The full form of DTSI is "Digital Twin Spark Ignition."
Two sparks, offset by a time interval, is used to ignite the fuel air mixture. The initial spark burns most of the mixture while a second spark is used to burn the rest. This increases fuel economy as less unburnt fuel escapes through the exhaust port. It also provides increased power.
A knock occurs when the fuel is ignited while the piston is undergoing the compression stroke not when it is going back. When the second spark fires, the amount of charge in the cylinder is considerably less and therefore the pressure spike created by it does not produce any jerking effect.
DTSI system has been the driving technology in the new generation motor cycles to be more fuel economical & to meet the emission standards. We are all aware of Internal Combustion engine with single spark-plug system. DTSI engines use two spark plug one at the top of the combustion chamber & the other somewhere in-between the TDC & BDC of the piston. The piston position is sensed digitally -the top spark plug is activated & as the piston moves down with the power stroke the second spark plug is activated.
With the first spark the combustion mixture burns & produces the required force but the flame propagation dies of early without the whole air+fuel mixture being burnt completely. Activating the second spark plug digitally helps in burning the complete A/F mixture resulting in fuel economy & better emission control.