The tendency of diesel engines to have high NOx emissions relative to future limitations is not fully compensated by their low HC and CO levels. Late fuel injection lowers fuel economy and water injection increases cost, though either can lower NOx. Use of exhaust gas recirculation, through requiring precise controls, has been found effective by Robert Bosch engineers employing a system which senses both air and fuel flow and limits exhaust gas recirculation (EGR) to provide clean combustion. If part of the intake air is replaced by exhaust gas, the cylinder's oxygen content is decreased, delaying the oxidation of the nitrogen in the intake air during combustion. The specific heat of exhaust gas is greater than that of air, also aiding in the reduction of combustion temperature and delaying nitrogen's oxidation. With increasing EGR, NOx emission decreases; HC and soot emission decreases; HC and soot emission is also lowered. A further increase in EGR results in an increase in soot, HC, and CO emission as well as fuel consumption, all as a result of the reduced oxygen content. With still greater EGR combustion misses occur.

Media Info

  • Pagination: p. 46-51
  • Serial:
    • Automotive Engineering
    • Volume: 86
    • Issue Number: 7
    • Publisher: Society of Automotive Engineers (SAE)
    • ISSN: 0098-2571

Subject/Index Terms

Filing Info

  • Accession Number: 00183327
  • Record Type: Publication
  • Source Agency: Engineering Index
  • Files: TRIS
  • Created Date: Nov 14 1978 12:00AM