Open Integrated Laboratory Stand for Research on Biogas as an Alternative Fuel in Compression-Ignited Engines "Loop rates can reach 25 ns due to the base clock frequency of 40 MHz FPGA in the CompactRIO system. With the current hardware configuration we could precisely drive the injectors with the times as short as 40 µs 60 µs in fully deterministic way." - Michał Śmieja, Uniwersytet Warmińsko-Mazurski w Olsztynie, Wydział Nauk Technicznych, Katedra Mechatroniki i Edukacji Techniczno-Informatycznej ( http://www.uwm.edu.pl/wnt/mechatronika/) The Challenge: Developing a unified tool chain to simplify testing internal combustion engines and simplifying data processing with unified timing and triggering capabilities. The Solution: Using LabVIEW software and the CompactRIO platform to control various components of the laboratory and to get time-synchronized measurements. Author(s): Michał Śmieja - Uniwersytet Warmińsko-Mazurski w Olsztynie, Wydział Nauk Technicznych, Katedra Mechatroniki i Edukacji Techniczno-Informatycznej ( http://www.uwm.edu.pl/wnt/mechatronika/) Sławomir Wierzbicki - Uniwersytet Warmińsko-Mazurski w Olsztynie, Wydział Nauk Technicznych, Katedra Mechatroniki i Edukacji Techniczno-Informatycznej (http://www.uwm.edu.pl/wnt/mechatronika/) Michał Kozarzewski - National Instruments (http://www.ni.com/) Governments are reducing the risk connected with importing fuels and are instead looking for available alternative, low-cost energy sources. The reasons for this shift include trends toward reducing harmful emissions, an unstable world economic situation, finite fossil fuel resources, and uncertainties of the business relationship with oil exporters. Governments invest in research on new propulsion methods, including using gases like ubiquitous methane. For this research project, we needed to find new possibilities for using standard, commercially available internal-combustion, pressure-ignited engines, often referred as diesel engines, with a mixture of methane and standard diesel petrol. Basic Theory of Dual-Fuel Diesel Engines There are two fuel components in a dual-fuel diesel engine. These include standard diesel fuel, also referred to as liquid fuel, and methane, also referred to as gaseous fuel, which comes from biogas. In the process of combustion, the combustion chamber must exceed the temperature of auto-ignition of methane (which is around 630 C). Gas fuel is injected into the combustion chamber as an air-gas mixture. A small portion of liquid fuel is injected at the end of the compression stroke, which ignites gas fuel through its self-ignition. The diesel fuel is injected via common rail system, which delivers the liquid fuel to the combustion chamber from the high-pressure system through the electromagnetic injectors. The pressure in the system varies from 40 to 260 MPa. The common rail system comprises three main subsystems: A low-pressure system responsible for delivering appropriately purified fuel under pressure to the high-pressure pump which, depending on the applied solution, reaches 0.7 MPa in some systems A high-pressure system, composed of a high-pressure pump, a fuel container, and injectors, that is responsible for generating a required pressure and delivering it to the injectors, which spray the fuel in the combustion chamber An electronic control system responsible for controlling all the elements of the system, which include a controller, sensors that constantly inform the controller about performance parameters of the engine, and the actuators that are responsible for changes in the sets of working elements System Components and Laboratory Concept The laboratory equipment consists of: A methane delivery system, with bottles, reducers, and regulators of gas mass flow, that is controlled with the RS232 communication standard and analog I/O devices. Read the Full Case Study Figure 1. Methane Delivery System A common rail unit, which is a custom-made system that helps control parameters such as rotation of the high-pressure pump, efficiency of the pump, and fuel pressure in the fuel accumulator. Fuel pressure accuracy is better than 1 MPa. 1/12 www.ni.com
Figure 2. Common Rail Control System The dynamometer AMX211 produced by Automex. The system is controlled with controller area network (CAN) communications. The unit under test is a one-cylinder YANMAR diesel engine that is air cooled, direct injected, and features: Maximum rotational speed of 3,600 rpm Displacement of 435 cm 3 Compression ratio of 20:1 Peak power of 7.4 kw Modified position sensor with accuracy of up to 0.35 degrees Figure 3. Communication Between Elements of Test Stand Modern laboratories for designing and testing internal combustion engines are composed of many independent elements that control and measure various parameters of the engines and test equipment. Those include injectors control, common rail pressure control, dynamometer, ECUs, fuel-mixers and much more. With all the devices coming from various vendors and not having the unified toolchain, the effort needed to even start conducting the research is significant. Also, lack of unified timing and triggering capabilities makes the data processing very challenging. We used the CompactRIO (http://www.ni.com/compactrio/) platform as the main control unit for the test bed. In the final stage, we expected the researcher to be able to control all the components in the laboratory, acquire all the data in a synchronized manner, and control the object in real time, with the possibility of changing the controller parameters online by changing the settings on the user interface or reacting to the events (measurement-based control). Also, we wanted all the measurements and settings recorded with precise timestamps for further offline analysis. In the system, we used numerous modules for measurements and control. These include modules for analog input for accelerometers for knock detection, digital inputs for quadrature, encoders for shaft position, CAN modules for controlling the AMX211 braking unit, RS232 to control the methane delivery system, and more. Also, with the NI Direct Injector Driver System, we could control the injectors with currents up to 30 A and voltage up to 175 V. With the modular approach, a single CompactRIO device can control other systems, without the need to design, prototype, and deploy custom-made electronics. Figure 4. Recorded Voltage Changes at the Coil at Different Fuel Pressure Values 2/12 www.ni.com
Figure 5. Relation Between High-Voltage Value V H, and Value of the Injected Fuel Dose Figure 6. Control Work Engine Test Bench AMX211 Analyzing the changes in the overall efficiency of the engine showed us that at low loads in the event of engine power, overall efficiency of methane was reduced due to the deterioration of the combustion mixture (lean-burn). At higher loads, the efficiency of an engine fed by methane is only slightly less than that of the liquid fuel supply. See example measurements in the pictures below. Figure 7. Exhaust Emission O 2 in the Function of Load Engine Figure 8. Exhaust Emission CO 2 in the Function of Load Engine Figure 9. Exhaust Emission CO in the Function of Load Engine Figure 10. Exhaust Emission HC in the Function of Load Engine Function of Load Engine Figure 11. Exhaust Emission HC in the Function of Load Engine Figure 12. Overall Efficiency of the Engine in the Figure 13. Pressure Waveforms for Common Rail Tuning 3/12 www.ni.com
FPGA in Engine Control We needed high control loop rates because of the need for precise injected fuel volumes. Loop rates can reach 25 ns due to the base clock frequency of 40 MHz FPGA in the CompactRIO system. However, with the current hardware configuration we could precisely drive the injectors with the times as short as 40 µs 60 µs in fully deterministic way. Low jitter results when the functionality of the modules is directly coded in hardware rather than software. Another benefit of FPGA is the ability to reconfigure it using graphical system design software. This is important in a project in which the final functionality of the system is defined by many years of experiments and consequently the cost, both financial and of time, of custom electronics would be significant. Also, the FPGA connects directly to the I/O interfaces of the CompactRIO system, so reactions can be faster compared to processor-based decisions. Reaction to digital lines is at the level of 100 µs and for analog input it is 1 µs. The speed of the module, not the FPGA, limits those values. Graphical System Design Software The backbone of the system is LabVIEW (http://www.ni.com/labview/) graphical system design software, which provides a means to: Design the FPGA functionality (control algorithm, reaction to I/O, triggering, defining the parameters of direct injector module) Develop and execute real-time application on the embedded controller (low-jitter PID, datalogging with common timestamps) Create user interface objects such as waveform charts; graphs; gauges; meters for displaying parameters like injectors current/voltage, motor s torque, and rotational speed; pressure in the common system; pressure the cylinder in the function of shaft s position; controlling the braking system; and more Deploy the whole hardware and software system as a software-designed prototype to control the real object, which is called rapid control prototyping or fast prototyping Figure 14. YANMAR Engine on the AMX211 Test Bench With the open architecture, we could quickly design new control algorithms and add new functionalities. The system evolved from sheer direct injector control system to laboratory control system, which helped set the parameters of dynamometer, fuel mixer, and common rail unit to name a few. Future Steps Future steps include developing the gaseous feeding system and expanding the monitoring capabilities of the system. The research will help determine the efficiency and fuel consumption of such systems, possible improvements in delivery method (pressure, injection duration, and timing), and liquid/gaseous ratio. The test station is universal so future next-generation control systems can be also validated. Author Information: Michał Śmieja Uniwersytet Warmińsko-Mazurski w Olsztynie, Wydział Nauk Technicznych, Katedra Mechatroniki i Edukacji Techniczno-Informatycznej ( http://www.uwm.edu.pl/wnt/mechatronika/) ul. Słoneczna 46A Olsztyn 10-710 Poland 4/12 www.ni.com
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YANMAR Engine on the AMX211 Test Bench Methane Delivery System Common Rail Control System 6/12 www.ni.com
Communication Between Elements of Test Stand 7/12 www.ni.com
Voltage Changes at the Coil at Different Fuel Pressure Values Relation Between High-Voltage Value VH, and Value of the Injected Fuel Dose 8/12 www.ni.com
Control Work Engine Test Bench AMX211 Exhaust Emission O2 in the Function of Load Engine 9/12 www.ni.com
Exhaust Emission CO2 in the Function of Load Engine Exhaust Emission CO in the Function of Load Engine 10/12 www.ni.com
Exhaust Emission HC in the Function of Load Engine Exhaust Emission HC in the Function of Load Engine 11/12 www.ni.com
Overall Efficiency of the Engine in the Function of Load Pressure Waveforms for Common Rail Tuning Legal This case study (this "case study") was developed by a National Instruments ("NI") customer. THIS CASE STUDY IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND AND SUBJECT TO CERTAIN RESTRICTIONS AS MORE SPECIFICALLY SET FORTH IN NI.COM'S TERMS OF USE ( http://ni.com/legal/termsofuse/unitedstates/us/ (http://ni.com/legal/termsofuse/unitedstates/us/)). 12/12 www.ni.com