Rudolf Diesel

What was actually filed

Diesel recorded that on 30 March 1895 he applied for patent no. 86633, covering the starting procedure he had already worked out during his Augsburg engine trials. Those trials had resumed on 26 March, after an interruption of roughly four and a half months.

The invention was a device for starting a four-stroke internal-combustion engine by temporarily operating it as a two-stroke compressed-air machine. It was not the foundational patent for the diesel engine.

The famous patent was two years older

Diesel's foundational German patent, no. 67207, was filed in 1892 and granted on 23 February 1893. The German Patent and Trade Mark Office says the self-ignition engine it described was impractical, and that patent no. 82168 of 1893 corrected the error.

His early patent history therefore runs across several distinct filings: 67207 for the initial principle, 82168 for the correction, and 86633 for the starting device.

Filing is not granting, and not an engine

The date records the application. The Deutsches Museum archive dates the resulting German patent document no. 86633 to 27 April 1896.

Diesel still had only experimental machinery. No working engine was unveiled that day, and the production-ready prototype and its certification tests were nearly two years away.

That surviving 1897 prototype weighs about 5,950 kilograms and is rated by the museum at 20 PS.