Combustion Chamber Of Engine Research Articles

Research on accelerated thermal fatigue testing and life prediction of Al-Si alloy pistons under start-stop cycles

As one of the most critical components in the combustion chamber of diesel engines, pistons operate under high temperature and pressure conditions for extended periods, which increases the likelihood of failures such as thermal fatigue. This paper first utilizes finite element simulation to obtain the temperature and stress field distribution of an Al-Si alloy piston under actual engine conditions. The results indicate that the throat area of the piston is the most susceptible to fatigue failure. Based on this, accelerated thermal fatigue tests were conducted to study the influence of various experimental factors on piston life, as well as to analyze the weight of each factor. Results from macroscopic and microscopic analyses of cracks using a scanning electron microscope show that fatigue cracks originate at the interface between the aluminum matrix and the detached hard particles. The cracking at the piston throat exhibits clear characteristics of ductile fracture, which is the result of cumulative fatigue damage. Therefore, from the perspective of continuum damage mechanics, it is considered to characterize the equivalent stress using the average loading rate during the loading phase and the maximum axial temperature gradient, establishing an experimental life prediction model for Al-Si alloy pistons.

A microwave discharge in high-velocity flows initiated by a half-wave antenna

A microwave discharge in high-velocity (150—250 m/s) air flows induced on a half-wave vibrator is studied. A cw magnetron microwave generator with a frequency of 2.45 GHz and an output power of up to 5 kW was used for initiation of the microwave discharge. The high-speed video imaging was used for studying the discharge structure, determining the diameter and length of the plasma channel as a function of flow velocity and pressure. Electron concentration and temperature, along with characteristic gas temperature, were determined based on the optical spectra. The possibility of using this microwave discharge for ignition of hydrocarbon–air mixtures in combustion chambers of ramjet engines is proved experimentally.

A molecular dynamics study on the supercritical evaporation of liquid ammonia under forced convection conditions

Although the behavior of the supercritical transition during the evaporation of liquid fuels in engine combustion chambers has been studied by many researchers, the effects of convection on the phase transition of liquid fuel in supercritical environments have been little studied. Previous studies mainly focused on hydrocarbon fuels for supercritical evaporation, with fewer on the zero-carbon liquid ammonia fuel. Aiming at the above deficiencies, this study used molecular dynamics simulations (MD) to explore the phase transition of liquid ammonia in a nitrogen supercritical environment under forced convection conditions. The Peng-Robinson equation of state (PR-EoS) was used to calculate the vapor–liquid equilibrium of the ammonia–nitrogen system to determine the supercritical transition time of liquid ammonia under forced convection conditions. The effects of forced convection on the heat and mass transfer process and the evolution of the liquid-phase region and the vapor–liquid interface region were analyzed. It was found that forced convection can promote the mass and heat transfer process and accelerate the phase transition of liquid ammonia to some extent. Forced convection may have a greater effect on the single-phase diffusive mixing process compared to the two-phase evaporation process. The increase in the interfacial thickness under forced convection conditions is mainly attributed to the temperature increase promoted by convection. The interfacial temperature dominates the development of its thickness and the thickness is approximately linear with temperature during the diffusive mixing stage. The shear effect induced by convection has an inhibitory effect on the diffusion of ammonia molecules within the interface region along the vertical convection direction. The cases in this study indicate that forced convection may promote the supercritical transition of liquid ammonia. In addition, a dimensionless number κ was proposed to explore the possibility of scaling up the MD results to the engineering scale.

Study of chemiluminescence of methane–air flame stabilized on a flat porous burner

In this work, the spatial distribution and spectral characteristics of the chemiluminescence of chemically excited species, OH∗ and CH∗, are experimentally and numerically studied by using a stationary premixed methane–air flame stabilized on the surface of a flat porous burner for various equivalence ratio and normal pressure. Numerical simulations are carried out using detailed reaction mechanisms, and the experimental study includes high-resolution spatial and spectral optical measurements. Despite the data reported in the literature, it is found that (i) the rotational degrees of freedom of OH∗ and CH∗ are not in thermal equilibrium with the surrounding gas and therefore cannot be used to measure flame temperature; (ii) there is no direct correlation between the heat release rate and the distribution of OH∗ and CH∗; (iii) the detailed reaction mechanisms not only quantitatively, and also qualitatively differ in description of the OH∗ and CH∗ concentrations. Since the chemically excited species are well localized in a direction normal to the flame surface, they are demonstrated to be a very accurate markers of flame location. The shape of the combustion front can be reconstructed and resolved up to the accuracy of tens of microns, which is very important for estimation of blow-off critical parameters and measurement of the laminar burning velocity.Novelty and significance statementCurrently, there is a growing interest in the development of sensors for combustion control systems, including active control and suppression of instabilities, in combustion chambers of various devices and engines based on chemiluminescence of excited reaction species. The possibility of non-invasive determination of parameters such as flame temperature, stoichiometry, heat release rate location, etc. using this technique is discussed. We have found that most of these parameters cannot be estimated either due to fundamental limitations or insufficient knowledge of the reaction kinetics involved in the production of these species. Nevertheless, since OH* and CH* are well localized in the direction normal to the flame surface, they can be used as very accurate markers of flame shape and position, allowing us to reconstruct the flame surface to within tens of microns resolution, which is very important for estimating blow-off critical parameters and measuring laminar burning velocity.

Experimental Study on the Mass Flow Rate Characteristics of a Fluidized Bed Powder Fuel Feeding System

In this study, a fluidized bed powder fuel feeding system that controls flow using the principle of two-phase gas-solid choking is proposed. Experiments based on real-time weighing methods were conducted to explore the flow rate characteristics under various total pressure and throttle-orifice area conditions. The experimental results showed that as the total pressure increased, the powder flow rate first decreased and then increased. To achieve the same increase in powder mass flow rate by altering the pressure, fine powder requires a greater pressure increment than coarse powder. A choked flow formula based on the gas-solid two-phase nonequilibrium model was derived, for investigating the influence of these two factors on the powder flow rate. Compared with the experimental results, this formula predicts the powder flow rates within a 20 % error margin. This model provides more precise guidance for engineering designs. The studied powder fuel-feeding system was connected to a powder engine, and hot-fire tests were conducted. The results showed that the pressure fluctuation in the powder engine combustion chamber did not exceed 2.5 %, confirming the feasibility and stability of the powder supply in the fluidized bed powder fuel feeding system.

Large eddy simulation of highly underexpanded sonic jets from elliptical nozzles

The injection of high-pressure jets into quiescent air poses significant challenges in fluid dynamics, pertinent to various industrial engineering applications. This study used large eddy simulations on a massively parallel computational framework, employing a grid of over 600 million nodes, to investigate the behavior of highly underexpanded sonic jets from elliptical nozzles at a nozzle pressure ratio of 15. Three elliptical nozzles, with aspect ratios of 1.5, 2.2, and 3.0, each having a sectional area equivalent to that of a circular jet with a diameter of D=1 mm, were analyzed. The aim was to clarify the gasdynamic and mixing characteristics of these jets to guide the design of next-generation injectors. A detailed analysis of the flow provided insights into the mechanisms of turbulence generation and Reynolds stress anisotropy. This was achieved using the componentality contour approach and a modified barycentric color mapping scheme, offering valuable reference data for developing lower-order models. The results indicate a non-axisymmetric radial expansion of the jet boundary in all elliptical injectors, leading to an axis switch phenomenon. The use of elliptical orifices was found to reduce jet penetration, mitigating issues such as fuel impingement in small engine combustion chambers and promoting improved air–fuel mixing quality.

Thermal protection technologies for solid propellant rocket engines

The article examines the thermal insulation characteristics of materials used in solid-fuel rocket engines manufactured in the United States, France, Italy, Japan, and other developed nations. The internal surfaces of combustion chambers in these rocket engines are subject to significant stress under thermo-mechanical loading conditions, necessitating specialized protection. The authors identify four categories of reinforced elastomeric materials that most effectively meet stringent requirements. Due to their adaptability, these materials may serve as versatile heat insulators and may be employed in a variety of high-temperature and corrosive surroundings.

Simulation of intra-chamber processes in a low-thrust rocket engine with a hydrogen-air mixture and counterflow cooling

The principles and methods of improvement of thrust, efficiency and cooling of rocket engines for space flight safety are of great interest for aerospace industry. The development of reliable and durable low-thrust rocket engines for space missions seems to be one of the important areas of development of the rocket and space industry. Issues related to the implementation of a new direction related to the design of propulsion systems for orientation systems of upper stages of launch vehicles using environmentally friendly fuel components are considered. A mathematical model is developed and numerical modelling of processes in the combustion chamber of a low-thrust rocket engine with gaseous fuel components (hydrogen and oxygen) is carried out. The model takes into account the presence of a cooling jacket. The mathematical model includes the effects of turbulence, combustion of a gaseous fuel mixture, kinetics of hydrogen combustion, and radiation. As a result of calculations, distributions of flow quantities in the combustion chamber and thermal loads on its walls are obtained. The influence of hydrogen mass flow rate on the efficiency of the working process and the dependence of thrust on hydrogen mass flow rate are discussed. The results of numerical modelling are compared with the data of a physical experiment obtained through fire tests of an engine model made of stainless steel on a three-dimensional printer.

Development of methods for adapting gas-diesel engines of agricultural tractors to LPG operation

This article describes the methods of organizing the non-detonation combustion of liquefied petroleum gases (propane-butane mixtures) (LPG) in the cylinder of a gas-diesel engine with a starting dose of no more than 25%, at maximum power modes. The addition of a part of the exhaust gases and water in a vaporous state to the fuel mixture, when using a nickel-based catalyst in the combustion chamber of a gas-diesel engine, which triggers the conversion reaction of lower alkanes, ensures reliable non-detonation combustion of the fuel charge. The nickel catalyst is an oxygen carrier, which ensures cyclical reactions near its surface in the combustion chamber of a gas-diesel engine: metal oxidation during purging of the combustion chamber; conversion of alkanes at compression and combustion cycles. The problem of carbonization of the catalyst is solved by burning deposits during the combustion of the fuel charge. The organization of a fuel vapor-gas-air mixture with subsequent combustion in the presence of a catalyst provides improved environmental, fuel and economic characteristics of a gas-diesel engine in the entire range of operating modes and increases its reliability.

The effect of spatial non-uniformity on multiple transient modes of detonation onset in a three-dimensional channel

The study of the transient combustion modes is one of the key topics when considering the safety of space flights. Control of detonation onset has a dual application. First, the search for ways to prevent detonation modes in case of accidental fuel releases for fire safety issues of launch systems and the avoidance of accidents with rocket engines at a launch site and in near-Earth space. Second, the study of detonation and the possibility of using it to create propulsion systems based on detonation combustion of fuel. The paper shows the effect of the presence of spatial non-uniformities on the promotion of detonation in the chamber. Various geometries with and without obstacles and cavities are considered. It is demonstrated that the presence of obstacles accelerates the transition to the detonation process on the one hand, but on the other hand the presence of obstacles in combustion chamber could be the cause of incidental uncontrolled ignition, which ruins stable operation of an engine. The results of theoretical studies of the working cycle of the combustion chamber of a pulsed detonation engine are presented. Theoretical estimates for thrust characteristics are obtained.

Comparison of fluid structure downstream of an evaporative flameholder with subsonic uniform and subsonic-supersonic inflows

Subsonic uniform and supersonic mixing flows are widely present in the combustion chamber of a multi-mode combined scramjet engine, where the significant pressure, velocity, and temperature gradients of the two impose severe limitations on flame propagation. The vortex structures downstream of an evaporative flameholder were experimentally measured under subsonic-supersonic mixing inflow and subsonic uniform inflow. Results indicate that, under subsonic-supersonic mixing inflow conditions, an asymmetric vortex structure in the recirculation zone is formed due to the presence of a subsonic-supersonic shear layer, which exerts compressive or stretching effects on the recirculation zone downstream of the flameholder, in contrast to the symmetric dual-vortex structure observed under subsonic uniform inflow conditions. The asymmetric recirculation zone displays fluid being entrained from one vortex to another, with the degree and direction of entrainment dependent on the supersonic expansion state. Additionally, a simplified flow field structure is proposed for comparing the differences between the subsonic-supersonic mixing inflow and subsonic uniform inflow, along with the introduction of five regions and two stages to describe the flow field structure downstream of the flameholder under subsonic-supersonic mixing inflow. Analysis of the flow characteristics downstream of the flameholder under subsonic-supersonic mixing inflow and subsonic uniform inflow conditions can offer design insights for the combustion scheme of aerospace-integrated propulsion systems.

Research on maintenance decision-making approach based on dynamic opportunistic window

We have developed a maintenance decision-making approach based on the dynamic opportunistic window, utilizing algorithms such as k-mean clustering, expected maximum, and parameter estimation to address the lack of a reasonable basis for the duration and divided number of opportunistic windows in current maintenance decision-making. Firstly, we have comprehensively summarized the multi-stage opportunistic maintenance decision-making approach, focusing on its current strengths and limitations. Secondly, the modeling concept of the dynamic opportunistic window is analyzed, and the underlying assumptions are established. Furthermore, it elaborates on the theoretical foundation of the proposed approach through a detailed modeling process. Finally, we validate the proposed model by conducting experiments on tandem components from the main combustion chamber in an aero engine. The experimental results demonstrate the significant value of the proposed approach in enhancing equipment reliability and optimizing maintenance support resources.

Configurable combustion models of combustion chamber of microturbine engine with possibility of connecting various physico-chemical processes

Configurable combustion models of combustion chamber of microturbine engine with possibility of connecting various physico-chemical processes

Influence of spray-to-spray interaction after wall impingement of spray flames on diesel combustion characteristics

The influence of spray-to-spray interaction after wall impingement of spray flames on the combustion characteristics in high pressure and high temperature ambient gas like in combustion chambers of diesel engines was examined with a constant volume vessel. Fuel was injected onto a flat wall from two nozzles to form two parallel, adjacent sprays in the vessel, causing the spray-to-spray interaction after the wall impingement. The combustion was analyzed with the rate of heat release calculated from the pressure transition in the vessel and the spray flame was visualized by high-speed video. The 310 nm UV light images of the chemiluminescence from OH radicals are recorded to demonstrate the reaction activity in the spray flame. The images of transmitted light throughout the constant volume vessel were recorded to visualize the soot formation and oxidation processes as well as to quantify the soot concentrations as the KL factors. The results showed that the rate of heat release from the main combustion decreases and the afterburning increases with the spray-to-spray interaction after the wall impingement of the spray flame. Combustion suppression with the spray-to-spray interaction occurred in all the conditions of the experiments here when changing the distance from the nozzle to the impinging wall between 25 and 40 mm and the fuel injection pressures between 100 and 200 MPa. Inside the spray-to-spray interaction zone, the chemiluminescence from OH radicals is weaker, supporting the inactive combustion due to difficulties of the air entrainment, and the lower transmitted light intensities with larger KL factors, indicating higher soot concentrations. The spray-to-spray interaction zone on the impingement wall advances toward the inside of the vessel between the sprays and it moves away from the wall, entraining the unutilized air and causing a relatively active combustion as well as rapid soot oxidation during the late afterburning stage.

Analysis of cooling effects and measurement errors in water-cooled thermocouples for total temperature measurement in aviation engine combustion chambers

Accurate measurement of the total temperature in the main combustion chamber of an aviation engine is crucial for assessing engine performance. However, a significant challenge exists in balancing the heat transfer errors caused by the necessary cooling of the measuring device with measurement precision. The research employs a combination of numerical simulations and experimental methods to investigate this issue. The numerical simulations utilized the Reynolds-averaged Navier Stokes (RANS) coupled with a conjugate heat transfer approach to study the primary flow characteristics and heat transfer properties within the combustion chamber and the probe body. The experiments were conducted in a heat-calibration wind tunnel, validating the results of the numerical simulations. The results show that by implementing water cooling, the probe's body temperature can be reduced from 1200 °C in high-temperature conditions to 400 °C, with localized temperature imbalances still present in the edge areas of the probe. Tracing the cooling water path reveals that the vertical bends in the internal channels lead to an increase in localized pressure loss of the cooling water. The study quantitatively analyzes measurement errors caused by three heat transfer modes: radiation, convection, and conduction. In low-load conditions of the combustion chamber, heat conduction plays a dominant role, with measurement errors due to conduction reaching up to 70 % of the total measurement error. Radiation further increases the temperature measurement errors of the thermocouple's junctions near the chamber wall. As the combustion chamber temperature increases, entering high-load conditions, the cooling effect of water becomes limited, reducing conduction errors and increasing radiation errors. In these conditions, radiation errors constitute 60–70 % of the total measurement error. It suggests the importance of considering temperature corrections when using water-cooled temperature measurement devices. The research reveals several crucial insights regarding the performance and limitations of water-cooled thermocouples.

Laser ignition versus conventional spark ignition system performance for hydrogen-enriched natural gas-air mixtures in a constant volume combustion chamber

This study compares the performance of a laser ignition system vis-à-vis a conventional electrical spark ignition system in a constant volume combustion chamber. A custom-built constant-volume combustion chamber was used to compare the performance of the laser and spark ignition systems. A combination of three lenses in the optical path was used to create laser plasma in the constant volume combustion chamber. Initial chamber pressure and temperature were maintained constant at 4 bar and 150 °C during the experiments. The effect of hydrogen enrichment of compressed natural gas on combustion was assessed for three relative air–fuel mixture strengths (λ: 1.0, 1.2 and 1.4) to compare the performance of both ignition systems. The laser ignition system exhibited superior combustion characteristics to the spark ignition system. The combustion duration of laser ignition was considerably lower than spark ignition. Three hydrogen-enriched natural gas blends (10HCNG, 20HCNG and 40HCNG) were assessed and compared with baseline compressed natural gas. Hydrogen enrichment improved the combustion characteristics, increasing the excess chamber pressure and reducing the combustion duration. Two locations were taken for assessing the performance of the laser ignition system in this study. The first location was the same as the spark from a conventional electrical spark ignition system, and the second was at the centre of the constant volume combustion chamber. The central location of laser ignition showed a higher reduction in the combustion duration than baseline spark ignition and its corresponding laser ignition, indicating its superiority. The ability to choose an ignition location centrally in the engine combustion chamber emerged to be a main advantage of laser ignition systems.

Increasing the efficiency and stability of fuel supply to the combustion chamber of a liquid rocket engine by spray nozzles

In this paper, various configurations of jet nozzles are analyzed, as well as their design. The effects of the inlet chamfer of jet nozzles on their flow rate and range are considered. It is shown out that today it is expedient to make precision micro-holes of the nozzles using high-precision three-dimensional electric-erosion equipment. The optimal design parameters of jet nozzles are also determined.

Prediction of engine combustion chamber outlet temperature field based on deep Learning: Application in aero-engine life extension control

One of the current research hotspots is the prediction of combustion chamber flow field based on deep learning methods, but how to effectively utilize these prediction results is a key issue that needs to be addressed urgently. This paper further proposes a study on the predictive control method for engine life extension considering the dangerous point temperature of turbine guide vane based on the prediction of combustion chamber outlet temperature field. Firstly, a combustion chamber outlet temperature distribution prediction model is established through Computational Fluid Dynamics (CFD) numerical simulation and inception deconvolution network, and integrated into the variable cycle engine component level model to achieve real-time prediction of combustion chamber outlet temperature distribution. Furthermore, based on this, the dangerous point temperature of the high-pressure turbine (HT) guide vanes is introduced as a constraint into the prediction optimization, and a predictive control method for engine life extension considering the thermal mechanical fatigue life (TMFL) of the guide vanes is proposed. The simulation results show that compared to the traditional LEC control method, the temperature at the critical point of the blade is reduced by 12.28 K, and the TMFL of the blade is increased by 29.23 %. The research results of this article provide a good application example for predicting the temperature distribution at the outlet of the combustion chamber, expanding the application scenarios for predicting the flow field parameters inside the engine.

Investigation of Mild Carbon Steel Immersed in Jatropha Biodiesel Fuel: Spectroscopic and Surface Studies

The use of renewable energy fuels in the automobile industry has seen progressive interest and increased research in recent times. Different types of steel alloys have been considered as materials in the construction of the fuel delivery and storage systems of the automobile engines which are conduit for passage of these biofuels to the specific engine combustion chamber. The nature of the interactions between the surface of the mild steel alloy and the specific biodiesel molecules needs to be interrogated to ascertain the extent and degree of biodiesel activity-induced corrosion. In this study, FTIR, UV-Vis spectrometry and optical microscopy techniques were used to elucidate on the biodiesel molecule-mild steel surface interphase interactions. UV-Vis investigation revealed pronounced peaks around 900 nm and 1050 nm consistent with signals due to poly-unsaturated components of the biodiesel. FTIR analysis showed peaks around 1700 cm-1 which indicated the presence of C=O and C-O functional groups that is associated with triglycerides. Peak signals around 2950 cm-1 are attributed to anti-symmetric and symmetric stretching vibration of C-H in CH2 and CH3 while peaks around 1150 cm-1 indicated the stretching vibration of C-O ester. The results revealed jatropha biodiesel-induce corrosion was physically adsorbed on the steel surface leading to surface degradation over time and were evident in the optical surface micrographs which were equally supported by the FTIR and UV-Vis analyses. Thus, carbon steel alloy material selection and testing to ascertain compatibility and effectiveness is vital when biodiesel is to be used as fuel in automobile engines.

New technologies in combustion chambers of aircraft turbine engines

The paper presents the projected emissions of combustion components over the next few years. The basic tasks that a modern combustion chamber must fulfill were defined. The process of hydrocarbon combustion in the theoretical and actual cases was analyzed. The assessment evaluates the effect of engine operating parameters such as rotational speed, thrust, temperature downstream the compressor and combustion on the formation of toxic combustion components. The paper also presents alternative fuels. One of the most promising aspects related to the matter is the use of sustainable aviation fuels - SAF. Alternative methods of powering aircraft engines, such as hydrogen or nuclear propulsion, were presented. An analysis on the latest combustion chamber design systems that allow to reduce the amount of exhaust gasses emitted into the atmosphere was conducted.