The two-spark or twin-spark plug technology used in many motorcycles, currently also the subject of a court dispute on patent rights, may be much ado about nothing that much.
According to independent automobile engineers, this technology’s performance is about the same as a motorcycle fired by a single spark plug. In other words, the twin spark plug technology, whose usage is being contested by Bajaj Auto and TVS Motor Company, does not deliver any better mileage and acceleration than that derived from a single spark plug.
Industry experts point to the 1,000cc and above motorcycles like Suzuki’s Hayabusa and Yamaha’s YZF R 1, that attain higher speeds using a single spark plug. Engineering experts say if the combustion chamber, the place where fuel and air is mixed in a controlled manner, is well designed, the need for two spark plugs does not arise.
“It’s all about design. If you have an optimally designed combustion chamber, then I believe a single spark plug is adequate to obtain the same performance and fuel efficiency as that from a twin spark plug. There are no outstanding benefits to be got from the twin spark plug system, except that it represents a totally new design,” says J P Subramaniam, head of the department of mechanical engineering in IIT, Delhi.
A combustion chamber is inside the motorcycle engine. Any unburnt fuel is released as waste in the exhaust pipe. The idea of a second spark plug was born to avoid this wastage, where the unburnt fuel is also combusted and turned to energy. Automobile engineers say fuel is wasted if the design of the combustion chamber is less than optimal.
According to the description, the second spark plug produces a spark a few seconds after the spark fired by the first spark plug. While the first spark plug burns up to 70 per cent of the fuel, the remaining fuel will be burnt by the second spark plug.
A patent dispute on the twin spark plug between Bajaj Auto and TVS Motor began in 2007. The next hearing will be held at the Madras High Court in November. Officials from both companies are under court orders preventing them from speaking to the media.
“I tend to agree with the engineers who advocate a single spark plug. If the design of your combustion chamber is optimal, then all parameters like fuel efficiency and emission standards obtained from a single spark plug are as good as those achieved from a twin spark plug. If the design is not optimal, then it results in unburnt fuel accumulation, necessitating the need for an additional spark plug. It all depends on the design, which is critical,’’ says Dinesh Tyagi, director (technical), of the National Automotive Testing and R & D Infrastructure Project, Natrip.
Two-wheeler manufacturers like Bajaj Auto and Royal Enfield who feature this technology in their motorcycles say the twin spark plugs do increase fuel efficiency and enhances performance. Comparison of ARAI-certified mileage data from the top four motorcycle companies’ 150cc motorcycles reveals another picture. Mileage squeezed out from the Pulsar 150cc motorcycle featuring the digital twin spark ignition technology (DTSi) is almost the same as from other 150cc models featuring a single spark plug. (see mileage table)
On performance metrics like acceleration and top speed, the Pulsar’s acceleration is the same as other 150cc motorcycles that are fired by a single spark plug. The Pulsar 150cc reaches 0–60 km per hour in 5.45 seconds, which is more than the Honda 150cc Unicorn’s 5.28 seconds, and less than Hero Honda Hunk’s 5.57 seconds.
Top speeds notched by the digital twin spark ignition (DTSi)-enabled Pulsar 150cc is 114 km per hour which is the same as the Honda Unicorn’s 114 km/hr.
A top engineer from a Japanese two-wheeler company says: “We did feature twin spark plug technology in our motorcycles earlier. With technological advancements, especially in the design and construction of motorcycle engines, the efficiency squeezed from two spark plugs could now be got from a single spark plug.”
“Technically both are right. That is, manufacturers who use twin spark plugs and those that use single spark plug. It also depends on the design of the engine. If a system is designed to use twin spark plugs, so be it. But the efficiency obtained from a single spark plug now is the same as that obtained from two spark plugs,” said G K Sharma, former director (technical) of Natrip.
Professor Subramaniam says the usage of twin spark plugs from an engineering perspective occupies extra space, and imposes additional costs to the consumer, since two spark plugs have to be maintained.
The first twin spark engine was featured in an Alfa Romeo racing car in 1910 and has been incorporated in commercially produced cars since 1950.
