England, 20 January 2010. How soon will we see people driving sustainable motorcars that reduce the impact on fossil fuels and reduce pollution? While many people assume, and hope, that the next generation motorcar will be powered either from a rechargeable battery, or an internal combustion engine using bio-fuels, there are problems associated with these methods. Andrew Porter looks into the sustainability issue of bio-fuels to power internal combustion engines, and presents the bright prospect of fully-optimised electric cars inspired by the old diesel electric railway locomotive.
Limitations of Biofuels
Biofuels are being promoted, by some, because of the current liquid-fuel based infrastructure delivery system, and the continued use of internal combustion engines within cars. This is a convenient arrangement too for Governments as it requires less spending to change present systems to accommodate bio-fuels. Governments can also retain their source of income through taxation from fuel duty, with little change being required.
The problem arises when seeking to locate sufficient production quantities of bio-fuels, without disrupting food production. In other words, the world needs food, therefore, the best compromise would be to have waste food crop material for producing bio-fuel. However, there is insufficient food crop waste material to meet the present road vehicle fuel demands. In many areas, biofuel is added to diesel or petrol to reduce the total fossil fuel derived fuel load. As it stands, biofuel is not a solution.
The Potential of Electric Car
The all-electric car is a desirable solution and the good news is, electric motors are already available. Electric motors that are above 90% efficient are also viable. The benefits of regenerative braking to recover what would otherwise be waste energy add another bonus.
The Tesla and the GT Lightning are examples of electric cars that already exist. The GT Lightning is a high performance car with a sleek, sporty body, with a top speed of over 130 mph, acceleration of less than 5 seconds from 0 to 62 mph, (0 to 100 kph) 10 minutes for a full battery recharge, and 186 miles (300km) per charge. This provides what, as first, is an impressive electric car.
High performance GT LightningSuch a car however requires a substantial level of electrical power to recharge the battery. In many cases, particularly in the UK, the bulk of the electrical energy generated is produced by the combustion of fossil fuels within electricity generating stations. In other words, this equation still relies upon fossil fuels.
For such a car to be really viable, and practical, electricity generating stations have to provide a dramatic increase in capacity, as a ten minute recharge period requires more than what can be provided by a standard domestic electricity outlet.
Governments would need to provide a substantial investment into new, clean electricity generating stations. Fuel filling stations would also need to become car-recharging stations, where the Government could, or rather would impose taxation and car electricity duty in the same manner as present taxation and fuel duty. Which gives me serious doubts on whether the present infrastructure could not accommodate such cars.
Railway Trains and The Principle of Optimum Speed
For many decades, railway trains have used diesel electric transmission as an efficient method of powering locomotives and trains. The principle is based upon the observation, without electronic intervention, of having an internal combustion engine running at an optimum speed. This means that the engine can be designed to mechanically optimise the point of fuel injection, valve opening and closing, and engine speed, so that all the conditions for maximum energy transfer efficiency are achieved.
This is helped, considerably, by having the internal combustion engine powering an electrical generator, so that the internal combustion engine remains at a constant operating speed. This overcomes the problems of variable speed; internal combustion engines that only have one speed where the optimum conditions for maximum energy transfer efficiency are present, and either side of this speed, the percentage of energy wasted increases.
With a variable speed engine, the conditions for maximum efficiency are often missed, except when a continuously variable gear system is used, such as the original DAF *Variomatic system. In the case of diesel electric railway locomotives, the mechanically perfected constant running speed to match the maximum engine energy transfer efficiency means that the electrical generator is used, under control, to power electric motors to move the train.
Even though this is not used extensively yet, this also allows the motors to act as regenerative brakes. The dissipated energy is recovered and stored in rechargeable batteries, which can then be used in combination with the electrical generator output to assist in accelerating the railway locomotive when required. To this extent, the idea of diesel electric traction is rather old, using well-established technology, and is well understood.
The Fisker Karma Emulates Diesel Electric Trains
The Fisker Karma is the first attempt to emulate, and even goes beyond the technology used within diesel electric railway locomotives, insofar as the car can operate from just the battery, or the output from an electrical generator. Like the railway locomotive, the car is always running from electrical energy that powers electric motors.
The car can, for up to 50 miles, operate purely from a lithium ion battery which powers the movement of the car. With photovoltaic cells used on the roof, a notable amount of recharging takes place, without needing to connect to an electricity grid based supply. With this mode of driving, it is possible for a refuel of petrol/gasoline to only be needed once a year.
The car also contains an internal combustion engine, where this is used to recharge the batteries and power the car when needed. Similar to the diesel electric railway train, the car engine does not drive the car directly, but is operated at an optimum condition for maximum energy transfer efficiency. In this case, by using precision electronic control of fuel injection timing, independent because no direct mechanical drive from the engine is used, means optimised point of injection is assured, along with the optimum point of ignition, also under electronic control. The removal of mechanical links to set timing for fuel injection and ignition allows the best possible efficiency to be attained, and maintained.
Regenerative braking is also a standard feature, so that the energy otherwise lost during the braking process on conventional cars is recovered. This is done by reconfiguring the motors as electrical generators, and using the battery as a load for the generators.
The concept is to use the best of existing and emerging technologies and to combine these to produce a motor car that is fuel efficient; one that does not need the electricity grid supply. This is possibly a good, interim car before pure electric cars emerge, but only once clean, efficient electricity generation methods are in place.
The Fisker Karma provides good performance in terms of size, that is, a four-door saloon car capable of accelerating from 0 to 60 mph (98 kph) in less than six seconds, 125 mph (200 kph) top speed, and eliminates the need to charge from main grid electricity supplies, whilst returning an excellent fuel economy of up to 120 miles (193 kilometres) per UK gallon (4.54 litres) of fuel.
The gas/electric Fisker Karma with solar roof.
Conclusions
Present generation cars using internal combustion engines suffer from less than idea energy transfer efficiency, party because the engine runs at a variable speed. Without precision electronic control of fuel injection and ignition, rather than mechanical timing systems, means that the engine only has one, precise speed where the optimum conditions for maximum energy transfer efficiency takes place. Outside of these conditions, increasing fuel energy is wasted. In addition, the braking process often uses disc brakes or similar, that whilst these are effective, they simply waste, rather than recover the energy dissipated during the braking process.
If bio-fuels are to be used within existing cars means that to continue with present reciprocating internal combustions engines powering the car through a gearbox and clutch, means that the fuel demands are simply too high to make bio-fuels viable as a complete replacement for fossil fuels. Even if food crop waste material were to be used for bio-fuels, there would need to be a dramatic reduction in the fuel required before this could be viable. The attraction, however, is the limited changes to the existing motoring infrastructure, and Government based taxation.
Pure electric cars may soon emerge to compare with fossil fuel powered cars, but only once the electricity generating capacity has risen to a level to make this sustainable, using ecologically acceptable means of generating electricity, and to instigate the necessary infrastructure to facilitate fast electricity recharging stations in the same way as present fuel refilling stations are used.
A better approach is to adopt, and improve upon the concept applied extensively within the railway sector by using petrol electric, or diesel electric cars, where the internal combustion engine is optimised to run at the best speed for maximum energy transfer efficiency, but instead of using a clutch and gearbox between engine and wheels, the engine powers an electrical generator. The output from the electrical generator then powers electric motors that provide the motive force for the car. In return, to slow the car, the electric motors are reconfigured as electrical generators, and loaded with a fast charge battery, so that the vast bulk of the braking energy is recovered. The electrical generator and battery energy can then be used to accelerate the car when next needed.
The notable increase in fuel efficiency of a petrol electric, or diesel electric car, also aided with solar panels on the roof for recharging when stationary, means that the fossil fuel, be it petrol or diesel is dramatically reduced, possibly by a factor of three. Consequently, this leaves scope to introduce
bio-fuels, as the demand for fuel would be considerably less. In fact, this may provide an ideal tool to gradually phase in dramatically better cars in terms of fuel efficiency, along with viable bio-fuels, pushing conventional cars using direct drive internal combustion engines into the shade.
Finally, efficient, petrol electric, and/or diesel electric cars may provide an excellent intermediate step between present generation cars, and 100% pure electric cars, once the latter has emerged as being as good as conventional cars, along with an ecologically viable, sustainable means of generating electricity.
*The Variomatic System enables the engine to run at a constant, optimum speed, or by using electrical sensors and precision electronic systems to precisely inject the fuel and ignite the fuel through always sensing the absolute optimum point in time relative the engine speed, temperature, piston positions, and so on.
Bibliography
a) http://karma.fiskerautomotive.com/
b) http://www.lightningcarcompany.co.uk/home.php