4.0 CATEGORIES OF I&M TEST TYPES

There are various types of tests followed for I&M certification of vehicles (Figure-3). Some countries follow relatively simple procedure like measurement of volumetric concentrations in % or ppm while some follows the developed mass emission measurements in g/km. The type of test procedure followed is a very significant criterion which defines the effectiveness of the I&M system. For instance, measurements of volumetric concentrations do not really reflect the real emission performance of the vehicle whereas mass emissions measurements resemble more realistic conditions of the on-road vehicles. But, volumetric measurement also in a way may give some directional emission performance status of a vehicle as it is capable to determine if the vehicle is in good operational/mechanical condition or not. However, parameters like ease of measurement, infrastructure requirements, capital, etc. play important role in selection of the type of test for the I&M system.

Measurement of volumetric emission concentration (% or ppm) and mass emission measurements differs a lot in regard to the effectiveness of the tests, infrastructure and facility requirements, test time, etc. For instance, a gasoline passenger car and a motorcycle, both when tested for volumetric emissions may emit 3% CO but g/km emissions of CO under mass emission tests is sure to be high for the car. Thus repeatability and real on-road emission patterns are best represented in a mass emission test. Some commonly used procedures for the above types of tests are:

4.1 Mass Emission Tests

IM240: Inspection/Maintenance-240-seconds is a shortened version of the Federal test Procedure (FTP), where the vehicle is given minimal conditioning and is tested when fully warm. Thus it can be conducted outside the laboratory in a well-equipped inspection station. It is a loaded-mode transient dynamometer test, which measures the mass of emissions collected over a 240 second, two mile driving cycle.

IG240: (Inspection Grade IM240) is a version of the IM240 test, which utilizes less expensive inspection grade equipment. Like the IM240, it is a transient mass emission test, which utilizes the same driving cycle. This test is designed primarily for use in decentralized programme.

RG240: (Repair Grade IM240) is another version of the IM240 test utilizing even less expensive repair shop grade equipment than the IG240. The equipment measures the concentration of emissions and using the estimated volume of exhaust it calculates a mass emission value. It is designed for use in vehicle repair facilities to assist in repairing vehicles failing an IM240 or IG240 test.

BAR31: This is a short loaded-mode dynamometer test utilizing similar equipment as the IM240. The driving cycle has been truncated to 31 seconds, with the vehicle sharply accelerating and decelerating through the test. A vehicle is allowed three chances to pass the test before failing in this test.

IM93/CT93: Connecticut 93 is a short version of the IM240 utilizing the first hill of the IM240 cycle. This test is basically the first 93 seconds of the IM240 test.

IM147: This test is actually phase two of the IM240 test. The major difference is in the application of a retest algorithm which determines whether a failing vehicle needs preconditioning before a final failure determination is made. Up to three consecutive IM147 drive cycles may be run on a vehicle before the vehicle fails the I & M test.

VMASS: This is a test methodology utilizing a transient I & M test which could employ any driving cycle such as, IM240, BAR31, CT93 or IM147. The VMASS system converts a concentration measurement to a mass measurement. The VMASS system utilizes the oxygen content of the exhaust as the reference gas in determining volume.

4.2 Volumetric Concentration Tests

Idle: This is an Un-loaded test for measuring volumetric concentration of exhaust gases of vehicle at idle or high-idle for 30 seconds.

Steady Speed (SS): This is a loaded, volumetric concentration test at 60 mph for 180 seconds.

Acceleration Simulation Mode (ASM): This series of loaded-mode steady-state emissions tests measures exhaust concentrations from motor vehicles operated on a dynamometer. This test series measures vehicle meissions under a loaded condition that simulates an acceleration event. As utilized, the ASM steady-state test measures vehicle emissions at 15 mph (ASM 5015), 25 mph (ASM 2525) and 45 mph (ASM 2545). The representative tests subject the vehicle to load conditions, which are based upon the maximum acceleration event in the FTP. These percentages are 50%, 25% and 25% respectively.

Remote Sensing: This test measures the ratio of carbon monoxide, exhaust hydrocarbons and nitrogen oxide emissions to carbon dioxide emissions as a vehicle drives through an infrared and an ultraviolet light beam. The absorption of specific light frequencies from these beams by the vehicle's exhaust, allows the determination of these ratios and a calculated emission concentration for each. Latest remote sensing tests are capable of reading black smoke from diesel vehicles.

BAR97: This is California's specification for emissions testing equipment. Utilizing these specifications, the same test equipment may perform either an ASM or idle test depending on the availability of the dynamometer.

Out of all the above, IM240 is the most accurate test available in I&M programmes and this test representing real life emission patterns achieves substantial emission reduction benefits. This also provides diagnostic information for repairs. However, this requires expensive test equipments and the total cost of the programme is very high.

The SS and ASM tests are low cost alternative tests but may not be as effective as IM240 and may give high false failure problem when stringent standards are used. Moreover, they do not represent realistic mass emission performance of on-road vehicles.

Most of the Asian countries use idle test for petrol vehicles and free acceleration for diesel vehicles. European countries use idle check for old vehicles, high-idle for new cat fitted closed loop vehicles and free acceleration for diesel vehicles. In the U.S.A., 15 states use idle or 2 speed idle (idle+high-idle) tests, 8 states use ASM, 12 states use IM240 whereas places like New York, Washington, etc. all use mass emission measurement techniques.

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