Carbonaceous material associated with potent carcinogens such as 3-4 benz(a)pyrene (BaP) and other polynuclear aromatic (PNA) hydrocarbons constitutes by far the greatest part of the particulate found in the exhaust gases of an internal combustion engine.
The probable precursors of carbon particles are radicals formed in the incomplete combustion zone while their nucleation is made possible by ions originating in the flame.
Ion current instantaneous values were measured by means of a modified Langmuir's probe, thus calculating thickness and speed of the flame in an engine cylinder. Relations between ion current and collected soot weight were examined. Fuel quality and additive influences over carbon and PNA formation were obtained.