Combustion Systems Research Articles

In Situ Formation of Titanium Diboride/Magnesium Titanate Composites by Magnesiothermic-Based Combustion Synthesis

In situ formation of TiB2–Mg2TiO4 composites was investigated by combustion synthesis involving the solid-state reaction of Ti with boron and magnesiothermic reduction of B2O3. Certain amounts of MgO and TiO2 were added to the reactant mixtures of Ti/B/Mg/B2O3 to act as the moderator of highly exothermic combustion and a portion of the precursors to form Mg2TiO4. Two combustion systems were designed to ensure that synthesis reactions were sufficiently energetic to carry on self-sustainably, that is, in the mode of self-propagating high-temperature synthesis (SHS). Consistent with thermodynamic analyses, experimental results indicated that the increase in pre-added MgO and TiO2 decreased the combustion temperature and propagation velocity of the flame front. MgO was shown to have a stronger dilution effect on combustion exothermicity than TiO2, because the extent of magnesiothermic reduction of B2O3 was reduced in the MgO-added samples. In situ formation of the TiB2–Mg2TiO4 composite was achieved from both types of samples. It is believed that, in the course of the SHS progression, Mg2TiO4 was produced through a combination reaction between MgO and TiO2, both of which were entirely or partially generated from the metallothermic reduction of B2O3. The microstructure of the products exhibited fine TiB2 crystals in the shape of short rods and thin platelets that existed within the gaps of Mg2AlO4 grains. Both constituent phases were well distributed. A novel and efficient synthesis route, which is energy- and time-saving, for producing Mg2TiO4-containing composites was demonstrated.

The Research and Development of a Jet Disturbance Combustion System for Heavy-Duty Diesel Engines

Herein, a diesel engine jet disturbance combustion system was proposed to achieve efficient and clean combustion under heavy load conditions in heavy-duty diesel engines. The key components of the combustion system were designed, and a research platform was constructed. Focusing on the internal combustion conditions of the disturbance chamber and the developmental path of high-speed jets, the design and comprehensive optimization of the jet disturbance combustion system were carried out. Following optimization, the peak internal heat release rate increased from 86 J/deg to 269 J/deg, and the cumulative heat release increased by 112 J, significantly enhancing the energy of the disturbance chamber jet. Then, considering combustion optimization and the heat transfer loss from the piston, it was determined that the optimal configuration for the disturbance chamber jet channel angles was 60 deg inter-channel angle and 10 deg channel incidence angle. This configuration allowed the disturbance chamber jet to precisely disturb the concentrated mixture area in the middle and late stages of combustion. The intervention of the disturbance chamber jet provided sufficient energy for the fuel–air mixing process and complicated the gas flow state in the main combustion chamber. Despite its low-momentum density, the residual mixture in the cylinder maintained a high mixing rate after the end of the fuel injection process. Single-cylinder engine test results showed that a diesel engine using this jet disturbance system and a 180 MPa common rail pressure fuel system achieved 52.12% thermal efficiency.

Precipitation of metallic Ni clusters in alumina scale during high-temperature oxidation of NiAl in water vapor

Water vapor is ubiquitously present for energy conversion and combustion systems, yet its effect on the oxidation of crucial structure components of heat-resistant alloys remains elusive. Departure from the well-established phenomenon of exclusive alumina growth from the NiAl oxidation in dry O2, we demonstrate that the NiAl oxidation in H2O results in the precipitation of a significant number of metallic Ni clusters within the Al2O3 scale by adsorbing Ni atoms from the alloy through a vacancy-assisted solute capture solute capture process of the enhanced oxide/alloy interface migration. The Ni clusters initially have a hcp structure at small sized, transitioning into an fcc structure when their size exceeds ∼12.5 nm. Using atomistic modeling, we show that the dissolution of a high concentration of H derived from H2O into the oxide scale is the key to stabilizing the hcp Ni structure. Subsequent coarsening of the hcp Ni clusters lowers the H concentration, leading to the hcp → fcc transformation. These results provide mechanistic insight into the effect of water vapor on the long-term stability of the structure alloys by influencing the oxidation-induced mass transport across the scale/alloy interface and microstructure evolution within the oxide scale.

Design and variable scale optimization of flare gas recovery process for hydrogen production

Flare systems are equipped in refining and petrochemical industries to ensure operation safety. However, flare gas sent directly to the flare system for combustion wastes energy and pollutes the environment, so it is of great significance to recover and comprehensively utilize flare gas. A new process of hydrogen production with flare gas recovery is proposed in this paper, which not only solves the problem of environmental pollution but also makes rational use of energy and improves economic benefit. Firstly, the flare gas recovery process for hydrogen production is designed by coupling the poly-refrigerant integrated cycle operation method with the chemical looping combustion sorption enhanced steam methane reforming method. Secondly, key parameters such as reactor temperature, H2O/CH4 molar ratio, and CaO/CH4 molar ratio are optimized through sensitivity analysis with CH4 conversion, H2 yield, H2 purity (dry basis), and CO2 capture rate as indicators. Thirdly, computational fluid dynamics simulation is carried out to validate the above macroscopic analysis results and further optimize the process at the mesoscopic level. The effects of different bed heights on hydrogen purity are analyzed to determine the optimal bed height for the reformer reactor, which strengthens the performance of the equipment. Finally, the process is probed by an economic analysis, which shows that 68.7 tons/year of hydrogen is produced when the recovery of methane from flare gas reaches 137.3 tons/year. This determines the economic feasibility of the process. The significance of this paper lies in: a novel green process using flare gas recovery to produce high-purity hydrogen with the conversion from waste gas to new energy realized with the concept of “turning waste into treasure”; a new way of combining meso-level and macro-level, variable-scale optimization of the process parameters; the recycling of other short-chain hydrocarbon-containing waste gases.

Brief Review of Recent Achievements in the Flamelet Manifold Selection and Probability Density Distribution for Flamelet Manifold Variables

Abstract The flamelet model is a commonly used tool for turbulent combustion simulations in the engineering field due to its computational efficiency and compatibility with complex chemical reaction mechanisms. Despite being widely used for decades, the flamelet model still faces challenges when applied to complex flame configurations, such as partially premixed flames, inhomogeneous inlets, supersonic combustion, or multiphase combustion. The principal challenges are posed by the uncertainty of the presumed shapes for probability density functions (PDFs) of the flamelet tabulation variables and the coupled process of turbulent diffusion and chemical reaction in turbulent combustion. Recent progress is reviewed from the viewpoint of the reaction manifold, with connections made to other combustion models, as well as the determination of joint (or conditional) PDFs for flamelet manifold parameters (e.g., progress variable, scalar dissipation rates, etc.). Promising improvements have been outlined in computational efficiency and the accuracy of predicted variable fields in simulating complex combustion systems (such as turbulent inhomogeneous combustion, combustion with multi-regime modes, and two-phase combustion). Advances in computational resources, direct numerical simulation data, artificial intelligence, stochastic simulation methods, and other dimension-reduction combustion models will contribute to the development of more accurate and efficient flamelet-like models for engineering applications.

EFFECT OF RESIDENTIAL STOVE TECHNOLOGY ON GASEOUS EMISSIONS FROM BIOMASS COMBUSTION

The growing use of biomass for cooking and heating raises environmental concerns about atmospheric air pollution from flue gases emitting during its combustion. In this work, the gaseous emissions from two residential wood stoves were examined. Emissions from conventional single-stage and triple-stage combustion logwood stoves were compared using Eucalyptus grandis (EUG) and Pinus elliottii (PIE) woods as fuels. Carbon monoxide emissions were reduced in 102% and 240%, when PIE and EUG wood logs were burned in triple-stage combustion stove. The triple combustion system showed total volatile organic compounds and formaldehyde emissions higher than obtained in conventional system possibly due to the mixture of both gaseous emissions with water vapor releasing during combustion. The results indicated that the utilization of triple combustion stove with some adjustments would be beneficial to local air quality, individual health and reduced global climate change.

Gas turbine circumferential temperature distribution model for the combustion system fault detection

The gas turbine combustion system operates under harsh conditions, and any faults such as nozzle clogging, cracks, etc. can endanger the downstream components and cause catastrophic accidents. Thus, monitoring the combustion system status and detecting its performance degradation timely are crucial for gas turbine safety. The current predominant method for monitoring involves analyzing exhaust gas temperature (EGT) dispersion, utilizing thermocouples placed at the turbine outlet to indirectly assess combustion system performance. However, the EGT is affected not only by faults but also by various non-fault disturbances, such as operational conditions, atmospheric variations, compressor performance degradation, and uneven hot gas mixing and rotating. To improve the sensitivity of fault detection, it is necessary to investigate how various factors affect the EGT dispersion and differentiate between EGT changes due to interference and those due to combustion system faults. However, using actual operational data from gas turbines to analyze and reveal these impact mechanisms is challenging. Therefore, this paper develops a gas turbine model for combustion system fault detection that accurately reflects the uneven circumferential distribution of EGT. The model incorporates a multi-combustor burner, a multi-channel turbine, and a module for simulating the mixing and rotating of the hot gas. Using this model, simulations are conducted to study the effects of non-fault interference factors, such as variations in ambient temperature, fuel flow changes, and compressor performance degradation, on EGT distribution. Additionally, simulations are conducted to analyze the effects of faults, including combustor cracks, uneven fuel distribution, and the coupling of interferences with faults, on EGT distribution. By comparing the normal and abnormal modes, the study reveals the different EGT responses due to non-fault interferences and combustion system faults. Based on these findings, a fault detection method for coupled conditions is proposed. The research results provide a basis for the fault detection of combustion system, enabling practitioners to reduce interference in fault detection and to increase the detection sensitivity.

Numerical Assessment of a Rich-Quench-Lean Staging Strategy for Clean and Efficient Combustion of Partially Decomposed Ammonia in the Constant Pressure Sequential Combustion System

Abstract In a future energy system prospective, predictably dominated by (often) remote and (always) unsteady, nondispatchable renewable power generation from solar and wind resources, hydrogen (H2) and ammonia (NH3) have emerged as logistically convenient, chemically simple and carbon-free chemicals for energy transport and storage. Moreover, the reliability of supply of a specific fuel feedstock will remain unpredictable in the upcoming energy transition period. Therefore, the ability of gas turbine combustion systems to seamlessly switch between very disparate types of fuels must be ensured, aiming at intrinsically fuel-flexible combustion systems, i.e., capable of operating cleanly and efficiently with novel carbon-free energy vectors like H2 and NH3 as well as conventional fossil fuels, e.g., natural gas or fuel oils (back-up feedstock). In this context, a convenient feature of Ansaldo's constant pressure sequential combustion (CPSC) system, resulting in a fundamental advantage compared to alternative approaches, is the possibility of controlling the amount of fuel independently fed to the two combustion stages, depending on the fuel reactivity and combustion characteristics. The fuel-staging strategy implemented in the CPSC system, due to the intrinsic characteristics of the auto-ignition stabilized reheat flame, has already been proven able of handling fuels with large hydrogen fractions without significant penalties in efficiency and emissions of pollutants. However, ammonia combustion is governed by widely different thermo-chemical processes compared to hydrogen, requiring a considerably different approach to mitigate crucial issues with extremely low flame reactivity (blow-out) and formation of significant amounts of undesired pollutants and greenhouse gases (NOx and N2O). In this work, we present a fuel-flexible operational concept for the CPSC system and, based on unsteady Reynolds-Averaged Navier–Stokes (uRANS) and large eddy simulation (LES) performed in conjunction with detailed chemical kinetics, we explore for the first time full-load operation of the CPSC architecture in a Rich-Quench-Lean (RQL) strategy applied to combustion of partially-decomposed ammonia. Results from the numerical simulations confirm the main features of ammonia-firing in RQL operation already observed from previous work on different combustion systems and suggests that the CPSC architecture has excellent potential to operate in RQL-mode with low NOx and N2O emissions and good combustion efficiency.

Characteristics of combustion and ash deposition for pulverized coal combustion under various thermal loads: An experimental study in an 80 kWth combustion system

Characteristics of combustion and ash deposition for pulverized coal combustion under various thermal loads: An experimental study in an 80 kWth combustion system

Mechanism-enhanced data-driven method for the joint optimization of boiler combustion and selective catalytic reduction systems considering gas temperature deviations

A novel optimization framework for boiler combustion and selective catalytic reduction systems (BCSCRSs) that accounts for flue gas temperature deviation and integrates prior knowledge is proposed. Initially, single-factor hot-state experiments on the BCSCRSs are conducted to yield samples for model training. By integrating monotonic relationships from the experimental data into the fusion monotony–support vector regression model, more reasonable estimates and trends of the prediction targets (e.g., CO and NOx concentrations, and unburned combustibles) are obtained compared to those of the model without prior knowledge. Based on this model, the inequality-constrained reference vector-guided evolutionary algorithm is employed for multiobjective combustion optimization considering the constraints of gas temperature deviation in the horizontal pass. The corresponding Pareto-frontier solutions that serve as boundary conditions for the second-stage optimization are obtained. The second-stage optimization comprehensively considers the total operating cost of the BCSCRSs, the denitrification fraction in the NOx formation and removal processes, and safety concerns related to steam tube overheating and ammonia slip. Several noteworthy results are derived: the adjustment of the burner tilt angle presents a trade-off between eliminating gas temperature deviation and reducing NOx formation. An optimal point can be identified by comparing the magnitudes and variations of different BCSCRSs objectives.

Experimental studies of air ozonization influence on pollutants emission in vortex ignition-stabilizing modules of gas turbine combustion chambers

Reduction of pollutant emissions into the atmosphere is an urgent task of modern gas turbine engineering development. Such substances that have a negative impact on the environment include nitrogen oxides and carbon monoxide. The article provides a review of the existing methods for reducing the emissions of pollutants used in the combustion of hydrocarbon fuels in the combustion chambers of gas turbine units, as well as indicates promising technologies developed based on these methods. Justification is presented of the necessity to study the method of ozonization of air supplied to the fuel combustion zone to reduce the content of pollutants in its combustion products. The purpose of the study was to develop recommendations for reducing pollutant emissions within a given range of variations regime parameters. To perform the necessary set of experimental studies, a specialized laboratory stand was created, the combined circuit and measurement scheme of which is given in the article. A rather detailed description is given of the structural elements of the stand and, in particular, of the subject of research — a full-scale vortex ignitionstabilizing module of the combustion chamber of a gas turbine unit, an electric ozonator, air and combustible gas supply systems, an exhaust system with a central fan, control and measuring instruments and fittings. The tests were carried out in accordance with specially developed methods of controlling the stand operation in three modes: startup; transfer from one steady-state mode to another; stop. The influence of air ozonization on combustion processes in the vortex ignition-stabilizing module was determined by the content of nitrogen oxides and carbon monoxide in it. The factors that influence the decrease in the concentration of carbon monoxide in the combustion products during the combustion of air in ozonized air have been determined. The methods of calculation determination of combustible gas and air parameters — mass flow rates, flow velocities and dynamic heads — are described. The results of the performed experimental studies are presented in graphical interpretation, their detailed analysis is given, on the basis of which recommendations on practical use of the method of air ozonization are given.

Research on low‐carbon system of biomass combustion and solar‐energy power generation based on MP‐PIC simulation

AbstractTo vigorously reduce CO2 emission in the energy sector is an inevitable choice to achieve world's carbon emission reduction and to accelerate the construction of a modern energy system. The development of CO2 capture, utilization, and storage technology (CCUS) is of great significance for promoting low carbon utilization of traditional energy and realizing the low carbon transformation of coal power industry. The joint development of biomass combustion integrated with new energy technology and consideration of fuel conversion CO2 capture from the source is a technical solution with high efficiency and low energy consumption in coordination, which will bring new development opportunities for conventional thermal power industry. In this study, a low carbon system of collaborative renewable energy CO2 source capture is constructed. Numerical simulation method of multiphase flow coupled with thermal mass transfer and chemical reaction of the combustion mathematical model is employed to study the combustion characteristics in the biomass combustion system. The combustion efficiency, carbon conversion, and pollutant emissions are calculated compared with the conventional coal combustion system. Hydrogen production and CO2 emissions are analyzed based on life cycle assessment method. The energy integration full‐chain system of geological storage and CCUS is optimized, which is committed to achieving nearly zero carbon emission in the thermal power industry, contributing to the global low CO2 emission work.

Multivariate Signal Prediction Using Attention Transfer Learning for Early Detection of Thermoacoustic Instabilities

The prediction and control of thermoacoustic instability play a crucial role in combustion systems. This paper presents a novel methodology that employs attention transfer learning for the prediction of multivariate thermoacoustic signals, including acoustic pressure and heat release rate. By leveraging attention transfer learning, the proposed model can be generalized to thermoacoustic signal prediction under a variety of conditions with little additional training resources. Experimental data from various conditions in annular combustors are employed to evaluate the predictive performance of the model. The results demonstrate its ability to accurately predict future pressure signals over a wide-ranging time horizon while maintaining consistent dynamics, thus providing valuable information for active control. The proposed model is expected to be an effective step toward a data-driven solution for the early detection of thermoacoustic instability.

An efficient combustion concept for low calorific gases

The main features of low calorific gases as those from biomass gasification processes, landfills, mines and sewage sludge are well known. They can be expressed as low calorific values, high water content, corrosive actions and composition changes. Due to these characteristics there are up to date no combustion systems available which are capable to utilise such gases efficiently. The ordinary combustion concepts frequently do not guarantee sufficient flame stability. The high emissions of harmful substances as CO and NOx are another problem. Because of mentioned difficulties it is necessary and also a challenge to develop an efficient and flexible combustion system which can handle these problems. Through several matching steps of numerical and experimental investigations Gaswärme-Institut e. V. Essen (GWI) developed a progressive combustion system based on the concept of continuous air staging (COSTAIR). Burner tests at a small scale thermal load of 30 kW proved a stable combustion and low NOx and CO emissions for different qualities of low calorific gases. The best design of a small scale burner was transferred to larger thermal loads by applying of scale-up criteria. Already achieved experimental results at 200 kWth confirmed the efficient performance and the high potential of the burner for use of low calorific gases.

Post‐combustion capture and other Carbon Capture and Sequestration (CCS) technologies: A review

AbstractTechnologies for capturing and storing carbon dioxide (CO2) and strategies for sequestering carbon dioxide have received a lot of interest in recent years as potential remedies for the curtailment of the growing concerns of emissions of greenhouse gases and global warming. This article provides a comprehensive analysis on the trends in research and development in the area of CO2 carbon capture and sequestration at the moment. The review explores various technological approaches for capturing CO2 from industrial emissions, such as post‐combustion capture systems, pre‐combustion capture systems, and oxy‐fuel combustion system. It also gives a major insight into the post‐combustion capture of carbon by means of a summary, information obtained via a personal interview with a Combustion Based Unit (CBU) plant manager. Additionally, different methods for storing and sequestering the aforementioned gas, including geological and oceanic archiving, and mineralization, are examined. By synthesizing the findings from a wide range of studies and research papers, this literature review provides valuable insights into the current technologies for CO2 capture, storage, and sequestration, contributing to the ongoing efforts in addressing climate change and achieving sustainable development goals.

Forklifts, Automated Guided Vehicles and Horizontal Order Pickers in Industrial Environments. Energy Management of an Active Hybrid Power System based on Batteries, PEM Fuel Cells and Ultracapacitors.

The renewable energies together with other technologies in low CO2 emissions and the efficiency must be the base of the most sustainable new energetic system. Currently the logistics industry has a large number of vehicles (forklifts, horizontal order pickers, automated guided vehicles AGVs, tow vehicles, captive fleets applied to logistic...) intended to transport goods inside the plant. A problem associated with these logistic vehicles (electric or combustion type) is the charging time and balancing time in the batteries. Solution to the problem approached would be a system that requires a power charging times relatively short (similar to filling in the combustion system) and at the same time that have zero emissions (do not forget that they are operating in a closed environment). Typically, automated guided vehicles and forklifts are operated with lead acid batteries. The replacement of the traction battery with active hybrid power supply provide advantages as longer operating time, no recharging batteries, sizing of the fuel cell can be reduced and energy recovery during braking. Thus, energy management of an Active Hybrid Power System based on Li+ batteries, ultracapacitors and PEM fuel cells, is presented in this paper. Original lead-acid battery can be easily replaced by this new system implemented for industrial vehicles.

Reacting Flow Prediction of the Low-Swirl Lifted Flame in an Aeronautical Combustor With Angular Air Supply

Abstract The development of lean-burn combustion systems is of paramount importance for reducing the pollutant emissions of future aero engine generations. By tilting the burners of an annular combustor in circumferential direction relative to the rotational axis of the engine, the potential of increased combustion stability is opened up due to an enhanced exhaust gas recirculation between adjacent flames. The innovative gas turbine combustor concept, called the short helical combustor (SHC), allows the main reaction zone to be operated at low equivalence ratios. To exploit the higher stability of the fuel-lean combustion, a low-swirl lifted flame is implemented in the staggered SHC burner arrangement. The objective is to reach ultralow NOx emissions by complete evaporation and extensive premixing of fuel and air upstream of the lean reaction zone. In this work, a modeling approach is developed to investigate the characteristics of the lifted flame in an enclosed single-burner configuration, using the gaseous fuel methane. It is demonstrated that by using the large eddy simulation method, the shape and liftoff height of the flame are adequately reproduced by means of the finite-rate chemistry approach. For the numerical prediction of the lean lifted flame in the SHC arrangement, the focus is on the interaction of adjacent burners. It is shown that the swirling jet flow is deflected toward the sidewall of the staggered combustor dome, which is attributed to the asymmetrical confinement. Since the stabilization mechanism of the low-swirl flame relies on outer recirculation zones, the upstream transport of hot combustion products back to the flame base is studied by the variation of the combustor confinement ratio. It turns out that increasing the combustor size amplifies the exhaust gas recirculation along the sidewall, and increases the temperature of recirculating burned gases. This study emphasizes the capability of the proposed lean-burn combustor concept for future aero engine applications.

Simulation Study on the Combustion and Emissions of a Diesel Engine with Different Oxygenated Blended Fuels

Aiming to achieve the goal of efficient and clean combustion in internal combustion engines, simulations are used to change the physicochemical properties and molecular configuration of fuels by adding oxygenated fuels such as alcohols, esters, ethers, etc., so as to achieve the purpose of improving combustion and reducing emissions. In this paper, blends of oxygenated fuels, including n-butanol, DME, DMC, and diesel fuel with different oxygen-containing functional groups, were selected for simulation to reveal the chemical mechanisms of fuel oxygen on combustion and pollutant generation in the combustion system and to deeply explore the mechanism and influence law of the different forms of oxygen bonding on the generation and oxidation of carbon smoke. At the same fuel oxygen content, the differences in the fuel physicochemical properties and reaction paths resulted in different effects of the different oxygenated fuels on the in-cylinder oxidative activity and different inhibition abilities of carbon smoke precursors. Compared with pure diesel, n-butanol, and DME, which promoted OH generation, DMC inhibited OH generation, so the oxidation activity of diesel/n-butanol was the highest, and that of diesel/DMC was the lowest; meanwhile, the two O atoms in the DMC molecule formed CO2 with one C atom, which reduced the utilization efficiency of the O atoms, whereas each O atom in the n-butanol and DME fuels took away one C atom, so the utilization efficiency of O atoms was higher. The individual oxygenated fuels themselves had different abilities to contribute to carbon smoke precursors, and the above combined factors led to reductions of 8.7%, 32.6%, and 85.4% in soot emissions from the addition of DMC, DME, and n-butanol compared to pure diesel fuel, respectively, at the same oxygen content. At a medium load, the addition of n-butanol, DME, and DMC reduced NOx emissions by 0.5%, 1.7%, and 3.3%, respectively. Thus, it is shown that DMC has a more significant effect on NOx emission reduction.

Numerical investigation on turbulent flame jet characteristics of a pre-chamber fueled with CH4/O2 and CH4/NH3/O2 mixture under different initial pressures

Ammonia is a very potential carbon-free alternative fuel with extremely low reactivity. The application of ammonia in internal combustion engines faces the risks of ignition failure, low burning rate, and poor combustion stability. Pre-chamber turbulent jet ignition (TJI), which can provide much more ignition energy, is a promising method to ignite ammonia fuel. However, the transient propagation process of pre-chamber jet flame has not been fully investigated yet. In this paper, the propagation characteristic of methane jet flame was numerically studied based on a constant volume combustion system. The supersonic jet flame propagation and Mach disk phenomenon were further analyzed with numerical methods. And the propagation characteristic of methane/ammonia mixed jet flame was investigated. According to the results, the formation and propagation process of methane jet flame has different characteristics at different stages. In High-speed development stage (Stage II) and Low-speed oscillation development stage (Stage III), the penetration distance of flame jet tip is almost proportional to the penetration time. However, the penetration speed of the two stages is significantly different. The change trend of the jet velocity at the outlet of orifice hole can also be divided into four stages: slow increasing, rapid increasing, gradual decreasing, and periodic oscillation. The periodic oscillation of the jet tip velocity and the jet velocity at the outlet of orifice hole is caused by the effect of forward and reverse shock waves. The calculation results of CH4/NH3/O2 mixture jet flame show that the addition of ammonia has significant effects on the flame propagation process in PC, the thermodynamic state of PC, and the propagation characteristics of jet flame. With the increase of ammonia proportion, the maximum pressure of PC gradually decreases and the pressure rise rate slows down. Meanwhile, the two-stage (the high-speed development stage and the low-speed development stage) characteristic of jet propagation process gradually disappears. And the addition of ammonia is more likely to destroy the two-stage characteristic under low initial pressure.

Advanced hybrid combustion systems as a part of efforts to achieve carbon neutrality of the vehicles

Global goals, including those of the EU, are focussed on transition to the green, circular and low-carbon economy. The intention within the framework of EU is to achieve the zero level of CO2 emissions for the new cars till the year 2035. An important part of this plan is the agreement between Germany and the European Union that the new vehicles equipped with the internal combustion engines can continue to be sold only in such a case if they will use solely the climate-neutral fuel. Therefore, the future will probably belong to application of the advanced low-temperature technologies in combination with the climate-sustainable fuels (e.g. synthetic fuels, hydrogen). The presented scientific-research work introduces two new low-temperature combustion systems, which were developed and patented at the national level. At the same time, these new combustion systems are tested in cooperation with a reputable automotive producer. It is necessary to emphasize such a positive fact that the obtained results prove relevance of the innovative combustion systems as well as their possible future applicability in the real vehicles as a part of the advanced hybrid drive system.Graphical abstractHighlightsNowadays, the significant efforts are focussed on reduction of gaseous emissions generated by the transport, what is resulting in development of electromobility.CO2 neutrality in the transport sector cannot be reached by the electromobility alone. A potential solution is a combination of the sustainable fuels and advanced low-temperature combustion technologies.These two systems, which are presented in the article, were the subject of experimental research and development.DiscussionWithin the EU, there are strong efforts for a total restriction of internal combustion engines. The German Association of Automotive Industry (VDA) declares that “CO2 neutrality in the transport sector cannot be solved by the electromobility alone”. The official statement of VDA continues: “Even if, in ideal case, we had 15 million electric cars on the roads in 2030, most of the vehicles will still be equipped with combustion engines. Nowadays, 280 million cars are using combustion engines in everyday operation in the EU and there are 1.5 billion of them worldwide. Climate-neutral transport is impossible without new structure of global vehicle fleet and its decarbonisation”. According to VDA, the only solution, how to reduce emission footprint, using the current vehicle fleet, is application of the synthetic fuels. Therefore, still more resources should be invested into research and development of new sustainable fuels.