An Engine Without a Spark Plug
The working principle Diesel conceived was wholly different from the by-then-widespread gasoline engine — relying not on a spark plug to ignite but first compressing air to extremely high pressure to raise its temperature above the fuel’s auto-ignition point, then injecting the fuel into this mass of hot, high-pressure air to ignite of itself; this "compression" rather than "spark" working principle made the diesel engine’s thermal efficiency markedly higher than the contemporary gasoline engine, the core technical advantage by which the diesel later long dominated heavy transport and industrial power.
The Mystery of the Disappearance on the English Channel
On the night of 29 September 1913 Diesel took a mail steamer from Antwerp, Belgium, to London, and the next morning the crew found his cabin empty and he had vanished for good; a body was recovered at sea days later, but, soaked for days, could not be fully identified, and the officials at last gave no conclusive verdict; since the disappearance coincided with his negotiations with the British navy over using the diesel engine for submarine power, the event has since been shrouded in unconfirmed conspiracy theories, one of the famous unsolved mysteries in the history of technology.