I found out that the GEnx engine uses a TAPS (Twin Annular Premixing Swirler) combustor. Is it a single or dual annular combustor ?
See this question. It is a single annular combustor (one ring of full nozzles). I think that "twin" refers to the fact that within a single fuel nozzle, there are two different fuel streams: the main stream and the pilot stream. This video might also help explain it a bit.