A partial combustion burner is introduced as a cleaning system for the tar content of gaseous (bio) fuel. The results of experiments, using a synthetic low calorific gas mixture, demonstrate the effectivity of the proposed process. In these experiments naphthalene is added as a model tar component. The effect of partial combustion of the fuel gasmixture on the naphthalene is examined for different air/fuel ratios (gimel) and varying hydrogen-methane fuel concentrations. For a fuel gasmixture with high methane concentrations or for higher gimel-values the total tarcontent slightly decreases. In this case the naphthalene polymerises, i.e. forms higher ring components and sometimes even turn into soot. At lower gimel's and higher hydrogen concentrations the tarcontent strongly decreases. Moreover, the naphthalene is now cracked, i.e. converted into lighter tars and permanent gases. It is found that, for fuel gases representative for biogasification products and at a gimel of 0.2, the presented burner reduces the tar content of the gas with over 90% by cracking. The paper ends with a short discussion on the conditions that may determine the cracking/polymerisation mechanism. (c) 2005 Elsevier Ltd. All rights reserved.