Alternative Cars, Part 1 Electric

Every few years a new type of car engine hits the headlines. It might run on compressed air; it may be a steam car or it might use a turbine for propulsion. But no matter how laudatory the media coverage, after a while the design inevitably disappears back into insignificance.

So why does the internal combustion engine – either spark or compression ignition – so dominate?

Is it, as some suggest, that vested interests keep a lid on anything that might upset their applecart?

Or is it that the investment that existing car companies have in their technology is so massive that even if an alternative was found, the advantage of changing to the new approach would have to be enormous for it to be financially worthwhile?

Or is it purely technical – no designs exist that can better current engines’ fuel economy, packaging, emissions and power outputs?

In the main, it is the latter. Despite the enormous intrinsic disadvantages of the internal combustion engine (pistons that start and stop, combustion that is occurring in a constantly changing environment, high frictional loads, poor low speed torque, the need to keep it turning over even when you’re stationary), it is currently still the best car engine.

And it’s not like other approaches haven’t been tried!

So let’s take a look at some of the other forms of motive power that are suitable for cars – and what the current disadvantages and advantages are.

We’ll start off with battery-electric cars.

Electric Cars

The electric car is amongst the most fascinating of alternative power concepts. That’s not only because it has in the past proved commercially very successful but also because as time passes, the advantages of this form of propulsion are becoming increasingly pronounced.

Function

In concept, a battery electric car is very simple. Electrical storage batteries chemically store electrical power. The batteries are charged from the home mains power distribution system.

In the car, the batteries drive an electric motor via a speed controller. The driver operates the speed controller to regulate how much power the motor develops. When the car is stopped (eg at a red traffic light), the car is using almost no power. (Only enough current is being drawn to run the control system, lights, etc.)

In a further refinement, it is relatively easy to regain the energy normally lost during braking. To achieve this, the electric motor is seamlessly altered in function to become a generator, so slowing the car and putting energy back into the battery. Friction brakes are still fitted to bring the car to a complete halt but the wear they undergo is greatly lessened.

Advantages

The power that electric cars use is gained from large power generating stations. These power stations are very efficient at turning fuel into electricity - much more efficient than a petrol or diesel engine used in a car. The power stations can also use renewable energy – eg hydroelectric power – and so the generation of the electricity can result in very low emissions. Other renewable energy power stations – tidal, wave power, solar, geothermal – can seamlessly integrate into the system. The charging infrastructure is also already in place – electricity is available almost everywhere that cars are driven. Finally, since most cars would be charged late at night when electrical loads are lower, the required increase in generating power would be manageable – and perhaps even negligible.

Electric cars are quiet and have no direct emissions of pollutants – in fact, for the purpose of meeting emissions legislation, they have zero output of pollutants. Because of the way in which an electric motor generates its torque, electric motors are very suitable for driving vehicles. There is no need for a clutch and only a limited need for a gearbox. For example, four, five, six, or eight-speed transmissions (as being fitted to some current petrol engine cars) are not needed.

Electric motor technology is well established. Manufacturing plants for electric motors are widespread and the engineering understanding of these motors is great. The efficiency of electric motors is very high.

The electronic control technology for driving powerful electric motors exists – it is used in industry and in electric railway locomotives. Compared with the control systems used in the first electric cars sold in the 1920s, current electronic control systems are far more efficient (ie they waste much less power), are more compact and allow for easier driver control.

The integration into current cars of electrically-driven systems also lends themselves to a pure electric car. For example, power steering, air-conditioning compressors, door locks, window winders, seat adjusting, cooling fans and so on are these days often all electrically driven.

Finally, electric motors require very little lubricating oil. The environmental consequences of disposing of vast quantities of waste oil produced by internal combustion engines are therefore obviated.

Disadvantages

There is only one technological hurdle preventing electric cars dominating our city streets. And that is battery technology.

Despite major improvements in battery technology – from lead acid to nickel cadmium to nickel metal hydride to lithium ion – batteries remain heavy and low in energy density. One litre of petrol has far more energy stored in it than one litre of battery volume – and if you compare weight, the story is even worse. The electric cars currently being developed (see Electric Success?) are usually small cars of lightweight construction – and yet the battery pack still typically weighs one-third to one-half the total weight of the car.

In addition to high weight and low capacity, batteries have a limited life. The Toyota Prius, a hybrid petrol/electric car that uses a nickel metal hydride battery pack, has extraordinarily sophisticated battery charge/discharge computer control – for example, in service, the battery is never fully charged or fully discharged. Additionally, the battery pack is internally temperature monitored and fan cooled. However, the NHW10 model (released in 1998) is now suffering widespread battery failure.

The cost of replacing the batteries in an electric car can be expected to remain high – perhaps as much as one-third the price of the new car.

Finally, the energy that you can get out of a battery is always less than the energy you put in. This ratio is dependent on the type of battery but can be quite low – eg twice as much energy goes in as comes out. This failing makes the battery the weakest link in the chain between the original energy source (eg coal at the power station) and the power available at the wheels.

In the early part of last century it wasn’t at all clear which automotive engine would win the race. A book I have on automobile engineering, published in the US in 1919, gives near equal weighting to steam cars, electric cars and cars powered by gasoline engines. Electric cars were by no means a weird minority but were used for “pleasure cars” (ie normal private vehicles) and light commercial delivery vehicles. From around 1913, here is a Model 71 Detroit Electric Automobile... ...and a Detroit worm-drive rear axle and motor assembly. By far the majority of the section devoted to electric cars is spent on the maintenance, charging and replacement of lead acid and nickel iron (“Edison”) batteries. Then, as now, batteries were the Achilles heel of electric cars.

Solution

The technology to provide viable electric cars currently exists. Lithium ion batteries have reached the stage of development that would allow them to power a small car that suits most people’s daily use. On-road performance would be better than comparable petrol or diesel engine small cars, emissions from the car would be zero and total ownership cost less than for current cars.

But three things are needed:

1. The commitment by a major car manufacturer to produce and sell such a car in large numbers over the long term. The companies currently developing electric cars are vastly undercapitalised and have a poor understanding of car manufacture and retailing.

2. Automatic recharging, where the owner doesn’t need to plug a cable in but instead just parks at the same spot at their house each night. Rather like electric toothbrushes charge their batteries, recharging could occur inductively. This seamless recharging would allow a small range (eg 150 kilometres) to be unnoticed by most drivers.

3. Cars are leased rather than bought. The lease payments are fixed for a set period (eg 5 years) and included in that cost is full maintenance of the vehicle (including battery replacement if required). Recycling of worn-out batteries would also occur. Such a leasing approach could be made very attractive to consumers as it wouldn’t be hard to demonstrate that the total cost of car ownership is less than the cost of owning and running an internal combustion engine car.

Conclusion

Of all the alternatives to current engines, electric cars are the most promising. They’ve been very successful in the past and the developments in electronic control systems and batteries have reduced the technological hurdles. Add to that the familiarity that consumers have with electric motors (compared with, say, steam power!) and increasing societal environmental concerns and the time is right.

Next week: solar cars