ENGINE AFTER-RUN

THE PROBLEM OF ENGINE AFTER-RUN (DIESELING) HAS COME UNDER CLOSE SCRUTINY IN A VEHICLE TEST PROGRAM AT GM. RESULTS: (1) INCREASED ENGINE IDLE SPEED, LEAN IDLE MIXTURES, AND RETARDED BASIC SPARK TIMING INCREASE POSSIBILITIES OF AFTER- RUN. FOR EACH OF THESE VARIABLES, AFTER-RUN INCREASES AS THROTTLE OPENING INCREASES. UNFORTUNATELY, PREVENTING AFTER- RUN BY ADJUSTING ENGINE-OPERATING VARIABLES CONFLICTS WITH CURRENT EMISSION-CONTROL SYSTEMS REQUIRING HIGH IDLE SPEEDS, LEAN MIXTURES, AND RETARDED SPARK TIMING. (2) OF ALL THE FUEL VARIABLES STUDIED, RESEARCH-OCTANE NUMBER HAD THE GREATEST EFFECT ON AFTER-RUN; DECREASING THE RESEARCH-OCTANE NUMBER OF THE FUEL INCREASES AFTER-RUN FREQUENCY AT CONSTANT ENGINE-OPERATING CONDITIONS. THE RESEARCH-OCTANE LEVEL REQUIRED TO PREVENT AFTER-RUN INCREASES AS THE ENGINE-IDLE SPEED INCREASES. MOTOR-OCTANE NUMBER, FUEL SENSITIVITY, AND HYDROCARBON COMPOSITION DID NOT AFFECT AFTER-RUN FREQUENCY. (3) IN A SURVEY OF DIFFERENT MAKES AND MODELS OF 1971 CARS, AFTER-RUN OCCURRED WITH 4 OF THE I0 CARS WHEN THEY WERE ADJUSTED TO MANUFACTURER'S IDLE SPECIFICATIONS. SIX OF THE 20 VEHICLES WERE FACTORY-EQUIPPED WITH "ANTI-DIESELING" SOLENOIDS, AND TWO OF THESE EXPERIENCED AFTER-RUN, BUT AT A LOWER FREQUENCY THAN WHEN TESTED WITHOUT THE SOLENOID. (4) AFTER-RUN EXHAUST WAS OBNOXIOUS AND CAUSED SOME EYE IRRITATION. CONCENTRATIONS OF HYDROCARBONS, NITRIC OXIDE, AND TOTAL ALDEHYDES WERE 2500, 5, AND 125 TIMES GREATER, RESPECTIVELY, IN AFTER-RUN EXHAUST THAN IN NORMAL IDLE EXHAUST. AFTER-RUN EXHAUST CONTAINED 1000 TIMES HIGHER ACROLEIN CONCENTRATION THAN THAT WHICH HAS CAUSED NOTICEABLE EYE IRRITATION IN OTHER EXPERIMENTS. /SAE/

  • Publication Date: 1972-4

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  • Accession Number: 00223768
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 9 1972 12:00AM