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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SuperTruck II Program and Waste Heat Recovery Systems

Familiar to many, the 2011 SuperTruck program was a five-year challenge set by the U.S. Department of Energy to create a Class-8 truck that improves fuel efficiency by 50 percent.  Hoping for even more groundbreaking achievements this time around, the Department of Energy has initiated a second five-year program to bring further fuel-efficiency advancements and near closer to eventual commercialization.  Cummins, Peterbilt, Daimler Trucks North America, Navistar, and Volvo Group remain the five teams involved in this R&D endeavor.  Michael Berube, head of the Energy Department’s vehicle technology office mentioned “SuperTruck II has set goals beyond where the companies think they can be.”  SuperTruck II is looking for a 100 percent increase in freight-hauling efficiency and a new engine efficiency standard of 55 percent.  With such lofty goals, the SuperTruck II development teams will need to tackle improvements in freight efficiencies from all sides.

Figure 1 - Daimler SuperTruck
Figure 1 – Daimler SuperTruck

Material considerations, body aerodynamics, low-resistance tires, predictive torque management using GPS and terrain information, combustion efficiency, and several other improvements methods on the first iteration have demonstrated how the SuperTruck II will require a multi-phase and integrated systems approach to achieve equally successful numbers. However, with an engine efficiency target that is 31 percent above the SuperTruck’s first go around, special attention will be required on engine advancement to achieve an efficiency standard of 55 percent.

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Upcoming Webinar: Design and Optimization of Axial and Mixed Flow Fans for High Efficiency and Low Noise

Thursday, May 18 | 10:00 – 11:00 AM EST

Axial Fan CAD Image
Registration is now open for our May webinar demonstrating best practices for the development of competitive, high efficiency, and low noise axial and mixed flow fans for different aerodynamic loadings.

Axial and mixed flow fans have been in high demand for a number of years. The application of these machines span many different industries including HVAC, automotive, appliance, military equipment, and much more. Like many other types of turbomachinery, changing industry standards and market trends have resulted in fierce rivalry to compete on lifespan, efficiency, environmental and user friendliness, and overall quality. With this in mind, it goes without saying that companies are looking for tools needed to develop highly efficient equipment while minimizing noise as quiet fans are typically more desirable which results in higher demand and marketability.

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Air Conditioning in Automotive

Car AC
Source

While the term of air conditioning in relation to automotive might instantly correlate to a system which provides passenger with a comfortable air temperature/environment, HVAC systems also are used for heating and cooling of batteries in such application as well as cooling of the vehicle fuel systems. Thermal management for automotive application isn’t easy though. Many factors have to be accounted for in order to build a dependable cooling system.

While talking about HVAC concerns and challenges which arise in automotive application, the biggest inconvenience commonly comes down to the lack of cold air produces. Mobile refrigeration/air conditioning systems come with quite a few concerns from two sides: the refrigeration side, where it removes heat and injects cold air, and from the electrical side which provides control. From the system, the most common challenges are found in moisture –which would fail the cooling system if present in the air, soiled condenser which would block air flow, and various other mechanical complications which might occurs.

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Foil Air Bearings for High-Temperature Turbocharger Applications

Within the realm of turbocharging, there are a number of different design challenges that influence the design process on both large-scale marine applications and smaller-scale commercial automobile applications.  From aerodynamic loads to dynamic control systems to rotor dynamics and bearing challenges, turbochargers represent a special subset of turbomachinery that requires complex and integrated solutions.  Turbocharger rotors specifically, have unique characteristics due to the dynamics of having a heavy turbine and compressor wheel located at the overhang ends of the rotor. The majority of turbocharger rotors are supported within a couple floating-ring oil film bearings.  In general, these bearings provide the damping necessary to support the high gyroscopic moments of the impeller wheels.  However, there are several disadvantages of working with these oil systems that have allowed different technologies to start to surface for these turbomachines.  With the floating-ring oil models, varying ring speed ratios and oil viscosity changes significantly influence the performance of the rotor dynamic model.

Dan blog bearing for turbochargers
Figure 1 – Floating-Ring Bearing Model for a Turbocharger

The application of oil-free bearings have started to emanate due to the overall consistency of their performance and the minimized heat loss associated with air as the damping fluid. Studies on these bearing types for turbomachinery applications are neither trivial nor unique, as they have seen plenty of exposure within the commercial and military aircraft industries within turbo compressors and turboexpanders. However, the success of these specific applications are due to the fact that these turbomachines operate with light loads and relatively low temperatures. The main design challenges with foil air bearings are a result of poor rotor dynamic performance, material capabilities, and inadequate load capacities at high temperature/high load applications.

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Simultaneous Design for Turbocharger Compressors and Turbine Wheels

AxSTREAM Blade Profiling
Figure 1- AxSTREAM 3D Blade Profiler for Radial Designs

Increasing regulation for reducing emissions has forced the automotive industry to accept different technologies over the years in order to stay ahead of the market. In an industry that is so accustomed to internal combustion engines, new solutions such as electric motors and turbocharger systems have allowed experts in other industries to cultivate an influence in the automotive market. Specifically in the realm of turbomachinery, increased development has gone into designing turbochargers in order to minimize the effect and size of internal combustion engines. Design challenges are inherent in the fact that an engine is a positive displacement device whereas the turbocharger falls under aerodynamic turbomachinery. The two separate machine types have distinctly different flow characteristics, and the proper sizing of a turbocharger for its parent engine requires proper modeling of the engineering system as a whole.

In general, initial turbocharger sizing becomes a matter of obtaining the necessary boundary conditions required for a preliminary design. A thermodynamic cycle analysis of an ICE-Turbocharger system will allow the designer to obtain an initial idea of the bounds

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Axial Compressor Challenges in Hyperloop Designs

Back when the California high-speed rail project was announced, Elon Musk (CEO of SpaceX and Tesla Inc. and perhaps the most admired tech leader of present day) was not only disappointed with this project, but also introduced an alternative to this system called the Hyperloop in 2012.  Since the abstract of this project was introduced, many engineers around the world have started to evaluate the feasibility of this “5th Mode of Transportation”.

Hyperloop Alpha Conceptual Design Sketch
Hyperloop Alpha Conceptual Design Sketch

The general idea for the Hyperloop consists of a passenger pod operating within a low-pressure environment suspended by air bearings.  At the realistic speeds estimated by NASA of 620 mph, the pod will be operating in the transonic region.  While Japan’s mag-lev bullet train has succeeded at achieving speeds of up to 374 mph, the scale and complexity of a ground transportation system rising above 600 mph bring to surface an unusual number of engineering challenges. As well, brand new designs such as the one proposed by Musk have a certain amount of risk involved due to this technology inherently having no previous run history on a large scale.

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The Future of Turbocharger Technology

­One of the main setbacks in scaling different turbochargers for diesel, petrol, and gas engines is the inherit variability that different turbochargers would exhibit at low or high RPMs. In order to understand this further, a common term used to describe a flow characteristic of these machines is the A/R ratio.  Technically, this ratio is defined as the inlet cross-sectional area divided by the radius from the turbo center to the centroid of that area (Figure 1).  This ratio is essentially a metric for the amount of air that is allowed into the turbine section of the turbocharger.

Ratio visualization
Figure 1 – A/R Ratio Visualization

For smaller turbochargers, lower A/R ratios allow the fast exhaust velocities to drive the turbine at lower speeds.  This results in a more responsive engine and overall higher boosts at lower RPMs.  However, once a vehicle starts to navigate at a higher RPM, smaller turbochargers experience a significant reduction in performance due to the high backpressure present in the system.  This occurs because of the low A/R ratio limits the flow capacity and does not allow a sufficient amount of air to feed into the turbine.  The same effect is present for larger turbochargers, only in reverse.  They will perform most efficiently at higher RPMs, but in turn exhibit a significant reduction in performance at lower RPMs.

In order to overcome this phenomenon, many engineers have developed more complex turbocharger systems over the years, which attempt to leverage the benefits of each type of turbo.  One of the first solutions to this dilemma was the twin turbo: simply comprised of two separate turbochargers operating in the system in parallel or in series.  The problem with this system is that it disproportionately increases the cost, complexity, and space necessary for implementation.

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Turbocharger Design and Industry Usage Discussion

An opportunity to discuss turbocharger usage and design with Softinway engineer Ursula Shannon in a question and answer format:

What are some of the major current turbocharger design challenges?

When it comes to turbocharger design, there are two challenges that engineers generally face. “Turbo lag” and turbo boost power at varying engine RPMs. “Turbo lag” is the time that it takes for the engine to produce enough exhaust to start the turbocharger “working”. This can vary greatly depending on engine size, turbocharger geometry, exhaust output etc. Ideally, engineers want to reduce this “Turbo lag” by as much as possible in any given situation, as during that time, the exhaust is “wasted” in a sense. Finding the most efficient configuration with all of the parameters in mind can be a very challenging scenario from a design perspective.

The turbo boost design challenge is one of efficiency at variable exhaust outputs. A smaller charger for example will start to boost at lower engine speeds while a larger one will start to boost at engine speeds. The trade off however is that a smaller turbo will start to create what is known as back pressure at higher speeds, and this results in a loss of potential power. A larger turbocharger, will be able to create more overall boost at higher speeds, however the “Turbo Lag” is more pronounced as more engine exhaust is required. Minimizing these trade offs is another key challenge in turbocharger design.

Finally, the process of turbocharger design process itself is complex, and requires highly specialized software such as our own here in Softinway (AxSTREAM).

Turbocharger blog 3

AxSTREAM Turbocharger Design Software ( Flowpath Design and Optimization )

turbocharger blog 2

AxSTREAM Turbocharger Design Software (Compressor 1D Design and Analysis)

What are some design changes do you see coming to turbochargers in the future?

As I mentioned some of the challenges engineers face in turbocharger design, currently many technologies and methods are being developed to alleviate some of the issues faced.

Two stage turbochargers are good example of trying to offer a solution to the boost powers at varying engine outputs, using a smaller turbocharger that operates at low RPMs and a larger turbocharger that operates at higher RPMs.

Electronic energy storage setups are currently being developed and used in European race cars which uses the output side of the turbocharger as a sort of generator which stores energy in a battery from turbocharger operations and acts as a boost during a turbocharger’s lag period.

Continue reading “Turbocharger Design and Industry Usage Discussion”

Will gas turbines be the next generation of automotive propulsion?

Almost every car produced nowadays is propelled by a Reciprocating Internal Combustion Engine (RICE). Fueled by gasoline or diesel, these engines have pistons inside the cylinders which move up and down, compressing and expanding the mixture. They are connected to a crankshaft that converts the movements into a rotational motion to turn the wheels that move the car.

Big engine makers are constantly researching and developing to make engines lighter, more powerful, more fuel efficient, and more environmentally friendly. But isn’t there a better way to power the automobile Industry?

After WWII, the gas turbine (GT) engine (turbojet) was a trend for aircraft propulsion. A few companies did some research and explored the idea of using a GT to power a car. The GTs mentioned here are evidently not turbojets, but turboshafts where almost any power is used from exhaust. Instead there is a power turbine activated by the combustion gases that would be connected to a gearbox and consequently to the wheels.

Figure 1 - GM Firebird II
Figure 1 – GM Firebird II

The first company to ever build a GT car was Rover in 1950 with the JET 1. A few years later GM also built a number of futuristic prototypes called the Firebirds.

While some companies came up with GT cars, it was Chrysler that invested the most in this concept, spending a lot of time and money doing R&D for almost 20 years (from 1950 to 1970).

Figure 2 - Chrysler Gas Turbine, 1962
Figure 2 – Chrysler Gas Turbine, 1962

For the first time ever in 1963, more than just a prototype came out and fifty-five cars were built and given to people to try as a daily mode of transport. Although reviews were generally good, the project did not go any further.

Figure 3 - A 831 Gas Turbine
Figure 3 – A 831 Gas Turbine

The car used the A-831 GT, a dual spool, and free shaft engine with an output of 130 horse power, weighing 410 lbs. It comprised a single stage centrifugal compressor rotating at a maximum of 44,600 rpm (CR=4:1), the air, after leaving the compressor, would go through 2 regenerators working as heat exchangers using hot gases from the exhaust to increase temperature before the combustion to reduce fuel consumption. From the combustion chamber, the gases travelled by a single stage axial turbine that activated the compressor and the accessories and posteriorly through a variable geometry power turbine nozzle, to control the amount of gas that would go through, before the free single stage axial power turbine that was connected to a Torqueflit, 3 speed automatic transmission.

Chrysler ended up destroying all but nine of the cars.  Today they are in museums or in Jay Leno’s garage.

Why didn’t a car with a well-reviewed engine and a futuristic concept stick? Why are GTs present in so many industries but not in Automotive? They’re faster, simpler, have a better power-to-weight ratio and require less maintenance.

While they have advantages, however, they also have some disadvantages. Some of the Chrysler car users mentioned a lack of engine brake, lack of support when maintenance was needed and noise. This could easily be solved, and Chrysler did fix some of this issues. What ultimately killed the project was the low throttle response in comparison to RICE and fuel consumption. GTs are very fuel efficient for high speeds with constant throttle, but cars operate at relativity low speeds with a big vary of throttle. This has a big impact in the GT fuel efficiency. Although the company tried to resolve this issue, the 1970’s oil crisis made the scenario even worse.

Figure 4 - Jaguar C-X75 GT
Figure 4 – Jaguar C-X75 GT

It’s possible that soon electric hybrid vehicles will mean the GT finally becomes a viable power source for cars. Whether braking or accelerating, the micro gas turbine runs at a relatively constant rpm and generates electricity to be stored in batteries. Those batteries are connected to electric motors (4 in the Jaguar C-X75 case, one on each wheel) that run the car. Two known prototypes are the Jaguar C-X75 using two 70kW micro turbines produced by Bladon Jets, and the Capstone CMT 380 using a single 30 kW micro gas turbine

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