Exhaust System Thermal Management: A Process to Optimize Exhaust Enthalpy for Cold Start Emissions Reduction

Paper #:
  • 2017-01-0141

Published:
  • 2017-03-28
Abstract:
Future vehicle North American emissions standards (e.g., North American SULEV 30) require the exhaust catalyst to be >80% efficient by 20 seconds after the engine has been started in the Federal Test Procedure. Turbocharged engines are especially challenged to deliver fast catalyst lightoff since the presence of the turbocharger in the exhaust flow path significantly increases exhaust system heat losses. A solution to delivering cost effective SULEV30 emissions in turbocharged engines is to achieve fast catalyst light-off by reducing exhaust system heat losses in cold start, without increasing catalyst thermal degradation during high load operation. A CAE methodology to assess the thermal performance of exhaust system hardware options, from the exhaust port to the catalyst brick face is described, which assures compliance with future emissions regulations. In addition to close-coupling of the catalyst, wastegate strategies, directed wastegate flow, engine displacement, and scroll configuration were studied with respect to the magnitude and preservation of exhaust energy delivered to the catalyst face. The concept of total sensible energy available at the catalyst face, and a measure of exhaust thermal efficiency is introduced as a means of quantifying the likelihood of successful catalyst lightoff prior to vehicle drive-away. Boundary condition definition, numerical requirements, and correlation to measured data are discussed.
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