Does the above name ring a bell with you? Of course it does! He’s the gent who invented the Clerk Cycle of engine operation. And who was the major maker of that type of engine in America? Joseph Reid. So now it all comes together for you. But for this article, we are going to journey across the pond to Scotland, and see what we can learn about this most interesting individual. It will be a good story.
Clerk was definitely a unique and gifted person. He was intelligent, diligent and thoughtful. Although his career developed into many different areas, he never forgot his love for the gas engine, and was always eager to learn more.
Clerk was one of the very early pioneers in the birth of the gas engine, and lived to see it become a successful everyday machine. Few others were given that pleasure.
Donald Clerk was born in 1819 in Argyle, Scotland, a rural area very near to the city of Glasgow. Clerk had a mechanical inclination and soon opened a blacksmith shop. Tools were crude then, but he persevered and became a master blacksmith. By 1871, he and his wife were living in Glasgow and his works employed five men and 10 boys! He and his wife had a large family of 10 children, Dugald being the oldest. Donald Clerk passed away in 1880 at the age of 61, and it is sad that he did not live to see Dugald’s many honors.
What it must have been like to live and work back then? Certainly very different from today. This was the era of the Industrial Revolution, which lasted essentially from 1740 to 1880. The world was changing, and one had to change to keep up with it, and the pace must have been hectic. Manufacturing was transitioning from cottage industries to huge factories. There were inventions galore. The cotton gin, the power loom, the sewing machine, the spinning jenny, the steam engine and the locomotive, just to name a few. Glasgow must have been busy and dirty. Factories sprung up, powered by crude steam engines whose boilers spewed forth black sooty smoke. And in the midst of this, Dugald saw opportunity.
Dugald Clerk was born into this scene on March 31, 1854. He was born in dirty, bustling, prosperous Glasgow, and he certainly made the best of it. At age 14, he entered apprenticeship at his father’s works. That was 1868, and he began learning the trade. He also apprenticed at the works of H.O. Robinson and Co. in Glasgow. It is interesting to note that Henry Robinson started making sugar processing machinery in 1843.
Robinson’s 1859 patent is seen above. Pretty crude, but it worked. Dugald’s apprenticeship ended in 1871.
From 1871 through 1876, Dugald studied chemistry and physics at both Anderson College in Glasgow, and Yorkshire College of Science in Leeds. During that time, he happened to see a Lenoir engine operate at a joiners shop in Glasgow, and a lifelong love affair with the gas engine was born. Etienne Lenoir, a Belgian engineer, patented the first successful gas engine on Jan. 24, 1860. This engine was in actual production and successful for its time. Its failure was its excessively high fuel consumption due to being non-compressing. In essence, it was copied from a double-acting steam engine, even to its slide valve. Intriguingly, Lenoir used high tension ignition and invented the spark plug, although many years lapsed before spark plugs were in common use.
Dugald built his first gas engine in 1876 in his father’s shop. This was really a modified Brayton engine, with Dugald trying to add compression to it for efficiency. Dugald was meticulous in his designs, using complicated mathematical calculations, and he had a deep understanding of thermodynamics, as well. It is notable that 1876 was the year of Otto’s patent of the 4-stroke cycle engine. Dugald made a true compression engine in 1878 that developed 3hp at 200rpm. It was exhibited at the Royal Agricultural Society’s show in July 1879. Unfortunately, there are no illustrations of these two engines.
George Brayton (1830-1892) was a gifted inventor and envisioned an engine that had its combustion inside the cylinder, unlike the steam engine with its external combustion. Born in Boston, Massachusetts, he started experimenting with internal combustion in the 1850s. In 1872, he patented his “Ready Motor,” as it could be started immediately and did not need time for a boiler to heat and produce steam. The Brayton was a constant-pressure ignition engine. It had two cylinders; one an air pump, and the other a combustion cylinder. The fuel mixture passed through a metal mesh between the cylinders and was ignited by a constant burning pilot flame.
The flame would not pass back through the mesh and cause havoc in the pump cylinder. Why not? Recall the mesh in the spout of a safety gasoline can! The main combustion then burned for the entire outward stroke of the piston at a constant pressure, and not as an explosion. These engines were quite popular and noted for their smooth operation and easy starting. In 1878, Dugald Clerk modified a 5hp Brayton, giving it spark ignition.
In 1877, Dugald joined the firm of Thomson, Sterne and Co. of Glasgow. This firm produced a variety of products including emery wheels, emery grinding machinery, feed water heaters and gas engines. He was happy, as his job was to invent, design, construct and test gas engines. And he did just that. He returned to the Brayton engine he had modified with a spark plug. He reasoned that by giving it compression he could increase its efficiency. It worked and he obtained his first patent that year, British Patent No. 252. This engine was quite successful and is shown below. In 1881, Dugald produced a true 2-stroke cycle engine that appeared quite modern. From this, some call him the father of the 2-cycle engine.
The 1881 engine is shown above. What a change from the earlier engine of 1877! Note that both these engines have the firm name on them. This engine was exhibited at the 1881 Paris Exhibition, where it won many praises. Truly, the “Clerk Cycle” was a successful reality. His engines were produced in considerable numbers until 1890 when the Otto patent expired.
The Clerk engines suffered a decline for a while, then enjoyed a resurgence as the need for a lighter engine per given horsepower emerged. Clerk continued with Thomson, Sterne and Co. until 1885. Clerk was granted over 20 patents during his long career, most concerning the gas engine.
The illustrations from his 1877 patent are shown in above. His one American patent of 1880 is illustrated on the opening page. All three of these engines seem crude, but definitely show progress. It is quite interesting to note that Dugald chose not to enter into the production of his engine, but leave someone else to it. He could gain the profits, but not be concerned with the business end and actual production, and could devote his time to improving his design. During that period, he resided at 42 Dalhousie Street in Glasgow. Note the modest home in the image below.
The Clerk Cycle
So what is the Clerk Cycle? Dugald set out to make an efficient engine, and to do so, he wanted it to have a power impulse on every revolution of the crankshaft, hence the 2-stroke cycle. In contrast, the Otto engine had a power impulse on every second revolution of the crankshaft, making it a 4-stroke cycle. So he studied other earlier engines, and was especially impressed with the Brayton. It had two cylinders, but no compression. Hmm! How could he make it better?
Clerk made an engine with two cylinders and two pistons, with the pistons placed 90 degrees out of phase with each other. One piston, the charging one, drew in the gas and air mixture through an automatic intake valve. On the charging piston’s return stroke, it pushed the mixture through an automatic crossover valve. The fuel now entered the power cylinder from the head end while the exhaust gases escaped through openings or ports in the cylinder wall. In essence, it was a “uniflow” engine, with the fuel entering one end of the cylinder, and the exhaust passing out the other end. This minimized the possibility of diluting the incoming charge with the spent exhaust gases. The power piston then proceeded forward to the head, causing compression, and near top-dead-center ignition took place. And so the cycle was repeated, with power on every stroke of the piston. The Clerk Cycle! It was very successful.
The above is a longitudinal cross section of the Clerk engine cylinders. B is the charging cylinder and D is the charging piston. Note that the charging cylinder is not cooled while the power one is. The charge is delivered into the power cylinder A through valve F. In this case it is a slide valve using open flame ignition. G is the combustion space. The exhaust escapes through ports, E, and the power piston is C. When asked, Clerk denied any attempt at supercharging and stated the charging piston is for fuel transfer only. The image below is a detail of the ignition valve.
Upon leaving Thomson, Sterne and Co., Clerk joined Richard Tangye’s firm in 1886 and moved to Birmingham, England. Tangye (1833-1906) was from Cornwall and became a mechanical engineer, manufacturing engines and all sorts of heavy equipment. One speciality was hydraulic equipment, focusing on lifting jacks. His jacks launched the iron-clad sailing steamship The SS Great Eastern in 1858. It was the largest vessel built at that time and measured 705 feet long and weighed 17,274 tons. Tangye’s motto became, “We launched the Great Eastern, and she launched us.” Clerk’s job with Tangye was to improve the 1877 2-cycle engine designed by James Robson. This was a 2-cycle engine much like the engines used in the American oil boom. Clerk succeeded in making it successful.
In 1888, Clerk entered practice as a consulting engineer in Birmingham. Soon, he partnered with Sir G. Croyden Marks, another noted mechanical engineer. The firm, Marks & Clerk, prospered and consulted in all types of engineering problems. One speciality was patent litigation. In 1911 it was recognized by one source as “the greatest firm of its kind in the world” It still exists today, with branches in all the major cities of the globe.
From 1892 to 1899, Dugald was the engineering director of Messrs Kynoch of Birmingham. This firm was a major ammunition manufacturer and played an important role in World War I. Clerk designed the equipment to manufacture various forms of munitions. During this time, he was also a consulting engineer to the Patent Shaft and Axletree Co. of Wednesbury.
During his long and distinguished career, Clerk wrote four classic engine reference books. In 1882 he wrote The Theory of the Gas Engine; in 1894 The Gas Engine; in 1897 The Gas and Oil Engine; and in 1909 The Gas, Petrol and Oil Engine. He also authored many academic papers and was a lecturer in great demand. During his later life, he was awarded five honorary doctorates. In 1908, he was elected into the Royal Society as a Fellow.
In 1902, Clerk became a director of the National Gas Engine Co. in Ashton-under-Lyne, England, where he took an active part in the design of the firm’s engines. He enjoyed the freedom there to further study thermodynamics and explore the uses of gas in heating and lighting. The image aove depicts a beautiful National of 1930 vintage. National was a huge firm that made a wide variety of engines, and they produced multi-cylinder vertical engines into the 1960s. Clerk became the chairman of the firm in 1929, and he retained this position until his death in 1932.
It is interesting to note that Dugald and his wife, Margaret, visited New York City in July of 1906. He was a consulting engineer and the purpose of the trip was business. They departed Liverpool, England, on July 3, 1903, and sailed on the RMS Caronia. Their American headquarters was the Savoy Hotel. One wonders if he made a trip to Oil City to meet Joseph Reid and study that engine? Perhaps we will never know!
From 1916 through 1918, during WWI, Clerk served his country in many ways. He was the Director of Engineering Research at the Admiralty, a member of the Advisory Committee for Aeronautics at the Air Ministry, Chairman of the Internal Combustion Engine Sub-Committee, and a member of the Munitions Inventions Committee. He was also Chairman of the Water Power Committee of the Board of Trade. For all this fantastic work, he was created a Knight of the British Empire in 1917. Now he was Sir Dugald Clerk!
Sir Dugald never really retired, but due to health issues moved to rural Ewhurst, Surrey, not far from London, where he could design, consult, invent or just relax. He certainly led a very full and fruitful life, and deserved all the honors bestowed upon him. Sir Dugald passed away at Ewhurst on Nov. 13, 1932, and is buried in the St. Peter and St. Paul Anglican Church’s cemetery. The Church is seen above. It is a very pastoral setting. At the time of his death, the value of his estate was 54,412 pounds (approximately $4.5 million in today’s dollars). His modest headstone is shown in photo below.
Sir Dugald was born before the invention of the gas engine, and grew up during the earliest days of gas engine development. He played an important part in its development from the very beginning. Apprenticed in the mechanical skills and educated in chemistry and physics, he loved to invent, calculate, design, build and improve. That was his life! The photo below ishis portrait on the year of his passing.
I wish to mention that I have searched many sources for the material used in this article. I have found some notable differences in information and have tried to choose the information that is most commonly acknowledged, as well as makes sense to me. This material is as accurate as I could make it. In the future, I plan to write an article comparing Clerk and Reid. I am sure there is more than a casual connection.
Paul Harvey is the founder of the Coolspring Power Museum. Contact the museum at P.O. Box 19, Coolspring, PA 15730, (814) 849-6883.