Micro-turbines for Extending Electric Car Range

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) [2]. Their concept car utilized a radial turbine in order to propel the vehicle using an advanced electronically controlled transmission system.

Figure 1
Figure 1: Toyota GTV engine [3].
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.

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Top 5 Best Practices for Selecting Software for Your Next Turbomachinery Design Project

The airport was bustling with people. The boards were a mixture of delayed and on-time flights. My flight to San Diego for the EUEC Conference was one of the delayed. This happens when you travel as much as I do, so I found a quiet spot to get a few hours of work in while I waited. In the café at JFK, I overheard a conversation between two other detained travelers discussing what they wish they knew before purchasing software tools and/or hiring external consulting companies.

Their pain points were identical to the pain points I’ve encountered in my decade plus years at SoftInWay meeting with design engineers, engineering managers, CxOs, and other non-technical people in my industry (simulation software and R&D of turbomachinery). Over the years, I have used the knowledge gained in my experience to help guide people in making big decisions such as purchasing turbomachinery design software or hiring consultants on a new project and I wanted to share with the blog community as well.

Here are the top 5 Best Practices I suggest everyone use before embarking on their next big software purchase or hiring consultants for their design project.

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A Small Review with a Big Context

This being my last post for 2017, I wanted to do a short review of what we have been discussing this year. During the beginning of the year, I decided to focus on the 3D analyses and capabilities that were implemented in our AxCFD and AxSTRESS modules for fluid and structural dynamics. With that in mind, my posts were tailored towards such, highlighting the importance of the right turbulence modelling for correct flow prediction. Among other topics, we studied the key factors that lead to resonance, the importance of not neglecting the energy transfer between fluid and structure, and the great advantage that increasing computing capacity offers to engineers in order to understand turbomachinery in depth. However, no matter how great the benefits are, the approximations and errors from CFD can still lead to high uncertainty. Together, we identified the most important factors, from boundary conditions all the way to mesh generation and simulation of cooling flows, and we put an emphasis on the necessary development of uncertainty quantification models. This 3D module related topic finished with an extensive article on fatigue in turbomachinery which plays a crucial role in the failure of the machine, and was the cause for many accidents in the past.

SoftInWay’s AxCFD Module

The second part of my posts focused on different industries that rely on turbomachinery as we tried to identify the challenges that they face. Being fascinated by the space industry along with the increasing interest of the global market for launching more rockets for different purposes, I started this chapter with the description of a liquid rocket propulsion system and how this can be designed or optimized using the AxSTREAM platform. Moving a step closer to earth, next I focused on the aerospace industry and the necessity for robust aircraft engines that are optimized, highly efficient, and absolutely safe. One of the articles that I enjoyed the most referred to helicopters and the constant threats that could affect the engine performance, the overall operation and the safety of the passengers. Dust, salt and ice are only a few of the elements that could affect the operation of the rotating components of the helicopter engine, which allows us understand how delicate this sophisticated and versatile aircraft is.
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Heat Balance Analysis of Thermal Energy Storage

A primary challenge of meeting the increased demand in energy is that energy supply and accessibility isn’t consistent throughout different geographical areas. Availability of energy sources is considered extremely critical in clean/renewable energy applications such as wind and solar where energy source is quite scarce and unreliable. Thermal energy storage in particular is often being looked into with the universal rise of energy demand from every part of the world. With the help of energy storage technology, it allows any excess of thermal energy to be stored and used at a later time/date where it’s needed.

Energy Storage
Source: http://www.climatetechwiki.org/sites/climatetechwiki.org/files/images/extra/storage.jpg

Thermal energy storage can be achieved with widely diverse technologies, including molten salt application. By heating the salt and storing it in insulated containers, users can pump out the salt to release the heat stored when the energy is needed. For example, with solar application the molten salt stores the excess heat that is produced during the day and releases it at night to produce electricity.
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Overcoming the Use of ICEs in Hybrid Electric Vehicles with Turbomachinery – Micro-Turbine Range Extenders – Part 2

As introduced in the last blog regarding Micro-Turbine Range Extenders, we will continue the discussion of turbine engine applications in the automotive sector in this blog.

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.

Figure 1 – Thermodynamic Formulation of a Micro-Turbine Range Extender Model in AxCYCLE™

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?

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The Simultaneous Simplicity and Complexity of Supersonic Turbines and their Modern Application

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 [11] 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.

Meanline Results of Supersonic Turbine in AxSTREAM
Meanline Results of Supersonic Turbine in AxSTREAM

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.

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Overcoming the Use of ICEs in Hybrid Electric Vehicles with Turbomachinery – Micro-Turbine Range Extenders

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.

Chrysler Turbine Car
Figure 1- Chrysler Turbine Car – Now at Display in the Walter P. Chrysler Museum

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.

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