Micro Turbines in Maritime Transportation

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Hello! Or should I say, welcome aboard! In this edition of micro gas turbines in transportation, we’re going to be looking at micro gas turbines in the marine world. Marine transportation presents its own set of unique challenges not seen in other forms of transportation; although some of the common challenges and hurdles will be seen here too. If you haven’t read the other entries, or the introduction, I highly recommend you do so here.

Out of all the different vehicles and forms of transportation that will be covered in this series, the boat as we know it is one of the oldest ways of getting about. From rowing to sailing to paddle wheels and engines, the boat has a long history of carrying every kind of good and being imaginable. Much like the topic of turbines, marine transportation can take up oceans of information; in fact you might say that it’s a whale of a topic.

Whale Whale Whale
Whale, here we are with another pun. I hope it brightens your day at least! Image courtesy of The Georgia Aquarium

This blog will specifically cover a brief history of motorized marine transportation, where/how micro turbines can be used, and the inherent advantages and disadvantages. Let’s get started!

A Brief History of Engines in Marine Transportation

Steamboats became popular in the 19th Century when the Industrial Revolution was in its early stages. Steam engines like the ones designed by James Watt were used to propel everything from small riverboats like the ones that went up and down the Missouri river, to oceangoing steamships. The engines typically drove a propeller or “screw” or a large paddle wheel like what is commonly seen on a watermill. Different steam engines in different configurations dominated marine transportation throughout the 19th century, and by the turn of the 20th century, large expansion engines began to be utilized for oceangoing ships like the Olympic-class ocean liners as well as warships. Read More

Micro Turbines in Automotive Applications

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Hello! Welcome to this edition of our series on micro turbines! Today we’ll be covering micro turbines and the roles they play in the automotive world.

“Big wheels keep on turnin’…”

Now here’s the real question, when you see that lyric which song do you think of first? Having gotten that stuck in everyone’s head, let’s get on with today’s topic: micro turbines in cars.

I mentioned in the intro to the series that when I think of micro turbines my mind immediately jumps to turbochargers like those used in reciprocating engines seen in cars, trucks, boats, and small airplanes.

A turbocharger, as commonly seen in automotive engines both large and small.

They are, in essence, the same, but also different. For example, a turbocharger uses exhaust gas from a reciprocating engine to drive a compressor to pull more air into the engine, while a micro turbine drives a compressor to pull air into a combustor and then also drives a generator to create electric power.

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E-Turbos: The Future of Turbocharger Technology

The Achilles heel of turbochargers has always been the time between pressing your foot to the gas pedal and waiting for the engine to respond with the desired power. This lapse in engine response, commonly termed turbo lag, is what has hindered turbochargers from delivering optimal performance. The aim of a turbocharger is to provide more power, better efficiency and less lag in power delivery. Engine efficiency is becoming more important than ever before, leading to the development of smaller engines. However, the power requirements are not decreasing which means the loss in engine displacement from small designs must be picked up with alternative technologies, such as turbochargers, which can help improve power delivery and fuel economy.

Figure 1: Garrett Motion electric turbocharger due for production in 2021. Source

Electric turbochargers (e-turbos) provide a solution to eliminating turbo lag while adding additional performance benefits. This allows for larger turbocharger designs which can provide larger power and efficiency gains, stay cooler over longer periods of use, and drastically improve engine responsiveness. Garrett Motion are developing e-turbos for mass market passenger vehicles set for launch in 2021, with a claimed fuel efficiency improvement of up to 10%. When used on diesel engines, this e-turbo could be up to a 20% reduction in NOx emissions. In most cases, fuel efficiency will be improved by about 2 – 4%. Other manufacturers such as Mitsubishi and BorgWarner are already developing their own electric turbos and are expected to have announcements in the near future matching the trend in e-turbo development.

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Series on Micro Gas Turbines And How They Can Make the World Greener

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If you’re familiar with turbomachinery, then you probably know the pivotal role they play in our lives. If you’re not, no biggie! Have a look at this blog where I discuss a world without turbomachinery. But where do microturbines fit in? I can’t speak for anyone else, but my mind immediately jumps to turbochargers in small-displacement car engines. There is, however, a whole slew of information, history, and applications for microturbines beyond being a component in your car.

The best place to start, is to establish just what a microturbine is and isn’t. Granted the prefix in the word is a dead giveaway, but just how small is a micro gas turbine?  In terms of power output, a micro gas turbine puts out between 25 and 500 kW. The size of these machines varies; some systems can be the size of a refrigerator, while others can fit on your desk. For reference, some of these machines are smaller than your average corgi!

Micro Gas Turbine and Corgi
Figure 1: A micro gas turbine with a pencil for scale (left) and your average corgi (right). Not very aerodynamic, but awfully cute. Source

In terms of components, microturbines typically consist of a compressor, combustor, turbine, alternator, generator, and in most machines, a recuperator. While incorporating a recuperator into a microturbine system comes with its own set of challenges, the benefits are often well worth it as efficiency when recuperated hovers around 25-30% (with a waste heat recovery/cogeneration system, efficiency levels can reach up to 85% though).

Figure 3: A commercial airliner's turbofan engine the common image that is conjured when one thinks of turbines in transportation
Figure 3: A commercial airliner’s turbofan engine; the common image that is conjured when one thinks of turbines in transportation.
History

When and how did the concept of micro gas turbines come about? After the advent of the jet engine in World War II and the prominence of turbochargers being used on piston-driven propeller planes during the war, companies started to see where else gas turbine technology could be utilized. Starting in the 1950’s automotive companies attempted to offer scaled down gas turbines for use in personal cars, and you can read our blog covering that more in-depth here. You can probably guess by the number of gas turbine-powered cars on the road today, that it wasn’t very successful.

Fast forward to the 1970s, companies started to take an interest in micro turbines for stationary power generation on a small, portable scale. Allison developed microturbine-powered generators for the military that showed substantially lower fuel consumption in initial testing. In the 80’s, GRI supported the AES program where they attempted to develop a 50kW turbine for aviation applications, using a heat recovery system to improve efficiency through a cogeneration system. More recently, companies like Capstone have worked with GRI on new projects to introduce microturbines to different industries where they could be useful, using the latest advancements in technology to ensure higher efficiencies and reliability of designs past. To discuss the current state of affairs for microturbines however, it might be good to list some of their present advantages and drawbacks, and then explore where in the world they could be most useful.

Micro Turbine Compressor
Figure 4: A micro turbine compressor model.

 

Advantages and Disadvantages of Microturbines

As with just about any other type of technology, microturbines have their own set of advantages and disadvantages as a result of their design that are seen in their different applications.

Advantages: 

  • – Lower emissions
  • – Lower noise level than comparable reciprocating engines
  • – Fewer moving parts with results in less maintenance needs
  • – Lower vibration levels
  • – Ligherweight, compact systems
  • – Diverse fuel selection (jet fuel, kerosene, diesel, natural gas)

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Disadvantages:

  • – Very low efficiency without recuperator/waste heat recovery system
  • – High work requires high speeds (30-120 krpm) for small diameters
  • – Poor throttle response
  • – Expensive materials required for manufacturing
  • – More sensitive to adverse operating conditions

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A Micro Gas Turbine
Figure 5: A Microturbine
Potential Transportation Industry Applications

There are a number of different industries which microturbines can be found both in and outside of the transportation. Throughout the upcoming months, we’ll be taking a closer look at:

  • – The Aviation Industry
  • – The Automotive Industry
  • – The Marine Industry
  • – The Rail Industry

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Each of these industries has at least one application where micro gas turbine technology has the potential to conserve fuel and lower emissions without compromising power. In the next entry, we’ll look at the current state of the aerospace industry and where/how micro gas turbines can improve upon existing technology.

If you want to learn more about designing a micro gas turbine, or about the tools our engineers and thousands of others around the world rely on for their turbomachinery designs, reach out to us at info@softinway.com

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Thermal Management in Automotive Electric Propulsion Systems

There is a growing interest in electric and hybrid-electric vehicles propulsion system due to environmental concerns. Efforts are directed towards developing an improved propulsion system for electric and hybrid-electric vehicles (HEVs) for various applications in the automotive industry. The government authorities consider electric vehicles one of several current drive technologies that can be used to achieve the long-term sustainability goals of reducing emissions. Therefore, it is no longer a question of whether vehicles with electric technologies will prevail, but when will they become a part of everyday life on our streets. Electric vehicles (EVs) fall into two main categories: vehicles where an electric motor replaces an internal combustion engine (full-electric) and vehicles which feature an internal combustion engine (ICE) assisted by an electric motor (hybrid-electric or HEVs). All electric vehicles contain large, complex, rechargeable batteries, sometimes called traction batteries, to provide all or a portion of the vehicle’s propelling power.

EVs propulsion system offers several advantages compared to the conventional propulsion systems (petrol or diesel engines). EVs not only help reduce the environmental emissions but also help reduce the external noise, vibration, operating cost, fuel consumption while increasing safety levels, performance and efficiency of the overall propulsion system. However, there are many reasons why EVs and HEVs currently represent such a low share of today’s automotive market. For EVs, the most important factor is their shorter driving range, the lack of recharging infrastructure and recharging time, limited battery life, and a higher initial cost. Though HEVs feature a growing driving range, performance and comfort equivalent or better than internal combustion engine vehicles, their initial cost is higher and the lack of recharging infrastructure is a great barrier for their diffusion. Therefore, industry, government, and academia must strive to overcome the huge barriers that block EVs widespread use: battery energy and power density, battery weight and price, and battery recharging infrastructure. All major manufacturers in the automotive industry are working to overcome all these limitations in the near future.

Common Types of Electric Vehicles
Classification of EVs according to the types and combination of energy converters used
Figure 1. Classification of EVs according to the types and combination of energy converters used (electric motor & ICE). SOURCE:[3]
A more universal EVs classifications is carried out based on either the energy converter types used to propel the vehicles or the vehicles power and function [4]. When referring to the energy converter types, by far the most used EVs classification, two big classes are distinguished, as shown in Figure 1, namely: battery electric vehicles (BEVs), also named pure or full-electric vehicle, and hybrid-electric vehicles (HEVs). BEVs use batteries to store the energy that will be transformed into mechanical power by electric motors only, i.e., ICE is not present. In HEVs, propulsion is the result of the combined actions of electric motor and ICE. The different manners in which the hybridization can occur give rise to different architectures such as: series hybrid, parallel hybrid, and series-parallel hybrid. All these different EVs architectures are shown in Figure 2.

Architectures of different EVs and HEVs
Figure 2. Architectures of different EVs and HEVs. SOURCE:[3]
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Unsteady Flow Simulation in Hydraulic Systems

[:en]An unsteady flow is one where the parameters change with respect to time. In general, any liquid flow is unsteady. But if a hydraulic system is working at constant boundary conditions, then the parameters of the fluid flow change slowly; thus this flow is considered steady. At the same time, if the parameters of the fluid flow oscillate over time relative to some constant value, then it called quasi-steady flow 1.

In practice, most fluid flows are steady or quasi-steady. Examples of the three flows are presented in Figure 1. Steady flow is presented by a simple pipe. The quasi-steady flow is represented by a sharpened edge channel. The unsteady flow is presented by an outflow from a reservoir.

Figure 1 - Different Types of Fluid Flow
Figure 1 – Different Types of Fluid Flow
Different Cases of Unsteady Flow

During operations, hydraulic systems act for long intervals at steady conditions which are called operating modes. Change between two different operating modes occurs over a short time interval (called a transient mode). If any hydraulic system works more than 95% of the time at these operating modes though, why is the unsteady flow is so important? Because the loads depend on time intervals. If the load is less, then the maximum system pressure is higher. Read More

An Introduction to Thermal Management in Electric Propulsion Systems

Reduction in CO2 emissions is driving the development of different electric, turbo-electric and hybrid electric propulsion systems for various applications and industries including space, aviation, automotive and marine. Electric propulsion (EP) is not a new concept, having been studied in parallel with chemical propulsion for many years. EP is a generic name encompassing all the ways of accelerating a propellant using electric power by different possible electric and/or magnetic means. The simplest way to achieve electric propulsion is to replace the heat generated by combustion in conventional chemical engines with electrical heating.

Electric propulsion systems offer several advantages compared to other conventional propulsion systems. It not only helps reduce the environmental emissions but also helps reduce fuel consumption and increases safety levels. Electric propulsion has become a cost effective and sound engineering solutions for many applications. Electric propulsion engines are also more efficient than others. It is proven to be one of the most energy saving technologies as we can use more renewable sources of energy (due to the versatility of electricity generation) instead of non-renewable sources of energy like gasoline. The major limitation of electric propulsion, when compared with conventional propulsion is limited by the available electric power capacity on board, this may be the reason, it is not the default propulsion system.

Electric Propulsion Architectures
Figure 1. Electric Propulsion Architectures. SOURCE: [4]
Generally, electric propulsion architectures vary depending on the application. Figure 1, above, shows the EP architectures for an aviation application. These architectures rely on different electric technologies (batteries, motors, generators, and so on). Typical aircrafts use gas turbine engines as the source of propulsion power, but all electric aircraft systems use batteries as the only source of propulsion power as shown in Figure 1 on the right. The hybrid systems use gas turbine engines for propulsion and to charge batteries which also provide energy for propulsion and accessories during one or more phases of flight as shown in Figure 1 on the left. Read More

Preventing Choke and Surge in a Compressor

Turbo Compressors are used to increase the pressure of a gas, which are required in propulsion systems like a gas turbine, as well as many production processes in the energy sectors, and various other important industries such as the oil and gas, chemical industries, and many more.

Such compressors are highly specific to the working fluid used (gas) and the specific operating conditions of the processes for which they are designed. This makes them very expensive. Thus, such turbo compressors should be designed and operate with high level of care and accuracy to avoid any failure and to extract the best performance possible from the machine.

Axial Compressor and Centrifugal Compressor in AxSTREAM
Figure 1 (A) Axial Compressor (B) Centrifugal Compressor in AxSTREAM®

Turbo Compressor Characteristic Curves

The characteristic curves of any turbo compressor define the operating zone for the compressor at different speed lines and is limited by the two phenomenon called choke and surge. These two opposing constraints can be seen in Figure 2.

Choke conditions occurs when a compressor operates at the maximum mass flow rate. Maximum flow happens as the Mach number reaches to unity at some part of the compressor, i.e. as it reaches sonic velocity, the flow is said to be choked. In other words, the maximum volume flow rate in compressor passage is limited by limited size of the throat region.  Generally, this calculation is important for applications where high molecular weight fluids are involved in the compression process.

Surge is the characteristic behavior of a turbo compressor at low flow rate conditions where a complete breakdown of steady flow occurs. Due to a surge, the outlet pressure of the compressor is reduced drastically, and results in flow reversal from discharge to suction. It is an undesirable phenomenon that can create high vibrations, damage the rotor bearings, rotor seals, compressor driver and affect the entire cycle operation.

Compressor Performance Curve
Figure 2 Compressor Performance Curve

Preventing Choke and Surge Conditions

Both choke conditions and surge conditions are undesirable for optimal operation of a turbo compressor.  Each condition must be considered during design to ensure these conditions are prevented. Read More

Digital Engineering Modern Turbomachinery Design Platforms

Automatic Turbocharger Compressor Design 

In the age of green energy and increased efforts to minimize our carbon footprint,  the design of a turbocharger plays an important role in reducing engine fuel consumption and emissions while increasing the performance.  When developing an engine with a turbocharger, the general approach is to select a turbocharger design from a product list. The primary issue with this approach is that it does not cover 100% of the requirements of engine characteristics, i.e. it has non-optimal construction for the engine being developed. The operational characteristics of an engine directly depends on the interactions between the system components. This non-optimal construction will always lead to a decrease in the engine’s performance. In addition, the iteration process of turbocharger selection is time and resource consuming.

That is why the most optimal way to develop an engine with turbocharging is to design a turbocharger from scratch; wherein the operational points of compressor needed to satisfy the engine’s optimal operation are known, i.e. compressor map (Figure 1). But how do we quickly get a compressor map? Even at the preliminary design level, the design of turbocharger flow path requires dozens of hours for high-level engineers. And what about less experienced engineers?

Figure 1 Compressor Map Generated in AxSTREAM
Figure 1 Compressor Map Generated in AxSTREAM®

Incorporating a digital engineering approach with a turbomachinery design platform such as  AxSTREAM® allows designers to find the compressor design with all the required constraints which correspond to the specified compressor map needed. The design process is presented in Figure 2. Read More

Role of AxSTREAM® in Radial Turbine Design

[:en]Radial turbines are quite popular for turbochargers and micro-gas turbines. They can also be found in compact power sources like in auxiliary power units of aircrafts. In short, they are suitable in power generation applications where expansion ratios are high and mass flow rates are relatively small. In a radial turbine, the flow enters radially and exits either axially or radially depending on whether it is an inflow or outflow type radial turbine. The most commonly used type of radial turbine is a radial-inflow turbine, in which the working fluid flows from a larger radius to a smaller radius. A centripetal turbine is very similar in appearance to the centrifugal compressor, but the flow direction is reverse. Figure 1 shows the radial-inflow turbine on the left and radial-outflow turbine on the right.

Radial-inflow turbine on the left; Radial-outflow turbine on the right
Figure 1: Radial-inflow turbine on the left; Radial-outflow turbine on the right

Nowadays, the popularity of radial-outflow turbines, in which the flow moves in the opposite direction (from the center to the periphery), is growing. With recent advancement in waste heat recovery applications, there has been a renewed interest in this type of turbines. These radial-outflow turbines are most commonly used in applications based on organic Rankine cycles (ORC).

The radial-outflow turbine design was first invented by the Ljungström brothers in 1912, however it was rarely used for a number of reasons. One of which was related to the decrease of turbine-specific work due to the increase of the peripheral velocity from inlet to outlet while expanding the vapor. Another reason was the usage of steam as a working fluid. It is known from thermodynamics that the expansion of steam is characterized by high enthalpy drops, high volumetric flows and high volumetric ratios. Thus, a significant number of stages are needed to convert the enthalpy drop of the fluid into mechanical energy.

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