The effects of secondary air injection on particulate matter emissions

Abstract

An experimental study was performed to investigate the effects of secondary air injection (SAI) on particulate matter (PM) emissions. SAI was developed to reduce hydrocarbon (HC) emissions and has been shown to be effective as a strategy to reduce HC emissions at cold-start. In general, cold-start emissions have become an increasingly important problem due to new, more stringent vehicle emissions regulations. Direct-injection, spark-ignition (DISI) engines, which emit high levels of PM, are growing in popularity because of their fuel efficiency improvements. Meeting PM emissions becomes a more difficult task due to more stringent standards and the greater adoption of DISI engines. This study seeks to investigate the potential use of SAI to reduce PM emissions in the exhaust system. Engine based experiments were conducted using a 2.0 L, turbocharged, DISI General Motors LNF engine. The engine was outfitted with a secondary air injection system and several thermocouples to measure exhaust stream temperature. A TSI Model 3934 Scanning Mobility Particle Sizer (SMPS) was used to measure particle emissions at various engine operating conditions and secondary air rates. PM reductions were observed for the engine conditions and SAI flow rates that were tested. The maximum particle number reduction achieved was 80%. Particle number and particle volume reduction were observed to correlate well with exhaust enthalpy release.