PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 1
parts. It should be noted that there are no adjustments necessary to the
engine when changing from one fuel to another.
f. Fuel Density Compensator. The multifuel engine operates on a
variety of fuels, with a broad range of viscosities and heat values. These
variations in the fuels affect engine output. Because it is unacceptable
for the power output of the engine to vary with fuel changes, the multifuel
engine is fitted with a device known as a fuel density compensator. The
fuel density compensator is a device that serves to vary the quantity of
fuel injected to the engine by regulating the fullload stop of the fuel
pump. The characteristics of the fuels show that their heat values decrease
almost inversely proportional to their viscosities. The fuel density
compensator uses viscosity as the indicator for regulating fuel flow. Its
operation is as follows:
(1) The fuel supply enters the compensator through the fuel pressure
regulator, where the supply pressure is regulated to a constant 20 psi
regardless of engine speed and load range.
(2) The pressure regulated fuel then passes through a series of two
orifices. The two orifices, by offering greatly different resistances to
flow, form a system that is sensitive to viscosity changes.
(a) The first orifice is annular, formed by the clearance between
the servo piston and its cylinder. This orifice is sensitive to viscosity.
(b) The second orifice is formed by an adjustable needle valve
and, unlike the first, is not viscosity sensitive.
(c) After the fuel passes through the two orifices, it leaves the
compensator through an outlet port. From here, the fuel passes back to the
(3) The higher the viscosity of the fuel, the more trouble it will
have passing through the first orifice. Because of this, the fuel pressure
under the servo piston will rise proportionally with viscosity. Because the
second orifice is not viscosity sensitive, the pressure over the servo
piston will remain fairly constant. This will