Juhun Song

IMPACT OF ALTERNATIVE FUELS ON SOOT PROPERTIES AND DPF REGENERATION

Abstract In this work, fuel formulation exerted a strong influence on the properties of diesel particulates leading to differences in oxidation rate. These differences were especially significant when comparing soot derived from the combustion of soybean oil-derived biodiesel fuel (B100) and soot obtained from combustion of a Fischer–Tropsch diesel fuel (FT). These 2 fuels mainly differ in fuel oxygen content. Although B100 soot possesses an initially ordered structure, it is 5 times more oxidatively reactive than FT soot. While the initial structure alone does not dictate the reactivity of diesel soot, the relative amount of initial oxygen groups is the more important factor governing the oxidation rate than the initial structure and pore size distribution. Therefore, incorporation of greater surface oxygen functionality in the B100 soot provides the means for more rapid oxidation and thereby enables efficient regeneration of the diesel particulate filter.

Combustion and emissions performance of low sulfur, ultra low sulfur and biodiesel blends in a DI diesel engine

Experiments were conducted with a commercially available six-cylinder, 4-valves per cylinder, turbocharged, direct injection (Dl) diesel engine. The engine was operated with low sulfur diesel fuel, ultra low sulfur diesel fuel and two other blends, low sulfur diesel fuel with 20 wt.% biodiesel and ultra low sulfur diesel fuel with 20 wt.% biodiesel, to investigate the effect of the base fuels and their blends on combustion and emissions. Combustion analysis, particulate matter emissions and exhaust gas composition (CO, NO x and total hydrocarbons) were determined at eight steady-state operating conditions according to the AVL 8-Mode test protocol. Combustion analysis showed at high load conditions a retarded start of injection, an earlier start of combustion and a lower premixed burn peak with ultra low sulfur diesel fuel. Mode averaged NO x emissions decreased with ultra low sulfur diesel fuel and biodiesel blends compared to low sulfur diesel fuel. A 20% PM reduction was observed with ultra low sulfur (15 PPM) diesel fuel compared to low sulfur (325 PPM) diesel fuel.

Spray and combustion visualization of a direct-injection diesel engine operated with oxygenated fuel blends

Abstract Experiments were conducted with a commercially available six-cylinder water-cooled turbocharged direct-injection diesel engine. The cylinder head was modified to permit access to the combustion chamber with an engine videoscope. The engine was operated with base diesel fuel (BP-15) and other blends, base diesel with 20 wt% biodiesel (B-20) and with 20wt% diglyme (O-20). A neat biodiesel (B-100) and a 95 wt% blend of diglyme with base diesel fuel (O-95) were also considered. These fuels were used for observing the effect of the fuel properties on injection timing, heat release, flame structure, and luminosity. All the tests were performed with the engine operated at light load (61 N m, 10 per cent of the rated load) and 1800 r/min. Visualization showed that the start of injection occurred 0.4° earlier with B-100 than with BP-15. B-100 showed the earliest start of injection among the fuels. An earlier start of injection was also observed with B-20 and O-20 blends compared with BP-15 fuel. Combustion analysis showed a lower premixed combustion heat release rate with the diglyme blends compared with the B-20, B-100, and BP-15. The highest premixed burn peak and the lowest premixed burn peak were observed with BP-15 and O-95 fuels respectively. It is difficult to distinguish between the spray flames of BP-15, B-20, B-100, and O-20. However, with much higher oxygen content in the O-95 fuel the natural luminosity of the flame was too faint for detection with the camera. The combination of combustion analysis and in-cylinder visualization employed in this study provides a unique opportunity to understand how oxygenates behave in a commercial engine.

Effects of exhaust gas recirculation on diesel particulate matter morphology and NOx emissions

Abstract Diesel particulate morphology and nitrogen oxides (NO x ) emissions were investigated in detail to reveal the effects of exhaust gas recirculation (EGR). The different rates of EGR were precisely controlled by using a customized engine control unit in a 1.7 l turbocharged common-rail direct-injection diesel engine. The tests, which combined two different EGR modes (i.e. constant boost pressure (CBP) and constant oxygen-to-fuel ratio (COFR)), were designed to decouple the effects of EGR thermal and dilution processes. Particulate samples were collected directly from the raw engine exhaust by using a novel thermophoretic soot-sampling system. The samples were examined and imaged with a high-resolution transmission electron microscope and quantitatively analysed by using a customized image-processing/data-acquisition system. Results showed that the particulate dimensions, number density of primary particles, and soot yield all changed significantly under various EGR rates. The NO x emissions also varied significantly as the EGR rate changed, showing a typical trade-off with respect to the data measured for particulate emissions. At low EGR rates, the thermal effect was the dominant phenomenon that affected the changes of the measured morphological characters, while at higher EGR rates the dilution effect became more important. However, the fractal geometry of diesel particulates did not change significantly between the two EGR modes, suggesting that the influence of EGR dilution was less than that of the thermal process. EGR operation providing a COFR at the same EGR rate yielded a significant benefit in particulate emissions and engine power output, while still maintaining the reduction of NO x emissions at a satisfactory level.

Determination of Char Oxidation Rates with Different Analytical Methods

Char oxidation experiments were performed with a sub-bituminous roto-middle coal in the Drop Tube Furnace (DTF) at atmospheric pressure condition. While temperatures varied between 900, 1100, 1400 , particle ℃ size, mass, particle temperature, and CO/CO2 concentration were obtained to be used for kinetic analysis of the char oxidation. This study addresses several different methods to analyze the char consumption rate, which are classified as energy balance method, ash-traced mass method, flue-gas based method, and particle size based method. The char consumption rate obtained with such methods was compared with the results of Monson et al. (24)

An Experimental Investigation of the Effect of Particle Size on the Combustion Characteristics of Pulverized Sub-Bituminous Coal with Low Calorific Value by Using an LFR System

In this study, the effect of particle size on the combustion characteristics of pulverized sub-bituminous coal was experimentally investigated. A laminar-flow-entrained reactor was designed and implemented to realize the desired heating ratio and temperature corresponding to the combustion atmosphere of a pulverized-coal-fueled furnace. The flame length and structure of burning particles according to different sizes were investigated. Coal combustion processes were clearly distinguished by direct visual observation of the flame structure. The onset point of volatile ignition is greatly affected by changes in the particle size, and the burning time of the volatiles is least affected by changes in the particle size. The length and instability of char flame also increase with the increase of the particle size. However, the char consumption rate within the residential time remains nearly constant.

Evaluation of bubble suspension behavior in electrolyte melts

The viscosity of a molten electrolyte mixture commonly used in direct coal fuel cells (DCFCs) was evaluated. The measurements were obtained from near the melting temperature to a high temperature at which a considerably bubbly flow was induced by decomposition. A gravity-driven capillary viscometer was employed to obtain the viscosity data under low Reynolds flow conditions, using a modified Poiseuille flow relationship. The importance of carbon dioxide addition in measuring the intrinsic viscosity was clearly observed. In addition, the effect of the bubble suspension on the viscosity was quantified in terms of the volume fraction and capillary number. The results showed that the increase in viscosity was best explained only by the difference in the volume fraction of spherical bubbles in the electrolyte melt.

Effect of Coal Properties on Combustion Characteristics in a Pulverized Coal Fired Furnace

This study is to investigate the effect of the moisture, volatile matter and particle size in the coal on the pulverized coal combustion characteristics using CFD. The results show that as the moisture content in coal increases, flame temperature decreases because of heat loss driven from latent heat of vaporization and reduction of heating value. As the volatile matter content in the coal increases, the temperature in the region near the burner increases, while the temperature in rear region of boiler decreases. The solution to keep the temperature in the rear region of boiler is suggested that particle size is needed to be larger. As the particle size increases, the temperature in the rear region of boiler show tendency to increase, for combustion burning time of coal could be extended.

A Numerical Study on the Effects of SOFA on NOx Emission Reduction in 500MW Class Sub-bituminous Coal-Fired Boiler

A numerical investigation has been carried out about the performance of a 500MW class tangentially coal-fired boiler, focusing on the optimization of separated overfire air (SOFA) position to reduce NOx emission. For this purpose, a comprehensive combination of NOx chemistry models has been employed in the numerical simulation of a particle-laden flow along with solid fuel combustion and heat and mass transfer. A reasonable agreement has been shown in baseline cases for predicted operational parameters compared with experimental data measured in the boiler. A further SOFA calculation has been made to obtain optimum elevation and position of SOFA port. Additionally, clarifying on the effect of SOFA on NOx emission has been carried out in the coal-fired boiler. As a result, this paper is valuable to provide an information about the optimum position of SOFA and the mechanism by which the SOFA would affect NOx emission.

Flash spray characteristics of a coal-liquid carbon dioxide slurry

Liquid carbon dioxide (LCO2) could potentially be utilized in coal gasification plants for effectively transporting coal particles, replacing conventional carriers such as water (H2O), particularly in wet-fed gasifiers. However, it is essential to understand the atomization behavior of LCO2 leaving an injector nozzle under both coal-free and coalfed conditions. We examined the atomization behavior of a coal-LCO2 slurry during the throttling process. The injector nozzle was mounted downstream of a high-pressure spray system. The effect of upstream pressure on flash atomization and devolatilization behavior was presented. Compared with the coal-LCO2 mixture, the spray pattern of the coal-water mixture was significantly different, since it evidenced a Rayleigh-type breakup mode. This difference indicates that the coal-water slurry did not transport the coal as effectively as the coal-LCO2 slurry.