Under pressure to meet the pollution limit set for 2000 A.D., manufacturers have rushed these engines to the market. Both Bajaj Auto Limited and TVS Suzuki Limited have launched scooters with four-stroke engines, named Legend and Spectra respectively. However, as these scooters have slower pick-up and will be 10 per cent costlier, manufacturers are sceptical about the demand for them.

LML Limited, for instance, is launching two four-stroke scooter designs next year. But the company's Executive Director, Marketing, R.K. Caprihan, says they are doing so only because their competitors have launched four-stroke scooters. ``Otherwise, we don't feel any need for it,'' says Caprihan.

He further points out that the difference between the fuel efficiency of a two-stroke and a four-stroke scooter is not substantial.``If four-stroke motorcycles are 20 per cent more fuel-efficient than two-stroke ones, this difference is around 10 per cent in the case of scooters.''

However, for environmentalists, even that is a crucial difference when the air is overburdened with pollutants. Besides, Indian manufacturers have long cited excuses for not switching over to four-stroke engines. For a time they gave the example of the West, where scooters have the conventional two-stroke engines.

But there is one major reason why India cannot afford to do the same. Unlike the West where two-wheelers are generally `fun' vehicles, in countries like India, Thailand and Taiwan, scooters and motorcycles are a common mode of transportation. Around 65 per cent of the total vehicle population in India comprises two-wheelers. During the '80s, the number of two-wheelers in the country rose by 561 per cent and is presently at more than 20 million.

According to the latest figures released by the Association of Automobile Manufacturers, the sale ofscooters registered a 10 per cent increase in the first quarter of this financial year as compared to the same period last year. While 10 per cent more mopeds were sold, the sales of motorcycles rose by 23 per cent.

A recent Centre for Science and Environment study -- titled Slow Murder -- says two-stroke engines account for 60 per cent of India's total petrol consumption and for nearly 70 per cent of the country's total hydrocarbon emissions. This is because a large part of the unburnt fuel in case of two-stroke engines escapes with the exhaust due its simple design.

However, manufacturers point out the practical difficulties of switching to four-stroke engines. While in motorcycles, these are still easy to fit, to do so in case of scooters is difficult. Caprihan points out that four-stroke engines generate more heat and therefore require better cooling. In case of motorcycles, this is taken care of as the engine is exposed. But in case of scooters, manufactures have to add a fan to facilitate cooling.``The fan takes up some power available to the engine,'' says Caprihan. Moreover, the metal sheet under the handle of a scooter increases the drag. All of this results in a substantial drop in the pick-up of the vehicle.

Also, adds Caprihan: ``The four-stroke engine is considerably more expensive, and in a competitive market, it does not make commercial sense to go in for this technology.'' The cost per four-stroke engine scooter will be Rs 2,500-3,000 higher than an average two-stroke engine scooter. The maintenance cost of a four-stroke scooter is also more.

But Central Pollution Control Board Chairman Dilip Biswas doesn't see this extra cost as unreasonable. As he puts it, the consumer has to bear a higher burden for protecting the environment.

There may be another solution to the problem, perhaps cheaper and more effective. LML is currently fitting some Supremo models with catalytic convertors on a random basis in the capital to test the effectiveness of convertors in scooters. Though a catalyticconvertor costs around Rs 1,000 and has to be replaced every third year, Caprihan insists its overall cost works out to less than the maintenance cost of a scooter with a four-stroke engine.

The Research and Development division of Indian Oil Corporation has developed a catalytic converter that suits all two-stroke vehicles. The oil company will formally launch this convertor on October 16.

Manufacturers, however, are not likely to rush in to upgrade their scooters. Despite the experiments LML is conducting, Caprihan says the company would not add a catalytic convertor to its vehicles, and risk a hike in prices, before January 1, 2000.

LML is also in the process of developing a fuel-injection system for scooters. This would distribute fuel more evenly to individual cylinders by means of a pump so that more power is developed and undesirable emissions reduced. That, according to Caprihan, will be a real breakthrough.

Companies have also introduced automatic oil mixing to deal with adulteration of 2Tlubricating oils used for two-stroke engines. The Bhure Lal Committee had recommended sale of petrol premixed with 2T oil to fight the menace as well as phasing out of two-stroke vehicles.

Premixed petrol is especially needed to stem the poison released by three-wheelers. They have the same engine capacity -- 150 cc -- as that of two-wheelers but carry more load in the form of a heavier body and more passengers. Moreover, three-wheeler operators are known to use cheaper and adulterated 2T oil to run their vehicles. This means that they not only consume more fuel for the same level of efficiency but also emit more exhaust. Still, precious little has been done on the three-wheeler front.

Only Bajaj Auto -- the largest three-wheeler manufacturer -- has developed a 175-cc, four-stroke pick-up van, which would be launched next year. Its 74-cc, four-stroke engine scooterette -- Sapphire -- would also arrive next year.

But CPCB chief Biswas wants manufacturers to do more. He insists they should make publicdisclosures of their vehicles' emission characteristics and not just be happy with fulfilling emission norms. Biswas says knowledge about what his tailpipe is emitting should be available to a consumer and automobile companies must introduce a device that will perform this function. He has an appeal for oil companies too. Says Biswas: ``It has taken us more than five years to get companies to introduce four-stroke technology for scooters. Oil companies must now make sure they supply cleaner fuel.''

But the answer -- like always -- ultimately lies in an efficient and environment-friendly public transport system, which would reduce the need for personal modes of transportation.

Why four-stroke engines?

In a two-stroke engine, the cycle of suction, combustion, expansion and exhaust is completed in a single revolution of the crankshaft. So every alternate stroke is a power stroke and the fuel consumption is higher, leading to higher emission levels. On the other hand, in a four-stroke engine, thecycle of suction, compression and combustion, expansion and exhaust is completed in two revolutions.

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