What is Indian driving cycle? What is the procedure adopted for it?
H.Mohammed Rafiq, Chennai
ANSWER: The driving cycle of any country is the probable plot of the vehicle speed right from the start of the engine through its journey over a prescribed time.
This information is acquired by averaging the extensive data when the vehicle is driven under actual service conditions on designated urban routes or on highways where the traffic density and driving pattern is representative of the prevailing working day pattern of the country.
The data is available as a plot of vehicle speed km/h versus time and is called the urban or highway driving cycle of the country.
The driving cycle is simulated on a test vehicle in a laboratory test called the constant volume sampling (CVS) system. This is like the treadmill in a hospital for exercising a patient without having him walk or run on the actual road encountering flat or a steep road at different speeds to examine his heart.
The vehicle is mounted on rollers and anchored. When the vehicle is driven according to the driving cycle, the rollers drive a dynamometer on which the various resistances corresponding to the driving cycle are imposed.
The tail pipe emissions are mixed with varying volumes of diluted air by a parallel path so that the total volume of the efflux is constant.
Part of the samples are bled and collected in bags during the duration of the test and analysed to give the volumetric composition in percentage or ppm.
These are in turn computed to mass emissions and expressed in g/km of drive according to the cycle. These emissions must conform to the limits mandated by the country, like EURO 2 or EURO 3.
Driving cycle is an expensive transient test procedure and reflects the average emission performance per km drive, integrating the total effects of the road infrastructure, traffic pattern and driving culture.
This is in no way an exact scientific test on the real time formation of pollutants. Indian driving cycle (IDC) was formulated around late 1985, after extensive road tests by the scientists at the automotive research association of India, Pune, when the mass emission norms came into being.
Since the IDC involves too many transients because of haphazard traffic situations in India, this is now only followed for two/three wheelers, which are common modes of transportation in Indian cities.
For passenger cars, the European driving cycle, with a modification to provide for a lower maximum speed practicable for India, is followed and is called the modified Indian driving cycle.
Heavier vehicles like buses and trucks (and tractors) are not subject to chassis dynamometer tests, but their engines only are tested on the laboratory test beds at steady state points at designated speeds, loads and time interval according to the schedule of the so-called 13-mode (or 8 mode for tractors) tests.
The emissions include in addition, smoke density (opacity) and particulars as applicable to diesel engines under regulation. But the emissions are computed as mass emissions in g/kWh and opacity expressed on standard Bosch or Hartrides scale.
The present thinking is to link the steady state tests (g/kWh) of the engine to transient tests (g/km) of the vehicle powered by the same engine by equitable assumption so that expensive CVS system tests are eliminated and India can have its own norms.
B. S. Murthy, Chennai
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