Computational Analysis of Premixed Syngas/Air Combustion in Micro-channels: Impacts of Flow Rate and Fuel Composition

Abstract

Due to increasing demand for clean and green energy, a need exists for fuels with low emissions, such as synthetic gas (syngas), which exhibits excellent combustion properties and has demonstrated promise in low-emission energy production, especially at microscales. However, due to complicated flame properties in microscale systems, it is of utmost importance to describe syngas combustion and comprehend its properties with respect to its boundary and inlet conditions, and its geometric characteristics. The present work studied premixed syngas combustion in a two-dimensional channel, with a length of 20 mm and a half-width of 1 mm, using computational approaches. Specifically, a fixed temperature gradient was imposed at the upper wall, from 300 K at the inlet to 1500 K at the outlet, to preheat the mixture, accounting for the conjugate heat transfer through the walls. The detailed chemistry of the ignition process was imitated using the San Diego mechanism involving 46 species and 235 reactions. For the given boundary conditions, stoichiometric premixed syngas containing various compositions of carbon monoxide, methane, and hydrogen, over a range of inlet velocities, was simulated, and various combustion phenomena, such as ignition, flame stabilization, and flames with repeated extinction and ignition (FREI), were analyzed using different metrics. The flame stability and the ignition time were found to correlate with the inlet velocity for a given syngas mixture composition. Similarly, for a given inlet velocity, the correlation of the flame properties with respect to the syngas composition was further scrutinized.

Investigating the Ignition and Stability Limits of Premixed Methane/Air Combustion in Micro-Channels

“…In the event of FREI, the flame could not sustain itself due to unrestrained heat loss through the microreactor wall; however, after the flame extinguished, the supply of the fresh fuel-air mixture eventually reached the high-temperature zone downstream of the channel and ignited again. Such phenomenon is detected numerically and experimentally in the literature [27][28][29]34]. To better comprehend the FREI phenomena, a specific case with an inlet velocity of 0.2 m/s is presented in this section.…”

“…Preliminary trials in the setup of the model utilized herein showed that such a time step is sufficient in producing accurate simulation results that successfully predict the ignition characteristics. Additionally, this time step has been shown in the literature to be sufficiently small for capturing the microscale combustion phenomena, including the ones of interest in this study [27,34]. Furthermore, with the flame thickness being of the order of 1 mm, the chosen grid size ensured that the flame characteristics were resolved sufficiently within circa 15 cells.…”

“…It should be noted that using HRR T for the ignition phenomenon analyses is a more common approach in the literature than using the axial temperature [18,22,28,34,36]; however, in the present work, the HRR T data were not directly implemented, as they typically produce noisy curves, which cannot be utilized to define such time-sensitive properties. Such noise is primarily attributed to the numerical artifacts resulting from the computational analysis; therefore, a smoothened HRR T data trace was plotted against the axial temperature to validate our approach and to make sure that the axial temperature data are technically supported and can be used as a metric to predict the ignition properties and the flame characteristics.…”

Fuel calorific value control process analysis and research based on IGCC power plant

“…The gas turbine can switch between fuel oil and fuel gas modes. While the fuel oil mode is primarily used during the initial ignition and later shutdown stages, the system transitions to the syngas combustion state once it achieves stability [30,31]. However, the complex composition of the syngas, along with the considerable variations in temperature and pressure, significantly impact the gas turbine's ability to maintain stable combustion operation.…”

Effect of Hard Coal Combustion in Water Steam Environment on Chemical Composition of Exhaust Gases

“…The transmission of heat, created during the combustion process, from the flame to the water steam introduced to the combustion chamber limits the participation of the thermal mechanism of nitric oxide creation, thus causing slight decrease in the NOx emission. Such a mechanism, in terms of low-temperature solid fuel boilers, has an insignificant effect on the amount of nitric oxides created during the combustion process because it is the fuel mechanism that has the greatest percentage of participation [21][22][23].…”