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
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
And it’s not like other approaches haven’t been
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
We’ll start off with battery-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.
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
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
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
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
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.
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.
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.
cars were by no means a weird minority but were used for “pleasure cars” (ie
normal private vehicles) and light commercial delivery vehicles.
around 1913, here is a Model 71 Detroit Electric Automobile...
a Detroit worm-drive rear axle and motor assembly.
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.
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:
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.
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.
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.
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