Effects of Secondary Air on the Exhaust Oxidation of Particulate Matters

Abstract

The effects of secondary air on the exhaust oxidation of particulate matters (PM) have been assessed in a direct-injection-spark-ignition engine under fuel rich fast idle condition (1200 rpm; 2 bar NIMEP). Substantial oxidation of the unburned feed gas species (CO and HC) and significant reduction of both the particulate number (up to ~80%) and volume (up to ~90%) have been observed. The PM oxidation is attributed to the reactions between the PM and the radicals generated in the oxidation of the feed gas unburned species. This hypothesis is supported by the observation that the reduction in PM volume is proportional to the amount of heat release in the secondary oxidation.

Analysis of Post-oxidation Phenomena in a Turbocharged DISI Engine Focused on Gas and PM Emissions and Gas Temperature

“…The wider investigation on the emissions such as, CO, CO2, THC, PM and H2 have been also performed in the post-oxidation phenomena and found emissions reduction along with the turboperformance improvement [1,2,3,7]. It was also noted that the efficient post-oxidation can be influenced with adequate mixing, temperature level and air and exhaust gas concentration in the exhaust manifold [7,8].…”

“…The in-cylinder combustion used rich air-fuel mixture and this rich excursion gives rise to the production of CO, THC, PM and H2 emissions. Then the scavenged O2 and emitted H2 play a key role for post-oxidation reaction with CO, THC and PM in exhaust manifold and in-turn can aid in increasing the temperature along with overcomming of decrease in temperature by heat absorption reaction [1][2][3][4][5]. Apart from this, TWC life time improvement and load reduction on catalyst, reduction in residual gas fraction, and knocking tendency reduction by the in-cylinder temperature decrease etc.…”

“…At the same time, less unburned fuel is brought into the catalyst, which prevents the catalyst from rising in temperature. In past, another methodology for the post-oxidation has been also adopted such as, secondary air injection in exhaust port that can enable secondary reaction (post-oxidation) and could increase enthalpy at turbocharger upstream and hence turbo-lag can be reduced [3][4][5][6][7].…”

Post-oxidation phenomena enhancement with scavenging and secondary air injection in exhaust manifold of a turbocharged GDI engine

“…It was noted that the substantial oxidation of the feed gas species as CO and HC and significant reduction of both particles number (up to ~80%) was observed. 16 The different fuel composition that influence post-oxidation in the cold state was investigated by Villforth et al The improvement in cold-start emissions was observed with different fuel compositions compared to existing types of market fuels. 17 The post-combustion of hydrocarbon was studied by Prabhu et al and noted that the exhaust temperature, diffusion rates, and fuel kinetics each play a sophisticated role in emissions levels.…”

Performance improvement of turbocharged SI engine by post-oxidation enhancement in exhaust gas in-homogeneity

“…As every chemical reaction has a specific requirement of temperature hence according to a study conducted by the Torsten Guenther et al, they had observed that a minimum exhaust gas temperature of 827°C had showed significant signs for the post-oxidation reaction to take place. 21 To attain such temperatures, the common method that is the choice for researchers is to alter the ignition timing of the engine. A study was performed in which it was determined that an ignition timing of 28° crank angle (CA) bTDC f was an optimal choice to attain the minimum temperature in order for the post-oxidation reaction to begin.…”