Study On Combustion And Emission Characteristics Of Hydrogen/n-butanol Compound Injection Engine

In order to solve the problems of energy shortages and environmental pollution faced by the country,in addition to developing new technologies to improve energy efficiency and reduce emissions,we can also find efficient and clean alternative fuels.Butanol fuel began to enter the field of vision of various countries because of its excellent physical and chemical properties and relatively simple industrial production method.Butanol has a high octane number and good anti-knock properties.It is suitable as an alternative fuel for gasoline engines.Its low calorific value is slightly lower than gasoline.It can ensure higher power when used in gasoline engines.The flame propagation speed is higher than that of gasoline and can be shortened.The combustion process enables the combustible mixture to burn more fully.At the same time,the butanol fuel itself contains oxygen,which optimizes the combustion and can also reduce the particulate emissions of the engine.But butanol fuel also has obvious shortcomings.It has high viscosity,poor vaporization and atomization properties,low saturated vapor pressure,and large latent heat of vaporization.This will cause unstable combustion process,large cycle fluctuations,increased HC emissions and cold start difficulties and a series of problems.As a clean and renewable energy,hydrogen has the advantages of wide ignition limit,low ignition energy and fast laminar flame speed.By injecting butanol fuel and hydrogen into the cylinder in the form of compound injection,the mixed combustion forms complementary advantages.Hydrogen In direct injection,the secondary injection technology is used,which not only improves the engine’s power and combustion characteristics,but also reduces the engine’s emissions.In order to study the combustion and emission characteristics of the hydrogen/n-butanol compound multiple-injection engine,this experiment designed and built a compound injection engine test platform with butanol port injection and hydrogen in-cylinder secondary injection,and designed and connected high-pressure hydrogen piping,and built a secondary hydrogen injection model based on the d SPACE rapid control prototype system to achieve precise control of main research parameters such as hydrogen injection timing,hydrogen injection ratio,hydrogen injection pressure,etc.,using different injection modes to form in the cylinder different hydrogen distribution conditions,research and analysis of the influence of different hydrogen distribution conditions on the combustion characteristics,power performance and emission characteristics of butanol engines.The main experimental work and related conclusions are as follows:1)In the intake stroke(240°CA BTDC),hydrogen with 5% energy ratio is injected by direct injection in the cylinder,and compared with the butanol port injection mode,the homogeneous distribution of direct injection in the hydrogen cylinder is studied for the effect of butanol.Influence of engine combustion and emission characteristics.The results show that direct injection of hydrogen during the intake stroke can form a homogeneous hydrogen distribution state in the cylinder,greatly improve the rapid combustion period in the combustion process,increase the temperature in the cylinder,promote the combustion process,and make the quenching layer harder.The thinner thickness reduces the HC emission of the engine,but improves the NOx emission of the engine.2)In the compression stroke(75°CA BTDC),hydrogen with 5% energy ratio is directly injected into the cylinder,and compared with the butanol port injection mode,the effect of the stratified distribution of direct injection in the hydrogen cylinder on the combustion and combustion of the butanol engine is analyzed.The results show that when hydrogen is directly injected during the compression stroke,the hydrogen will form a hydrogen rich zone near the spark plug,which helps to form a stable flame core,greatly shortens the flame development period of the combustion process,speeds up the entire combustion process,and improves the engine’s performance combustion characteristics and power.3)The influence of the ratio of the two injections on the combustion and emission characteristics of the butanol engine under the hydrogen in-cylinder secondary injection mode is studied.When the second injection ratio is greater,a hydrogen rich zone is formed near the spark plug.The lower the concentration of homogeneous hydrogen in the cylinder,the longer the period of rapid combustion,and the greater the output torque and average indicated pressure of the engine,which improve the combustion characteristics and power of the engine.In terms of emissions,the increase in the proportion of the second injection basically reduces the emissions of CO and unburned HC and increases the emission of NOx.However,when λ=1.2,the increase in the proportion of the second injection causes the increase emission of unburned HC,the decrease of NOx emissions.4)The influence of the timing of the second injection of hydrogen on the combustion and emission characteristics of the butanol engine was studied in the hydrogen in-cylinder secondary injection mode.As the timing of the secondary hydrogen injection continues to advance,the flame development period and the rapid combustion period in the combustion process both decrease first and then increase,and the output torque and average indicated pressure of the engine gradually decrease.There is no obvious uniformity rule that the engine’s emissions change with the time of the second injection of hydrogen.5)The influence of hydrogen injection pressure on the combustion and emission characteristics of butanol engines was studied under the condition of secondary hydrogen injection.With the continuous increase of hydrogen injection pressure,the flame development period and rapid combustion period of the combustion process are shortened,the output torque of the engine and the average indicated pressure increase,and the cycle variation is significantly reduced.In terms of emissions,as the pressure of hydrogen injection continues to increase,CO emissions have gradually decreased,and NOx emissions have gradually increased.