Study On Combustion And Emission Characteristics For Engine With Acetone-Butanol-Ethanol/Hydrogen Combined Injection

Since the birth of the automobile,the global automobile industry has maintained rapid development,and more and more new technologies have sprung up,but at present the most important issue for the automobile industry is how to find a solution to the energy crisis.In the context of China’s scarce petroleum resources,in addition to continuous innovation and solving energy problems from the engine technology level,a more feasible approach is to find alternative fuels.Among various types of biofuels,alcohol fuels have become a leader in mature production methods that can improve engine performance and reduce pollutant emissions.The nature of n-butanol is similar to that of gasoline,and its energy density is far higher than that of methanol and ethanol.However,from the perspective of practical application,the production cost of n-butanol is high and the purification is difficult.Therefore,if acetone-butanol-ethanol（ABE）,an intermediate product of butanol produced by traditional biological fermentation,can be directly applied to engine combustion.Then the cost of purifying n-butanol can be removed,and a large amount of resources can be saved.Some researchers have proved that the spray and combustion characteristics of ABE are very similar to those of n-butanol.They can also maintain the power of the engine and reduce emissions efficiently.In this thesis,ABE is used as the main fuel,and hydrogen is mixed into the cylinder through a dual-injection to improve combustion performance and reduce emissions of the ABE engine.The main purpose of this experiment is to investigate the influence of the mixing ratio on the combustion characteristics and emission characteristics of ABE engines during direct injection of hydrogen.In order to explore the change of the combustion and emissions of ABE with a small amount of hydrogen content,five hydrogen ratios are set as the main variable of the experiment in order to pursue a comprehensive research and analysis,the blending ratio includes 0%,5%,10%,15%,and 20%,which respectively represent non-doped,small-doped and large-doped hydrogen.Other experimental parameters include changing the excess air coefficient,ignition timing,speed,and load.The effects of direct hydrogen injection on the performance of ABE engines were investigated by measuring the combustion parameters,performance parameters,gas emission parameters,and particulate emission parameters of related engines.The specific conclusions are as follows:1)Injecting a small amount of hydrogen into the cylinder can enrich it around the spark plug and gradually dilute and stratify it outward.The 5%hydrogen doping ratio can significantly increase the pressure in the cylinder and advance the peak pressure cylinder angle.When the excess air coefficient increases,such asλ=1.2,the hydrogen doping ratio can be appropriately increased to 10%,which can effectively improve the pressure in the cylinder.In order to obtain a higher average indicated pressure（IMEP）,the ignition advance angle after the combustion rate is accelerated after hydrogen doping should be reduced by an appropriate amount,and the ignition timing is postponed from 15°CA BTDC to about 5°CA BTDC.The 5%hydrogen doping ratio can greatly improve IMEP,and the increase is more obvious under lean burn conditions.The maximum heat release rate gradually decreases with the increase of the excess air coefficient.After hydrogen doping,the addition of hydrogen significantly improves the combustion speed of the mixture in the cylinder.As the volume fraction of hydrogen increases,the flame propagation speed of hydrogen is fast.The characteristics can make the exothermic combustion of the mixed fuel concentrated,the larger the excess air coefficient,the more obvious the hydrogen improvement ability,which can effectively optimize the combustion.The maximum heat release rate decreases with the increase of the speed.Hydrogen doping can increase the maximum heat release rate.At low speeds of 1000r/min,hydrogen has a greater effect on the combustion rate.As the speed increases,hydrogen dope increases the maximum heat release rate.It is not obvious,so it can be explained that an appropriate increase of the hydrogen doping ratio at low speed conditions can increase the maximum heat release rate.2)CO emission increases first and then decreases with the increase of hydrogen content.When a small amount of hydrogen is added,the mixed gas in the cylinder presents a stratified state during ignition.The high combustion temperature and fast combustion speed near the spark plug shorten the high-temperature residence time and increase the low-temperature residence time.ABE has large latent heat of vaporization,poor formation of mixed gas and strong binding capacity of hydrogen and oxygen.As a result,some CO is not easy to be oxidized to CO₂.So CO increases when hydrogen is added.However,when the hydrogen ratio exceeds 10%,the mixed gas is relatively uniform,and the proportion of ABE fuel and C fuel decreases,so CO decreases.In order to obtain lower CO emission,ignition can be selected at 15°CA BTDC and the rotating speed can be controlled at about 1500r/min.3)The HC emission shows a downward trend with the increase of the hydrogen doping ratio.5%hydrogen doping ratio can improve the HC emission.Excessive hydrogen will not be further improved,and the improvement effect will be weakened under lean burn conditions.HC is relatively small when ignition occurs at the time of15°CA BTDC,and due to the increase of rotating speed,airflow movement increases and HC emission decreases greatly.With the increase of load,HC emission increases obviously and hydrogen doping can improve HC emission.4)Small hydrogen loading ratio（5%¹0%）can inhibit NO_X generation while improving power performance.This is because a small amount of hydrogen loading can delaminate the in-cylinder mixed gas.The mixed gas near the spark plug burns fast,shortening the combustion time and increasing the combustion temperature.However,due to the large latent heat of vaporization of ABE,the mixed gas formation is not good,local hypoxia and the residence time at high temperature are shortened,resulting in lower NO_X emissions.Under small load,appropriate hydrogen doping will reduce NO_X emissions to extremely low levels.5)In most operating conditions,the particle size distribution of particles is bimodal.With the advance of the ignition time,the particle accumulation state and the total number of particles first decrease and then increase.Under lean conditions,the number of particles is extremely low.When a small amount of hydrogen is added,the accumulated particulates will significantly increase,and as the hydrogen doping ratio further increases,the total number of particles will decrease overall,which indicates that hydrogen doping promotes the full combustion of the mixture and oxidizes the unburned soot.