We as human kind have always aimed at achieving something better, something bigger. This led to the research on gas turbines, which was mainly inspired due to the immediate requirement in the aerospace and power generation industry, to also look beyond the scope of aeronautics.
Today gas turbine technology is often used when dealing with aerospace and power generation industries, but believe it or not, gas turbine technology has been used in ground transportation too; notably locomotives.
The Early Applications
After the first world war, several countries had the expertise and the finances to invest in achieving the technological edge in the new post war era. The gas turbine technology was one such technological endeavor, and by the mid-20th century the gas turbine could be found in several applications. Birth of gas turbine locomotives can be credited to two distinct characteristics of these locomotives versus the contemporary diesel locomotives. First, there are fewer moving parts in a gas turbine, decreasing the need for lubrication. This can also potentially reduce the maintenance costs. Second, the power-to-weight ratio is much higher for such locomotives which makes a turbine of a given power output physically smaller than an equally powerful piston engine, allowing a locomotive to be powerful enough without being too bulky.
This might seem like a strange question, but we get ask this a lot. The question takes the form of: Can the sales side do a proper preliminary design and select the optimal machine (turbine/compressor/pump)? Is it possible for the design and application task to be integrated in a way allowing the application team the autonomy to make decisions without going back to the engineering team every time they get an inquiry? After realizing how large of a pain point this is for our clients, we decided to solve this problem for a major turbine manufacturer in Asia and in the process, provided a time-saving solution to maximize the returns for all the stakeholders.
The challenge came with the different competencies of the sales and design team. The sales/application teams are not necessarily experts in design while designers cannot double as application engineers to meet the sales requirements.
In our efforts to solve this issue, we worked with this turbine manufacturer. We listed all of their current processes, limitation, requirements, constraints, and etc. to explore the many possible ways to resolve this pain point. In the end, there were two solutions; (1) Develop custom selection software, or (2) Leverage the AxSTREAM® platform using AxSTREAM ION™.
Developing Custom Selection Software: Developing a custom selection software specific to the manufacturer where their application team can choose the optimal turbine based on expected customer needs. Developing such a custom system requires bringing together the expertise of different teams from turbomachinery (such as aero-thermal and structural) to software developer, testing, etc. Developing such a one-off system also takes considerable time at considerable cost. This approach could solve the current problem, but with rapidly changing technologies and market requirements, this is not a viable long-term solution.
Leverage the AxSTREAM® Platform using AxSTREAM ION™: We evaluated the limitation and possibilities of utilizing our turbomachinery design platform AxSTREAM® to meet the requirement of sales/application engineering team for today’s needs and in the future. We found the organization had a greater advantage using this existing platform rather than investing in the short-term solution of developing a custom selection software. Many of the building blocks required for customization are already available to use via an interface a non-technical sales person could easily use. This platform was utilized for meeting the requirement of this turbine manufacturer saving time and cost while resolving a large pain-point for the organization.
Bottoming cycles are generating a real interest in a world where resources are becoming scarcer and the environmental footprint of power plants is becoming more controlled. With this in mind, reduction of flue gas temperature, power generation boost, and even production of heat for cogeneration application is very attractive and it becomes necessary to quantify how much can really be extracted from a simple cycle to be converted to a combined configuration.
Supercritical CO2 is becoming an ideal working fluid primarily due to two factors. First, turbomachines are being designed to be significantly more compact. Second, the fluid operates at a high thermal efficiency in the cycles. These two factors create an increased interest in its various applications. Evaluating the option of combined gas and supercritical CO2 cycles for different gas turbine sizes, gas turbine exhaust gas temperatures and configurations of bottoming cycle type becomes an essential step toward creating guidelines for the question, “how much more can I get with what I have?” Read More
The modern gas turbine engine has been used in the power generation industry for almost half a century. Traditionally, gas turbines are designed to operate with the best efficiency during normal operating conditions and at specific operating points. However, the real world is non-optimal and the engine may have to operate at off-design conditions due to load requirements, different ambient temperatures, fuel types, relative humidity and driven equipment speed. Also more and more base-load gas turbines have to work at partial load, which can affect the hot gas path condition and life expectancy.
At these off-design conditions, the gas turbine efficiency and life deterioration rate can significantly deviate from the design specifications. During a gas turbine’s life, power generation providers may need to perform several overhauls or upgrades for their engines. Thus, the off-design performance after the overhaul can also change. Prediction of gas turbine off-design performance is essential to economic operation of power generation equipment. In the following post, such a system for complex design and off-design performance prediction (AxSTREAM®) is presented. It enables users to predict the gas turbine engine design and off-design performance almost automatically. Each component’s performance such as the turbine, compressor, combustor and secondary flow (cooling) system is directly and simultaneously calculated for every off-design performance request, making it possible to build an off-design performance map including the cooling system. The presented approach provides a wide range of capabilities for optimization of operation modes of industrial gas turbine engines and other complex turbomachinery systems for specific operation conditions (environment, grid demands more).
The concept of using gas turbines to power a car is not new. In fact, for many decades now, various car manufacturers have experimented with the idea of using either axial or radial gas turbines as the main propulsion of concept vehicles. In the 50’s and 60’s it was Fiat and Chrysler who introduced such concept cars. In those cases, the gas turbine was directly powering the wheels for propulsion. Toyota followed the same concept in the 80’s (Figure 1) . Their concept car utilized a radial turbine in order to propel the vehicle using an advanced electronically controlled transmission system.
The main advantage of a gas turbine compared with conventional reciprocating (or even rotary) car engines is the fact that it has a much higher power-to-weight ratio. This means that for the same engine weight, a gas turbine is able to deliver much higher power output. This is why aviation was one of the biggest adopters of this technology.
The development of turbine cooling is a process that requires continuous improvements and upgrades. A gas turbine engine is a thermal device and so it is composed of a range of major and minor cooling and heating systems. Turbine cooling is just a small part of the total engine system cooling challenges (combustor system cooling, heat exchangers, casings, bores, compressor and turbine disks, bearings and gears etc.). However, effective turbine cooling consists of the greatest economic factor when it comes to engine development and repair costs, representing up to 30% of the total cost.
As a thermodynamic Brayton cycle, the performance of the gas turbine engine is influenced by the turbine inlet temperature, and the raise of this temperature can lead to better performance and more efficient machines. Current advancements in the development of cooling systems allows most modern gas turbines to operate in temperatures much higher than the material melting point. Of course nothing would have been possible without the parallel development of advanced materials for structural components as well as advances in computing resources and consequently in aerodynamic design, prognostic and health monitoring systems and lifing processes. In particular, as far as the lifing of the machine is concerned, the high pressure (HP) turbine containing the most advanced high temperature alloys and associated processing methods, as well as the combustor which represents the key components that have limited life and tend to strictly dictate the cycles of operation and the allowable time on the wing.
Looking to solve the problem of range anxiety in electric vehicles, many companies have started exploring the business model of recharging electric batteries in automotive vehicles with a parallel turbine engine driving a generator – coined under the term ‘micro-turbine range extender’ (or MTRE). As seen in the turbine-powered car programs initiated in the 50s and 60s, issues with low efficiencies, slow throttle response, and capital cost of the powertrain rendered all of these programs futile shortly after their inception. However, the revolution of electric vehicles and hybrid technologies has allowed this technology to resurface from a different direction. With battery-driven electric motors designated as the main driver, these cars are equipped with a technology that has both energy efficient low-end torque as well as groundbreaking throttle response and many of the former drawbacks during its initial iterations are solved using an electric drivetrain. The turbine-engine, instead of operating as the main driver, will now only operate at its most efficient power output mode and work to simply drive electricity through the generator, recharging the vehicle’s battery packs. Acting as an isolated thermo-mechanical system, a micro-turbine range extender can be designed and optimized without having to worry about the varying duty cycles and idling that is inherent in the vehicle’s drivetrain. The thermodynamic model of a typical micro-turbine range extender can be seen below in Figure 1.
One application within commercial vehicles that has benefitted from this technology utilizes a MTRE system developed by Wrightspeed. The specific application lies within retrofitting refuse trucks with this electric powertrain in order to help them save an estimated $35,000 a year on fuel and maintenance costs. In such heavy-duty applications, it is obvious that the potential for fuel cost and maintenance savings is much higher due to the large fuel burning needed for these vehicles as well as the harsh drive cycle a refuse truck goes through. The question in the expansion of this technology generally comes in two forms: What makes the micro-gas turbine range extender a better alternative than a normal ICE hybrid option? – and – What is the viability of scaling this for consumer vehicles given the capital cost of the drivetrain?
Supersonic axial turbines have attracted interest in the industry since the 1950s due to the high power they provide, allowing a reduction in the number of low-pressure stages, and thus leading to lighter turbines as well as lower manufacturing and operational costs. Due to these valuable features, supersonic axial turbines are currently widely used in different power generation and mechanical drive fields such as rocket engine turbopumps [1, 2, 3, 4], control stages in high pressure multi-stage steam turbines, standalone single stage and 2-row velocity compound steam turbines [5, 6], ORC turbo-generator including geothermal binary power stations [7, 8, 9, 10], turbochargers for large diesel engines  and other applications. Therefore it is not forgotten, but instead a very important field in turbomachinery when highest specific power, compactness, low weight, low cost and ease of maintenance are dominant requirements. Especially nowadays, when development of small capacity reusable low-cost rocket launchers, compact and powerful waste heat recovery (WHR) units in the automotive industry, distributed power generation, and other fields are in extreme demand.
Typically, supersonic turbine consists of supersonic nozzles with a subsonic inlet and one or two rows of rotating blades. The turbine usually has partial arc admission. The total flow could go through either a single partial arc or several ones. The latter is typical for a steam turbine control stage or standalone applications. The inlet manifold or nozzles chests, as well as exhaust duct, are critical parts of the turbine as well. Due to the very frequent application of partial admission, it is not possible to implement any significant reaction degree. Thus, this kind of turbine is almost always an impulse type. However, some reaction degree could still be applied to full admission turbines. The influence of the rotor blades profile designed for high reaction degree on rotor-stator supersonic interaction and turbine performance is not well studied at the moment.
The concept of turbine-powered automotive vehicles is not necessarily an unfamiliar idea or a technology that has yet to be explored. In fact, several prominent automakers explored this concept as early as the 1950s and 60s – with real, functional prototypes. Notably, Rover-BRM in the UK as well as Chrysler and General Motors in the US employed turbine engine programs to test the viability of such engines in the commercial market. The Chrysler turbine engine program began its research back in the late 1930s and eventually ran a public user program from September 1964 to January 1966 where a total of 55 cars were built. General Motors had tested gas turbine-powered cars with its many iterations of the Firebird in the 50s and 60s. Rover and British Racing Motors developed several prototypes of their Rover-BRM concept that actually participated in the Le Mans race three years in a row, from 1963 through 1965. However, even Chrysler, which was considered the leader of gas turbine research in automobiles, had to eventually abandon their program in 1979 after seven iterations of the turbine engine. Many of the initial issues with heat control and acceleration-lag were improved during the program’s lifetime, but the program had never paid off in the retail automotive sector, and its continued development was deemed too risky for Chrysler at the time.
Several decades later, we are seeing a resurgence of turbine motors in automobiles, but now serving as a range extender generator for electric vehicles instead. As with many upcoming technologies, learning from past research and failed historical attempts can bring light to the most elegant and innovative solutions for today’s modern challenges. This revolution of an old concept shares many of the qualities that made turbine engines attractive back in its initial development phase. Such advantages include the ability to run on any flammable liquid and the high power density that results in a significantly lower weight and size contribution than its piston engine counterpart.
Steam turbine technology has advanced significantly since it was first developed by Sir Charles Parson in 1884 . The concept of impulse steam turbines was first demonstrated by Karl Gustaf Patrik de Laval in 1887. A pressure compounded steam turbine based on in de laval principle was developed by Auguste Rateau in 1896. Westinghouse was one of the earliest licensee for manufacturing steam turbines obtained from Sir Charles Parson and became one of the earliest Original Equipment Manufacturers (OEM) in power generation and transmission.
Over the years, as steam turbine technology advanced, the design principles were based on either impulse type or reaction type with reaction type being more efficient. Though impulse was not as efficient as reaction type, it gained popularity due to lower cost and compact size. With advances in design and optimization methods being employed, the efficiency levels between these two types are not very distant, ranging between 2 – 5% based on the size and application. Read More