The University of Wisconsin-Madison’s Engine Research Center (ERC) wanted to transform its existing diesel engine test cell into a versatile test cell with high altitude simulation capability. This upgrade was needed for research focused on the high altitude test of multi-fuel capable compression-ignition engines operating on diesel, jet fuels (including Sustainable Aviation Fuels (SAFs)), gasoline, and other alternatives for Unmanned Aircraft Systems (UAS) propulsion research. The ERC’s setup lacked the systems to simulate high altitude conditions.
ACS was selected as the provider through the state’s formal competitive bidding process.
The engine altitude test cell would need to replicate precise high altitude conditions, up to 26,000 feet above sea level, while absorbing engine powers up to 250 kW. This would require integrating advanced systems for temperature and pressure control, humidity regulation, and airflow measurement, alongside comprehensive data acquisition and engine control interfaces.
The ERC also wanted the test cell to have the flexibility to adapt to the needs of future research by allowing for testing of engines over a wide range of engine speeds and torque/power outputs.
ACS delivered a diesel and alternative fuel engine altitude test cell capable of simulating high altitude conditions for engines up to 250 kW of power output. The high altitude test cell can replicate altitudes from 900 to 26,000 feet with precise control of temperature, pressure, and humidity.
The ACS team designed and fabricated an altitude simulation system, combining procured and custom equipment. At its core is an engine intake and exhaust plenum connected downstream to a deep-vacuum pump and upstream to a custom-built restriction control valve which is fed by a Desiccant Air Handling Unit (DAHU). This integrated system allows the engine to ‘breathe’ in a carefully controlled, simulated high altitude atmosphere throughout testing.
Key to this system is the seamless interoperation of the DAHU, altitude valve, and liquid ring vacuum pump required to maintain test parameters. The air is conditioned through a custom-built DAHU that dehumidifies the intake air through a desiccant wheel, while heat exchangers, cooling coils, and heaters manage temperature. The altitude valve and vacuum pump work together to maintain precise altitude conditions, ensuring accurate and repeatable test results.
Locating a high-precision manufacturing partner to machine an altitude valve designed with the extremely tight tolerances required by UW’s specification was an unexpected challenge. ACS’ traditional supplier for the machined piece was no longer available and few suppliers were willing to bid due to the demanding specifications. Through persistent efforts by ACS’ Materials Manager, a suitable supplier was found to produce the customized altitude valve component.
The data acquisition system was built using LabVIEW within ACS’ Acselerant software platform. ACS controls engineers also developed a sophisticated PLC system to continuously monitor and coordinate key parameters such as temperature, pressure, and humidity across the DAHU, altitude plenum, and other critical sub-systems. This complex controller dynamically adjusts settings in real time to ensure that all conditions precisely match the setpoints required for testing.
ACS software engineers equipped the DAQ system with numerous channels to precisely measure airflow, fuel flow, engine performance, and other critical variables. The ERC identified a third-party, custom engine control hardware and software system that it preferred to use in the high altitude test cell. The ACS team integrated this system into their data acquisition architecture, providing seamless communication with the DAQ framework built by ACS. This integration provides the researchers the ability to directly and easily manipulate engine behavior and capture comprehensive data for in-depth analysis.
ACS delivered a high altitude engine test cell that met the ERC’s technical specifications, verified through rigorous commissioning and acceptance testing. The commissioning plan was developed collaboratively with the ERC team, outlining comprehensive procedures to validate the system’s full performance capabilities.
The process involved extensive factory testing by ACS to validate core systems, followed by several weeks of onsite testing and training at the ERC’s facilities. By the end of the site testing, the ERC staff demonstrated their ability to independently run and configure test scenarios, exhibiting a successful knowledge transfer.
With the test cell’s tight tolerances for temperature, pressure, and humidity control, the ERC can now reliably conduct high altitude experiments on a wide range of engine sizes.