From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of spray development from a magnetically actuated valve and a jerk-pump system.
| Identifier | ExFiles\Box 158\5\ scan0038 | |
| Date | 22th April 1939 | |
| 534 MAGNETIC INJECTION VALVE Fig. 9. The spray from a magnetically actuated spray valve. Showing the development of the spray as an average of several hundred injections. Effect of Operating Characteristics on Fuel Injected The fuel injected per cycle from the magnetically actuated spray valve should be proportional to the charge in, and the rate of discharge of, the condenser, according to the electrical analysis of the circuit. Fig. 11 shows the influence of pressure on the weight of fuel discharged for condenser capacities of 600 to 1300 mf. With constant fuel pressure, the quantity discharged increases with increase in the condenser capacity to 1100 mf., after which it is constant. For constant condenser capacity above 800 mf., and oil pressure to 4000 lb. per sq. in., the quantity of fuel discharged increases approximately as the square root of the pressure. With condenser capacities of 600 mf., the influence of fuel resistance on the valve is noticeable, in that the quantity discharged is maximum at a pressure of 2500 lb. per sq. in. These variations are of little importance to good engine operation, since the pressure for any system is constant and the charge of the condenser is manually controlled. The effect of engine speed (or injections per minute) on the rate of discharge when the pressure is held constant is shown in Fig. 12. With low condenser charge, the quantity injected decreases with increase in engine speed. Since the condenser charge is constant, this decrease was undoubtedly due to the disturbance set up in the oil by the plunger motion. Since the needle does not move its maximum allowable distance at low condenser capacity, the increased turbulence in the valve would tend to reseat the needle, thus decreasing the charge with increased engine speed. At higher condenser capacities the charge is independent of speed over the range tested. injections develop identically, then a group of photographs at uniform intervals of cam angle should appear as the development of a single spray photographed with a high-speed motion-picture camera. The results of such an investigation are shown in Fig. 9 for a cam speed of 600 r.p.m., 1300 mf. condenser capacity and 2100 lb. per sq. in. oil pressure. Certain characteristics can be followed through the development, indicating that the spray is reproducible. Furthermore, the penetration is uniform to the point of cut off, after which there is a decrease in tip velocity, due to the interruption of the core. In contrast to the spray from the magnetically actuated valve, Fig. 10 shows the spray development from the nozzle in a jerk-pump system. The nozzle orifice and conditions of operation were the same as for the magnetically actuated valve, i. e.{Mr Elliott - Chief Engineer}, orifice diameter 0.022 in.; nozzle opening pressure, 2100 lb. per sq. in.; pump speed, 600 r.p.m., and pump rack setting for the same quantity of oil as delivered with the magnetically actuated valve. A fuel line 20 in. in length connected the nozzle to the pump. The influence of the dynamics of the system are evident in the successive sprays. Bouncing of the needle, possibly due to the surges in the fuel line, are particularly evident in frames 3, 4, and 8. Several frames show exceedingly small quantities of fuel in the charge, indicating that although the nozzle opening pressure is set at 2100 lb. per sq. in., the actual pressure in the fuel line may be much less, or that the pump does not deliver identical quantities during successive strokes. The investigation shows very definitely that the spray from a jerk-pump system is not reproducible and that it is impossible to handle small quantities of fuel with the regularity obtained with the magnetically actuated spray valve. Fig. 10. The spray from the nozzle in a jerk-pump system. Showing the development of the spray as an average of several hundred injections. April 22, 1939 Automotive Industries | ||