Emission standards for new vehicles are ineffective without a comprehensive programme that ensures compliance. Effective test procedures are required to quantify vehicle emissions, both to verify compliance with standards and to estimate emissions in actual use. A consistent and replicable test procedure is required if emission regulations or economic incentive systems are to be enforceable.
The testing should be representative of m-use driving conditions and hence reflect real-world driving patterns. Since vehicles operate in a variety of speed-load conditions, it is important that testing procedures reflect these conditions. While U.S.A and Europe have already developed realistic driving cycles and are using them in emissions testing, India has developed a driving cycle only recently.
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Manufacturers are required to certify that each of their new vehicles complies with emission standards. Certification, which involves emissions testing of prototype vehicles prior to production, allows manufacturers to identify and correct problems prior to initiation of mass production of vehicles.
Testing is done by vehicle manufacturers and by government authorities. Assembly line testing is done by the government agencies during production to ensure compliance with applicable emission standards. Assembly line testing allows government authorities to identify non-compliant vehicles and take necessary measures (such as revoking the certification).
Recall and warranty procedures improve the emission testing procedures of the vehicle manufacturers. Recall programs allow manufacturers to design and produce vehicles with a margin of safety to avoid the costs and negative publicity, associated with recalls. Warranty against defective design or workmanship of vehicle’s emission control equipment allows manufacturers to design and produce vehicles with controlled quality, and consumers to have a resource for non-compliant vehicles resulting from vehicle manufacturer’s fault.
Evaporative emissions from gasoline—fuelled vehicles are measured either by collecting them in activated carbon traps or by putting the vehicle in an air tight housing and measuring the HC concentration. The evaporative testing procedures have been prescribed in India in Bharat stage 1 in 2000.
There are several procedures for measuring vehicle emissions for regulatory purposes. The most commonly used are the U.S federal, the European and the Japanese test procedures. India follows the European test procedures.
Exhaust Emission Testing for Cars:
For light duty vehicles, including two wheelers, emissions are measured by operating the vehicle on a chassis dynamometer while collecting its exhaust in a constant — volume sampling system. All the three test procedures (viz. American, European and Japanese) follow similar test procedure. The main difference among the procedures is the driving cycle for vehicles. The European test procedure is used in the European Union, most East European countries; China and India, where it includes an Indian driving cycle.
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In the U.S. federal test procedures, the vehicle is driven on a chassis dynamometer according to a pre-determined driving cycle using constant volume sampling system. Till recently, the test procedures (FTP 75) and the driving cycle were not covering the full range of possible speed and acceleration conditions that vehicles experience.
The air conditioner does not run during the FTP test procedure. Hence the FTP test procedure was recently replaced by a more stringent procedure known as US 06. This US06 test procedure includes the full range of speed and load conditions found in actual driving on U.S. roads.
The more aggressive driving and inclusion of testing the vehicle with air conditioner on, better reflects the actual emissions during warm weather. Recent legislation in the United States requires carbon monoxide testing at both —7°C and normal ambient temperature. The testing procedure in US06 takes care of this requirement.
The emissions test procedure for European passenger cars was defined by ECE regulation 15 and consists of three tests. Like the U.S procedure, the first test measures the exhaust emissions produced in a driving cycle on a chassis dynamometer. The second test samples tail pipe carbon monoxide concentrations immediately after the last cycle of the first test. The third measures crank case emissions.
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Compared with the U.S driving cycle, the European driving cycle is simple. It is a simplified representation of the driving cycle in a typical European urban center (such as Rome). The maximum speed of the European test cycle is 50 km. per hour. The recent studies indicate that the European test cycle under estimates actual emissions by 15-25 percent when compared with more realistic driving at the same speed. As testing is only conducted between 20°C and 30°C, low temperature carbon monoxide emissions are not controlled.
The Japanese driving cycle and the test procedure is similar to European one with a maximum speed of 70 kms per hour. Automotive Research association of India (ARAI), Pune developed a unique Indian driving cycle in 1996 and has modified it in 2000. It is mostly based on Mumbai driving conditions.
Exhaust Emission Testing for Heavy Duty Vehicles:
All the three test procedures (U.S, European and Japanese) follow the same test procedure-engine testing on engine dynamometer. All the three procedures measure exhaust emissions from the engine alone (removed from the vehicle), operating over a specified cycle on an engine dynamometer. The U.S test procedure involves transient changes in speed and load to mimic the actual operation in intra-city operation. The European and Japanese test procedures measure emissions at a number of steady-state conditions and combine these according to a weighting scheme.
The test results are reported in mass of pollutant emissions per unit of work output (grams per kilo watt hour or grams per bhp. hour) rather than mass of pollutant emissions per mile or km. The U.S EPA uses a conversion factor of 0.54 grams per bhp. hour to each gram per km.
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The comparative advantages of transient and steady-state test procedures have often been debated during the recent years. U.S authorities adopted the transient test procedure (replacing earlier steady state-tests) in 1985 arguing that steady-state tests do not adequately measure the air-fuel ratio during transient operations such as acceleration.
Diesel particulate matter and hydro carbon emissions in transient tests are generally found to be higher than in steady state tests. European authorities are planning to switch over to transient cycles. Studies indicate that using U.S EPA transient test for bus engines may under estimate actual emissions by a factor of three to six.
Given the significantly higher proportion of trucks and buses in India, it is necessary to develop test cycles that are more representative of operating conditions (low power to weight ratio and slower speeds) prevailing in the country.
Emission Testing for Two Wheelers:
The emissions test procedure for motor cycles in the U.S is the same as for light-duty passenger cars, except that the maximum speed is reduced for motorcycles with an engine displacement below 170 CC. For passenger cars and motor cycles with displacement over 170 CC the max. speed is 91 kilometer per hour, while for motor cycles under 170 CC it is 58.7 kms per hour. Testing is done on a single-roll dynamometer with a clamp to hold the motor cycle upright.
The European test procedure for larger two wheelers is the same as for cars. However for small mopeds of less than 50 CC, a separate procedure is prescribed. In European procedure, ECE regulation 47 defines the test procedures for emissions from vehicles with less than 50 CC engine displacement. The maximum speed in this test cycle is 50 kilometers per hour. The U.S does not regulate emissions from motor cycles with less than 50 CC engine displacement, but the U.S EPA is proposing to do so.
As with passenger cars, the present emission testing and driving cycle for motor cycles in U.S and Europe is inadequate. For example, in most of the modern motor cycles, the acceleration rate is more than 3.3 metres/second2, which is more than twice the maximum acceleration rate in the U.S test procedure and three times that in the European test procedure.
Evaporative Emission Test Procedure:
Evaporative emission control requirement applies to all the passenger cars, multi utility vehicles and heavy duty vehicles using gasoline fuel (but not diesel). California in U.S also tests motor cycles. Evaporative emissions from a passenger car is generally measured by two test methods – Charcoal Trap Method and Sealed Housing for Evaporative Determination (SHED) method.
In charcoal trap method, fuel evaporation sources are connected to the charcoal trap and the increase in HC concentrations in the charcoal trap is measured. This method is followed in japan. Charcoal trap method greatly under-estimates the actual evaporative emissions from a vehicle.
Sealed Housing Evaporative Determination (SHED) is a more accurate method and consists of collecting the evaporative emissions in a large sealed enclosure where the vehicle is parked. It is the test method recommended by the Society of Automotive Engineers (SAE) U.S.A.
In this method, all evaporative emissions from the test vehicle are contained in the sealed enclosure and increase in HC concentration over a period is measured. This method has been used in the U.S for many years and has been adopted in the European test procedure from the year 1991.
The Indian evaporation test is similar to the European test except for the driving cycle. Since the advent of evaporative emission control regulation in April 1996, all Indian passenger cars have undergone the evaporative emission test. It is now proposed to follow the revised 2000 driving cycle for regulatory emission tests.
The California Air Resources Board (CARB) and U.S.EPA standards limit evaporative hydrocarbon emissions to 2.00 grams per test which is considered effectively equivalent to zero emissions. In the recent test procedures, although the standards are the same as before, the more severe testing procedure and conditions impose more stringent requirements on manufacturers.
Evaporative emissions are measured by placing the vehicle in the enclosure of the SHED, which captures all vapours emitted from the vehicle as the temperature is increased from 15.6 to 28.9°C. This stimulates warming that occurs as the temperature rises during the course of a day. The California Air Resources Board Test procedure includes a 72 hour triple diurnal test cycle in a SHED that ranges between 18 and 41°C.
Running losses are measured by operating the vehicle on a chassis dynamometer through three consecutive driving cycles in a SHED at 41°C. The CARB and U.S.EPA evaporative emission tests have required vehicle manufacturers to design higher capacity evaporative emission control systems that achieve better in-use control even under extreme conditions.
Vehicle Emission Factors:
Emission factors are estimates of the pollutant emissions produced per kilometer traveled by vehicles of a given class. The emission factor is defined as the estimated, “average emission rate” for a given pollutant for a given class of vehicles. Estimates of vehicle emissions are obtained by multiplying an estimate of the distance traveled by a given class of vehicles by an appropriate emission factor.
Vehicle emission factors for a given jurisdiction should ideally be based on emission measurements performed on a representative sample of in-use vehicles from that area. Such data collection is expensive, however and requires facilities that few countries possess. Computer models are being used to estimate vehicle emission factors as functions of speed, ambient temperature, vehicle technology and other variables.
The emission factors are decided based on the testing of vehicles on a chassis dynamometer to the prescribed driving cycle. In addition to standard testing conditions, many vehicles are tested at other temperatures, with different grades of fuel and under different driving cycles.
There is considerable uncertainty about the applicability of emission measurements based on emission factors. The most important sources of uncertainty are the sensitivity of actual emissions to driving cycle, the wide variety of driving patterns, vehicle technologies, the effects of sampling error, etc.
The calculation of emission factors are based on average speeds, ambient temperatures, altitude, fuel volatility etc. Hence, any changes in these input assumptions can alter the resulting emission factors. Exhaust emission factors increase significantly at low temperatures, while evaporative emissions increase with increasing temperature.
HC and CO emissions per vehicle km. tend to increase at low average speeds, such as in congested city driving. NOx emissions tend to increase at higher speeds. Generally lower average speeds are due to traffic congestion and the increase in emissions under these conditions are due to the stop-and-go traffic in congested conditions.
In India, Central Pollution Control Board (CPCB) has worked out the emission factors for different types of vehicles (two wheelers, cars, trucks and buses) manufactured before and after 1995. It has also worked out the average vehicle utilization of different category of vehicles are communicated to the State Pollution Control Boards. Based on the number of vehicles in each category, the State Pollution Control Boards work out the pollution load per day in the major urban areas in their jurisdiction.
Emission factors are strongly influenced by the way a vehicle is driven-in particular, by the average speed and the congestion on the roads which are different for different cities. Hence emission factors for the same type and brand of vehicles can differ significantly between different cities. Similarly, depending on the size and sprawl, average vehicle utilization of vehicles can also vary between different cities. Hence the present system of working out pollution loads in Indian cities need modifications.
Vehicle emission factors and the average vehicle utilization per day of different types of vehicles should be developed for each major city based on the emission tests carried out under local conditions and should reflect actual in-use performance of vehicles. This ensures accurate emission factors, and it provides an effective methodology for calculating the daily pollution load in major cities.
Emission Testing Facilities in India:
Automotive Research Association of India (ARAI), Pune, Vehicle Research and Development Establishment (VRDE), Ahmadnagar and Indian Institute of Petroleum, (IIP), Dehradun are the test centers approved by the Ministry of Road Transport and High Ways for certification of emission compliance. Most of the emission testing for type approvals and conformity of production are carried out at ARAI, Pune.
According to Mashelkar Committee, the test facilities available at all these test centers are inadequate to meet the requirements of testing due to expansion of automobile industry, automobile market and the technological developments in vehicles. The introduction of stringent emission standards will require new test systems which are not available with these testing agencies.
It is expected that load for emission testing will increase with the implementation of stricter norms in future, requiring more development work by the industry which will also lead to increased testing load for type approvals. Further requirement of surveillance and monitoring emission norms compliance including emission warranty of the vehicles produced in the country will require more testing facilities in the country.
The facilities for testing of evaporative emissions and low temperature carbon monoxide emissions are not available in the country. It is necessary to develop adequate testing facilities in the country if the emission standards established from time to time are to be enforced.