A flame keeps burning by thermal feedback. The heat it gives out vaporizes incoming fuel, and raises it to combustion temperature. Sadly, the process is not particularly efficient. Vaporized fuel is never completely burnt in its passage through the flame. A little unburnt fuel, and a variety of partly burnt combustion products, always escape into the cooling flue gases. The result is soot, smoke, and frequently the need for a costly catalytic converter downstream, to oxidize the pollutants before they get away.

So Daedalus is planning an alternative form of energetic feedback. His idea is to beam intense microwaves into the burner or furnace. The hot, ionized combustion gases should be conducting enough to absorb the energy, which will make them hotter still. The beam should be concentrated just above or beyond the flames, to heat and oxidize the partially burnt gases before they can cool down. Visible smoke, in the form of carbonaceous particles, will be particularly well suppressed. Carbon is such a good conductor that the microwaves will keep it glowing until it has burnt completely. But microwaves seem to encourage chemical reactions not merely by heating, but also by direct molecular agitation. Nasties such as carbon monoxide and nitric oxide absorb them strongly, and should be rapidly reacted away.

The obvious application is to big power-stations. They could well afford to boost their combustion efficiency by feeding a bit of power back into their furnaces. Old, polluting coal-fired stations, and ecologically virtuous ones heroically trying to burn rubbish, would benefit the most. Indeed, even the Greens might applaud a guaranteed pollution-free, microwave-augmented incinerator.

The internal-combustion engine is a more daring challenge. DREADCO engineers are now plumbing microwave waveguides into the cylinders of a test diesel engine. A dynamo on the engine will power a klystron. At each moment of ignition, it will beam an intense microwave pulse into the firing cylinder, which will act as a frequency-swept resonant cavity. Smoke and partial-combustion products should vanish. They will be burned, not in a wasteful exhaust catalyser, but in the engine itself, thus raising its efficiency. Even the microwave energy beamed into the cylinders will boost the engine's power, and be partly returned to the dynamo generating it.