Investigation of fuel composition effects on particle and polycyclic aromatic hydrocarbon emissions

Particle emissions from combustion sources are a major environmental and health concern. Ease of use and cost makes additives an attractive option to reduce particle emissions. In this study the ability of additives to impact particle and PAH emissions was investigated using a modified single pulse shock tube. The shock tube was used to generate soot under fuel rich (phi = 3.0) conditions over a temperature range of 1650 to 1950 K and a pressure of ∼21 atm. A mixture of n-heptane (80 vol. %) and toluene (20 vol. %) was used as the base fuel and impact of nitromethane, NO2 and pyridine on soot yields was investigated. Both particulate and gaseous combustion products were collected and analyzed. The results show that addition of nitromethane has no impact on the particle yields but addition of NO2 lowered particle yields at the lower temperatures. However, the addition of pyridine led to higher particle yields at higher temperatures. An attempt was made to correlate the PAHs and NPAHs to the observed particle yields and to validate kinetic models for the base fuel and additives. It was observed that at the lower temperatures additives increased the yields of most PAHs. The kinetic models failed to predict experimental PAH observations. Further investigations showed that the kinetic models did not correctly account for the pre-ignition NO2 chemistry and the molecular growth to larger PAHs.; Ignition delay times measured showed that at lower temperatures addition of nitromethane yielded the lowest ignition delay than the base fuel and base fuel + NO2 mixture. Results also suggested that the methyl radical in nitromethane may have negated any reductions in soot yields that may have occurred from the NO2 present in nitromethane.; Results from spray combustion studies of diesel, diesel + lubricating oil mixtures, an additized JP-8 fuel, and two Fischer-Tropsch fuels are also presented and the impact of their difference in composition to soot yields is discussed. The results of spray combustion studies agree well with previous studies that showed that lower sulfur and aromatic contents lead to lower particle emissions and that increased lubricating oil consumption leads to higher particle yields.