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	     High-Tech I/M Tests
   Another important difference between the IM240 and traditional I/M tests is the
   way emissions are measured. The IM240 captures the entire exhaust stream during
   the test and measures the total mass of emissions from the vehicle (grams of
   pollutant per mile driven). Traditional tests measure the concentration of pollutants
   in exhaust (percent or ppm). Mass emissions are a more accurate way of measuring
   the emission performance of large and small engines and are more directly related
   to the  contribution that each car makes to air  pollution.  The IM240 also can
   measure fuel economy.

   The purge and pressure tests check for proper functioning of a vehicle's evaporative
   emission system. This control system prevents fuel vapors from escaping into the
   atmosphere. Evaporative emissions can be a much greater source of HC pollution
   than exhaust emissions, especially in hot weather when smog levels are highest.
   Traditional I/M tests cannot measure evaporatative emissions.

   The evaporative emission system uses engine vacuum to draw fuel vapors in the
   fuel tank and vapors temporarily stored in the evaporative canister into the engine
   for combustion. The purge test determines whether this system is functioning
   properly by measuring the flow of vapors into the engine during the IM240. The
   pressure test checks the evaporative emission system for leaks.
   IM240 Test Procedure
   The IM240 begins by driving the vehicle onto the dynamometer, activating vehicle
   restraints, properly placing the exhaust collection device, and positioning the
   auxiliary engine cooling fan. An inspector then "drives" the vehicle according to a
   prescribed cycle  displayed on a video screen.  The inspector follows the driving
   cycle by using the accelerator pedal and the brake to speed up or slow down just as
   if the vehicle were being driven on a city street.  A cursor on the video screen
   indicates vehicle  speed. The inspector adjusts the speed to keep the cursor on the
   trace. This technique is easily and quickly learned by anyone who can drive a car.

                            IM24O Driving Trace
                          6O   SO   10O  12O  14O

                                 Time (sec)
                                                  ISO  ISO  2OO  22O  24O
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	     High-Tech I/M Tests
  The length of the IM240 test varies depending on the vehicle's emissions.  To
  determine  emission  levels,  second-by-second   instantaneous  emission
  measurements are taken and integrated by a computer.  Failure levels for vehicles
  undergoing I/M tests are generally two to three times higher than manufacturer
  certification standards for new  cars. The computer continually monitors and
  assesses the emission levels during each  phase of the test and uses pass/fail
  algorithms to identify exceptionally clean or dirty vehicles.  As soon as  the
  emission rates indicate that a vehicle is exceptionally clean or dirty, the computer
  automatically notifies the inspector to stop testing. For vehicles that are close to
  maximum allowable emission levels, the test may continue for a full 240 seconds.
  Thus, while the complete driving cycle is 240 seconds long, the average test time
  will be only two to three minutes.
  IM240 Test Equipment

  The equipment needed to perform the IM240 is different from the equipment used
  for either the idle-type I/M test or the single-speed dynamometer tests used in
  some states (e.g., Arizona and Florida). These differences include dynamometer
  capabilities, video driver trace monitors, special sampling systems, and emission
  analyzers.  In addition, the high-tech test system will use computer controls with
  integrated quality assurance functions, and will be completely automated.

  The primary difference between the dynamometer used for the IM240 and those
  used  for single speed I/M tests is the addition of inertia flywheels.  The inertia
  flywheels used are based on the weight of the car being tested.  They allow the
  inspection test to simulate vehicle acceleration and deceleration by putting a  load
  on the engine.  This in turn allows the measurement of emissions under these
  normal driving conditions.  This type of dynamometer is widely available and is
  similar to the ones used by EPA and car manufacturers for new car certification.

  The selection of the inertia weight and test horsepower for an individual vehicle
  will be  automatically determined by computer so that the I/M inspector is  only
  required to drive the vehicle onto the dynamometer. Even the system used to  hold
  the vehicle on the dynamometer will be automatic in order to minimize test set-up
  time and improve testing efficiency.

  The vehicle's mass emissions are determined by collecting the entire exhaust flow
  from the tailpipe with a device known as a Constant Volume Sampler (CVS). The
  CVS dilutes the exhaust with fresh air and measures the flow rate of the mixture.
  Mass emissions (for each second) are calculated by multiplying this flow rate by
  the measured concentration of pollutants in the mixture. To arrive at the official
  test value in grams per mile,  the mass emissions for each second are added
  together; this sum is then divided by the distance  (number of miles) traveled over
  the 240-second test cycle.                    	_^___
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	     High-Tech VM Tests
    The fresh air dilution is vital because it preserves the integrity of the sample and
    because it protects the emission analyzers from high concentrations of water vapor
    produced by the vehicle.  The dilution process also allows the measurement
    system to accommodate the differences in exhaust flow between small engines and
    large engines while measuring the true amount of emissions from each type of
    engine.

    The dilute  sample, however, lowers  the  concentration of pollutants to  be
    measured, and hence requires more sensitive emission analyzers than those used
    by traditional I/M programs. In addition, the method for measuring HC emission
    uses a  different and more accurate technique  than traditional programs.  HC
    emissions are measured with a Flame lonization Detector (FID), while CO and
    carbon dioxide emissions are measured using non-dispersive infra-red analyzers.
    NOx emissions are measured with a chemiluminescense analyzer.
   (COMPUTER
       \
flEXHAUST!
  ANALYZERS
landCysJ
           INERTIA FLYWHEiLS
   Evaporative System Purge Test

   Since 1971, fuel tanks on cars have been designed as a closed system in which
   vapors that evaporate from the gasoline in the tank are not released into the
   atmosphere. The system is sealed and under pressure so that excess vapors are
   shunted to a container filled with charcoal known as the evaporative canister.

   The evaporative system purge test is used to determine whether fuel vapor stored
   in the evaporative canister and present in the fuel tank is being properly drawn into
   the engine for combustion.  If the purge system is not working properly, the
   evaporative canister can become saturated and start to vent hydrocarbons into the
   atmosphere. In addition to causing HC emissions, failure of the purge system
   wastes gasoline.
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	     High-Tech I/M Testa
   The purge test is conducted while the vehicle is undergoing the IM240 on the
   dynamometer. Purge flow is measured by simply inserting a flow meter at one end
   of the hose that runs between the evaporative canister and the engine.

   Determination of an acceptable purge rate is based on the total volume of gas that
   flows through the system during the IM240, not by instantaneous flow rates. The
   vehicle must have a minimum of 1 liter of volume in order to pass.  Most cars in
   proper working order will accumulate as much as 25 liters during the IM240 cycle.
   As soon as a vehicle exceeds 1 liter of volume, the purge test is complete. The entire
   IM240 driving cycle ends as soon as final results are determined for the emission
   test.

   The purge test requires a flow meter that can measure the total volume of flow over
   the transient cycle. Additionally, hoses and universal fittings are required to hook
   up the flow meter as indicated below. Finally, a computer is needed to control the
   test process, collect and record the data, and determine the pass/fail status.
                         Purge Test Schematic
         FILLER        FILLER NECK
          CAP
                             ROLLOVER VALVE
                                                           FLOW TRANSDUCER
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	     High-Tech VM Testa
   Evaporative System Pressure Test

   The pressure test checks the system for leaks that would allow fuel vapors to escape
   into the atmosphere.  A "pressure decay" method is used to monitor for pressure
   losses in the system. In this method, the vapor lines to the fuel tank and the fuel
   tank itself are rilled with nitrogen to a pressure of 14 inches of water (about 0.5 psi).
   To pressurize these components, the inspector must locate the evaporative canister,
   remove the vapor line from the fuel tank, and hook up the pressure test equipment
   to the vapor line.  After the system is filled, the pressure supply system is closed off
   and the loss in pressure is observed. If pressure in the system remains above eight
   inches of water after two minutes, the vehicle passes the test.

   A source of nitrogen, a pressure gauge, a valve, and associated hoses and fittings
   are needed to perform the pressure test.   In addition, a  computer is used to
   automatically meter the nitrogen, monitor the pressure, and collect and process the
   results.  Algorithms will be developed to optimize the test so that a pass/fail
   decision can be made in less than two minutes on most vehicles.
                        Pressure Test Schematic
                iKiVx     w  ^
                            NmWXJENCYUNDeB
   For Further Information

   The EPA National Vehicle and Fuel Emissions Laboratory is the national center for research
   and policy related to automotive pollution. Contact the Emission Planning and Strategies
   Division at 2565 Plymouth Road, Ann Arbor, MI 48105; or call 313/668-4456.
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