Emission performance of CNG debatable

By R. Prasad

CHENNAI, APRIL 22. The tardy way of converting the Delhi bus fleet to CNG without field-testing it in India has come in for sharp criticism. The Bhure Lal committee's insistence on CNG as the only fuel to be used has stymied the possibility of using any other fuel or upgrading the diesel technology to meet stricter emission norms. CNG is a clean fuel and was the best in 1998 when the committee submitted its recommendations to the Supreme Court.

Yet, the haste in introducing CNG that is purported to meet Euro- 4 norms is perplexing as even Europe is supposed to meet Euro-4 norms only by 2007-08. Incidentally, India has a road map for reducing sulphur content in diesel to 0.005 per cent by that time. Reducing the sulphur content in diesel along with other technological upgradation can help reduce vehicular emission. The exact time to implement Euro-4 norms in India will be decided only in 2005.

More baffling is the way the conversion is being rushed through when studies done abroad have called for more data before deciding on CNG as an automotive fuel. Follow-up studies on gas vehicles undertaken since the early 1990s by the Technical Research Centre of Finland have not been able to draw any conclusion on the dynamic emission performance.

More importantly, the conversion in Delhi had happened when several studies in Europe have questioned the real-life emission performance of gas-fuelled buses. According to the report prepared for the International Association for Natural Gas Vehicle (IANGV) technical committee last year, some gas engines do not perform well in real road driving conditions marked by acceleration, deacceleration, braking and cruising though favourable results were obtained in steady-state emission testing.

Unlike in the U.S., there is no transient testing (imitating city driving cycle) in addition to steady-state testing. The new European transient cycle transient testing will become mandatory starting with the Euro-3 emission regulations. And emission regulations for CNG will start only when the Euro-3 norms become applicable there. According to the IANGV report this implies that there has been no system in place in Europe to guarantee the emission durability of gas vehicles already plying. It further adds that emission performance of gas vehicles depends on the functioning of the fuel system and the catalyst and some kind of monitoring system has to be in place to be sure of the performance of the vehicles.

If Europe had not undertaken transient testing, does India at least have a chassis dynamometer to undertake testing of buses mimicking city driving? The answer is no. Even the Automotive Research Association of India (ARAI), the certifying agency in the country, does not have the facility. The chassis dynamometer that the ARAI presently has can only cater to the requirements of light commercial vehicles and not vehicles above 3.5 tonnes. It has never in the past been required to simulate the Indian city driving cycle and measure the emissions during such a cycle for a bus. But the need has now arisen.

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