Born: 1854 CE
Died: 1932 CE
Known for: Two Stroke Engine
Sir Dugald Clerk was a Scottish engineer who designed the world’s first successful two-stroke engine in 1878.
He was a graduate of Anderson’s University in Glasgow (now the University of Strathclyde), and Yorkshire College, Leeds.
Formed the intellectual property firm with George Croydon Marks, called Marks & Clerk. He was knighted on 24 August 1917.
Clerk’s name is also rendered as Clark in the archive of his works in the University of Glasgow.
Clerk’s work on the internal combustion engine:
Clerk began work on his own engine designs in October 1876. Clerk decided to develop an engine using compression, but with the 2-stroke cycle, as he could see benefit to weight and smoothness of operation through having twice as many power strokes.
Clerk initially experimented with engines that “were identical to the Lenoir in idea, but with separate compression and a novel system of ignition”, one of these was exhibited in July 1879.
However it was not until the end of 1880 that he succeeded in producing the Clerk engine operating on the 2-stroke cycle, which became the commercial product.
Clerk states “The Clerk engine at present in the market was the first to succeed in introducing compression of this type, combined with ignition at every revolution ; many attempts had previously been made by other inventors, including Mr. Otto and the Messrs. Crossley, but all had failed in producing a marketable engine. It is only recently that the Messrs. Crossley have made the Otto engine in its twin form and so succeeded in getting impulse at every turn.”
In “Gas and Oil Engines”, Clerk refers to the significant earlier gas engine patents of Barnett in 1838 and Wright in 1833.
In 1877 the Otto cycle was patented, immediately recognized to have a significant practical value. Clerk quickly followed with his concept of a two stroke engine of 1880, which would not infringe the Otto’s patent (being a four stroke engine).
Clerk describes a Cam bell engine as using his cycle, as follows: “It has two cylinders, respectively pump and motor, driven from cranks placed at almost right angles to each other, the pump crank leading.
The pump takes in a charge of gas and air, and the motor piston overruns a port in the side of the cylinder at out-end of its stroke to discharge the exhaust gases. When the pressure in the motor cylinder has fallen to atmosphere, the pump forces its charge into the back cover of the motor cylinder through a check valve, displacing before it the products of combustion through an exhaust port ; the motor piston then returns, compressing the contents of the cylinder into the compression space. The charge is then fired and the piston performs its working stroke. This is the Clerk cycle.”
The Clerk engine uses automatic ‘poppet’ type valves for inlet air and gas (one with spring assistance, one without), and a port in the cylinder uncovered by the piston for the exhaust valve. References to a Clerk engine with slide valve may refer to the earlier experiments with a Lenoir type engine.
The ignition is by carrying an external flame, using a modification of a method he developed in 1878.
Pumping cylinder vs supercharger:
Clerk’s engine was made of two cylinders one working cylinder and an additional cylinder to charge the cylinder, expelling the exhaust through a port uncovered by the piston. Some sources consider this additional cylinder the world’s first supercharger.
Clerk himself states that “It is not a compressing pump, and is not intended to compress before introduction into the motor, but merely to exercise force enough to pass the gases through the lift valve into the motor cylinder, and there displace the burnt gases, discharging them into the exhaust pipe.” Hence sources recognize it instead as a “pumping cylinder”, pointing out that it did not actually compress the fuel-air mixture, it simply moved the fresh mixture to the working cylinder to force out the gasses burnt previously.