Characterization of the Diesel Soot Oxidation Process through an Optimized Thermogravimetric Method

Abstract

A thermogravimetric analyzer (TGA) was used to oxidize real diesel soot produced in a modern four-cylinder, turbo-charged, diesel engine equipped with a common rail injection system. In the first part of the study, a large amount of soot produced with a variety of diesel fuels of current and future interest and in typical engine modes was collected. A thorough test matrix was designed and executed in the TGA to develop an optimized oxidation method, which allows for the determination of oxidation profiles, characteristic temperatures, and Arrhenius kinetic parameters. Such parameters are critical for modeling diesel filter regeneration and designing more efficient regeneration techniques. A comparison of this method to others proposed in previous literature is made, and the advantages are pointed out. In the second part, diesel and biodiesel soot produced in three engine operating modes (low, medium, and high load) was evaluated with the proposed method. The results showed that the effect of the fuel on the oxidation process was more significant than that of the engine mode. Biodiesel soot oxidation occurred at lower temperatures, proving the possibilities that this fuel offers for achieving more efficient filter regeneration. Although differences in the activation energy of diesel and biodiesel soot were not large, the oxidation rates of biodiesel soot were, on average, 1 order of magnitude above those of diesel soot.

Performance of diesel particulate filter catalysts in the presence of biodiesel ash species

“…This apparatus offers a simple and versatile performance combined with well-controlled experimental conditions [13]. The experiments performed, shown in Table 1, investigate the reactivity of mixtures of diesel PM, catalysts and various salts/simulated ash species (carbonates, phosphates and sulphates).…”

“…The development in sample mass as a function of temperature and time can be used for studies of characteristic oxidation temperatures as well as extraction of kinetic parameters [13]. A running average (upto 200 data points, corresponding to 15°C) was used to reduce signal noise and improve data interpretation, after it was verified that no data distortion occurred.…”

“…This work will mainly focus on the temperature at which the maximum mass loss rate takes place, but other additional characteristic temperatures (ignition/starting oxidation temperature, final oxidation temperature, etc.) have also been used in the literature [9,13,16]. An Arrhenius type equation, Eq.…”

“…(1), has been used to extract the kinetic data used to simulate the soot oxidation in a 10% O 2 atmosphere without water. A first order reaction with respect to soot and oxygen should be appropriate at the low temperature regime used in this study [13,16].…”

“…The introduction of biodiesel has been reported to cause an increased reactivity of particulate matter [13,14] and some changes in ash composition [6,15]. The increased reactivity has been attributed to a more open structure of the de-volatilized biodiesel PM, allowing swifter O 2 diffusion to reactive sites, which is supported by the extraction of overall ultra low sulphur diesel (ULSD)/ pure biodiesel (B100) kinetic data when normalising with the instantaneous surface area (E a = 113 kJ/mol) [14].…”