Automotive Technology International
More than 70 per
cent of distillate diesel fuel in 1995 was used
by three regions: Western Europe (25 per cent).
Asia (24.8 per cent) and North America (22 per
cent). As figures show, diesel use will
predominate over any alternative fuels, so it is
important to address the environmental
consequence of its use.
In recent years emissions have been reduced substantially due to a combination approach between engine manufacturers and fuel producers. Improvements in engine design have had the greatest effect, but better fuel quality has also allowed engine manufacturers to design the new-generation vehicles around cleaner fuels. However, the rise in diesel vehicle numbers will largely negate improvements achieved so far if further improvements are not made. Although engine manufacturers will need to make further progress, the role of cleaner fuels will become more important in reducing emissions as is reflected in the greater constraints being imposed on diesel quality, such as low sulphur, density, and cetane number.
To understand the necessity for additives to balance the fuel to meet legislative requirements, it is instructive to understand the constrains that refiners face when producing the fuel.
Diesel in Europe is mainly straight run material made by distilling crude oil. Straight run diesel is generally better quality than diesel that is produced from either catalytic cracking, thermal cracking or hydrocracking. Refiners need to balance the requirements for gasoline, kerosene, naptha, and diesel in the commercial market when determining whether straight run diesel production will be sufficient to meet these constraints, which affect the final quality of diesel in terms of its cetane number, density, 95 per cent distillation recovery temperature, aromatic content and so on. A number of fuel suppliers marketing their diesel as greener diesel employ this refining technique to produce more straight run diesel and take the lighter fractions. This ensures fewer emissions of hydrocarbons and particulates and black smoke, but fuel consumption is higher, because the fuels are less dense than conventional diesel.
These and other diesels are also treated with various additive packages to help meet legislative and functional standards. It has been estimated by the European oil industry association, Europia, that the environmental standards set for fuels in the year 2000 and beyond could cost the industry between $75 and $100 billion in investment. In light of this, the role of fuel additives in meeting the environmental standards economically becomes more important.
(Diesel fuels in Europe contain a number of additives)
Antioxidants, stabilisers and metal deactivators.
Distillate fuels made from thermal cracking are less stable and tend to oxidise, especially if heavy metal ions are present in the fuel. Antioxidants, stabilisers and metal deactivators are often used in small amounts to prevent oxidation.
Corrosion inhibitors. These are used to protect diesel fuel pipelines from rusting and contaminating the fuel and blocking filters in the distribution system.
Antistatic additives. These additives aid in dispersing the build-up of static during fast rates of pumping. Anti-icers. Diesel fuel contains small amounts of water, which may separate out at low temperatures. Anti-icers typically lower the freezing point and therefore prevent this condition from occurring.
Dehazers and demulsifiers. Finely dispersed droplets of water may give rise to haziness of fuel. To accelerate the clearance dehazer, additives are used. Demulsifier additives are used to avoid problems due to pick up of storage tank bottoms.
Biocides. These can prevent bacteria and fungi growth, which may occur in the bottom of fuel tanks.
Antifoamants. These are added to ease pumping and preventing spills.
Dyes and markers. These identify the different grades and differently taxed fuels.
Odours, masks and odourants. These reduce the unpleasant smell of diesel fuel.
The additives listed above are functional additives, which do not contribute to improvements in the emission performance of diesel fuel. Additives which improve the injection and combustion properties of diesel fuel are known as performance additives.
Performance additives
Detergents. These control the build-up of fuel deposits which impede combustion. Injector needles tend to foul with gummy deposits, resulting in mis-firing, power loss and increased smoke. Other symptoms may include noisy combustion, exhaust odour and heavy cold smoke.
Cetane improvers. Cetane improvers are compounds which raise the cetane number of the diesel fuel and reduce the delay between injection and ignition. An increase in cetane number usually leads to better combustion, less smoke and improved ignition.
Metallic combustion improvers. Traditional combustion improvers were organometallic compounds, which had a catalytic effect on the combustion process. These compounds were barium-, calcium-, manganese- or iron-based. Barium has now largely been discarded as an additive due to concerns about its effect on human health. At present, there is some interest in using these metallic compounds in combination with particulate traps. These compounds reduce the autoignition temperature of soot, thus allowing the soot to be ignited by the hot exhaust gases. Although still in use there is growing concern about the health effects of manganese and iron additives.
Non-metallic combustion improvers. A new generation of combustion enhancing additive has recently been introduced. Although research is continuing on this product, early results are interesting. This additive is primarily composed of various hydrocarbon compounds and works in two ways: by reducing the ignition delay of the diesel fuel and by improving the back end of combustion, reducing particulate and other emissions dramatically.
Non-metallic technologies can have a considerable impact on reducing diesel exhaust emissions and fleet trials in European diesel vehicles show that non-metallic technology is effective in operational use.
| Automotive Technology International 1999 | |
| The role of additives in
improving diesel performance S.O. Hayat, ChemEcol (UK) Limited |
|
| ABSTRACT |
In recent years emissions have been reduced substantially due to a combination approach between engine manufacturers and fuel producers. Improvements in engine design have had the greatest effect, but better fuel quality has also allowed engine manufacturers to design the new-generation vehicles around cleaner fuels. However, the rise in diesel vehicle numbers will largely negate improvements achieved so far if further improvements are not made. Although engine manufacturers will need to make further progress, the role of cleaner fuels will become more important in reducing emissions as is reflected in the greater constraints being imposed on diesel quality, such as low sulphur, density, and cetane number.
To understand the necessity for additives to balance the fuel to meet legislative requirements, it is instructive to understand the constrains that refiners face when producing the fuel.
Diesel in Europe is mainly straight run material made by distilling crude oil. Straight run diesel is generally better quality than diesel that is produced from either catalytic cracking, thermal cracking or hydrocracking. Refiners need to balance the requirements for gasoline, kerosene, naptha, and diesel in the commercial market when determining whether straight run diesel production will be sufficient to meet these constraints, which affect the final quality of diesel in terms of its cetane number, density, 95 per cent distillation recovery temperature, aromatic content and so on. A number of fuel suppliers marketing their diesel as greener diesel employ this refining technique to produce more straight run diesel and take the lighter fractions. This ensures fewer emissions of hydrocarbons and particulates and black smoke, but fuel consumption is higher, because the fuels are less dense than conventional diesel.
These and other diesels are also treated with various additive packages to help meet legislative and functional standards. It has been estimated by the European oil industry association, Europia, that the environmental standards set for fuels in the year 2000 and beyond could cost the industry between $75 and $100 billion in investment. In light of this, the role of fuel additives in meeting the environmental standards economically becomes more important.
(Diesel fuels in Europe contain a number of additives)
Antioxidants, stabilisers and metal deactivators.
Distillate fuels made from thermal cracking are less stable and tend to oxidise, especially if heavy metal ions are present in the fuel. Antioxidants, stabilisers and metal deactivators are often used in small amounts to prevent oxidation.
Corrosion inhibitors. These are used to protect diesel fuel pipelines from rusting and contaminating the fuel and blocking filters in the distribution system.
Antistatic additives. These additives aid in dispersing the build-up of static during fast rates of pumping. Anti-icers. Diesel fuel contains small amounts of water, which may separate out at low temperatures. Anti-icers typically lower the freezing point and therefore prevent this condition from occurring.
Dehazers and demulsifiers. Finely dispersed droplets of water may give rise to haziness of fuel. To accelerate the clearance dehazer, additives are used. Demulsifier additives are used to avoid problems due to pick up of storage tank bottoms.
Biocides. These can prevent bacteria and fungi growth, which may occur in the bottom of fuel tanks.
Antifoamants. These are added to ease pumping and preventing spills.
Dyes and markers. These identify the different grades and differently taxed fuels.
Odours, masks and odourants. These reduce the unpleasant smell of diesel fuel.
The additives listed above are functional additives, which do not contribute to improvements in the emission performance of diesel fuel. Additives which improve the injection and combustion properties of diesel fuel are known as performance additives.
Performance additives
Detergents. These control the build-up of fuel deposits which impede combustion. Injector needles tend to foul with gummy deposits, resulting in mis-firing, power loss and increased smoke. Other symptoms may include noisy combustion, exhaust odour and heavy cold smoke.
Cetane improvers. Cetane improvers are compounds which raise the cetane number of the diesel fuel and reduce the delay between injection and ignition. An increase in cetane number usually leads to better combustion, less smoke and improved ignition.
Metallic combustion improvers. Traditional combustion improvers were organometallic compounds, which had a catalytic effect on the combustion process. These compounds were barium-, calcium-, manganese- or iron-based. Barium has now largely been discarded as an additive due to concerns about its effect on human health. At present, there is some interest in using these metallic compounds in combination with particulate traps. These compounds reduce the autoignition temperature of soot, thus allowing the soot to be ignited by the hot exhaust gases. Although still in use there is growing concern about the health effects of manganese and iron additives.
Non-metallic combustion improvers. A new generation of combustion enhancing additive has recently been introduced. Although research is continuing on this product, early results are interesting. This additive is primarily composed of various hydrocarbon compounds and works in two ways: by reducing the ignition delay of the diesel fuel and by improving the back end of combustion, reducing particulate and other emissions dramatically.
Non-metallic technologies can have a considerable impact on reducing diesel exhaust emissions and fleet trials in European diesel vehicles show that non-metallic technology is effective in operational use.