NN OIL-ENGINED A.E.C. ON THE ROAD
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Road Test No. 49
DURING the past few weeks public attention has been drawn to the new production-type oil engine made by the Associated Equipment Co., Ltd., Southall, Middlesex. :eaders will recollect that this engine, which is made under .cro licence, possesses the remarkable speed range of 300 r.p.m. ) 3,000 r.p.m.; its maximum is approximately double that of ther well-known types. One of the excellent results of the esign is that the weight-to-power ratiois brought down to he very creditable figure of approximately 14 lb. per b.h.p., he rated output being 95 b.h.p.
.:Last week we were privileged to test a Majestic chassis— hat is, -the A.E.C. sixknner--Worporating one )f these new oil engines. it has been the aim of the technical staff of the A.E.C. to produce an oil engine capable of being substituted for a petrol engine, both as regards general dimensions and performance. . The former is not .a very troublesome matter, but the latter is most decidedly a -difficult task. How well it has been accomplished can be gathered from the following data concerning our test :—
Actually, the machine handed over to us was
the production type chassis, but it had an experimental cab and carried test weights; prior to our trial it had covered-about 5,000 miles on the road in the hands of the experimental department of the manufacturer. The one nonstandard feature was the use of 24-volt lighting and starting equipment, otherwise it was in the form in which it can be purchased for f1,360 as a chassis.
Starting from cold was accomplished by means of the electric motor, following the use of the heater plugs; t h e average time taken for this operation was about 14-20 seconds. When hot, we found that the engine started immediately the switch was depressed and fired on all six cylinders right away. It should be noted that this engine idles at 300 r.p.m., firing on all cylinders; consequently, the running is even, despite the low speed.
On the weighbridge the vehicle was found to weigh 11 tons 3 cwt. 3 qrs. without the personnel, and with the driver and two observers it totalled 11 tons 7 cwt. 2 qrs. Reference to the data in the accompanying panel shows how this total is arrived at.
Next, braking and acceleration trials were carried out. The braking was satisfactory in every way and the results are embodied in a graph. The vacuum for servo application is obtained from an exhauster on the engine, working in conjunction with a vacuum tank on the off side of the chassis. Normally, the gauge recorded 27 ins. of mercury. when running at about 30 m.p.h., and it dropped to 15 ins. after prolonged brake application, so that there was always an ample reserve with the oil-eng-ined A.E.C. After t h e luncheon stop the gauge re-. corded 15 ins., so that it was possible to employ servo braking with a " dead " engine.
With regard to the acceleration, it is interesting to note the straight-line characteristics of the curve for acceleration on top gear. From 8.7 m.p.h. to 26.1 m.p.h. the period occupied was 30 seconds, whilst using the gears (excluding first) the period was'33 seconds for a similar increase in speed.
On the road the speed range proved to be 6.09 m.p.h. to 39.15 m.p.h.—these figures and all Others in this article are corrected for a speedometer error. The final-drive ratio of the chassis was 9.33 to 1; the maximum engine speed was, therefore, in the neighbourhood of 3,000 r.p.m. With themore usual 8-to-1 axle ratio the maximum attained by these chassis is approximately 45 m.p.h.
As regards the general running of the engine the water temperature was 160 degrees F. Over about 15 m.p.h. the engine ran as silently as any petrol power unit and the best results, as regards absence of noise and pulling power, were obtained when the injector control was used identically as a good driver would employ the ignition-advance lever On a petrol motor. Anyone who can handle the more conventional type of vehicle would be able to drive the A.E.C. oil engine immediately and, what is more important, efficiently.
Probably the greatest achievement in connection with the A.E.C. engine is the absence of smoke. After the first few explosions when starting from cold there is no more visible emission from the exhaust pipe than in the case of the A.E.C. petrol engine. This is no doubt due to a combination of causes, such as the drawback of the fuel pump at the end of each delivery stroke, the use of closed nozzles, which are selfcleaning, and to the design of the injector cams. When over-running down Dashwoocl Hill there was not a vestige of smoke to be seen, despite the fact that the engine exerted the sole check upon the chassis, which was
travelling at about 25 m.p.h. The overrunning of the engine forms a most effective brake. It is important to note that the fuel is cut off so soon as the engine reaches 400 r.p.m., when the speed-control pedal is out of action. Therefore, when reaching a hill the driver takes his foot off what is norWally the accelerator pedal, and almost immediately the engine brake operates to the full, because pure air is being passed through the engine and compressed, are no firing strokes.
A defect with some oil engines is that a heavy flywheel and generally heavy rotating components involve a loss of time when gear-changing; with the high-speed A.E.C. engine this is definitely not the case. The delay may be fractionally longer than in the case of a petrol engine, but the gear lever can be operated either for upward or downward changes as quickly as is convenient for the average man.
Of absorbing interest, a course, is the fuel-consumption question. For our trial gas oil was used. Any other clean fuel of somewhere about the same specific gravity—.885,--could be used. We employed a graduated tank in the cab, and it was possible to watch the rate
of consumption closely. We carried out three runs, and the following data reveal that -the fuel consumption is, to a certain extent, dependent upon the road speed:—
Starting from High -Wycombe and travelling towards Oxford, we included the climb of Dashwood Hill; 1.45 gallon was used in covering 8.87 miles, including 1.3 mile in third gear. Despite the long climb of Dashwood the average speed was 22.2 m.p.h. With a 9.3 axle ratio such a rate of travel Involved a high crankshaft speed. The fuel consumption was 6.1 m.p.g. The minimum speed on Dashwood (New Hill) was 18 m.p.h. in third gear.
Turning around and returning to High Wycombe, the same 8.87 miles were covered on .65 gallon on top gear throughout, except at the start, and the cruising speed did not exceed 25 m.p.h., giving an average speed of 19.7 m.p.h. The fuel consumption rate was 13.6 m.p.g.
From High Wycombe to the A.E.C. works was 21.22 miles and the fuel used was 2.45 gallons. The average speed maintained was 21.9 m.p.h. and .8 of a mile in all was covered on third gear. The rate of fuel used was 8.66 m.p.g.
Summarizing these results, we get a consumption of 9.45 m.p.g. at an average speed of 21.26 m.p.h.., third gear being inuse for about 5 per cent. of the distance.
From the foregoing data it will be seen that the engWe is capable of reproducing the performance of a Pet:M.' -engine in a very satisfactory manner. The Majestic chassis proved throughout to be easy to handle, safe and to give easy riding. The petrol engine used in the Majestic has an output of 110 b.h.p.; the oil engine, hoWever, is of 95 b.h.p., but it stands all the more to its credit that such a flexible and comprehensive performance should have been put up by an engine of a smaller output.
The Associated Equipment Co., Ltd., does not claim to have attained perfection with its new oil engine and, whilst commending this modest attitude, we must express our satisfaction with the results obtained.