Sir Dugald Clerk (sometimes written as Dugald Clark) KBE, LLD FRS (1854, Glasgow – 1932, Ewhurst, Surrey) was a Scottish engineer who designed the world's first successful two-stroke engine in 1878 and patented it in England in 1881. He was a graduate of Anderson's University in Glasgow (now the University of Strathclyde), and Yorkshire College, Leeds (now the University of Leeds). He formed the intellectual property firm with George Croydon Marks, called Marks & Clerk. He was knighted on 24 August 1917. Life Dugald Clerk was born in Glasgow on 31 March 1854, the son of Donald Clerk a machinist and his wife, Martha Symington. He was privately tutored then apprenticed to the firm of Messrs H O Robinson & Co in Glasgow. From 1871 to 1876 he went to Anderson College in Glasgow studying engineering then to the Yorkshire College of Science in Leeds. In the First World War he was Director of Engineering Research for the Admiralty. He married Margaret Hanney in 1883. He died in Ewhurst, Surrey on 12 November 1932. Clerk's work on the internal combustion engine Clerk began work on his own engine designs in October 1878 after modifying a Brayton engine with a spark plug. Brayton engines (called "Ready Motors" were made from 1872 to 1876) and were one of the first engines to successfully use compression and combust fuel in the cylinder. Prior to this time the commercial engines available had been the Lenoir engine from 1860, a non-compression engine which worked on a double-acting two-stroke cycle, but spent half of each stroke drawing gas into the cylinder. The Hugon engine was a slightly improved version, but both were quite inefficient (95 and 85 cubic feet of gas per HP hour respectively). The next commercial engine available (from 1867) was the Otto & Langen a non compression, free piston engine, which used atmospheric pressure for the power stroke, and consumed about half the gas of the Lenoir and Hugon engines. It was in May 1876 that Otto developed his engine using the single-acting four-stroke cycle with compression in the cylinder. Clerk decided to develop an engine using compression, but with the two-stroke cycle, as he could see benefit to weight and smoothness of operation through having twice as many power strokes. "Clerk's initial experiment with a Brayton ready motor in 1878 led him to make improvements that would eventually result in the development