Alcohol Engines

Updated: 30 Mar Sept 2015

Alco-Vapor engine added
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This page deals with engines that use alcohol vapour or a water/alcohol mixture as a working fluid, rather than simply as a fuel to burn.

Alcohol vapourises easily, but that does not mean it is more efficient than water as a working fluid. Quite the reverse. See: Carnot's Law on the thermodynamics page.


AN ALCOHOL VAPOUR ENGINE DEMONSTRATION

Left: A toy steam-engine driven by alcohol vapour, with the exhaust combusting.

This scheme comes from the book "Engines" by E N da C Andrade, published G Bell & Sons in 1928. (A very engaging book that manages to deal with the complexities of thermodynamics in a most approachable way)
The author points that the alcohol vapour exhaust can be lit, though it would be wise to make sure that all the air has been driven out of the plumbing before trying it. This underlines that a non-condensing (total-loss) alcohol vapour engine is a grotesquely inefficient and expensive proposition. I hasten to add that the author was not claiming otherwise, but goes on to deal with the concept of Carnot efficiency.


THE HISTORY OF ALCOHOL VAPOUR ENGINES

The French journal Nature, (21 June, 1890) has this to say: "Artwright proposed and constructed, in 1797, an alcohol-vapour machine which worked well enough, but which did not survive, very probably because of the very imperfect construction of the time; substantial leaks of a relatively costly vapour would have made the system very uneconomic."

I have long suspected that "Artwright" should be "Arkwright", but actually it looks as though the name was Cartwright; the entry below refers to Dr Edmund Cartwright, but it only says he suggested an alcohol engine, not that he actually constructed one.

Left: The entry on alcohol engines from Knight's Dictionary

With a description of Howard's alcohol engine, patented in 1825.

From Knight's Practical Dictionary of Mechanics pub Cassell & Co, 1884.

Above: Howard's alcohol engine: 1825

Howard appears to have been fully aware of the need to minimise the losses through leakage of an expensive working medium. He used hot oil as a liquid piston. (Early experiments seem to have beeen done with mercury, but the cost of this for a large engine would have been crippling. Breathing the mercury vapour would probably have been crippling too) In the diagram above a flat dish D can be seen floating on the hot oil A in the middle cylinder. The oil was kept hot by the four Argand burners underneath. Alcohol was sprayed into the hot dish by the narrow pipe just above it, propelled by pump R, and flashed into vapour. This pushed down the oil and pushed up the piston in cylinder B on the right.
On the return stroke the alcohol vapour was pushed into the condenser on the left via pipe S. The condenser tubes U were wrapped in wet flannel, with air blown over them by a fan mounted on vertical shaft Z.

This engine, with its complexity and its interesting combination of alcohol and hot oil, seems wholly impractical. No wonder that according to Knight, it "...wearied out the patience or the means of its inventor...".


BINARY VAPOUR ENGINES

A binary vapour engine boils a mixture of liquids, usually water and some kind of alcohol. It doesn't appear to be a good idea, but that has not stopped a few people from trying it.


US NAVY EXPERIMENTS WITH WATER/METHANOL

In 1885 a commission of US Navy engineers tried out a mixture of water and 15% wood alcohol, Methanol was presumably chosen for its low boiling point, though this is fallacious. (see below) Perhaps they thought its toxicity would deter the crew from drinking it. Historically this approach has been of questionable effectiveness.

Above: An experiment with a binary working fluid- in this case water and methanol.

This is taken from the British journal Engineering for 9th Jan, 1885. Wood alcohol is methanol (methyl alcohol)

Note that the board of US Navy engineers had grave (and entirely justified) doubts about the thermodynamics of low-boiling-point liquids as working fluids. (Methanol boils at 64.7 degC) The US Navy has not always distinguished itself in this field.

The major problem with the later large-scale test seems to have been leakage; not good when the vapour leaking is toxic, inflammable and relatively expensive. Whether methanol really does leak out more easily than steam I have not so far been able to determine; presumably it depends on the size of the vapour molecule.
Another pitfall was clearly the tendency of this binary mixture to change its composition when boiled, so that the condensed liquid in the hotwell was much richer in methanol than the liquid in the boiler. For an ethanol-water mixture, the vapour would not boil off in the same proportions as in the liquid in the boiler unless the methanol concentration was a lot higher than 15%; ethanol-water forms a constant-boiling mixture at a concentration of 95.6% ethanol at 78.1 degC. However it appears that methanol does not form a constant-boiling mixture with water; see The Methanol Manual, on page 5. I'll leave it to someone who knows more physical chemistry than I do to evaluate what effect this would have had on the tests.

To learn more about constant boiling mixtures see here. (external site)


OLFELDT'S ALCO-VAPOR ENGINES: WATER/ETHANOL

Frank W Ofeldt is most closely associated with the naphtha launch, but when he left the Gas Engine and Power Company he produced the Alco-Vapor power plant for launches. This boiled a mixture of water and alcohol, not because the lower boiling-point of alcohol would make the engine more efficient (the exact opposite is true) but in not very impressive attempt to evade the USA regulations that required every steam launch to carry a licensed steam engineer. The naphtha launch was the first approach to this, and it seems to have worked in evading the law, at the cost of the inherent hazards in boiling petrol.

Nowhere have I found confirmation that 'alcohol' in this context means 'ethanol', but given the problems that were experienced when methanol was used, as described above, it seems extremely likely. In the journal MotorBoating (Nov 1942, p46-48) the proportion used was described as "a merely nominal amount of alcohol" and if the question had arisen, it is hard to see how Ofeldt could have argued at all convincingly that he was not building steam engines.

Olfeldt's personal history can be found on the page devoted to the The Petrol-Vapour Motors.

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