Introduction The use of diesel vehicles is constantly increasing mainly due to their inherent advantages, which in- clude fuel economy, durability, driveability, etc. [1]. The main issue concerning their use are the increased nitrogen oxides (NO x ) and particulate matter emis- sions (PM) [2]. Specifically, diesel PM represents an important health hazard a fact that has led the legisla- tion to adopt stringent emission standards. Diesel par- ticulate filters (DPF) are becoming wide spread as an effective measure to reduce PM emissions from diesel vehicles as they have filtration efficiencies close to 100% [3]. Due to the fuel penalty induced by the gradual loading of the filter, its periodical regenera- tion, i.e. the combustion of the accumulated particulates, is necessary [3]. It is therefore vital to fully understand, model and control the regeneration process in order to optimize the application and oper- ation of DPFs both for lifetime durability and fuel economy purposes. Consequently, the study of soot combustion for the extraction of kinetic data that can be coupled in modelling tools is very important. Dif- ferent experimental approaches have been used in the literature including thermogravimetric analysis (TG) [4–13], flow and bed reactors, etc. [14, 15]. When TG is used for the extraction of chemical kinetics data it has known experimental and computa- tional difficulties that include control of the reactant atmosphere [16], rate-controlling mass and heat trans- fer limitations [7, 8] as well as the choice of the opti- mal calculation method of the kinetic parame- ters, e.g. [17], which have led to extended debating about the reliability of its results. However, although TG cannot substitute in situ experiments, it is still an important experimental tool that has been used exten- sively for soot and carbon oxidation studies [e.g. 10, 13, 18], mainly because it represents a fast, economical and easy to use experimental solution. Although it is common to run non-isothermal TG using the same reaction gas throughout soot oxidation [6, 13], also a number of isothermal studies of soot re- activity are found in literature [4, 5, 7]. Non-isother- mal protocols are preferred because isothermal exper- iments necessitate more experimental time and more sample mass, while identical experimental conditions and homogeneous sample are also necessary. Also, in the case of exothermal reactions, such as soot oxida- tion, self-heating of the sample may occur leading to deviation from the desired isothermal conditions. However, the temperature gradients within the sam- ple are often neglected. This can be justified for smaller initial sample masses [7] and/or slower reac- tion [19], e.g. at lower O 2 concentration. Then the de- coupling of the effect of temperature and progress of reaction on the reaction rate and rate constant is possi- ble. Finally and despite the above mentioned limita- tions, isothermal studies are considered generally better for determining kinetic rates [18] while they also facilitate the investigation and modelling of reaction gas diffusion in the solid sample. 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2008 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands Journal of Thermal Analysis and Calorimetry, Vol. 95 (2009) 1, 141–147 ISOTHERMAL SOOT OXIDATION EXPERIMENTS WITH INTERMEDIATE GAS CHANGE IN A PERKIN-ELMER TGA6 Maria Kalogirou, P. Pistikopoulos, L. Ntziachristos and Z. Samaras * Laboratory of Applied Thermodynamics, Mechanical Engineering Department, Aristotle University Thessaloniki, P.O. Box 458 GR 541 24 Thessaloniki, Greece Two isothermal soot oxidation protocols were tested in a Perkin–Elmer TGA6: (1) the sample was heated under N 2 and then the re- action gas was introduced and (2) the sample was introduced after the empty furnace was heated under the reaction gas. The first protocol is common in soot oxidation studies, it gives a measure of the volatiles and is easier to handle, but as it is shown the deter- mined reaction rate may be falsified by the O 2 concentration. Using gas analysis it was found that ~2000 s are necessary for the complete gas change in the instrument. An instrument specific correction function involving the O 2 concentration and reaction order n with respect to O 2 was developed which allowed the correlation of the rates measured with both protocols. Keywords: evolved gas analysis, isothermal, oxidation, soot, TG * Author for correspondence: zisis@auth.gr