Combustion And Emission Characteristics Of A Diesel Dual Fuel Engine With High Pressure Airway Injection Of Ethylene Glycol/Direct Injection

Ethylene glycol,the simplest dihydric alcohol,has a high molecular oxygen content and a high cetane number,and it’s suitable as diesel additives to replace part of diesel and improve the combustion process of diesel engines.In addition,ethylene glycol has a wide range of sources and a large yield.It can be made from coal with a simple process and low cost.If ethylene glycol from coal can replace diesel in large quantities,it is of great significance to reduce diesel emissions,adjust China’s energy structure and reduce the dependence of oil on foreign countries.However,ethylene glycol is a polar molecule,which is difficult to dissolve in diesel,so it cannot be used in diesel engine simply by blending.Using the ethylene glycol&diesel dual fuel model can not only greatly improve the energy replacement rate of ethylene glycol,but also further reduce diesel emissions by regulating the fuel injection strategy.However,the kinematic viscosity of ethylene glycol is relatively high,and it is difficult to form a homogeneous mixture with fresh air if low pressure injection is used,which is not good for the combustion process of diesel engine.Therefore,this thesis innovatively proposes to increase the injection pressure of ethylene glycol,trying to improve the atomization conditions of ethylene glycol to further enhance the combustion efficiency of diesel engines and reduce pollutant emissions.The paper is supported by Innovation Capability Support Program of Shaanxi（Program No.2021TD-28）and Key Research and Development Program of Shaanxi（Program No.2019ZDLGY15-07）.Dual fuel combustion and emission characteristics are tested on a modified 4-cylinder turbocharged common rail diesel engine by high pressure injection of ethylene glycol in the inlet and direct injection of diesel in the cylinder.Firstly,the effect of the injection pressure of ethylene glycol（EGP）on the performance of the dual-fuel engine is studied.The engine speed is 1600rpm,and the BMEP is 0.42,0.70 and 0.92MPa,respectively.The EGP is selected as 5,10 and 20（MPa）,denoted as EGP5,EGP10 and EGP20;The substitution ratios are 0,5,10,15,20 and 25（%）,denoted as EG0,EG5,EG10,EG15,EG20and EG25.The results are as follows:At low load and in the same EGP,the peak pressure and the peak heat release rate decrease first and then increase with the increase of ethylene glycol substitution rate.At medium and high loads,with the increase of substitution rate,the curve of heat release rate in the main injection stage with the change of crankshaft angle gradually appears double peak.At the same load,the peak pressure in the cylinder has a slightly decreasing trend with the increase of EGP.At low and high loads,the ignition delay period is prolonged with the increase of EGP.The duration of combustion decreases with the increase of EGP at medium and low loads,but is almost unchanged at high load.The higher the EGP is,the higher the effective thermal efficiency is.However,there is no significant difference in the effective thermal efficiency between different EGP under high load.Under the same substitution ratio,the NO_x emissions of EGP5 are higher than those of EGP10 and EGP20 under medium and low loads,while the NO_x emissions of those three are basically the same under high loads,besides,the peak number concentration of EGP5 is higher than that of EGP10 and EGP20.When the substitution ratio increases,the number concentration of ultrafine particles gradually increases,and the peak number concentration shifts to the direction of small particle size.Next,the effects of injection time of ethylene glycol(T_EG)and pre-main injection interval(T_in)of diesel on engine combustion and emissions are also studied under the working conditions of 0.70MPa and 1600rpm.T_EG is selected as 0,240 and 480（℃A）,denoted as T_EG0,T_EG240 and T_EG480;T_in is selected as 8,10,12,14（℃A）.The research results are as follows:Under the same T_in conditions,the variations of the pressure and heat release rate of three T_EGwith the crankshaft angle are basically the same.The ignition delay period under different T_EG increases almost linearly with the increase of T_in,and the combustion durations lengthen with the increase of T_in.The effective thermal efficiency decreases with the increase of T_in.When T_in is 8°and 12℃A,the cyclic variation coefficient is relatively larger,but when T_in is10°and 14℃A,the cyclic variation coefficient is relatively smaller.The NO_x emission of the same T_EG decreases with the increase of T_in,and the NO_x emission is the lowest when T_in is 12℃A.The peak number concentration of ultrafine particles increases with the increase of T_in,and its peak number concentration shifts to the direction of small particle size.The weighted average particle size of ultrafine particles gradually decreases with the increase of T_in.Through the above experiments,it’s found that the ethylene glycol diesel dual fuel engine has good power performance and low emission level under medium and high loads,especially when the EGP is 20MPa,injection time of ethylene glycol is selected as 1-cylinder inlet starting point and the pre-main injection interval is 12℃A,the engine has great combustion and emission performance.