Otto or Not, Here it Comes

This article highlights the new ignition schemes for Otto cycle engines that seem to be bound for extinction. Ever since Nicolaus Otto demonstrated the first working four-stroke engine in 1876, engineers have been struggling to come up with ways to sidestep a fundamental limitation of an otherwise stellar design. The reciprocating engine is capable of generating high pressure with reliable sealing, but the volume swept out by the piston has had to remain fixed. Small engines use less internal reciprocating mass than large ones, so the energy to overcome friction decreases as size drops. Small engines are lighter than big ones, too. By recirculating exhaust gases back into the combustion chamber, however, Mitsubishi uses the exhaust to reduce NOx. Because the air-to-fuel ratio is so high, the exhaust gases, which normally hinder combustion, can be as much as 70 percent of the cylinder volume. At the same time, Mitsubishi uses a lean NOx catalytic converter.