Effects of iron-based fuel borne catalyst addition on combustion, in-cylinder soot distribution and exhaust emission characteristics in a common-rail diesel engine

In order to reduce soot emission and assist diesel particulate filter regeneration, iron-based fuel borne catalyst (Fe-FBC) was added into diesel fuel with Fe element mass fractions of 0, 200 and 400 mg/kg in the preparation of FBC fuels (marked as Diesel, Fe200 and Fe400). The in-cylinder soot distribution, pollutant emissions and particle physicochemical properties of FBC fuels were investigated on a visualization modified common-rail engine. The results show that the combustion starting point is advanced with Fe-FBC addition, while the maximum combustion pressure and heat release rate increase. The addition of Fe-FBC in diesel fuel will shorten ignition delay period, accelerate combustion process and lead to the increase of in-cylinder flame temperature, while the in-cylinder soot concentration and soot area occupation ratio are reduced significantly. HC, CO and soot emissions along with the unconventional emissions such as HCHO, CH3CHO and polycyclic aromatic hydrocarbons (PAHs) decrease at each load as the increase of Fe-FBC addition ratio. Compared with Diesel, the peak soot area occupation ratio and soot emissions of Fe400 decrease by 41.6% and 20.4% respectively at full load. It is also found that Fe-FBC addition decreases particle box-counting dimension, which indicates that the polymerization degree between the particles becomes weaker and their arrangement becomes more sparse and loose, so the oxidation characteristic temperature and the activation energy of soot particles decrease significantly. Fe-FBC addition can effectively reduce the type and content of PAHs and the high carbon atom number compounds in soluble organic fraction from exhaust particles.