BENZOLE-ALCOHOL MIXTURES.
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An Account of the Fuel Experiments Carried Out on the Bench and on a Public Service by the L.G.O.C.
By G. J. Shave, MIME., 111.I.A.E..
ACTUATED by the 'necessity of finding a suitable substitute for petrol, and at the request of .31r. Long's ,Inter-Departmental Committee on, Power Alcohol, dim to the fact that the adequacy of. the world's supply of. oil to meet the ever
increasing demands is seriously questioned, the company decided to carry out a series of experiments with benzole-alcohol with a view to ascertaining the most suitable mixture of these fuels for operating standard buses with " B " type engines. • Perhaps a foreword with regard to the general .eharacteristios of benzole and alcohol as fuels for use with internal-combustion engines may not be out of place before describing. the experiments that have been made.
Benzole is a product obtainedi by chemical treatment and distillation from coal tar. The production is limited by the amount of coal. which is subjected to distillation—either for the production of coal gas or metallurgical coke—the benzole being one of the minor byproducts.
Alcohol is produced from vegetable products, and the raw material' is practically limitless, so that no fear exists, as with coal and oil, of exhausting the supply. For this reason we felt it desirable to find '. aaamixture of these two fuels that would allow as large a proportion of alcohol as could be reasonably used, having, of course, due regard to the economy of fuel and the least amount of alteration necessary to convert .a standard petrol engine to burn this fuel. In discussing the merits of these fuels, we must take petrol as our standard for comparison, owing to the fact that the bus engine is designed and tuned-up for use with petrol. Although petrol has the greatest number of B.T.U.s per pound, benzoic has the greatest number of B.T.U.s per gallon. Alcohol by itself has approximately just over half the calorific val./e oil either of the other fuels. Compared with petrol, both benzole and alcohol are slow-burning fuels, and consequently the construction of the engine has to be somewhat modified to suit them. In the first place, compression has to be increased in proportion to the slowness of the burning of the mixture, and within the limits of ' the 'detonating temperature of the fuel and air mixture. The most suitable compression for certain mixtures and under fixed conditions has been determined by experiment. Looking at, the table of calorific value S and specific gravities, it will be noticed that benzoic stands highest in B.T.U.s per gallon, but the difference is very small between that and petrol. It follows from this that, although to obtain the best results from benzole .a different earburetter setting is required, it. is possible to run the engine with benzole \ ithout altering the compression. With regard to alcohol, however, owing to its slow combustion, it was found that good results could only be obtained by raising the compression to a very oonsiderable degree. Another point in connection with the use of these fuels is the temperature of the induction pipe. The temperature should be maintained so as to ensure the complete vaporization of the fuel.
Mixtures.
With regard to. the question of the mixtures of benzole and alcohol, it is possible to make a whole range of fuels which have various calorific values in B.T.U.s per gallon. Pure benzole.can be used as a fuel, and also pure alcohol and every proportion of mixture of these two fuels. Within this range of fuels comes the value of the present-day petrol, approximately 92 per cent. benzole and 8 per cent. alcohol ; so it is quite poesible to make a tare whichwhich can be used on the petrol engine and to compare favourably with petrol without making any change of compression or carburetter setting. This is not necessarily the best setting or conditions for using this mixture, nor is it necessarily the mixture of alcohol an benzole that can be obtained to produee the best, all-round results
Bench Tests., .
We determined first to commence with the 50 per cent. mixture. 1-lere we have a fuel the heat value of which, as compared with petrol, is as 12.5 is to 15, a difference which warrants considerable change in the compression of the engine and the setting of the carburetter.
Some 50 bench tests-were made on a 130 mm. by 140 mm. "B " type engine by means of a dynamometer. The compression, the setting of the carburetter, and the 4-reating of the induction pipe were the variable factors experimented on. As a result of this work, we found that with the 56 per cent. mixture the 12-3 lb. compression gave the best results. The valve setting found most suitable was the same as that in standard " B " type engines using petrol. The exhaust gases were analysed on this test (123 lb. compression), and showed a complete absence of carbon monoxide, with a slight
excess of oxygen, showing that the combustion of the fuel was complete. Following this, further bench tests were made toinvestigate the possibility of running " B " type engines standard in general details, but with higher compression on fuel mixtures with higher percentages of alcohol.
During these tests the large range of mixtures of air and fuel with which the engine could be run was particularly noticed. This was more noticeable when the ,alcohol was present in large proportion in the fuel, and proved conclusively the serviceability of fuel a containing alcohol. In these bench tests, -it may be a point of interest to mention that the full load fuel consumption of B.T.U.s per la.h.p. decreased as the percentage of alcohol became greater, up to the point where the compression was not sufficiently high (i.e., mixtures containing up to 70 per cent. or 80 per cent.alcohol). The half-load consumption gradually becomes greater, and the quarter-load rapidly becomes greater. This points to the effect due to the low compression obtained with small throttle openings, and it is suggested that the advantages gained at full throttle when using higher percentages of alcohol will be reduced by reason of the lowered economy at light throttle openings, especially on the type of engine on svhicla these trials were made. With reference to the shape of the combustion head, it is contended that the higher the compression is made with this engine the relatively worse effectwill the pockets have on the fuel corisumntion, more especially at the small throttle openings. This observation leads one to the conclusion that the greater the percentage of alcohol the more–important it is to design the engine for that special purpose. A.
• slow-burning fuel such as alcohol makes it possible
• to reach high thermal efficiency and great fuel 'economy. but in order to obtain the best results, it is -necessary to design the engine to suit the fuel. Generally speaking, such an engine, would have a long stroke and high compression with overhead valves. The importance of introducing sufficient heat thoroughly to vaporize the mixture cannot he over &nphasized. Briefly, to summarize the results of this range of tests, we may say:—
a) The greater the percentage of alcohol, the higher are the possible thermal efficiencies for the some compression. (b) The' greater the percentage of alcohol, the higher can the compression be raised with the consequent rise in the themal efficiencies.
(e) With high compression the ill-effects of valve pockets are more noticeable at small throttle openings than with low compression.
Road Tests.
In view of the promising results obtained on the bench with high compression, it was decided to put the engine tested into a bus chassis and conductsome road trials, the results of which are as follow :— The chassis with which these tests were made was a bus chassis fitted up as a lorry. The engine compression had been raised to 160 lb. per sq. in. by riveting aluminium plates to the top of the pistons. These plates were dome-shaped so as to follow, more or less, the contour of the cylinder head. In order to ascertain the mixture most suitable for use with this compression, the following mixtures were tried : — These tests were made on our standard test-run, eight miles out and eight miles return, and the roads on the whole were in a very lair condition, and generally in a dry state. The route is on the Epping road, through Woodford and Epping. It is an undulating road, the gradients being generally rising in the outward direction, so that the return route is rather the more favourable of the two.
It was observed that the best all-round results were obtained with the 70-•30 per cent. mixture, although the 50 per cent, mixture gave quite good
results. ,
Comparing the '70 per cent. mixture (high compression) and petrol (normal compression), we
On a 'Bench Test— . get :— • 70% Mixture: Petrol.
B.T.U. per Mile :.. 12,160 16,100 (normal speeds) Saving of B.T.U... — 24.5% — On Road-Service Test— ' B.T.U. per mile ... 14,100 . 15;810 Saving of B.T.U,.. — 10.8% —
Tests on Service.
After the road test, the same engine was transferred to a bus, the 'latter having been fitted with new fuel tank, pipes; and fittings. It was then put on service running on the 50 per cent. benzole, alcohol fuel. After -running on service for a. Month the new tank was found to have become porous and corroded, evidently from the action of the fuel. To further investigate the corrosive effect of this fuel, the laboratory undertook a series of experiments on the action of benzole, alcohol, and 50 per cent, mixture on different metals, and from their report it appeared that copper and iron are attacked -very badly_ by these fuels ; brass, zinc, aluminium, and tin are slightly attacked s and no action takes place' on lead.. It is important, therefore, that the fuel tanks andpipes should be lead coated. The tanks could be-made of sheet-iron coated with lead, and the pipes should. be of steel with an internal coating' of lead. A sample of sheet4ron suitable for this fairpose has been received. This metal is coated with an alloy 20 per cent. ‘tin and 80 per cent. lead. With regard to the carburetter, this can still be made.of brass, as the fuel affects the brass only very' slightly.. The results obtainedon service are as follow :—
Fuel Consumption.
Total Bus Avge. Fleet Avge
Itlilea to Date -to Date to Date, on Mixture. on Petrol. 75% benzole, 25% alcohol—
Bus No. :13 908... 4,597.7 ... — .. — Miles per gallon — ... 7.42 7.58 1 B.T.U. per mile — -... 18,980 ... 19,900 July, 95% benzoie, alcohol— r 161.h • Bus No. B 415... 2,632.4 ... — 1919.
Miles per gallon — ... 7.6 ... 7,58 B.T.U. per mile — 20,150 ... -19,900 j
80% benzole, 200:,:, alcohol—
Bus No. B 849... 6.746.4 ... — Miles per gallon ... 7.28 ... 7.55 W [E.
B.T.U. per mile — 19,780 ... 20,050 Sept., 50% henzole, 50% alcohol— r 10th
Bog No. B 1263 4,567.6 ... — — 1919.
Miles per gallon — 1.. 7.0 ... 7.55 B.T.U. per mile — ... 17,816 ... 20,050 j
From this it will be seen that the 50 per cent. benzole-alcohol mixture gives the most efficient result, consuming some l2 per cent. less B.T.U.s per mile than petrol. The next best resultis with 15 per cent. benzole and 25 per cent. alcohol.
to find out whether it was doing as well as if did when it was first sent out. The results obtained ,Referring again to the 50 per cent. mixture, the experimental engine which had been running in a " B " type bus was taken out for examination after running about six weeks on service. Before opening up this engine, a test was made on the stand 'show that the fuel consumption had somewhat increased and the b.h.p. had decreased as compared with the first teat ot this engine before being put into the bus. On opening up the engine, one cylinder was found to be badly. scored by a gudgeon pin.. The inlet valve pockets and so far as one inch under the valve heads were coated with a thick tax-like substance, choking to a large extent the passage. The exhaust valves were quite clean. ajrcl in good condition. There was not much deposit on the pistons. There was a little of this tar-like deposit in the induction manifold. The partial chok ing up of the inlet valve openings would probably account for the decrease in hp. observed on the second bench test.
It would seem advisable, therefore, periodically to examine the valves and induction pipe, say, every month, when running on this fuel. On the other hand, no ill-effects from the point of view of running on service were noticeable during the latter part of its run; in fact, the m.p.g. seemed to have been fairly well maintained throughout the whole period.
A further 14 buses were then worked on service, aria in the main were run on the 50 per cent, mixture of benzole-alcohol. During the period they were running the average fuel consumption was seven m.p.g. during the six weeks' operation of over 4,500 miles. At the same time, the average on petrol (for the same period) was 7.5 m.p.g. With regard to the experience obtained during this time, several features were observed which affected the economy of the fuel in various ways—colder weather, indifferent supplies of benzole, and the separation of water out of the alcohol. This, combined with the bad state of the roads, all 'contributed to lower the economy compared with the figures originally obtained. The benzole trouble was eliminated by getting fresh supplies up to standard specification. The excess of water in the alcohol may have been due to colder weather and more humid atmosphere; at any rate; it had the effect at the tune of making the bus difficult to start, and also of causing .trouble on services where mica plugs were used, owing to condensation of water on the plugs. This trouble was overcome by using plugs with porcelain insulation to within a short distance the psmnt. of the electrode. To eliminate the difficulty of the excess of water in the alcohol at sta* ing, a drain tap was fitted to drain off the water before starting up in the mornings. It is suggested as an explanation of the collection of water in the tank that -alcohol, benzole, and water are not completely ,miscible at low temperature. In mentioning these troubles, it should not be deduced that the experiments were unsuccessful, for, as a matter of fact, after the elimination of these earlier difficulties, the operationof the buseson service was entirely satisfactory. There was a noticeable absence of " pinking " or knocking in the engines, the running of whichwas good, developing and sustaining a high torque at low speeds. These features are attributed to the slow burning of the fuel. In spite of the higher compression, the garage staff have had no difficulty, other than the above-mentioned experience, in starting up the engines in the early morning. An average fuel consumption taken over a period of two winter months with some half-dozen buses in service works out as follows: 50 per cent. mixture, 6.05 m.p.g. Petrol (fleet average), 7.19 m.p.g.
During the summer months the comparison was as follows:— 50 per cent. mixture 7.0 m.p.4. Petrol (fleet average), 7.55 m.p.g.
When 'considering these figures, regard must 'be paid to the fact that it is difficult to estimate the economy effected by using the 50 per cent. mixture as against petrol, as we purchase our fuel by galluns and not by B.T.U.e.
Comparative Cost of Fuels.
We cannot justly compare the price paid for petrol, benzole, and alcohol owing to the abnormal • state of the markets, and in the case of alcohol, the heavy Goyernment duty imposed. However, this report mainly deals with the advantages end disadvantages of running buses on 50 per cent. benzole-alcohol mixtures from a technical point of view to assist in determining whether the advantages gained warrant an encouragement of the pro duction of these fuels by the Government and a revision of the taxation. On the basis of equal cost per gallon, say; 25d. per gallon, we ing comparison in B.T.U.s per td. Petrol. Benzale-Alcohol. get the follow 50% B.T.17. per id. 6,050 5,000 B.T.131. per mile 20,050 17,816
Cost per mile 3.3d.
. This shows that petrol has 20 per cent, more heat value per id. than the 50 per cent, mixture, but the latter is 12 per cent, more economical. The difference in cost is, however, only 8 per cent., the petrol being the cheaper fuel on the assumption of equal cost per gallon. Apart from the question of greater heat economy, the running of the engine is very much better than when using petrol. The question of using alcohol as a motor fuel has been gone into in the past, but, owing to the illegitimate uses to which it might be put and the high taxation involved, no serious attempt has been made by the Government to relax the legislative restrictions in dealing with this spirit for motorfuel purposes. _Methylated spirit is a commercial alcohol that has been denatured by the admixture of other substances to make it undrinkable. The main, addition is 10 per cent wood naphtha (or methylating alcohol), which latter substance reduces its efficiency as a fuel.
It is suggested that a way out of the difficulty would`be for the Government to authorize a motor fuel made of definite proportions of alcohol and benzole, such as 50 per cent, mixtures here reviewed. The alcohol would thus be denatured by the benzoic, and the mixture might be sold as a Government fuel, the mention of alcohol being omitted. The taxation on this fuel should not be higher than that on petrol. It moi'y be mentioned that this procedure should not adversely affect the revenue, insomuch as this fuel would be in addition to the alcohol for other trade purposes, and on which the present duties would be still demanded.
We have now discontinued this experiment, and are confining our attention to experiments with mixtures of alcohol and ether, and alcohol, benzole and ether. made for the benzole in the denaturedalcohol (this being determined at 71 8 per cent.), and the mixture used had the following composition:— Alcohol 65 per cent.
Benzole 30 per cent.
Ether 5 per tent.
The specific gravity of this mixture was .8265 at 60 deg. F.
Preliminary tests were carried out for the purpose of getting the best all-round setting. Three types of induction pipe were used—plain, exhaustheated, and water-jacketed—the last giving the best results, while the exhaust-heated pipe gave the worst.
It was possible to start from cold easily, using either plain or water-jacketed induction pipes, though in the latter case steady running was not obtained until the engine had become hot.
The bench test results show that, compared with petrol, the power at speeds below 900 r.p.m. are slightly better, while at high speeds they fall off. The consumption is, however, slightly higher with this mixture than with petrol, this being rather more marked at quarter load. The acceleration was good from 360 r.p.m. in all cases, and there was a complete absence of knteking and pinking.
The-analysis of an exhaust gas sample gave satisfactory figures, the absence of carbon monoxide indicating that combustion was complete. The plugs and valve caps were removed alter the test, and only the slightest deposit was noticed on them. There was no objectionable smell from the exhaust.
The calorific value of the mixture was calculated. The thermal efficiencies obtained wifli this mixture are higher than the figures obtained for petrol. It is to be particularly noticed that the complete test was carried out on a standard " B " type engine of normal compression.
Experiments of this kind entail a considerable amount of work, and we trust that the results of our efforts may be of some use in determining what is to be the ultimate substitute for petrol.
. We are fast squandering the oil that has been stored ih the fuel beds of the world, and it seems, so far as our present knowledge takes us, that it is to the fuels experimented with that we must turn for our salvation.