Laurian Tiberiu MOCANU - AEROSTAR SA
Alexandru Tristian BALMUS - AEROSTAR SA
Since 1953, Aerostar SA has been a major provider of products, services, and support for several air and ground forces and the civil aviation market (industrial and operators) worldwide. A prime business field is the overhaul of turbojet engines for fighter aircraft, with more than 6,000 units repaired.
Our original test bench for turbojet engines was 40 years old, but the building and the heavy equipment was still in good condition. The data monitoring/recording installation became obsolete and many of the parameters were manually recorded. For example, the highly dynamic parameters were recorded on film in a data recorder (FDR) type and the fuel flow measurement was based on the gravimetric method (such as measuring the time the engine consumes a certain amount of fuel) several times during an engine run.
We intensively used this complex installation when gas consumption was not a primary issue. The total fuel consumption for each engine is counted in several tens of tons. Now, any percentage cut in fuel consumption represents a significant cost reduction, considering the increasing price of fuel. The fuel consumption reduction implies a CO2 emission reduction as well, thus it is beneficial for the country.
By the end of the 1990s, the FDR-type film recorder’s failure and obsolescence required us to replace it with a new acquisition system with the following features:
- New types of sensors for pressure, temperature, vibrations, RPM, and thrust
- Commercial off-the-shelf (COTS) data acquisition system with eight modules to acquire highly dynamic signals from the new transducers
- Pentium PC-based control computer with Visual Basic data acquisition and database software and a MATLAB® 4.2 application for graphics
In the last several years, the aviation market faced new challenges in the context of the global economy. New requirements to meet in testing turbojet engines included lower total fuel consumption for engine test runs, reduced CO2 emissions, reduced noise pollution, enhanced accuracy in monitoring the process, automatic calculation of reporting parameters, remote access to the testing process, and video monitoring of the engine in all regimes.
Based on the existing facilities and new requirements, we faced several challenges. We had to maintain high accuracy with the previous implementation, so new installations would not disturb the operation of the existing system. We also had to keep working during the transition phase so as not to interrupt the regular testing of the turbojet engines for current customers. Finally, we had to incorporate existing data in new databases to take advantage of valuable existing data and expertise.
With the above requirements and challenges in mind, we developed a new data acquisition system. We added the new components to existing components to complement the features and fulfill our requirements.
At the core of the newly added equipment, is the NI CompactDAQ system with an NI cDAQ-9172 eight module chassis and the following appropriate modules to acquire signals from sensors:
- Three NI 9203 8-channel, ±20 mA, 16-bit analog input modules
- One NI 9221 8-channel, 12-bit analog input module
- One NI 9422 8-channel, 24 V sinking/sourcing, channel-to-channel isolated digital input module
- Three spare modules
A key component is the Coriolis mass flow meter. With this high-accuracy transducer, instantaneous flow measurement is possible, making the highly problematic gravimetric method unnecessary. Using the permanent in-line measurement of the fuel rate, we saved hundreds of kilograms of fuel during each engine test run. The Coriolis flow meter electrical interface is an RS485 and the communication protocol is MODBUS RTU.
Due to safety constraints, personnel cannot enter the engine chamber for inspection and adjustments during an engine run in the higher regimes. Therefore, to visually inspect various areas of the running engine, we installed a video monitoring system in the engine chamber. The video monitoring system consists of a PTZ camera connected to a PTZ remote control and a PC with a video acquisition board.
Each activity is controlled by a Pentium 4 dual-core PC with two LCD widescreen monitors, a keyboard, mouse, color printer, LAN adapter, and TV tuner. The system acquires data from the NI CompactDAQ chassis via USB. It reads the fuel mass flow rate and total fuel consumption from the Coriolis flow meter via USB to an RS485 intelligent converter. It interfaces with the existing COTS data acquisition system using an RS232 line in an ingenious CSMA/CD arrangement that mimics Ethernet in parallel with an older Pentium PC still working as a backup. Finally, it displays and records the video monitoring images (see Figures 1 and 2).
To create the software, we took advantage of the native parallel processing capabilities of LabVIEW and the multicore architecture of the new PCs. The application performs the following tasks:
- Acquires data with an NI-DAQmx driver for the NI CompactDAQ chassis and modules
- Communicates with the old COTS data acquisition system and the Coriolis flow meter, supported using NI MODBUS library
- Displays values on numeric and virtual dials of the front panel indicators and graphs/charts plot
- Automatically calculates indirect parameters
- Automatically archives data in the database
- Prints data using the printer (hardcopy)
- Facilitates remote operation and surveillance using the LabVIEW Web Server
Figure 3 shows the control panel of the main virtual instrument (VI).
During software development and when integrating the hardware, the NI Romania support team provided valuable advice in real time by phone and email. They shared their best practices for configuring the system and performing continuous streaming of data from the data acquisition modules.
An economic impact analysis of the new features reveals several positive points in the process of a turbojet engine test run. It reduces the amount of time for a fuel flow measurement (Coriolis instead of gravimetric). It also eliminates the need for manual readings by using an instantaneous DAQ recording, which reduces the engine runtime, supports troubleshooting and engine-run adjustments using real-time graphics and video monitoring/inspection in all regimes, and reduces the adjustment time of the engine. These positive points have lead to lower fuel consumption and CO2 emissions.
Laurian Tiberiu MOCANU