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A numerical study on the effects of air/fuel configuration on NOx emissions control using methane fuel combustion at different thermal intensity was conducted in this paper. The investigation employed the structure of small combustors which are influenced by some combustion factors. The layout is produced through diverse air and fuel injection configurations selected due to their potential on distinct combustion characteristics. In reverse configurations mode, the air injection port is located at the exit end of the combustor; while in the forward configurations, the air injection port is placed at the reversed end of the combustor exit, with a change of fuel position. Our investigation indicated that in both non-premixed and premixed combustion modes, the NOx discharge is extremely low. However, in premixed combustion mode, the forward and reverse flow configuration (FP, RP) premixed produced a significantly low level of NO and CO compared to the other air configurations in non-premixed at all equivalence ratios Φ The investigation observed that any changes to the fuel injection position affect the mixture preparation, resulting in premature combustion at very low emissions, hot spots and increased emissions. The reverse-cross-flow configuration (RC1) has more potential to attain lower NO (approximately 1.30E-05 ppm) together with low CO (approximately 223 ppm) emissions when compared to the other flow configuration (RC2 and RC3). More so, a lower combustor volume leads to a very high thermal intensity of 324–393 MW/m3-atm thus resulted in a reduced residence time and gas recirculation, and high CO and NOx emissions. [ABSTRACT FROM AUTHOR]

Flameless combustion techniques have created a huge opportunity in the patronizing high number of combustible fuel materials. This opportunity is connected with its potential in providing acceptable features of the combustion regime, mostly centered on mixing the working medium (reactants) above the temperature of auto-ignition of the fuel. Recent research has provided some potential of flameless combustion towards pollution reduction and energy generation. However, this technology still requires more attention to improve its versatility. The effect of flameless combustion on emissions reduction and its performance enhancement both on biofuels and fossil products is reported in this paper. Flameless combustion follows mixture before oxidizes in the combustion process, thus generates lower NOx emissions with clear and flameless of very little visible radiation. Similar values in the area of pollutant emissions for all studied fuels, especially with bio-fuel showed that flameless combustion yields good results both on conventional and diluted fuels. The review still points that flameless combustion regime modelling might not be capable of predicting intermediate species for reducing the emissions to zero level due to some inherited properties in the operation. Assessing the thermal performance of flameless combustion, showed similar temperature distribution for all the fuels studied, although bio-fuel temperature observed little below, due to the inert gases of CO2 of large amount towards cooling the reactants. Challenges like wall-flame quenching and residence time were discovered on micro-scale combustors. The report suggests that little modifications on the flameless combustor in the area of wall-flame quenching will contribute to solving the NOx emission problems. [ABSTRACT FROM AUTHOR]