Fuel additives

Details Fuel additives Fuel additives

2000-06-30

2002-12-03

Toomer, Cephia D. (Department: 1714)

Fuel and related compositions

Liquid fuels

Aluminum or heavy metal, other than lead, containing

C044S361000, C044S362000, C044S363000, C044S365000, C044S373000, C044S385000, C044S439000, C044S450000

Reexamination Certificate

active

06488725

ABSTRACT:

The present invention relates to the use of fuel additives in the regeneration of particulate filter traps, e.g. diesel particulate filter traps. The invention further relates to fuel additives suitable for use in such a process.
Products from the combustion or pyrolysis of hydrocarbon fuels include carbon monoxide, nitrous oxides (NO
x
), unburned hydrocarbons and particulates. These particulates include not only those particulates which are visible as smoke emission, but also unburned and partially oxidised hydrocarbons from fuel and the lubricants used in engines.
Diesel particulates, i.e. particulates from the combustion or pyrolysis of diesel fuels, comprise inorganic ash (due to engine wear particles and combustion products of lubricant oil additives), sulfuric acid (due to sulfur in diesel fuel) and hydrocarbons from incomplete fuel combustion. The hydrocarbons are typically further divided into SOF (solvent organic fraction, i.e. material extractable in e.g. CH
2
Cl
2
) and a hydrocarbonaceous soot. Diesel smoke represents the obscuration of visible light by emissions of particulates (black smoke) and/or that arising from condensation of unburned or partially burned fuel (white smoke), typically during cold-start.
The emission of black smoke from diesel engines is a well-known problem. In addition to being unsightly, such emissions contain particulates and unburned hydrocarbons which are understood to represent a hazard to health. In particular, unburned hydrocarbons emitted into the atmosphere are irritant astringent materials. Further, in a problem recently highlighted for diesel fuels, emissions of particulate matter of less than 10 micrometers (&mgr;m) of principle dimension (“PM10 matter”) are claimed to cause 10,000 deaths in England and Wales and 60,000 deaths in the USA annually (see New Scientist, March 1994, p.12). It is suspected that these smaller particles penetrate deeper into the lungs and adhere. Whilst the mucocilliary system is thought to have evolved to cope with airborne dusts, pollens etc., this does not cope well with smaller particles, especially those of less than 2.5 &mgr;m aerodynamic diameter.
Diesel fuels and diesel engines are especially prone to the emission of high levels of small size soot particulate matter in the exhaust gas. This is particularly so when the engine is highly loaded, worn or badly maintained. Particulate matter is also emitted from diesel engine exhausts when operated at partial load and these emissions are normally invisible to the naked eye.
Legislation now exists in many countries that is designed to control pollution from diesel engines. More demanding legislation is planned. A number of ways are being examined to enable diesel engines to run and comply with the developing legislation. Engine designs to give effective combustion within the cylinder are being developed. The engine designs developed to achieve low levels of emission are well known to those familiar with the art and examples of such designs are given in S.A.E. International Congress (February 1995) S.A.E Special Publication SP-1092. However, the drawbacks to engine management solutions such as these include cost, complexity and the poor capability for retrofitting.
As part of the process of reducing emissions from the diesel engine many modern engine designs use a technology known as Exhaust Gas Recirculation (E.G.R.) in which exhaust gas recycled in a controlled way to the intake of a diesel engine can contribute to the reduction of certain emissions species, mainly oxides of nitrogen (NOx). However, there are two significant drawbacks associated with the use of E.G.R. Firstly, particulates production and hence emission is increased, and, secondly, soot particles in the exhaust gas are recirculated within the engine. Thus, in addition to any emissions problems encountered, engines running with E.G.R. for prolonged periods of time can become choked with carbon particulates in areas such as the exhaust gas recycle lines and control valves, inlet ports and valves, and the piston top ring lands. Even the piston rings themselves can become choked in the ring grooves.
Also, carbon and other particles become deposited in the engine lubricant so causing its premature deterioration.
As an alternative and/or adjunct to means of reducing the production of particulates or other pollutants, various post-combustion treatments have been proposed. These include De-NOx catalysts, hydrocarbon oxidation catalysts and the use of particulate filters, especially diesel particulate filters (DPFs), capable of oxidising collected material. The use of DPFs is particularly desirable in the light of recent evidence to suggest that the mass of particulates emitted may be of less importance than the number of ultrafine particles (usually regarded as those having a diameter of 2.5 &mgr;m or less). Furthermore, DPFs can function without the need to further reduce fuel sulfur levels.
Particulate filter traps (also referred to as particulate filters or particulate traps) are well known to those familiar with the art. Some examples are discussed in “Advanced techniques for thermal and catalytic diesel particulate trap regeneration”, S.A.E. International Congress (February 1985) S.A.E. Special Publication-42: 343-59 (1992) and S.A.E. International Congress (February 1995) S.A.E. Special Publication SP-1073 (1995). Diesel particulate filter traps exhibiting high efficiency for particles of aerodynamic diameter 10 &mgr;m and below have been demonstrated (Dementhon et al., SAE 972999).
A problem associated with the use of particulate filter traps is that of trap blockage which causes an increase in exhaust back pressure and a loss of engine efficiency and/or “chimney fires” resulting from sudden and intense burn off of soot from highly loaded traps.
Catalytic devices have been used to aid in trap oxidation. NO
2
is known as a powerful oxidant. Using a by-pass system it is possible to produce high concentrations of NO
2
in the exhaust gas when regeneration is required. However, these devices require a low sulphur fuel (<50 ppm) to avoid increased sulfate emissions when using this method. Also, low speed engine operation can cause carbonaceous deposits to form on the active parts of the diesel engine oxidation catalyst and so inhibit the effectiveness of the catalyst until a sufficiently high gas temperature is available to regenerate the catalyst active surface.
DPFs which feature ‘washcoats’ comprising metal ions capable of catalysing soot oxidation are also known in the art, see A Mayer et al. SAE 960138, R W McCabe and R M Sinkevitch SAE 870009 and B Engler et al. SAE 860007. These do offer improved regeneration under ideal or near-ideal conditions, but suffer the potential for blocking of the active sites by the coating of soot deposited under conditions adverse for regeneration.
A number of fuel additives have been proposed in an attempt to solve the problems inherent in the use of diesel particulate filters (see, for example, Miyamoto et al. SAE 881224; Martin et al. I. Mech. E. November 1990; Lepperhoff et al. SAE 950369; Rao et al. SAE 940458; Ise et al. SAE 860292; and Daly et al. SAE 930131) These additives serve to reduce the soot ignition temperature such that suitable conditions for trap regeneration (i.e. decrease in back pressure) occur at high frequency during normal driving. However, in general such additives also require the back-up of some active management system capable of triggering a regeneration following prolonged periods of abnormal use, such as idling. In this situation the additives serve to reduce the energy input required to initiate regeneration.
Iron-based additives are known for use in the regeneration of particulate filters and are described, for example, in WO-A-92/20762.
The use of alkali and alkaline earth metal-based additives for the regeneration of diesel particulate filters is described, for example, in WO-A-96/34074 and WO-A-96/34075.
The present invention seeks to provide improved fuel additives capable of the regeneration of particulate filt

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