The problem of tar entrainment in the gas stream had been solved by designing downdraft gasifiers where the gasifying agent enters from the top and the gaseous products leave the reactor through a bed of hot ash at the bottom. A schematic of this reactor is shown in Fig. 10.1b. The main advantage of downdraft gasifiers lies in the possibility of producing a tar-free gas from high volatile fuels which will be suitable for engine applications. This is due to the fact that most of the tar is cracked when passing through the hot ash before exiting the reactor. A major drawback of this type of gasifier is its inability to operate with a wide range of fuels. In particular, fluffy, low density materials can cause flow problems, like an excessive pressure drop, requiring the solid fuel to be pelletized or briquetted before use. Downdraft gasifiers also suffer from slagging when operating with fuels characterized by high ash content. Compared to updraft gasifiers, downdraft systems show lower efficiencies resulting from a lack of internal heat exchange as well as the LHV of the gas.