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This study provides a preform design approach for uniform strain distribution in forging products based on a convolutional neural network (CNN). The appropriate preform design prevents underfill problems by improving the material flow inside forging dies and achieving a uniform strain distribution in forging products. The forging deformation process and mechanical properties are improved with a uniform strain distribution. The forging and strain distribution results are analyzed through rigid–plastic finite element forging simulations with different initial geometries. The simulation data are fed into the CNN model as an input array, from which the geometric characteristics are extracted by convolution operations with filters (weight array). The extracted features are linked to the considered initial shapes, which are input into the CNN model as an output array. The presented model derives the preform shape for a target forging with uniform strain distributions using the training weights. According to the training database, the proposed design method can be applied to different forging geometries without any iterations. By creating a number of low-level CNN (LC) models based on the training data, the efficiency of the preform design can be improved. The best preform among the derived preform candidates is chosen by comparing the forging results. Compared with previous studies using the same design criteria, the proposed model predicted the preform with a strain distribution improved by 16.3–38.4%.

Sheets’ buckling instability, also known as oil canning, is an issue that characterizes the resistance to denting in thin metal panels. The oil canning phenomenon is characterized by a depression in the metal sheet, caused by a local buckling, which is a critical design issue for aesthetic parts, such as automotive outer panels. Predicting the buckling instability during the design stage is not straightforward since the shape of the component might change several times before the part is sent to production and can actually be tested. To overcome this issue, this research presents a robust prediction model based on the convolutional neural network (CNN) to estimate the buckling instability of automotive sheet metal panels, based on the major, minor, and Gaussian surface curvatures. The training dataset for the CNN model was generated by implementing finite element analysis (FEA) of the outer panels of various commercial vehicles, for a total of twenty panels, and by considering different indentation locations on each panel. From the implemented simulation models the load-stroke curves were exported and utilized to determine the presence, or absence, of buckling instability and to determine its magnitude. Moreover, from the computer aided design (CAD) files of the relevant panels, the three considered curvatures on the tested indentation points were acquired as well. All the positions considered in the FEA analyses were backed up by industrial experiments on the relevant panels in their assembled position, allowing to validate their reliability. The combined correlation of curvatures and load-displacement curves allowed correlating the geometrical features that create the conditions for buckling instability to arise and was utilized to train the CNN algorithm, defined considering 13 convolution layers and 5 pooling layers. The trained CNN model was applied to another automotive frame, not used in the training process, and the prediction results were compared with experimental indentation tests. The overall accuracy of the CNN model was calculated to be 90.1%, representing the reliability of the proposed algorithm of predicting the severity of the buckling instability for automotive sheet metal panels.

Energy prediction and starvation have become an essential part of process planning for the XXI century manufacturing industry due to cost-saving policies and environmental regulations. To this aim, the research presented in this paper details how machine learning-based algorithms can be an effective way to predict and minimize the energy consumptions in the widely spread radial-axial ring rolling (RARR) process. To analyze this bulk metal forming process, 380 numerical simulations have been developed using the commercial SW Simufact Forming 15 and considering three largely utilized materials, the 42CrMo4 steel, the IN 718 superalloy, and the AA6082 aluminum alloy. To create the database for both multi-variable regression and machine learning models, ring outer diameters ranging from 650 mm to 2000 mm and various process conditions including different sets of tool speeds and initial temperatures have been considered. For the case of the multi-variable regression model, to account for all the cross-influences between all the parameters, a second-order function including 26 parameters has been developed, resulting in a reasonable average accuracy (94 %) but also in an impractical huge equation. On the other hand, the machine learning model based on the Gradient Boosting (GB) approach allows obtaining a similar accuracy (96 %) but its compact form allows a more practical utilization and its training can be expanded almost indefinitely, by adding more results from both numerical simulations and experiments. The proposed approach allows to quickly and precisely predict the energy consumption in the RARR process and can be extended to other manufacturing processes.

In this study, the combustion characteristics of low heating value gases (LHVGs) consisting of methane, propane, and nitrogen are investigated experimentally and numerically. For the experiment, a coaxial non-premixed jet-type burner is used to study the flame stability limit and flame length. In order to investigate the effects of the propane in the LHVG on the flame characteristics, a fuel consisting only of methane and nitrogen with the same heating value is also studied. For the numerical analysis, the 2D commercial software FLUENT with the reduced GRI 3.0 detailed reaction mechanism is used to study the flame structure. According to the results, the flame length of LHVGs declines with decreasing heating value for the same Reynolds number. Especially, the slope of the normalized flame according to Reynolds number decreases from 0.179 of methane to 0.111 of LHVG 6000. The flame stability limits decrease significantly when the heating value decreases, and no lifted flame is observed when the heating value of fuel is extremely low. Numerical results also show that flame length is shortened by up to 34% as the heating value decreases from methane to LHVG 6000. The flame thickness becomes narrower as the heating value decreases.

An experimental and computational investigation on the fundamental combustion characteristics of methane (CH4)-ammonia (NH3) blends is conducted to confirm their potential as a clean fuel with low carbon dioxide (CO2) emissions and determine their reasonable burning conditions, considering counterflow nonpremixed CH4 NH3/air flames. Extinction limits and structure of the nonpremixed CH4 NH3/air flames are measured and predicted. Results show that flames gradually become orange and the flame thickness increases with NH3 addition, compared with the pure CH4/air flames. Also, flames can sustain less NH3 at high strain rates. Compared with the pure CH4/air flames, CH4 NH3/air flames exhibit remarkable reduction of CO2 emissions with moderate reduction of combustion stability limits and no remarkable temperature drop in the flame, supporting the potential of CH4 NH3 blends as a clean fuel with low CO2 emissions. However, additional investigations for reducing the enhanced NOx emissions mainly via the fuel NOx mechanism with NH3 addition are needed. Finally, the quantitative discrepancy among the present measurements and predictions merits the development of a new reaction mechanism which is optimized for the reaction of CH4 NH3 fuel blends and air.

A computational investigation on the characteristics of nitrogen oxides (NOx) emissions for counterflow nonpremixed water (H2O)-laden methane (CH4)/air flames is conducted since a detailed observation of NOx formation for fuel having naturally high H2O vapor content is necessary. Using a detailed kinetic mechanism, NOx emissions are predicted for low and high flame strain rates (a), and the reaction paths are investigated. With H2O addition NOx emissions are reduced due to the chemical process as well as the thermal process such as diluting and cooling effects, the latter is more dominant than the former in NOx reduction, and the thermal and prompt NO mechanisms become less dominant for the chemical process. With increasing a, NOx emissions are also reduced, and it is mainly due to the thermal process. Reaction NH + O = NO + H in the prompt pathway is the major reaction step that results in reducing NO emissions via the chemical process due to H2O addition for both low- and high-stretched flames, though reaction N + OH = NO + H in the thermal pathway is also the major reaction step for the high-stretched flames. In addition, for the high-stretched flames the NO2 pathway in NO production becomes relatively more important with H2O addition.

Structure and extinction limits of counterflow nonpremixed water (H 2 O)-laden methane (CH 4 )/air flames at various pressures are computationally investigated to better understand combustion processes of fuel having naturally high H 2 O (vapor) content under elevated pressures. Using a detailed kinetic mechanism and a statistical narrow-band radiation model, the flame structure and extinction limits are predicted for elevated pressures and a wide range of flame strain rates and compared with those at atmospheric pressure. Results show that with increasing pressure the maximum flame temperature increases and the extinction limits are generally extended due to the reduced amount of dissociation and the enhanced radiation reabsorption of H 2 O, indicating that flames can sustain more H 2 O vapor at elevated pressure. The concentration of active radicals and the flame thickness decrease with increasing pressure. The observed flammable range of the H 2 O to CH 4 molar ratio at elevated pressures is comparable to that found in self-sustained combustion of CH 4 hydrates at atmospheric pressure, and the chemical effects of H 2 O addition on flame structure are insignificant. Elevated pressure enhances the formation of soot precursors such as acetylene (C 2 H 2 ), implying an opposite tendency from the water addition effects.

In this paper, multiaxial fatigue experiments on a hyperelastic rubber-like material made of polychloroprene rubber (CR) reinforced with tungsten nano-particles have been carried out on notched specimens and hourglass specimens, utilized for limiting dome height fatigue tests. Based on the uniaxial (Choi et al., 2020) and multiaxial fatigue experiments, a semi-empirical e-N fatigue model is proposed, allows accounting for both material anisotropy and complex stress states, showing an average error of 20.7%. Furthermore, six machine learning models have been employed for the fatigue life prediction and shown that the Deep Neural Network is the most accurate, with an average error equal to 14.3%.

The effects of the number of heat exchanger modules on thermal characteristics were experimentally studied in a premixed combustion system with a cross-flow staggered-tube heat exchanger. The various heat exchanger modules, from 4 to 8, combined with a premixed burner were tested to investigate the performance of the heat exchanger through the surface area of the heat exchanger at various equivalence ratios. Additionally, the performance of the heat exchanger was analyzed by applying entropy generation theory to the heat exchanger system. As a result, although the heat transfer rate increases with the increase of the equivalence ratio, the NOx and CO concentrations also increase due to the increasing flame temperature. In addition, the entropy generation increases with an increase of the equivalence ratio. Furthermore, the heat transfer rate and the effectiveness are increased with the increase of the number of the heat exchanger modules. Also, the effectiveness is sharply increased when the number of the heat exchanger modules is increased from 4 to 5. Consequently, the optimal operating conditions regarding pollutant emission, effectiveness and entropy generation in this experimental range are 0.85 for the equivalence ratio and 8 for the number of heat exchanger modules.

In order to better understand combustion processes when large amounts of water (H2O) naturally incorporate into the fuel stream, e.g., the combustion of methane (CH4) hydrates and H2O/fuel emulsions, the extinction limits and structure of counterflow nonpremixed flames of mixtures of H2O vapor and CH4 and air were identified experimentally and computationally. With H2O vapor addition, the maximum flame temperature was experimentally determined, while the flame structure and extinction limits were computed using a detailed kinetic mechanism. Predicted and measured tendencies of the maximum flame temperature for various conditions exhibit encouraging agreement and thus justify using the computational results to analyze the detailed flame structure and determine the extinction limits. The extinction limits (in terms of the H2O to CH4 molar ratio) are reduced with increasing strain rates, implying that flames can sustain more H2O vapor at low strain rates. Thus, the maximum flame temperature at the extinction limits increases with increasing strain rates because there is less H2O to act as a thermal sink. The observed flammable range of the H2O to CH4 molar ratio is comparable to that found in self-sustained combustion of CH4 hydrates. The chemical effects of H2O addition on flame structure are insignificant.

This paper presents an objective evaluation method for the perceived quality of a car horn sound based on a psychoacoustic metric and subjective test. A new psychoacoustic metric called the “spectrum decay” (SD) is developed to evaluate a luxury timbre in the sound quality of the horn. The SD slope is found from spectrum analysis of the interior sounds produced by car horns. The interior sounds are measured and recorded from ten sampled passenger cars. The measured horn sounds are also evaluated subjectively by 41 subjects to extract the “luxury” factor. To validate the SD slope, eight synthetic sounds with a variety of SD slopes are designed. The synthetic sounds are also subjectively evaluated by the same 41 subjects. Two sound quality indexes for car horn sound are developed based on the correlation between the SD slope and subjective ratings of the synthetic sounds. One index uses a linear relationship between the SD slope and subjective rating but has a limit to its utility (i.e., the SD slope should be less than 10). The sound quality indexes are applied to the estimation of sound quality of horn sounds of ten passenger cars measured inside the cars. Correlations between the estimated subjective rating and subjective ratings evaluated by the subjects are sufficient (linear index: R = 0.84 p < 0.004, nonlinear index: R = 0.91, p < 0.001) for validation of the sound quality index.

In this study, the characteristics of NOx emissions for CH4/air non-premixed flames using EGR (exhaust gas recirculation) methods were investigated using the AI-EGR (air-induced-EGR) and FI-EGR (fuel-induced-EGR) methods. For the fundamental experiment, coaxial non-premixed flames were verified using the non-premixed mode in a changeable EGR hybrid combustion system. For the numerical simulation, the 2-D commercial FLUENT program was used to verify the distributions of the flame temperature and mole fraction of the NO emissions. Additionally, the swirling non-premixed flames were tested to investigate a practical combustion system. Based on experimental results, the reduction rates of EI NO X for the FI-EGR method and the AI-EGR were approximately 29% and 28% for an EGR ratio of 20% and 25%, respectively, which represented the maximum range needed to generate a stable flame. Based on numerical results, the FI-EGR method was determined to be more effective than the AI-EGR method in reducing NOx emission because the high temperature region and the OH distribution region of the FI-EGR method were narrower. According to the results from the swirling flames, the reduction rates of EI NO X for the FI-EGR method and the AI-EGR were approximately 49% and 45% for an EGR ratio of 15% and 25%, respectively.

The laminar burning velocity of syngas-air premixed flames was measured with various equivalence ratios from 0.5 to 5.0 and a mole fraction of H2 from 0.05 to 0.75. The laminar burning velocity was experimentally determined using a Bunsen flame according to the cone angle and surface area methods. A premixed code with a USC-II detailed reaction mechanism was used for the numerical calculations to predict the laminar burning velocity and to examine the relationship between the burning velocity enhancement and the hydrogen- related reactions. The results indicate that an appropriate method for the measurement of laminar burning velocity is necessary in the H2/CO/air syngas premixed flame. In addition, the burning velocity linearly increased with the increase of the H2 mole fraction in the syngas mixture, although the burning velocity of H2 was 10 times larger than that of CO. This result is attributed to the rapid production of H-radicals at the early stage of combustion. Furthermore, the predicted mole fractions of H and OH radicals increased with the increase of H2 mole fraction for a lean syngas mixture. However, the mole fraction of OH radicals, an indicator of heat release rate, decreased for rich syngas mixture, resulting in a reduction of the laminar burning velocity, even with an increase of the H2 mole fraction.

The present study demonstrates the potential of hydrogen (H2)-doped ammonia (NH3) as a carbon-free fuel. The extinction limits, flame temperature and morphology of the counterflow nonpremixed NH3–H2/air flames at elevated temperatures and normal pressure are experimentally determined. Also, the detailed flame structure and the extinction limits are computed using a detailed kinetic mechanism. Results show that the blow-off limits, the concentration of radicals H, OH and O and the maximum flame temperature are enhanced with H2 substitution in NH3/air flames. This supports the potential of H2 as an additive for improving the reactivity and ignition of nonpremixed NH3/air flames and thus the potential of H2-doped NH3 as a carbon-free fuel. Meanwhile, the extinction limits (in terms of the mole fraction of NH3 in the fuel gas) and the maximum flame temperature are reduced with increasing strain rates, indicating that flames can sustain more NH3 at low strain rates. Also, it is observed that the blow-off limits and the maximum flame temperature are enhanced with increasing air temperature. Measured and predicted tendencies of the extinction limits and temperature for various conditions show encouraging agreement, but quantitative discrepancies among the measurements and predictions merit additional consideration in boundary condition modeling and the reaction mechanism.

This study presents fundamental research on the development of a new boiler that is expected to have a higher efficiency and lower emissions than existing boilers. The thermodynamic efficiency of exhaust gas recirculation-condensed water recirculation-waste heat recovery condensing boilers (EGR-CWR-WHR CB) was calculated using thermodynamic analysis and was compared with other boilers. The results show the possibility of obtaining a high efficiency when the temperature of the exhaust gas is controlled within 50–60 °C because water in the exhaust gas is condensed within this temperature range. In addition, the enthalpy emitted by the exhaust gas for the new boiler is smaller because the amount of condensed water is increased by the high dew-point temperature and the low exhaust gas temperature. Thus, the new boiler can obtain a higher efficiency than can older boilers. The efficiency of the EGR-CWR-WHR CB proposed in this study is 93.91%, which is 7.04% higher than that of existing CB that is currently used frequently.

This paper presents a novel approach to apply the physiological signal of the human brain to the sound quality evaluation of automotive sound. In the previous work, psychoacoustic metrics were applied to the sound quality evaluation of automotive sound. Loudness among psychoacoustic metrics is used for one of major sound metrics for the objective evaluation of the sound quality of the acceleration sound inside a car. Subjective evaluation of the sound quality of the acceleration sound shows different results depending on the two different groups of participants. One group liked powerful sound when a car is accelerated: the other group liked the refine sound. Loudness of the acceleration sound is not correlated with the subjective rating of the former group whilst it is correlated with that of the latter group. This evaluation suggests that for the people who like the powerful acceleration sound, it needs to find the sound metric for the objective evaluation of the sound quality of the acceleration sound. In this paper, a driver’s brain signal is measured using electroencephalography (EEG) when a driver hears the acceleration sound of passenger cars. The signal is analyzed to obtain the relationship between brain signals and human perception. According to these results, the alpha wave correlates to the human perception of powerful sound quality of passenger cars. This interesting relationship can be used for objective evaluation of passenger car sounds.

The boiler of a premixed combustion system with EGR (exhaust gas recirculation) is investigated to explore the potential for increasing thermal efficiency and lowering pollutant emissions. To achieve this purpose, a thermodynamic analysis is performed to predict the effect of EGR on the thermodynamic efficiency for various equivalence ratios. Experiments of a preheated air condensing boiler with EGR were conducted to measure the changes in the thermal efficiency and the characteristics of the pollutant emission. Finally, a 1-D premixed code was calculated to understand the effect of the EGR method on the NO reduction mechanism. The results of the thermodynamic analysis show that the thermodynamic efficiency is not changed because the temperature and the amount of the exhaust gas are unchanged, even though the EGR method is implemented in the system. However, when the EGR method is used with an equivalence ratio near 1.00, it is experimentally verified that the thermal efficiency increases and the NO x concentration decreases. Based on the results from numerical calculations, it is shown that the NO production rates of N + O 2 ↔ NO + O and N + OH ↔ NO + H are remarkably changed due to the decrease in the flame temperature and the NO mole fraction is decreased.

The combustion stability (extinction) limits and nitrogen oxide (NO x ) emissions of nonpremixed ammonia (NH 3 )–hydrogen (H 2 )–air flames at normal temperature and pressure are studied to evaluate the potential of partial NH 3 substitution for improving the safety of H 2 use and to provide a database for the nonpremixed NH 3 -substituted H 2 –air flames. Considering coflow nonpremixed NH 3 –H 2 –air flames for a wide range of fuel and coflow air injection velocities ( V fuel and V coflow ) and the extent of NH 3 substitution, the effects of NH 3 substitution on the stability limits and NO x emissions of the NH 3 –H 2 –air flames are experimentally determined, while the nonpremixed NH 3 –H 2 –air flame structure is computationally predicted using a detailed reaction mechanism. Results show significant reduction in the stability limits and unremarkable increase in the NO x emission index for enhanced NH 3 substitution, supporting the potential of NH 3 as an effective, carbon-free additive in nonpremixed H 2 –air flames. With increasing V coflow the NO x emission index decreases, while with increasing V fuel it decreases and then increases due to the recirculation of burned gas and the reduced radiant heat losses, respectively. Given V coflow / V fuel the flame length increases with enhanced NH 3 substitution since more air is needed for reaction stoichiometry. The predicted flame structure shows that NH 3 is consumed more upstream than H 2 due to the difference between their diffusivities in air.

In order to estimate the combustion characteristics and the gas interchangeability for natural gas with various compositions per each production area, equivalent gas are using to replace natural gas. It is known that an equivalent gas has the same the heating value, the compression factor, the relative density, CO emission and the burning velocity as the original natural gas. However, it is not reported that the flame shape and thermal efficiency and NOx emission by real gas appliance. In this study, equivalent gas was examined the validation to replace natural gas. The CO emission the burning velocity and the flame temperature were reconfirmed, and the flame shape, the NOx emission and the thermal efficiency were numerically and experimentally investigated. As results, there was not a large difference between natural gas and equivalent gas. This result demonstrated that there was no problem using equivalent gas to replace natural gas.

This study investigated the characteristics of heat transfer and pressure drop for cross-flow heat exchanger of premixed combustion system. The premixed burner was in front of a heat exchanger, and the number of heat exchanger modules was changed to investigate the characteristics of NOx and CO emissions with various equivalence ratios. In addition, the effectiveness, entropy generation and pressure drop were calculated by various number of heat exchanger modules and the performance of heat exchanger was analyzed by the exergy loss.

This research was conducted to experimentally compare the emission characteristics and thermal efficiency of porous-media types of burners and to determine which types to use with a condensing boiler to be developed later. Three types of porous-media burners; metal fiber (MF), ceramic (CM) and stainless steel fin (SF) were used with a commercial heat exchanger and tested for various equivalence ratios and burner capacities. The MF burner had the lowest CO emissions of the three burner types, and the SF burner had the highest CO emissions. However, The MF burner had the highest NO x emission and thermal efficiency, and the SF burner had the lowest NO x emissions and thermal efficiency. In other words, the smaller the burner porosity was (porosity: SF x and CO emissions with respect to the Korean industrial standard and European norms, the most appropriate burner type for the condensing boiler is the MF burner. The optimal operating equivalence ratio was 0.80 for the range of experimental factors considered in this research.

In this study, an investigation into the gas interchangeability and combustion characteristics of various gas compositions for domestic appliances was performed. In order to suggest the appropriateness of gas interchangeability using the specific gravity (SG) and the Wobbe index (WI) values, combustion characteristics included incomplete combustion and flame lifting were measured and observed for the upper and lower limits using the gas-oven as a domestic partial-premixed type appliance and the condensing boiler as a domestic premixed type appliance. The flame was stable, and the CO and NOx concentrations increased when the WI and SG values increased. Specifically, the behavior of the flame lifting changed between WI values of 52.0 MJ/Nm3 and 53.0 MJ/Nm3. The CO and NOx concentrations of the reference gas were approximately 173 ppm and 74 ppm for the gas-oven and 175 ppm and 35 ppm for the boiler, respectively. Consequently, a WI value of 53.0 MJ/Nm3 can be considered the flame lifting limit as the lower limit for gas interchangeability. For the upper limit of gas interchangeability, the CO and NOx concentrations varied significantly with the type of burner.

This study was experimentally investigated NOx and CO emissions characteristics with various equivalence ratios using premixed type of burner installed small heat exchanger. The effectiveness of heat exchanger and the entropy generation number were also calculated. As results, the heat transfer rate increases with increasing equivalence ratio due to increase the flame temperature. According to the emission characteristics and the effectiveness, the optimal operating equivalence ratio is 0.75 in the range of this experiment. Consequently, the area of the heat exchanger should be increased to reduce the entropy generation number and to increase the effectiveness.

The need for composites has been increasing in various industries because composites have good mechanical properties for their weight and superior stiffness and strength. The composites addressed in this study were multi-pore aluminum foam with a specific gravity of 1/10 composed of solid aluminum metal. This composite has excellent impact energy-absorption capability. In this study, impact tests on an aluminum foam core sandwich composite with a porous core were conducted to examine its mechanical properties. The specimen was a sandwich structure with an aluminum foam core, and different impact energies, such as 50J, 70J, and 100J, were applied to the specimen. Consequently, a maximum load of 5.5 kN occurred when the striker penetrated the upper face sheet in all experiments. The maximum load occurred at 4.2 ms for 50J, 3.5 ms for 70J, and 3.0 ms for 100J, indicating that the greater the impact energy was, the shorter the time was until the maximum load. After the maximum load occurred, that is, after the penetration of the upper face sheet, the striker penetrated 10 mm further, causing the core to be damaged in the 50J test, while the lower face sheet remained intact. In the 70J test, the striker penetrated the core and caused damage to the upper face sheet at 10 ms. Finally, in the 100J test, the striker penetrated both the upper face sheet and core and even the lower face sheet at 10 ms. Given the result above, the maximum load occurred when the striker penetrated the upper face sheet and the sandwich composite with aluminum foam core; the load then gradually decreased and then rapidly increased when the striker reached the lower face sheet, and the maximum load lasted slightly longer than the time required for the upper face sheet to be penetrated.

In this research, a boiler in a premixed combustion system used to achieve exhaust gas recirculation was investigated as a way to achieve high thermal efficiencies and low pollutant emissions. The effects of various exhaust gas recirculation (EGR) ratios, equivalence ratios and boiler capacities on thermal efficiency, NOx and CO emissions and the flame behavior on the burner surface were examined both experimentally and numerically. The results of the experiments showed that when EGR was used, the NOx and CO concentrations decreased and the thermal efficiency increased. In the case of a 15% EGR ratio at an equivalence ratio of 0.90, NOx concentrations were found to be smaller than for the current operating condition of the boiler, and the thermal efficiency was approximately 4.7% higher. However, unlike NOx concentrations, although the EGR ratio was increased to 20% at an equivalence ratio of 0.90, the CO concentration was higher than in the current operating condition of the boiler. From the viewpoint of burner safety, the red glow on the burner surface was noticeably reduced when EGR was used. These results confirmed that the EGR method is advantageous from the standpoint of reducing emission concentrations and ensuring burner safety.

The purpose of this study is investigated on the combustion and the thermal characteristics of porous media burners which are many using for a condensing boiler recently. In addition, results of this study will be used the fundamental information to decide the burner type which will be applied to the future development of EGR(Exhaust gas recirculation) condensing boiler. Two flat type of burners made of a the metal fiber(MF) and the ceramic(CM) were selected and examined, experimentally. As experimental results, the emitted CO concentration of CM was higher than that of MF. However, the NO concentration of MF was higher than that of CM. The efficiencies of both burners were increased as increasing the burner capacity. While the efficiency of MF was higher than that of CM, regardless of the burner capacity. In the experimental range, MF is appropriated for the burner material and 0.8 of equivalence ratio is an optimal operation condition, regarding of the proportional control, the thermal efficiency and emitted NO and CO concentration based on the regulations of KS B standard and EN 677 standard.

In this study, it was experimentally investigated the effect of the clearances distance between the rod and the impinging plate on characteristics of the thermal flow. For the heat transfer enhancement of wall jet region, the right triangle and the square rods were arranged in front of the impinging plate with various clearance distances. As results, the heat transfer enhancement rate of potential core region at H/B

The effect of the distance between the burner and the heat exchanger on the heat transfer characteristics and NO x and CO emission characteristics in a compact combustion system was studied. The premixed burner was installed in front of a heat exchanger, and the distance between the burner and the heat exchanger was varied from 30 mm to 50 mm to experimentally investigate the effect of distance for the counter flow and the parallel flow conditions. Distances in the type A, type B and type C heat exchangers were 30 mm, 40 mm and 50 mm, respectively. The results showed that NO x concentration increased at the same equivalence ratio for both flow conditions as the distance between the burner and the heat exchanger increased. On the other hand, CO emission increased for both flow conditions due to the quenching effect as the distance between the burner and the heat exchanger decreased. In the experimental range, the optimal equivalence ratio of heat exchanger type A was 0.75 to minimize pollutant emission. At this condition, the NO x and CO emissions were 32.3 ppm and 85.6 ppm, respectively, and the effectiveness was 0.797.

The combustion stability limits and nitrogen oxide (NOx) emissions of burner-stabilized premixed flames of ammonia (NH3)-substituted hydrogen (H2)–air mixtures at normal temperature and pressure are studied to evaluate the potential of partial NH3 substitution to improve the safety of H2 use. The effects of NH3 substitution, nitrogen (N2) coflow and mixture injection velocity on the stability limits and NOx emissions of NH3–H2–air flames are experimentally determined. Results show a reduction of stability limits with NH3 substitution and coflow, supporting the potential of NH3 as a carbon-free, green additive in H2–air flames and indicating a different tendency from that for no coflow condition. The NOx emission index is almost constant even with enhanced NH3 substitution, though the absolute value of NOx emissions increases in general. At fuel-rich conditions, the NOx emission index decreases with increasing mixture injection velocity and the existence of coflow. The thermal deNOx process in the post-flame region is involved in reducing NOx emissions for the fuel-rich flames.

In this study, the heat transfer characteristics and NOx and CO emissions of a heat exchanger were investigated using a premixed burner. The experiments involved changing the distance between the burner and heat exchanger to 30, 40, and 50 mm with various equivalence ratios. The results showed that the NOx and CO emissions increased as the equivalence ratio was increased because the flame temperature increased, regardless of the distance between the burner and heat exchanger. In particular, the CO emission increased significantly as the distance between the burner and heat exchanger was decreased. The optimal equivalence ratio for the A-type heat exchanger (distance between the burner and heat exchanger: 30 cm) was 0.7 in the experimental range. In this case, the CO and NOx emissions were 94.5 ppm and 11.2 ppm, respectively, and the efficiency was 84.1%.

The potential of partial ammonia substitution to improve the safety of hydrogen use was evaluated computationally, using counterflow nonpremixed ammonia/hydrogen/air flames at normal temperature and pressure. The ammonia-substituted hydrogen/air flames were considered using a recent kinetic mechanism and a statistical narrow-band radiation model for a wide range of flame strain rates and the extent of ammonia substitution. The effects of ammonia substitution on the extinction limits and structure, including nitrogen oxide (NOx) and nitrous oxide (N2O) emissions, of nonpremixed hydrogen/air flames were investigated. Results show reduction of the high-stretch extinction (i.e., blow-off) limits, the maximum flame temperature and the concentration of light radicals (e.g., H and OH) with ammonia substitution in hydrogen/air flames, supporting the potential of ammonia as a carbon-free, clean additive for improving the safety of hydrogen use in nonpremixed hydrogen/air flames. For high-stretched flames, however, NOx and N2O emissions substantially increase with ammonia substitution even though ammonia substitution reduces flame temperature, implying that chemical effects (rather than thermal effects) of ammonia substitution on flame structure are dominant. Radiation effects on the extinction limits and flame structure are not remarkable particularly for high-stretched flames.

In this research, design factors for a heat exchanger and boiler were investigated using a simplified model of a heat exchanger and pilot condensing boiler, respectively. Specifications of each heat exchanger component (e.g., upper heat exchanger (UHE) and lower heat exchanger (LHE); coil heat exchanger (CHE); baffles) were investigated using a model apparatus, and the comprehensive performance of the pilot gas boiler was examined experimentally. The heating efficiency of the boiler developed was about 90% when using the optimal designed heat exchangers. Compared to a conventional Bunsen-type boiler, the heating efficiency was improved about 10%. Additionally, NO x and CO emissions were about 30 ppm and 160 ppm, respectively, based on a 0% O 2 basis at an equivalence ratio of 0.70, which is an appropriate operating condition. However, the pollutant emission of the boiler developed is satisfactory considering the emission performance of a condensing boiler, even though CO emission must be reduced.

This study experimentally examined a cylindrical multi-hole premixed burner for its potential use for a condensing gas boiler, which produces less NOx emissions and performs better. In this study, the hole diameters and the arrangement of a multi-hole burner were investigated using a flat burner model. The combustion characteristics for the flame stability as well as the NOx and CO emissions were examined using a cylindrical burner. For an optimal operating condition, the equivalence ratio for the cylindrical burner was between 0.70 and 0.75. For this condition, the turn-down ratio was 3:1 or higher, which was suitable for appropriate control of the boiler operation. The NOx and CO emissions were less than 40 ppm and less than 30 ppm, respectively, for a 0% O2 basis. The LPG and LNG were able to be used in this type of burner because there was no phenomenal difference in the stable combustion region between them.

The effects of CO-tubes insertion on NO x (nitrogen oxides) and CO emissions from a compact heat exchanger were numerically simulated using a quasi one-dimensional premixed flame model, and the results were compared to experiments with a laboratory-scale heat exchanger and a commercial compact condensing boiler with a heat exchanger installed. The “CO-tubes” means that pre-cooling tubes were inserted between the burner and the main heat exchanger to reduce CO concentration. In the numerical results, the outlet concentration of NO increased as the distance between the burner and the CO-tubes was increased up to 3 cm. However, NO concentration was little affected by the CO-tubes when the distance was greater than 3 cm. Additionally, the concentration of CO reached a minimum at the distance of 3 cm. CO concentration increased when the distance from the burner to the CO-tubes was increased or decreased between 2 cm and 3 cm. These simulated results showed good agreement with the experimental results using a laboratory-scale heat exchanger. However, the maximum and minimum distances for NO and CO concentrations were different. When the CO-tubes were subsequently applied in a working commercial boiler, CO concentration was dramatically reduced by the CO-tubes and NO concentration was also slightly decreased.

The estimation method of the interchangeability in a partial premixed appliance about various compositions of natural gases using equivalent gases, experimentally. The results of the experiment in which equivalent gases were used compared with those obtained in experiments in which natural gases were used; Images of flames, lift-off limits, CO emissions, and incomplete combustion indices in KS standard for the domestic gas range were considered. From the comparison, it was observed that the length and color of the flame of the equivalent gases were almost the same as those of imported natural gases. Further, in the case of gases with Wobbe indices greater than 51 MJ/m

The combustion characteristics of a cyclone jet hybrid combustor using a combination of swirling premixed and jet diffusion flames were experimentally investigated to achieve high flame stability and low pollutant emissions. Two kinds of combustion modes were examined: the diffusion combustion (DC) mode, which consists of swirling air flow and jet diffusion flame, and the hybrid combustion (HC) mode, which consists of swirling premixed and jet diffusion flames. In the HC mode, the effects of fuel nozzle geometry on fuel–air mixing were investigated in terms of flame stability and pollutant emissions. The results showed that the HC mode can significantly reduce soot, CO, and NOx emissions in a stable flame region compared to the DC mode. However, CO emission in the HC mode increases drastically when overall equivalence ratios drop below 0.75. By modifying the fuel nozzle for the jet diffusion flame, it was found that increases in fuel–air mixing using the improved nozzle provide a stable flame region approximately twice as wide as that of the fuel nozzle using a single hole. In addition, a multi-hole fuel nozzle shows a NOx reduction of 55% compared to that of the DC mode.

The effects of turbulence intensity of an ambient air flow on flame structure and NO x formation were investigated experimentally in hydrogen/air nonpremixed flames. To identify the effect of sole turbulence intensity, a new combustor with a turbulence generator, which can increase the turbulence intensity of air stream under the condition of an identical mean velocity, was adopted. The experiment was conducted with and without the turbulence generator for the two fuel cases of H 2 : N 2 = 1 : 1 and H 2 : N 2 = 1 : 2 , by volume. As a result, as the turbulence intensity increased, the reducing effect of NO x was more significant in the condition of a higher flame temperature. In addition, the conversion ratio from NO to NO 2 increased. Two major factors can reduce the production of NO x as the turbulence intensity increases: significant NO x reduction corresponding to about 70% was found in the upstream region due to the increase in the strain rate effect and in the downstream region due to the rapid mixing effect. From these results, it is possible to conclude that adjustment of turbulence intensity is a very useful method to reduce NO x emission in hydrogen nonpremixed jet flames.

In this paper, a unidirectional carbon-fiber composite is both experimentally and numerically investigated to study the nonlinear material behavior of impacted double cantilever beam (DCB) specimens. For the impact analysis, the load and the displacement applied from pin onto end block as well as the crack energy release rate are measured and compared with the finite element analysis results. The energy release rate is a critical measure of the resistance to crack propagation, which can be estimated by the force and displacement at the crack tip. It is found that the energy release rate measured from impact tests on the specimens is well predicted by the finite element model suggested in this study.