**2. The background of fuel injection process and its impact on combustion**

Obtaining the desired operational engine parameters like break mean effective pressure (BMEP), overall engine efficiency, or environmental indexes (exhaust emissions, noise), essentially depends on the combustion rate, and previously on formation of flammable mixture. It particularly comes true in case of a direct injection engine. As far as a quality of combustible mixture is concerned, both the appropriate fuel atomization and fuel mixing with the air charge is important here, just as the precise metering of fuel amount injected in every cycle, and providing equal amounts of fuel for each cylinder of the engine. In direct injection engines, a fuel injection system has the main responsibility for creating proper fuelair mixture, which can be characterized by an appropriate macro- and microstructure. Air swirl has a minor importance here, or even can make the whole process worsened due to cylinder wall wetting possibility.

On the whole, the mere combustion process is sensitive to many factors which may be classified into four groups (Wajand, 1988):


These considerations indicate that the fuel injection parameters are important factors affecting combustion process and consequently the engine parameters, what has been also verified by experimental studies (Kuszewski & Szlachta, 2002; Zabłocki, 1976).

A process of fuel injection into the engine cylinder might be described by parameters related to injection rate and spray characteristics. The set of injection rate parameters consists of:


Presently, the pressure-accumulative fuel systems with electronically controlled injectors are widely used, e.g. Diesel common rail (CR) one. In such systems, the injection rate essentially depends on two parameters: the shape of electrical signals in the injector and the hydraulicmechanical characteristic of the injector. The change of pressure in the fuel storage is so small and affects fuel injection rate so little that it can be neglected in simulation works on engine operation.

The fuel spray characteristics may be described by the following parameters:


68 Fuel Injection in Automotive Engineering

methods allow boundary-free analyzing and may narrow the range of further experiments.

Fuel injection in combustion engines belongs to the most important working processes. Particularly, in direct injection (DI) engines, both gasoline and diesel one, it truly triggers and controls combustion, influencing all output engine performances together with exhaust emissions. Thus, improving of combustion engines should always consider fuel injection optimization, before other kinds of engine processes are being tested. Techniques harnessing mathematical simulations are the good ways to do this in the first stage. Such approach will

**2. The background of fuel injection process and its impact on combustion** 

Obtaining the desired operational engine parameters like break mean effective pressure (BMEP), overall engine efficiency, or environmental indexes (exhaust emissions, noise), essentially depends on the combustion rate, and previously on formation of flammable mixture. It particularly comes true in case of a direct injection engine. As far as a quality of combustible mixture is concerned, both the appropriate fuel atomization and fuel mixing with the air charge is important here, just as the precise metering of fuel amount injected in every cycle, and providing equal amounts of fuel for each cylinder of the engine. In direct injection engines, a fuel injection system has the main responsibility for creating proper fuelair mixture, which can be characterized by an appropriate macro- and microstructure. Air swirl has a minor importance here, or even can make the whole process worsened due to

On the whole, the mere combustion process is sensitive to many factors which may be

physical and chemical properties of fuel, e.g. fractional and chemical composition,

structural properties of the engine, e.g. combustion chamber shape, main engine

operation and regulation conditions of the engine: rotational speed of the crankshaft,

 fuel injection system layout that generates fuel delivery process with the specific fuel spray parameters; it influences directly combustion rate, as is discussed above.

These considerations indicate that the fuel injection parameters are important factors affecting combustion process and consequently the engine parameters, what has been also

A process of fuel injection into the engine cylinder might be described by parameters related to injection rate and spray characteristics. The set of injection rate parameters consists of:

verified by experimental studies (Kuszewski & Szlachta, 2002; Zabłocki, 1976).




cetane/octane number, temperature of fuel (auto)ignition, etc;

dimensions, compression ratio, materials used, etc;

engine load, ignition (or start of injection) timing, etc;

They are also much more time and cost-efficient than test bed investigations.

be shown further.

cylinder wall wetting possibility.

classified into four groups (Wajand, 1988):


Preparation of flammable mixture in a direct injection engine becomes involved not only with strategy of fuel delivery, but also with areal distribution of fuel in the cylinder space. It should be noticed that a lot of factors influencing the fuel injection rate also plays an important role in fuel atomization quality, resulting in fuel mixing with air inside the cylinder.
