In the present work, the influence of a very early pilot injection on pollutant formation was investigated in a Common-Rail DI Diesel engine. The engine was operated at conventional part-load conditions at 2000 rpm, an EGR variation was done and the injected fuel mass was 15 mm^3/cycle. The Nozzle type were conical and flow optimized geometries (ks nozzle) with hole diameters of 0.141 mm, length of hole of 1mm and the Spray Cone Angles were 148° and 120°
Experimental Setup and Measurement Techniques
The experimental investigation of the effect of a very early pilot injection on pollutant formation in a Common-Rail DI Diesel engine was carried out on a production-type GM FIAT 1.9 l CDTI ECOTEC Diesel engine. The 4-cylinder engine utilizes a Common-Rail fuel injection system, variable geometry turbocharger (VGT), an exhaust gas recirculation system, and an intake throttle valve. The engine has four valves per cylinder, centrally located injectors, and a re-entrant type combustion chamber. All relevant engine data are given in Table 1. The mounting of the engine on the test bench is shown in Fig. 1. The production of this engine is certified to meet EURO IV emission standards.
Engine Type Bore [mm] Stroke [mm]
Compression Ratio DI, 4-cylinder, charged, 4-stroke 82.0 90.4 1900 18.3 Combustion Chamber Re-entrant type Max. Power [kW (PS)] 110 (150) @4000rpm
Injection System The engine is equipped with a second-generation Bosch Common-Rail injection system that was used for all experiments reported in this study. Regular Diesel fuel was used in the experiments. A summary of the most important properties of the used Diesel fuel is shown in Table 2.
3 (kg/m ) Viscosity at 313K (mm2/s)
fuel) Lower Heating Value (MJ/kg-fuel) 53.6 834.2 2.892 539.7 619.0 9.0 43.163
A Common-Rail fuel system allows for variable pressures (up to 1600 bar), timing, and numbers of injections. Second-generation Bosch injector systems allow for up to five injections (for example, two pilot, one main, and two post injections) per cycle. VGTs have flexible vanes, which move and let more air into the engine, depending on the load. This technology increases both performance and fuel economy. Turbo lag is reduced, as the turbo impeller inertia is compensated using VGT along with an EGR valve. An intake throttle valve supports high flow rates of exhaust gas recirculation. According to conditioning modules for engine testing, the following applications were used: - Intake Air Conditioning - Fuel Conditioning and Measurement - Engine Oil Conditioning and Engine Coolant Conditioning.
The air-flow rate was measured using a laminar flow element. AVL 733, a dynamic fuel meter, was used for fuel metering. An air-conditioning system determined and maintained the preset temperature and pressure of the intake air. Pressure data was collected for one cylinder. Measured emission data included smoke number, NOX, HC, and CO. AVL 415, a variable sampling smoke meter, provided exhaust smoke levels. An engine dynamometer (AC/DC type) was used to measure engine torque. The measuring equipment used in the experiments is summarized in Table 3.
CO, CO2 NOX HC Fuel Particulate matter
Advance Options Analysatormodul Magnos 16 ECO Physics CLD 700 EL ht Advance Options FIDAnalysatormodul MultiFID 14 (THC C3) Variable Sampling Smoke Meter AVL 415
AVL 733
A Bosch-type flow bench [
The investigations were carried out for a conventional medium-load point at 2000 rpm, a fuel amount of 15 mm^3/cycle, an external EGR rate variation and 700 bar rail pressure.
In order to get a reference point in the first experiment the fuel mass of 15 mm^3/cycle was injected via a single injection. Secondly, 1/15 of the total fuel mass was pre-injected at a distance (dSOI) of the 70 CA deg respect to the SOI main injection or 80 deg. BTDC, in this case the fuel mass of the main injection was 14 mm^3/cycle and Thirdly, a pilot injection was done 60 deg. BTDC also with a mass fuel of 1 mm^3/cycle and a Main injection with 14 mm^3/cycle. See figure 2
All experiments were carried out first with the spray cone angle 148° and the same experiments also were done with the spray cone angle 120°. See Figure 3.
This work was only experimental but numerical support is expected. A very early pilot injection has the intention to prepare good conditions for the combustion. The Soot and NOx emissions for the For the pilot injection events the HC and CO emissions are increased. These results were expected because at very early injection times like 60 or 80 deg. BTDC the pressure, temperature and density in the combustion chamber are very lower and therefore the spray penetration is longer, that means, the fuel spray is impinging on the cylinderwall. In the figure 5 and 6 the HC and CO emissions are showed for a SCA 148°.
Due a better quality of the combustion the HC and CO are lower but unfortunately the NOx emission increases due at the high temperature. In relationship to the pilot events there are not advantages with respect to the HC and CO emissions. However the HC and CO emissions for the SCA 120 are decreased with respect to the SCA 148°. See figure 7 and 8. For the nozzle with the SCA 148° the IMEP is for the single injection the largest. That means, the fuel consumption is higher for the cases with pilot events. This is a consequence that the spray of the pilot injections is impinging on the cylinder walls. In the figure 9 is showed the IMEP versus NOx for the SCA 148. For the nozzle with SCA 120 the IMEP for the single injection event is similar to the experiment with the SCA 148. However, the pilot injection at 60 deg. BTDC showed a similar value of IMEP in comparison to the single injection. An optimal injection strategy is necessary in order to reduce the NOx, Soot, HC and CO emissions and to move the combustion phasing after the top death center. Therefore is necessary to do a lot of experiments using different start of injection times for the main- and pilot injections in order to find the optimal.
Use of a very early pilot injection reduces mainly the Soot and NOx emissions but increase the HC and CO emissions.
A drastic reduction of HC and CO is possible by using of one smaller Spray Cone Angle.