Daimler and Diesel retained the long-established steam engine hardware when converting to internal combustion but, because the metals were unable to withstand the new high temperatures, they introduced cooling systems.
Without cooling, temperatures and pressures nearly double. This entails new materials for the piston and cylinder –industrial ceramics – and the replacement of the traditional oil separation between piston and cylinder (the oil would boil away). The only realistic alternative is using gas bearings, an established technology, but so far not for engines. Fortunately all engines already have a gas flow known as engine blow-by, which in uncooled engines can be adapted as a gas bearing.
Today, the con-rod linking piston to crankshaft imposes severe side and twisting loads on the piston around the mid-point of its travel. In most embodiments, a gas bearing cannot handle the side loads, so new layouts are called for.
Figure 1 schematically shows one of the many possible uncooled engine layouts, with two combustion chambers of toroidal or doughnut shape operating in the two-stroke mode, shuttling a single unconventionally shaped piston between them, all inside a thermally and acoustically insulating casing. By making the piston hollow and providing a series of ports, traditional valves, springs, rockers and camshafts can be eliminated. Figure 2 shows what such an assembly might look like.
The configuration of Figure 1 has no plumbing for either cooling or piston-cylinder oil systems, so engines can in effect become snap-in boxes or cartridges, illustrated diagrammatically in Figure 3.
Optionally a generator can be placed inside the casing, with its waste heat energy partly recovered by the engine. The box becomes a generator set, with electrical rather than rotational power out, as shown by way of example in Figure 4.
To find out more about the Litus pre-production prototypes program and its background, please request the Engine Project Summary.