Unleaded petrol: Safer than leaded?

By Kardono

JAKARTA (JP): Lead gasoline car emission is now widely debated. It has been linked to health disorders such as neurological damage and heart disease in adults and learning disabilities and decreased IQs in children.

The state-owned Pertamina oil company launched unleaded gasoline in August 1995. It was entitled BTT (Bahan Bakar Tanpa Timah). The government plans to use this to gradually phase out lead gasoline.

The World Bank has urged all nations to phase out lead gasoline because of related health problems.

Studies in the U.S. by Caio Koch-Weser (a World Bank representative) have suggested that for every dollar invested in unleaded gasoline a community will save ten dollars in health and other costs.

The cheapest and most efficient way to make unleaded gasoline is to add tetra ethyl lead (TEL) to gasoline. This process raises the price of unleaded gasoline. The market price of normal gasoline is Rp 700 (US$ 0.3) compared to around US$ 0.4 for unleaded.

Adding lead alkali anti-knock compounds to gasoline increases octane quality (RON). RON or research octane number is an international measure of gasoline quality. A higher number means higher octane quality - RON numbers for gasoline generally fall between 80 and 98.

Typically, a car designed to run on 98 RON gasoline will have a 10 to 15 percent better fuel economy than one designed to run on 90 RON fuel.

Many older cars cannot use unleaded fuel. Leaded gasoline lubricates an engine's exhaust valve seats. Older cars have engines with cast-iron cylinder heads with `soft' valve seats. If these cars use unleaded fuel, the valves may recess into their seats which causes engine damage.

Most modern cars are fitted with catalytic converters which stop this problem occurring.

Fuel additives, made of sodium, potassium and phosphorus, help older cars use unleaded fuel, but they are not as effective as leaded fuel, especially when engines are under stress. On the other hand, unleaded fuel containing these additives cannot be used in modern catalyst engines.

When reducing or eliminating lead in gasoline, refineries must add certain components to maintain octane quality. These components include benzene, toluene, xylenes and ethyl benzene.

Also to enhance octane quality, a refinery is likely to use an aromatic or oxygenates such as ethers, methanol or ethanol.

These components, added in 5 to 15 percent concentration, are not cost-effective and may cause technical and environmental problems.

There is no doubt that high lead levels are dangerous. Lead can affect the central nervous system and cause hypertension, increased coronary heart disease, cardiovascular disease and damage brain development in children. Lead can also cause deposits in engines and exhaust systems.

Unleaded fuel has been promoted as a replacement to leaded fuel but there are environmental problems associated with unleaded fuel which may be more dangerous.

It is well known that aromatic hydrocarbons in gasoline are carcinogenic, with benzene being the most potent. Increased exposure to benzene in gasoline is reported to contribute to increased incidence of leukemia. Unleaded fuel requires greater use of aromatics.

Increased aromatics also increase ozone levels. The aromatic and olefinic components of gasoline produce photochemically reactive exhaust emissions. That is, they will create ozone.

The aromatic, olefins and oxygenates in unleaded gasoline produce health and environmental dangers greater than lead when unleaded fuel is used in cars not fitted with catalysts. The carcinogenic component of such emissions is benzene. Leukemia and lung cancer are caused by monoaromatic compounds in emissions including toluene and xylenes, polyaromatic hydrocarbons (PAHs), formaldehyde and other aldehydes.

Gasoline containing elevated levels of aromatics also have a higher calorific value. Such fuels have been shown to produce greater amounts of nitrogen oxides in car emissions.

Good catalysts fitted to well maintained cars are likely to significantly reduce hazardous emissions. But a question mark remains over the durability of catalysts, especially three-way catalysts. We must also see to regular inspection and maintenance of catalyst-equipped cars.

Three-way catalysts, which control hydrocarbon, CO and NOx exhaust emissions, necessitates electronic fuel injection, either multipoint or throttle body, to ensure correct fuel metering.

This is required to maintain an air-fuel ratio which is at or near a stoichiometric (14.7:1) point so that the catalyst can simultaneously convert HC, CO and NOx into harmless products.

It is widely recognized that, even in a new car, deposits will build-up on the inlet valves of fuel injectors and in the combustion chamber which can lead to more exhaust emissions.

Deposits formed in these sensitive areas are largely due to olefins and aromatics in fuel which polymerize and decompose into carbonaceous products.

Clearly, reducing risks from leaded fuel has created other dangers associated with the increased use of aromatics in unleaded fuel, especially in non-catalyst and poorly serviced cars.

Window: Uleadeed fuel has been promoted as a replacement to leaded fuel but there are environmental problems associated with unleaded fuel which may be more dangerous.