Bajaj Auto and Hero Honda have been trading punches for the last few months. Not literally, of course, but more on a figurative sense, contesting whether the demand for bikes in the 100cc segment is declining and whether the 100cc+ segment, including the 125cc category, will be the new choice for entry-level bike buyers.

Hero Honda thinks that the 100cc segment is not headed southward and Bajaj opines that the segment will stagnate and eventually decline since bike buyers will graduate to the bigger-engined category just above the entry-level.

But with a 100cc bike in its portfolio, Bajaj’s proclamation that it will exit the current entry-level segment was rather bold and must have been backed by a breakthrough that it must have managed and which it is focusing on for its future bikes. That in-house technological research and development effort that was being widely speculated about was finally unveiled late last week.

The latest technology that Bajaj is showcasing is a 125cc engine that has the newly developed ‘DTS-Si’ (Digital Twin Spark-Swirl induction) technology. The new engine with swirl induction is expected to give an amazing mileage of 109 km per litre under ideal (standard) test conditions, which is higher than the mileage the current 100cc motorcycles offer.

Bajaj feels that with this breakthrough technology, it has the potential and opportunity to offer an upgrade to the 100cc bike customer, a two-wheeler with an engine which offers the best of both worlds — 100cc type mileage and 125cc-class performance.

The technology has been designed and developed completely by ‘**Ahead’, Bajaj Auto’s in-house R&D. Can it revolutionise the industry by turning out to be India’s most fuel-efficient two-wheeler engine.

In a conventional single-spark-plug-equipped combustion chamber, and the rate of combustion is relatively slow. The spark plug, usually situated at one end of the combustion chamber, ignites the air-fuel mixture and the ensuing flame spreads like a slowly inflating balloon. There is an inevitable delay for this inflating balloon to reach the furthest part of the combustion chamber. So, there are pockets of poor combustion within the chamber and, overall, the combustion is slow and inefficient.

The Digital Twin Spark–ignition (DTS-i) technology that Bajaj developed a few years ago and has incorporated in many of its current engines, takes care of the slow rate of combustion in a simple but novel way. The cylinder head is equipped with two spark plugs, instead of the usual one. By generating two sparks at either ends of the combustion chamber, (approximately 90° to the valve axis) the air-fuel mixture gets ignited in a way that creates two flame fronts and, therefore, a reduction in flame travel of the order of 40 per cent is achieved. A fast rate of combustion is achieved leading to faster rise in pressure. The obvious outcome of this is more torque, better fuel efficiency and lower emissions.

While that sounds logical and simplistic, TVS Motor claims that the same effect is achieved by employing a single spark plug with differential sparking cycles.

The DTS- i is the mother technology for the latest Digital Twin Spark–Swirl induction or DTS-Si technology.

Thanks to DTS-i, a fast rate of combustion and, therefore, the resulting fast rate of pressure rise, is harnessed by optimally positioning this pressure. Bajaj R&D observed that when burning lean air-fuel mixtures, the two plugs provide rapid combustion, but at light loads, opportunity exists to further improve the combustion quality. Usually under such conditions, the quality and concentration of the air-fuel mixture will vary from one area to another within the combustion chamber. However, combustion efficiency in lean air-fuel mixture conditions can be further improved by generating high turbulence in the combustion chamber.

Bajaj R&D says that combustion chambers having low turbulence give rise to propagation of a flame front, which is akin to that of a gradually expanding balloon. This results in a slower rate of combustion and thus slower rate of pressure rise. The end result is lower efficiency.

When high turbulence is generated and combustion takes place, the surface of the ballooning flame front fragments itself, with projection like fingers, and this increases its surface area, thereby improving combustion further.

However, the straight ports used in conventional engines have limitations in generating high swirl values due to their geometry. One of the ways of generating more turbulence or swirl is to have a port configuration that promotes this phenomena. To generate the required level of swirl, an offset port configuration was arrived upon and optimised by Bajaj engineers.

Incorporated in the new engine, this results in a swirling motion of the incoming charge, which decays itself into turbulence as the piston moves in the Induction and Compression strokes. This results in the air-fuel mixture being more thoroughly mixed and spread around the combustion chamber.

Sparks provided by the twin spark plugs ignite this highly turbulent and compressed air-fuel mixture, leading to a flame front with high surface area, resulting in a rapid rise of pressure due to quick combustion. The values of turbulence achieved now, are substantially higher than that of a straight port cylinder head, such as in the Pulsar. A combination of DTS-i and Swirl induction thus provides extremely rapid combustion, resulting in higher efficiency.

Swirl induction has been used in passenger cars with great success. This is the first time that a similar technology has been adopted in a two-wheeler engine in India. How efficient and successful it is at improving the on-road performance of a two-wheeler is something that we can check out next month when Bajaj launches its first bike on the new technology platform.

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