Carbon in diesel participate matter: Structure, microwave absorption, and oxidation

The structural, microwave absorption, and oxidation characteristics of diesel particulate matter (DPM) collected from a CAT 3304 diesel engine are reported. The x-ray diffraction of DPM yields the characteristic peaks of pregraphitic carbons (cokes and pitches), and its modeling yields d₍₀₀₂₎ ≍ 3.429 Å and a crystallite size of about 20 Å. The real and imaginary parts of the dielectric constant ∊ = ∊′ + i∊″ are measured at 8.7 GHz using the cavity perturbation technique. The measured values for the DPM are ∊′ = 8.6 ± 1.7 and ∊″ = 7.4 ± 1.5, compared to ∊′ ≍ 1.0 and ∊″ ≍ 6 × 10⁻⁵ for the ceramic trap material used for collecting DPM. The oxidation products of the DPM, analyzed by FTIR spectroscopy, are found to contain CO₂ and CO with a peak yield occurring around 500 °C. Since microwave power absorption is proportional to ∊″, these results show that selective microwave heating of the DPM in the ceramic traps should be a very efficient process with CO₂ and CO as the main oxidation products.