Chapter energy and technology the enhancement of skin

6.7. The internal (infernal) combustion engine

The steam engine, as applied to vehicles, had three fundamental disadvantages, which were gradually recognized. The first, and most obvious, was that a steam engine needed either a large water tank and frequent water refills, or an external condenser to recycle the steam. The first option worked fairly well on the railways and for large ships, but not for smaller applications, especially private cars. The famous “Stanley Steamer” won a lot of races in the early days because of its high torque, but it needed frequent drinks of water. It is said that the demise of the early steam-powered automobiles was because the horse troughs – where horses used to drink along the roads – disappeared along with the horses themselves. The Stanley steamers, which had no condenser, were left (so to speak) “high and dry”. The later “Doble”, built in the 1930s, had a condenser that worked fine, but only a few were produced. It was too expensive and too late.

The second fundamental disadvantage of steam was that high efficiency requires high temperatures (the Carnot law). It follows that a really efficient steam engine needs to use special steel alloys for the boiler that do not lose their strength at high temperatures. Plain old carbon steel is not strong enough. In modern steam-electric generating plants it is necessary to use more expensive alloys containing more exotic metals like manganese, molybdenum and nickel. These special steels might be economically justified in large central station power plants, but not in engines for cars or trucks. (Jet aircraft are another story.) The third disadvantage, related to the second, is that the condenser makes the engine considerably heavier and bulkier than a comparable gasoline powered ICE.

The reciprocating (piston) internal combustion engine (ICE) avoids all these problems. Instead of making high pressure steam to drive the pistons (or turbine wheels) it makes use of the high temperature exhaust gases from the combustion itself.¹⁴ There is no need for a condenser because the exhaust gas returns to the atmosphere as air pollution, but that is another problem. Problem #1 is thereby avoided. Problem #2 is avoided also, because the combustion process in an ICE is intermittent, not continuous. After each explosion of the compressed fuel-air mixture, the temperature drops rapidly as the gaseous combustion products expand and energy is transferred to the piston.

The temperature of the metal inside the cylinder and the piston itself never gets too hot because the metal is a good heat conductor that conducts heat away from the surface where the combustion takes place, between explosions. So, it turns out that a cast iron engine block works just fine. In the case of gas turbines, stronger alloys are needed, which is why gas turbines came along much later and are not nearly as cheap (or mass-producible) as ICE piston engines.

Of course, the stationary steam engine did have one great advantage: It could use cheap coal, or coke, available everywhere (by the mid-19^th century), as a fuel. However, the rapid expansion of coking to feed the new blast furnaces of the Ruhr valley in Germany created plenty of by-product coke-oven gas which needed a market. Moreover the use of “town gas” for street lighting and interior lighting in offices, hotels and restaurants had already created a system of gas pipelines in the major cities. Widespread availability of coke-oven gas, a by-product of the steel industry, enabled (and possibly stimulated) the development of internal combustion engines. The early driving force behind his innovation was the need for more efficient and cheaper prime movers. This was especially true for the smaller machine shops and manufactories that were springing up along the Rhine River and its tributary, the Ruhr.

Cologne-based entrepreneur-inventor Nikolaus Otto's commercially successful high compression gas engine, the “Silent Otto” (1876) was the culmination of a series of earlier inventions. Some of the most noteworthy were the prototype "explosion engines" of Street (1794), and Cecil (1820) and the first commercial stationary gas engines built by Samuel Brown in the 1820's and 1830's. Key steps forward were taken by Wright (1833) and Barnett (1838), who was the first to try compression. Lenoir (1860) built and commercialized a double-acting gas engine modelled on the double-acting steam engine invented by James Watt. Like Watt's engine, it did not compress the fuel-air mix. These engines were quite successful, despite being very inefficient (about 4%). The so-called "free-piston" engine, invented by Barsanti and Matteucci (1859), was briefly commercialized by Otto and Langen (1867). The first self-propelled vehicle was built and operated by Siegfried Marcus (1864-68) in Vienna. It was shown at the Vienna Exposition in 1873. But it was a one-of-a-kind, dead-end, project.

The need to compress the fuel-air mixture prior to ignition had been recognized already (by Barnett) in the 1830s. But the first to work out a way for the pistons to perform the compression stage before the ignition – now known as the "4 stroke" cycle – was Beau de Rochas (1862). Not for another 14 years, however, was this revolutionary cycle embodied in Nikolaus Otto's revolutionary commercial engine (1876). The "Silent Otto" rapidly achieved commercial success as a stationary power source for small establishments throughout Europe, burning illuminating gas, or coke-oven gas, as a fuel. Otto's engine produced 3 hp at 180 rpm and weighed around 1500 lb. It was very bulky by today’s standards, but much more compact than any comparable stationary steam engine. By 1900 there were about 200,000 of these gas-fired engines in existence. They still had to be attached to long rotating shafts that drove machines by means of belts. (Those shaft-and-belt combinations were replaced, after 1900, by electric motors.)

The next challenge was to make the engine smaller and lighter, as well as more powerful. The key to increasing the power-to weight ratio was to increase the speed. The prototype automobile engine was probably a 1.5 hp (600 rpm) model weighing a mere 110 lb. It was built by Gottlieb Daimler (who had once worked for Otto) and his partner, Wilhelm Maybach (1885). They built 4 experimental vehicles during the years 1885-1889. These were not the first self-propelled vehicles – “automobiles” – but they were the first ones with a commercial future.

The first practical car that did not resemble a horse-drawn carriage without the horse was Krebs’ Panhard (1894). Benz did introduce the spark-plug, however, a significant advance over Otto's glow-tube ignition. A large number of subsidiary inventions followed, ranging from the carburetor (Maybach 1893), the expanding brake (Duryea 1898), the steering wheel (1901), the steering knuckle (Eliot 1902), the head-lamp, the self-starter (1912), and so on.

The success of the spark-ignition high compression "Otto-cycle" engine created enormous interest in the technical possibilities of compression engines. Rudolf Diesel realized that higher compression made the engine more efficient. He also discovered that, above a certain compression (about 15:1) there was no need for spark ignition, as the compressed fuel-air mixture becomes hot enough to self-ignite. And the fuel need not be as volatile as gasoline; heavier oils work OK. The compression-ignition internal combustion engine was patented by Rudolf Diesel in 1892. It was first commercialized for stationary power in 1898, but development was very slow because the need for very high compression (more than 15:1) resulted in technical and manufacturing difficulties. Diesel power was adopted for the first time for railway use by the Prussian State Railways (1912), and for marine use shortly thereafter. Diesel-electric locomotives for railway use were finally introduced in the 1930's by General Motors. The first automobile diesel engine was introduced in the 1930's by Mercedes Benz, but penetration of the automobile market has been negligible until the 1980s, when the turbo-diesel was introduced. Diesel power dominates the heavy truck, bus, rail and off-road machinery fields today, and is rapidly penetrating the automobile market in Europe, today.

Figure : Power-weight ratios for internal combustion engines

The single most important technological barrier in the way of practical self-powered road vehicles (until Daimler) was the lack of a prime mover with sufficient power in a small enough "package". The same barrier applied even more strictly to heavier-than-air craft. The key variable is power-to-weight ratio. In retrospect it is clear that the minimum feasible level for road vehicles was about 50 kg per hp, or about 0.02 hp/kg. The Daimler-Maybach engine achieved 35 kg/hp or 0.0275 hp/kg in 1886. Cars did not become truly practical until further developments brought the engine weight down (or the power up) to around 7 kg/hp or roughly 0.15 hp/kg. See Figure 28.

Actually, the 1901 Mercedes Benz engine produced 35 hp. with an engine weighing 215 kg (6.2 kg/hp). (The “Mercedes” car was named after the 10 year-old daughter of an early investor, Emil Jelinek.) But the Manly engine, designed specifically for Langley's "Aerodrome" (1903), achieved 52 hp in a package weighing only 68 kg. or about 1.3 kg/hp. This was an improvement over the original Daimler-Maybach engines by a factor of 38! The early aircraft engines obtained part of their "punch" by the use of special high octane fuels (e.g. benzene) that permitted higher compression ratios, and hence greater power, but which could not by produced in large enough quantities for normal automotive use. Obviously practical air transportation (which came much later) required substantial further progress in increasing the power-to- weight of the engines. Progress in gasoline refining technology in the 1930's and 1940s played a major role in this.

It is worth mentioning that the performance improvements of gasoline engines since 1886 also resulted partly from thermodynamic efficiency improvements somewhere in the neighborhood of a factor of two or three. The point is that, higher efficiencies did not save energy. On the contrary, energy consumption for automotive and air transportation has “sky-rocketed”. (No pun intended.) It is a good example of the so-called “rebound effect”, where an efficiency gain results in lower prices and that, in turn, drives higher demand {Herring, 2009 #6241}.

Actually the greatest efficiency improvement came about in the 1920s as a result of the discovery of tetra-ethyl lead as an octane additive. All engines before that time were effectively limited to a compression ratio of 4:1, because they were forced to burn gasoline. Higher compression ratios led to explosive pre-combustion before the cylinder completes its stroke. This had an effect known as “knocking”, that sharply reduced efficiency and damaged the machinery. The solution, tetraethyl lead, was discovered in 1921 by Thomas Midgeley. He was a chemist working in a tiny firm Dayton Engineering Laboratory in Dayton Ohio, under Charles Kettering. (Kettering’s firm merged with GM where it became the Delco division.). Tetraethyl lead was commercialized by GM and Standard Oil of N.J. under the trade name “Ethyl”. Later, it is said that the giant German chemical firm IG FarbenIndustrie, spend many millions of Deutschmarks trying to find a way to avoid the Ethyl patents, but without success.