Research On Fuel Injection Control Strategy Of Dual Fuel Engine Based On Fuel Characteristics

For a long time,in the internal combustion engine research process through the optimization of combustion process to achieve internal purification has attracted much attention,and the new combustion mode to improve the thermal efficiency and reduce emissions has also become a research hotspot.Based on the idea of synergistic control of fuel physical and chemical properties and combustion boundary conditions,this paper explores the RCCI combustion mode controlled by fuel reactivity.Through the inlet jet low reactivity fuel,multistage jet high reactivity fuel in cylinder,flexible control low reactivity of fuel and direct injection high reactivity of fuel energy,experimental study on the characteristics of fuel injection parameters and the fuel on RCCI engine combustion,the influence of the performance and emissions,fuel feature is proposed based on the fuel injection control strategy under the condition of.In this paper,a four-cylinder turbocharged and intercooled diesel engine was transformed into a single-cylinder dual-fuel compression ignition engine.Two sets of fuel injection control systems were established based on open ECU(NI2106),namely inlet injection and direct injection in the cylinder.The active control and flexible adjustment of the intake flow and fuel injection parameters were realized by using the simulated pressurization system.A combustion data acquisition and emission testing and analysis system was established to realize the realtime measurement and analysis of combustion characteristic parameters and pollutant emissions in the cylinder.The main research contents and conclusions are as follows:(1)The effects of low reactive fuel energy ratio on the combustion,performance and emissions of the RCCI engine were first carried out,and the optimal port fuel injection ratio was determined.The test results show that the ratio of highly reactive fuel to energy decreases at a higher gasoline ratio(60%-70%),and a large amount of homogeneous mixture has been formed in the cylinder before the ignition.The combustion process is similar to homogeneous charge compression combustion,showing a higher peak heat release rate and a larger pressure in the cylinder,which seriously affects the engine performance.At a lower gasoline ratio(30%-40%),the reduction of gasoline ratio leads to a reduction in the pre-mixture in the cylinder,a reduction in the premixed combustion ratio,and an increase in the diffusion combustion ratio,resulting in higher particulate emissions.When the premixed rate is 50%,PM emissions can be effectively reduced on the basis of a small increase in NOx,and the burst pressure in the cylinder can also be reduced to make the combustion process more stable.According to the above analysis,50% gasoline ratio is the best airway fuel injection ratio.(2)Reaction control Combustion process of compression ignition is based on the activity of the fuel and the mixed gas reaction layered collaborative control,direct injection fuel injection strategy is an important way to control the combustion mode and achieve clean combustion.Based on coal-based synthetic oil/gasoline and diesel/gasoline based integrated fuel,keep unchanged airway jet fuel proportion(50%),the experimental study on the direct injection of fuel injection advance two pieces timing,main injection timing,main injection quality than spraying the influence law of parameters for the engine combustion and emissions,put forward the best fuel injection control strategy based on engine performance.The results show that in the strategy of two direct injection,the formation and combustion process of the in-cylinder mixture are influenced by two fuel injection.Pre-injection is beneficial to improve the reactivity of the mixture in the cylinder.Early pre-injection timing can make the highly reactive fuel injection into the piston extrusion area and the cylinder wall gap,improve the reactivity of the fuel at the low temperature gap,thus reducing HC、CO and PM emissions.The reaction activity stratification of the mixture is mainly controlled by the timing of the main injection.The earlier the timing of the main injection is,the longer the ignition retardation period of the main injection is,the more obvious the stratification of the mixture is.The local equivalent ratio gradient of the mixture increases,and the combustion temperature and combustion rate increase,so the HC 、 CO and PM decrease.With the increase of the preinjection mass ratio,the reactivity of the mixture in the cylinder can be improved and the emissions of CO and PM can be reduced.However,with the increase of the preinjection mass ratio,the ignition time is gradually changed from the control of the timing of the main injection to the control of the chemical reaction kinetics of the mixture,resulting in large negative work of compression and affecting the engine performance.(3)On the basis of the above research,the injection control parameters within the operating condition of RCCI are optimized by using the value function.The results show that under low load conditions(IMEP=6.5bar),both coal based synthetic oil and diesel fuel need earlier preinjection timing to improve the reactivity of the pre-mixture in the cylinder.At the same time,coal based synthetic oil needs lower premixed ratio and earlier primary injection timing to achieve optimal engine performance,while diesel oil needs higher premixed ratio and later primary injection timing to achieve optimal engine performance.Compared with diesel,the PM and CO emissions of coal-based synthetic oil are reduced by 50% and 33%,respectively.At moderate load conditions(IMEP=8.5bar),both fuels require a higher premix ratio to achieve optimal engine performance.For coal-based synthetic oils,due to the high cetane number,it is necessary to postpone the pre-injection timing to about-24° CA ATDC to avoid excessive pressure rise rate.With the increase of the temperature and pressure in the cylinder and the adoption of a larger premixed proportion,the mixing degree of the mixture in the cylinder is improved,and the indicated thermal efficiency is increased.The indicated thermal efficiency of the two fuels reaches more than 50%.With the further increase of load,in high load condition(IMEP = 10.5 bar),in order to avoid the engine detonation,two only lower proportion of premixed fuel that can be used to meet the requirements,inadequate mixed results in a mixture in the cylinder,fuel atomization is poorer,causing higher PM emissions,by contrast,found that the particulate emissions almost are the same.