Effect of Producer Fuel on Efficiency
Page 33
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Abstracts From a Valuable Paper Read Before The Institution of Automobile Engineers 'Which Deals With the Perfotmance of a Converted Petrol Engine
THE latest report of the Automobile Research Committee, which is published in the Journal of the Institution of Automobile Engineers for May, deals with the performance of a converted petrol engine with different producer fuels, the authors being Mr. J. Spiers, M.Sc., and Dr. E. Giffen, Technical Assistant and Director of Research respectively, of the I.A.E. Research Department.
The unit tested was a 6-litre petrol engine with a Government emergency gas producer, the six fuels used comprising anthracite, activated anthracite, low-temperature coke, high-temperature (Birmingham) • coke, activated hightemperature coke and charcoal _ It was found that the easiest starting was attained with charcoal, although 1.t. coke proved little inferior; anthracite was somewhat variable, but usually good in this respect, and activated anthracite showed some improvement in consistency. The h.t, coke, whether activated or not, was poor in this quality, although improvement was effected by pre-heating the air and feeding .water to the tuyere; it
. proved an advantage, to add the water as soon after lighting as possible: Anthracite, whether activated or not, showed serious loss in starting (Frailties when used fuel (bottoms) was mixed with new fuel This deterioration was also shown, although to a lesser degree, with 1.t. coke. The h.t. variety showed na change in starting quality after use.
Power With Various .Fuels .
Using dry blast, the average power given by 100 per cent, new fuel was greatest with anthracite in both qualities, and lowest with h.t. coke, 1.t. coke and charcoal occupying an intermediate position.. Employing the air pre-heater and additional water, brought the power output with h.t. . coke (activated and unactivated) up to the level given by charcoal and 1.t. coke The admixture of Used fuel gave an appreciable reduction with both anthracite and 1.f, coke, h.t. cokes not being affected. Thus, in the 100 per cent. used condition, h.t. coke (with wet blast) gave power equal to that from anthracite and superior to that frOm 1.t. coke. Air pre-heating and water addition had little effect upon the power output with new anthracite, but appreciable improvement with 100 per cent, used fuel.
As regards flexibility, the best was given by charcoal and 1.t. coke, anthracite being the. worst; h.t. cokes with wet blast were superior to anthracite, and activation appeared to be an advantage.
Ttie hydrogen content varied widely with both anthracite and 1.t. coke, and, in practice, it would be difficult to obtain optimum ignition timing under all conditions with these fuels. On the other hand, the content with li.t. cokes and charcoal remained fairly constant, and such fuels may show to advantage under road conditions.
Rate of Fuel Consumption The rate of fuel consumption in pounds per hour varied little with all fuels, including petrol, at the same engine speed, the only exceptions being charcoal, which gave high rates, and the h.t, cokes, if account be taken of the water necessarily used under wet-blast conditions. No clinker trouble was experienced with any of the fuels used, although It, coke caused choking of the filters at frequent intervals, the h.t. cokes giving no trouble in this respect. Another important point was that cylinder wear was not excessive with any of these fuels.
Previous reports on the loss of power involved in the conversion of a petrol engine to producer-gas operation have been concerned with the effect of variations in gas quality, air/gas ratio, volumetric efficiency and ignition timing. The improvement in efficiency and performance resulting from the use of increated compression ratios has also been studied, whilst the effect of additions of petrol in helping to recover lost power has also been investigated.
Throughout these tests, however, the fuel used was anthracite, and a prominent feature of the results was a wide
variation in gas quality occurring during any one test run. This variation was convenient fon Jest purposes as it permitted a study of the effect of wide changes in gas calorific value on engine power, hut such changes are most undesirable under road-operating conditions, as they involve continual adjustment of, the air/gas ratio and ignition timing if maximum output is to be obtained throughout. The highest gas calorific value and engine power occurred with anthracite in the early stages of the run, and for such a short period that it may be considered beneficial to sacrifice performance if gas of uniform quality can be obtained.
interesting Comparative Results
It proved that anthracite-is still the best fuel as regards output, although only by a small margin, and in 100 per cent. new condition charcoal, It. coke and h.t. coke (with wet blast) give practically the same power. With any admixture of used fuel, h.t. coke becomes superior to the 1.t., and in 100 per cent. used condition there is no appreciable difference between h.t. coke and anthracite, unless pre-heater and .water addition be used with the latter, when it again shows slight superiority.
As regards engine flexibility, charcoal and 1.t. coke showed appreciably shorter recovery times after a shutdown period than did the h.t. cokes and anthracite; in fact, the last named was worst in this respect, for during the whole of the shut-down period the air control had iiadually to be closed in order to keep up engine speed. With all other fuels this was required only when the shut down' period exceeded about 20 minutes. Activated h.t. coke war the only fuel tested v Inch did not require adjustment of air control during the shut-down period.
An interesting result was obtaired from anthracite when used with water addition in the•producer equipped with the pre-heater. Although the air control required adjustment, this was neither so frequent nor so drastic as with dry blast; thus the performance under variable load is appreciably improved.
Hydrogen's Effect on ignition
Tests of the influence of hydrogen content on ignition timing to,give maximum power showed that, compared with the timing giving such power on petrol, the variation is small over the engine speed range. It sh,ould be pointed out that with petrol the advance is limited at all speeds by the onset of detonation, whereas with producer gas this does not occur. Only with hydrogen contents of the order of 15 to 20 per cent, is thq ignition timing with producer gas comparable with that for petrol, and for the more usual content of about 7 per cent., timing must be advanced from 6 to 15 degrees (crankshaft) as compared with that for petrol, if maximum power is to be obtained.
Little difference was found between the' fuels as regards consumption, and between them and petrol on a weight basis, except charcoal, which was much higher, but the total weight of fuel and water consumed becomes considerably higher for lit., cokes.
As regards oil viscosity, this increased after running for only a comparatively short time on producer gas, and increased with further running, irrespective of the fuel used. It was more pronounced at low than at high temperatures. The ash content of the oil also increased progressively with the running period.
In general, the mechanical condition of the engine remained good throughout the test period, and at the end a check test run on petrol showed a power output only slightly below that given on this fuel at the beginning of the period covered by the present report; the loss amdunting to only some 2 lb. per sq. in. b.m.e.p. throughout the speed range, although the engine had run for 333 hours-on the test bed and had not been stripped for top overhaul for 83 hours. Pistons and rings were in excellent condi. tion. There was no scoring. of the former, and the bearing surfaces of the rings were highly polished.