Injection Equipment Simplified
Page 62
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IF when the oil-engined tractor was first I introduced, there had been stops and screws on the fuel-injection equipment which could have been adjusted by the " tinkerers " or so-called "Diesel experts," it would have been necessary to supply one service man for each tractor sold. This was the opinion expressed by Mr. C. G. A. Rosen, lvf.E., M.S.A.E., consulting engineer to the Caterpillar Tractor Co., U.S.A., in a lecture on "Significant Contributions of the Diesel Research Laboratory," which was read to the Institution of Mechanical Engineers, in London, last week
Outlining the precepts of desigh necessary for tractor fuel-injection apparatus, Mr. Rosen said that the equipment should be proof against all field adjustments by the operator. Fuel-injection pumps and injectors should be calibrated, timed and set at the factory. and supplied in pack form as service replacements. These units should be as easy to replace as sparking plugs and magnetos in spark-ignition engines.
This is the practice of the Caterpillar company Mr. Rosen briefly described the development of pumps and injectors, and the apparatus used in research In the process of designing the fuel pump, a short groove was ground round part of the periphery above the cut-off spiral of the plunger, which altered the injection characteristics at part throttlz A36 opening. This—he termed it " the idle groove "—had the effect of reducing Diesel knock in a pre-combustion engine.
Transparent cylinder heads had been made to enable the combustion characteristics to be recorded by a Fastax motion-picture camera at 4,000 frames per second.
Fundamental disadvantages were revealed in the Danielsson check valve, which was found, in his observations, to interfere with the injection cycle. it tended to slow down the beginning of the injection, causing either late injection timing at high speeds, or, if that were compensated for, early engine timing at low speeds.
Another disadvantage discovered was interference causing surge in the fuel pressure in the injector pipes. The first surge is sufficient to cause a brief opening of thk injection valve several crankshaft degrees after injection should have been completed. Furthermore, the closing action of the check valve determined the residual pressure. Experience proved that high residual line-pressure preceded a relatively short injectionbeginning lag, whilst a low residual linepressure preceded a relatively long beginning lag.
These objections have been overcome by using a disc-type check valve, which permits the residual pressure to drop well below the injector opening pressure, and it has eliminated the possibility of eight-stroking. This wafer valve is especially beneficial in the precombustion-chamber engine.
Lubrication film on the pistons and rings had been studied visually by fitting the engine with a glass cylinder block, said Mr. Rosen. Using this transparent block in conjunction with a stroboscope and the Fastax camera, a record, had been secured of the retention of oil at the top of the piston. To obtain clarity in the films, the oil was dyed a deep blue.