This is a micro cache near the plaque!

The world's first successful heavy oil engines were invented and built by Herbert Akroyd Stuart in Fenny Stratford. 

 

There is a plaque commemorating this at the westerly end of Denmark Street in Fenny Stratford opposite The Foundry public house - though the location of Akroyd Stuart's workshop is usually given as "Bletchley", which is a larger town adjoining Fenny Stratford. These engines were precursors to what is now known as the Diesel engine: Rudolf Diesel based his designs (1892) on Akroyd Stuart's proven inventions (1890) of direct (airless) fuel injection and compression ignition. An experimental model was tried out at the offices of the Fenny Stratford Times Newspaper, and the first production models were installed at the nearby Great Brickhill Waterworks where they were in operation from 1892 to 1923. (It has been argued that engines of this type might have become known as "Akroyds", had Diesel not been a rather paranoid person not prone to giving other inventors credit.)