Dual ignition

[1][2] In aircraft and gasoline-powered fire fighting equipment, redundancy is the prime consideration, but in other vehicles the main targets are efficient combustion and meeting emission law requirements.

[3] Dual ignition promotes engine efficiency by initiating twin flame fronts, giving faster and more complete burning and thereby increasing power.

[6] The 2012 Ducati Multistrada was upgraded with "twin-plug cylinder heads for smoother, more efficient combustion", the change contributing to a 5% increase in torque and a 10% improvement in fuel consumption.

[7] Early BMW R1100S bikes had a single spark plug per cylinder, but after 2003 they were upgraded to dual ignition to meet emission law requirements.

The MidWest AE series Wankel aero-engine has twin plugs per chamber, but these are placed side-by-side, not sequentially, so their main purpose is to give redundancy rather than improved combustion.

[10] Richard W. Dilworth of the Electo-Motive Corporation devised a system, using four spark plugs and one carburettor per cylinder, in order to burn "distillate" fuel in train car engines.