**3. Diesel injection systems development forecasts**

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 reduction of CO2 emission – the supposed greenhouse effect cause.

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 noise NOx and smoke emission can also be reduced.

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

**Section 1** 

**Fuel Properties as Factors** 

**Affecting Injection Process and Systems** 

as IV generation injectors) provides the possibility of application of variable injection rate and fuel injection pressure around 250 MPa. The introduction of such injector is signalized by Bosch (so-called HADI system – Hydraulically Amplified Diesel Injector).
