Inspection Info - Description of the Tests

D147 Test Procedure for Diesel Vehicles

  1. All diesel-powered vehicles are driven on a transient drive cycle using the second phase of the IM240 driving trace. This gives a test duration of 147 seconds. The cycle appears essentially the same as is used for gasoline vehicles. Diesel vehicle emissions testing will be conducted only in Lane 1 at all AirCare Inspection Centres.
  2. The dynamometer inertia and horsepower is taken from the EPA look-up table for an equivalent gasoline vehicle, whenever such exists. In other cases, as for gasoline vehicles, which do not appear in the look-up table, the inertia and horsepower is taken from the look-up table default values.
  3. The opacity is measured using Wager opacity meter carts, modified to accommodate the increased exhaust mass-flow by increasing the pipe diameter (equal to actual optical path length) to 4 inches.
  4. When it exits the opacity cart, the exhaust is removed via the 700-CFV IM240 blower, using ducting which bypasses the IM240 CVS and sampling systems.
  5. Opacity is measured continuously throughout the 147 second test. The analogue voltage output from the opacity meter is passed to the measurement system, which performs the following functions:
    • Signal filtering to remove high frequency transients
    • Analogue to digital conversion with 0.5 second averaging period
    • Identification of peak 0.5 second averaged value
    • Ambient conditions correction
    • Beer-Lambert horsepower correction
  6. The ambient conditions correction and the Beer-Lambert correction is performed in accordance with the equations which appear in appendices to SAE J1667 [external link].
  7. The standard optical path length, on which the Beer-Lambert correction is taken from the table, is based on the age and engine size of the vehicle. This avoids the need for an additional database of light-duty diesel vehicle horsepower ratings, and is analogous to using a mass emissions standard for spark-ignition engine vehicles.
  8. The value obtained after applying these calculations to peak 0.5s averaged value is taken as the vehicle opacity reading.
  9. Pass/Fail decision is made by comparing the vehicle opacity reading with the maximum allowable emissions standards, which currently are set at 30%.
  10. Diesel vehicles which can not be run on the dynamometer receive a high-idle test, with three high-idles being performed within the normal 147 second measuring period. The measurement protocol is the same as if an actual driving cycle was performed.
  11. The Vehicle Inspection Report (VIR) includes a section specifically for diesel tests.
  12. The Diagnostic Trace Report (DTR) provides a second-by-second plot of corrected opacity readings for all vehicles which fail inspection.

Watch a video describing the D147 test procedure.