Chapter 4 Principles of Engine Operation 81 Copyright Goodheart-Willcox Co., Inc. Types of Fuel Injection Systems Diesel engines are equipped with one of seven dis- tinct types of fuel injection systems: ❑ Individual pump systems. ❑ Multiple-plunger, inline pump systems. ❑ Distributor pump systems. ❑ Pressure-time injection systems. ❑ Unit injector systems. ❑ Hydraulic electronic unit injector systems. ❑ Common rail injection systems. Individual Pump Systems In an individual pump system, a small pump, which is contained in its own housing, supplies fuel to one cylinder, Figure 4-40. Consequently, there is a pump for each cyl- inder. This type of system is found on large-bore, slow- speed, industrial or marine diesel engines and on small, air-cooled diesels. Individual pump systems are not cur- rently used on high-speed diesel engines. However, for a time, some heavy-truck engine manufacturers used indi- vidual pumps with integrated electronic controls. These were referred to as Electronic Unit Pumps (EUPs). Multiple-Plunger, Inline Pump Systems The multiple-plunger, inline pump system uses indi- vidual pumps that are contained within a single injection pump housing. See Figure 4-41. The number of pump plungers in the housing is equal to the number of engine cylinders. The pump plungers in inline pump injection pumps are operated from a pump camshaft. In a multiple-plunger, inline pump system, fuel is drawn from the fuel tank by a fuel supply or transfer pump, passes through primary and secondary filters, and is deliv- ered to the injection pump housing at a pressure between 10 and 35 psi. All individual pumps in the housing are subject to this fuel. Fuel at each pump is timed, metered, pressurized, and then delivered through a high-pressure fuel line to each injector nozzle in firing order sequence. To meet with more stringent emissions standards and performance requirements, multiple plunger, inline pump systems have been adapted for use with various levels of electronic controls. Distributor Pump Systems Distributor pump systems, Figure 4-42, are used on small to medium diesel engines. These systems do not have the capability to deliver sufficient fuel volume or fuel pres- sures for heavy-duty, large-displacement, high-speed diesel engines, such as those used in trucks. Distributor pump fuel injection systems are sometimes called rotary pump systems. Injection pump Figure 4-41. Multiple-plunger, inline fuel injection pump. This pump is used on many mobile applications and is very popular with many engine manufacturers. Delivery valve holder Delivery valve Pump barrel Pump plunger Control rack Control sleeve Plunger return spring Roller tappet Figure 4-40. Individual plunger and barrel pump that is driven off the engine camshaft. These are found on only a few small and very large diesel engines. Hydraulic head Figure 4-42. In a distributor fuel injection pump (cutaway shown), a single pumping element dispenses fuel to all injec- tors. (AMBAC International)