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Assessing Combustion Chamber Efficiency: Testing and Techniques

This guide explores the factors influencing combustion chamber efficiency, including air/fuel movement, combustion turbulence, intake design, and exhaust gas recirculation (EGR). It details manual compression testing methods, with vacuum testing being the easiest approach to assess cylinder sealing. Individual cylinder tests provide insights into vacuum readings and possible performance issues. Additional discussions cover running compression tests to evaluate volumetric efficiency and cylinder balance. The guide emphasizes the importance of good cylinder seals for optimal engine performance.

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Assessing Combustion Chamber Efficiency: Testing and Techniques

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  1. DETERMININGENGINE CONDITION

  2. COMBUSTION CHAMBER EFFICIENCY • AFFECTED BY: • AIR/FUEL MOVEMENT • COMBUSTION TURBULENCE • INTAKE DESIGN • EGR • COMBUSTION CHAMBER DESIGN

  3. MANUAL COMPRESSION TESTING (CYL. SEALING) • EASIEST MANUAL TEST IS A VACUUM TEST • EACH CYLINDER IS A INDIVIDUAL AIR PUMP • THERE MUST BE A GOOD CYLINDER SEAL TO HAVE GOOD VACUUM • ANY CYLINDER LEAK WILL SHOW ON VACUUM GAUGE

  4. VACUUM C24-25 • Measured in Inches of Mercury (Hg) • A Reduction of 1 inch of vacuum per 1000 feet increase in altitude • Pounds Per Square Inch Absolute (PSIA) • Air moves rapidly from a High pressure to a low pressure

  5. L138 VACUUM TESTING PROCEDURES • CRANKING VACUUM • IDLE VACUUM • IDLE THROTTLE ANGLE CHECK • 2500 RPM VACUUM • PISTON RING TEST • IDLE/DRIVE TEST • CRUISE TEST • VAC AT W.O.T. AND AFTER W.O.T.

  6. TYPICAL VACUUM READINGS • CRANKING VACUUM 3-5” • IDLE VACUUM 18” • IDLE THROTTLE ANGLE 0” • 2500 RPM VACUUM 20” • VAC TEST PROCEDURE CAN IDENTIFY POTENTIAL PROBLEMS • COMPRESSION TEST CAN PINPOINT

  7. COMPRESSION TESTING

  8. READING COMPRESSION GAUGE • 1ST PUFF - SHOULD BE 50% OF FINAL PUFF (INDICATOR OF CYLINDER WALL AND RINGS) • ALL READINGS UNIFORM • IF REAL HIGH - CARBON BUILD-UP • IF CHANGE ON ONE CYL - POSSIBLE STICKING VALVE

  9. COMPRESSION AND VACUUM • BOTH REQUIRE GOOD CYLINDER SEAL • LACK OF CYLINDER SEAL WILL PREVENT PRESSURE TO RISE HIGH ENOUGH TO IGNITE THE MIXTURE • COMPRESSION & VAC TEST INDICATES CYLINDER SEAL, RUNNING COMPRESSION TEST INDICATES VOLUMETRIC EFFICIENCY

  10. CYLINDER BALANCE

  11. MANUAL CYLINDER BALANCE • SHORTING PLUG ONE BY ONE • TIME CONSUMING • DON’T OPEN CIRCUIT SECONDARY CIRCUIT • WILL PINPOINT LOW POWER OUTPUT OF A CYLINDER

  12. OTHER CYLINDER BALANCE TESTS • ELECTRONICALLY PERFORMED BY ENGINE ANALYZER • CRANKING TEST • AMPS PER CYLINDER • RELATIVE COMPRESSION

  13. CYLINDER CONTRIBUTION • FUEL DISTRIBUTION • DUAL PLANE • SINGLE PLANE • LOW RISE • HIGH RISE

  14. COMPUTER CONTROLLED ENGINE POWER BALANCE • DISCONNECT O2 SENSOR • INITIAL TIMING MODE • DISCONNECT EGR • STABILIZE MAP IF APPLICABLE • STABILIZE FUEL PRESSURE • STABILIZE IDLE CONTROL • PREFERRED TEST RPM 800-1200 RPM

  15. VOLUMETRIC EFFICIENCY

  16. MANUAL TEST OF VOLUMETRIC EFFICIENCY • CAN TEST AT: • CRANKING • IDLE • SNAP ACCELERATION

  17. CRANKING COMPRESSION TEST • SLOW CRANKSHAFT SPEED/CYLINDER COMPLETELY FILLS/ HIGH COMPRESSION • CHECK OVERALL MECHANICAL CONDITION • CHECKS FOR LEAKS

  18. IDLING COMPRESSION • AIR RESTRICTED BY THROTTLE PLATE • CRANKSHAFT SPEED 4 TO 5 TIMES CRANKING SPEED • LESS AIR ENTERING CYL PER ENGINE CYCLE • TYPICALLY 50 TO 60 PSI CON’T NEXT SLIDE

  19. IDLE TEST, CONT’D • MUST “BURP” GAUGE • IF RPM BROUGHT UP SLOWLY TO 1500 RPM, PRESSURE GOES DOWN TO ABOUT 40 PSI. • NO MANUFACTURER’S SPEC COMPARE WITH OTHER CYLINDERS

  20. SNAP ACCELERATION • QUICKLY SNAP-OPEN THROTTLE, THIS REMOVES THROTTLE PLATE RESTRICTION • READINGS SHOULD INCREASE TO 80% OF CRANKING COMPRESSION • HIGH READING:RESTRICTION IN EXHAUST OR VALVE TRAIN • LOW READINGS: RESTRICTED INTAKE OR CARBON ON VALVE

  21. LAB EXERCISE • VACUUM TESTS • CYLINDER BALANCE • SEVERAL METHODS • RUNNING COMPRESSION TEST

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