Laser ignition and flame characteristics of pulsed methane jets in homogeneous isotropic turbulence without mean flow

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>The influence of turbulence on the minimum ignition energy (MIE) and ignited flame characteristics is investigated for pulsed methane diffusion jets ignited by laser-induced plasma. The methane jet is injected in a volume of homogeneous and isotropic air turbulence without mean flow, with the level of turbulence being controlled independently. The study is carried out for a range of fuel jet (<I>Re</I> <SUB>jet</SUB>) Reynolds number, namely 1000, 2000, and 3000, and a range of turbulent (<I>Re</I> <SUB>λ</SUB>) Reynolds number, namely 0–207. The results show that the position of the maximum intensity of flame emission was randomly scattered due to the fact that the ignited flame is deflected from the nozzle axis by the turbulent velocity fluctuations. The effect is more profound at higher <I>Re</I> <SUB>jet</SUB>. The value of the MIE, determined according to 50% ignitibility of mixture, increases by a factor of 2 for an increase of <I>Re</I> <SUB>λ</SUB> from 0 to 207 and by a factor of 5 for an increase of <I>Re</I> <SUB>jet</SUB> from 1000 to 3000. Two trends are observed on MIE with <I>Re</I> <SUB>λ</SUB>. For low <I>Re</I> <SUB>λ</SUB>, MIE is independent of <I>Re</I> <SUB>λ</SUB>. Past a critical value of <I>Re</I> <SUB>λ</SUB>, MIE increases as a linear function of <I>Re</I> <SUB>λ</SUB>. This transition occurs at critical values of <I>Re</I> <SUB>λ,c</SUB> = 158, 197 and 202 for <I>Re</I> <SUB>jet</SUB>= 1000, 2000 and 3000, respectively. The mean value of MIE for ignition before and after transition is a linear function of <I>Re</I> <SUB>jet</SUB>. The difference between the mean value of MIE before transition and after transition is around 5mJ for all considered <I>Re</I> <SUB>jet</SUB>.</P>