The fortunes of the Stirling engine subsequent to the original revival are largely in terms of the legendary rhombic drive engine, and of substantial programs of collaborative development between Philips, United Stirling Sweden, General Motors, MAN/MWM, Ford, and MTI (Mechanical Technology Inc.). There have also been independent research and development projects. The latter have generally been to a smaller scale, but the contributions have been out of proportion to respective budgets and manpower levels.
The digital computer emerged in the 1960s as the key to understanding the cycle gas processes. Cycle theory and simulation evolved more or less in parallel with engine development, but the open literature is confined to reports of the findings of the independent researchers who, on the whole, were not in the best position to compare the predictions of theory with experimental measurement. Possibly for this reason there was little evidence at any given moment of a beneficial influence on gas circuit design.
For technology to flourish the insight yielded up by individual advances has to be distilled to its essence and made accessible for others to build on. If each researcher has to replicate the work of every other, progress is minimal. The basic requirement for a technology to advance, therefore, is communicable insight. The failure of analytical and numerical studies to yield this contribution to thermodynamic design would be its most striking feature but for a still more remarkable aspect. By 1960, the literature on the core component, the regenerator, had already advanced in scope, depth and sophistication beyond the total output on the Stirling cycle to the time of this present writing. Yet until very recently (mid-1990s) no significant attempt has been made to bridge the gap between the two sciences.