Automotive exhaust emissions are covered by regulations in most of the countries. Through the years, the number of regulated pollutants have steadily increased, the statutory limits have become more severe, and the countries more numerous. The first requirements remained quite vague, such as the West German law of 3rd February 1910¹ stating that: "Vehicles must be safe and built so as to preclude any nuisance for the public, by smoke or odour.

The US was the first country to introduce emission standards for automobiles. The first regulations in the United States, enacted in California in 1959, eliminated crankcase emissions (blow-by) and limited CO and HC.² The first federal standards under the Clean Air Act, which applied to 1968 model vehicles, were published in the Federal Register in 1966.³ These standards correspond roughly to the values set in California in 1960.

Successive amendments in 1968, 1970, etc converted the standards from pollutant concentration values to pollutant mass values. These values were expressed as mass emitted per unit distance travelled, based on an imposed driving cycle. the Constant Volume Sample (CVS) method⁴ was used to accumulate the emissions corresponding to the driving cycle. The standards, which initially covered CO and unburnt HC emissions, were then extended to NOx and particulate, which subsequently covered the diesel engines.

Interim standards were established during the years 1975 & 1976 and with availability of technology these standards were tightened and given form in the US Clean Air Act of 1990.

Most emission standards of other countries have drawn heavily on the US standards. While all states in the US have to meet this legislation individual states are allowed to have stricter standards than these. The State of California has always been a leader in emission control legislation and has generally adopted stricter standards than the rest of the US. The main reason for this is the very poor quality of air in the Los Angeles area.

In Europe⁵ in 1956, the VDI (Verein Deutscher Ingenieure) was asked to draft pollution directives. Around 1961, a Franco German committee focussed its attention on the reduction of CO and unburnt HC. In France, exhaust fumes have been regulated since 1963,⁶ crankcase gas emission since 1964,⁷ and idling CO emissions since 1969.⁸ Since the traffic conditions in European cites are significantly different from those in American cities, a different driving cycle was adopte, which was based primarily on Pars Traffic conditions.

Furthermore, given the diversity of the types of vehicles drive in Europe (size and drive system), the statutory limits were adjusted in accordance with the weight of the vehicles affected.

Emission regulation in Europe have traditionally been formulated by the United Nations Economic Commission for Europe (UN-ECE). Some countries like Austria, Sweden, Norway and Switzerland have however decided to revoke the ECE regulations and have adopted the US standards for cars.

In Japan⁹, the first measure concerning CO were enacted in 1966 and then extended to CO and NO_x in 1973. These standards involve both concentratons and mass emissions limits relative to driving cycles specific to Japan. Japan has had a very complex regulation due to a multiplicity of testing procedures. Thus comparisons with the US or ECE regulations is difficult. However Japan has fairly strict standards that compares well with those in the US. South Korean standards were implemented in 1987 and have been high from the beginning.

Closer to India in terms of level of development, Brazil has traditionally built its standards on the US model – with a time lag however. Present standards are equivalent to the US 1985 standards.

Mission regulation in India
Emissions legislation was first implemented in India in the year 1991. Two sets of standards were prepared under the headings Type approval and Conformity of Production. The first sets the standard for a paticular model of vehicle and is a basic requirement for the vehicle to be taken to the production stage. The second sets the standard for any vehicle (taken at random from production ) must be met for the production to be allowed to continue.

The testing method initially used was the warm start method which is less stringent than the cold start method adopted in the ECE. Thus the same vehicle would give approx. 20% higher emissions when tested using the ECE method. However India shifted to the cold start method from 1996 on. Further, limits on crankcase emissions and evaporative emissions were incorporated in 1996.

The government has already come out with emission regulation standards for 2000 which will be closer to European and American standards. These standards were to have come into forces earlier; however they were postponed due to the inability of Indian manufacturers in meeting them.

The Indian standards have been lenient and all Indian companies have been able to meet them comfortably. A new set of limits were set in 1996 which were again easily met. The standards for 2000 ( which were set in 1996 ) are however closer to world standards.

Regulatory test procedures
To be able to check the application of regulation in measurement conditions that are as reproducible as possible, it was necessary to develop standard running procedures for the vehicles to be checked. These procedures were associated with analytical methods that were also regulated. The same cycles are also used to measure the specific fuel consumption of the vehicles. The cycles correspond to a sequence of speeds as a function of time carried out on a chassis dynamometer.

Different test cycles have been adopted by different countries. These have been discussed as follows:

i. American Test Cycles

FTP - 72 (UDDS)¹⁰: The U.S. FTP-72 (Federal Test Procedure) cycle is also called Urban Dynamometer Driving Schedule (UDDS) or LA-4 cycle. The same engine driving cycle is known in Sweden as A10 or CVS (Constant Volume Sampler) cycle and in Australia as the ADR 27 (Australian Design Rules) cycle.

FTP-75¹⁰:The U.S. FTP-75 (Federal Test Procedure) cycle is derived from the FTP -72 cycle by adding a third phase of 505s, identical to the first phase of FTP-72 but with a hot start. Thus, the entire FTP-75 cycle consists of the following segments:
-cold start phase
-transient phase
-hot start phase.

The following are basic parameters of the cycle:
Distance traveled: 11.04 miles (17.77 km)
Duration: 1874s
Average speed: 21.2 mph (34.1 km/h).

Figure 1. FTP-75 Cycle
The emissions from each phase are collected in a separate teflon bag, analyzed and expressed in g/mile (g/km). The weighting factors are 0.43 for the cold start, 1.0 for the transient phase and 0.57 for the hot start phase.

ECE R49: The R49 is a 13-mode steady-state diesel engine test cycle introduced by ECE Regulation No.49 and then adopted by the EEC (EEC Directive 88/77, EEC Journal Officiel L36, 8 Feb. 1988). It is performed on an engine dynamometer operated through a sequence of 13 speed and load conditions. Exhaust emissions measured at each mode are expressed in g/kWh. The final test result is a weighted average of the 13 modes. The test conditions and weighting factors of the R49 cycle are shown in in Table 1 The areas of circles in the graph are proportional to the weighting factors for the respective modes.

The running conditions of the R49 test cycle are identical to those of the US 13-mode cycle. The weighting factors, however, are different. Due to high weighting factors for modes 6 and 8 (high engine load), the European cycle is characterized by high average exhaust gas temperatures.

ECE + EUDC Test Cycle: The ECE+EUDC test cycle is performed on a chassis dynamometer. The cycle is used for emission certification of light duty vehicles in Europe. It is also known as the MVEG-A cycle. The exact definition of the cycle can be found in the EEC Directive 90/C81/01.

The entire cycle includes four ECE segments, Figure 1, repeated without interruption, followed by one EUDC segment, Figure 2. Before the test, the vehicle is allowed to soak for at least 6 hours at a test temperature of 20-30°C. It is then started and allowed to idle for 40s. According to the European cycle proposal for the year 2000, that idling period is to be eliminated, i.e., engine would start at 0s and the emission sampling would begin at the same time.

Emissions are sampled during the cycle according the "Constant Volume Sampling" technique, analysed, and expressed in g/km for each of the pollutants.

Figure 1. ECE 15 Cycle
The ECE cycle is an urban driving cycle, also known as UDC. It was devised to represent city driving conditions, e.g. in Paris or Rome. It is characterized by low vehicle speed, low engine load, and low exhaust gas temperature.

Figure 2. EUDC Cycle
The EUDC (Extra Urban Driving Cycle) segment has been added after the fourth ECE cycle to account for more aggressive, high speed driving modes. The maximum speed of the EUDC cycle is 120 km/h. An alternative EUDC cycle for low-powered vehicles has been also defined with a maximum speed limited to 90 km/h.

TABLE: 1.3 SUMMARY OF PARAMETERS FOR ECE AND EUDC

TABLE: 1.4 JAPANESE 6-MODE CYCLE FOR DIESEL VEHICLES¹⁹

TABLE: 1.6 JAPANESE 6-MODE CYCLE FOR HEAVY DUTY VEHICLES (GASOLINE OR LPG)

10-Mode Cycles: This cycle reproduces urban driving after a warm start. It corresponds to a distance of 0.064 km at an average speed of 17.7 km/h and lasts 135s. The cycle is performed six times after warming the vehicles at 40km/h for 15min. The emissions measured in the last five cycles are expressed in g/km (Fig___). t therefore represents a route of 3.32km, carried out in 675s, at a maximum speed of 40 km/h, with 26.4% of the time at idle.

11-mode cycle: this cycle simulates driving on an urban expressway after a cold start. It includes starting the engine at a temperature of 20 to 30° C. After an idling period of 25, a distance of 1.021 km is traveled at an average speed of 30.6 km/h for 120 s. The emissions measured in this ccle are expressed in g/test. (Fig___).

New 10- to 15-mode Cycle: The previous 10-mode cycle limited to 40km/h was extended at a maximum speed of 70km/h (Fig___). It represents at a distance of 4.16km, completed in 660s at an average speed of 22.7 km/h, with 31.4% of the time idling.²⁰ This test is applicable to new gasoline and diesel vehicles manufactured after November 1991. It has been applied since October 1993 to test vans under 2.5t and the results are expressed in g/km instead of ppm.

New 13-mode cycle for heavy vehicles: The previous 6-mode cycle for the same type of vehicle is replaced by a 13-mode cycle carried out in a stabilised conditions and measured values are expressed in g/kWh instead of volumetric concentration.²⁵ This new cycle, which emphasizes on low speed driving, is identical for gasoline and diesel vehicles. Only the weighting factors are applied to each mode are different. (Fig__ and Fig__).

TABLE: 1.7 BREAKDOWN OF THE OPERATING CYCLE USED FOR THE TEST

Modified Indian driving cycle for year 2000

TABLE 1.8 OPERATING CYCLE ON THE CHASIS DYNAMOMETER (PART ONE)

TABLE: 1.9 OPERATING CYCLE ON THE CHASIS DYANAMOMETER (PART II)