The higher the viscosity of the fuel, the more trouble that 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 constant. This will cause a pressure differential that increases proportional with viscosity, in turn, causing the piston to seek a position in its bore that becomes higher as viscosity increases.

The upward movement of the servo piston will move a wedge-shaped moveable plate, which will decrease fuel delivery. A lower viscosity fuel will cause the piston to move downward, causing the pump to increase fuel delivery.

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.

Q10. For what does MITAC stand?

Q11. In a sleeve metering injection system, at what rate does the constant bleed valve return fuel to the fuel tank?

Q12. In a sleeve metering injection system, where is the automatic advance unit mounted?

Q13. In a scroll metering fuel system, where is the transfer pump located?

Q14. What three rotating members revolve on a common axis within a distributor-type fuel injection system?

Q15. In a distributor-type fuel injection system, what controls the maximum amount of fuel that can be injected?

Q16. What component maintains fuel pressure in the DB2 governor housing?

Q17. At what pressure range does the relief valve on a Detroit diesel engine bypass fuel back to the inlet side of the fuel pump?

Q18.What type of injector is used in a Detroit diesel engine?

Q19. What number of crankshaft revolutions is required to time all the injectors in a two-cycle Detroit diesel engine?

Q2O. On a Cummins engine using a PT fuel system, what device is used to control exhaust smoke during acceleration?

Q21. How is the PT pump timed to the engine?

Q22. On a Cummins engine that has a Celect system, the ECM determines engine idle speed at start- up, based on data relayed by what sensor?

Q23. On a Cummins engine that has a Celect system, the gear pump delivers fuel to the fuel manifold at what pressure?

Q24. In the Celect system, what component within the injector receives signals from the ECM that controls the start of injection?

Q25. What type engine uses an American Bosch fuel injection system?

Q26. What device used with the PSB American Bosch fuel injection pump allows the use of fuels with different viscosities and heat ranges?

SUPERCHARGERS AND TURBOCHARGERS

LEARNING OBJECTIVE: Describe the operation of and the differences between superchargers and turbochargers.

Supercharging and turbocharging is a method of increasing engine volumetric efficiency by forcing the air into the combustion chamber, rather than merely allowing the pistons to draw it naturally. Supercharging and turbocharging, in some cases, will push volumetric efficiencies over 100 percent.

SUPERCHARGERS

A supercharger is an air pump that increases engine power by pushing a denser air charge into the combustion chamber. With more air and fuel, combustion produces more heat energy and pressure to push the piston down in the cylinder. There are three basic types of superchargers: