Research On Laminar Flame Characteristics Of Ammonia Fuel Compound Combustion Based On Optical Diagnosis

The application of zero-carbon/low-carbon fuels in powertrains is becoming a hot topic of research to meet the "dual carbon" strategic objective and the need for energy restructuring.Ammonia and hydrogen,as carbon-neutral fuels with a wide range of feedstock sources,are expected to be ideal energy carriers for the green,low-carbon transition of powertrains,but a range of safety and cost issues in the production,transportation and storage of hydrogen have constrained its industrialisation.As a new energy carrier and zero-carbon fuel,the application of ammonia is strategically important for achieving carbon neutrality in power plants.Early studies have shown that ammonia fuels suffer from slow combustion rates,high ignition energy,narrow combustibility range,high auto-ignition temperatures,long quenching distances and long ignition delay time,which have led to reduced combustion performance and deteriorating emissions in practice.This study is based on a project of the National Natural Science Foundation of China(NSFC)and the Natural Science Foundation of Jilin Province(NSFJ)to investigate the influence of ethylene and acetylene with different fuel molecular structures on the laminar flame characteristics of ammonia fuel combustion at different blending ratios and equivalent ratios,based on optical diagnostic non-contact testing techniques.Based on the Gülder burner,a laminar flow combustion test platform was built for the combined combustion of ammonia and combustion fuels.The test platform was equipped with three optical test methods:high-speed photography,planar laser-induced fluorescence and laser Raman scattering,and a self-designed data processing program.Based on the numerical calculation platform of chemical kinetics,the chemical reaction mechanism that can be used for the compound combustion of ammonia fuel is constructed and verified,and the chemical reaction kinetic mechanism of the compound combustion process of ammonia and its combustion fuel is studied in depth.The main research elements and conclusions are as follows:1.The effect of ethylene and acetylene blending ratio and equivalent ratio on the flame stability of laminar flow of ammonia fuel compound combustion was investigated experimentally based on high-speed photography and planar laser-induced fluorescence technique.The study found that the flame stability of ammonia fuel was improved by using acetylene fueled with C≡C compared to ethylene fueled with C=C,with a significant reduction in flame lift distance and flame area fluctuation.The flame stability of ammonia fuels is improved by using acetylene fueled with C≡C as opposed to ethylene fueled with C=C,with a significant reduction in flame lift distance and flame area fluctuation rate.The increase in the proportion of ethylene blending improves flame stability by enhancing the strength of the low temperature reaction phase of the composite combustion flame,while the increase in the proportion of acetylene blending improves flame stability by enhancing the strength of both the low and high temperature reaction phases of the flame.2.The effect of ethylene and acetylene blending ratios and equivalence ratios on the combustion pollutants in the laminar flame of ammonia-fueled composite combustion was investigated experimentally based on the planar laser-induced fluorescence technique.It was found that acetylene has a higher production of benzene and PAHs than ammonia/ethylene flames due to its special C≡C,that ammonia/acetylene flames have a higher production of unburned CH and unburned NH3 than ammonia/ethylene flames due to its rapid flame development rate,and that ammonia/acetylene flames have a higher production of NO,N2O and NO2 than ammonia/ethylene flames due to its high flame temperature.3.The effect of blending ratio and equivalence ratio of ethylene and acetylene on ammonia-hydrogen cracking and C-N cross-reaction in ammonia-fueled composite combustion laminar flow flames was investigated experimentally based on laser Raman scattering technique.It was found that acetylene blending was more effective than ethylene blending in increasing the degree of ammonia-hydrogen cracking,which in turn increased the flame temperature and flame development rate.At the same time,acetylene doping is more effective than ethylene doping in promoting the formation of CN,a key component of the C-N cross-reaction,while inhibiting the formation of HCN,thus facilitating the ammonia/acetylene flame ammonia-hydrogen cracking reaction.4.The chemical kinetic behaviour of the combustion process of ethylene and acetylene blended with ammonia fuels has been investigated by means of sensitivity analysis,ROP analysis and chemical reaction path analysis.It was found that the ammonia/ethylene oxygenation and oxidation reactions are more intense than ammonia/acetylene and the dehydrogenation and oxidation reactions are less intense than ammonia/acetylene.Analysis of the key radical reaction NH3+H=NH2+H2 for ammonia-hydrogen cracking revealed that the chemical reaction rate of ammonia/acetylene increased by 17.14%compared to ammonia/ethylene,facilitating ammonia-hydrogen cracking.In addition,the C-N cross-reaction was found to influence the low and high temperature exothermic stages,ammonia-hydrogen cracking and NO production by means of chemical reaction pathway analysis,mainly by varying the production of key intermediates HNCO,NCO,HCN and CN during the complex combustion process.