This high pressure fuel is then introduced into a commutator head or distributor assembly that diverts it to the proper injector and cylinder according to the engine firing order. A solution to this problem is the distributor pump, where one central pumping element is used to produce the high injection pressure. The cost of such fuel systems is rather high and is difficult to justify especially in small passenger car size engines. This high precision machining is required throughout the mechanical components of the injection system to maintain accurate metering and injection timing within 1° crankangle. High pressure pumping elements consisting of plunger and barrel combinations are made of high strength tool steel and extremely close tolerances are kept between the sliding/rotating parts.
Since the unit pump system uses a separate pump for each cylinder, this configuration falls in fact somewhere in between the P-L-N and the unit injector systems we will discuss the unit pump system in the Unit Injector/Pump paper.
Each unit pump is installed on the engine in close proximity to the cylinder it serves and is driven by the camshaft of the engine. In older versions of these engines, unit pump systems were used to maintain short injection lines between the pump and injector.
Examples of this type of application include the DDC/MTU Series 2000 and MTU/DDC Series 4000 engines. This is the case in large marine and stationary power plants where the sheer size of the engine prohibits the use of short injection lines. In some cases, the shortest possible line may still be too long for an in-line pump to operate effectively. In their attempt to minimize complications from line dynamics, designers strive to keep the total line length as short as possible. With highly pulsating systems and pressure waves traveling through narrow pipes, line dynamics can be difficult to manage and may cause erratic injection behavior at the nozzle. Engine and fuel system designers strive to have the pump location such that all of the injection lines are equal in length between the injection pump and the entry to the injectors. The pump is usually gear-driven by the crankshaft and is positioned in a central location relative to the engine assembly. In-line pumps, serving multi-cylinder engines, house as many pumping elements as there are cylinders in the engine. Most P-L-N systems can be classified into three categories, based on the type of the injection pump, as follows:
A variety of P-L-N configurations have been developed, with different technical and/or economic justifications. The pump-line-nozzle injection system is so-called for producing high fuel pressure in a pumping element, transferring the fuel pressure pulse through a high pressure injection line, and then spraying this fuel into the cylinder via the nozzle of an injector. Due to its historical significance, knowledge of the P-L-N system is essential for understanding the principles and the ongoing evolution of the diesel injection system. While the P-L-N system has been displaced by common rail and unit injector type fuel injection systems in new engine designs for markets with the most stringent emission standards, this fuel system does remain popular in markets with less stringent emission standards. The pump-line-nozzle (P-L-N) system, also called the pump-pipe-nozzle system, was for many decades the dominant type of diesel injection system in practically all diesel engine applications. Electronically Controlled P-L-N Systems.The P-L-N system is being displaced by other fuel injection system types in new engine designs. In newer versions, a number of parameters are controlled electronically. In its “classic” version, the system is controlled mechanically through specialized components such as the governor. The P-L-N system can utilize in-line, distributor/rotary, and unit injection pumps. Abstract: In pump-line-nozzle (P-L-N) diesel fuel injection systems, the pump is connected with the injection nozzle through a high pressure fuel line.