The use of diesel fuel to power a solid oxide fuel cell (SOFC) presents several challenges A major Issue is deposit formation in either the external reformer the anode channel or within the SOFC anode itself One potential cause of deposit formation under autothermal reforming conditions is the onset of gas-phase reactions upsteam of the catalyst to form ethylene a deposit precursor Another potential problem is Improper mixing of the fuel air and steam streams Incomplete mixing leads to fuel rich gas pockets in which gas phase pyrolysis chemistry might be accelerated to produce even more ethylene We performed a combined experiment/modeling analysis to identify combinations of temperature and reaction time that might lead to deposit formation Two alkanes n-hexane and n-dodecane were selected as surrogates for diesel fuel since a detailed mechanism is available for these species This mechanism was first validated against n-hexane pyrolysis data It was then used to predict fuel conversion and ethylene production under a variety of reforming conditions ranging from steam reforming to catalytic partial oxidation Assuming that the reactants are perfectly mixed at 800 K the predictions suggest that a mixture must reach the catalyst in less than 01 s to avoid formation of potentially troublesome quantities of ethylene Additional calculations using a simple model to account for improper mixing demonstrate the need for the components to be transported to the catalyst on a much shorter time scale since both the relatively lean and relatively rich regions react faster and rapidly form ethylene (c) 2010 Elsevier BV All rights reserved