Test methodologies adopted by the Department of
Environmental Protection include the snap-acceleration
test, and power brake
test for determination of exhaust smoke opacity from heavy-duty diesel vehicles (HDDVs). In a roadside
environment the snap acceleration test is utilized.
Periodic inspection of HDDVs may utilize either
of the snap-acceleration, rolling-acceleration or
the power brake tests.
must conform to the specifications set forth by
of Automotive Engineers Recommended Practice J-1667.
This is the preferred test method. This test can be performed on any vehicle regardless of engine speed or transmission type. Vehicles are rapidly accelerated in low gear or "Drive" - for manual or automatic transmissions respectively - to maximum governed RPM while the smoke opacity is measured.
During this test, the vehicle is held stationary with wheel chocks as the engine is rapidly accelerated - "snapped" - to maximum governed RPM with the transmission in neutral. A smoke meter is used to determine the average opacity over several accelerations.
Power Brake Test:
This test is only required on vehicles with an automatic transmission AND a high-speed engine. The vehicle is held stationary with all brakes applied and the transmission place in "Drive". The accelerator is fully depressed and help up to ten seconds but typically about three seconds while the smoke opacity is measured.
view the actual step by step test procedures, and
their application to specific vehicle types, see N.J.A.C.
7:27B-4 - Air Test Method 4: Testing procedures
for Motor Vehicles.
opacity is a measurement of light extinction, or
the blackness of the exhaust plume, expressed as
a percentage. 100% opacity would be completely dark,
and 0% would be totally transparent. The black smoke
we see in diesel exhaust is composed primarily of
carbon particles resulting from the combustion of
opacity limit is measured at the peak, or darkest
point, of the exhaust cloud. This measurement is
most commonly taken during the snap acceleration
test, where the vehicle is at idle, with all brakes
off, and the throttle is "punched" to
the floorboard, initiating the exhaust cloud. Opacity
is measured as a surrogate for particulate matter.
table below illustrates the approximate opacity
of our current emission
use a laser beam directed at a photo-receptor cell,
to measure the exhaust smoke plume. The laser
is either directed through the plume itself, or
a sample, or "plug" of smoke is directed
into a chamber through which the laser beam passes.
As noted above, the degree to which the beam is
obscured from the receptor cell is translated into
a percentage, where a value of 100% means that the
light is completely blanked out.
approves opacimeters for use by the diesel PIFs.
of approved opacimeters
are placed upon owner or lessee, not
The fine for a first offense is $700, reducible
to $150, with proof of repair.
For second and subsequent offenses the fine is $1300,
reducible to $500 with proof of repair.
Failure to comply with the annual inspection requirement
carries a fine of $500.