Emissions: Overview
by David Finlay (16 December 1999)
In a business as complex that of as designing and building cars, there are always many issues to deal with, but there is usually one which dominates all the others, or at least is the subject of the most publicity and discussion.
Since the 1950s, styling, fuel economy and safety have been the key concerns at various times. Now it's the turn of emissions, which reached the top of the list in the early 1990s and will probably be there for several years into the new century.
Global pollution has, of course, become a major talking-point generally. It's quite natural that when public opinion swung in this direction, cars - polluting objects which roam the world in their millions - should come under scrutiny, and entirely proper that something should be done to clean them up.
And an enormous amount has been done. In fact, the magnitude of the improvement is one of the few things that the motor industry could actually boast about far more than it does.
In rough terms, to make a car move under its own devices you pour petrol in one end and set fire to it. The force of the resulting explosion is used to turn the wheels. This, as your physics teacher told you, is a conversion of energy, and as such is broadly similar to lighting a candle, kicking a football or eating a hamburger.
Furthermore, your teacher will have added, conversion of energy also results in some sort of waste product. The candle gives off smoke, the impact of boot against ball produces sound, and . . . well, you know about the hamburger.
Burning petrol produces a number of waste products which cause varying degrees of concern. The three important ones are as follows:
Carbon monoxide (CO), which is poisonous.
Hydrocarbons (HC), the result of not burning all the fuel properly, which are dirty.
Oxides of nitrogen (NOx), a by-product of heating air, which combines with moisture in the atmosphere to create acid rain.
The most famous antidote to dirty emissions is the catalytic convertor, a required item on any new car sold in the UK since 1993. Catalysts contain precious metals which react with the more harmful parts of the exhaust gas and turn them into safer stuff - carbon monoxide becomes carbon dioxide, for instance.
But improvements have also come in other ways. Simply building engines more precisely is one. Another is the electronic control of ignition and fuel injection, which means that the engine ignites just the right amount of fuel at just the right time.
The results are amazing. According to Community Emissions Directive (CED) 3, which becomes law in 2000 but has been easily met by most cars for several years, a car can produce no more than 2.3 grams of carbon monoxide for every kilometre it travels, averaged out over a standard test route. That's about half a dozen parts per million, compared with the sixty thousand which was common before 1970, when the only ruling on what came out of the exhaust pipe was that you could see through it.
CARkeys will be looking into this subject in more detail over the coming weeks, but here are two final points to consider. The USA, and California in particular, is the home of restrictive emissions legislation. Fine, but it applies to passenger cars, which sell in far smaller numbers than pickup trucks. And are the emissions rules as tight for pickups as they are for cars? No. Not even close.
And what about centrally heated houses? Domestic heating systems are much more common than cars, often run for days at a time, burn their fuel very inefficiently and have almost no emission control beyond making sure the waste products don't leak into your living room.
In other words, if you really want to do the environment a favour, sell your house and live in your car instead.
