Researchers from Japan Aerospace Exploration Agency (JAXA) assessed the impact of measurement errors on the engine control and suggested a regulation law appropriate for these motors
Hybrid propulsion offers significant advantages such as efficient propulsive performances, use of bio-based propellants, and low costs. Moreover, the propellants in the hybrid propulsion system are non-explosive and stored separately, which offers higher level of safety compared to other chemical engines. These systems can be throttled, reused, and ignited or extinguished several times. However, in hybrid engines, the fuel regression rate relies on the heat transfers at the fuel grain surface. It may be challenging to achieve high thrust levels as the fuel regression rate in hybrid engines is generally low.
An Altering-intensity Swirling-Oxidizer-Flow-Type (A-SOFT) engine is used in order to overcome the oxidizer to fuel ratio (O/F) shift due to the fuel regression. Now, a team of researchers from JAXA by conducted an error propagation analysis regarding the thrust and the O/F ratio to assess the impact of measurement errors on the engine control. Moreover, the team developed a regulation law that is appropriate for Altering-intensity Swirling-Oxidizer-Flow-Type engine applications. A feedback control loop was used to perform numerical simulations of a simplified hybrid motor. This in turn helped to validate that the regulation law.
The team found that the requirements of measurement precision to fit a desired precision on the thrust and the oxidizer to fuel ratio control can be determined. To aid in designing the engine and the Resistor-Based Sensors (RBS) based on propagation analysis, two methods were proposed and numerical simulations were performed with simple thrust profiles. The team also validated the productivity of the proposed regulation law for these configurations. The researchers used RBS for measurement of the fuel regression rate to verify the viability Altering-intensity Swirling-Oxidizer-Flow-Type feedback loop control. The research was published in the journal MDPI Aerospace on June 3, 2019.