**1. Introduction**

Current development of automotive industry is conditioned by the minimization of negative effects in relation to the environment. It results from the restrictions regarding exhaust emission limits which are introduced by the consecutive standards but it also guarantees market success of a given vehicle. Research carried out regarding customer preferences in UE countries have confirmed that during the purchase of a car they make decisions based on vehicle's ecological properties and the safety of use in road conditions. Next follow such criteria as performance and durability, which has so far been dominant. The obtainment of desirable operational indices by diesel engine depends to a high degree from the injection systems applied in these engines.

The recent years show the gradual and conspicuous progress in the development of structures and methods of control of injection systems in high-speed diesel engines designed for heavy duty vehicles. The stimulation of such progress is forced by the legislative norms and the market, as it often happens to technical equipment. In case of high-speed diesel engines these are the multi-aspect law regulations concerning overall environment impacts: the emission levels, noise spectrum and recycling compliance. On the other hand, the vehicle users expect the further minimization of operating costs, expressed mainly by the reduction of fuel consumption, maintaining the vehicle dynamic properties at the same time. The above circumstances caused significant acceleration of research and development work related to high-speed diesel engines. The improved environmental and operating parameters are determined by the process of formation and combustion of the fuel-air mixture. The process of creating the proper macro- and microstructure of the mixture is significantly affected by the fuel injection system; therefore the progress in this field is most conspicuous.

### **2. Requirements towards high-speed diesel engine injection systems**

The operation of the piston combustion engine consists in the transformation of the chemical energy contained in the fuel supplied to the combustion chamber into the mechanical work received as the torque on the crankshaft end. In order to perform the chemical transformation into the mechanical work in a high-speed diesel engine, one should:

A Look at Development of Injection Systems

accumulation systems usually exceeds 160 MPa.

**3. Diesel injection systems development forecasts** 

the reduction of CO2 emission – the supposed greenhouse effect cause.

the noise NOx and smoke emission can also be reduced.

for High-Speed Direct Injection (HSDI) Diesel Engines 3

common-rail system. It is pressure-accumulation system, where the fuel pumping process is functionally separated and does not affect an injection rate. Thus, the accumulation systems provide a flexible rate of injection at the request of a particular engine design and the amount of fuel injected. They allow a freely-set multiple injections towards lowering noise level of the engine and reduction of the exhaust emissions. The pressure obtained in the

Everything indicates that the development of high-speed diesel engines in the nearest future shall still be determined by the gradual reduction of the exhaust emissions and reduction of noise, together with a simultaneous increase in fuel economy. These trends concerning the exhaust emissions reduction since the introduction of Euro 1 standard can be illustrated by the consequent Euro levels. The data analysis proves the dramatic changes in legislation limitations within relatively short time intervals. Obtaining a reasonable compromise between fuel economy and exhaust emissions, particularly in the scope of NOx and PM emission, is the most difficult challenge at present. Fuel consumption restriction is related to

The further simultaneous reduction of fuel consumption and pollutant contents in the exhaust gases may only be achieved through the introduction of state-of-the-art supply systems combined with the change of the rate of the combustion process. The leading automotive manufacturers carry out intensive work on reduction of power losses and achievement of general efficiency of diesel engines approaching 50%. Reduction of friction and thermal losses is very important for decrease of fuel consumption and the level of exhaust emissions, nevertheless the optimum rate of the combustion process shall always remain decisive for obtaining the demanded results. Therefore, the present works concentrate mainly on the issues related to examine as many physicochemical phenomena conditioning the proper combustion as possible. The theoretical analysis and experimental research indicate that the nature of the rate of the combustion process should be conspicuously modified. Providing the desired heat release rate is principally conditioned by the rate of the injection process, controlled by the injection systems. The application of a multiple injection is necessary here. At present, a standard five-phase fuel injection is applied. Each phase performs a specific function before and after the main injection. The pilot injection affects the noise reduction due to the reduction of the combustion pressure acceleration dp/dφ. The pre-injection intensifies the combustion of PM particles in the filters, whereas the secondary injection increases of NOx conversion in the DENOx catalytic reactor. Particularly the pilot injection and its time interval from the beginning of the main injection is significant for the combustion process. Due to the required limits in pressure growth and heat release rate during the initial combustion phase, especially at partial loads,

The multiple fuel injection strategy requires the application of fast, new generation injectors. At the present stage of development such injectors are piezoelectric driven. They are characterized with shorter time of response than the electromagnetic injectors. The short response time enable to perform the multiple injections with very low level of fuel amount dispersion and with more accurate timing. Another characteristic of a piezoelectric injector are its much smaller dimensions. The further development of piezoelectric injectors (labeled


The supply of fuel in an appropriate amount and its penetration and distribution inside the combustion chamber are included in the injection system task. It directly creates the quality of the mixture prepared and the rate of the combustion process, which in turn translates into operating and environmental parameters as well as the engine operation economy. Out of the numerous factors influencing the quality of the combustible mixture preparation and the proper combustion that are directly dependent on the injection systems, the following can be enumerated:


The significance of the factors varies and is mainly related to the injection system (indirect of direct injection), type of combustion chamber and requirements related to a specific engine type. The optimization of the high-speed diesel engines requires the matching of the injection system parameters to the loads and engine speeds, inherently related to the operation of traction engines and varying in real time. The accomplishment of this task requires precise control over the injection process and the parameters of its rate. The basic requirements made towards the injection systems, that are to comply with the currently applicable standardization and homologation regulations concerning the purity of exhaust and noise of operation as well as the reduced fuel consumption, may include:


In order to fulfill the requirements of the modern high-speed diesel engines, the injection systems must be electronically controlled. As the example of such systems is a widely used




The supply of fuel in an appropriate amount and its penetration and distribution inside the combustion chamber are included in the injection system task. It directly creates the quality of the mixture prepared and the rate of the combustion process, which in turn translates into operating and environmental parameters as well as the engine operation economy. Out of the numerous factors influencing the quality of the combustible mixture preparation and the proper combustion that are directly dependent on the injection systems, the following can

The significance of the factors varies and is mainly related to the injection system (indirect of direct injection), type of combustion chamber and requirements related to a specific engine type. The optimization of the high-speed diesel engines requires the matching of the injection system parameters to the loads and engine speeds, inherently related to the operation of traction engines and varying in real time. The accomplishment of this task requires precise control over the injection process and the parameters of its rate. The basic requirements made towards the injection systems, that are to comply with the currently applicable standardization and homologation regulations concerning the purity of exhaust







vapor self-ignition temperature,




and engine temperature,

engine speed and engine temperature,

the current operating conditions of the engine,

speed and thermal condition of the engine,



and noise of operation as well as the reduced fuel consumption, may include:

engine load,

be enumerated:

mechanical work.

common-rail system. It is pressure-accumulation system, where the fuel pumping process is functionally separated and does not affect an injection rate. Thus, the accumulation systems provide a flexible rate of injection at the request of a particular engine design and the amount of fuel injected. They allow a freely-set multiple injections towards lowering noise level of the engine and reduction of the exhaust emissions. The pressure obtained in the accumulation systems usually exceeds 160 MPa.
