Riding the "Red Devil", world's most powerful narrow gauge steamlocomotive. The cape gauge (1067 mm or 42 inch) 4-8-4 "Northern" was rebuilt in 1981 by the english mechanical engineer David Wardale from a locomotive 25NC from 1953, built by Henschel/Germany. One of the many improvements was the introduction of the Gas Producer Combustion System (GPCS) for a clean high efficiency combustion. You can see five orange holes in the side of the firebox, which are secondary air admission ducts. A description of the system by the originator, Livio Dante Porta, argentinian engineer: It essentially consists in transforming the firebed into a gas producer by making it very thick. Only 30% (20% in the case of biomass) of the combustion air passes as primary air through the grate, thus leading to an almost negligible particle entrainment. The secondary air makes up the lion's share of the air needed for combustion and creates an intense turbulence in the flame space so that the gas phase combustion can proceed to the degree of completeness required to meet pollution laws. While it appears to have that extreme simplicity characterizing great inventions, its thermodynamics are extremely complicated – after all just an intellectual problem.