Study On The Combustion Performance Of Turbocharged Direct Injection Gasoline Engine With Intake Port Water Injection

GDI gasoline engines develop in the direction of being small,reinforced,which makes the engine’s thermal efficiency increase,and inevitably brings problems such as knocking and excessive exhaust temperatures.In order to meet the stringent emission standards,the engine often sacrifices its economy performance.Water injection technologies of engine have the advantages of suppressing knocking,reducing exhaust gas temperature and NO_X emissions theoretically,and will meet the needs of engines in the future.This research focused on intake port water injection technology and the intake water injection devices and the control system were modified and designed based on a4-cylinder GDI gasoline engine.The experiment and Python theoretical calculation,one-dimensional performance and three-dimensional CFD simulation of the engine are combined as the method to study the influence of water injection on its combustion performance and explore the potential of the intake port water injection technology in improving engine’s performance.The evaporation of water in the cylinder depends on the environmental conditions.Under the conditions of the gasoline engine’s environment in-cylinder during intake stroke,the maximum saturated water-fuel ratio is less than 0.7;the saturated water-fuel ratio goes up with the increase of the ambient temperature,decreases with the rise of environmental pressure,and the maximum temperature drop of the environment in-cylinder could be obtained when the mass of water reaches a saturated water-fuel ratio.The engine experiment with intake port water injection shows that water vaporizes with the absorbability of heat,which reduces the temperature in-cylinder,and water also dilutes the concentration of the fuel and the concentration of oxygen in the mixture after its gasification,so that the flame propagation speed in the cylinder is reduced and the whole combustion phase and the combustion center of gravity lag,the combustion temperature and pressure in the cylinder,and the exhaust gas temperature both decrease accordingly;the high water injection pressure can promote water’s atomization,and can also obtain a shorter water injected pulse width and extend the mixing time of water in-cylinder,which are both beneficial to the mixing between water,air and fuel,and improve the combustion in-cylinder.When water is injected under the 50%load of engine with the help of optimizing ignition angle and the power compensation,there is no loss in engine’s power and economy,but the NO_X and CO emissions are reduced.While under the 100%load of engine with the water-fuel ratio near to 0.3,the engine achieves a significant reduction in fuel consumption at the expense of a little loss in power with the optimization of ignition angle and the equivalent ratio combustion in-cylinder;besides,engine’s knock,exhaust temperature,and CO,HC,and Soot emissions are all improved availably.The one-dimensional GT calculation shows that after optimizing the ignition angle and increasing the boost pressure at 100%load with water injection,the loss of power can be can compensated,while the fuel consumption and exhaust temperature are reduced and the rich mixture is improved.In addition,the results of three-dimensional CFD simulation demonstrate that when water is mixed with air and fuel in-cylinder,the micro-explosion effect promotes the crushing and atomization of the fuel,improves the distribution of the mixture,and reduces the area of mixture being too rich or too thin in-cylinder.At the same time,the addition of liquid water increases the density and inertia of the flow field in-cylinder,and the turbulent kinetic energy increases and the distribution of high turbulent kinetic energy further expands,which promotes combustion and the spread of the flame to a certain extent.Water participates in the combustion reaction,which increases the concentration of OH radicals and CH₂O in-cylinder.OH radicals can promote the crack and the energy’s release of fuel,and improve combustion further in-cylinder,while the significant generation of CH₂O means the beginning of combustion’s deterioration,and the incompletely oxidation of CH₂O also illustrate the insufficient combustion of the fuel in-cylinder with too much injected water.