| With the increasingly serious problems of energy and environment,it is the main research direction of engine industry to seek new energy as alternative fuel of engine.As a kind of alternative fuel with abundant reserves,favorable price,good emission performance and high safety,natural gas has been widely concerned,and the development of natural gas engine has become a research hotspot in the industry.However,because the natural gas engine adopts the form of gas injection,there are many problems,such as low charging efficiency,complex structure layout,high knock probability and so on.For this reason,the concept of "liquid injection in LNG cylinder" is put forward in the industry.The engine adopting this injection mode can not only solve the above problems well,but also utilize the latent heat of vaporization of liquid natural gas in the cylinder,effectively reduce the maximum temperature in the cylinder,and then reduce the generation of NOx.As the research is in the initial stage,the current research is still in the stage of simulation.However,with the deepening of research,simulation must be combined with test,so the design of the preliminary test bench is particularly necessary.Based on the fuel supply system of LNG engine using HPDI technology,a set of LNG high pressure liquid injection fuel supply system including dual fuel injectors is designed to meet the needs of subsequent tests.First of all,the existing LNG fuel supply system is analyzed and studied.At the same time,according to the particularity of LNG high-pressure liquid injection,the pressurization mode,heat insulation mode and pressure stabilizing mode in the design scheme are determined.Based on the high-pressure common rail injector,a dual fuel injector suitable for this system is designed,and a design scheme of LNG highpressure liquid injection fuel supply system is obtained.Then,the model of the whole LNG high pressure liquid injection fuel supply system is built by using AMESim software.Secondly,the AMESim model of the new dual fuel injector is used to analyze the working characteristics of the injector under different important parameters,such as LNG pressure,diesel pressure,plunger diameter of the control cavity top rod,oil inlet hole diameter and so on.It is verified that the new injector can realize the asynchronous injection of dual fuel in theory.Finally,according to the rule analysis,the optimal design parameters of the dual fuel injector are obtained: the diameter of the plunger is 4.2mm,the diameter of the oil inlet hole is 0.28 mm,and the other parameters can be directly used in the design of the prototype injector.Finally,the AMESim model of LNG high-pressure liquid injection fuel supply system is used for simulation calculation,and the average pressure fluctuation,peak pressure and rail pressure establishment time are selected as the characterization parameters of the pressure fluctuation characteristics of highpressure pipeline,and the influence laws of the changes of the speed of LNG low-temperature plunger pump,the structure parameters of buffer pipe and high-pressure oil pipe on the pressure fluctuation characteristics of high-pressure pipeline are studied,The simulation results show that the reasonable design parameters of high-pressure pipeline can better restrain the pressure fluctuation on the basis of ensuring a faster rail pressure establishment time.Considering the influence of various characterization parameters,it is confirmed that the structural parameters of high-pressure pipeline from LNG low-temperature plunger pump to buffer pipe are: pipe diameter 3mm,length 300mm;the structural parameters of high-pressure pipeline from buffer pipe to dual fuel injector are: pipe diameter 3.5mm,length 700mm;the diameter of buffer pipe is 14 mm,length 300 mm. |
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