Motor Vehicle Pollution and better Fuels

Motor Vehicle Pollution, Alternative Renewable Fuels and Energy Conserving Devices

This note discusses motor vehicles with particular emphasis on pollution and measures which may be taken to reduce it. In the process, alternative fuels and energy conserving design are highlighted.

Motor vehicles contribute significantly to greenhouse gases but nevertheless the rise and rise of petrol, diesel and kerosene vehicles continues at an alarming rate.
Not only do vehicles contribute net carbon gases, mainly CO and CO2, into the atmosphere which contribute to global warming and climate change but the products of combustion also produce additional local pollution. Locally the emission of nitrogen oxides, sulphur and carbon particulates (soot) can be very detrimental to health. We draw the distinction between local and global effects because all fuels have different pollution profiles and an individual, for example such as a mayor, may be only interested in curbing local pollutants. We feel that both are important but the minimisation of greenhouse gases is vital, and green, renewable fuels usually emit low local pollution levels anyway.
The apparently illogical passion to burn fossil fuels this way stems from three main factors: consumer demand, supplier economics and national interests. These driving forces are fundamentally underpinned by the fact that petroleum products (from oil and gas) are, for the time being, readily available and cheap at source. Further, up to now, there has been little in the way of competitive alternatives.
Consider these three factors:

Consumers see motor transport as attractive because of the independence it confers to transfer themselves and freight from place to place conveniently. Aircraft are perhaps the ultimate example of freedom since they enable us to move anywhere on the globe in a matter of hours. A car is also a socially desirable possession which often enhances personal status and is, to many, a pleasure to own and drive.

Suppliers are the nations who have oil as a natural resource in their territory and they are complemented by companies who process and distribute the refined fuels. The major oil producing nations have economies based on their oil reserves and have strong vested interests in the continuation of international demand for the fuel. Multinational firms have invested huge amounts in oil exploration, extraction, refinement and delivery and there are enormous profits to be made.

National interests are often associated with prosperity and the ability to wage war. Prosperity is measured by the individual by their standard of living which is closely linked to transport costs, a politician who maintains low fuel prices is likely to be popular. Both the capacity to be an aggressor or to defend against an aggressor are dependent, to a large extent, on the ease with which troops and armaments can be mobilised, deployed and delivered to strategic positions.

There are no totally satisfactory competitors at the moment to oil based fuels but below we discuss some imminent developments.
Oil and gas are hidden treasures buried in the ground, so oil and gas raw materials are intrinsically cheap, requiring only the costs of finding and taking; and that is not all. There are three other features that make derivatives such as petrol, diesel and kerosene uniquely attractive: their very high energy densities, the speed of recharging and the existing world-wide distribution network.
Look at these three features in more detail:

Energy densities are of prime importance because the fuel has to be carried in the vehicle if it is to have mobility in 2 or 3 dimensions. Ground based transport can move in 2 dimensions and aircraft in 3. If the fuel is not carried on the vehicle, an umbilical link ties it effectively to a 1 dimensional fixed path, for example an electric train or tram.
To illustrate the difference in energy densities let's take three alternative and new clean energy sources which could give 2 dimensional flexibility: rechargeable electric batteries, hydrogen gas and Fuel Cells (which are batteries energised by some form of hydrogen). Rechargeable batteries are relatively expensive and heavy (due to their low energy densities) and so, currently, they are impractical in many cases. If you take a comparison between the energy stored per unit weight of petrol and lead-acid batteries the ratio is about 500:1; even with nickel-metal hydride batteries (another possible contender), the ratio approaches 300:1. Lithium-ion is becoming a practical, commercial energy storage device for use in motor vehicles, it has an energy density some 30% to 60% higher than Ni-MH but the supply of Lithium can make the cost volatile.
Pure Hydrogen would be ideal, if sustainably derived, but unfortunately this is a gas and so by definition has a very low density. Extreme compression or cryogenic temperatures are needed to overcome this problem which poses technological problems and adds safety concerns, although the latter are exaggerated because the techniques are well tried and proven.
Fuel Cells are based on hydrogen but liquid compounds containing hydrogen can be used instead of pure hydrogen. Such a system can, theoretically, have energy densities approaching those of the conventional combustion engine but if this means using petroleum compounds then its main advantage is lost.
[For a useful reference on Energy Densities try the pdf article: "Fuels of the Future for Cars and Trucks", Dr. James J. Eberhardt, Energy Efficiency and Renewable Energy, U.S. Department of Energy, 2002 Diesel Engine Emissions, Reduction (DEER) Workshop, San Diego, California, August 25 - 29, 2002. Click here for the pdf.]

Speed of recharging is a crucial factor and the comparisons are easy to make. How long does it take to recharge your car (in other words fill the tank with petrol), about three minutes? Even allowing for the further three minutes it takes queuing to pay, that is incredibly fast and by comparison it might take half a day to recharge a set of batteries using today's technology.

A distribution network of conventional oil-based fuels is now established world-wide. For alternative fuels it might take a long time to build up even a fractional infrastructure to compete with existing service stations. However that is not necessary if the alternative fuel could be supplied and handled within the existing infrastructure.

Are there any competitors at all in practice? Well, when it comes to cars, buses and lorries there are some developments. Private and fleet cars are so numerous that they contribute significantly to the greenhouse effect so they form an important group.
We can identify several possible alternatives which go some way towards reducing pollution:
[Note: to access reference articles for more information on each topic, click on the adjacent orange buttons.]

Biodiesel (a Biofuel)

Compression ignition internal combustion engines are common and are traditionally fuelled by diesel derived from petroleum oil. Thankfully diesel is a compound which can be replaced with biodiesel which is an organically based product and is renewable. It is relatively easily produced from plant and animal oils, fats and greases. Biodiesel also gives other benefits in the pollution stakes. Biodiesel definitely gets the 'thumbs up'.

Liquefied Petroleum Gas (LPG)
An alternative to petrol (gasoline) it offers lower local pollution levels than normal fuels and vehicles that run on LPG (or are converted to) receive some subsidies in the UK. This fuel is compatible with petrol and many vehicles can run on either (dual-fuel vehicles) so the limited distribution of LPG is not a problem. Its main claims to fame are its reduced local pollution and it is also cheaper to run. Since it is petroleum based (oil or natural gas) it is not renewable and does not qualify for tackling climate change. Now if we could have a Liquid Renewable Gas that would be worth shouting about.

Liquefied Natural Gas (LNG) and Compressed Natural Gas (CNG)

In practice, LNG and CNG are replacements for petro-diesel and suitable for heavier freight vehicles. Natural gas is intrinsically cleaner than petroleum gas but since it is a fossil fuel it is not renewable and contributes to global warming. At a local level it produces much less pollution than petrol or diesel and its use attracts financial incentives. The fuel tanks are specially designed for intense refrigeration (LNG) or high pressure (CNG) which makes them larger and heavier.

Ethanol and Methanol

Can be used as alternatives or complements to petrol (gasoline) and can give less local pollution. If the raw source is petroleum then they are not renewable but they can be produced organically (eg from sugar cane) and then they can contribute real advantages in reducing climate change. Producing these alcohols organically can also bring economic benefits, for example, to farmers.

Fuel Cells

Fuel cells are not, strictly speaking, renewable or alternative energy, they are engines which convert energy; the energy source is actually hydrogen. We include them here because potentially they could be so important in the battle for clean and efficient energy. They are not new but the technology is complex and research and development is needed to make them more accessible. The hydrogen fuel can be derived from a variety of sources. Ideally they could be fuelled by pure hydrogen, manufactured by a renewable process, but on the other hand, they might be fuelled by some hydrocarbon compound. If the source of energy is renewable then we have a desirable situation but if it is petroleum derived, for example, then it is not a renewable system. There are developments which indicate that fuel cells may provide an important source of energy in transport applications.

Hybrid engine systems
These use internal combustion engines in tandem with battery-driven electric motors to conserve energy, and a few domestic cars are now in production. The batteries are charged from the kinetic energy of the vehicle (eg when braking). Japan is leading the way with at least two production models and theoretically you should be able to go out and buy one of these, although our attempts to see one in the flesh, so to speak, met with no success. The Toyota Prius and the Honda Insight are cars which use Nickel-metal Hydride batteries (designed, it is claimed, to last as long as the car) and these are charged by the petrol power unit (via an alternator) during normal driving. Power is delivered to the wheels by either unit or both depending on the demands such as acceleration, during cruising or braking. The two vehicles use slightly different power sharing systems but the outcome is similar. Currently the vehicles are dearer, for their class, than petrol and diesel cars (even taking into account subsidies in the UK) and they only mitigate the problem of carbon emissions, they don't solve it. Nevertheless the energy that is regenerated is truly green.
One advantage of the electric system over the petrol engine is the torque available over a wide speed range, a normal car has several gears to narrow the speed range in use.

[Further information on Hybrid Cars is available on the main Motor Vehicle page.]

In summary:
Petrol and diesel fuelled vehicles have a strong track record and a very strong popularity because of the cheap and flexible fuel characteristics. It seems unlikely that they will be replaced in their entirety for the foreseeable future. Unfortunately this state of affairs is going to continue the trend to change the climate detrimentally. On the other hand there are development programmes which address the problem, if only in a small way at the moment.
Biodiesel is a green fuel that deserves more attention and better concessions than it currently gets, in the UK.
LPG, as a fuel, appears currently to be a relatively wide-scale method of reducing local pollution, and it also makes for cheaper driving with the large tax concessions. It is primarily suited to cars and small petrol vehicles and the cost benefits are mainly applicable where high mileages are the norm. Fleet vehicles, local authorities and some small road transport utilities are well suited to the technology. More filling stations and purpose built vehicles are coming on stream.
LNG and CNG attract similar comments as LPG but the fuel is suited to large diesel vehicles. We think that the money used to subsidise these fuels and LPG could better be spent on encouraging the use of other fuels such as biodiesel and organically derived ethanol and methanol.
Ethanol and Methanol can be green fuels if only they are derived from sustainable energy crops. Despite their lower energy densities they hold significant potential for low global pollution.
Fuel Cells are high profile devices hyped for their promise. Technologically they are indeed very interesting and hold great potential for flexibility. The bottom line is, however, that development is needed and they must be engineered to be charged with green fuel.
Hybrid vehicles are still in the beta stage, but they can be bought now. The proportional saving of energy (more mpg) is truly green. If we are optimistic perhaps the hybrid cars will start an alternative approach to transport, increasingly using efficient electrical motors.
Aircraft Transport seems to be tied irrevocably to petroleum fuels for the foreseeable future hence they will remain global-warming behemoths. The only way to reduce their detrimental effect would seem to be a special taxation with the proceeds being used to offset their polluting contribution. Since governments are reluctant to do this we suggest paying a voluntary tax each time you fly by planting a few trees via, for example, The CarbonNeutral Company scheme.