potential to drastically improve engine efficiency while minimizing environmental impact.This paper provides a comprehensive analysis of cutting-edge combustion techniques, with a focus on strategies that balance the trade-off between fuel efficiency and emission reduction. Prominent among these strategies is Homogeneous Charge Compression Ignition (HCCI), which utilizes a lean, premixed air-fuel mixture to achieve spontaneous ignition at low temperatures, significantly reducing NOx and PM emissions. Another promising technique, Reactivity-Controlled Compression Ignition (RCCI), leverages the controlled use of two fuels with different reactivity levels, enabling precise control over the combustion process and enhancing both fuel efficiency and emission control. In contrast, Gasoline Direct Injection (GDI) technology improves fuel atomization and combustion control by injecting fuel directly into the combustion chamber, leading to higher efficiency and power output, albeit with challenges related to particulate emissions.In addition to these combustion strategies, this paper explores the role of Low-Temperature Combustion (LTC), which operates at reduced in-cylinder temperatures to mitigate the formation of NOx and soot, as well as the potential of advanced ignition systems like plasma or laser-based ignition to improve lean-burn combustion processes. Furthermore, the paper examines the integration of renewable fuels, such as hydrogen and biofuels, with advanced combustion techniques to support the global transition toward cleaner energy.The analysis also considers technological enablers such as variable valve timing (VVT), turbocharging, and sophisticated exhaust after-treatment systems that complement these advanced combustion strategies. Moreover, the application of simulation and optimization tools, including computational fluid dynamics (CFD) and machine learning (ML), is highlighted as essential for refining engine design and optimizing combustion processes.Despite the notable progress, challenges remain in terms of system complexity, control precision, and expanding the operational range of these advanced combustion techniques. As the automotive industry moves towards electrification and hybridization, advanced IC engine combustion strategies will continue to play a crucial role in improving vehicle performance and sustainability. This paper concludes by outlining the future prospects for further optimizing combustion efficiency and integrating renewable fuels in next-generation IC engines, thereby contributing to a cleaner, more efficient transportation sector.