Effects of post-injections strategies on uHC and CO at gasoline PPC conditions in a Heavy-duty optical engine

Paper #:
  • 2017-01-0753

Published:
  • 2017-03-28
Abstract:
Gasoline partially premixed combustion (PPC) has shown potential in terms of high efficiency with low NOx and soot emissions. Despite its benefits, emissions of unburned hydrocarbons (uHC) and carbon monoxide (CO) are the main shortcomings of the concept. These are caused by overlean zones near the injector tip. However, previous diesel low temperature combustion (LTC) research have demonstrated post injections to be an effective strategy to mitigate these emissions. The main objective of this work is to investigate the impact of post injections on CO and uHC emissions in a non-swirling geometry. A blend of primary reference fuels, PRF87, having properties similar to US pump gasoline was used at PPC conditions in a heavy duty optical engine. The start of the main injection was maintained constant. Dwell and mass repartition between the main and post injections were varied to evaluate their effect. All points were run at 7 bar IMEPg. High-speed imaging of the natural combustion luminescence was used, together with measurements of performance, and engine out emissions. Results show reduction in both CO and UHC with close coupled injections. The reduction is most significant in CO, especially with the smaller sized post injections. Retarded post injections does not show much improvement UHC, although CO remains low for small post injections. Looking at the imaging the luminosity is visible in the near injector region for the retarded small post injections. With the larger post injection, the momentum leads to a longer penetration before igniting the fuel.
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