Polycyclic Aromatic Hydrocarbon and Soot Emissions in a Diesel Engine and from a Tube Reactor

Abstract An investigation into the exhaust emissions of carcinogenic polycyclic aromatic hydrocarbons (PAHs) from a diesel engine was reported. The study is reinforced by the experimental results obtained from a tube reactor aimed at examining the PAH formation processes from these fuels. The paper cantered on the 16 priority PAHs suggested by the United States Environmental Protection Agency (US-EPA). These PAHs were produced by burning conventional diesel fuel and a few binary fuels prepared by blending various proportions of toluene into heptane. Special consideration was given to the B2 subgroup of PAHs which are known human-carcinogens. Both the gas born (smaller) PAHs, as well as the larger PAHs, adsorbed onto the particulate were investigated. The engine used was a single-cylinder, light duty, high speed, diesel automotive research engine run at an Indicated Mean effective pressure (IMEP) of 7 bar. Particulate matter was also produced in a tube reactor at temperatures ranging from 1050 to 1350 °C under pyrolysis (oxygen-free) conditions to study PAH and soot formation in conditions which resemble, to an extent, those found in the core of diesel engine fuel sprays. In the diesel engine, it was found that exhaust PAHs were influenced by combustion characteristics like heat release rates and ignition delay. However, in the quiescent oxygen-free conditions of the reactor, chemical composition of the fuels and temperature dominated PAH formation.