Fuel Density Compensator

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 full-load 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

pump.

(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

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