Engine knocking, in which fuel ignites unevenly along the cylinder wall resulting in damaging percussive shock waves, is a problem that automakers have struggled to mitigate since the days of the Model T .The industry’s initial attempts to solve the problem, namely tetraethyl lead, were, in retrospect, a huge mistake, having stunned and stunned an entire generation of Americans with its neurotoxic byproducts.
Dr. Vaclav Smil, a professor emeritus at the University of Manitoba in Winnipeg, examines the short-sighted economic reasoning that leads to leaded gas instead of a national network of ethanol stations in his new book. Invention and Innovation: A Brief History of Hype and Failure. Lead gas is far from the only presumptive breakthrough that happens like a lead balloon. Invention and innovation it’s full of stories of the most well-intentioned, ill-conceived, and generally half-assed ideas, from airships and hyperloops to DDT and CFCs.
MIT Press
Excerpt from Invention and Innovation: A Brief History of Hype and Failure by professor Vaclav Smil. Reprinted with permission from The MIT Press. Copyright 2023.
Just seven years later, Henry Ford began selling his Model T, the first affordable and durable mass-produced passenger car, and in 1911 Charles Kettering, who later played a key role in the development of gasoline with lead, he designed the first practical electric starter motor, which he avoided. dangerous crank And while hard surfaced roads were still scarce even in the eastern part of the US, their construction began to accelerate, with the length of the country’s paved highway more than doubling between 1905 and 1920. Not least, decades of crude oil discoveries accompanied Advances in refining provided the liquid fuels needed for the expansion of new transportation, and in 1913 Standard Oil of Indiana introduced William Burton’s thermal cracking of crude oil, the process that increased the performance of gasoline while reducing the proportion of volatile compounds that make up the majority of natural gasolines.
But having more affordable and more reliable cars, more paved roads, and a reliable supply of adequate fuel still left a problem inherent in the combustion cycle used by car engines: the propensity for violent knocking (pinging). In a perfectly working gasoline engine, gas combustion is initiated solely by a timed spark at the top of the combustion chamber, and the resulting flame front moves uniformly through the volume of the cylinder. Knocks are caused by spontaneous ignitions (small explosions, mini-detonations) that take place in the remaining gases before they reach the flame front initiated by the spark. The knocks create high pressures (up to 18 MPa, or nearly 180 times the normal atmospheric level), and the resulting shock waves, which travel at speeds greater than sound, vibrate the walls of the combustion chamber and produce the sounds indicative of a knock, malfunction. engine
Knocking sounds alarming at any speed, but when an engine is running at high load it can be very destructive. Severe knocks can cause brutal irreparable engine damage, including cylinder head erosion, broken piston rings, and melted pistons; and any knock reduces the efficiency of an engine and releases more pollutants; in particular, it causes higher nitrogen oxide emissions. The ability to resist knocking, i.e. fuel stability, is based on the pressure at which the fuel spontaneously ignites and has been universally measured in octane numbers, which are usually displayed at stations of service with bold black numbers on a yellow background.
Octane (C8H18) is one of the alkanes (hydrocarbons with the general formula CnH2n + 2) that make up between 10 and 40 percent of light crude oil, and one of its isomers (compounds with the same number of carbon atoms and hydrogen but with a different molecular structure), 2,2,4-trimethylpentane (iso-octane), was taken as the maximum (100 percent) on the octane scale because the compound completely avoids any knock. The higher the octane rating of gasoline, the more resistant the fuel is to knocking, and engines can run more efficiently at higher compression ratios. American refineries now offer three octane grades, regular gasoline (87), mid-grade fuel (89), and premium fuel blends (91-93).
During the first two decades of the 20th century, the earliest phase of the expansion of the automobile, there were three options for minimizing or eliminating destructive knocks. The first was to keep the compression ratios of internal combustion engines relatively low, below 4.3:1: Ford’s best-selling Model T, launched in 1908, had a compression ratio of 3.98:1. The second was to develop smaller but more efficient engines that run on better fuel, and the third was to use additives that would prevent misfire. Keeping compression ratios low meant wasting fuel, and reduced engine efficiency was a particular concern during the years of rapid economic expansion following World War I, as increased car ownership by more powerful and more spacious cars led to concerns about long-term suitability. of the domestic supply of crude oil and the growing dependence on imports. Consequently, additives offered the easiest way out: they would allow lower quality fuel to be used in more powerful engines that ran more efficiently at higher compression ratios.
During the first two decades of the 20th century there was considerable interest in ethanol (ethyl alcohol, C2H6O or CH3CH2OH), both as an automobile fuel and as a gasoline additive. Numerous tests showed that engines using pure ethanol would never knock, and blends of ethanol with kerosene and gasoline were tested in Europe and the US. Well-known proponents of ethanol included Alexander Graham Bell, Elihu Thomson, and Henry Ford (although Ford did not, as many sources mistakenly do, design the Model T to run on ethanol or to be a dual-fuel vehicle; it had to be fed). for gasoline); Charles Kettering considered it the fuel of the future.
But three disadvantages complicated the large-scale adoption of ethanol: it was more expensive than gasoline, it was not available in sufficient volumes to meet the growing demand for automotive fuel, and to increase its supply, although only used as a dominant additive. have claimed important parts of agricultural production. At the time, there were no affordable and direct ways to produce the fuel on a large scale from abundant cellulosic waste such as wood or straw: the cellulose had to be first hydrolyzed by sulfuric acid and then fermented the resulting sugars. This is why ethanol fuel was mostly made from the same food crops that were used to make (in much smaller volumes) alcohol for drinking and medicinal and industrial uses.
The search for an effective new additive began in 1916 at Charles Kettering’s Dayton Research Laboratories with Thomas Midgley, a young mechanical engineer (born in 1889), in charge of the effort. In July 1918, a report prepared in collaboration with the US Army and the US Bureau of Mines listed ethyl alcohol, benzene, and a cyclohexane as compounds that produced no knock in engines d ‘high compression. In 1919, when Kettering was hired by GM to head its new research division, he defined the challenge as preventing a looming fuel shortage: the U.S. domestic supply of crude oil was expected to would disappear in fifteen years, and “if we could succeed.” increase the compression of our engines. . . we could double the mileage and thus extend that period to 30 years.” Kettering saw two routes to that goal, using a high-volume additive (ethanol or, as tests showed, fuel with 40 percent benzene that eliminated any time) or a low-percentage alternative, similar to but better than the 1 percent iodine solution, which was accidentally discovered in 1919 to have the same effect.
In early 1921, Kettering learned of Victor Lehner’s synthesis of selenium oxychloride at the University of Wisconsin. Tests showed it to be a highly effective antiknock compound but, as expected, also highly corrosive, but led directly to consideration of compounds of other elements in group 16 of the periodic table: both diethyl selenide and tel diethyl chloride showed even better striking properties, but the latter compound was poisonous when inhaled or absorbed through the skin and had a strong garlic smell. Tetraethyl tin was the next compound found to be modestly effective, and on December 9, 1921, a 1 percent solution of tetraethyl lead (TEL) – (C2H5)4 Pb – produced no knocking in the engine test, and it was soon found to be effective even when added in concentrations as low as 0.04 percent by volume.
TEL was originally synthesized in Germany by Karl Jacob Löwig in 1853 and had no previous commercial use. In January 1922, DuPont and Standard Oil of New Jersey were contracted to produce TEL, and in February 1923 the new fuel (with the additive mixed into gasoline at the pumps by simple devices called distillers) became available of the public at a small number of service stations. Even as the commitment to TEL progressed, Midgley and Kettering admitted that “alcohol is unquestionably the fuel of the future”, and estimates showed that a 20 percent mixture of ethanol and gasoline needed in 1920 could be supplied using only 9 percent. of the country’s grain and sugar crops while providing an additional market for US farmers. And during the interwar period, many European countries and some tropical countries used blends of 10 to 25 percent ethanol (made from surplus food crops and paper mill waste) and gasoline, it is true for relatively small markets such as family car ownership before World War II. Europe was only a fraction of the US average.
Other known alternatives included vapor-phase cracked refinery liquids, benzene-gasoline blends from naphthenic crudes (which contained little or no wax). Why did GM, well aware of these realities, decide not only to go the TEL route but also to claim (despite its own correct understanding) that no alternatives were available: “As far as we currently know, tetraethyl lead is the only available material that can produce these results”? Several factors help explain the choice. The ethanol route would have required the large-scale development of a new industry dedicated to an automotive fuel additive that could not be controlled by GM Also, as already noted, the preferred option, producing ethanol from cellulosic residues (crop residues, wood), rather than from food crops, was too expensive to be practical. In fact, the large-scale production of cellulosic ethanol through new enzymatic conversions, which was promised to be of historical importance in the 21st century, has failed its expectations, and by 2020, the production of large-volume ethanol in the United States (uti lized as an anti-knock additive) continued to rely on corn fermentation: in 2020 it claimed almost exactly one-third of the country’s corn crop.
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