Ashing affects the analysis. The fuel ashing temperature and the atmosphere influence the melting of inorganic matter which form the ash sample.
An advanced analysis includes dissolving the fuel and an elemental analysis of the solution, allowing to measure all the inorganic elements, without ashing. The evolution of the fraction of melt of inorganic matter present in the fuel, as a function of temperature and combustion atmosphere, is a better indication of the fuel behaviour. This can be numerically predicted with BIOFACT.