Infra-red measuremnts of the combustion of particular matter (PM) deposited on the surface of a single layer diesel particulate filter (DPF) showed that it may proceed in three different modes: either by a moving hot zone emanating from a single ignition point, or hot zones generated at several different ignition points or uniform combustion all over the surface. The velocity of the downwards moving temperature front exceeds that of the upstream front bounding the hot zone. The number of ignition points increases as the PM loading is decreased. The highest temperature rise is obtained by a downward moving hot zone. Avoiding this mode of combustion decreases the probability of excessive hot zone formation during the PM regeneration. (C) 2009 Elsevier Ltd. All rights reserved.