Effects of Pressure and Coal Rank on the Oxy-Fuel Combustion of Pulverized Coal

Pressurized oxy-fuel combustion technology is the second generation of oxy-fuel combustion technology and has low energy consumption and low cost. In this research, a visual pressurized flat-flame reaction system was designed. A particle-tracking image pyrometer (PTIP) system based on a high-speed camera and an SLR camera was proposed. Combining the experimental system and data-processing method developed, the ignition and combustion characteristics of a single coal particle between 69 and 133 μm in size were investigated. The results indicated that at atmospheric pressure, the ignition delay time of ShanXi (SX) anthracite coal was longer than that of ShenHua (SH) bituminous coal, while that of PRB sub-bituminous coal was the shortest. As the pressure rose, the ignition delay time of the PRB sub-bituminous coal and SX anthracite coal showed a continuous increasing trend, while the ignition delay time of SH bituminous coal showed a trend of first increasing and then decreasing. Moreover, pressure also affects the pyrolysis process of coal. As the pressure increases, it became more difficult to release the volatiles produced by coal pyrolysis, which reduced the release rate of volatiles during the ignition stage, and prolonged the release time and burning duration time of volatiles.

A study on the influence of ignition energy on ignition delay time and laminar burning velocity of lean methane/air mixture in a constant volume combustion chamber

This study presents the effect of ignition energy (Eig) on ignition delay time (tdelay) and uncertainty of laminar burning velocity (Su0) measurement of lean methane/air mixture in a constant volume combustion chamber. The mixture at an equivalence ratio of 0.6 is ignited using a pair of electrodes at the 2-mm spark gap. Eig is measured by integrating the product of voltage V(t) and current I(t) signals during a discharge period. The in-chamber pressure profiles are analyzed using the pressure-rise method to obtain tdelay and Su0. Su0 approximates 8.0 cm/s. Furthermore, the increasing Eig could shorten tdelay, leading to a faster combustion process. However, when Eig is greater than a critical value, called minimum reliable ignition energy (MRIE), the additional elevating Eig has the marginal effect on tdelay and Su0. The existence of MRIE supports to optimize the ignition systems and partly explains why extreme-high Eig>> MRIE has less contribution to engine performance.

Single Droplet Combustion Characteristics of Petroleum Diesel- Philippine Tung Biodiesel Blends

The purpose of the present study is to investigate the effects of fuel blending of petroleum diesel and biodiesel made from Philippine Tung on the combustion characteristics of fuel droplets. In this study, petroleum diesel was mixed with biodiesel at volume percentages of 0 to 100 % to produce 5 fuel blends. The ratios of fuel blends (petroleum volume/biodiesel volume) were 100:0 (P100), 75:25 (BP25), 50:50 (BP50), 25:75 (BP75) and 0:100 (B100). Single droplet combustion experiments were prepared to understand the combustion characteristics at 3 levels of ambient pressure (100, 200 and 300 kPa). Observations were carried out on the ignition delay time, the burning rate constant, droplet temperature, and the flame visualization. The results showed some effects of the adding of biodiesel in petroleum diesel and the chamber pressure on droplet combustion characteristics. The adding of biodiesel into petroleum diesel resulted in a shorter ignition delay time and higher burning rate constants. But, the lower heating value of biodiesel caused the lower flame temperature. The possibility of micro-explosion also increased due to the mixing of fuel. On the other hand, increasing the chamber pressure also resulted in shorter ignition delay, higher burning rate, and higher combustion temperature. The higher ambient pressure also compressed the flame dimension and enhanced the onset of micro-explosion. HIGHLIGHTS The adding of biodiesel into petroleum diesel with different physical and chemical properties impacts the droplet combustion behavior, especially on the characteristics of burning rate, ignition delay time, flame temperature, and micro explosion The high content of unsaturated fatty acids and oxygen in Philippine Tung biodiesel improves the ignition delay time and burning rate constants of the blended fuel, but, the lower heating value causes the lower flame temperature The multi-components of fatty acids with different boiling points in Philippine Tung oil promote the micro-explosion in the combustion of the mixtures of biodiesel and petroleum diesel fuel GRAPHICAL ABSTRACT

Chemical Kinetic Study on Dual-Fuel Combustion: The Ignition Properties of n-Dodecane/Methane Mixture

The natural gas (NG)/diesel dual-fuel engine has attracted extensive attention in recent years, and the influence of ignition delay on the engine is very important. Therefore, the research on the ignition delay of NG/diesel dual fuel is of great significance. In this work, a simplified n-dodecane mechanism was used to study the effect of methane mixture ratio on the n-dodecane ignition process. The results showed that the ignition delay time increased with the increase of methane content by changing the mixing ratio of methane and n-dodecane. However, the effect of methane on the ignition delay time gradually decreases when the content of the n-dodecane mixing ratio is greater than 50%. It was also found that with the increase of n-dodecane content, the reduction degree of the ignition delay time of the whole reaction system decreased and the negative temperature coefficient (NTC) behavior increased. Moreover, when the initial pressure increased from 20 bar to 60 bar, the thermal effect of methane also increases from 7.03% to 9.55%. The relationship between ignition characteristics of methane-n-dodecane and temperature was studied by changing the initial temperature. Furthermore, the evolution of species in the ignition process of the whole reaction system was analyzed, and the decomposition of n-dodecane first occurs in the reaction n-C12H26 + O2 = R + HO2 to form R and free radicals; however, the reaction CH4 + OH = CH3 + H2O dominates with the increase of the methane mixing ratio and inhibits the ignition process. Through the analysis of reaction paths, sensitivity, and rates of production and consumption of methane/n-dodecane, it was explained how n-dodecane accelerates methane ignition through the rapidly formed free radicals.

Modeling of a Reduced Hybrid H2–Air Kinetic Scheme Integrating the Effect of Hypersonic Reactive Air with Supersonic Combustion

A hybrid H2–air kinetic scheme of 11 species and 15 reactions is developed, which is capable of simulating the high-temperature air reaction flows and H2–O2 combustion flows respectively or simultaneously. Based on the Gupta scheme, the mole fraction varying with a Mach number at specific conditions is analyzed, and the weakly-ionized 7-species 7-reaction scheme is selected. The effect of nitrogenous species on the H2–O2 combustion is analyzed by a zero-dimensional simulation of steady-state and unsteady-state combustion under specified conditions, and the selected dominant nitrogenous reaction N + OH = NO + H is distinguished by the production rate of the nitrogenous species. The thermodynamic properties are verified by comparison using the NIST–JANAF database. The reaction rate coefficients of the dominant reaction of the hybrid kinetic scheme distinguished by a sensitivity analysis are corrected. The proposed kinetic scheme is validated by a zero-dimensional calculation of the ignition delay time and two-dimensional computational fluid dynamics (CFD) simulation with finite-rate chemistry on the shock-induced sub-detonative and super-detonative combustion. The ignition delay time of the hybrid kinetic scheme is almost in the middle between the Shang scheme and Jachimowski scheme, and all the calculated ignition delay times are acceptably greater than the experiments due to the errors of the experiments and numerical models. The clearly captured bow shock wave and combustion front using the hybrid kinetic scheme and Shang scheme are almost the same, which is strongly consistent with the schlieren image. In addition, a good agreement of the flow characteristics and mass fraction of the species along the stagnation line is also obtained, which indicates the accuracy and reasonableness of the hybrid kinetic scheme to simulate hybrid H2–air reactive flows.