27 Agustus 2009

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 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.

Based on DTS-Si technology, the new engine is expected to give good mileage without compromising on performance.
The technology

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.

Swirl induction

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.

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