Dual-mode Combustor Research Articles

Experimental investigations of combustion oscillation modes in a large-aspect-ratio dual-mode combustor equipped with multi-strut

The annular scramjet combustor is considered one of the best configurations for a wide-speed-range combined engine, owing to its superior thermal protection performance and optimal geometric compatibility with rockets and turbines. To investigate the effect of fuel injection methods on the flame oscillation characteristics in the annular combustor, a scaled-down experiment was conducted on a fan-shaped combustor with a high aspect ratio equipped with multiple struts, utilizing liquid kerosene as the fuel. A series of experiments were conducted at the combustor inlet conditions of Ma = 2.7, Pt = 1.68 MPa, and Tt = 1640 K. High-speed cameras and pressure measurements were used in the experiments, and the flame images were processed using proper orthogonal decomposition. The findings revealed that under single-strut and multi-strut injection conditions, the flame oscillated in two modes: shear layer oscillation and central flame oscillation. As the equivalent ratio of injection strut increased, the oscillation frequency increased from 25 to 284 Hz, and the oscillation mode transition caused by the adverse pressure gradient occurred. The flashback was closely related to the combustion mode, and the distinct flame propagation processes under supersonic and subsonic flow conditions resulted in different oscillation characteristics. The experiment demonstrated that the flashback issue could be mitigated by increasing the spacing between the fuel injection struts. The study in this paper will provide important references for future research on flame oscillation and propagation characteristics in high-aspect-ratio annular combustors.

Numerical Investigation of Combustion Mechanism with Multi-Position Injection in a Dual-Mode Combustor

To improve the flame propagation, combustion stability, and uniformity of the temperature field, multi-position injection is applied in a dual-mode combustor by controlling heat release in different locations. Using the chemical reaction of the finite rate combustion model and the detailed reaction mechanism of hydrogen combustion as described by Jachimowski, the influence of different multi-position injection patterns in a dual-mode combustor is analyzed. The one-equation Large Eddy Simulation (LES) turbulence model was chosen to define the sublattice turbulent viscous terms in a three-dimensional scramjet model. Based on a combustion chamber, the effect of the injection equivalent ratio (0.35–0.70), the relative position of the nozzle holes, and the injection pressure on the combustion process and flow field characteristics are analyzed with multi-position injection. The combustion efficiency, total pressure recovery coefficients, and pressure distribution under different operation conditions are compared. We observed that the combustion intensity increases and the upstream combustion shock string distance becomes greater with increased equivalent ratios. When the global equivalent ratio of multi-position injection remains unchanged, the arrangement of nozzles with the small injection spacing, i.e., two injection holes arranged face to face on the upper and lower walls, or the setting of multiple injection holes with the same pressure, can effectively increase the stability rate of the combustion flow field. In addition, the combustion efficiency at the outlet and the internal pressure of the combustion chamber in the stable state are also improved, relative to the increased total pressure loss.

Dual combustion oxyhydrogen-diesel: Effects on internal components of engine

In Mexico, diesel is the second most used fuel, representing 28% of the national consumption, being the largest greenhouse gas emitter. In this work, the diesel engine can run smoothly in dual combustion mode diesel fuel/oxyhydrogen gas (OH2G) because OH2G fed to the diesel engine is limited by the volume available in the combustion chamber; this allows the timing and pressure in the combustion chamber to be kept within the limits of the engine y a combustion without detonations was observed, the existing infrastructure is used, and the consumption of diesel and contaminants emissions could be reduced. This study shows the effects produced in the engine combustion chamber by the dual combustion process of diesel fuel/oxyhydrogen after 500 h of operation. Two air-cooled mono-cylinder diesel engines with a displacement of 405 cm3 were operated; a D100 engine was operated with 100% diesel and OH210 engine in dual combustion (diesel fuel/oxyhydrogen) was operated. Both engines were maintained at 40% load with respect to their maximum power during 500 h OH2G was generated in situ by alkaline electrolysis, and a flow of 2 sL min-1 was fed through the intake port during the suction stroke of the engine. Visual analysis, weight and dimensions of the engine parts, metallographic analysis, oil analysis, and electrolyte drag were used to determine the effects on the component materials. For the engine with dual combustion, diesel fuel/oxyhydrogen, was no structural damage to the engine components, although a slight corrosion onset was observed in some components, such as the piston ring. Moreover, iron and aluminum in the oil were off-standard, which is attributed to the corrosion processes occurring because of water steam containing electrolyte traces being fed to the engine with the oxyhydrogen gas. This implies that more oil changes are necessary within a short period. Therefore, a more robust gas purification process will be implemented, and the injection system will be optimized.

A Study on LPG injection based speed regulator for dual fuel diesel engine

Diesel engines are popularly interested due to their great economic efficiency and the high amount of harmful emissions released. The conversion of using multi-fuel engines aims to reduce emissions, and diversifying alternative energy sources to replace diesel fuel, is a potential solution. This paper presents a method to convert the fuel system of the DI-diesel engine type Vikyno RV125 to LPG-diesel dual combustion mode and preliminarily evaluate performance characteristics operating with the LPG injection-based speed regulator. An LPG injector controller circuit was actuated to operate the engine with different load modes up to 5.0kW at corresponding engine speeds. The air intake manifold was modified to calibrate the air-mass flow to effective performance. The experimental result revealed that the changed system could operate in LPG-diesel dual combustion mode. The operating stability of the engine was recognized at speeds up to 1600rpm. A study on engine exhaust emissions will be performed in the next research stage.

Ram to scram mode transition in a simulated flight acceleration

Thrust abruption due to mode transition could be catastrophic for hypersonic vehicles. To understand the underlying physics, a direct-connected transient Flight Trajectory Simulator 1 (FTS-1) has been developed at the Institute of Mechanics, Chinese Academy of Sciences. This facility uses advanced high-speed measuring techniques, including thrust and static wall pressure measurement, and Schlieren and hydrocarbon radical chemiluminescence (CH* chemiluminescence) imaging. Kerosene-fueled dual-mode combustor experiments are designed in an acceleration trajectory. The basic operation parameters and the flame and flow dynamics of the acceleration induced mode transition are evaluated. Discussions are given on the triggering mechanisms responsible for the ram to scram mode transition in a simulated flight acceleration.

Combustion Instability due to Combustion Mode Transition in a Cavity-Stabilized Scramjet

This study experimentally investigates flame dynamics during a combustion-driven mode transition in a cavity-stabilized scramjet model with an inlet Mach number of 2.2 using a split fuel injection scheme. Fueling into the cavity was gradually increased while keeping a constant global equivalence ratio of 0.3. A cavity-fueling percentage below 15% resulted in low-intensity combustion that corresponded to operation in scram mode. Redirecting 29% of the fuel from the upstream injection port to the cavity yielded flame spreading into the main flowpath, inducing intense combustion. A sharp pressure rise and an intense combustion region in the diverging section suggest dual-mode combustion, with thermal choking and a pseudoshock formation downstream of the cavity. An intermediate cavity-fueling fraction of 21% led to a low-frequency instability () with intermittent transitions between the combustion modes, indicating operation at the thermal choking limit. Spectral and modal analyses of chemiluminescence images and static-pressure measurement indicate peak response at 10–20 Hz and , originating from oscillations in the air heater and a fuel jet instability, respectively. Thermally chocked conditions significantly amplify oscillations at these frequencies. At the thermal choking limit, there was high-amplitude response at , preventing stable dual-mode operation.

Experimental flameholding performance of a scramjet cavity with an inclined front wall

This paper presents experimental data examining the flameholding performance of a scramjet cavity with an inclined front wall. Mach 8 flight-equivalent flows were delivered to the axisymmetric, cavity combustor via the T4 reflected shock tunnel. The combustor model was designed to permit interchangeable cavity geometries. Each examined cavity maintained a length-to-depth ratio of 4, with a depth of 8 mm and cavity close-out angle of 22.5 deg. The first examined cavity possessed a 90 deg front wall/step, while the second examined cavity inclined the front wall at 45 deg. Ethylene fuel was injected at a variety of mass flow rates to examine both scram-mode, jet-wake anchored and dual-mode combustion, with data measurements obtained via wall-mounted static pressure sensors. The steady nature of these combustion modes during the shock tunnel test time was demonstrated. Minimal differences in combustion-induced pressure rises were observed between the two cavity geometries across each fuelling condition. This indicates that the low pressure, quasi-stagnant region downstream of a 90 deg step is not essential to attaining robust flame-anchoring in a scramjet combustor. Chemically reacting, Reynolds-averaged Navier-Stokes computations were performed for the three dimensional combustor. Only minor mixing and combustion performance differences were noted between each geometry/fuelling permutation. It was noted that the 45 deg cavity retained more robust vortex structures within the cavity, with the 90 deg cavity seeing complete breakdown of the cavity vortex structures. This work indicates that the cavity front wall could be further modified with minimal impacts on flameholding performance.

Prediction model of temperature field in dual-mode combustors based on wall pressure

Effective acquisition of the complex flow fields in dual-mode combustors is valuable in improving dual-mode combustor performance. Introducing deep learning methods for fast flow field prediction is an effective way to provide high-quality temperature fields in a dual-mode combustor. A data-driven model to obtain temperature fields based on wall pressure of a dual-mode combustor is proposed in this paper. The temperature fields in dual-mode combustors depend on the combustor geometry, incoming flow condition, and equivalent ratio. The prediction model takes convolutional neural network as the main framework and includes multiple branches. The trained temperature field prediction model can effectively output the temperature distribution of the combustor with the input of wall pressure. The temperature field prediction accuracy has been discussed in depth. From the analysis results, the effectiveness and accuracy of the approach have been demonstrated under the current dataset.

Learning-based supervisory control of dual mode engine-based hybrid electric vehicle with reliance on multivariate trip information

The combination of electrification and advanced dedicated hybrid engines (DHEs) has been attached with promising prospects for the abatement of fuel consumption and emissions. To explore the potential of this solution, experimental data are used from a high-efficiency DHE operated under dual-mode combustion: the lean-burn spark-induced compression ignition (SICI) and the stoichiometric spark ignition (SI). This work endeavors to develop the integrated energy management and engine control system for such DHE-based plug-in hybrid electric vehicles (PHEVs), to this end, the synergy of artificial intelligent control and trip preview can be exploited to boost the control performance, with the engine combustion process being optimally controlled in transient. This paper presents a multistate deep reinforcement learning (M−DRL)-based energy management strategy (EMS) with a discrete–continuous hybrid action space to select optimal combustion mode while output continuous engine power demand, and its state space is expanded to incorporate the multivariate traffic and terrain information processed by a spatio-temporal data processing (STDP) framework in real time. Comprehensive experiments are carried out to validate the capability of the proposed method, based on a standard driving cycle and a real-world driving cycle in China with real-time traffic data recorded. The results indicate that the proposed M−DRL strategy avoids frequent switchover of engine operation modes as well as achieves more than 93% of the dynamic programming’s performance in terms of the fuel consumption and NOx emissions abatement.

Experimental and numerical study of flow and ignition and lean blowout characteristics of jet-cooled wall flameholder in a dual-mode combustor

The wall flameholder is one of the credible alternatives to realize pilot ignition in augmented/ramjet combustors. To overcome the ablation for a long-term operation, two types of jet cooling, external-inhaled air and pressure-driven jet cooling, are proposed for the wall flameholder. In this work, the flow and combustion process in a laboratory scale rig is studied for different cooling schemes and cooling conditions using experimental and numerical methods. Flow analysis in pressure-driven jet cooling scheme shows that the flow field of flameholder is influenced significantly by the cooling hole angle on the oblique plate α and on the rear plate β. In particular, the cooling jet angle combinations (α=30o, β=30o) and (α=90o, β=150o) are the two schemes with the most different characteristics. To investigate the effects of jet cooling type and cooling jet angle on the flow, ignition, and lean blowout (LBO) characteristics, the two distinctively different angle combinations are applied to form two kinds of jet cooling schemes mentioned above. Results suggest that the jet cooling type has less impact on the flow field but more influence on the flow loss than the cooling jet angle. The ignition performance of cooling schemes with α=30o and β=30o is better than that of those with α=90o and β=150o, but it has a more significant flow loss. The LBO limits of external-inhaled air cooling are lower than that of pressure-driven jet cooling. Moreover, the ignition and LBO limits decrease gradually with the increased mainstream temperature and they are only slightly affected by the mainstream velocity. Notably, the pressure-driven jet cooling scheme can slightly reduce the flow loss but it leads to a deteriorated ignition and LBO performance. The external-inhaled air cooling scheme with α=30o and β=30o has an excellent ignition and LBO performance, and the ignition and LBO limits increase with the increasing cooling air flow rate and the decreasing cooling air temperature.

Realization of Dual-Mode Combustion by Changing the Geometry of the Model Combustion Chamber Flow Part of a Ramjet Engine

Realization of Dual-Mode Combustion by Changing the Geometry of the Model Combustion Chamber Flow Part of a Ramjet Engine

Hierarchical energy management strategy for plug-in hybrid electric powertrain integrated with dual-mode combustion engine

The dedicated hybrid engines (DHEs) with dual-mode combustion technology can drastically reduce the fuel consumption and emissions while guarantee the power density. This paper aims to investigate the optimal control of such DHE-based plug-in hybrid electric vehicles (PHEVs) under real driving conditions, with minimum fuel penalties caused by transient engine dynamics. For this purpose, the benefits brought by artificial intelligent control and traffic preview in terms of energy efficiency can be combined with the advantages of advanced combustion engine. This paper presents a hierarchical energy management strategy (HEMS) to realize the synergy of global and instantaneous optimization. At the cloud level of HEMS, dynamic programming is applied to obtain optimal combustion mode and state of charge reference trajectories in a receding horizon. At the powertrain level, deep reinforcement learning with a ranking-prioritized experience replay algorithm is used to output optimal engine power and combustion mode for the energy management. To evaluate the proposed strategy, a dual-mode engine with homogeneous charge compression ignition and spark ignition systems is tested and mapped, with which the PHEV is modeled in GT-Suite and Matlab/Simulink. Comprehensive experiments are carried out to verify the optimality, generalization and robustness based on a standard driving cycle and a real-world driving cycle in China with GPS data recorded. The results show that the HEMS avoids frequent switching of combustion modes and outperforms the conventional methods by more than 4% and 10% in terms of fuel economy and NOx emissions, respectively, with random initial and terminal conditions.

Comparative study of energy losses related to the ring pack operation in homogeneous charge compression ignition and spark ignition combustion

Low-temperature combustion in homogeneous charge compression ignition (HCCI) engine is one of the most promising technologies allowing to meet future emission targets for internal combustion engines. Whereas majority of research is centred on combustion itself, this paper for the first time points out the piston's energy losses induced by friction and blow-by in HCCI engine with negative valve overlap. The energy losses for HCCI and spark ignition (SI) operating modes were compared and thoroughly analysed with the use of the ring pack model. The input data for the simulations came from measurements made on a single-cylinder research engine capable of dual-mode combustion. The energy losses associated with friction of the rings against the cylinder varied from 8.2% of the indicated energy at the lowest load to 2.2% at the highest load tested, and were higher than in the SI mode by approximately 7%. The losses due to the gas leakage through the ring pack in the HCCI mode varied from 8% to 3.3%, respectively, and these losses were about twice as high as in the SI engine. The results demonstrated that energy losses due to blow-by are comparable with the friction losses of the rings, which are usually regarded as the prime source of inefficiency.

Estimation of vitiation effects on flameholding and mode transition in a dual-mode supersonic combustor

To estimate the vitiation effects of test air on flameholding and mode transition in a direct-connected dual mode combustor, an experimental study was conducted with two types of air heater (electric heater and methane combustion heater) at various kerosene equivalence ratios. Total temperature, total pressure and Mach number of combustor entrance were matched in comparative tests. The lean blowout limits, wall pressures and mode transitions were compared. For clean air heater, the lean blowout limit occurred at the equivalence ratio of 0.105, while for methane combustion heater, it occurred at 0.135. Considering mode transition, the combustor operated in subsonic combustion mode at kerosene equivalence ratio above 0.30 with clean air; while for methane combustion heater, mode transition from supersonic to subsonic combustion occurred at equivalence ratio of 0.33. This indicated that the test data should be fully evaluated when using a combustion heater, especially in lean blowout limit and mode transition.

Fuel/Air Mixing in Reacting and Non-reacting Flows within a Dual-mode Combustor

Fuel/Air Mixing in Reacting and Non-reacting Flows within a Dual-mode Combustor

Analysis of flow-field in a dual mode ramjet combustor with boundary layer bleed in isolator

A two-dimensional Reynolds averaged Navier Stokes (RANS) simulation of a dual mode ramjet (DMRJ) combustor is performed, modeling the University of Michigan dual-mode combustor experimental setup operating in reacting mode with different equivalence ratios (φ). The simulations are carried out using a k-ω SST turbulence model and a steady diffusion flamelet model for non-premixed combustion. Air enters the isolator at Mach 2.2, stagnation pressure and temperature of 549.2 kPa and 1400 K respectively. Hydrogen is injected transverse to the flow direction and upstream of the cavity flame holder to simulate ramjet (φ = 0.29) and scramjet (φ = 0.19) modes of operation. Wall static pressure plots are used to validate numerical results against experimental data. Analysis of flow separation in ramjet mode due to the presence of a shock train in the isolator is carried out by means of numerical Schlieren images overlapped with contours of negative axial velocity, showing the effects of shock wave boundary layer interaction (SWBLI). Active control through wall normal boundary layer bleed in the separated flow region is implemented, which weakens the shock train and moves it downstream closer to the cavity. Bleed results in an improved stagnation pressure recovery in ramjet mode, with a marginal increase in combustion efficiency.

OH visualization of ethylene combustion modes in the exhaust of a fundamental, supersonic combustor

Abstract This work examined combustion modes in a fundamental, axisymmetric, supersonic combustor at flight equivalent Mach numbers ranging from 7.5 to 9.0. Ethylene was injected at a variety of mass flow rates to examine both scram-mode, jet wake stabilized and dual-mode combustion. At higher flight Mach number conditions, the fuelling rate required to transition from scram-mode to dual-mode combustion increased. Distributions of the OH radical were observed using planar laser-induced fluorescence (PLIF) in a cross-sectional plane immediately downstream of the combustor exit, and analyzed according to their variation in the radial and circumferential dimensions. It was observed that radial centroids of the ring-like OH PLIF signal for the scram-mode cases approached the centerline linearly with increasing equivalence ratio, but the dual-mode cases appeared to randomly fluctuate in the observed exhaust cross-section. The distributions of scram- and dual-mode cases were clustered in specific regions on plots of circumferential variation as a function of radial centroid, with a jet wake stabilized case appearing between the two clusters. These clusters may be used to help identify scram- and dual-mode combustion in future experiments.

Aerodynamic performance enhancement of a variable-geometry dual-mode combustor designed by the method of characteristics

Wide-range scramjet is a part of the key power systems in future reusable hypersonic aircrafts, only the wide-range combustors with great performance can make the scramjet operate in a wide speed range. Through the method of characteristics, this paper designed a wave-elimination variable geometry combustor with a 20° deflection angle. The numerical simulation of the cold flow shows that the aerodynamic performance of the smooth wave-elimination combustor is greatly improved compared to the deflected combustor, and this improvement is more obvious at high operating Mach number. Also, the total pressure recovery coefficient of the wave-elimination combustor is above 0.8 when the combustor operates in different expansion ratios and freestream Mach numbers. The experimental study found that, under the expansion ratio of 1.8, the 20° wave-elimination combustor has a higher internal pressure compared with the 12° deflected combustor. In addition, the total pressure recovery coefficient is increased by 14.8% and 12.6% at the equivalent ratio of 0.6 and 1.0. This verified the advantage of the wave-elimination design, and proved that the wave-elimination design of the combustor is of great significance in improving the performance of the variable-geometry combustor.

Experimental Scramjet Combustion Modes of Hydrocarbon Mixtures at Mach 8 Flight Conditions

Shock tunnel experiments are presented that examine combustion modes of ethylene and a 64/36% ethylene/methane mixture under Mach 8 flight-representative conditions within an axisymmetric scramjet cavity combustor. Combustion modes (scram-mode and dual-mode) are presented via streamwise pressure measurements and visualized via planar laser-induced fluorescence (PLIF) of the hydroxyl (OH) combustion radical in the combustor exhaust plume. Ethylene-fuelled experiments developed scram-mode combustion under lean fuelling, whereas increased fuelling anchored combustion to the fuel injector wake. Further fuelling increases to stoichiometric levels developed dual-mode combustion. Exhaust OH PLIF indicated ethylene scram-mode combustion developed combustion products primarily in the wall-adjacent regions, whereas asymmetric flowfields were noted for the dual-mode. The addition of methane inhibited reactions, with no scram-mode combustion observed at even fuel-rich conditions. Higher fuelling rates developed dual-mode combustion with comparable pressure rises to the ethylene-fuelled dual-mode cases. OH PLIF indicated reduced concentration of OH for the ethylene/methane mixture. This work confirms the retarding influence of methane upon the reaction pathways of ethylene and reaffirms that fuels do not react independently in gaseous mixtures.

Dual/scram-mode combustion limits of ethylene and surrogate endothermically-cracked hydrocarbon fuels at Mach 8 equivalent high-enthalpy conditions

This paper examines the scram/dual-mode combustion limits of hydrocabon fuels within a Mach 8, scramjet combustor. Flight-equivalent flows were delivered to the axisymmetric, cavity combustor via a reflected shock tunnel. Two scramjet fuels were examined: ethylene and a surrogate mixture representing endothermically cracked n-dodecane. Combustion modes were examined via static pressure sensors and through both chemiluminescence imaging, and planar laser induced fluorescence (PLIF) of the OH combustion radical in the combustor exhaust plume. Ethylene-fuelled experiments developed scram-mode combustion under reduced fuelling conditions, experiencing shock wave dominated flowfields. OH PLIF diagnostics indicated such combustion modes developed a ring-like structure of combustion products, primarily axisymmetrically adjacent to the combustor wall. Increased fuelling anchored combustion downstream of the fuel injector, while further increases instigated dual-mode combustion. In this mode, subsonic combustion regions combine with the supersonic coreflow to permit the transfer of information upstream with substantially increased pressure encountered. Optical diagnostics indicate broadly asymmetric, unsteady combustion features. The surrogate mixture representing endothermically cracked n-dodecane experienced rapid onset from no-combustion (optically confirmed) to fully developed dual-mode combustion at critical fuelling rates. OH PLIF signals and chemiluminescence of this fuel were weaker than comparable ethylene cases, indicating potential differences in combustion pathways.