Electric Car Range Extender
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The automobile industry is under great stress to do more to improve the fuel efficiencies of their vehicles and the dilemma caused by the economic crisis has given government strong leverage to speed up the process. The industry response has been to gradually introduce a widening choice of hybrid models using about 20% less fuel. The premium being charged for hybrid models so far has amounted to about 16%. These mileage improvements fall short of the future fleet average CAFÉ standards of 35 mpg. Hybrids are distinct from electric vehicles in that they are mechanically driven, and use electric motors indirectly to drive the vehicle under low power conditions when the engine would be inefficient. The more advanced hybrids use smaller engines to which the electric motor adds power when the drive load exceeds the engine’s capacity. In most hybrids the electric motor also serves as a generator to absorb part of the vehicles’ braking energy. A next-generation movement toward electric vehicles in which the wheels are directly driven electrically was accommodated by the development of higher-density storage batteries which can depend on utility electricity to recharge them. These plug-in cars tend not to take into account the energy expended by the power utilities to generate the electricity, nor the greenhouse gas emissions it causes. They also take credit for low electricity rates at low demand times of day, which only works when the fleet of plug-in cars is relatively small and ignores the certainty that universal use will bring electricity rates to oil price equivalents. The weight and cost of storage batteries militates in favor of incorporating on-board power generators to extend the range of electric vehicles; hence the term "range extender". These range extenders are usually gasoline-fueled, internal combustion engines driving electric generators with peak thermal efficiencies of under 30%.
CEC has designed, developed and marketed environment-friendly, energy-efficient, CBC power-generating systems to conserve energy and reduce greenhouse gas emissions for the past several years. Prior to that, its predecessor company designed and developed a gas turbine range extender for electric vans and municipal busses. The successful enterprise arising from that program became the Capstone Turbine Corporation. While the CBC has many applications, the automotive one is particularly attractive, because it holds the great promise of drastically improving the fuel economy of automobiles to well in excess of 100 miles per gallon, while reducing vehicle weight and cost, simplifying its maintenance, and substantially extending its reliable lifespan. On top of that it offers very low harmful emission rates, near-silent operation, very wide fuel flexibility and diminishes the need for plug-in charging stations. Furthermore, it does so using a small fraction of the battery capacity currently installed in hybrids or planned for plug-in cars. The principal advantage of a closed Brayton cycle (CBC) power plant is its high thermal efficiency over most of the operating range of a car’s propulsion system. Much as hybrids use stored power until the car’s engine can operate most efficiently, the CBC attains a similar result with fewer batteries. The comparative curve makes it obvious why this is possible. Instead of shutting down the motor when the car is decelerating, at low power, or stationary as the hybrid does, the CBC continues to contribute power to the batteries until traction demand exceeds a level at which the CBC is at least 20% efficient. The rest of the state of charge management is conducted much as it is in existing hybrid cars, providing for dynamic braking and topping the car’s propulsion needs when the maximum output of the engine is exceeded. Another major difference between an internal combustion engine and a CBC is that the CBC has no shaft output, since the alternator is driven internally by the low pressure turbo compressor at high speed which makes its weight and size amazingly small. The other advantage is that it reduces the mixing of power to a purely electrical function. It simplifies the car to an electric traction machine, drawing power from two sources, without any need for expensive, complicated mechanical transmissions.
To illustrate this we used an inbound journey from the west San Fernando
Valley, along the 101 freeway to the southbound leg of the 405 freeway over
the steep Sepulveda Pass. In this case we simulated the Series 3 BMW sedan
with the following characteristics: Drag coefficient 0.30, frontal area
22.57 sq ft, weight 4,389 lb, rolling resistance coefficient 0.008, CBC
design output 60 kW, regenerative braking recovery 70%, traction motor
efficiency 94%, storage turnaround efficiency 99% (Lithium Ion assumed),
power conditioning efficiency 96%.
Our simulation shows that a 60 kW solution can work and would result in fuel
economy of 110 mpg.
This involves constant exchange of power between the batteries and the engine, during which input and discharge losses occur in and out of the batteries. With lead and nickel-based cells these losses were significant. Fortunately, the turnaround efficiency of Lithium-Ion batteries has rendered this loss less important which substantially helps the CBC.
The amount of electrical storage required is also quite modest as show in the diagram of State of Charge (SOC) throughout the particular Los Angeles journey. To be conservative and mindful of the care required to manage Lithium Ion batteries safely, a storage capacity of 80 watt-hrs would probably be sufficient. That is twenty times less than a Prius uses.
Other principal CBC benefits are that it is inherently quiet, operates free of vibration, needs no lubricants or scheduled maintenance, while offering exceptional reliability, long service life, light weight and low manufacturing cost. The CBC provides the opportunity to introduce an innovative car model to mature markets, such as the United States and Europe, with exceptional fuel economy, agile performance, low vehicle weight—which translates to lower vehicle costs—and almost no maintenance. It achieves this with minimal use of stored power and has no need for plug-in facilities. A vehicle in this size bracket with a 60 kilowatt CBC power plant would be capable of traveling more than 100 highway miles (160 km) on a gallon of gasoline, and around 50 mpg (4.7 liters per 100 km) in heavy urban traffic. That is spectacular enough to offer car manufacturers an opportunity to rapidly enter established automobile markets long before sufficient charging stations are in place to support plug-in cars. Power generation in an electric vehicle must be responsive to its acceleration needs. Major automotive companies require power response rates from a standing start to half the power shift demanded, in 300 milliseconds. To accomplish this with a CBC power generator requires air to be added to the loop very quickly. Since the loop operates at sub-atmospheric pressure, air is sucked into the loop through a control valve, which can mean making the inlet port disproportionately large. Alternatively, air under pressure can be added. This could come from a continuously-replenished compressed air reservoir, since the total amount of air in the loop is relatively small.
A third way is to use ultra-capacitances in the manner they are already used to help accelerate transit busses. They are essentially, high-cycle life, high-energy capacitors capable of cycling millions of times, with virtually no maintenance and good survivability at extreme temperatures. They can be made from basic affordable materials in automotive market quantities, still power-rich enough for peak load application. These should not be confused with more expensive ultra-capacitors that use carbon nanotubes or other highly porous materials to achieve battery-like storage capacities.
CEC has refined its car engine design for ultimate mass-produced car use, and is in a favorable position to build a small number of pre-production units for road testing in on-going electric vehicle projects. Hence, CEC has remained in touch with leading automobile manufacturers. Given the current preoccupation with better, fuel-efficient car choices, CEC expects the conversations to intensify.
The company is anxious to proceed with the fabrication of engines for road testing, and considering the desperate financial condition car manufacturers are in, it feels the need to raise the required capital from sophisticated private investors. The investment is quite nominal relative to the commercial prospects for such a power plant. Anyone interested in reviewing a Private Placement Memorandum is invited to e-mail us.
While the CBC cycle is not proprietary, having been patented in 1872 by George Brayton, CEC’s specific design details are highly proprietary and could lead to one or more interested parties offering to adopt the system on condition that they have exclusive rights for a significant period of time in return for participating in the development of production engines and the tooling to permit their mass production. Preliminary SWOT analysis:Strengths:The closed Brayton cycle proved its reliability without maintenance while powering low-orbit, surveillance satellites during the 1960s. The manufacturing state-of-the-art for high-speed turbo compressors and innovative heat transfer components have since improved tremendously, rendering commercial production of closed Brayton cycle systems cost-competitive. Its forerunner company having designed and developed the Capstone Micro Turbine, Creative Energy Concepts brings unique experience to the creation of an uncommonly durable and reliable energy system for automotive use. Because of the challenging economic times facing the world, the cost of transportation is bound to remain under scrutiny with much emphasis on fuel economy. The potential for continued shortfalls in world oil supplies strongly motivates car manufacturers to achieve progressively higher fuel economies in new vehicle models. The results so far have favored greater use of electric traction—initially in hybrid applications—now again returning to purely electric drives. This placed more emphasis on denser means to store electricity, leading at this stage to the development of Lithium-Ion batteries which raised the specter of “fueling” cars from the conveniently available electricity grid. Unfortunately, the power grid in highly industrialized communities, where most cars are sold, is woefully inefficient—providing less than one part of electricity for every three parts of heat energy used. As long as petroleum-fueled, internal combustion car engines remain even more wasteful, the justification for using grid power is obvious. Sadly, in large economies, including fast-growing Asian ones, coal-fired power plants predominate, producing massive amounts of carbon dioxide—not an environmentally friendly source of transportation fuel. Furthermore, the lack of world agreement on climate change—particularly in advanced economies—has forced power companies to postpone or even shelve plans for capacity expansion. The economic recession is likely to disguise the ultimate need for power, and set the stage for shortfalls and brownouts when the economy rebounds. The power companies have been the most visible, key proponents of plug-in cars, contending that recharging can be accommodated economically during hours of slack remand without adding new capacity. Large-scale acceptance of plug-in vehicles will change those dynamics, ultimately raising electricity rates to oil-equivalent levels. At that point there will be no justification left for plug-in cars. Instead of investing heavily in plug-in infrastructures, most nations would be better served by using more efficient car engines, capable of running on a wider variety of fuels besides oil-based ones. The Company believes its closed Brayton cycle engine, its “CBC Solution”, has the necessary characteristics to fill the engine void. The objective is to allow car companies to build mechanically simpler vehicles that weigh and cost less, offer exceptionally good fuel economy, provide significantly longer, trouble-free service lives and are environmentally friendly. Weaknesses:The CBC Solution imposes different perspectives on car designers who may have significant investments in the status quo. These may range from different mind-sets, to concerns about the obsolescence of physical plant and equipment as well as other technologies. For example, an electric car has no need for continuously variable transmissions or other hybrid mechanical accoutrements. The use of a CBC engine can dramatically reduce the amount of electrical storage needed in the car, which will unfavorable impact battery manufacturers. Fortunately, they are likely to be too busy gearing up to meet the needs for storage to make (even heavily subsidized) solar and wind power generators economically viable. It took a leap of faith by Honda and Toyota to bring about the Insight and Prius hybrids and a great deal of subsequent price support to commercialize them. At first, other car companies followed tentatively. They are now paying the price of catching up. Even the lesser step of reviving previous experimental electric car technologies was taken reluctantly and still carries a great deal of risk to commercialize them, as shown by the Chevy Volt program. The same type of commitment is required to bring to market an acceptable closed Brayton cycle engine even though its upsides in vehicle fuel economy and vehicle profitability promise to be exceptional. Opportunities:Alternative opportunities to foster acceptance of closed Brayton cycle car engines are in their use for military and other specialized vehicle applications, including water and airborne vehicles. Additionally, a mass produced CBC vehicle engine will find multiple opportunities in stationary applications from portable generators to cogeneration plants. Threats:The most ominous threat would be a concerted effort by the power companies, and ironically some of the environmentalist groups, to defeat a program that could compete with the plug-in car concept. Clearly, manufacturers of storage cells suitable for vehicular use will discourage the acceptance of a CBC car engine. |
The
external-combustion, closed-Brayton-cycle power plant (“CBC”),
as show by the brown curve offers significantly higher efficiencies than
internal combustion engines. More importantly, the CBC's characteristics
offer high efficiencies where it matters most in an automobile, as shown by
the average power levels for city and highway driving. This is because in a
closed cycle. the power output is controlled by varying the air
pressure (density) in the loop, which results in close-to-constant
efficiencies all the way from 8% to 100% output.
Another
way is to assist the power generator with stored power. In this case that
would come from a sufficient number of Lithium-Ion batteries to prevent
dangerously high rates of discharge. A lithium 3.6 volt cell is the
equivalent of three 1.2 volt NiCad or NiMH cells. A Lithium-Ion cell can be
deep cycled since it maintains a constant voltage for over 80% of its
discharge curve and delivers full power down to 80% depth of discharge (DOD)
as compared with 50% for a lead acid equivalent. It also has high coulombic
efficiency with capacity discharged over capacity charged (turnaround) of
near 100%. They last longer with partial charges rather than full charges,
but there can be degradation when discharged below 2 volts. Their internal
resistance is high with the potential of being damaged at very high
discharge rates or if shorted. Of interest in this application is that the SOC
of Lithium-Ion cells is more complex to measure than other cell chemistries
where the SOC can easily be extrapolated from a simple measurement of the
cell voltage. The flat discharge characteristic of Lithium cells makes it
impossible to measure SOC this way and methods such as coulomb counting have
to be employed. The constant-current, constant-voltage controlled charge
system of Lithium batteries make them vulnerable to damage if the upper
voltage limit is exceeded. Special precautions must be taken when the
battery is fully charged to avoid overcharging. In this application battery
management has to be done in real time, rapidly changing charging and
discharging conditions as the vehicle accelerates and brakes