Experimental On The Influence Of Spray And Combustion Characteristics About Pilot Injection Of Split-Injection On Main Injection Under Gasoline/Diesel Blended Fuels

At present,the world faced a series of social problems,such as energy shortage and environmental pollution.Global promotion of energy conservation,environmental protection and sustainable development had become the main development strategy.As one of the main sources of petrochemical fuel consumption and pollutant emissions,diesel engines have become the mainstream research direction to improve engine thermal efficiency and reduce emissions.Improved engine thermal efficiency and lower emissions had become the mainstream research.Among them,the process of fuel spray and combustion have an important impact on thermal efficiency and emissions during engine operation.Recent studies have shown that the use of high-pressure injection,multiple injection strategies and changes fuel properties combined with new combustion modes(HCCI,PCCI,RCCI and LTC)can better solve the above problems.The constant volume combustion chamber(CVCC)can simulate the high temperature and pressure environment of the engine cylinder Therefore,the research of blended fuel multiple-stage injection strategy by use CVCC and visualization optical method has significance guiding for the design of real engine injection strategy and piston bowl.In this paper,low cetane number,strong volatility,low kinematic viscosity gasoline was blended in diesel combined with the split-injection strategy and optical method.The effects of injection pressure,ambient temperature,pilot injection ratio and dwell time on the spray and combustion characteristics of two fuels(diesel and G20)investigated.The LED-Mie scattering spray test bench was built based on a CVCC and a high-speed digital camera.The effects of different parameters on single injection and main injection of split-injection sprays were studied.The results show that: The spray penetration distance of single injection are basically the same,the spray cone angle of G20's single injection is slightly larger than diesel when the ambient temperature is 300 K.The initial spray penetration distance of two fuels single injection is basically the same,it is found that the injection pressure has less influence on the spray penetration as the spray reaches a steady state,when the ambient temperature is 850 K.At the same time,it is found that the spray penetration distance of main injection of split-injection is basically the same as the single injection from the initial stage.Then about 200?s,the spray penetration distance of main injection is slightly smaller than the single injection.The pilot injection ratio and dwell time have little effect on the spray penetration distance and spray cone angle of main injection of split-injection.The Laser-Mie scattering and chemiluminescence combustion test bench was built based on CVCC and high speed digital cameras.The effects of different parameters on single injection and main injection of split-injection combustion were studied.The results show that: The initial ignition mode of two fuel's single injection has slightly different,and the ignition mechanism of the main injection of split-injection at the pilot ratio of 10% is different from 20% and 30%.At the same time,it is found that the ignition delay and combustion duration is decreased,while the flame lift-off length and liquid length increased with the injection pressure increase at single injection condition.Compared to single injection condition combustion characteristics,the main injection of split-injection has the following characteristics.The initial ignition position is closer to the nozzle,the ignition delay is greatly shortened,the combustion duration increase,the flame lift-off length greatly reduce,and the liquid length decrease.At the same time,as the ratio pilot injection amount increase,the ignition delay period fluctuates,the combustion duration increases,the flame lift-off length slightly increase,and the liquid phase length decrease.The ignition delay and flame lift-off length of G20 single injection are greater than diesel,while the combustion duration and liquid length are less than diesel under the same experiment conditions.The ignition delay,combustion duration,flame lift-off length,and liquid length of split-injection's main injection of G20 are all smaller than diesel.In this paper,the research reveals the effect of changing fuel physical properties on the characteristics of fuel spray and combustion.The effects of pilot injection on main injection spray combustion characteristics about two fuels injection strategies were studied and some meaningful conclusions were obtained.There are some innovation in the optical test method to realize the simultaneous measurement of various data,and it has certain guiding significance for the research on the selection of subsequent fuel physical properties and injection strategy.