A Preliminary Study Of Combustion Performance And Emission Characteristics Of A Single-Cylinder Spark-Ignition Engine Fuelled With Partially Dissociated Ammonia

The combustion of fossil fuels causes the emissions of large amounts of carbon dioxide,which is argued by some to lead to a series of environmental problems.In the field of transportation,ammonia is considered as a carbon free fuel for internal combustion engines as an alternative to fossil fuels.Numerous studies have shown that ammonia has the potential to be used as a fuel for spark ignition internal combustion engines.However,the use of ammonia in internal combustion engines is limited by its high ignition energy,high auto-ignition temperature,low flame propagation speed and narrow combustibility limits.One way to use ammonia as a fuel for spark ignition internal combustion engines is to partially dissociate ammonia into a mixture of ammonia,hydrogen and nitrogen before the ammonia injects the cylinder of the internal combustion engine.Previous studies have demonstrated that the presence of hydrogen significantly improves the ignition and combustion characteristics of the ammonia partially dissociation gas.Research on ammonia partial dissociation gas in spark-ignition internal combustion engines is very limited,and there is a lack of systematic and in-depth knowledge,and the reported studies vary from time to time.The purpose of this thesis work is to systematically investigate the combustion and emission characteristics of ammonia partial dissociation gas in spark ignition internal combustion engines,the outcomes of which will provide a good basis for the technical application and future development of ammonia as a carbon-free fuel in spark ignition internal combustion engines.The specific research objectives of this paper include:(1)to systematically investigate the effects of the degree of ammonia dissociation on the dynamic characteristics,ammonia combustion efficiency,and emission characteristics of spark ignition internal combustion engines,and to determine the appropriate range of ammonia dissociation degree for ammonia internal combustion engines;(2)to examine the effects of total ammonia flow rate on the dynamic characteristics,ammonia combustion efficiency,and emission characteristics of ammonia partial dissociation gas internal combustion engines,and to predict the range of total flow rate for this ammonia internal combustion engine;(3)to clarify the equivalent ratio on the dynamic characteristics,ammonia combustion efficiency,and emission characteristics of the ammonia partial dissociation gas internal combustion engine,and to enhance the understanding of the combustion process of ammonia partial dissociation gas in the internal combustion engine.Among them,the internal combustion engine dynamic characteristics specifically include speed,torque,power and brake thermal efficiency;the study of ammonia combustion efficiency includes the study of ammonia concentration in exhaust gas,ammonia combustion efficiency and exhaust gas temperature;the exhaust gas emission characteristics include the study of nitrous oxide,nitrogen dioxide and nitrous oxide concentration in the exhaust gas of internal combustion engine.The effect of the degree of ammonia dissociation on the dynamic characteristics of ammonia internal combustion engines shows that increasing the ammonia dissociation degree from 20%–50%can significantly improve the dynamic characteristics of internal combustion engines,while the difference in the dynamic characteristics of internal combustion engines is not significant when the ammonia dissociation degree is from 50%–70%.Increasing the ammonia dissociation degree from 30%–70%can reduce the ammonia concentration in the exhaust gas,increase the ammonia combustion efficiency and reduce the exhaust gas temperature.In addition,increasing the ammonia dissociation degree increases the concentration of nitric oxide,nitrogen dioxide and nitrous oxide in the exhaust gas of the internal combustion engine.The total ammonia flow rate on the dynamic characteristics of the ammonia internal combustion engine shows that the dynamic characteristics of the internal combustion engine increase continuously at the total ammonia flow rate of 15–22.5 L/min,while the total ammonia flow rate of 25 L/min causes the dynamic characteristics of the internal combustion engine to remain unchanged or even decrease.According to the study of the concentration of ammonia in the exhaust gas and the ammonia combustion efficiency,25 L/min ammonia flow rate will cause a significant increase of ammonia concentration in the exhaust gas and decrease of ammonia combustion efficiency,resulting in fuel waste.In addition,the study on the total flow rate on the NO_xemission showed that the concentration of nitric oxide and nitrogen dioxide decreased at 15–17.5 L/min total ammonia flow rate;at 20–22.5 L/min total ammonia flow rate,the concentration of nitric oxide and nitrogen dioxide increased first and then decreased,and reached the maximum at 1500 rpm;and at 25 L/min total ammonia flow rate,the concentration of nitric oxide and nitrogen dioxide increased and then decreased.The concentration of nitrous oxide decreased continuously with the increase of total ammonia flow rate.The effect of equivalence ratio on the dynamic characteristics of the internal combustion engine of ammonia partial dissociation gas showed that the torque,power and brake thermal efficiency of the internal combustion engine increased and then decreased during the equivalence ratio increase from 0.84 to 1.39,and reached the maximum at the equivalence ratio of 1.12.The ammonia concentration in the exhaust gas increased slowly with the increase of the equivalent ratio,and then increased significantly when the equivalent ratio reached 1.23;the exhaust gas temperature also decreased significantly after the equivalent ratio was higher than 1.23;and the ammonia combustion efficiency decreased significantly when the equivalent ratio was higher than 1.12.In terms of equivalence ratio on NO_x emissions,it was found that increasing the equivalence ratio led to a decrease in the concentration of nitrous oxide,while the concentrations of nitrogen dioxide and nitrous oxide increased slightly at equivalence ratios lower than 1.05,but both decreased significantly at equivalence ratios higher than 1.05.This study has furthered the understanding of the combustion characteristics and emission characteristics of ammonia partial dissociation gas in an internal combustion engine.The effects of ammonia dissociation degree,total ammonia flow rate and equivalent ratio on the internal combustion engine,as well as the further understanding of ammonia combustion,provide scientific basis and theoretical support for the development and application of ammonia as a fuel for internal combustion engines.