The dua
l sequential ignition system optimizes the timing of each spark plug based on engine speed and engine load. The intensive combustion at all engine speeds not only controls knocking, but also permits a much higher compression ratio (10.8:1) to achieve a higher output with less fuel consumed compared to a conventional design.Key to the i-DSI engine is rapid, intensive combustion, using two spark plugs in each cylinder mounted diagonally opposite one another, and a very compact, high-swirl combustion chamber made possible by the narrow (30°) valve angle and SOHC single pivot cylinder head.
Each pair of spark plugs is fired sequentially with the interval between the two depending on engine rpm and load. The intake side plug ignites first, then as the flame propagates, the exhaust side plug is fired (before top-dead-centre), and the flame expands rapidly into the whole area to achieve complete combustion. This arrangement provides much faster combustion and higher cylinder pressures to provide high engine output.
