Study On Ignition Characteristics Of Ammonia And Ammonia-hydrogen Mixture Fuels

Global fossil fuels are increasingly exhausted,and carbon dioxide emissions are becoming more and more serious.Ammonia gas not only has high energy density,but also does not produce CO₂ when burned,so it is highly valued by scholars at home and abroad.On the one hand,studying the ignition characteristics of ammonia and ammonia/hydrogen mixture fuel can provide corresponding basic test data for the optimization of the current ammonia mechanism,and on the other hand,it can provide theoretical basis for the optimization of the in-cylinder combustion control of ammonia/hydrogen dual-fuel engine.In this study,the visual shock tube test platform was used to carry out the ignition characteristics tests of ammonia under different initial conditions（temperature,pressure,equivalent ratio and dilution gas）and ammonia/hydrogen mixture under different hydrogen addition conditions.The mechanism was optimized through the measured ignition delay time data.Finally,the simulation and chemical dynamics analysis were carried out based on CHEMKIN software and optimization mechanism.The main conclusions of the study are as follows:（1）The ignition delay time of ammonia decreases exponentially with the decrease of reciprocal temperature,increases with the increase of equivalent ratio,and decreases with the increase of pressure.Under high temperature conditions,the ignition delay time is gradually weakened by pressure with increasing pressure.With the increase of equivalent ratio,the ignition delay time is gradually enhanced by equivalent ratio.When nitrogen is used as the dilution gas,it will have chemical effect on the ignition process of ammonia gas and inhibit the ignition.（2）Adding hydrogen can shorten the ignition delay time of ammonia nonlinearly.With the increase of hydrogen addition amount,the activation energy of the fuel decreases and the reactivity of the mixed fuel increases.With the increase of hydrogen addition amount,the activation energy of the mixed fuel is sensitive to the temperature change,and the activation energy increases with the increase of the reciprocal temperature.（3）Sensitivity analysis of fuel ignition delay time under different initial conditions was carried out,and the corresponding reaction path analysis was carried out.The results show that under different initial conditions,the primary reactions with the greatest promoting effect on ammonia ignition are all R5:H+O₂=O+OH,and the primary reactions with the greatest inhibiting effect are different under different initial conditions.The sensitivity of ignition delay time shows that the temperature change has a great effect on the reaction of NH₂,but not on the reaction of N₂H₂,and the pressure change has a great effect on the reaction of H₂NO.（4）Reaction path analysis found that:The reaction pathways in which H,OH,O and NH₂ free radicals are involved account for a large proportion of the total reaction channels.When the hydrogen addition level changes from 0%to 5%,the ignition delay time is significantly shortened,but the reaction channel remains unchanged,and the consumption in the reaction channel does not change significantly.When the hydrogen addition level changes from 5%to 70%,the proportion of the consumption of reaction channels involving H in the reaction path increases,and the dehydrogenation of HNO to NO begins to take place through the reverse reaction path.