An Experimental Study Of Gasoline And Blended Fuel Compression Ignition Combustion

High octane number(ON)fuels have high resistance to auto-ignition and are helpful for preparing homogeneous mixture.These fuels have the great potential for achieving higher loads with clean combustion and high efficiency.Compression ignition with high octane number fuels has been widely concerned by domestic and foreign researchers.However,there are several obstacles for applying high octane number fuels,such as combustion stability at low load without inlet heating,combustion robust at high load condition.This dissertation studied the effects of injection parameters and initial inlet conditions on combustion stability,robust and emission performance at low load with gasoline compression ignition.Especially,at low and high load condition,the controlling method of cylinder charge for high efficiency and clean combustion is studied.At last,a comparative study of the fuel reactivity effect on combustion is studied by different gasoline and diesel blended fuels,and find a high octane fuel which is suitable for the stable combustion of the engine without intake air heating,and expand the maximum load of clean and high-efficiency combustion by using this fuel.Study on combustion stability under small load shows that shorten ignition delay of gasoline can improve the combustion stability and thermal efficiency by increasing inlet temperature and pressure,coolant temperature,reducing injection pressure,EGR etc.Optimal controlling the intake pressure,EGR and injection ratio can effectively control the heat release rate and combustion ringing intensity,and realize clean and high-efficiency combustion.Such as using 50%of the first injection ratio and the injection timing for(-70,-24),controlling the oxygen concentration in the vicinity of 17.5%,while the cylinder charge density near 30.6kg/m~3,can realize indicated thermal efficiency as high as 52.7%at 6bar IMEPg,meanwhile RI is only4.3MW/m~2.At high load condition,reducing the oxygen concentration in the cylinder can control the combustion robust.By controlling the oxygen concentration near 14.5%,NOx emission can be controlled within 0.4g/kwh.By using the Retarding Intake Valve Closing Timing system(IVCT)can realize high efficiency and clean combustion.Because it can reduce the effective compression ratio and compression temperature in cylinder,increase fuel ignition delay,therefore soot emission and heat transfer loss reduced.Such as by using IVCT,with 3.0bar inlet pressure,can realize52.3%indicated thermal efficiency at 16.5bar IMEPg,which higher than the same mass of intake air condition by 2.4%.Coupled with IVCT system,optimal controlling the pilot injection ratio and injection timing,increasing the intake pressure can accelerate the mixing rate of fuel and reduce the fuel oxygen equivalence ratio.by delaying the main injection timing can shorten the mixing time of main injection fuel,which can reduce the combustion robust.At the same time,the total heat capacity and absolute oxygen content of the tank are high,the heat transfer loss rate and the incomplete combustion loss rate are reduced,which is beneficial to improve the average indicated thermal efficiency.Such as with IVCT and 3.4bar inlet pressure,using 100MPa injection pressure and 9.39%pilot injection ratio,can realize 53.7%of thermal efficiency and clean combustion at15bar IMEPg.Compared with the same injection rate with 3.1bar inlet pressure and IVCT case,the efficiency is increased by nearly 1%.Increasing the proportion of gasoline in gasoline and diesel blended fuel,the octane number of blended fuel is increased,and the increase of octane number is proportional to the proportion of gasoline.When the proportion of gasoline in blended fuels is up to 90%,the combustion process of mixed fuel are close to that of G100fuel.At same inlet condition,reducing fuel reactivity can reduce the heat transfer loss,but the loss of incomplete combustion loss is higher than the reduction rate of heat transfer loss,while the exhaust loss rate is changed small,as a result the indicated thermal efficiency decreased.Optimizing intake pressure,EGR rate,injection pressure and injection timing parameters can effectively control the combustion process of different gasoline and diesel blended fuel,and achieve clean and high-efficiency combustion.Finally,using G90 blended fuel can realize the stable operation of the small and medium load compression ignition combustion without intake air heating,and expand clean and high-efficiency combustion load to 80%of the original engine.