Blow-By Gases as Indicator of an Engine’s Condition

FEV BlowByRate determines the mechanical condition of the engine

8. June 2015 | Software & Testing Solutions

The FEV BlowByRate device makes easy determination of the condition of valve guides, piston rings, pistons and cylinder walls possible without engine disassembly.
The system provides conclusions about possible wear by measuring the blow-by gas quantity.  blow-by gases generally pass out of the cylinder via leaks – for example at the pistons, piston rings and/or valve guides – or through the bearings and bearing seals into the crankcase and escape through the crankcase ventilation.  A significant increase or decrease in the blow-by gas volume can indicate engine damage, more rapid piston ring run-in wear, or liner scoring due to deposits.  By recognizing changes in the engine early, testing periods can be shortened and significant damage can be potentially prevented.  Early detection also helps to avoid the introduction of major defects in test vehicles, since such problems can now be identified in earlier phases.

Continuous measurement, easy communication with automation systems

The FEV BlowByRate works using the differential pressure principle. The blow-by gas is passed through a measuring tube that contains an aperture at its center, which creates a flow-dependent pressure difference that is dependent upon the blow by-quantity. The resulting flow-dependent pressure difference is monitored by a differential pressure sensor that is processed in the evaluation unit.
The measurement results are output via an RS232, USB interface or via analog channels.
To avoid an influence of drift in the differential pressure sensor on the measured results, two solenoid valves are installed between the pressure sensor and the aperture measuring tube enabling automatic zeroing. The sensor inputs to the differential pressure sensor can be switched at regular intervals to the environment and the time period between two null points is adjustable. However, the high quality of the device limits the need for frequent zeroing, allowing continuous measurements over long periods of operation.



Robust, reliable and accurate

The FEV BlowByRate is characterized by a robust, reliable construction and precise blow-by measurement – despite the contamination that is entrained in the blow-by gas. An integrated display shows the current blow-by value, the measuring range and any error messages. Range changes are easily achieved using the membrane keypad. The FEV BlowByRate can be easily calibrated by the operator, and aperture changes can be achieved without tools.


Operation purpose of blow-by measurement:

  • Engine development: Improvement in the areas piston rings, pistons, and cylinder liners
  • Engine production: Differences of blow-by that are above average, normally indicate manufacturing defects
  • Engine maintenance:  A simple evaluation of the run-in progress by monitoring blow-by
  • Stationary engines: Early indication of changes via continuous monitoring of the engine, avoiding more significant damage


Modular FEV BlowByRate system components

  • Evaluation unit
  • Measuring tube with aperature
  • Mounting plate
  • Vibration damper
  • Connecting hoses between the vibration damper and
    measuring tube
  • Adapter parts between measuring tube and connecting hose
  • Optional pressure sensor for the measurement of crankcase pressure, manifold vacuum, differential pressure ∆p, intake manifold / crankcase


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