Application of Lean Flames in Internal Combustion Engines

One of the two main ‘drivers’ for the adoption of lean flames in internal combustion (IC) engines has been the potential to reduce the emission of some pollutants. Since Bernard Lewis wrote these words in 1970, the same year as the enactment of the landmark extension to the Clean Air Act (CAA) – the so-called ‘Muskie’ Act – the design and technology behind IC engines for automobile application have seen many changes that indeed greatly reduced pollution. These include the widespread introduction of gasoline injection systems, three-way catalysts, the high-speed direct injection (DI) diesel engine, turbocharging, and high-pressure commonrail technology, to name a few at random. The related science has also progressed in ways amply described elsewhere in this volume: As to whether this has constituted ‘no special feat’, the reader will decide. Be that as it may, research into combustion in IC engines is now arguably going through one of its most exciting phases in the quest to ‘burn materials completely’, that is, with as little pollution as possible and with as much thermodynamic efficiency as possible. This part of the chapter describes the way in which engineering design can exploit combustion, predominantly lean combustion, in IC engines not only to reduce pollution, but also – by promoting fuel-conversion efficiency, the other main ‘driver’ – to husband the finite resource of petroleum-derived fuels [2].