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In this study confirmed the reduction effect of pollutant by applying Fi-EGR and FPI-EGR to hybrid combustion system realizing premixed flame and non-premxied flame at once. The results showed that NOx emission index decreased significantly in case of adopting EGR. Additionally, the hybrid combustion system with EGR resulted in a better performance compared to usual non-premixed combustion system such that it can reduce NO x emission at equivalent EGR ratios. Especially, in the case of 25% of FI-EGR ratio at hybrid combustion system that the ratio of non-premixed and premixed is 50 : 50, NOx emission index reduction rate was about 59% compared to NO x emission of non-premixed combustion system without EGR and in the case of 15% of FPI-EGR ratio at hybrid combustion system that the ratio of non-premixed and premixed is 70 : 30, NO x emission index reduction rate was about 48% compared to NO x emission of hybrid combustion system without EGR. Key words : Hybrid combustion, Exhaust gas recirculation (EGR), NO

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 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.

In this study, the CH4/air lean-rich combustion system with exhaust gas recirculation (EGR) was investigated to explore the potential for lowering pollutant emissions. To achieve this purpose, experiments of lean-rich combustion system with EGR were conducted to measure the changes in the characteristics of the pollutant emission and flame shape with various equivalence ratios and EGR rates. Here, this study was applied to the fuel distribution ratio of 3:1 for the formation of the lean and rich flames. Additionally, the results were compared with CH4/air lean premixed combustion system. The results show that flame shape of lean-rich combustion system was determined by lean and rich equivalence ratios (ΦL and ΦR) and stratified flame was formed with increasing ΦR. According to the pollutant emission characteristics based on experimental results, the NOx and CO emission index (EINOx and EICO) decreased with increasing EGR rate. Especially, in the range needed to form a stable flame, the reduction rates of EINOx and EICO were approximately 47% and 48% for an EGR rate of 25%, global equivalence ratio of 0.85 and ΦL of 0.80 compared with lean premixed combustion system (Φ = 0.78).

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.

The experiment was conducted to measure temperature and pressure around operating portable butane gas ranges with oversized cookwares. In this experiment, portable butane gas range with different safety equipment and two kinds of oversized cookware, each of which is made of aluminum alloy and rock, was used. As a result, temperature of the bottom of the butane and the pressure of butane barrel tend to aligned with each other. Through this result, it is reasonable that a safety criteria can be decided based on the temperature of the bottom of butane. Especially, portable butane gas ranges are safely conducted under the condition of the temperature is under 50 degree and pressure is under 500 kPa, respectively, at the bottom of the butane barrel.

We examined the characteristics of NO x emission for CH4/air non-premixed flames using the exhaust gas recirculation(EGR) methods, which are the air-induced EGR(AI-EGR) and fuel-induced EGR(FI-EGR) methods. Our experimental results show that the NO x emission index(EI nox ) decreased with increasing EGR ratio. In the range needed to form a stable flame, the reduction rate of EInox for the FI-EGR method was approximately 29% when the EGR ratio was 20%, and the reduction rate for the AI-EGR method was approximately 28% with 25% of the EGR ratio. According to the flame structure based on numerical results, high temperature regions for the FI-EGR method were narrower and lower than those for the AI-EGR method at the same EGR ratio. Furthermore, based on the experimental results for swirl flames, the reduction rate of EI nox for the FI-EGR method was approximately 49% with 15% of the EGR ratio, while the maximum reduction rate for AI-EGR method was approximately 45% with 25% of the EGR ratio. Consequently, we verified that the FI-EGR method was more effective than the AI-EGR method in reducing NO x emission for non-premixed flames with EGR. We expect that the results of this study will provide fundamental information relating to hybrid combustion systems, which can be used in the design of combustion systems in the future.

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.

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.

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.