Experimental Study of Physical and Chemical Properties of Soot under Several EGR Conditions

Exhaust Gas Recirculation (EGR) is an effective method to reduce Nitrogen Oxide emissions. In recent years the trend of increasing EGR rate in-cylinders is an integral part of most improvements in combustion technology developments. The object of this work is to study the influence of EGR rate on the physical and chemical properties of soot particles. Soot from several operating points of a diesel engine run were collected on a high temperature filters. The pressure drop behavior during the soot loading was monitored then the soot permeability was calculated. Afterwards, the soot primary size was calculated from the obtained data and it showed good correspondence to the actual measurement. It is confirmed that all the soot primary sizes were around 22 nm in diameter. In contrast, the soot aggregate sizes and the soot concentrations were found to increase with increasing EGR rate. Subsequently, Oxidation tests were conducted to evaluate the reactivity of the soot. It is observed that soot oxidation temperatures varied in the range of 500 to 600 degree Celsius (C). Whatever the engine conditions are, the high EGR rate provides less reactive soot comparing to the soot of low EGR rate. The soot oxidation rates were analyzed with a previously developed multi-population model to assess the kinetics and the mass fractions of the respective soot populations. The results of both the multi-population model and the experiment were in good agreement, and formed the basic tool for the quantification of the EGR rate on the various fractions of soot.