The internal-combustion engine is a very imperfect device. It breathes air, burns fuel in it imperfectly, and returns highly polluting gases to the atmosphere. Daedalus sees this gas-phase reaction as the central problem. He is trying a new twist: he wants the engine to burn an aqueous foam.

A foam of inflammable gas mixture has many advantages. First, the engine could be fed with several streams of foam, each with its own concentration of fuel. The stratified charge, that dream of motor engineers, would be a reality at last. The centre of each cylinder could receive a rich mixture, while the walls received a much more dilute one, or even pure air. Flame would then never touch the walls. Pollutants, mainly created by premature quenching of the reaction on the cylinder surfaces, would never form.

When a combustible foam burns, its bubbles are shocked into bursting before the flame reaches them. What actually burns is a gas mixture loaded with aqueous droplets. These should go to steam, which would usefully increase the pressure of the expanding gas while moderating its temperature. Water injection can be used to increase the thrust of jet engines at take-off, and has often been advocated for internal-combustion engines.

The exhaust stream, of course, would be a pure hot gas. But Daedalus would like to enclose that in foam as well. Particulates and acidic combustion products would be trapped in the foam walls. They would be discharged not into the air, but as a ribbon of foam on the road, ultimately to be washed into the drainage system. It would provide a temporary white road marking, indicating to following traffic the presence, track and probable distance of the foam-laying vehicle ahead — a useful adjunct to road safety.

To complete the scheme, Daedalus would like to lubricate the engine with the same aqueous detergent system from which the foam is generated. This is a tough technical challenge. With good fortune, a foam engine would run so much cooler than a conventional one that the sliding surfaces could be made not of metals (for which hydrocarbon oils seem the only reliable lubricants) but from specialized plastics or ceramics. Ignition is an even tougher challenge; no sparking plug will work in the wet. A chemical system, based perhaps on spontaneous igniters such as silicon or phosphorus hydrides, may be needed.

David Jones