Increasingly higher demands are being placed on modern diesel engines. The focus is not only on exhaust emissions but also on increasing environmental awareness and the demand for increasingly better economy and enhanced driving comfort.
This requires the use of complex injection systems, high injection pressures and accurate fuel metering by fully electronically-controlled systems.
The high injection pressures convert the fuel, via the injector nozzle, into tiny droplets, which, again due to the high pressure, can then be optimally distributed in the combustion chamber. This results in fewer unburned HC (Hydrocarbon)s, less CO (Carbon Monoxide) and fewer diesel exhaust particulates being produced in the subsequent combustion stage.
In addition, the optimized mixture formation reduces fuel consumption.
Diesel knock caused by the combustion process of an engine with direct injection is significantly reduced by means of additional pilot injection (pilot injection). NOX (Oxides Of Nitrogen) emissions can also be reduced by using this method.
Demands for better driving comfort also influence the requirements placed on today’s diesel engines. In particular, the importance of noise and exhaust emissions continues to increase. This leads to increased demands being placed on the injection system and its control, e. g.:
• high injection pressures,
• shaping of injection timing characteristics,
• pilot injection,
• injected fuel quantity, start of injection and boost pressure values adapted to every operating condition,
• load-independent idle speed control,
• closed loop EGR (Exhaust Gas Recirculation),
• low injection timing and injected fuel quantity tolerances and high degree of precision for the entire service life,
• options to interact with other systems, such as the lectronic Stability Program, PATS (Passive Anti-theft System),
• comprehensive diagnostic facilities,
• substitute strategies in the event of faults.
The common rail injection system has a large range of features to meet these demands.
In common rail injection systems, pressure generation is separate from the injection process. The injection pressure is generated independently of engine speed and injected fuel quantity.
With this type of diesel injection or engine management system, the driver does not have a direct influence on the quantity of injected fuel, because, for example, there is no mechanical connection between the accelerator pedal and the injection pump. Here, the injected fuel quantity is determined by various parameters. These include:
• driver demand (accelerator pedal position),
• operating state,
• engine temperature,
• effects on exhaust emissions,
• prevention of engine and transmission damage,
• faults in the system.
Using these parameters, the injected fuel quantity is calculated in the PCM and fuel injection timing and injection pressure can be varied.
The fuel is metered fully electronically via piezo elements controlled by the PCM which are located directly in the fuel injectors.
The fully electronic diesel engine management system features a comprehensive fail-safe concept (integrated in the PCM software). It detects any deviations and malfunctions and initiates corresponding actions depending on the resulting effects (e.g. limiting the power output by reducing the quantity of fuel).