Acetylene is however one of the less promising substances as it has the disconcerting property of exploding with extreme violence if the absolute pressure of the gas exceeds about 29 psi. (200 kPa) Most regulators and pressure gauges read gauge pressure rather than absolute pressure so the safe limit for acetylene is actually only 15 psig (101 kPa). No other substance need be present for an explosion; oxygen is not required. The explosion is due to acetylene reacting with itself, typically forming benzene and/or vinylacetylene. These reactions are highly exothermic. Acetylene is however very useful for cutting and welding, and is therefore shipped and stored dissolved in acetone contained in a metal cylinder with a porous filling called Agamassan, which makes it reasonably safe to transport and use.
Acetylene itself is not especially toxic but when generated from calcium carbide it can contain traces of highly toxic impurities such as phosphine and arsine.
Compression of the fuel/air mixture before its ignition is essential for an internal combustion engine to have a reasonable efficiency. We can see that a fuel that explodes violently at only 15 psi gauge, even without air present, is not likely to be a good start.
This did not deter J K Rush, who wrote this rather vacuous article some time around 1905. He claims that acetylene was currently being used in engines:
"Acetylene Gas Engines"
"Until recently it has not been practical to use acetylene for gas engines, owing to the fact that but very few acetylene generators generate acetylene at a temperature low enough to obtain a purity of gas or quantity sufficient to bring about the practical use of acetylene in an engine, but there are some generators producing acetylene of a sufficiently low degree of temperature to bring about a purity of quality and increase of volume of acetylene to such an extent that cooking and heating with acetylene has not only been made practical and profitable to many who are now using acetylene, but its use is now applied very practically to engines, which have been formerly used with gas and gasoline.
"Of course, engines used for this purpose are especially constructed, owing to the fact that a much smaller quantity of acetylene is required, when properly mixed with oxygen, to bring about good results in an engine than is used when coal gas is applied. A engine of this kind may be applied for running various kinds of machinery for factory purposes and the generator used for furnishing acetylene for heat, light and power. The heat may be used in the laboratory, the light for illuminating the entire premises, acetylene as applied to the engine, power for the entire institution - all supplied from one source. Te advent of the acetylene engine in the field of active industry will be a great boon to the trade generally, inasmuch as in many places acetylene generators will be purchased strictly for the sake of obtaining the gas for power purposes.
"A country home or estate may now be fitted out with an acetylene plant, whereby the lighting of the buildings, as well as the grounds, is supplied from the machine, acetylene for heating and cooking purposes in the culinary department and hot water heating appliances in the bath room. The acetylene engine can be used for the purpose of forcing water through pipes in the most modern manner possible to conceive of, thus supplying the suburbanite with all the luxuries of city life so far as these particular items are concerned.
"It is very interesting indeed to know the various uses to which acetylene is being applied. There is hardly a day at the present time but what some new application is made of this valuable combination of carbon and hydrogen. e see it in use on all up-to-date automobiles, launches, bicycles and many other similar uses, where the very brightest and best results are desired by way of illumination. ow, since the acetylene engine has come into the field, it would not be at all surprising to see within the next year at the automobile show, an automobile propelled as well as illuminated with acetylene."
This article is taken from The Plumbers' Trade Journal reprinted in Amateur Work Magazine Volume 5, 1906".
THE BARKER-WHITE ALCOHOL-ACETYLENE SYSTEM: 1907
The Barker-White system ran an engine on a mixture of alcohol and acetylene. An ordinary carburettor gave an alcohol/air mixture, and the system then relied on the water that made up about 10% of the current commercial alcohol, to react with calcium carbide and generate acetylene. This made the alcohol burn more rapidly while the alcohol suppressed the exposive tendencies of the acetylene. Relying on what must have been a variable amount of water in the alcohol to set the critical amount of acetylene burnt sounds very dodgy to me.
Left: Barker-White test engine: 1907
Source currently unknown
Left: Barker-White engine test: 1907
Source currently unknown
Left: Extract from From Acetylene, the Principles of Its Generation and Use Leeds & Atkinson
Leeds and Atkinson also give us a report on tests with carburetted acetylene:
"Lepinay has described some experiments on the comparative technical value of ordinary acetylene, carburetted acetylene, denatured alcohol and petroleum spirit as fuels for small explosion engines. One particular motor of 3 (French) h.p. consumed 1150 grammes of petroleum spirit per hour at full load; but when it was supplied with carburetted acetylene its consumption fell to 150 litres of acetylene and 700 grammes of spirit (specific gravity 0.680). A 1-1/4 h.p. engine running light required 48 grammes of 90% alcohol per horse-power-hour and 66 litres of acetylene; at full load it took 220 grammes of alcohol and 110 litres of acetylene.
A 6 h.p. engine at full load required 62 litres of acetylene carburetted with 197 grammes of petroleum spirit per horse-power-hour (uncorrected); while a similar motor fed with low-grade Taylor fuel-gas took 1260 litres per horse-power-hour, but on an average developed the same amount of power from 73 litres when 10 per cent. of acetylene was added to the gas. Lepinay found that with pure acetylene ignition of the charge was apt to be premature; and that while the consumption of carburetted acetylene in small motors still materially exceeded the theoretical, further economics could be attained, which, coupled with the smooth and regular running of an engine fed with the carburetted gas, made carburetted acetylene distinctly the better power-gas of the two."
From Acetylene, the Principles of Its Generation and Use Leeds & Atkinson, pub Griffin 1910, 2nd edn p263
This book can be downloaded for free from the Cornell Library.
Acetylene was 'carburetted' by saturating it with petrol vapour in a crude carburettor. Possibly this retarded its tendency to explode on compression. It is not surprising that Lepinay found that "with pure acetylene ignition of the charge was apt to be premature." What is perhaps surprising is that the whole engine did not explode.
Despite using the full resources of the Interwebs, all that has been discovered so far about M'sieur Lepinay is that his first initial was A.
By 1944 Germany was experiencing crippling shortages of fuel for motor vehicles. In that year Panther tanks we fitted with acetylene bottles for use in training at Eisenbach in Thuringia, the base for the 1st Panzer Division. Presumably some modification of the engine was required; normally its Maybach engine ran on petrol. Turning coal into acetylene is much easier than turning coal into petrol.
Left: Acetylene-powered Panther tank: 1944
Left: Acetylene-powered Panther tank: 1944
In spite of it all, interest in acetylene as a fuel for engines is still alive, for one reason- you can make it out of coal rather than oil. This is the abstract of a paper Evaluation of acetylene as a spark ignition engine fuel by David L Hilden and Russell F Stebar, published in 1979 in the International Journal of Energy Research, Volume 3, Issue 1, pages 59–71.
"In spite of its known shortcomings as a fuel for spark ignition engines, acetylene has been suggested as a possible alternative to petroleum-based fuels since it can be produced from non-petroleum resources (coal, limestone and water). Therefore, acetylene was evaluated in a single-cylinder engine to investigate performance and emission characteristics with special emphasis on lean operation for NOx control. Testing was carried out at constant speed, constant airflow and MBT spark timing. Equivalence ratio and compression ratio were the primary variables.
"The engine operated much leaner when fuelled with acetylene than with gasoline. With acetylene, the engine operated at equivalence ratios as lean as 0·53 and 0·43 for compression ratios of 4 and 6, respectively. However, the operating range was very limited. Knock-induced preignition occurred either with compression ratios above 6 or with mixtures richer than 0.69 equivalence ratio.
"Both the indicated thermal efficiency and power output were less for acetylene fuelling than for gasoline.
"Acetylene combustion occurred at sufficiently lean equivalence ratios to produce very low NOx and CO emissions. However, when the low NOx levels were achieved hydrocarbon control was not improved over that with gasoline.
"Despite the potential for NOx control demonstrated in this study of acetylene fuelling, difficulties encountered with engine knock and preignition plus well-known safety problems (wide flammability limits and explosive decomposition) associated with acetylene render this fuel impractical for spark ignition engines."
Unfortunately the explosions and general safety problems, as expected, make it unusable as a fuel by itself.