TRIZ Solves A Reliability Problem Concerning A Space Shuttle Class Main Engine
Editor | On 16, Jan 1999
Zinovy Royzen, President
TRIZ Consulting, Inc.
TRIZ is the Russian acronym for The Theory of Inventive
Problem Solving. TRIZ is a unique knowledge-based technology for accelerated development of design concepts. The power of TRIZ is based on the understanding of the evolution of successful products, generalization of the ways used to solve problems in the most innovative inventions, and ways to overcome psychological barriers. Classical TRIZ is described in books and papers by Genrich Altshuller, the creator of TRIZ, and his followers.
This paper describes application of Advanced TRIZ to a reliability problem concerning a Space Shuttle Class Main Engine (SSCME). Advanced TRIZ, a further development of TRIZ by Zinovy Royzen, guides you in analyzing your system in order to identify the best opportunities for its development and the best use of its resources. Application of Advanced TRIZ to the problem has helped to develop concepts allowing improvement of the reliability of an SSCME without any changes to the hardware.
It has become increasingly important to develop successful new generations of products while shortening development cycles and reducing project spending. In the most difficult cases, a desired improvement in one area causes a deterioration in another area. Very often, a trade-off solution is accepted, while a breakthrough solution is needed. For example, if an attempt to increase the reliability of a product increases its weight and cost, a trade-off solution suggests neither best reliability nor minimum weight and cost.
In problem-solving, Advanced TRIZ systematically analyzes the problem as an innovative situation and applies a series of step-by-step guidelines to generate solution lternatives, improving the desired product parameters while minimizing product changes and costs.
This paper briefly describes application of two techniques of Advanced TRIZ. They are TOP Analysis and Direct Ways to Eliminate a Harmful Action. TOP Analysis is the advanced development of Altshuller’s Substance-Field Analysis. The Direct Ways are a class of
Standard Techniques, the advanced development of Altshuller’s set of 76 Standard Solutions. In Direct Ways, Altshuller’s five Standard Solutions to eliminate a harmful action were reformulated, detailed, and combined into four, then two new techniques were added. The Direct Ways offer six step-by-step techniques to eliminate a harmful action.
Applying the Advanced TRIZ methodology from the beginning of your project can save you much time and effort in your search for breakthrough concepts. As an example, consider the following case study.
2. NEW DEVELOPMENTS OF TRIZ USED IN THE CASE STUDY
Genrich S. Altshuller, the creator of the Theory of Inventive Problem Solving, elaborated a method and a set of symbols for describing generic types of problems and their solutions. The method was called the Substance-Field Analysis (SFA).
Altshuller’s model of the simplest useful system is composed of three elements — the tool, the object, and the field. There are two ways of describing a useful system.
Figure 1. Model of the simplest useful system
Figure 2. Model of the simplest useful system having a harmful action
The progression from words to symbols was to inventive problem solving something like the progression from words and numbers to letters symbolizing constants and unknowns in algebra, from words to symbols in logic, or from words to symbols in chemistry.
The next step in the development of TRIZ required improvement in modeling. The models describe a useful system but not the useful function. The useful function has one more element — the product of the function.
TOP Analysis was developed by Zinovy Royzen in 1989. TOP stands for Tool, Object, Product.
Figure 3. Model of a useful function
Figure 4. Model of a harmful function
TOP Analysis is an integral component of Advanced TRIZ methods for analyzing a situation in product development that needs breakthrough concepts. Modeling functions helps one to understand the product performance and formulate problems to solve. Modeling a function by describing all four components — the tool, the object, the action, and the product — improves understanding of the function, the available resources, and the best ways for improvement.
TRIZ classifies problems in innovation into five generic types. Presence of a harmful or undesired function is one of the most difficult types. Very often an attempt to eliminate an unwanted function deteriorates a useful function of the product or increases its cost. As a result, a trade-off solution is accepted, while a breakthrough solution is needed.
3. A RELIABILITY PROBLEM CONCERNING AN OXIDIZER TURBOPUMP
An oxidizer turbopump is one of the most complex and expensive components of an SSCME. It feeds the main combustion chamber with oxygen. The turbine of the oxidizer turbopump is rotated by a high velocity flow of very high temperature oxygen, called GOX (gas oxygen). The turbopump is made of material that resists working temperature oxygen.
Failure of the oxidizer turbopump can be caused by a dust particle or other wearing particle in the GOX. Colliding with the hardware, a particle, having a very high velocity because of the flow of GOX, would increase the temperature of the hardware in the proximity of the collision to a level beyond which its material could not resist the oxygen. Ignition of the hardware generates more heat and could result in complete failure of the oxidizer turbopump and, as a result, the complete failure of the whole engine.
4. SUMMARY OF ANALYSIS OF THE FAILURE
Problem 1. A particle collides with hardware (for example, with the
Problem 2. The heated material of the blade does not resist the
Figure 5. Analysis of the zone of the harmful action
Analysis of the SSCME
The engine includes a tank with liquid hydrogen, a tank with liquid oxygen (LOX), the main combustion chamber, and the nozzle.
The fuel (liquid hydrogen) passes through a high-pressure fuel turbopump before cooling the main combustion chamber and nozzle. The fuel is vaporized during the cooling process. After cooling, the fuel is split between two preburners.
The preburner of the fuel turbopump is fed by a fuel-rich mixture. The preburner produces a high velocity flow of high temperature hydrogen that rotates the turbine of the fuel turbopump.
The preburner of the oxygen turbopump is fed by an oxygen-rich mixture, composed approximately 98-99% of oxygen. The oxygen turbopump preburner produces a high velocity flow of high temperature oxygen that rotates the turbine of the oxidizer turbopump.
Figure 6. Simple schematic of SSCME
5. SUMMARY OF APPLICATION OF THE DIRECT WAYS
Application of the Direct Ways to Problem 1 led to formulation of the following approaches to solving the problem.
Try to insulate the blade from the particle.
Try to introduce a field that will prevent the collision (for example, by repelling the particle).
Try to protect the blade by capturing the particle before it reaches the blade.
Try to modify the particle to make it harmless in the case of collision (for example, melt or evaporate the particle).
Try to modify the blade to be nonsensitive to the collision (in other words, so the collision would not increase the temperature of the blade). This approach leads to formulation of the following physical contradiction: the temperature of the blade has to be increased by colliding particles, but the temperature of the blade must not be increased to the point of resisting GOX.
Application of the Direct Ways to Problem 2 led to formulation of the following approaches to solving the problem.
Try to insulate the heated blade from the GOX. A technology to plate the hardware of the oxidizer turbopump with ceramic is known. This technology was developed in Russia. It is a very expensive technology. In addition, the ceramic plating would increase the weight of the engine. Furthermore, if the ceramic is not strong enough, it could cause engine failure.
Try to modify the GOX. If GOX is replaced by hydrogen, for example, the possibility of burning the hardware will be eliminated completely. This technology is known as a Full-Flow Staged Combustion Cycle Engine System. It has another potential for failure if high-temperature hydrogen mixes with the pumped oxygen in the oxidizer turbopump. (Elimination of potential mixture of high-temperature hydrogen with pumped oxygen in the oxidizer turbopump is an interesting problem to consider, but it was beyond the initial objectives of the project.)
Try to reduce the temperature of GOX. The technology reducing the temperature of GOX without any reduction of the power of the oxidizer turbopump is known as a Full-Flow Staged Combustion Cycle Engine System. The power of the turbopump depends on the velocity and mass of the driving flow. In the known technology, all oxygen that is not directed to the fuel turbopump preburner passes through the oxidizer turbopump. Increase of the mass of the driving flow reduces the required velocity, resulting in reduction in the temperature of GOX.
Try to modify the heated blade. Try to increase the resistance of the blade material to oxygen. This is a materials problem. Materials having high resistance to oxygen do not necessarily have strong mechanical strength. Increasing the resistance of the material to oxygen very often causes increase of the weight of the turbopump.
Try to cool the blade to the working temperature, at which it resists oxygen. This raises subsequent problems: 1) how to cool the heated blade, and 2) how to keep the temperature of the cooled zone of the blade from falling below the working temperature (otherwise, the performance of the pump would be deteriorated). An obvious resource for cooling the blade is LOX. But using it as a coolant presents some constraints: it is difficult to maintain working temperature by cooling using LOX, and it is difficult to have LOX in the time and place of an accidental collision.
TRIZ requires consideration of all resources, including GOX and the blade itself. From analysis of the simplified schematic of the engine, it is known that GOX is not pure oxygen. GOX includes 1-2% of water vapor as a result of burning hydrogen. Water vapor is an excellent coolant. It is already at the working temperature and ready to cool the blade down to the working temperature. It was necessary to make calculations to determine how much water vapor is required, but the concept does not require any changes in the hardware of the engine.
TRIZ is a logical, knowledge-based technology for conceptual design.Application of TRIZ guides users in analyzing their systems and formulating the best directions for improvements. Application of TRIZ helps users meet objectives of new product development projects with less cost and without any unwanted effects, by maximizing utilization of the resources of the system. TOP Analysis improves the effectiveness of system analysis and problem formulation. Direct Ways to Eliminate a
Harmful Action help in formulating a set of mutually exclusive but collectively exhaustive best possible improvements. This set is the basis for both short-term and long-term planning of innovation.
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