Mixture Ratio Control Research Articles

Failure Mode Investigation and Redundancy Management of an Electromechanical Control Actuator for Launch Vehicle Application

Electromechanical actuators (EMAs) are increasingly being used in aircrafts under the More Electric Aircraft initiatives. New satellite launch vehicles are being configured with EMA for the thrust vector control and mixture ratio control systems. Analysis of failure modes and their effects in the design stage of a new system is an essential exercise to be done for safety–critical applications of aircraft and human-rated launch vehicle. The thrust vector control system used in the terminal stage of a satellite launch vehicle which does not have any fault tolerance, referred hereafter as no redundancy actuator (NRA), is considered for the case study. At first, a thorough study is conducted on the failures encountered in the NRA and the corrective actions to be taken to avoid these failures in the new design are identified. Improvement in fault tolerance is attempted in two phases. In the first phase, the redundancy features are incorporated in the electrical systems of the actuator such as electric motors and sensors which form part of the closed loop system, leading to the electrical redundancy actuator (ERA). The next logical step is to use a high redundancy actuator (HRA) having fault tolerance to stuck and loose failures in its moving elements such as ball bearings, ball screws and motors. In this paper, failure mode and effects analysis (FMEA) of the existing and the two proposed configurations is carried out. The HRA is designed following the failure mode avoidance technique through four strategies, which are relaxing a constraint limit, using physics of incipient failure, having different operating modes and exploiting dependencies among failure modes. It is concluded that the HRA configuration eliminates a number of single failure points present in NRA and ERA, and it is found to have a better fault tolerance to the failures in its electrical and mechanical elements.

Growth Responses of Eggplant (Solanum melongena) to Hydrophilic Polymer Mixture Ratio in Growing Medium for Lower Maintenance Urban Agriculture via Green Roofs

This study was conducted to investigate the influence of hydrophilic polymer (HP) mixture ratio (Control, 1.0%, 2.5%, 5.0%, and 10.0%) on growth of eggplant (Solanum melongena) for lower maintenance urban agriculture via green roofs. Although it was not statistically significant (p > 0.05), substrate temperature was decreased as hydrophilic polymer mixture ratio were increased. High substrate water content (95%) was found consistently in growing media under elevated hydrophilic polymer mixture ratio at over 5% during the entire growing period. Substrate electronic conductivity was increased as hydrophilic polymer mixture ratio were increased. Growth index was decreased as hydrophilic polymer mixture ratio was increased. It was reduced about 1/3 and 1/5 compared to that of Control in HP5.0 and HP10.0 treatment plants, respectively. Number of leaves, leaf length, and leaf width were decreased in following order: Control> HP1.0> HP2.5> HP5.0> HP10.0 treatments. There numbers were significantly lower in HP5.0 and HP10.0 treatment plants. Dry weight of shoot and root were decreased as hydrophilic polymer mixture ratio was increased. They were reduced by 1/4 compared to those of Control treatment plants. In addition, visual value was decreased as hydrophilic polymer mixture ratio was increased. Plants grown in HP1.0, HP2.5, and HP5.0 treatments all survived. However, plants grown in the HP10.0 treatment had the lowest survival rate (56%) after 3 months of growing. These results indicate that the advantage of adding hydrophilic polymer to green roof growing media may greater during dry periods. However, the proper mixture proportion of hydrophilic polymer should be determined according to different characteristics of growing media and plant species.

Study on the Compressive Strength and Mixing of Ultra-High Performance Concrete

The test in order to obtain liquidity, higher intensity ultra-high performance concrete(UHPC), in the course of preparation, high intensity quartz sand to replace the ordinary sand,reasonable mixture ratio control low water-cement ratio,the incorporation of part of the test piece ofsteel fibers, produced eight specimens . In the ordinary molding and the standard conservation 28d thecase, the ultra-high-performance concrete compressive strength of more than 170MPa.Thepreparation of the test method and test results will provide the basis for further study of the law of themechanical properties of ultra high strength properties of concrete.

Study on Mixture Ratio Control of Bipropellant Propulsion System on Satellite Based on Bypass Control System

Bipropellant propulsion system (MON-1MMH) provides motivation for orbit transfer, attitude control and station keeping, is mainly applied for GEO satellite. Most bipropellant propulsion systems of satellite do not have the ability to control mixture ratio of oxidizer and fuel. The primary function of bypass control system, as an important part of bipropellant propulsion system, is to control helium pressure in the propellant tanks in order to control mixture ratio. This paper researches adjustment of mixture ratio for bipropellant propulsion system. Mathematical model for key components in bypass control system of bipropellant propulsion system and a reasonable model for system simulation combining the practical work of system is established. Through the dynamic simulation of Bang-Bang control with on-off solenoid valve for the adjustment of mixture ratio, structure parameters, working parameters and precision of feedback are all be considered for influence of system performance. The main factors affecting system performance are found out. The researches provide theoretical foundation for engineering implementation.

Mixture ratio control of liquid propellant engines

PurposeDevelopment and application of a new systematic approach for design of a control system in order to control the mixture ratio of liquid propellant engines.Design/methodology/approachThe design approach is based on a full nonlinear dynamic model of the engine, and the controller design method is based on describing function models of the engine coupled with the factorization theory. The presented systematic design procedure is comprised of five primary steps. The developed software for the design approach is in the MATLAB environment.FindingsIt is found that the presented design approach may successfully be used to control the mixture ratio of a class of liquid propellant engines whose control loops are decoupled. The performance and robustness of the designed controller is found to be satisfactory.Research limitations/implicationsAt present, the research is limited to liquid propellant engines whose control loops are decoupled.Practical implicationsThe major outcome of this research is that complicated hydromechanical control valves that are used to control the mixture ratio may be replaced by simple microprocessor based servomechanisms that drive simple valves. This will allow for the engine to accept various set point values for mixture ratio as is required in multi‐regime engines.Originality/valueThis is the first paper in the area of mixture ratio control of a liquid propellant engine that is based on the application of describing function approach coupled with the factorization theory.

Oxidizer Control and Optimal Design of Hybrid Rockets for Small Satellites

The parameters that affect the design of a hybrid rocket for small satellites are highlighted, and the benefit of the oxidizer flow rate control is analyzed. A single-port circular-section polyethylene grain is considered; the oxidizer is 85% hydrogen peroxide. The engine design is optimized to search for the minimum engine mass when the initial satellite mass and the required velocity increment are assigned. First, the simplest blowdown feed system is considered. The analysis shows that the optimal design depends on a lower limit for the regression rate and sometimes on a further constraint, which is related to the occurrence of thermal choking. The initial values of the mixture ratio, the thrust level and the initial port area to the throat area ratio seem to be the most important parameters for an optimal design. As far as the oxidizer flow rate control is concerned, several control strategies, namely, constant mixture ratio, repressurization, constant combustion chamber pressure, and constant propellant tank pressure, are compared to the simplest blowdown system. The constant mixture ratio control is the worst case, as the mass and volume are similar to the blowdown case, while a large thrust variation occurs. Repressurization reduces the thrust variation. Constant pressure controls (both combustion chamber and tank pressures) guarantee a quasi-constant thrust and reduce engine dimensions, with a limited mass penalty.

5666923 Hydrogen enriched natural gas as a motor fuel with variable air fuel ratio and fuel mixture ratio control: Collier Robert Kirk; Hoekstra Robert Louis; Mulligan David Neal; Hahn Douglas Edward Merritt Island, FL, United States assigned to University of Central Florida

This paper proposes a novel nonlinear controller that exactly linearizes the dynamics of the air/fuel(A/F)-ratio loop in spark-ignition engines. Using nonlinear models of all relevant parts and ideas taken from the feedback linearization approach, a nonlinear state feedback is derived that both performs the usual fuel-film compensation and removes the inherent nonlinearity of A/F-ratio loops. It is shown that the proposed controller has certain similarities to known pragmatic solutions. Some questions connected to the realization (state observation, disturbance decoupling, etc.) are also discussed.

Optimization of a Dual-Mixture-Ratio Hydrogen-Fuel Rocket

The problem of optimizing rocket performance in the absence of gravitational and aerodynamic forces is analyzed by considering the possibility of varying the propellant mixture ratio. The rocket operation with a piecewise constant mixture ratio, that presents lower complexity in comparison to a continuously variable mixture ratio, is examined in this paper. The theory of optimal control is applied in order to minimize either the gross mass or the dry mass for the assigned pay load and velocity increment, when the tank mass is assumed to be proportional to the propellant volume. The approach is more flexible than the classical one (i.e., the ordinary differentiation of the function to be minimized), as it can easily be extended to cases where the performance index is not an explicit function of the parameters (for example, if gravitational and aerodynamic losses are taken into account). The results show that mixture-ratio control can significantly improve rocket performance and that most of the benefit is obtained simply by dividing the trajectory into two phases with different constant mixture ratios. single-stage-to-orbit (SSTO) vehicle feasible. The continuous control of the mixture ratio renders the engine design more complex, whereas comparable benefits can be obtained by means of a simpler control law, namely, the dual mixture-ratio operation, which is the main object of this analysis.

Development of small centrifugal pumps for an electric propellant pump system

Small centrifugal pumps with low specific speeds have been designed, manufactured and performance tested at Volvo Flygmotor AB under a contract from the European Space Agency (ESA) over the period mid-1985 to mid-1988. The development of the pumps is a part of the work carried out to develop an Electric Propellant Pump System (EPPS) for the storable propellant monomethyl hydrazine (MMH) and nitrogen tetraoxide (NTO). Supporting technology development has been funded by the Swedish Delegation for Space Activities (DFR) and Swedish Space Corporation (SSC) together with Volvo Flygmotor. The main advantages of a typical EPPS communication satellite application are weight and volume reduction of the propellant system compared with a pressure-fed system. Active engine mixture ratio control and improved propellant utilization are also possible. Refuelling in space is another potential application where EPPS can be used. The development work was focused on communication satellite apogee propulsion and used the MBB 3 kN engine as reference. This paper presents the pump design and analyses and the results from the test campaigns of three different pump configurations, carried out with water as test liquid. The head rise, efficiency and suction performance together with other characteristics are also given. The planned next development step is to demonstrate pump performance in the propellants and primarily in NTO. The step is funded by (DFR)/(SSC) together with Volvo Flygmotor.

Measurement and Control of the Solid-Gas Mixture Ratio in Two-Phase Flow

Automatic control technique does not seem to be applied very much to the field of solid particle handlings, because no adequate device is available to measure and to manipulate the flow rate of solid particles.According to previous report, the solid-gas mixture ratio can be calculated using the two pressure differences of a two phase flowmeter. In this paper, therefore, a specific servo-computer is employed “on line” for this purpose.The mixture ratio is continuously measured within the accuracy of ±5% and successfully contr olled using an electromagnetic vibrating feeder as the manipulating device. In the mixture ratio control, an upside weir should be attached to the feeder trough to get wider manipulating range. The inverse response appears in the mixture ratio by the difference of dynamic characteristics between high and low pressure side s of a transmitter. Therefore, particular attention should be paid to select a transmitter in order t o get a quick and stable response.