• Applied Chemistry for Engineering
• /
• v.18 no.3
• /
• pp.255-261
• /
• 2007

The catalytic behavior of the manganese oxides was studied for the selective catalytic reduction with ammonia at a low temperature condition under $200^{\circ}C$. Outlet unreacted ammonia increases with decreasing temperature and increasing $NH_3/NOx$ mole ratio, however $NO_2$ shows an opposite result. $NO_2$ is generated by the adsorption of NO on the catalyst and the following oxidization to nitrates. Unreacted NH3 slip is not observed even at the $NH_3/NOx$ feed ratio above 1.0 due to the reaction between formed nitrates on the catalyst and adsorbed ammonia. The addition of Zr increases $NO_2$ generation, whereas the addition of CeO2 on the catalyst decreases $NO_2$ generation. Furthermore, the additon of the metal oxide induce DeNOx efficiency to reduce.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.6
• /
• pp.587-597
• /
• 2010

Air-staged combustion is known to be one of the techniques of NOx reduction. The objective of this study is to determine the optimal ratio of air flow distributed for CCOFA and SOFA; at this optimal ratio, the combustion and exhaust emission characteristics of a pulverized coal-fired boiler are maintained at a satisfactory level. A numerical investigation was performed at various airflow ratios of 16.7/83.3%, 25/75%, 50/50%, 75/25%, and 83.3/16.7%. An inert gas was considered as a substitute for air to isolate the effects of the cooling process and chemical reaction on NOx reduction; during NOx reduction in air-staged combustion, both the effects typically occur simultaneously. The results of our study show that the optimum condition, under which the maximum NOx reduction and highest boiler efficiency can be obtained, corresponds to the equal splitting of the over-fire air between CCOFA and SOFA.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.1
• /
• pp.32-38
• /
• 2003

Staged combustion, such as air- and fuel-staging, is a relatively well-known technique fur reduction of NOx emission and used in combination with other techniques nowadays. However, the design variables are still selected depending upon operating conditions. There are many variables tested to investigate the NOx emission characteristics fur changing of fuel or air velocity, swirl intensity, and staging ratio of air and fuel in multi-staged burner. In air-staging case, the fuel-rich condition of the primary combustion zone is very helpful to reduce NOx emission and its range is known to be restricted by the increase of carbon monoxide. However, in many cases carbon monoxide level is not too high to be restricted operating condition. So we tried to expand the equivalence ratio range to the richer condition in the primary combustion zone and certificate the function of each burner component and its contribution to the overall NOx production.

• Journal of Mechanical Science and Technology
• /
• v.16 no.7
• /
• pp.950-958
• /
• 2002

The combustion characteristics of a low NOx burner using reburning technology have been experimentally studied. The return burner usually has three distinct reaction zones which include the primary combustion zone, the reburn zone and the burnout zone by provided secondary air. NOx is mainly produced in a primary combustion zone and a certain portion of NOx can be converted to nitrogen in the rebury zone. In the burnout zone, the unburned mixtures are completely oxidated by supplying secondary air. Liquefied Petroleum Gas (LPG) was used as main and reburn fuels. The experimental parameters investigated involve the main/reburn fuel ratio, the primary/secondary air ratio, and the injection location of rebury fuel and secondary air. When the amount of return fuel reaches to the 20-30% of the total fuel used, the overall NO reduction of 50% is achieved. The secondary air is injected by two different ways including vertical and parallel injection. The injector of secondary air is located at the downstream region of furnace for a vertical-injection mode, which is also placed at the inlet primary-air injection region for a parallel-injection mode. In case of the vertical injection of the secondary air flow, the NOx formation of stoichiometric condition at a primary combustion zone is nearly independent of the rebury conditions (locations, fuel/air ratios) while the NOx emission of the fuel-lean condition is considerably influenced by the reburn conditions. In case of the parallel injection of the secondary air, the NOx emission is sensitive to the air ratio rather than the fuel ratio and the reburning process often coupled with the multiple air-staging and fuel-staging combustion processes.

• Journal of Power System Engineering
• /
• v.6 no.1
• /
• pp.27-35
• /
• 2002

In this paper, the effect of oxygen component in fuel on the exhaust emissions has been investigated for direct injection diesel engine. It is tested to estimate change of engine performance and exhaust emission characteristics for the commercial diesel fuel and oxygenate blended fuel which has four kinds of mixed ratio. And, the effects of exhaust gas recirculation(EGR) on the characteristics of NOx emission and brake specific fuel consumption rate have been investigated. Dimethyl carbonate(DMC) contains oxygen component 53.3% in itself, and it is a kind of effective oxygenated fuel of carbonate group that the smoke emission of DMC is reduced remarkably in comparison with commercial diesel fuel, that is, it can supply oxygen component sufficiently at higher loads and speeds in diesel engine. It was found that simultaneous reduction of smoke and NOx was achieved with oxygenated fuel and EGR method.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.2
• /
• pp.122-128
• /
• 2010

To meet the NOx limit without a penalty of fuel consumption, urea-SCR system is currently regarded as promising NOx reduction technology for diesel engines. SCR system has to achieve maximal NOx conversion in combination with minimal $NH_3$ slip. In this study, the performance characteristics of urea-SCR system with open loop control were assessed in the European Transient Cycle(ETC) for heavy duty diesel engine. The SCR inlet temperaure varied in the range of 200 to $340^{\circ}C$ in the ETC cycle. Open loop control calculated the urea flow rate based on the NOx and NSR map which gave for each combination of SCR inlet temperature and space velocity the normalized $NH_3$ to NOx stoichiometric ratio which resulted in a steady-state $NH_3$ slip of 20ppm. During the ETC cycle, the open loop control with the optimized NSR offset achieved NOx reduction of 80% while keeping the average $NH_3$ slip below 10ppm and maximum 20ppm. It was also found that NOx sensor was cross-sensitive to $NH_3$ and a control strategy for cross-sensitivity compensation was required in order to use a NOx sensor as feedback device.

• Journal of Power System Engineering
• /
• v.17 no.6
• /
• pp.149-155
• /
• 2013

Since bio-diesel oil has a merit that it satisfies both demand of substitution for fossil fuel and reduction in carbon dioxide emission, it is widely used in diesel engines by blending in gas oil in small quantity. It is needed to reduce in NOx emission in some way or others if blending ratio of bio-diesel oil is going to increase, because it is demerit that bio-diesel oil emits more NOx emission than gas oil. In this study, it was accomplished to optimize 3 factors what effect on NOx emission as blending ratio of bio-diesel oil, injection timing and common rail pressure with an introduction of a design of experiments, in order to minimize a number of tests. It was cleared that to introduce the design of experiments was very available in NOx optimization.

• Journal of the Korean Society of Combustion
• /
• v.12 no.4
• /
• pp.14-21
• /
• 2007

In order to enhance combustion efficiency, oxygen-enriched combustion is used by increasing the oxygen ratio in the oxidizer. However, since the flame temperature increases, NOx formation in the furnace seriously increases for low oxygen enrichment ratio. In this case, reburning is a useful technology for reducing nitric oxide. In this research, experimental studies have been conducted to evaluate the hybrid effects of reburning/selective non-catalytic reaction (SNCR) and reburning/air staging on NOx formation and also to examine heat transfer characteristics in various oxygen-enriched LPG flames. Experiments were performed in flames stabilized by a co-flow swirl burner, which were mounted at the bottom of the furnace. Tests were conducted using LPG gas as main fuel and also as reburn fuel. The paper reported data on flue gas emissions, temperature distribution in furnace and various heat fluxes at the wall for a wide range of experimental conditions. Overall temperature in the furnace, heat fluxes to the wall and NOx generation were observed to increase by low level oxygen-enriched combustion, but due to its hybrid effects of reburning, SNCR and Air staging, NOx concentration in the exhaust have decreased considerably.

• Journal of Environmental Science International
• /
• v.22 no.11
• /
• pp.1481-1498
• /
• 2013

The SCR (selective catalytic reduction) system is highly-effective technique for NOx reduction from exhaust gases. In this study, the effects of the direction and size of nozzle and the ammonia injection concentration on the performance of SCR system are analyzed by using the computational fluid dynamics method. When the nozzle is arranged in zigzaged direction which is normal to exhausted gas flow, it is shown that the uniformity of gas flow and the NH3/NO molar ratio is improved remarkably. With the change of the ammonia injection concentration from 0.2 vol%(wet) to 1.0 vol%(wet), the uniformity of gas flow shows a good results. As the size of nozzle diameter changes from 6 mm to 12 mm, the uniformity of gas flow is maintained well. It is shown that the uniformity of the $NH_3/NO$ molar ratio becomes better with decreasing the ammonia injection concentration and the size of nozzle diameter.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.22 no.7
• /
• pp.84-89
• /
• 2014

Not only the emission regulation of on-road vehicle engine, but also emission regulation of off-road engine have been reinforced. It is the reason of wide application of emission reduction technology for off-road engines. In this study, optimization of engine parameters (Injector hole number, Injection timing and EGR rate) for reduction of NOx and smoke emissions were conducted by using the analysis of sensitivity and S/N ratio of Taguchi method(DOE). As results, this paper shows optimum value of the parameters for NOx and smoke emission reduction. From the result of reproducibility verification, it is final that the prediction value of NOx and smoke has the error of below 10%. Consequently, the method and results of this study will be used for quantitative reference to EGR control mapping in next study.