Impact of exhaust gas recirculation (EGR) on soot reactivity from a diesel engine operating at high load

• This paper describes the effect of EGR on soot reactivity at high load.
• Combustion duration obviously increases as EGR rate increases.
• Soot with highly ordered graphitic structure presented at high EGR level.
• OC fraction in particle sampling decreases with the increase of EGR.
• Soot generated at high EGR level exhibits greater thermal stabilities.

Past work demonstrated that the exhaust gas recirculation (EGR) enhanced the soot reactivity from a diesel engine operating at low load. In this paper, reactivity of diesel soot generated from a common rail diesel engine at high load (75% load, 336 N m) under 0, 10% and 30% EGR was studied. Combustion properties of the diesel engine with the diffusion-dominated heat release patters under the high temperature and low-fuel ratio condition resulted in the combustion duration increased 39.8% as EGR rate increases from 0 to 30%. Correspondingly, noticeable changes in nanostructure, carbonaceous components and oxidative reactivity with the increase of EGR have been observed. The soot with highly soot-EC content, highly ordered graphitic structure and low organic carbon (OC) fraction in the particle sample presents at high EGR level, which is the consequence of the longer combustion duration and the decrease of air-fuel ratio. Both of highly ordered graphitic structure and low OC fraction in the particle sample are responsible for the observed decrease of soot reactivity with the increase of EGR at high load.