Theoretical Investigation on Feedback Control of Hybrid Rocket Engines

Abstract

Despite the fact that hybrid propulsion offers significant benefits, it still suffers from some limitations such as the natural oxidizer to fuel ratio shift which induces variations of the engines’ performances while operating. To overcome that issue, Japan Aerospace Exploration Agency (JAXA) has been studying an innovative concept for several years based on the combination of controlled axial and radial oxidizer injections, called altering-intensity swirling-oxidizer-flow-type engine. This type of motor is theoretically capable of managing both the thrust and the oxidizer to fuel ratio independently and instantaneously by using a feedback control loop. To be effective, such engines would require in-flight instantaneous and precise thrust and an oxidizer to fuel ratio measurements as well as an adapted feedback control law. The purpose of this study is to investigate the effect of measurement errors on the engine control and to propose a regulation law suitable for these motors. Error propagation analysis and regulation law are developed from fundamental equations of hybrid motors and applied in a case where resistor-based sensors are used for fuel regression rate measurement. This study proves the theoretical feasibility of hybrid engines feedback control while providing some methods to design the engine and regression rate sensors depending on the mission requirements.

Bridging the Technology Gap: Strategies for Hybrid Rocket Engines

“…Therefore, either the fuel production and general development of HRE needs to reach a more mature stage (with the growing number of successful tests of large engines of numerous hybrid startups hinting at considerable progress), or the engine needs to be actively controlled to match the desired thrust levels. The signal to close the loop can be either the oxidizer mass flow, the chamber pressure, the thrust, or the instantaneous regression rate [60,87,88].…”

“…On a related note, closed-loop control has been investigated for A-SOFT (Altering-intensity Swirling Oxidizer Flow Type) engines [87,91]; however, the goal in these studies was to minimize the O/F shift. Therefore, the studies concerning this issue are discussed in Section 3.5.…”

Modeling and CFD Simulation of Regression Rate in Hybrid Rocket Motors

“…Several aspects of hybrid rockets make them an attractive technology for next-gen propulsion, such as simplicity, low cost, safety, reliability, environmental friendliness, thrust modulation and the ability to be restarted [1][2][3][4][5][6]. Nevertheless, sufficient maturity has not yet been attained and nowadays, no system has reached full operational status, even if this could happen in the near future [7][8][9][10][11][12][13].…”

Reconstructed Ballistic Data Versus Wax Regression-Rate Intrusive Measurement in a Hybrid Rocket

“…For this reason, instantaneous accurate in-flight fuel mass flow rate measurement is required [17]. With this regard, the main shortcoming of a RBS system is that it is able to provide only average values of the regression rates over time periods which cannot be chosen too short (because of the precision of the measure) and, on the other side, cannot be too long (because of the substantial changes in the thermo-fluid dynamic conditions in the combustion chamber).…”