Non-uniform Mixtures Research Articles

Flame propagation characteristics of non-uniform premixed hydrogen-air mixtures explosion in a pipeline

Hydrogen, as a clean and promising energy carrier, is considered a viable alternative fuel for the future. However, accidental hydrogen leakages and explosions pose considerable safety concerns in hydrogen energy applications and process industries. This study investigated the flame propagation characteristics of non-uniform premixed hydrogen-air mixtures in a rectangular closed duct with a length-to-diameter ratio of 5.78, taking into account varying equivalence ratios and diffusion times. First, numerical simulations using FLUENT were conducted to model the hydrogen diffusion process in a confined space, determining the hydrogen concentration evolution post-leakage. After approximately 200 s of diffusion, the premixed hydrogen-air mixtures remained in a state of homogeneous mixing, with the hydrogen concentration stabilizing at approximately 1.25 × 10−2 kg/m³. Subsequently, experimental observations were performed using a visual pipeline system, high-speed photography, and flame structure analysis. These experiments examined inhomogeneous hydrogen-air mixtures under seven different equivalence ratios and five different diffusion time conditions. The effects of equivalence ratios and diffusion times on flame propagation characteristics were analyzed. The results revealed that equivalence ratio significantly influenced the flame structure, with higher equivalence ratios producing more pronounced flame surface wrinkles. However, the typical evolution of the tulip flame remained consistent. At a constant equivalence ratio, flame propagation velocity exhibited an initial increase followed by a decrease over time. These findings demonstrate that turbulence intensity accelerated the flame propagation in non-uniform premixed hydrogen-air mixtures. This study underscores the importance of further research on hydrogen safety fundamentals and technologies to develop comprehensive safety standards.

Experiments on critical behavior of oblique detonation wave in stratified mixtures

Two-stage gas-gun ballistic experiments are performed to investigate the feasibility of stratified mixtures with variable global equivalence ratios Φglobal for the formation of sphere-induced oblique detonation wave (ODW) and quantify their critical behaviors, which include local quenching and transitional structure to ODW, by testing conventional detonation criteria for uniform mixtures. 2 Φglobal H2 + O2 + 3Ar mixtures are tested with different concentration gradients for each fuel-lean/fuel-rich global composition. Opposite responses are observed depending on the global equivalence ratio: the lean mixture of Φglobal = 0.7, which forms ODW in the uniform mixture, fails partly in the strongest stratification, whereas the richest mixture of Φglobal = 2.0 turns to ODW in the strongly stratified conditions. As elucidated in the authors' previous work, Chapman–Jouguet (C–J) theory, including the curvature effects, reproduces the wave angles of the stable ODWs, as well as provides a good prediction on the local quenching of ODW occurring in the area with less reactive composition. Comparison of different wave regimes observed in the explored conditions reveals that wave curvature governs the critical behaviors of ODW far away from the projectile, whereas the initiation structure around the projectile is also influenced by the non-dimensional diameter. Surface energy theory is proven to quantify well the initiation structure on the projectile using a local equivalence ratio. These results indicate a new possibility of controlling the methodology of ignition and stabilization of detonation in aerospace engines, in which perfect mixing is difficult and non-stoichiometric and non-uniform mixtures are expected.

Effect of composition gradient on detonation initiation in fuel-rich hydrogen-air mixtures in an obstructed channel

Numerical simulations were performed to study the effect of composition gradient and obstacle arrangement on detonation initiation in fuel-rich hydrogen-air mixtures. A third-order WENO method with adaptive mesh refinement (AMR) was used to solve the unsteady, fully-compressible, reactive Navier-Stokes equations coupled to a calibrated chemical-diffusive model (CDM). An obstructed channel at a blockage ratio of 0.3 filled with non-uniform hydrogen-air mixtures of an average H2 concentration 50 vol% was considered. The results show that unilateral obstacle arrangement is more conducive to flame acceleration (FA) and DDT than bilateral obstacle arrangement for both homogeneous and inhomogeneous mixtures. For inhomogeneous mixtures, the flame accelerates faster, and the detonation onset time is shorter when obstacles are placed on the sidewall with a hydrogen concentration closer to the stoichiometric ratio than the those when obstacles are placed on the other sidewall. However, the placement of unilateral obstacles on either the upper or lower sidewall does not significantly affect the DDT run-up distance. Besides, for fuel-rich inhomogeneous hydrogen-air mixtures, detonation tends to be initiated in the regions of high H2 concentration. Idealized models were introduced to simplify the intricate interactions of the reaction waves and flow fields to better understand the connection between H2 concentration distribution and detonation initiation. The analysis suggests that the minimum shock strength required for detonation initiation decreases with increasing equivalence ratio. This is supported by a kinetics analysis with detailed reaction model, which shows that ignition delay increases with decreasing equivalence ratio when detonation is about to be initiated.

Experimental study on the explosion behavior of nonuniform hydrogen/methane/air mixtures in a duct

An experimental study is performed on the explosion behavior of a nonuniform hydrogen/methane/air mixture with varying hydrogen volume fractions (α(H2)) in the fuel used and different mixing levels of the fuel/air mixture (characterized by the diffusion time (td) of the hydrogen/methane mixture). Results show that both α(H2) and td considerably impact the explosion behavior of the nonuniform hydrogen/methane/air mixture. Increasing α(H2) and td can increase the uniformity of the hydrogen/methane/air mixture. A triple flame is observed in highly nonuniform mixtures instead of the finger- and tulip-shaped flames seen in more uniform mixtures. The shape of the flame front varies with the degree of fuel/air mixing. As α(H2) and td increase, the propagating flame gradually transitions from a triple flame to a tulip-shaped flame. The flame tip velocity and overpressure increase with α(H2) and td. For a fixed td, the flame tip velocity and overpressure increase slightly as the α(H2) rises from 0 to 40% and rapidly for a large α(H2). These findings suggest that improving the uniformity of hydrogen/methane/air mixtures could increase the severity of explosions for fuels with high hydrogen contents.

The Mechanism of Resonant Amplification of One-Dimensional Detonation Propagating in a Non-Uniform Mixture

The propagation of detonation waves (i.e., supersonic combustion waves) in non-uniform gaseous mixtures has become a matter of interest over the past several years due to the development of rotating detonation engines. It was shown in a number of recent theoretical studies of one-dimensional pulsating detonation that perturbation of the parameters in front of the detonation wave can lead to a resonant amplification of intrinsic pulsations for a certain range of perturbation wavelengths. This work is dedicated to the clarification of the mechanism of this effect. One-dimensional reactive Euler equations with single-step Arrhenius kinetics were solved. Detonation propagation in a gas with sine waves in density was simulated in a shock-attached frame of reference. We carried out a series of simulations, varying the wavelength of the disturbances. We obtained a non-linear dependence of the amplitude of these pulsations on the wavelength of disturbances with resonant amplification for a certain range of wavelengths. The gain in velocity was about 25% of the Chapman–Jouguet velocity of the stable detonation wave. The effect is explained using the characteristic analysis in the x-t diagram. For the resonant case, we correlated the pulsation period with the time it takes for the C+ and C− characteristics to travel through the effective reaction zone. A similar pulsation mechanism is realized when a detonation wave propagates in a homogeneous medium.

Structural and Mechanical Properties of SiC-Rich By-Products of the Metal Grade Si Process

Mechanical properties of composites produced from the SiC-rich furnace slag using traditional stone and ceramic machining technologies were studied. A non-uniform mixture of coarse monocrystalline SiC grains soaked with Si-metal and glassy oxide phases represented the microstructure of dense monolithic SiC-rich samples. The fracture mechanism of coarse-grained SiC-rich composites was susceptible to the grain size/sample geometry and machining conditions yielding flexural strength in the range of 50-106 MPa and high compression strength of 750 MPa. Despite inhomogeneous macro and microstructure, mechanical and thermal properties are comparable to the traditionally produced siliconized SiSiC ceramics. It opens up the opportunity for the circular economy and value-added recycling of the Si/FeSi industries’ wastes.

Local Structure of Nonuniform Fluid Mixtures Containing Associating and Chainlike Molecules from a Multilayer Quasichemical Model.

In this work, we develop a theory for predicting details of the local structure in nonuniform multicomponent fluids that may contain chainlike and associating components. This theory is an extension─to the fluid interfaces and mesoscopic structures of different geometry─of the multilayer quasichemical model originally proposed by Smirnova to describe liquid solution in the vicinity of a planar solid wall. The basis of the theory is the "cut-and-bond" approach, much in spirit of SAFT, where an infinite attraction between the separated monomeric units of a chainlike molecule mimics the chemical bonds of the chain. We describe the equilibrium structure of the mixture, including the spatial distribution of the monomeric units and the local orientation of the chemical bonds in chainlike molecules, and discuss the contribution of chemical bonds to the local chemical potential in a nonuniform fluid. To test the new theory, we apply it to mixtures containing combinations of model components: a strongly associating solvent, an inert substance of varying chain length, and a chainlike amphiphile. To compare predictions from the multilayer model with the results of continuous description of nonuniform fluids, we also address the square-gradient theory and derive an analytical expression for the influence parameter that takes into account pair correlations in the quasichemical approximation. The multilayer quasichemical model developed in this work predicts formation of aggregates in liquid solution and describes the local structure of the interfaces between the coexisting liquid phases in the mixture. Our theoretical predictions agree on a qualitative level with the accumulated knowledge about the structure of different types of systems studied in this work.

Numerical Simulation of Gas Explosion with Non-uniform Concentration Distribution by Using OpenFOAM.

Gas explosions in coal mines have occurred occasionally, which may cause casualties and economic losses. In the actual mine roadway, the gas concentration distribution is uneven because the gas density is lower than that of air. Gas explosion characteristics of uneven gas distribution with the concentration gradient in mine roadways were analyzed by using the open-source computational fluid dynamic code OpenFOAM. The flame and pressure characteristics were calculated, and the flame and shock wave propagation laws of the non-uniform gas-air mixture explosion with different concentration gradients were analyzed and compared with the uniform gas-air mixture gas. The results show that when the overall gas concentration is the same, the flame velocity and the pressure growth rate of the uniform gas explosion are lower than those of the non-uniform, but the pressure peaks of both are similar. At the same time, when the initial volume concentration is 10%, the non-uniform gas explosion has the highest flame propagation velocity and peak value. The peak explosion pressure of different concentration gradients is proportional to the initial concentration. The above studies clarified the characteristics of gas-air mixture explosions with concentration gradients and provided theoretical support for the prevention and control of gas explosion disasters.

Effects of transverse concentration gradients on the vented explosion of methane-air mixtures

Experiments were performed in a 90-L vessel with a side vent to investigate the effects of transverse concentration gradients on the vented explosion of non-uniform methane-air mixture. Controlled by a mass flow meter, methane was injected uniformly into the vessel through 18 nozzles that are evenly distributed at the top to configure a methane-air mixture with an average methane volume fraction of 10.9%. Various transverse concentration gradients were obtained by altering the free diffusion time of the methane in the vessel. The deflagration flame was recorded through a high-speed camera at a frequency of 1000 Hz, and the internal overpressure at different locations was captured through three piezoelectric sensors. Experimental results reveal that larger concentration gradient resulted in lower flame propagation rate, longer time for the burst of the vent cover, and stronger pressure oscillations. Concentration gradient affects the typical flame structure, especially the formation and development of the tulip flame. Under the present experimental conditions, Helmholtz oscillations occurred in all tests. Concentration gradient has a negative correlation with the frequency of Helmholtz oscillations but a positive correlation with the duration of oscillations. In conclusion, the variation of concentration gradient obviously affects flame propagation and pressure evolution during vented explosions, which deserves more attention in the design of explosion protection.

Direct detonation initiation in hydrogen/air mixture: effects of compositional gradient and hotspot condition

Two-dimensional simulations are conducted to investigate the direct initiation of cylindrical detonation in hydrogen/air mixtures with detailed chemistry. The effects of hotspot condition and mixture composition gradient on detonation initiation are studied. Different hotspot pressures and compositions are first considered in the uniform mixture. It is found that detonation initiation fails for low hotspot pressures and the critical regime dominates with high hotspot pressures. Detonation is directly initiated from the reactive hotspot, whilst it is ignited somewhere beyond the non-reactive hotspots. Two cell diverging patterns (i.e. abrupt and gradual) are identified and the detailed mechanisms are analysed. Moreover, cell coalescence occurs if many irregular cells are generated initially, which promotes the local cell growth. We also consider non-uniform detonable mixtures. The results show that the initiated detonation experiences self-sustaining propagation, highly unstable propagation and extinction in mixtures with a linearly decreasing equivalence ratio along the radial direction, i.e. 1 → 0.9, 1 → 0.5 and 1 → 0. Moreover, the hydrodynamic structure analysis shows that, for the self-sustaining detonations, the hydrodynamic thickness increases at the overdriven stage, decreases as the cells are generated and eventually becomes almost constant at the cell diverging stage, within which the sonic plane shows a ‘sawtooth’ pattern. However, in the detonation extinction cases, the hydrodynamic thickness continuously increases, and no ‘sawtooth’ sonic plane can be observed.

Effects of ignition position on the explosion of methane-air mixtures with concentration gradients

To investigate the effects of ignition position on the explosion of non-uniform methane-air mixtures, experiments were carried out in a closed pipe of 1 m length and 0.3m × 0.3 m cross-section. Methane is uniformly charged at the top of the pipe and then diffused freely, creating a concentration gradient. The concentration gradient of the methane-air mixture depends on the diffusion time. The effects of the three ignition positions – top (IP1), center (IP2) and bottom (IP3) - on the flame propagation at different ignition delay time (tig) were investigated. The ignition position and tig are the key factors influencing the success of ignition. For IP2 and IP3, the flame propagation velocity increases with the increase of tig, but the flame propagation velocity at IP1 does not change significantly with an increase in tig. When tig ≤ 25min, the temperature (Tmax) and maximum overpressure (Pmax) in the pipe at IP1 are significantly higher than those at IP2 and IP3. When the methane-air mixtures are nearly uniform, the Tmax and Pmax at different ignition locations are almost identical. The maximum pressure rise rate, (dP/dt)max, was affected by the flame pipe collision and different flame shapes caused by the ignition position.

Explosive characteristics of non-uniform methane-air mixtures in half-open vertical channels with ignition at the open end

In this study, the explosive characteristics of non-uniform methane-air mixtures in a 1.5 m half-opened vertical channel with ignition at the open end were experimentally studied. The results revealed significant oscillation characteristics in the flame image, velocity, and pressure variations. Notably, a strong similarity was observed between the flame velocity and pressure profiles. Furthermore, it was experimentally demonstrated that the explosion characteristics of methane-air mixtures in vertical channels with the same average volume fraction differed. These variations in characteristics were attributed to the degree of non-uniformity, where both the direction and steepness of the methane concentration gradient influenced the explosion flame behavior. When the diffusion time was very short, resulting in a small concentration above the channel and a large gradient, an obvious cusp appeared at the flame front, which was absent in the case of longer diffusion times. In addition, as the methane diffusion time increased, the methane in the vertical channel gradually accumulated upward. Consequently, the time required to reach maximum velocity and pressure after ignition decreased, leading to a larger maximum amplitude. In summary, our study highlights the importance of considering non-uniformity and diffusion time in understanding the explosion characteristics of methane-air mixtures in vertical channels.

Numerical approach to theoretical aspects of wedge-induced oblique detonation wave in a hydrogen concentration gradient

The present study conducts numerical simulations of oblique detonation wave (ODW) induced on a wedge in the concentration gradient of a hydrogen–air mixture. As a continuation of the author's previous work on the morphology of the initiating flame in a non-uniform mixture, the concentration gradient is provided only to the ODW front to address its theoretical characteristics: the propagation velocity and structures of post-shock reactive flow associated with the Chapman–Jouguet and Zeldovich–von-Neumann–Doering theories, respectively. Applying a Gaussian distribution of the hydrogen mole fraction to the ODW front induces a curved shape that is concave or convex in fuel-rich or fuel-lean compositions, respectively. The local wave angle on a curved ODW matches the one-dimensional theory in a uniform mixture, which proves its robustness in predicting the detonation velocity in a non-uniform mixture. Furthermore, tracing streamlines with different compositions reveals that the flow path and variations in temperature and pressure are almost coincident with those predicted by one-dimensional and uniform assumptions. The slight variation among the different conditions is attributed to the effects of two-dimensional convergence/divergence that are intensified at stronger gradients. The understanding achieved in the present study will also benefit the evaluation of propagating detonation in a non-uniform mixture layer formed in propulsion devices.

Numerical modeling of local scour of non-uniform graded sediment for two arrangements of pile groups

A three-dimensional (3D) non-hydrostatic numerical model is established to investigate local scour around four aligned circular piles in uniform and non-uniform sediment mixtures and to provide information for improving scour countermeasures design. In the current study, unsteady Reynolds averaged Navier–Stokes (URANS) equations along with a Re-normalization Group (RNG) k–ε model were applied to simulate the flow field. A non-uniform sediment transport model was applied to estimate the bedload transport. The simulations lasted up to 8 h. The laboratory results of a reference single pile case in uniform and non-uniform sediment were utilized to validate the simulation results of bed elevation changes and time evolution of scour depth and reflected a good agreement. The influence of pile spacing for two arrangements of pile groups, one column (tandem) and two columns (non-tandem) of four aligned piles, on spatial/temporal variations of the bed surface in both sediment bed configurations are discussed in detail. The results reveal the significant effects of the pile spacing on the flow field and patterns of scour hole formation and sediment deposition. In general, lower pile spacing results in more scour upstream of the front pile(s) and shifts deposition more downstream due to the existence of higher energy in the wake region of the piles for both sediment types. Side scouring dominates for non-uniform sediment around each pile due to flow deviating because of the presence of relatively larger particles in front of the pile(s). For non-uniform sediment, deposition begins to develop at the exit area of the scour hole and enhances boundary resistance to scour. The knowledge gained from this study is suitable for the accurate determination of riprap dimensions around the front pile(s) and rear piles in a pile group.

Combustion characteristics of nonuniform methane-air mixtures in the duct

In this study, an experimental duct was divided into two sections (ducts A and B) and filled with methane-air mixtures at various equivalence ratios. The combustion characteristics of non-uniformly distributed methane-air mixtures were studied experimentally, and the effect of ignition position on them was analyzed. The results showed that the a change in the equivalence ratio in duct A had a more visible effect on flame propagation. As the ignition position moved toward the open end, rapidly oscillating pseudo-flat structures and distorted tulip structures were observed in the right flame, and the bimodal pressure waveform was transformed into a unimodal waveform. While the propagation of the LFF (i.e., the flame front that propagated to the left open end) is the main reason for the pressure increase, the RFF (i.e., the flame front that propagated to the right closed end) also exerted a certain influence on the second peak. The stretching effect of the LFF and the Rayleigh-Taylor instability jointly cause oscillations in the RFF. We also observed that the maximum flame propagation velocity and peak overpressure varied in a consistent manner, both increasing first and then decreasing as the ignition position approaches the open end.

Experimental Study of Effect of Injection Timing on Port Fuel Injection Gasoline, Port Fuel Injection Compressed Natural Gas, and Direct Injection Compressed Natural Gas Engine Performance, Combustion, and Emissions Characteristics

Abstract Compressed natural gas (CNG) has gained popularity due to its wide availability, higher efficiency, and lower emissions compared to gasoline. However, the lower flame speed characteristics of CNG with conventional port injection reduce the CNG engine volumetric efficiency and power output. CNG's lower gas jet momentum during a low load operation creates a non-uniform air-fuel mixture that affects ignition and combustion quality. Direct injection of CNG with optimum injection timing is expected to improve volumetric efficiency, ignition quality, and combustion process. In this study, a comparative study on the effect of end-of-injection (EOI) timing on volumetric efficiency, thermal efficiency, combustion duration, and emissions was carried out in a single-cylinder port fuel injection (PFI) spark-ignition engine using gasoline and CNG, and direct injection (DI) spark ignition engine using CNG. The experiments were performed at two-part load operations of 20% and 40% throttle at 900 and 1500 rpm. Experimental results indicate that the PFI CNG engine is more influential in EOI timing than gasoline engines. The performance of the PFI CNG engine is improved when the injection occurs during the intake valve open period compared to the closed valve period with higher thermal efficiency, volumetric efficiency, and indicated mean effective power (IMEP). A shorter flame development angle and combustion duration were observed when EOI timing was in the open intake valve condition. DI CNG improved volumetric efficiency at advanced EOI timing compared to the PFI CNG engine. However, the combustion process is critically dependent on injection timing and air-fuel mixing duration. A three-dimensional computational fluid dynamics simulation was conducted to evaluate the effect of advanced and retarded EOI timing on DI CNG engine's in-cylinder turbulent kinetic energy development and in-cylinder equivalence ratio near the ignition point. An excess advanced EOI timing resulted in stratified rich and retarded EOI timing results in loss of turbulence energy, leading to a slightly rich and lean mixture for advanced and retarded EOI timing, respectively. Hence, an optimum EOI timing provides a conducive environment to initiate the combustion and flame front propagation. Further, advanced EOI timing was required at higher throttle opening and engine speed. The emissions in DI CNG were also greatly affected by EOI timing.

Experimental Proof of Concept of a Noncircular Rotating Detonation Engine (RDE) for Propulsion Applications

A noncircular engine cross-section could provide great flexibility in the integration of propulsion into the airframe. In this work, a tri-arc RDE was constructed and tested as an example of noncircular cross-sectioned RDE. The operational characteristics of detonation wave propagation and thrust performance were investigated and compared with an equivalent circular RDE under the same operating conditions. High-speed camera images, short-time Fourier transform (STFT), and fast Fourier transform (FFT) were used for the investigation. The tri-arc RDE showed very similar characteristics to the circular RDE but exhibited slightly better stability and propulsion performance than the circular RDE. We consider that repeated curvature changes positively affect the stability of detonation wave propagation. The experimental data show contradicting results from the numerical analysis with a homogeneous mixture assumption in which the detonation pressures at the convex corner were greater than those at the concave corner. It is reasoned that the tri-arc injector design provides a non-uniform mixture composition, resulting in a strong detonation at the convex corner. Overall, the noncircular RDE of a tri-arc shaped cross-section is demonstrated, one which performs slightly better than an ordinary circular-shaped RDE both in detonation stability and performance.

Detonation simulations in supersonic flow under circumstances of injection and mixing

The unsteady, reactive Navier-Stokes equations with a detailed chemical mechanism of 11 species and 27 steps were employed to simulate the mixing, flame acceleration and deflagration-to-detonation transition (DDT) triggered by transverse jet obstacles. Results show that multiple transverse jet obstacles ejecting into the chamber can be used to activate DDT. But the occurrence of DDT is tremendously difficult in a non-uniform supersonic mixture so that it required several groups of transverse jets with increasing stagnation pressure. The jets introduce flow turbulence and produce oblique and bow shock waves even in an inhomogeneous supersonic mixture. The DDT is enhanced by multiple explosion points that are generated by the intense shock wave focusing of the leading flame front. It is found that the partial detonation front decouples into shock and flame, which is mainly caused by the fuel deficiency, nevertheless the decoupled shock wave is strong enough to reignite the mixture to detonation conditions. The resulting transverse wave leads to further mixing and burning of the downstream non-equilibrium chemical reaction, resulting in a high combustion temperature and intense flow instabilities. Additionally, the longitudinal and transverse gradients of the non-uniform supersonic mixture induce highly dynamic behaviors with sudden propagation speed increase and detonation front instabilities.

Flame acceleration and transition to detonation in non-uniform hydrogen-air mixtures in an obstructed channel with different obstacle arrangements

Numerical simulations were performed to study flame acceleration (FA) and deflagration-to-detonation transition (DDT) in non-uniform hydrogen-air mixtures in an obstructed channel. The fully compressible reactive Navier-Stokes equations coupled to a calibrated chemical-diffusive model were solved using a high-order numerical method on a dynamically adapting mesh. The simulations are in satisfactory agreement with previous experiments. For the cases with average H2 concentration 30 vol%, the presence of composition gradient weakens FA and causes delayed DDT due to lower total heat release since the unburned material is either fuel-rich or fuel-lean, although the composition gradient leads to more unburned pockets. The effects of obstacle arrangement and blockage ratio were explored in the mixtures with a linear gradient at 50 vol% average H2 concentration. The results show that FA and DDT can be promoted by increasing blockage ratio from 0.3 to 0.6 or placing obstacles along the sidewalls with lower H2 concentration because the formation and flame properties of unburned pockets are enhanced. An analytical model for predicting FA in fuel-rich non-uniform mixtures is suggested and validated against the numerical simulations. The model shows that flame acceleration rate mainly depends on blockage ratio and the thermal expansion ratio in unburned pockets.

Laser welding Al–Si coated hot stamping steel in conduction mode: weld formation and Al-rich microstructure

The non-uniform mixture microstructure is always revealed in laser welds of Al–Si coated hot stamping steel. It is very necessary to understand aluminum-rich segregation on phase morphology evolution. At same time the uniform and high aluminum welds were tried to obtain by replacing keyhole mode with conduction mode. The uniform fusion zones contained 3–6 wt.% Al, higher than normal keyhole welds. The weld microstructure was mixed of delta ferrite, lath martensite and few discussed needle phases with different morphology. Lower Al region revealed high fraction of island martensite, when aluminum content w(Al) > 5 wt.%, the needle phase was precipitated from the matrix of delta ferrite. High resolution transmission electron microscopy confirmed it long periodical stacking ordered structure in body-cubic crystal matrix.