A Rich-Catalytic Lean-burn (RCL (R)) combustion system was developed for operation on natural gas, but also provides significant advantages for fuel-flexible operation on non-methane fuels. Most notably, fuel-rich operation limits the extent of catalyst-stage reaction based on available oxygen, regardless of the fuel's intrinsic reactivity on the catalyst. Thus, similar catalyst and reactor performance can be obtained for widely varying fuel types. In addition, catalytic pre-reaction extends the combustor's lean flammability limit for all fuels, allowing low-temperature combustion of both conventional and low-heating-value fuels, with concomitant low NOx emissions. This paper presents test results for RCL (R) combustion with various fuel types, including gaseous, pre-vaporized liquid, and simulated low-Btu fuels. Although these fuels have widely varying proper-ties, a single type of catalytic reactor was successfully tested for all of these fuels by modifying only the fuel delivery system upstream of the reactor. Test results show similar reactor performance for all fuels tested. (c) 2006 Elsevier B.V. All rights reserved.