The bandpass filtered images of impinging flames in an opposed multi-burner (OMB) gasifier was visualized by a CCD camera combined with a high temperature endoscope. A filtering and image processing method by use of three bandpass filters was applied to subtract soot and CO2* contributions in the CH* band and obtain the CH* chemiluminescence of impinging flames. The results show that a clear reaction core is generated in the impinging zone of four-burner impinging flames. The size of the reaction core is affected by the O/C equivalence ratio ([O/C](e)) and the impingement effect is relatively stronger at lower [O/C](e). The flame lift-off length in the gasifier is jointly controlled by the syngas concentration and the diesel atomization effect. The impingement effect shortens the flame lift-off length. The relationship between the syngas concentration and the maximum CH* intensity makes it possible to evaluate the syngas concentration from CH* intensity. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 2007-2018, 2017