In the last 250 years engines of various kinds have played an important role in our civilisation, and a bit of history helps put into perspective the achievements of the various pioneers. My own interest was reawakened by the Mercedes-Benz DiesOtto engine, which has focused attention on the various engine cycles.
Engines that employ heat to liberate the chemical energy locked in a fuel can be classified as either employing internal or external combustion, according to whether the fire is inside or outside the engine. For example, a steam engine operates with an external heat source, but a petrol or diesel engine utilises internal combustion. Internal combustion engines employ either spark ignition or compression ignition. In this article I’ll be looking at the history of spark ignition engines.
Early engines
At the beginning of the 17th century, the possibility of building an engine using heat to do work was in the minds of a number of people and, by the end of the century, the first crude examples began to appear. Many inventors thought of using gunpowder as a fuel, because it’s interesting to note that a gun is just an internal combustion engine that throws its piston away every time it fires.
In 1673 the Dutchman Huygens became the first inventor to employ a piston working inside a cylinder, and built an internal combustion engine that used gunpowder as fuel. He had to involve the Frenchman Denis Papin to help with the design of the valve gear, so this engine became known as the Huygens-Papin engine. The powder was ignited underneath a piston at the bottom of a cylinder, thus driving the piston upwards, and driving the air out past leather tubes filled with nozzles to act as valves. The atmospheric pressure on top of the piston then drove the piston downwards. The engine worked after a fashion, but was obviously very inefficient.
The first engine to actually do any useful work was Englishman Thomas Savery’s steam engine, patented in 1698. It was able to raise water by suction to a height of eight metres. Another Englishman, Newcomen, built a vastly improved steam engine in 1712, and this was sold in relatively large numbers. At this point I’ll leave external combustion engines and concentrate on internal combustion power units, but it must be noted that the Newcomen engine’s success stopped internal combustion research for close on 100 years.
An engine designed by yet another Englishman, John Barber, in 1791 is worth a mention, because it was nothing less than a crude gas turbine, although it wasn’t very practical. He used gas from wood, coal or other substances that was generated in a huge vessel whose only exit led the gas to a mixer, where it was mixed with air, and then to his “exploder”. There it was ignited and the resulting mixture of flame and gas drove the vanes of a paddle wheel.
Robert Street, another Englishman, who took out a patent in 1794, has the honour of building the first vaguely practical internal combustion engine. Spirits of turpentine or petroleum were sprinkled onto the bottom of the cylinder, and evaporated by an external fire. The up-stroke of the piston admitted a certain quantity of air, which mixed with the inflammable vapour. Next, a flame was sucked in from a burning wick outside the cylinder, through a valve uncovered by the piston, and the resulting combustion forced the piston further up the bore. This movement could be used to drive a water pump.
Samuel Brown, also an Englishman, took out two patents, in 1823 and 1826, for an engine running on gas, and his engines were most likely the first to do actual work. In 1833 another Englishman, Wright, designed the first governor to control the speed, by regulating the amount of gas entering the engine. His engine was a vertical double-acting unit that had one cylinder and piston, with combustion taking place alternately at either end of the cylinder. The piston and piston-rod were hollow, and the cylinder had a water jacket to counteract the intense heat of the double explosion. Ignition was obtained by an external flame and a touch hole.
The above account is just a short summary of the various ideas that were patented at the time, but the honour of having invented and introduced the first practical working gas engine is generally given to Frenchman Etienne Lenoir. His engine contained no new ideas, but was able to work silently and rapidly, and was most likely the first to employ electric ignition. His patents date from 1860, and the engines were built for him by Marinoni, a French engineer. Two sizes, developing six and 20 horsepower respectively, were built, and these were undoubtedly the first practical working internal combustion engines, because in the next five years about 350 were made in France, and 100 in England.
In subsequent years, engines running on gas, produced in various ways, became almost as common as steam engines. They had the major advantage of not needing a boiler, and therefore were less likely to explode, something that happened frequently on badly maintained steam engines.
The Otto or four-stroke cycle
Enter the German, Nikolaus August Otto, a grocer, partnered by compatriot Eugen Langen, an engineer. Their first engine, dating from 1867, was based on the ideas of the Italians Barsanti and Matteucci, who had proposed the free piston idea ten years earlier. By sheer perseverance and determination, Otto overcame the many practical difficulties that the Italians could not overcome, and produced a free piston engine. This employed a single piston, moving in a long vertical bore, that was allowed to move freely upwards when combustion occurred, but engaged a rack that transferred its downwards movement to a flywheel. This did not produce much power, because the piston mass and the difference between the atmospheric pressure above and the partial vacuum below the piston were the only driving forces. This first Otto and Langen engine soon outsold the Lenoir engines, because it was more economical to operate. However, the excessive noise made by the rack and the unsilenced combustion meant that many purchasers developed love-hate relationships with their engines.
However, in 1876 Otto exhibited the engine that made his name a household word throughout the world. Previously, virtually all gas engines were two-strokes, ie producing one power stroke per revolution, and most of them did not compress the mixture inside the cylinder to any worthwhile extent before combustion. Otto thought that compressing the mixture before the spark occurred (Otto used an external flame) would stratify (ie separate into layers) the charge. He thus introduced four separate strokes for the sequence of events in the engine, to create the famous “Otto silent” engine that made him famous, and which, to this day, dominates the motoring world.
The company was reorganised to increase production, and Gottlieb Daimler was appointed technical director; he chose Wilhelm Maybach as chief engineer. These two names crop up repeatedly in automotive history. The new engine was not only silent, but a lot more efficient than any of the earlier engines. Otto thought the increased efficiency was due to the slow combustion speed of his engine, but in reality it was due to the newly added compression stroke.
Otto looked forward to patenting this engine, but it was not to be. Beau de Rochas, a French railway engineer, a friend of Lenoir, patented a theoretical concept for an engine that employs the “highest possible pressure” and the “greatest possible expansion”. The patent was granted in 1862 and lapsed after two years, most likely because the inventor did not build such an engine. This would seem to provide an open and shut case in favour of Otto, but in 1886 the German authorities refused to grant a patent to Otto, and he died a disappointed man five years later.
These early engines could seldom exceed a few hundred r/min, but the German, Gottlieb Daimler (1834 – 1900), soon changed that. He is one of the pioneers whose life has been well documented, no doubt because the company he founded still exists. Daimler was born in Schorndorf near Stuttgart, served an apprenticeship as a gunsmith, then studied at the Stuttgart Polytechnic, and ended up working in a locomotive construction plant. He soon started to experiment with gas engines, and when he heard of Lenoir’s engine, he went to Paris to see him, but was not allowed into the workshop because he was (correctly) regarded as a German spy. His interest in engines was now really aroused, and he asked the manager of the locomotive company, Friedrich Messmer, to let him go so that he could spend more time on engine experimentation.
Amazingly, Messmer not only advised him to go England, to see the fruits of the industrial revolution, but also paid for the trip. He looked at the level of precision engineering in Leeds and Manchester, and learned about the importance of standardisation at Whitworth in Coventry, then returned to Germany in 1862, and worked as a manager of an engineering works until 1872. He then joined Otto, whose company was by now called Gasmotorenfabrik Deutz, where he served as managing director from 1872 to 1882, when he retired to start his own company, taking Wilhelm Maybach with him.
Up to this time, most engines ran on whatever combustible gas could be found, either from natural sources or produced artificially, but Daimler introduced a fuel refined from the lighter hydrocarbons, now known as petrol, which had initially been used as a cleaning fluid. He also realised that smaller engines running at higher speeds could produce as much power as the slower and larger units, but would be cheaper to produce and easier to transport. In fact, before his time, most engines were too heavy and bulky to fit into a horseless carriage.
Daimler introduced an elementary carburettor, hot tube ignition, and managed to increase the maximum engine speed to 720 r/min. This first engine was soon developed into a power-unit dubbed the “grandfather clock”, because the vertical cylinder above a large flywheel housing resembled such timepiece. This was the father of all modern petrol engines, and Daimler fitted a 212 cm3 version into his first four-wheeled car, patented in August 1885, and driven for the first time in November 1885. Soon afterwards, he used his engines to create the first truck, the first motorbike, and the first motor boat. Initially, Daimler was concerned that he would have to pay royalties to Otto, but Maybach guessed that Otto would not get a patent, and encouraged Daimler to produce vehicles for sale. The following year, Maybach’s prediction proved to be correct, as I’ve already mentioned.
At the same time, and close by, another German, Karl Benz, was experimenting with two- and four-stroke engines running on petrol, and fitted a four-stroke engine to a three-wheeler, which ran a few months before the Daimler carriage, making Benz the first man to create a successful petrol-engined car. It’s interesting to note that the companies started by these two pioneers merged in 1926. Daimler died in 1900, but Benz lived on until 1929. Can you imagine what it must have felt like to be one of the initiators of such an exciting industry, and to have lived long enough to see the progress being made?
The two-stroke cycle
Most of the above engines operated in such a way that they produced a power stroke for every revolution, so that technically they were two-strokes, but very few used any form of compression. However, the modern two-stroke petrol engine is closely related to the two-stroke gas engines experimented with by Englishman Dugald Clerk from 1876 onwards. He took a cue from Otto, and tried to introduce a compression phase into his engine, and only succeeded after four years of trial and error. His first engine employed two cylinders; one to transfer the mixture into the power cylinder and one to produce the power. This idea was taken up by a number of early two-stroke designers, but virtually all modern two-stroke petrol engines rely on crankcase compression to transfer the mixture.
The Atkinson/Miller cycle
One of the disadvantages of the Otto cycle is the fact that the intake and exhaust strokes are the same length. A long exhaust stroke extracts more energy from the expanding gases, but a long intake stroke will lead to a loss of energy because the piston has to do an excessive amount of work to compress the mixture, resulting in high pumping losses.
This objection is taken care of by the Atkinson cycle engine, dating from the 1890s, which employs a hinged con-rod, and a third link whose pivot point can be moved to change the stroke length. This means the engine can operate on different intake and compression stroke lengths.
Another way to achieve the same result is the Miller cycle, dating from the 1940s. The engine looks completely normal but employs valve timing that shortens the effective compression stroke. In a normal engine, the intake valve stays open for about 30 degrees after bottom dead centre on the compression stroke, but with the Miller cycle the intake valve stays open for about 100 degrees. This means some of the intake mixture is forced back into the inlet manifold at the beginning of the compression stroke, which reduces the pumping losses as well as the potential power output, but by careful adjusting of valve timing such an engine may be up to 10 per cent more efficient. In fact, such an engine is sometimes called a five-stroke, with the strokes being intake, flowback, compression, power and exhaust.
Some modern engines, notiably the Toyota Prius and some Mazda models, employ a Miller cycle to reduce fuel consumption, although Toyota calls it the Atkinson cycle. In the Prius, the drop in power output resulting from this cycle is augmented by employing an additional electric power source, but Mazda uses a supercharger to improve the output of its Miller engine.
