Investigation Of Injection Characteristics Of Diesel Injector With Renewable Syntetic Oxygenated Fuels Using Experiment And CFD Simulation

The diesel engine is wildly used in the world.The injection characteristics have great influences on the air and fuel mixture formation and combustion,which affect the power,economy and emission.Synthetic oxygenate fuels are important fuels in the category of low carbon renewable fuels for diesel engine.The aim of this work is to investigate the hydraulic injection characteristics with different synthetic oxygenated diesel fuels including Butyl formate,Polyoxymethylene dimethyl ether(PODE),Butanol and Octanol.A two-layered 8-hole solenoid injector of a heavy-duty engine with the injection inclination angle(the angle between the centre axis of the needle and the centre axis of the hole)of 75° was used for the investigation.The vertical height difference of the axis of the upper-and lower-layered hole is0.20 mm.The challenge with regard to the investigated synthetic fuels is to use an injector without any modification.The hydraulic injection characteristics of the injection were evaluated by the following values: The injection rate,injection gravimetric quantity,injected amount of energy,standard deviation of the injection quantity,coefficient of variation of the injected quantity,injection duration and injection delay at various pressures and energizing times.The injection rates were measured by long tube method in a fuel pump test bench.This work is split into three parts.As part of the preliminary investigation,the physical properties of the fuels were determined using standardized analysis methods.The second step is the experimental investigation of the hydraulic characteristics of different renewable synthetic oxygenated fuels.This is necessary to validate the numerical results.The last step involves a CFD(Computational Fluid Dynamics)simulation of injection process with neat diesel and renewable synthetic oxygenated fuels at 100,150 and 200 MPa injection pressures.The injection rates of PODE are slightly higher than B0 at all injection pressures.Butyl formate has a higher injection rate at all injection pressures and energizing times compared to B0.Due to the high viscosity of Octanol,it is difficult to measure a stable injection rate under low injection pressures and short energizing times.The difference in injection rates between Octanol and B0 is small especially with long energizing times.At higher injection pressures and longer energizing times,the influence of the fuel on the injection quantity becomes more relevant,while the influence of the fuel on the injection delay and injection duration was found to be small.In summary,from the aspect of the hydraulic injection characteristic,as a neat fuel,PODE could not replace the fuel B0 because of its low injected energy.Alternatively,PODE blends with diesel could increase the injection energy,implying that PODE and Butyl formate could be used as additives blending with B0.Besides,Octanol is suitable to replace B0 as a neat fuel.Finally,it can be summarized that all investigated synthetic oxygenated fuels show the potential to replace B0 in different ways,unless the features of each fuel are taking into account.For instance,the low injected energy of PODE must be considered due to its very similar density and viscosity.The somewhat lower low heat value of Butanol should be taken into account when considering it as an alternative fuel.The high viscosity of Octanol should be considered,because it will lead to failure of the injection at low injection pressures and short energizing times.The results clearly show that based on the hydraulic injection characteristics,the investigated fuels can be used in today’s modern electronically controlled common-rail injection systems in diesel engine with small adaptions.An empiric correlation between the discharge coefficient and the Reynolds number(Renumber)was determined,which can be used to calculate the discharge coefficient through Reynolds number.The discharge coefficients of Butyl formate and PODE behave differently compared to B0.The Re-numbers of Butyl formate and PODE are higher due to their lower viscosity.PODE has lower Cv(Flow coefficient)values,especially at short energizing times.The Re-numbers of Octanol and Butanol are in the same range,and the Cv values tend to be slightly higher than that of B0.The 3D-model of the two layered 8-hole solenoid injector under 150 MPa and 700 μs was established,and the discrepancies in injection characteristics between holes from two different layers of the injector were investigated.The model was validated by presenting consistent injection rates between the simulation and the experiment.The numerical results indicate that all fuels showed only slight deviations from B0 at various injection pressures.The cavitation and velocity for the synthetic fuels are similar to that of B0.This indicates the suitability as fuel without major adjustments to the injector.The absolute velocities of the synthetic fuels differ from B0,especially PODE,which has significantly slower velocities in the outlet and in the injector.However,it does not lead to a lower injection rate since this is compensated by the higher density.This is because the injection rate depends not only on the density,but also on the effective area and effective velocity.The lower velocity is overcompensated by the higher density,resulting in a higher injection rate.Butyl formate has a higher total injection rate compared to B0,but the difference between the individual layers is smaller than that of B0.The cavitation of Butyl formate hardly differs from that of B0.For Octanol,its viscosity is different from that of B0,the cavitation and velocity behaviour are similar to B0.This is due to the similar density.In addition,it is found in the simulation that the fuel vapor fraction in the lower layered hole is smaller than that of the upper layer for all investigated fuels.The cavitation in the lower layered hole is smaller than that of the upper layer.This represents that the effective flow area in the lower layered hole is bigger than that of the upper layered hole.The average velocity and the fuel injection quantity in the lower layered hole is bigger than in the upper layered hole.This tendency is identical with the measured cycle injection quantities of upper and lower layered holes of the same type injector.