Diesel engines used in passenger cars in recent years have undergone major changes, these basically aim to have a cleaner engine in pollutant emissions according to standards established for these engines, in addition to improving performance and smoothness of travel as it is in gasoline versions.
Manufacturers have allocated resources, incorporating new technology to the engine, both in the mechanical part,
injection system and electronic management. This has resulted in most brands today having diesel engine versions.
Oblivious to this change by building indirect injection engines that meet the current standard of our market and direct injection engines,
Engine that has been developed more since there are two variants:
- TDI Engines
- SDI Engines
The SDI version is only available in four-cylinder engines, however the TDI version is available in three-cylinder engines, four-cylinder engines, V6, V8 and currently the engineering flagship VW the V10.
The injection system used for these engines are.
- Rotary pump
- Pump Injector
- Common Rail
Aims and Objectives:
- Classify and analyze the different diesel engine injection and management system
- Diagnose possible breakdowns that may occur in these systems
- Master the methodology for repairing breakdowns.
Diesel engines work according to the combustion method:
- Through the compression work of a piston, the air contained in a cylinder is heated so strongly that it quickly exceeds the ignition temperature of the fuel used. Compressors in modern diesel engines reach values of between 30 and 60 bar and the compressed air is heated to temperatures of between 700 and 900 degrees Celsius.
- Under these conditions, fuel is introduced into the heated air as finely dosed as possible, thus obtaining a rapid gasification and on the other hand starts its self-ignition.
- The pusher piston receives the pressure of the heat generated in the combustion, which forces it to generate work.
This description is still valid today for currently manufactured diesel engines. Compared to the gasoline engine, diesel has the great advantage of being more effective. It can convert into power up to 40% of the energy potentially contained in diesel. The gasoline engine reaches only 30%.
The disadvantage is that originally these engines were heavy, slow and noisy, characteristics that made them only be used in industrial engines and heavy vehicles.
Over time these drawbacks have been significantly reduced being widespread use of these engines in passenger cars.
Types of Diesel Engines
Unlike the petrol engine, in diesel the mixture is always formed in the combustion chamber. The configuration of the combustion chamber is therefore a decisive feature for the engine power. There are many variants, but two versions are generally used.
- Indirect injection
In indirect injection, fuel is injected into a chamber in the cylinder head. (e.g. turbulence chamber, pre-chamber).
This chamber is connected to the cylinder via a small channel.
When the air is compressed, part of it goes up through the duct to the pre-chamber, producing a high turbulence. As soon as the fuel is injected, combustion begins in the pre-chamber. Through the pre-chamber pipe, combustion propagates to the cylinder.
The advantage of this system is that in the pre-chamber there are greater turbulences that provide a good mixture of fuel and air. In this way a more progressive combustion is possible, thus reducing vibrations and noises.
- Direct Injection
In these systems the fuel is injected directly on the piston head where the combustion chamber is carved.
Thanks to the compact combustion chamber, a better use of the fuel energy and therefore a lower consumption is achieved.
A disadvantage of this system is that when the pressure increases very quickly after ignition, the typical noises of a diesel engine are produced. In order to reduce noise in passenger cars, a number of additional design measures have been developed, such as the spiral inlet channel for finer mixture formation.
Types of direct injection used
Three different injection systems are currently used in direct injection engines:
- Rotary pump system.
- Pump injector system.
- Common Rail System.
Rotary pump system
The pump sucks the fuel from the tank, creates the high injection pressure and distributes it to the injector of each cylinder via pipes.
Basically we have two types of pumps. The VP 37 for four-cylinder engines (both TDI and SDI) and the VP 44 for V6 engines.
The two pumps generate and distribute the high injection pressure to the cylinders, the internal difference lies in the way the pressure is generated and the amount of fuel to be injected is regulated.
The VP37 generates approximately 950 bar, while the VP44 generates 1200 bar. In addition, the dosing unit is regulated by means of a servo motor in the first one and a solenoid valve in the second one.
System with injector pump
Each cylinder has its own pump, so the injector and the pump are one piece. The camshaft, via a special cam, pushes a piston into the injector and thereby creates the injection pressure. The pressure is up to 2050 bar.
A pre-pump and a fuel distribution line to the injectors complete the system. Each injector pump has a solenoid valve, which is electrically excited by the engine control unit, in order to regulate the amount of fuel to be injected into each cylinder, as well as to determine the timing of injection.
Common Rail System
Common Rail is also referred to as an accumulator injection system.
Pressure generation and fuel injection are carried out separately in the Common Rail system.
A separately housed high-pressure pump generates a continuous pressure. This pressure is built up in a pipe (Rail) and supplied to the injectors via short injection tubes.