3D-CFD In-Nozzle Flow Simulation and Separate Row Injection Rate Measurement as preparatory steps for a detailed Analysis of Multi-Layer Nozzles C. Menne1*, A. Janssen1, M. Lamping2, T. Körfer2, H.-J. Laumen2, M. Douch2, R. Meisenberg2 1 Institute for Combustion Engines RWTH Aachen University, Germany 2 FEV Motorentechnik Aachen, Germany Multilayer nozzles for diesel engines with parallel or convergent nozzle hole arrangement and small noz- zle hole diameters offer the potential to combine good mixture preparation with high spray penetration and air utilization at medium and higher load engine operating points. Advanced experimental injection rate measurement and 3D CFD in-nozzle flow simulation allow the determination of the detailed boundary conditions at the nozzle outlet for layer I and II of the nozzle and show that also for equally sized holes especially during the phase of needle opening different injection rates occur for upper and lower row. Introduction The effects of smaller spray holes with in- Modern Diesel engines have to comply with creased efficiency have been discussed in detail in very stringent emission standards and, in parallel the past. Smaller spray holes result in reduced have to achieve market acceptance with excellent droplet diameters and, subsequently, in an in- performance and fuel consumption. Besides the creased air entrainment into the fuel sprays and combustion system itself and the air path including enhanced mixture formation [2]. Therefore, the turbocharging, the Fuel Injection System (FIE) is in implementation of smaller spray holes typically the center of development focus. In the past, high results in an improved NOx-PM tradeoff at part injection pressure levels with more than 1600 bar load operation, whereas the hydraulic flow rate is and multi-injection capability in conjunction with reduced due to the diameter reduction which typi- highly accurate and reproducible injection quanti- cally affects the full load performance negatively ties have been enablers for the wide acceptance of [1]. direct injection diesel engines and the achievement Consequently, the idea arises, to combine small of EURO-4 and -5 without DeNOx aftertreatment. spray hole diameters with a sufficient hydraulic In order to maintain the efficiency benefit of Diesel flow, which leads to a significant increase of spray engines also in comparison to modern turbo- hole numbers. But not only overall hydraulic flow charged direct injection gasoline engines and to rate is important. If the impulse of a single sepa- comply with future CO2 and emission legislation rate spray is not sufficient to penetrate the com- further development in the field of injection equip- plete piston bowl under high load in-cylinder condi- ment is necessary. One proposal is to further re- tions, poor air utilization and subsequent soot duce spray hole diameter to improve mixture emissions can be a consequence. One approach preparation. Fig. 1 shows the general development to combine good mixture formation due to small of spray hole number and nozzle orifice diameters nozzle hole diameters with adequate spray im- versus time. pulse is to use multi layer nozzles with nozzle EU1 EU2 EU3 EU4 5 holes arranged in groups. In the course of a public 9 220 financed research program the potential of grouped multi layer nozzles shall be analyzed with Spray Hole Diameter [µm] the help of fundamental spray investigations in Number of Spray Holes [-] 8 200 high pressure vessels and detailed 3D CFD spray simulations. As a first step to gain a detailed un- 7 180 derstanding of the underlying mechanisms of multi- layer nozzles, the injection rate was determined 6 160 separately for layer I and II of the nozzle. These investigations were accompanied by 3D CFD in nozzle flow simulations to understand the ob- 5 140 served effects. Optical Schlieren investigations Number of Spray Holes were used to validate in nozzle flow simulations Spray Hole Diameter and injection rate measurements. 4 120 1985 1990 1995 2000 2005 2010 Year Investigated Nozzle Layout Fig. 1: Evolution of Spray hole number and spray Within the overall research project numerous hole diameter multi layer nozzles with grouped nozzle holes were * Corresponding author: menne@vka.rwth-aachen.de Towards Clean Diesel Engines, TCDE2009 investigated. The chosen approach for layer as- signed injection rate measurement and accompa- nying in nozzle flow simulation and optical valida- tion shall be presented at the example of a multi layer nozzle with parallel nozzle holes. The main parameters of the investigated nozzle are shown in Table 1. Fig. 2: Tool for separate layer injection rate measurement The lower chamber of the injection rate meas- urement tool is connected to an injection rate ana- lyzer with high resolution data logging capabilities Table 1: Geometric data and layout of the and a precise fuel mass measurement. A compari- investigated nozzle ADD NOZZLE INLET VCO MICRO son of injected fuel mass via upper and lower noz- SAC zle layer is shown in Fig.3. Injection Rate Measurement The realized injection rate is one of the key in- put parameters for spray and overall combustion simulation. For the investigated multi layer nozzles, where the nozzle holes are arranged on an upper and a lower row, the overall injection rate is not sufficient to describe the nozzle behavior as it can- not be assumed that the injection rate is compara- ble for holes of the upper and lower row. Especially for nozzle concepts with varying hole diameters for upper and lower row and during the needle open- ing phase a significant difference in injection rate can be expected. In order to analyze the impact of multi layer nozzle concepts on spray propagation, mixture preparation and finally combustion and emission formation it is necessary to measure and analyze these differences in injection rates. Fig. 3: Ratio of Fuel Mass injected via upper and In order to minimize the necessary machining lower nozzle row effort and possible impact of any machining on the nozzle behavior, a high precision measurement The separate injection quantity measurements tool was developed, adapted to the different nozzle for the upper and lower layer show that especially geometries and calibrated. The nozzles are pre- for low rail pressure levels, e.g. 800 bar and injec- pared with a 0.2 mm wide groove, which is ma- tion durations with energizing times less than 400 chined on the entire circumference of the nozzle micro seconds the fuel quantity that is injected via tip. The groove is located between the upper and the upper row is up to 25% higher in comparison to lower nozzle layer and is a defined surface for the fuel quantity that leaves the lower layer. A sealing which also ensures that the injector is cen- measured injection rate profile for a typical pilot tered in the layer separator tool. Figure 2 shows injection as shown in Fig. 4 with an energizing time the developed injection rate measurement tool. of 300 micro seconds and a rail pressure of 800 bar confirms the results of the fuel mass meas- urements. upper row, the throttling results in a higher injected fuel mass via the upper orifice under these bound- ary conditions. Fig. 4: Injection Rate for upper and lower layer (800 bar; 300micro seconds energizing time) 3D – CFD In Nozzle Flow Simulation In order to better understand the experimental results a 3D CFD simulation model was created with StarCD. To reduce calculation time and meshing effort a sector mesh for one pair of nozzle holes was set Fig. 6: Velocity Vectors for almost closed needle po- up. Fig. 5 shows the realized mesh. sition in upper orifice (VCO-type),(800 bar Rail Pressure) Fig. 5: Sector mesh for 3D CFD Simulation Model Fig. 7: Velocity Vectors for almost closed needle po- sition in lower orifice (Micro-Sac-type), Steady state flow calculations were carried out for (800 bar Rail Pressure) three different needle lift positions: 1) almost closed / slightly open 2) mid-open position 3) completely open As especially for low rail pressures and short ener- References gizing times, differences in injection rate and sub- sequent injected fuel mass could be identified for [1] M. Lamping, T. Körfer, H.-J. Laumen, H. Rohs, S. upper and lower row, high emphasis was put on Pischinger, H. Neises, H. Busch simulations with a mesh corresponding to needle Einfluss des hydraulischen Düsendurchflusses auf lift position 1). Figures 6 and 7 show the obtained das motorische Verhalten bei Pkw-DI-Dieselmotoren velocity vectors for the simulated flow fields in the 8. Tagung Motorische Verbrennung, 2008 area of the upper and lower orifice. The low needle [2] Y. Matsumoto, J. Gao, M. Namba, K. Nishida Mixture Formation and Combustion Processes of lift and subsequently reduced cross section, avail- Multi-Hole Nozzle with Micro Orifices for D.I. Diesel able for the flow from the upper part of the injector Engines to the lower orifice in the micro sac area has a SAE Paper 2007-01-4050 significant throttling effect. In spite of the signifi- cantly improved conditions for the flow at the im- mediate orifice inlet in the micro sac and the worse conditions at the valve-covered-orifice (VCO) in the