Investigation On The Enhancement Of Low-pressure Ignition Of The Hydrocarbon Fuel

Flying higher,faster and farther is the eternal pursuit of the aircraft.Flight vehicles usually fly in a limited range of velocity and altitude,which is called the flight envelope.For the military airplane,a higher flight altitude means a better anti-hit performance.Similarly,it is meaningful for passenger aircrafts to fly higher due to a lower flight resistance and fuel cost.However,the air pressure is much lower when an aircraft is fling at a higher altitude and it is challenging the ignite hydrocarbon fuels at low pressure.Researchers have done some research on the low-pressure ignition of hydrocarbon fuels and the challenges of low-pressure ignition have been identified.They have interpreted the difficulty of low-pressure ignition from different perspectives.However,there is no generallyaccepted explanation on the difficulty of low-pressure ignition until now.Furthermore,it is almost impossible to find a method to enhance the lowpressure ignition of hydrocarbon fuels.As a result,this paper firstly proposes a theoretical model of the low-pressure ignition.Furthermore,this paper puts forward a method to enhance the low-pressure ignition of hydrocarbon fuels.Finally,some experiments are conducted to test whether the method is applicable or not.Details are as follows:Firstly,in order to understand the low-pressure ignition in essence,this paper proposes a theoretical model of the low-pressure ignition limit,analyzing the parameters which affect the low-pressure ignition limit.Then a method for enhancing the low-pressure ignition of hydrocarbon fuel is suggested.The parametric analysis on the theoretical model of lowpressure ignition limit indicates that the reaction order and activation energy are the only two parameters influencing the low-pressure ignition limit.Because different reaction orders and activation energy result in different reaction pathways,we propose modifying the reaction pathway to enhance the low-pressure ignition of hydrocarbon fuels.Then,an additive design is used to modify the reaction pathway of hydrocarbon fuels,finally enhancing the low-pressure ignition.Regarding the additive,methoxydiethylborane(MDEB)is selected.By means of pyrolysis/gas chromatography-mass spectrometry and electron paramagnetic resonance,the oxidization routine of hybrid hydrocarbon fuels is measured.Compared with the traditional oxidization routine of hydrocarbon fuels,it is indicated that the oxidization of MDEB generates alkoxy radicals,which attack the hydrocarbon molecules,accelerating the generation of hydroxyl free radicals,finally enhancing the low-pressure ignition of hydrocarbon fuels.Finally,a low-pressure experiment is designed to investigate the effect of MDEB on the low-pressure ignition limit of hydrocarbon fuels.The low-pressure experiment is utilized to measure the low-pressure ignition limits of hydrocarbon fuels and MDEB/hydrocarbon hybrid fuels.The results show that the MDEB can extend the low-pressure ignition limit of hydrocarbon fuels(n-decane,n-hexadecane and RP-3 kerosene).20% MDEB makes the minimum hot-surface ignition temperature at 1 bar of ndecane,n-hexadecane and RP-3 kerosene decreased by 470 ?,415? and 460?.Based on the research above,this paper has established a theoretical model of low-pressure ignition limit and found the relationship between the reaction pathway and low-pressure ignition limit,successfully selecting the additive to modify the reaction pathway of hydrocarbon fuel oxidization,finally enhancing the low-pressure ignition of hydrocarbon fuels.The key points of this paper are as follows:(1)Through establishing the theoretical model of the low-pressure ignition limit,the relationship between the reaction pathway and low-pressure ignition limit is found;(2)We successfully design the additive to modify the reaction pathway of hydrocarbon fuels,finally extending the low-pressure ignition limit.The investigation above provides a new solution to enhancing the low-pressure ignition of hydrocarbon fuels,which is meaningful in enlarging the flight envelope of aircrafts and saving the great fuel costs for airlines.