Engine trouble

The sword of Damocles has been hanging on the two-wheeler industry ever since India got into the business of tightening emission standards in 1990. But now with further tightening of the norms in 2000 and the proposed revision of the norms in 2005 and subsequently in 2009, the possibilities of further improvements in engine technology to meet these norms seem quite remote. Unless there is a major technological breakthrough in the conventional two-stroke engine technology, industry pundits fear that the ubiquitous Indian two-wheeler sector may die a natural death.

The Society of Indian Automobile Manufacturers ( siam ) claims that the proposed emission standards for two-wheelers for 2005 would be the strictest in the world. But no one in the industry seems to know which engine technology — two or four-stroke — would survive the future revisions. Even siam admits that the feasibility of making norms stricter in 2009 would have to be reviewed in 2005, as there is no engine technology in the world today which can meet such stringent norms.

What’s more polluting?

Two-wheelers constitute 60 per cent of the total vehicles on the road in India and are responsible for as much as 70 per cent of the total hydrocarbons ( hc ) emissions. This is because the conventional design of the two-stroke engine allows almost 15-25 per cent of the fresh fuel charge to escape unburnt.

Policy-makers in other countries with large two-wheeler fleet have come down heavily on two-stroke vehicles. For example, Taiwan has mandated a standard for hc and no x (oxides of nitrogen) for two-stroke vehicles which is half of that of four-strokes vehicles. As two-stroke engines emit more hc , it becomes impossible for them to meet this standard. In Rome, two-stroke vehicle owners have to pay heavier taxes, thus Italy has tried to phase-out two-stroke vehicles by providing a disincentive to consumers.

The Delhi government is even considering a ban on registration of two-stroke two-wheelers. The worried industry has two immediate strategies available to get out of the impasse — either to modify the conventional two-stroke engine technology and fit catalytic converters or replace two-stroke engines with improved four-stroke powered engine.

Yet experts feel that from the environmental perspective there is no obvious choice between two-stroke engine and four-stroke vehicles as both these engine technologies in their conventional form, have their relative advantages and disadvantages. While the hc emissions of conventional two-stroke engines are higher than those of four-stroke engines. no x and carbon monoxide (CO) emissions of four-stroke engines are considerably higher (see graph: Comparative emissions ).

By virtue of its construction and modes of operation, the maintenance and adjustments required by two-stroke engines are fewer and simpler. The operating cycle in a two-stroke engine is completed in one revolution of the crankshaft compared to two revolutions in a four-stroke. Therefore, theoretically a two-stroke engine develops twice the amount of power for the same size resulting in a much lower weight than their counterparts. The simplicity of construction and fewer moving parts also help to reduce the weight. Less weight results in reduced fuel consumption for the same payload. Moreover, they can maintain their performance over a longer period.

However, four-stroke engines require valves and valve train mechanisms, such as camshaft and timing chain to control intake, combustion and exhaust processes. As a result, these engines require more frequent maintenance and adjustments due to the wear and tear of these moving parts. Lack of timely maintenance and adjustments can cause the performance of the four-stroke engines to deteriorate over a period of time. The most important feature of the four-stroke engine is its superior fuel efficiency.

One of the most important environmental objection to four-stroke two wheelers is that it emits higher no x emissions compared to two-stroke two-wheelers. According to siam, no x emissions from four-stroke engines fitted with catalytic converters is as much as 13 times that of two-stroke vehicles fitted with catalytic converter.

One way to mitigate the problem is to employ the three-way catalytic converter ( twc ), which is also used in passenger cars. But this is not easily adaptable on smaller four-stroke engines of two-wheelers. And even if it were used, it would result in substantially higher initial cost, which would prohibit the consumer from buying the product. Another option to reduce no x emissions is to use richer air fuel mixtures. But again this would take its toll on fuel economy and would result in an increase in co and hc emissions. To deal with this, a dual bed catalytic converter would need to be used. But this would make the whole process highly complicated. Experts are thus yet to come out with an optimum solution for four-stroke vehicles to meet the future emission norms, which would comply to emission norms and would give good fuel economy.

To meet the India 2000 norms, two-stroke engines have been fitted with a catalytic converter that scavenge exhaust gases but the durability of catalytic converter of two-stroke scooters is low. Four-strokes engines use a technology called the secondary air injection system while some models use a catalytic converter to reduce emissions further. Experts believe a further 25-30 per cent reduction in co emissions is possible if the secondary air injection technology is used for four-stroke vehicles.

Meanwhile, the two-wheeler manufacturing companies seem to be keeping all their options open. Currently, about 30 per cent of Bajaj two wheelers run on four-stroke engines. By and large Bajaj motorcycles run entirely on four-stroke engines. But Bajaj Auto has a four-stroke model in each of the segments including scooters, motorcycles, three wheelers and other lighter vehicles, says N V Iyer, general manager, Bajaj Auto Limited. “ TVS -Suzuki is planning to have models fitted with both two-stroke engines and four-stroke engines in all segments of vehicles,” says M N Muralikrishna, vice president (technical), TVS- Suzuki Limited.

Immediate solutions

The two-wheeler industry now claims that even the research and development ( r&d) worldwide has been unable to find the solutions to the small two wheeler segment. One possible way to meet future emission standards is the use of two-stroke technology along with the incorporation of a proficient fuel injection system, with better scavenging facilities for minimisation of unburnt fuel escaping. This technology would also need innovations to minimise the use of lubrication oils and the use of a catalytic converter to reduce emissions of exhaust gases. But this technology is not yet commercially viable. Iyer points out that “price competitiveness is important as India is an extremely price sensitive market.”

Both two-wheeler manufacturing companies TVS- Suzuki and Bajaj Auto confess having perused possibilities of incorporating a new fuel injection system in two-stroke engines in collaboration with some multinational companies. “As early as in the late 1980s, TVS- Suzuki worked on a project with a distinguished research company and developed a Semi-Direct-Injection System on one of its two-stroke vehicles. While technical results were satisfactory, it was not commercially viable,” comments Muralikrishna.

Bajaj Auto in cooperation with an Australian company called Orbitel had also tried developing a similar kind of technology but these plans could not materilise into a meaningful solution. Several organisations are trying to develop this technology. Some of them include Ficht (Germany), Bosch (Germany), avl (Austria), Orbitel Engines (Australia), Institute of French Petroleum (France), Sagem (France) and Ricardo (England). But no company has successfully achieved this as yet claim Indian two-wheeler manufacturers.

Unless there is a breakthrough in the direct fuel injection system, the solution to emission problems will lie in the adoption of alternative fuel technologies.

Reported by Lopamudra Banerjee

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