The trade-off between engine operating efficiency and oxides of nitrogen (NOx) emissions in a prechamber three-valve, stratified charge engine is examined in a series of parametric studies using an improved model developed at Massachusetts Institute of Technology. Engine geometric, operating, and combustion parameters are varied independently and the effects on brake-specific-fuel-consumption (BSFC), exhaust temperature and brake-specific nitric oxide (BSNO) observed. Parameters studied include the following: timing of the start of combustion, overall air/fuel ratio, prechamber air/fuel ratio at the start of combustion, main-chamber combustion duration, prechamber size, exhaust gas recirculation (EGR), and load. A faster combustion duration in the main combustion chamber gives lower BSFC and exhaust temperature. At a constant overall air/fuel ratio, combustion duration and optimum timing combined with increased stratification in the engine at start of combustion will serve to increase BSFC, decrease exhaust temperature slightly, and will almost always decrease BSNO. Increasing the stratification at the start of combustion increases the proportion of the exhausted NOx formed in the prechamber. Changes in prechamber volume at constant combustion duration produce only modest changes in BSFC and BSNO. As for load, the major effect of decreasing brake mean effective pressure (BMEP) from the midload base study point of 59 psia at constant combustion duration and optimum timing is a rapid increase in BSFC. Increasing BMEP from the base point results in both decreased BSFC and increased BSNO. EGR increases at constant combustion duration and optimum timing reduces BSFC, BSNO, and exhaust temperature. The three-valve, stratified charge engine has much leaner operation because of its rich prechamber mixture at the time of spark and its jet ignition process in the main combustion chamber. Control measures are needed for hydrocarbon emissions, which increase because of the substantial reduction in mean exhaust temperature due to leaner operation.

  • Supplemental Notes:
    • Presented at the SAE Congress and Exposition, Detroit, 27 February-3 March 1978.
  • Corporate Authors:

    Society of Automotive Engineers (SAE)

    400 Commonwealth Drive
    Warrendale, PA  United States  15096
  • Authors:
    • Wall, J C
    • Heywood, J B
    • WOODS, W A
  • Publication Date: 1978

Media Info

  • Features: References;
  • Pagination: 28 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00395649
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: SAE 780320, HS-025 418U
  • Files: HSL, USDOT
  • Created Date: Jun 30 1985 12:00AM