Preheat Temperature Research Articles

Heat input optimization for the ignition of self-sustained smoldering remediation of contaminated soils using concentrated solar power

In this paper, we explore the industrial-scale feasibility of using concentrated solar power (CSP) as the heat source in the smoldering remediation of petroleum-contaminated soil. Approximately 5 L soil samples were loaded in a narrow-channel reaction chamber and heated from the bottom with CSP to identify the required heat input to achieve ignition. Both petroleum and granular activated carbon (GAC) were used as combustible media. GAC was selected as a cleaner-burning alternative to petroleum and could emulate petroleum-contaminated soil at a mixture of 40 g GAC per kg pool sand on a 1.5 cm bed of GAC. This mixture of GAC showed robust ignition with a minimum power input of 240 W, which was slightly higher than the power input required to ignite industrially generated petroleum-contaminated soil. Preheat temperatures in excess of 300°C were achieved in most experiments, allowing for robust ignition of the smoldering remediation process. CSP was collected using parabolic reflectors 600 mm in diameter and was delivered to the reaction chamber with fiber optic bundles. Each solar concentrator delivered between 50 and 80 W to the reaction chamber, and four concentrators were required to reliably achieve the required power input.

Excited state lifetime of electron trapping centres in alkali feldspars

The development of the infrared photoluminescence (IRPL) signal enables the direct non-destructive probing of the trapped electron population in feldspars. Whilst IRPL offers new perspectives for luminescence dating, it also enables detailed, site-selective measurements of the dosimetric defects emitting IRPL at 880 nm (IRPL880) and 955 nm (IRPL955), allowing improved understanding of luminescence phenomena in feldspars.We perform time-resolved IRPL measurements to investigate the excited state lifetimes of IRPL880 and IRPL955 electron trapping centres in chemically and structurally different feldspars. We analyse the time-resolved off-time data with three exponentially decaying components. The contribution of the fast component (τ1) fitted to the IRPL880 data is minor and its lifetime is consistent with the switch off time of the 830 nm excitation laser. The two longer lifetimes (τ2 and τ3) dominate the IRPL880 and IRPL955 signals. The τ2 values range from 2 μs to 6 μs for IRPL880 and from 2 μs to 7 μs for IRPL955, whereas τ3 ranges from 7 μs to 25 μs for IRPL880 and from 8 μs to 22 μs for IRPL955, with an average cluster value of ∼20 μs. We observe a weak decreasing trend in τ3 lifetime with decreasing K-feldspar content. Systematic thermal depletion of the trapped electron population results in decreasing τ2 lifetimes with increasing preheat temperature, but a negligible change in τ3. We suggest that time-resolved-IRPL lifetimes not only reflect the exited state lifetime of the electron trapping centre, affected by excited-to-ground state transition as well as tunnelling, but also a direct recombination from the band-tail states. The long excited-state lifetime of the order of 20 ∼ μs (the average cluster value) allows for tunnelling induced recombination from the excited state, which is supported by the fact that reported lifetimes for time-resolved-IRSL (infra-red stimulated luminescence) are shorter than those of time-resolved-IRPL.

Numerical Analysis and Experimental Study on Side Dam Temperature and Stress Field of Two‐Roll Casting

The side sealing technology is crucial for ensuring the quality and process stability in twin‐roll casting (TRC). Investigating the temperature and stress distribution in side dams under operational conditions is vital, especially in understanding the causes of side dam fractures. Optimal performance of side dam materials is achieved when the boron nitride (BN) matrix is fine and homogeneous, with zirconium dioxide (ZrO2) and silicon carbide (SiC) particles evenly dispersed throughout. The fracture of the side dam after casting is mainly caused by BN interlamellar tear. The coexistence of BN lamellar tearing and BN layer fracture leads to the fracture of the side dam during the casting process. Through finite element simulation, the effects of variables such as pouring temperature, preheating temperature, and side dam thickness on temperature and stress distribution were analyzed. The findings indicate that a preheating temperature range of 1200–1300 °C minimizes thermal stress in the side dam. Building on these findings, a composite structure for the side dam is developed. Both internal and external composite structures have shown significant effectiveness in reducing thermal stress. These results are pivotal in extending the service life of side dams and enhancing the stability of the TRC process.

Effects of fuel preheat temperature on soot formation in methyl linolenate co-flow diffusion flames

Effects of fuel preheat temperature on soot formation in methyl linolenate co-flow diffusion flames

Achieving Metallurgical Bonding in Aluminum/Steel Bimetallic Castings

Aluminum castings are increasingly being used in automotive powertrain and structural applications for vehicle lightweighting. Cast aluminum parts often need to be machined and joined to steel components in multi-material systems. Bimetallic components produced by casting aluminum over steel substrate are advantageous due to the elimination of machining and traditional dissimilar material joining processes. However, forming a strong metallurgical bonding during overcasting process has been challenging. In this paper, the effects of processing conditions such as substrate surface preparation, pre-heating temperature, melt conditions as well as casting design were studied by investigating the bimetallic interfaces for aluminum A319 casting alloy and a high alloy steel substrate in a sand-casting process. Zn and Al-based substrate coatings were evaluated. The experimental results suggest a metallurgical bond between aluminum and steel can be formed during the sand-casting process via high temperature diffusion with or without coatings. Al-based substrate coating prior to overcasting results in the formation of a continuous layer of intermetallics at the bimetallic interface, with large Al–Si–Fe intermetallics penetrating the cast aluminum.

Effect of a Substrate’s Preheating Temperature on the Microstructure and Properties of Ni-Based Alloy Coatings

Laser cladding is a new technology to fabricate a coating on the surface of a metal substrate. The properties on copper substrates are usually not very good due to the high thermal conductivity and reflectivity. The appropriate preheating temperature is helpful to fabricate coatings with good quality and properties, especially for copper substrates. In order to investigate the effect of different preheating temperatures, four coatings with different preheating temperatures (100, 200, 300 and 400 °C) were fabricated via a laser on a copper substrate. The microstructures and properties of four coatings were investigated using SEM, XRD, EDS, a Vickers microhardness meter, a wear tester and an electrochemical workstation. The results show that the elements from Ni-based alloy powder were uniformly distributed among the binding region, which obtained a good metallurgical bonding. The microstructure was mainly composited of cellular, dendrite and plane crystals, and the main reinforced phases were γ (Fe, Ni), Cr0.09Fe0.7Ni0.21, WC and Ni3B. The values of average microhardness of the four coatings were 614.3, 941.6, 668.1 and 663.1 HV0.5, respectively. The wear rates of the four coatings were 9.7, 4.9, 12.5 and 13.3 × 10−5 mm3·N−1·m−1, respectively, which were less than that of the copper substrate (4.3 × 10−3 mm3·N−1·m−1). The decrease in wear rate was due to the existence of the reinforced phases, such as WC, Ni3B, M7C3 (M=Fe, Cr) and Cr0.09Fe0.7Ni0.21. The fine crystals in the coating preheated at 200 °C also improved the wear resistance. Additionally, the minimum values of corrosion current density were 3.26 × 10−5, 2.34 × 10−7, 4.02 × 10−6 and 4.21 × 10−6 mA·mm−2, respectively. It can be seen that the coating preheated at 200 °C had higher microhardness, lower wear rates and better corrosion resistance due to the existence of reinforced phases and fine and uniform crystals.

Influence of Preheat Temperature Variation on Single Screw Extrusion for Characterizing PLA, PCL, and HA Biocomposite Filaments

Fractures and ligament injuries often require bone fixation, commonly through Open Reduction and Internal Fixation (ORIF) with compression plates and screws. Additive manufacturing (AM) techniques are considered sustainable due to their potential to reduce emissions and have a minimal adverse impact on the environment. Currently, there is extensive research into producing biocomposite filaments, though there remains limited exploration of the impact of preheat temperature on filament properties. This research explores the effects of varying preheat temperatures in a single screw extruder to achieve biocomposite filament as candidate for biodegradable bone implants. Biocomposite filaments made from Polylactic Acid (PLA) and Polycaprolactone (PCL) in an 85:15 ratio, with 5% hydroxyapatite (HA) derived from green mussel shell waste. Biocomposite mixture was cut into sub-5mm fragments and extruded at 175°C with preheat temperatures between 159°C and 168°C. Filaments were used to fabricate specimens via a 3D printer, following ASTM D790 standards. Specimens were analyzed using X-Ray Diffractometer, Fourier Transform Infrared, Scanning Electron Microscope, density measurements, three-point bending tests, and biodegradation assessments. Results show that preheat temperature variations significantly affect the filament’s crystallinity index, impacting density and mechanical properties. Higher preheat temperatures result in a lower crystallinity index, decreasing density and potentially increasing degradation rates.

Energy-Efficient Parametric Optimization of Al7178/TiB2/SiO2 Hybrid Nanocomposites through SN ratio and ANOVA method

This work focused on the energy-efficient fabrication of Al7178 based hybrid nanocomposites reinforced with TiB2 & SiO2 by using the stir-casting technique. The investigation aimed to optimize process factors including stirring speed, stirring time, reinforcement weight percentage, and preheat temperature, to improve the tensile strength of the Al7178/TiB2/SiO2 hybrid composite. The Taguchi method and ANOVA were employed to analyze the influence of these parameters on tensile strength. SN ratio analysis helped to identify the optimal parameter settings. Results confirmed that preheat temperature, stir time, and reinforcement weight percentage had a statistically significant impact on tensile strength. Optimal conditions were identified as 800 rpm, 740°C of preheat temperature, 8 wt% of reinforcement, and 9 minutes of stir time, lead to a substantial improvement in tensile strength. These conclusions contributed to the development of energy-efficient and high-performance Al-based hybrid composites.

Topology characteristics of liquid ammonia swirl spray flame

The utilization of liquid ammonia in gas turbines can reduce energy loss and start-up time. However, the flash boiling phenomenon and the high latent heat of liquid ammonia make the spray flame difficult to stabilize. Increasing the preheated air temperature or adding a small amount of hydrogen as a piloted fuel are considered as effective methods to enhance the stability. To understand the flame topological structure, simultaneous Mie scattering and planar laser-induced fluorescence of OH (OH-PLIF) techniques were used to visualize the liquid ammonia spray structure and flame region information. Results show that the liquid ammonia swirl spray flame exhibits the flame topological structure of distinct zoning characteristics, including the droplet zone, the mixing zone, and the flame zone. Increasing the preheated air temperature accelerates the evaporation of liquid ammonia, leading to an increase in the local equivalence ratio and radial flame splitting. At lower air temperature conditions, increasing the hydrogen blending ratio has minimal impact on the flame topological structure. However, at higher temperature conditions, hydrogen blending significantly promotes reaction intensity upstream and reduces the flame lift-off height, which makes the mixing zone smaller. In general, to achieve a better flame stability effect, the two factors need to be reasonably matched, which has important reference value for the development of liquid ammonia fueled gas turbine combustors.

ESR and luminescence thermochronometry of the Rhône valley, Switzerland

The impact of Quaternary glaciations on rates of erosion remains disputed. This is mainly due to a lack of geochronological data that cover the timespan of 103−106 years. To fill this temporal gap, we develop electron spin resonance (ESR) thermochronometry using both the Al- and Ti-centres in quartz. The combination of ESR thermochronometry with numerical modelling allows rock cooling histories to be determined, enabling changes in erosion rates to be related to glacial advance. In this study, we conducted a series of laboratory experiments using samples from the upper Rhône valley (Switzerland) that is thought to have substantially deepened around 1 Ma ago. Ten quartz samples, from a transect collected near Sion, were used to (i) optimize the measurement protocol (i.e., preheat conditions), (ii) constrain ESR signal growth and thermal stability of the Al- and Ti-centres to estimate trap kinetic parameters; and (iii) invert the ESR data to constrain rock cooling histories. A preheat plateau experiment showed that 170 °C is the appropriate preheat temperature whilst sensitivity changes are not significant. For most samples the Ti-centre has higher thermal stability than the Al-centre, although the thermal stability of the different samples investigated is highly variable. Preliminary inversion results yield consistent cooling histories of around 30−60 °C/Myr during the Late Quaternary period, except for two valley bottom samples that suggest more rapid rock cooling.

Challenges and opportunities to develop the method of joining dissimilar material aluminium-steel by using Rotational Friction Welding (RFW)

The combination of the lightweight AL 6061 and high-strength steel SWRM 1008 is utilized by the industrial sector, including the automotive industry to make bumper reinforcement. The properties of AL 6061 and SWRM 1008 steel have specific differences so an appropriate welding method is needed. This is a challenge and an opportunity for its application in the future. Rotational friction welding (RFW) is one of several welding processes that can be applied to join AL 6061 with SWRM 1008 and furthermore, the welding is environmental. The occurrence of diffusion between AL 6061 and SWRM 1008 is influenced by the heating temperature and forging pressure. Due to different melting temperature the steel in this research has been preheated. Al 6061 has a lower melting temperature than SWRM 1008 and a male-female shape has been made so that excessive upset did not be overformed and the forging process ran optimally. The welding process used rotational friction welding between Al 6061 and SWRM 1008 with preheat temperature 3500C, rotational speed 800 rpm, friction pressure 2 Mpa, and forging pressure 3 Mpa. The results of the joining were then tested for tensile strength and micro-photos. The preheat to SWRM 1008 before the welding process causes softening of the aluminium surface immediately after contact. Excessive softening of the aluminium surface establishes an upset before diffusion occurs. IMC will form well under high shear stress and forging pressure. The welding process at low pressure obtained a connection tensile strength value of 65.2Mpa even though it had been preheated before welding took place. From this research, we can know if rotational friction welding gives opportunities to join the AL 6061 with SWRM1008.

Experimental investigation and modeling of boundary layer flashback for non-swirling premixed prevaporized n-propanol/air and /isopropanol/air flames

The idea of utilizing lean, premixed and prevaporized (LPP) combustion could be a step towards sustainable aviation in the future, with the absolute absence of soot particles and very low nitrogen oxide emissions. However, premixing with compressed hot air presents a challenge for both conventional jet fuel and synthetically produced sustainable aviation fuel (SAF) due to self-ignition and flashbacks. Our group is thus seeking LPP-compatible advanced sustainable aviation fuels, which are evaluated based on their flashback propensity. Preliminary studies indicate that short-chain alcohols, with their higher ignition delay times and lower flame velocities, may be appropriate for LPP combustion concepts. In this study, the isomers of propanol, n-propanol, and isopropanol, are the first representatives of the short-chain alcohols to be investigated experimentally and numerically with respect to their flame stability limits. The experimental determination of stability limits for n- and isopropanol/air premixed flames was conducted on a generic, non-swirled atmospheric burner for an equivalence ratio range of 0.82 to 1.11. A fully automated measurement procedure was used to generate 119 measurement points with Reynolds numbers in the range from 1430 to 2750. The influence of the positional isomerism and of the preheat temperature (422 K, 446 K and 466 K) of the unburned mixture are investigated. A clear influence of the isomeric fuel structure is found. A theoretical analysis shows that it can be related to the different laminar flame speed and laminar flame thickness of the isomers. Moreover, a detailed analysis shows that the critical velocity gradient concept to describe boundary layer flashback is well usable with a Péclet number model.

Effect of RAP's preheating temperature on the secondary aging and performance of recycled asphalt mixtures containing high RAP content

Plant-mixed hot recycling technology is widely used. Due to concerns about the road performance of recycled asphalt mixtures with high RAP content, the content of RAP is strictly limited, which has negative impact on ecological and economic benefits. Low preheating temperature of RAP material is an important reason for reduced performance of recycled asphalt mixtures containing high RAP content. At the same time, excessive preheating temperature of RAP materials can cause secondary aging of asphalt in RAP. This study regarded the preheating temperature as a variable. Rheological and spectroscopic tests such as DSR and BBR, and FTIR tests were conducted to investigate the effect of RAP preheating temperature on the secondary aging of RAP. Afterwards, the influence of raising preheating temperature of RAP on the performance of recycled asphalt mixtures was explored synthetically. When the preheating temperature is below 160 ºC, there is no significant secondary aging of aged asphalt in RAP. However, when the preheating temperature increases to 180 ºC, the rheological properties of aged asphalt undergo certain changes. Increasing the preheating temperature of RAP can significantly improve the low-temperature crack resistance and fatigue performance of recycled asphalt mixtures by reason of maximally activating the aged asphalt. Increasing the preheating temperature of RAP does not weaken the high-temperature anti-rutting performance of recycled asphalt mixture. It is recommended to control the preheating temperature of RAP at 160 ºC in the design and production process of hot recycled asphalt mixtures.

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

Numerical Simulation on Solidification during Vertical Centrifugal Casting Process for TC4 Alloy Wheel Hub with Enhanced Mechanical Properties.

The Ti-6Al-4V (TC4) alloy wheel hub has exhibited some defects that affect the properties during the vertical centrifugal casting process. Therefore, the analysis of the solidification process would contribute to solving the above-mentioned problems. In this study, an orthogonal experimental design was employed to optimize the process parameters (rotational speed, mold preheating temperature, and pouring temperature) of the vertical centrifugal casting method. The effects of process parameters on the velocity field, temperature field, and total shrinkage porosity during the solidification process were explored, and the microstructure and mechanical properties of the wheel hub prepared by the vertical centrifugal casting method were also investigated. The results showed that the rotational speed mainly induced the change of the velocity field. The pouring temperature and mold preheating temperature affected the temperature field and solidification time. Based on the analysis of the orthogonal experiment, the optimal parameters were confirmed as a rotational speed of 225 rpm, mold preheating temperature of 400 °C, and pouring temperature of 1750 °C, respectively. The simulation results of total shrinkage porosity were in agreement with the experiment results. The wheel hub was composed of nonuniform α and β phases. The lath α phase precipitated from larger β grains with different orientations. Compared with the other samples at different locations, the α phase in the PM sample (middle of the TC4 wheel hub) displayed high peak intensity and uniformly distributed β phase along the radial direction of the wheel hub. Moreover, the PM sample revealed a higher tensile strength of 820 MPa and similar Vickers hardness of 318 HV compared with the other samples at different locations, which were higher than those of rolling and extrusion molding. This experiment design would provide a good reference for the vertical centrifugal casting of the TC4 alloy.

Exergoeconomic Evaluation of a Cogeneration System Driven by a Natural Gas and Biomass Co-Firing Gas Turbine Combined with a Steam Rankine Cycle, Organic Rankine Cycle, and Absorption Chiller

Considering energy conversion efficiency, pollution emissions, and economic benefits, combining biomass with fossil fuels in power generation facilities is a viable approach to address prevailing energy deficits and environmental challenges. This research aimed to investigate the thermodynamic and exergoeconomic performance of a novel power and cooling cogeneration system based on a natural gas–biomass dual fuel gas turbine (DFGT). In this system, a steam Rankine cycle (SRC), a single-effect absorption chiller (SEAC), and an organic Rankine cycle (ORC) are employed as bottoming cycles for the waste heat cascade utilization of the DFGT. The effects of main operating parameters on the performance criteria are examined, and multi-objective optimization is accomplished with a genetic algorithm using exergy efficiency and the sum unit cost of the product (SUCP) as the objective functions. The results demonstrate the higher energy utilization efficiency of the proposed system with the thermal and exergy efficiencies of 75.69% and 41.76%, respectively, while the SUCP is 13.37 $/GJ. The exergy analysis reveals that the combustion chamber takes the largest proportion of the exergy destruction rate. The parametric analysis shows that the thermal and exergy efficiencies, as well as the SUCP, rise with the increase in the gas turbine inlet temperature or with the decrease in the preheated air temperature. Higher exergy efficiency and lower SUCP could be obtained by increasing the SRC turbine inlet pressure or decreasing the SRC condensation temperature. Finally, optimization results indicate that the system with an optimum solution yields 0.3% higher exergy efficiency and 2.8% lower SUCP compared with the base case.

Soot and PAH formation in laminar diffusion flames of RP-3 jet kerosene and its surrogates at preheat temperature

For investigating the effects of preheat temperature on the soot/PAH formation of RP-3 kerosene surrogates, planar laser-induced incandescence (PLII), planar laser-induced fluorescence of PAH (PAH-PLIF) and chemical kinetic simulation are conducted in several laminar diffusion flames. The goal is to provide a surrogate that matches well with the soot formation characteristics of RP-3 kerosene and to investigate the mechanism behind the temperature sensitivity of different surrogates. Firstly, surrogate S1 (30.3% n-hexadecane, 39.8% iso-cetane, 29.8% o-xylene, in mole fraction) is formulated to obtain a surrogate with good reproducibility of soot formation characteristics corresponding to the RP-3 jet kerosene. Compared with another reported surrogate S2, S1 presents a higher soot yield due to its higher PAH formation and a stronger soot formation propensity. With elevated preheat temperature, soot yield of all the studied flames gets higher, and the temperature sensitivities for soot formation of S1 and S2 are shown with little difference. By further analyzing the PAH results experimentally and numerically, the temperature sensitivity for soot yield of S2 is more closely related to the temperature sensitivity of PAH precursors, while the subsequent processes after soot inception may be more important to the temperature dependence of S1.

Isolation and characterization of a new potential source of bioactive peptides: White mulberry (Morus alba) fruits and its leaves

In this study, white mulberry (WM; Morus alba L.) and its leaf (WML) were hydrolyzed using enzymes at different preheating temperatures (50, 60, 70, 80, and 90 °C) with distilled water at a ratio of 1:10 (w/v). Pepsin, trypsin, chymotrypsin, and alcalase were employed for enzymatic hydrolysis, aiming to investigate the impact of heat treatment and enzymatic hydrolysis on bioactive properties; in particular, angiotensin-converting enzyme-inhibitory (ACE-i) and antioxidant activities. The highest hydrolysis efficiency was observed when using pepsin. The smaller peptides with <3 kDa had better ACE-i and antioxidant activities in both WM and WML samples. Regarding antioxidant activity, the highest level was identified at a preheating temperature of 90 °C in the WM sample, and at preheating temperatures of 50 °C and without heating in the WML samples. In conclusion, heat treatment and enzymatic hydrolysis were found to be a positive impact on ACE-i and antioxidant activities under various conditions. Moreover, the proteins derived from WM and WML were rich in the sources of potential ACE-i and antioxidant peptides.

Experimental Investigation of the Effect of Superheated Liquid Fuel Injection on the Combustion Characteristics of Lean Premixed Flames

Abstract The effect of superheated liquid fuel injection on the performance and emissions of a single nozzle combustor was investigated. Combustion of the lean premixed flames was achieved using a combination of jet and swirl as a stabilization method. In a nonreactive setup, the optimum transition temperature of Jet A-1 fuel from liquid to superheated vaporized state was analyzed. In a subsequent reactive setup, a series of tests were conducted with the liquid fuel at low and elevated temperatures. The experiments were conducted at ambient pressure and various air and fuel preheat temperatures, axial swirlers, thermal powers, adiabatic flame temperatures, and flame tube diameters. Concentrations of nitric oxide (NOx) and carbon monoxide (CO) in the flue gas were measured. The operating conditions were systematically selected according to the design of experiments (DOE) method. The results showed that the adiabatic flame temperature caused the most significant change in combustion emissions and the position and shape of the reaction zone, while the superheated fuel injection had only a minor effect because the liquid fuel droplets were largely vaporized before entering the reaction zone through the integration of a swirler and a prefilmer. The use of the axial swirler and prefilmer allowed the combustor to operate in both spray and fully vaporized fuel conditions. As a result, very low emission concentrations of NOx (≈5 ppm) and CO (≈6 ppm) were achieved. The median flame length and height above the burner of the characterized flames showed competitive values of 32 mm and 50 mm, respectively. Lean blowout limits of less than 1500 K were achieved. Two different flame modes were observed during the experiments. By increasing the bulk velocity of the combustor, its hysteresis was resolved, resulting in stable and reliable flames with a wide low-NOx operating range.

The role of the microstructural changes during induction preheating on the HAZ liquation cracking susceptibility of Ni-based superalloy

This work presents the influence of high-frequency induction preheating (900, 1000, 1100 °C) on liquation crack formation in the René 108 Ni-based superalloy. The investigation was divided into two parts: (1) characterization of the material's microstructure after preheating and (2) determining the influence of preheating on liquation cracking during autogenous gas tungsten arc welding. During preheating, the dissolution of γ′ precipitates showed accelerated progress with increase in temperatures. This dissolution involved the continuous thinning of each precipitate, as well as more intricate mechanisms, such as splitting. The mean size of the secondary γ′ decreased from 0.32 to 0.26 μm. In the heat-affected zone (HAZ) induced by welding, constitutional liquation of mainly γ' precipitates, with a contribution of M23C6 carbides and M5B3 borides, was observed. The formation of a thin non-equilibrium liquid film along high-angle grain boundaries led to the crack initiation and their further propagation during cooling. The eutectic γ–γ' re-solidification products were visible on the crack edges independently of preheat temperature. Preheating at 900 °C decreased the length and amount of liquation cracks, while preheating at 1100 °C allowed to prevent them due to the liquid-healing effect.