The Effects of Engine Variables and Exhaust Gas Recirculation on Emissions, Fuel Economy, and Knock-Part II 760198

Steady-state data obtained from a 400 CID V-8 conventional engine at one speed/load/compression ratio combination are reported to show the effect of engine emission constraints on fuel consumption and octane number for trace knock. The important trends shown by these results were:
  • Various calibration combinations of air/fuel (A/F) ratio, exhaust gas recirculation (EGR), and spark retard can be used to control NOx emissions. A substantial reduction in NOx emissions was achieved by using EGR and optimized spark timing without suffering a fuel economy penalty; but hydrocarbon (HC) emissions tended to be high.
  • When both HC and NOx emissions were reduced by optimal adjustments of EGR and spark timing, fuel consumption was increased, but octane number for trace knock was decreased.
  • At controlled NOx emission levels, the lowest HC emissions were obtained at A/F ratios of 16 to 18:1.
  • The minimum achievable HC emission level increased with decreasing NOx emissions.
  • Injection of secondary air at the exhaust ports generally decreased HC emissions at A/F ratios richer than stoichiometric when the engine exhaust temperatures were greater than 1100°F. Use of secondary air at lean A/F ratios increased HC emissions.
In general, through the use of the basic engine parameters investigated, the substantial reduction in engine emissions of HC and NOx was associated with a fuel consumption penalty and with a reduction in the octane number for trace knock measured under the emission test conditions.


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