Research Improves the Breed of Oil Engines
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TO know what goes on inside the combustion chamber before, during and after the explosion; to know, factually, what happens to the piston, connecting rod and crankshaft as the result of the performance of the engine cycle; to discover the effects of these happenings on the metals of the cylinder, valves, pistons and other parts —these are the ambitions of the research engineer in every branch of automobile engineering.
After years of experiment in these directions, F. Perkins, Ltd., Peterborough, has established a completely up-to-date research department, known within the establishment as the "Technical Department" and under the direct control of Mr. Frank Perkins, chairman and managing director. Mr. M. Vulliamy supervises research and Mr. W. Spoor design and development.
Special Requirements
The problem that the depahment has tried to solve has not been so much that of finding equipment, as of adapting and improving what is available to meet its special and peculiar needs. The Perkins high-speed oil engine is unusual in several of its fundamental features, and the nature of the research has been correspondingly affected.
An outstanding achievement in instrument building is one which is almost a test laboratory in itself. Its technical description is "a two-channel recording zathode-ray oscillograph with additional time and event marking tube and separately visibly 6-in. monitor cathoderay tube." This is an unique machine and has been specially built to the research department's own design.
It can register and record pressure variation from as little as 1/200 lb, per sq. in. up to 20 tons per sq. in. In any particular investigation the variations are shown on the cathode-ray tube and can at the same time 'be photographically recorded on.a time base of 1/10, 1/50, 1/200 or 1/1,000 second. Variation of pressure in the combustion chamber—at one end of the scale—and
the almost imperceptible variations in pressure within the crankcase, caused by slight piston blowby, may be recorded on the film or measured on a sensitive meter.
The same apparatus can be used for recording engine noises or vibrations, Employed in conjunction with the now familiar wire-resistance strain gauges, it can also record stresses and strains in any part of the engine.
The facility for recording these functions and effects on a widely varying time base is immensely valuable. Variations in pressure, vibration and stresses can be measured with extraordinary accuracy.
There is, of course, the further advantage in these photographic records, that they are available always for comparison with subsequent records.
The cathode-ray osciliograph is also used for the measurement of torsional vibration of crankshafts. A seismic electro-magnet pick-up is employed. It is mounted on a calibrating rig and provides high-frequency angular variation of known amplitude.
One of the most important quantities to measure in internal-combustionengine research is the amount of air taken in by engines and consumed. On this the power which can be obtained from an engine mainly depends.
For this purpose calibrated noizles are used. The drop in pressure of the air being drawn through by the engine under test is a measure of the rate of air flow. Another piece of equipment measures the air being burned, Meters
sensitive to a much smaller gas flow are used to measure the amount of blowby in engines.
For determining the best shapes of the air passage in a cylinder head to provide air circulation in the cylinder, a rotating vane anemometer is used, in conjunction with a stroboscope. Several devices have been produced to investigate the efficiency of combustion in high-speed oil engines. One indicates variations of fuel-air ratios inside the combustion chambers. A chemical mixed with the fuel causes deposits to be made, which vary according to the air-to-fuel ratio in different parts of the combustion chamber.
Exhaust Density Measured The research section has also designed and constructed meters for measuring the exhaust-smoke density of engines on the production test beds.
An important factor in ensuring uniformity of engine performance s exactitude in dimensions of atomizer spray holes. A metering device h is been devised of a type suitable to check these dimensions in the special two-jet atomizers used in the Perkins engine.
Two features are common to all these pieces of equipment. They are (a) he universal use of electricity, in one form or another, as a means for testing, observation and record: and ibt the provision for remote indication sf whatever is going on. The engine tester is able to sit in a sound-proof cabin and check performance. free from the disturbances of noise, smell, etc., inseparable from the running of an internal-combustion unit.
The foregoing are the highlights of an interesting demonstration of up-iodate research laboratory equipment. In all there are 32 separate items.