A Shock Tube Study Of Dimethyl Ether Ignition Effected By NO₂

As the main producer of energy,the combustion of fossil fuels is contributed to the increased pollution,driving the search for clean alternatives and advanced combustion strategies.Dimethyl ether?DME?is an alternative to diesel for its high cetane number?55?60?and soot-free combustion,the high-temperature oxidation of DME/air mixture generates nitrogen oxides?NOx?,which is one of the major air pollutants.The NOx emission can be lowered by exhaust gas recirculation,and the recirculated NOx will affect the fuel combustion process significantly.Thus,a well-validated DME/NOx kinetic model is desirable for the development of DME combustion.In this paper,we study the reason why NOx promote DME ignition with a combustion shock tube,an updated kinetic model is proposed and validated using Chemkin ? and Senkin,main works are as follows:Firstly,a shock tube facility together with the gas delivery device,electro-heating diaphragm bursting device,pressure test and spectral measurement system was established.The shock tube has a 50 mm inner diameter,and is separated into two parts:a 3.26 m long driver section and a 4.52 m long driven section.Under the contact surface tailoring conditions,test time in shock experiment is up to 7?8 ms.Secondly,DME ignition is studied experimentally,and the pressure and OH*emission histories are recorded simultaneously.Ignition delay times are measured at temperature of 1170?1510 K,pressure of 4?18 atm,and equivalence ratio of 0.1?2.0.With the increasing of temperature or pressure or equivalence ratio,ignition delay times decrease significantly,while the effects of equivalence ratio on ignition delay times are negligible at high temperature.Thirdly,the role of NO₂ in DME ignition is investigated using a shock tube.Ignition delay times are measured at 987?1517 K and 4 and 10 atm.Different DME concentrations?equivalence ratios:0.5?2.0?and NO₂ concentrations?blending ratios of NO₂/DME:0%,30%,and 70%?are explored.NO₂ promotes DME ignition,and the promoting effect becomes more pronounced at high NO₂ concentrations or low temperatures.NO₂ addition also augments the influence of the equivalence ratio on ignition delay times.Finally,four detailed reaction mechanisms from the literature are examined against the ignition data,and an kinetic model?called AMD mechanism?with updated NOx sub-mechanism is proposed and validated in comparison to experiments.On the basis of the updated model,sensitivity analysis,reaction flux analysis,and rate of production analysis are conducted to provide details on the kinetic effect of NO₂ on DME ignition.