The EFI control system 10 is disclosed in conjunction with a compression ignition engine 12 where the parameters of fuel quantity and injection timing are controlled on the basis of a plurality of engine operating conditions. The parameter of fuel quantity is obtained from a comparison of com-puted values of percent load fuel quantity and full load fuel quantity with the lesser of the two being selected. The percent load fuel quantity has a proportional component that is a function of actual engine speed and commanded engine speed , and an integral component that is related to cumulative speed error The full load fuel quantity is a function of actual engine speed and manifold air density The parameter of injection timing is obtained from a summation of two computed quantities for injection advance. One quantity is a function of actual engine speed and the selected fuel quantity
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Bentley term their Bentayga diesel simply Diesel Principles[ edit ] Diagram of the common rail system Solenoid or piezoelectric valves make possible fine electronic control over the fuel-injection time and quantity, and the higher pressure that the common rail technology makes available provides better fuel atomisation.
To lower engine noise , the engine's electronic control unit can inject a small amount of diesel just before the main injection event "pilot" injection , thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.
While these older systems provide accurate fuel quantity and injection timing control, they are limited by several factors: They are cam driven, and injection pressure is proportional to engine speed. This typically means that the highest injection pressure can only be achieved at the highest engine speed and the maximum achievable injection pressure decreases as engine speed decreases.
This relationship is true with all pumps, even those used on common rail systems. With unit or distributor systems, the injection pressure is tied to the instantaneous pressure of a single pumping event with no accumulator, thus the relationship is more prominent and troublesome.
They are limited in the number and timing of injection events that can be commanded during a single combustion event. While multiple injection events are possible with these older systems, it is much more difficult and costly to achieve.
This characteristic results from "dumb" injectors in the cylinder head which open and close at pressures determined by the spring preload applied to the plunger in the injector. Once the pressure in the injector reaches a predetermined level, the plunger lifts and injection starts. The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure.
This accumulator supplies multiple fuel injectors with high-pressure fuel. This simplifies the purpose of the high-pressure pump in that it only needs to maintain a target pressure either mechanically or electronically controlled. The fuel injectors are typically ECU-controlled. When the fuel injectors are electrically activated, a hydraulic valve consisting of a nozzle and plunger is mechanically or hydraulically opened and fuel is sprayed into the cylinders at the desired pressure.
Since the fuel pressure energy is stored remotely and the injectors are electrically actuated, the injection pressure at the start and end of injection is very near the pressure in the accumulator rail , thus producing a square injection rate. If the accumulator, pump, and plumbing are sized properly, the injection pressure and rate will be the same for each of the multiple injection events.
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