A deep understanding of soot production in flames is mandatory to control this pollutant emission and design zero emission combustors. In this context, we propose to combine Auto-Compensated Laser-Induced Incandescence (AC-LII) and Separated-Pulse LII (SP-LII) approaches to measure three relevant soot quantities using a single experimental setup: soot volume fraction \(f_v\) , absorption function \(E(m_\lambda )\) , and gas temperature \(T_0\) . In theory, this combination is quite simple as it requires measuring the LII signal at two wavelengths for a reduced number of laser fluences. However, in practice, this combination is not trivial since each LII approach has its own limitations. Specifically, the SP-LII approach requires low laser fluences to guarantee a linear relation between the peak laser-induced soot temperature \(T_M\) and laser fluence F, namely the linear regime. At the same time, \(f_v\) values estimated using the AC-LII technique strongly depend on the laser fluence, a well-know behaviour referred to as the ‘ \(f_v\) anomaly’, especially at low fluences. Thus, in this work, we establish a procedure to reduce the ‘ \(f_v\) anomaly’ when performing in-flame measurements at low laser fluences so to allow a combination of AC-LII and SP-LII methods. For this, this work mainly focuses on the contribution of the background subtraction on the ‘ \(f_v\) anomaly’ when considering measurements in the linear regime observed at low fluences. First, we theoretically quantify the error on the estimation of \(T_M\) and \(f_v\) due to background subtraction. Then, a two-loop iterative procedure is proposed to correctly estimate \(T_M\) , \(T_0\) and \(E(m_\lambda )\) . This is necessary to reduce the ‘ \(f_v\) anomaly’ and to correctly predict \(f_v\) in the linear LII regime. Finally, the accuracy of the combined AC-LII/SP-LII approach is evaluated by comparing the obtained results with reference state-of-the-art data for \(f_v\) , \(T_0\) , and \(E(m_\lambda )\) . This comparison demonstrates, for the first time, the feasibility of a combined AC-LII/SP-LII strategy to obtain \(f_v\) , \(T_0\) , and \(E(m_\lambda )\) fields from a single LII setup, once the proposed procedure for background subtraction is implemented to partially correct the ‘ \(f_v\) anomaly’.
