Promising Producer-gas Tests with
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Compression Ignition
Good Results from ii A.E.C. Operated by Cement Marketing Co., Ltd., Using Pilot Injection of Oil Fuel
CONVERSIONS to producer gas of compression-ignitioe, engines have been made in two ways—by lowering the compression, fitting an electric ignition system and supplying gas and air through a mixing valve of the type used for petrol-engine conversions, or by retaining the high ratio and the injection system, feeding the gas into the ordinary air igtake and injecting small quantities of liquid fuel to ignite the mixture of air and carbon-monoxiae.
Whilst the former appeared to be gaining popularity when producer gas first came into the limelight as a promising solution to the petrol-shortage problems, the latter has certain attractions that might be eipected to put it ahead of the other. Among these may be narged the facts that only minor engine altegations are needed, that reversion to liquid-fuel running can be made at any time, that the gas can be "laced up " with oil fuel for spells of higher power, and that the high thermal efficiency afforded by the high-compression ratio is not sacrificed.
Influended by these considerations, the road transport engineering department of the Cement Marketing Co., Ltd., wishing to investigate producer-gas possibilities for effecting economies in the Consumption of imported oil fuel, embarked upon experiments based on this " pilot-injection " scheme.
An A.E.C.,four-cylindered engine, of 6.6 litres capacity, with Ricardo or swirl-chamber head, was selected for the tests, which were carried out first on a dynamometer. Alteration to the engine involved blanking off the air inlet at the fan end, opening it up at the Olywheel end, and welding on a short stub to facilitate the fitting of the gas mixer.
A third fuel stop was arranged on the fuel-injection pump, giving three positions—idling, minimum and maximum fuel injections the minimum position was, of course, for use with a gaseous fuel mixture. A telescopic pump-control rod was arranged between the cross shaft behind th cylinder and the fuel pump. This telescopic rod was spring-loaded, one way only, that is, to open position. Reverse motion was positive, so that the usual means for stopping the engine could be employed, A control lever and rod were added to the control cross shaft for operating the gas throttle. These were the only alterations necessary to the engine. For the generation of gas, a producer was selected of the typo in which provision is made for variation of tuyere size in conjunction with gas-throttle opening.
Testing operations were begun with a gas mixer similar in design to that generally supplied by producer-plant makers, having air inlets and gas throttle separately controlled. With this arrangement, however, gas production
was poor and starting difficult. Further, power output was low, being only 21 b.h.p. at 1,210 r.p.m. Accordingly, a new gas mixer was designed and made. This was, in • effect, a venturi or choke tube, having a centrally disposed, gas inlet, throttle-controlled, and adjust.
able in relation to the venturi. The air stream was unrestricted, so that, irrespective of the position of the gas throttle, volumetric efficiency was not impaired, thus ensuring that compression pressure was sufficient for the ignition. This is of prime importance. In addition, the oil-engine feature of controlling power output by varying the quantity of fuel admitted was retained, and at all times a clean exhaust was observable.
Gas production improved as a result of this alteration, . and b.h.p. rose to 39 at 1,210 r.p.m., whilst the maximum ' output was 46.6 b.h.p. at 1,600 r.p.m.
' This progress having been achieved, the dynamometer tests were concluded and the apparatus was installed in s four-wheeled lorry for trials on the road. These were of a comparative nature, returns being obtained using gas and liquid together while carrying a load giving a gross weight of 8i tons, and compared with figures obtained from tests on only liquid fuel with a gross weight of 12 tons, We give the results of the former trials, with those serving as a basis for comparison following them in parentheses:— Maximum speed on the level, 22 m.p.h. (35 m.p.h.) hill-climb, 4 m.p.h, in first gear (19 m.p.h. in third gear) ; acceleration in fourth gear' fro,m 10 m.p.h. to 20 m.p.h., 101 secs. (24 sees.); acceleration from rest to 20 m.p.h., 205 secs. (33 secs.) ; liquid fuel consumption rate a.g. 20 m.p.h. 12.2 m.p.g. (7.2 m.p.g.).
As mentioned earlier, the maximum output developed on gas, liquid-fired, was 46.6 b.h.p. at 1,600 r.p.m, This compared with 82 b.h.p. using 100 per cent. oil fuel, at 1,800 Bench consumption tests gave 2.43 pints per hour (for ignition purposes) when running at 1,210 r.p.m. with a 42-1b. brake load. Under the same conditions the consumption with 100 per cent. liquid fuel VMS 11.55 pints per hour. Drawing conclusions from these sets of experiments, the engineer who conducted them makes the following statement:— Firing the as by injecting a small quantity of liquid fuel proved reliable and satisfactory. A gas mixer which does not restrict cylinder filling proved by far the hest apparatus. Better consumption might be obtained if smaller-diameter injection-pump elements were used and if close attention were paid to their calibration at smallvolume injection. He adds that he hopes the experiments may help other investigators in the apelication of gaseous fuel to compression-ignition engines.