IMPACT OF DIFFERENT IN-CYLINDER PRESSURES ON HYDRAULICAL PERFORMANCES OF THE DIESEL FUEL INJECTION SYSTEMS

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1 PAPER REF: 3032 IMPACT OF DIFFERENT IN-CYLINDER PRESSURES ON HYDRAULICAL PERFORMANCES OF THE DIESEL FUEL INJECTION SYSTEMS Alexandru Bogdan Muntean (*), Cristian Soimaru, Sorin Sacareanu, Ruxandra-Cristina Stanescu D02-High-Tech Products for Automotive, Faculty of Mechanical Engineering, Transilvania University of Brasov, Romania. (*) ABSTRACT The fuel injection-system is responsible for supplying the compresion ignition engines, with fuel. This system is verry complex, and the injection performances as: injection flow rate shape, injected quantity, rail pressure, are beeing influenced by other working parameters. One major parameters is the cylinder back pressure. Further, we will present some results from hydraulical investigation, which was made on common rail injection system, with CRI 2.16 Bosch Injectors. The goal of the study was to observed the impact of different cylinder back pressure on hydraulical performances of the fuel injection system. INTRODUCTION Nowadays, diesel engine specialist are making hard effort to determine and controll the real injected quantity for pilot, main, and post injection during engine running. They can only measure the total quantity per engine stroke. The fuel injection process is starting, during the compression stroke, when the in cylinder pressure is increasing, due to piston motion from bottom top dead center BTDC, to top dead center TDC. Fig.1 In Cylinder - Back Pressure description EXPERIMENTAL SET-UP Description of the test rig Moehwald CA 4000 ICEM15 1

2 Porto/Portugal, July 2012 The hydraulical investigation on fuel injection system, was made, using Moehwald CA 4000 fuel injection test bench, for generating the fuel high pressure, in order to achive the injection process. Fig.2 Moehwald CA 4000 Fuel injection test bench Technical Data: Details: - Test sample Passenger car and truck or heavy duty CRsystems incl. ECU or components - Test medium acc. to ISO 4113, i.e. Shell calibration fluid 1404 (real Diesel as option) - Motor power/torque/speed Passenger car and truck: -44 KW -0 => 6000 rpm -210 Nm Heavy duty: -71 KW -0 => 3100 rpm -675 Nm - Pressure measurement 1 sensor bar, other sensors as option - Injector control ECU or test control device (e.g. Crest, PEM, PEP, Erphi, FI²RE) - Injection quantity measurement various alternatives: EMI, Injection analyzer, KMM, VSE, Coriolis etc - Fuel supply unit double pump l/min IAV-Injection analyzer system The figure below shows the component parts of the Injection Analyzer System: Hydraulic unit (1-left), Software (2-top center), Control unit (3-bottom right). 2

3 1 2 3 Fig.3 IAV-Injection Analyzer system Technical details: - Direct stroke-to-stroke measurement of injection rates - Direct stroke-to-stroke computation of injected masses or injected volumes in real time - Up to seven partial injection events detectable per stroke - Measurement range mg/stroke or mg/stroke and mg/stroke - Measurement accuracy: +/- 0.2 mg/stroke or +/- 0.6 mg/stroke and +/-1% of the measured value - Ambient temperature range -30 C to +130 C - Smallest detectable injection interval ~30 μs - Selectable fuel back pressure: bar The physical measurement principle is based on injection rate indicator (also known as tube indicators) Injector Piezoelectric pressure sensor Nitrogen (System-pressure) Fuel (System-pressure) Fig.4 IAV-Hydraulic Unit The physical measurement principle is based on injection rate indicator (also known as tube indicators) Injection rate (mm 3 /ms) is produced from the following equation: ICEM15 3

4 Porto/Portugal, July 2012 Injected fuel quantity (mg/ms) is calculated on the basis of: where: f 1 - Tube cross sectional area a - Fuid sound velocity p(t) - dynamic pressure increase in measurement tub Calibration fluid for Diesel injection equipment testing As calibration fluid for injection equipment tests, it was used SHELL ISO-4113 fuel. Some fuel technical features are beeing presented in the table below: Measurement procedure In order to have a better overview on the impact of different back pressures on hydraulical performances of the fuel injection system, we had build up the following test matrix.(table 1) 4

5 Tabel.1 Fuel injection system - Test matrix The set up values for injected quantity are beeing presented in the coloums, for different rail pressure (rows). We had chosen injected quantity from 0.25 mg/stroke => 100 mg/stroke In this range we can find values for pilot injection or post injection (0.25 mg/str 3 mg/str), but also values for main injection (5 mg/str 100 mg/str). Rail pressure values, which was adopted, describe the fully range of diesel operational points: Idle=250bar, Part Load = bar, Full Load = bar. The little boxes which are marked by XXX, were the tested points. The test procedure was starting by setting up the injected quantity, for an certain value of the rail pressure and for 50 bar in cylinder back pressure. Further we had modify the in cylinder back pressure to the following absolute values: 75 bar, 100 bar, 25 bar, whitout any correction of the solenoid energizing time. After every modification of the in cylinder pressure and stabilising the process, the injected value and the fuel injection flow rate was analysed using IAV-Injection Analyzer. The error bar which is presented in the charts bellow, is ±0.1 mg for low injected quantity (0.25 5mg/str), and ±1 mg for high quantity (30 100mg/str). RESULTS Following we are presenting the test results: Fig.5 Impact of different cylinder back pressure on Fuel injected quantity- Q_set=0.75mg ICEM15 5

6 Porto/Portugal, July 2012 Fig.6 Impact of different cylinder back pressure on Fuel injected quantity- Q_set=1mg Fig.7 Impact of different cylinder back pressure on Fuel injected quantity- Q_set=3mg Fig.8 Impact of different cylinder back pressure on Fuel injected quantity- Q_set=5mg 6

7 Fig.9 Impact of different cylinder back pressure on Fuel injected quantity- Q_set=30mg Fig.10 Impact of different cylinder back pressure on Fuel injected quantity- Q_set=50mg CONCLUSIONS AND DISCUSSION 1) For low set up injection quantity (0.25 3mg/str) we can observe that back pressure (P_Back) has a significant impact on injected quantity. Increasing P_Back, leads to 25% more fuel injected. 2) Choosing medium values of the injected quantity( ~15 mg),we can observe that in cylinder back pressure has a small influence on total injected quantity 3) For high values of the injected quantity( mg), the increasing of the in cylinder pressure has no significant impact. 4) In cylinder Back Pressure is not the only parameter which is affecting the total injected quantity (Q_inj). We can observe small differences of Q_inj, when we are applying other Rail Pressure. Small P_Rail leads to increasing of Q_inj. One of the explanation, why increasing P_Back, leads to increasing Q_inj is the interacttion forces which are present in the injection process (Fig.11). As we mentioned before, the energizing time of the injector solenoid, was kept unchanged during changing P_Back. The ICEM15 7

8 Porto/Portugal, July 2012 external forces (P_Back), action on fuel spray, respectively on the fuel which is running through the nozzle holes. Fig.11 Injection procces forces interaction If we are increasing the P_Back, the nozzle needle will stay longer lifted (Fig.12). This fact, means that injection time will increase and more fuel will flow trough nozzle. The opposite phenomenon we are meeting when the back pressure is lower than the set value. Fig.12 Operational stage of the solenoid injector As we saw, the injection process is sensitive to many parameters. Therefore, the engineers which are working to improve diesel combustion, must control verry precise the injected 8

9 quantities. First step to achiev the set up injected quantity might be the Closed Loop Needle Control technology or direct driving of the injector needle. ACKNOWLEDGMENTS - This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), financed from the European Social Found and by the Romanian Government under the contract number POSDRU/88/1.5/S/ It is acknowledged that parts of this study was done at HMETC (Hyundai Motor Europe Technical Center)-Russelsheim, Germany. REFERENCES Garrett T.K., The motor vehicle, Thirteenth Edition, Butterworth-Heinemann, 2001 Oprean I.M., Automobilul modern-cerinte, Restrictii, Solutii, Editura Academiei Romane, 2003 Moehwald CI4000 Technical sheet IAV-Injection Analyzer technical book ISO 4113, Second edition bmwland.co.uk ICEM15 9