buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

178 Vasile Gabriel Nenerica et al.
i) To raise fuel pressure to a specified value and to spray into the
combustion chamber so that air and fuel mixture is as good as possible and
combustion is more complete.
ii) Fuel injection-start at some point and finish within a well established
time.
iii) Fuel-injection to be made in accordance with the engine combustion
process in terms of position and shape of the jet.
iv) To inject an appropriate amount of fuel to the engine load at any time.
Since fuel injection should be done with great precision, both in volume
and time, and at a very high pressure, it is required that the clearances among
moving parts that are pumping circuit be very small (1-3 microns). This leads to
the need of a better execution of the pumping element , the relief valve and the
spray especially with the highest precision encountered in engineering. As a
result, size, shape and mutual position deviations of these parts work surfaces
are prescribed and produced in very tight limits, and the same surface roughness
is very small that the injection equipment is manufactured at high precision,
which requires special attention from the operation and repair units.
Fuel injection equipment is made up, in the order passed through by the
fuel, of the following: fuel tank, fuel pump, low pressure pipes, filter battery
(pre-cleaning filter and final filter), the injection pump with regulator, high
pressure pipes, injection and spraying.
The main functions of the high pressure system are provided by the high
pressure injection pump. Thus, the pressure of injection, the dosage amount of
fuel per cycle and cylinder, the injection advance, as well as the optimum
injection characteristics during injection are achieved by the injection pump.
Injection pumps are classified according to several criteria:
І. Depending on the service cylinder engine there can be distinguished:
a) individual pumps;
b) injector pump;
c) rotary distributor pumps;
d) pump line, characteristic of this class is that each cylinder of the
engine is served by one outlet item.
II. After dose adjustment method of diesel:
a) invariable aspiration and partial discharge (eg, piston pumps, gate);
b) variable intake and total discharge (rotary distributor pumps);
III. By mode of operation of the pumping element:
a) mechanical (cam);
b) electromagnetic actuator;