Oil is becoming scarcer and progressively more expensive, and as a consequence road transport is in crisis. It is only by developing ever more economical cars and alternatives such as hybrid and electric cars that the remaining resources can be eked out until entirely new technologies, such as fuel cell powered cars, become available.
Over recent years major motor manufacturers, often in partnerships with universities and research organisations, have been developing increasingly efficient cars. Here we will look at how they have reached the current position and how much further they are likely to go.
Just a few years ago, an economical car would deliver at best around 50 mpg. Nowadays it is not at all unusual to find cars with fuel economies of 75 mpg or even better, and even some relatively high performance cars can return around 60 mpg.
There are five basic ways to make a car more fuel efficient. These are the reduction of drag by employing sophisticated aerodynamic design; the reduction of weight, for instance by replacing heavy metallic components with their lightweight carbon fibre equivalents; more efficient generation of power using more efficient engines; developing more efficient ways to transmit the power to the wheels, in other words a more efficient drive train; and harvesting power lost by braking, for instance kinetic energy recovery systems.
In terms of aerodynamics, there is not much further to go. Modern cars use wind tunnel data in their design and this has allowed drag factors to be reduced to very low levels.
Currently the use of carbon fibre components in racing and supercars is standard, but for ordinary road cars it is prohibitively expensive. However, as manufacturing techniques improve and new developments are made, these will eventually trickle down.
Harvesting power from braking has made a significant headway, though it still has a long way to go. Energy storage using improved battery technologies will help. There is a huge amount of heat lost through engine cooling and exhaust emissions, and it is theoretically possible to harvest some of this energy too, and although the technology has not yet been developed, new thermoelectric materials that can convert exhaust heat directly into electricity are being trialled.
The development of more efficient engines has made tremendous progress over recent years and most of this is due to advanced in the development of advanced engine control systems, associated sensors and software. There is still plenty of space for further improvements and the Holy Grail is to be able micro-manage every individual piston stroke.
Power is transmitted from the engine to the wheels via the drive train which includes the gearbox. Drive train efficiencies have improved considerably over recent years, but they are still quite inefficient by virtue of the fact that they consist of so many moving parts. Using lighter materials helps, but new revolutionary ways of accomplishing the task are being developed in a number of centres.
The potential of all these developments is hybrid cars that are capable of around 100 mpg. It can’t come too soon.
