FR2720405A1 - Reduction of carbonaceous particulate emissions in vehicle exhausts - Google Patents

Abstract

Carbonaceous particulates ('soot') containing rare-earths are treated by contact at 200-400 deg.C with an O2-contg. gas whose O2 partial pressure is at least 3% of atmospheric. Also claimed are: (1) Fuel additive comprising a cpd. of a rare-earth of oxidation state greater than three and a cpd. of a transition metal or another rare-earth; and (2) soot made by combustion of fuel containing this additive.

Description

METHOD FOR REDUCING THE EMISSION OF SOOTS OF AN ENGINE
INTERNAL COMBUSTION, COMPOUNDS OF LANTHANE
AND THEIR USE TO REDUCE POLLUTION
The present invention relates to a method for reducing the emission of soot from an internal combustion engine. More particularly, it relates to the use of lanthanum and various lanthanum-containing compounds as promoters for soot combustion.

When burned in an internal combustion engine, and especially in a diesel engine, carbonaceous products tend to form soot that are deemed harmful both for the environment and for health.

For a long time, techniques have been sought which would make it possible to reduce the emission of these carbonaceous particles, generally referred to as "soot". This research must take into account restrictions on the emission of carbon monoxide and / or gases known to be toxic and mutagenic such as nitrogen oxides.

Among the many solutions that have been proposed to reduce these carbon emissions, that of adapting on the exhaust line a filter capable of stopping almost all (at least 80% by weight) of the carbonaceous particles induced by combustion various fuels, seems to have more and more the favor of specialists.

Once the gas filtration option adopted, there remains a problem to be solved namely the accumulation of soot in the filters. Indeed soot cause in the first time an increase in pressure drop and, in a second time, a start of shutter that leads to a loss of efficiency of the internal combustion engine.

Many attempts have been made to burn these soot. It has been proposed to cause the combustion of these soot intermittently either by electric heating or by heating with the flame of a fossil igniter fuel.

It was also considered the possibility of drawing the heat necessary for the ignition of these soot in the engine itself by a skilful management of gas flows so as to heat the soot accumulated in the filter and ipso facto to cause their inflammation ( temperature of about 500 ° C. It has also been proposed to introduce ignition catalyst precursors in the various fuels so as to reduce the temperature threshold at which the soot ignition is spontaneous.

These techniques, in particular that of the combination of the increase of the soot temperature using a suitable circuit, and transient, of the exhaust gases with addition of precursor (s) of oxidation catalyst (s) have at least partially solved the problem.

However, on the one hand the ignition temperature remains relatively high and secondly the intermittent and brutal combustions may damage the filter and alter its filtration capacity either by cracking due to thermal shock, or even by fusion.

Therefore, it is an object of the present invention to provide a soot combustion catalyst which can lower the ignition temperatures to values below 500 ° C.

Another object of the present invention is to provide a method of using these catalysts which avoids sudden, violent and sudden ignitions leading to damage to the filter.

Another object of the present invention is to provide a method of the above type which makes it possible to avoid that during the ignition phase at any point in the filter the temperature reaches 1000.degree. C., advantageously 900.degree. preferably 700 ° C.

Since it is difficult to measure local temperatures, it has been established that the above constraints correspond to maximum gas temperatures at the filter temperature of at most about 600 ° C ("about" means here that the zeros, which here are position zeros, are not significant digits), preferably at 500 ° C.

These and other objects which will become apparent are achieved by means of a method for reducing the soot emission of an internal combustion engine in which the exhaust gases are passed through a filter. particles and into which is introduced into the combustion chambers an additive containing lanthanum.

According to one of the embodiments of the present invention, the lanthanum is added to the fuel in the form of a salt or a stable sol.

The use of rare earths as combustion aids has long been described in the prior art, but lanthanum has only been cited incidentally, or rather accidente, as a member of this family.

More recently, in a comprehensive study conducted at the French Institute of Petroleum on various rare earths and on their ability to catalyze the oxidation of soot, M.

DESOETE has shown that lanthanum has no catalytic properties on carbonaceous particles.

This article published in English and entitled "Catalysis of soot combustion by metals oxides" dated February 1988 and published under the reference 35991 (available on public demand) clearly shows in Figure 10 the absence of effect of the oxide of lanthanum.

In a completely surprising manner, the soot formed by the introduction of lanthanum-based compounds into the circuits of internal combustion engines, and in particular diesel engines, have the property of being significantly more flammable, i.e. with a lower ignition temperature than soot prepared without additives.

The introduction of lanthanum compounds can be achieved in particular by the introduction of lanthanum compounds in the fuel to be introduced into the engine.

Another possibility is to introduce the lanthanum in various forms via air, including air when mixed with engine exhaust gas, when a fraction of the exhaust gas is recycled in the engine. In this case, the lanthanum compounds incorporated in the recydified soot are introduced into the engine.

One of the most practical ways to introduce lanthanum into the engine circuit is to introduce it into the fuel either as salt or as soil.

These compounds, salts or sols, advantageously comprise products that are not harmful for combustion or for the environment.

Thus, it is preferable that the salts or the sols are prepared from hydrocarbon compounds such as carbon-acid salts, whether of the carboxylic type or of the mobile-hydrogen compound type such as, for example, acetylacetonates.

It is also possible to envisage sulfur-type acid compounds such as sulfuric acids (alkyl or aryl acid sulphates) or sulphonic acids. However, these latter acids have the disadvantage of increasing the sulfur content of the fuel.

In general, the carboxylic acid salts of C2 to C20, preferably of
C4 to C15, are among the best suited for this purpose.

To obtain a good catalysis of the soot combustion, it is advisable to ensure in soot a satisfactory concentration of the lanthanum and its possible adjuvants of potentiation; this concentration is advantageously between 500 ppm and 10%, preferably between at least 1000 ppm (weight of metal contained relative to the total mass of the soot, including the compounds which they have adsorbed) and at most 5% by weight. average.

In most engines marketed today, it is advantageous to introduce lanthanum, with its attendant impurity (s) and adjuvant (s), at a content between 10 and 1000 ppm in the fuel. These values are expressed in contained metal.

Advantageously, contents ranging from 20 to 200 ppm, preferably from 50 to 150 ppm, are used.

Some internal combustion engines, such as gasoline engines and some diesel engines being tested and developed, produce or are expected to produce less soot. Since only the regeneration effect of the filter is sought (and not the general improvement of the combustion), this makes it possible to reduce the quantities of lanthanum to be introduced; in fuel, when this mode of introduction has been favored; and more generally in the combustion chamber. This reduction is done in proportion to the production of soot to maintain the lanthanum content in said soot.

 It is advantageous that the form in which lanthanum is introduced induces the formation of aggregates of lanthanum oxide crystallites where the largest dimension of said aggregate is between 20 angstroms and 10,000 angstroms (2 and 1000 nm), preferably between 100 and 5000 angstroms (10 and 500 nm), for which the size of the crystallites is between 20 and 250 angstroms (2 and 25 nm), preferably between 50 and 200 angstroms (5 and 20 nm).

According to the present invention, it has also been shown that lanthanum is an element capable of potentiating, or being potentiated by, other elements that are particularly capable of catalyzing the oxidation of carbonaceous products and those inducing defects in the crystal lattice. lanthanum oxide.

 It has thus been shown that the transition elements, that is to say the metals in which one of the underlays d is being filled, give marked effects of synergy with lanthanum. This synergistic effect is also demonstrated with the other elements of the layers f being filled, and in particular with the other rare earths including yttrium.

The most marked results are those of lanthanum associated with manganese, copper, cobalt and / or iron. Also of particular interest are other rare earths, including yttrium, alone or in mixtures.

The lanthanum content relative to the sum of the metallic elements contained in the adjuvant is generally between 5% and 95%. Advantageously it is at least 50%, preferably 80%
Elements potentiating, or potentiated by, lanthanum are introduced as can be this element.

As mentioned above, another object of the present invention is to provide a process which allows a regeneration which can be described as low temperature particulate filters.

This goal is achieved by a process using the lanthanum compounds discussed above.

This process consists of:
- introducing into the fuel a derivative of lanthanum as specified above at
a concentration of between 10 ppm and 500 ppm (by weight), preferably
between 20 ppm and 200 ppm (in contained metal);
- collect on a filter the soot produced by the internal combustion engine, the
the temperature of the gases entering the filter being chosen in the range 100 -
400 OC (in this description the position zeros are not digits
significant, except where specified), and allow soot to accumulate
until reaching a diet where a notable fraction of the soot is
compensated by burning soot in the soot cake on the filter and not
provide for no forced regeneration as long as the pressure loss caused by the
soot does not exceed a value chosen in advance and advantageously not exceeding
not 500 millibars.

Indeed, according to the present invention, it has been shown that there can be regenerations at temperatures as low as about 100 ° C. During a cycle of a European engine, there can be sudden variations temperature in the exhaust gases which can, without reaching the maximum value above (ie the minimum temperature fatal to the filter (s)), allow to obtain a partial or complete regeneration.

The elements promoting this low temperature regeneration are the oxygen content and the content of hydrocarbon compounds.

With regard to the oxygen content, it is preferable that the oxygen content is at least 3%, preferably about 5%.

With regard to the presence of hydrocarbon compounds in the exhaust gas, it is preferable that the volatility of and the content of the hydrocarbon compounds of the gases and their temperature are such that, at the temperature where the soot accumulates in the filter with particles, the content of volatile hydrocarbon compounds in the soot is at least equal to 10%, preferably a quarter, more preferably one half of the dry mass.

By volatiles is meant all hydrocarbon compounds, especially those existing in the exhaust gas, which at 600 ° C are in the form of gas.

 It is desirable that these hydrocarbon compounds have a boiling point of between 100 and 600 ° C.

This regeneration generally occurs when the content of hydrocarbon compounds in the gases is greater than or equal to 10 ppm, preferably greater than 20 ppm.

The filtration mode according to the preferred embodiment of the invention generally operates only during a part of the engine speeds, because some of the regimes generate gases whose temperature is of the order of 500 C and which therefore cause a Progressive and often complete regeneration of the filter.

Exogenous regeneration can only be considered when it is desired to maintain a particularly low level of pressure drop. As exogenous regeneration, it is then advisable to consider regenerations carried out by a point and not global overheating on all the filter. This possibility is only interesting because occasional overheating does not result in a complete and complete regeneration of the filter.

The point overheating can be achieved by any means known to those skilled in the art such as for example microresistances distributed over the surface of the filter, metal particles heated by eddy currents, mini-arcs (or sparks, or the like).

 It should be noted that the temperature of the gases entering the filter can vary within the temperature range 100-400 ° C. These variations, which can be deliberately caused, promote regeneration and allow a pressure drop to be maintained. low value.

The value of the pressure drop chosen in advance is preferably between 100 and 400 millibars, preferably between 150 and 300 millibars.

The lanthanum adjuvants according to the present invention have the advantage of avoiding sudden regenerations. Thus, when using transition metal-based additives (i.e. metals in which one of the underlays d is being filled) alone, the low temperature regenerations are either non-existent or lead to sudden ignition leading to high temperatures that could damage filters.

On the contrary, in the case of elements containing lanthanum-based derivatives, a state is reached quite rapidly and after an accumulation phase in the filter, in which the quantity of soot arriving on the filter is compensated for by numerous random combustions. , but not brutal, having occurred in the mass of soot accumulated on the filter.

 This results in slight thermal effects as well as much smaller changes in pressure drop.

The following nonlimiting examples illustrate the invention.

TESTING ON ARTIFICIAL SUITS
Soot production method
The soot is obtained by pyrolysis of fuel containing the additive. A tube called "reactor tube" is traversed by a gaseous flow consisting of a mixture of nitrogen and oxygen 98/2 (by volume). The reactor tube is heated by means of a furnace and the gas flow is thus brought to 1200 ° C. Upstream of the furnace, the fuel oil, with or without additive, is sprayed very finely.The oil droplets are transported by the gas stream and are also raised to 12200C.

Under these conditions, the fuel oil partially burns and forms soot. The soot is then collected downstream of the pyrolysis furnace by filtration of the gas stream. If the fuel contains a metal additive, the metal is in the form of oxide intimately mixed with the soot.

The injection rate of the fuel oil upstream of the pyrolysis furnace is adjusted to 10 mVh. Under these conditions the average diameter of the elementary particles of the soot produced by pyrolysis is identical to that of the soot produced by a diesel engine.

According to the studies carried out by the Applicant, the metal additives are used at a concentration in the diesel fuel such that the metal concentration in the diesel is between 0 and 200 ppm. Under these conditions, the metal concentrations in the soot produced by a motor fueled with an additized diesel are between 0 and 4%.

Since the final concentration of catalyst in soot is one of the important parameters that condition the ignition temperature, it was necessary to find out what metal concentration in the fuel oil was needed to obtain the same metal concentration in the soot obtained by pyrolysis.

It has been shown that it is necessary for the metal concentration in the fuel oil to be increased by 20 relative to the concentration of additive in the diesel fuel.

The range is thus of the order of 0 to 4000 ppm by weight.

In conclusion, for the soot obtained by pyrolysis to be representative of the motor soot, the concentration of additive in the fuel oil must be multiplied by 20.

Soot studies by THC or ATG
The soot produced by the pyrolysis furnace can be recovered in ATG.

The conditions are as follows:
Sétaram material: model TG92
Gas flow 2.3 I / h
Air gas
Increasing temperature from 20 to 900 ° C at 1 0 C / min
Soot mass analyzed 20 mg
The ATG records the remaining soot mass as a function of time. By convention we define the ignition temperature as the abscissa of the point defined as the intersection of the baseline at the origin with the tangent to the curve where the rate of combustion is maximum (ie at point of inflection of the curve called "S-).

Study of the reactivity of soot obtained by pyrolysis of aazoles containing additives composed of Lanthanum, copper and cobalt
Copper and cobalt are two metals that are known for their ability to lower the ignition temperature, are known to be toxic and induce hazardous thermal shocks to the filter. One of the objects of the present study was to show the synergy that exists between a metal such as copper or cobalt with respect to lanthanum.

The soots were all produced by the method described above and their burning ability was measured by ATG. the metal concentrations in the fuel oil are certainly very high, but they give indications on an implementation on engine test bench with concentrations in the diesel fuel used as fuel corresponding to about 1 / 20th of the concentrations in the fuel oil.

Additives used
The names of the additives used for this study, and their characteristics are grouped in Table 1:
TABLE I
Characteristic of the additives used

<tb><SEP> Name <SEP> of <SEP> additive <SEP> Concentration <SEP> of <SEP> metal <SEP> in
<tb><SEP> additive <SEP> in <SEP>%
<tb> Cekanoate <SEP> of <SEP> Copper <SEP> 9.2
<tb> Octoate <SEP> of <SEP> cobalt <SEP> 10
<tb> Octoate <SEP> of <SEP> Lanthanum <SEP> 10.23
<Tb>
The tables below give the soot ignition temperatures as a function of the metal concentration in the fuel oil.

TABLE 2
Ignition temperature as a function of concentration
of metal acting alone in fuel oil (comparative examples)

<tb><SEP> n0 <SEP> CONCENTRATION <SEP> IN <SEP> METALS <SEP> TEMPERATURE <SEP> (in <SEP>'C)
<tb> EXAMPLE <SEP> IN <SEP> THE <SEP> FIOUL
<tb><SEP> (mmol / kg)
<tb><SEP> Lanthanum <SEP> Adjuvant <SEP> of <SEP> Conc. <SEP> Of Inflam- <SEP> Abay
<tb><SEP> lanthanum <SEP> total <SEP> mation <SEP>
<tb><SEP> 1 <SEP> 0 <SEP> 490 <SEP> 0
<tb><SEP> 2 <SEP> Copper <SEP>: <SEP> 3.04 <SEP> 3.04 <SEP> 470 <SEP> -20
<tb><SEP> 3 <SEP> Copper <SEP>: <SEP> 7,14 <SEP> 7,14 <SEP> 375 <SEP> -115
<tb><SEP> 4 <SEP> Copper <SEP>: 10.7 <SEP> 10.7 <SEP> 370 <SEP> -120
<tb><SEP> 5 <SEP> Copper <SEP>: 14.2 <SEP> 14.2 <SEP> 360 <SEP> -130
<tb><SEP> 6 <SEP> Copper <SEP>: 17.8 <SEP> 17.8 <SEP> 360 <SEP> -130
<tb><SEP> 7 <SEP> Copper <SEP>: <SEP> 26.8 <SEP> 26.8 <SEP> 355 <SEP> -135
<tb><SEP> 8 <SEP> Copper <SEP>: <SEP> 28.5 <SEP> 28.5 <SEP> 355 <SEP> -135
<tb><SEP> 9 <SEP> Cobalt <SEP>: <SEP> 3.56 <SEP> 3.56 <SEQ> 435 <SEP> -55
<tb><SEP> 10 <SEP> Cobalt <SEP>: <SEP> 7,12 <SEP> 375 <SEP> -115
<tb><SEP> 11 <SEP> Cobalt <SEP>: 10.7 <SEP> 10.7 <SEP> 355 <SEP> -135
<tb><SEP> 12 <SEP> Cobalt <SEP>: <SEP> 14.3 <SEP> 14.3 <SEP> 365 <SEP> ~ <SEP> -125
<tb><SEP> 1.3 <SEP> Cobalt <SEP> :: 17.8 <SEP> 17.8 <SEP> 335 <SEP><SEP><SEP> -155
<Tb>
TABLE 3
Ignition temperature as a function of concentration
lanthanum acting alone in the fluff

<tb><SEP> CONCENTRATION <SEP> IN <SEP> METALS <SEP> | <SEP> TEMPERATURE <SEP> (in <SEP>'C)
<tb> EXAMPLE <SEP> IN <SEP> THE <SEP> fuel
<tb><SEP> (mmol / kg)
<tb><SEP> lanthanum <SEP> adjuvant <SEP> of <SEP> concen- <SEP> of inflam- <SEP>
<tb><SEP> lanthanum <SEP> treatment <SEP> mation <SEP> sement <SEP>
<tb><SEP> total
<tb><SEP> 14 <SEP> 14.3 <SEP> 0 <SEP> 14.3 <SEP> 410 <SEP> -80
<tb><SEP> 15 <SEP> 38.9 <SEP> 0 <SEP> 38.9 <SEP> 400 <SEP> -90
<Tb>
TABLE 4
Ignition temperature according to the
composition of adjuvants in fuel oil

<tb><SEP> n0 <SEP> CONCENTRATION <SEP> IN <SEP> METALS <SEP> TEMPERATURE <SEP> (in <SEP> C)
<tb> EXAMPLE <SEP> IN <SEP> THE <SEP> FIOUL
<tb><SEP> (mmol / kg)
<tb><SEP> Lanthanum <SEP> Adjuvant <SEP> of <SEP> Conc. <SEP> Of inflam- <SEP> Abay <SEP>
<tb><SEP> lanthanum <SEP> total <SEP> mation <SEP>
<tb><SEP> 16 <SEP> 7,14 <SEP> Copper: 3.56 <SEP> 10.7 <SEP> 380 <SEP> -110
<tb><SEP> 17 <SEP> 7,14 <SEP> Copper: 7,14 <SEP> 14.3 <SEP> 375 <SEP> -115
<tb><SEP> 18 <SEP> 7,14 <SEP> Copper: 10.7 <SEP> 17.8 <SEP> 370 <SEP> -120
<tb><SEP> 19 <SEP> 10.7 <SEP> Copper: 3.56 <SEP> 14.3 <SEP> 400 <SEP> -90
<tb><SEP> 20 <SEP> 8.53 <SEP> Copper <SEP>: <SEP> 7.14 <SEP> 15.7 <SEP> 360 <SEP> -130
<tb><SEP> 21 <SEP> 14.3 <SEP> Copper <SEP>: <SEP> 3.56 <SEP> 17.8 <SEP> 380 <SEP> -110
<tb><SEP> 22 <SEP> 9.03 <SEP> Copper: <SEP> 8.83 <SEP> 17.8 <SEP> 370 <SEP> -120
<tb><SEP> 23 <SEP> 5.40 <SEP> Copper: <SEP> 5.28 <SEP> 10.7 <SEP> 405 <SEP> -85
<tb><SEP> 24 <SEP> 9.00 <SEP> Copper: <SEP> 26.8 <SEP> 35.8 <SEP> 340 <SEA> -150
<tb><SEP> 25 <SEP> 13.44 <SEP> Cobalt <SEP>: <SEP> 12.18 <SEP> 25.62 <SEP> 360 <SEP> -130
<tb><SEP> 26 <SEP> 5.62 <SEP> Cobalt: <SEP> 5.09 <SEP> 10.71 <SEP> 377 <SEP> -113
<tb><SEP> 27 <SEP> 4.70 <SEP> Cobalt <SEP>: <SEP> 6.11 <SEP> 10.81 <SEP> 360 <SEP> -130
<tb><SEP> 28 <SEP> 7,14 <SEP> Cobalt: 3.56 <SEP> 10.70 <SEP> 395 <SEP> -95
<tb><SEP> 29 <SEP> 7,14 <SEP> Cobalt: <SEP> 7,14 <SEP> 14,28 <SEP> 365 <SEP> -125
<tb><SEP> 30 <SEP> 7,14 <SEP> Cobalt <SEP>: <SEP> 10.71 <SEP> 17.85 <SEP> 355 <SEP> -135
<tb><SEP> 31 <SEP> 10.75 <SEP> Cobalt: 3.56 <SEP> 14.31 <SEP> 350 <SEA> -140
<tb><SEP> 32 <SEP> 10.75 <SEP> Cobalt <SEP>: <SEP> 7.14 <SEP> 17.89 <SEP> 360 <SEP> -130
<tb><SEP> 33 <SEP> X <SEP> 14.28 <SEP> Cobalt: 3.56 <SEP> 17.84 <SEP> | <SEP> 375 <SEP> -115
<Tb>
TESTING ON MOTOR BENCH
Tests have been carried out on a new engine type F8Q 706, and the particle filter used is an EBERSPACHER particle filter number 2626000415. This filter is equipped with two thermocouples, one upstream, the other downstream. The tests were carried out on particle filters which have undergone several loadings and several regenerations. Indeed, the first effects are relatively erratic.

These tests are tests on stabilized particulate filters (DPF).

The tests are carried out in isoegime, the speed being expressed in revolutions per minute.

The results obtained either without an additive or with a lanthanum octoate additive introduced into the fuel at a rate of 100 ppm of lanthanum are collated in the following tables.
TABLE 5
Tests without additives

<tb> REGIME <SEP> T. <SEP> ech. <SEP> T. <SEP> SMB <SEP> dp <SEP> 02 <SEP> HC <SEP> CO <SEP> with <SEP> or <SEP> without
<tb><SEP> upstream <SEP> | <SEP> FAP <SEP> additive
<tb><SEP> FAP
<tb><SEP> trlmn <SEP>"C<SEP> | <SEP> C <SEP> bar <SEP> mbar <SEP>% <SEP> ppm <SEP> glh <SEP> ppm <SEP> g / hr
<tb><SEP> 1500 <SEP> 503 <SEP> 4.15 <SEP> 769 <SEP> - <SEP> | <SEP> - <SEP> - <SEP> - <SEP> - <SEP><SEP> without
<tb><SEP> 2500 <SEQ> 432 <SEP> 382 <SEP> 4.15 <SEP> 853 <SEP> 9.2 <SEP> Without
<tb><SEP> 4000 <SEP> 451 <SEP> 419 <SEP> 1.55 <SEP> 1154 <SEP> 11.2 <SEP> Without
<Tb>
TABLE 6
TESTS IN ISOREGIME WITH SALT OF LANTHANE

<tb><SEP> T. <SEP> with <SEP> or <SEP> without
<tb> REGIME <SEP> T. <SEP> upstream <SEP> upstream <SEP> PME <SEP> dp <SEP> 02 <SEP> HC <SEP> CO <SEP> additive
<tb><SEP> FAP <SEP> FAP
<tb><SEP> rpm <SEP> C <SEP> C <SEP> bar <SEP> mbar <SEP>% <SEP> ppm <SEP> g / h <SEP> ppm <SEP> g / h
<tb><SEP> 1500 <SEQ> 460 <SEP> 388 <SEP> 6.4 <SEP> 705 <SEP> 5 <SEP> 10 <SEP> 0.4 <SEP> 150 <SEP> 12 <SEP> with
<tb> there is no regeneration

<tb><SEP> 1500d <SEP> 295 <SEP> 241 * <SEP> 2.5 <SEP> 663 <SEP> 13.5 <SEP> 46 <SEP> 1.9 <SEP> | <SEP> 160 <SE> 13.4 <SEP> with
<tb> a <SEP> 2500 <SEP> 371 <SEP> 331 * <SEP> 3.5 <SEP> 821 <SEP> 10.8 <SEP> 29 <SEP> 1,9 <SEP> 140 <SEP> 18, 3 <SEP> with
<tb> b <SEP> 2500 <SEP> 285 <SEP> 251 * <SEP> 2.2 <SEP> 943 <SEP> 13.8 <SEP> 32 <SEP> 2.2 <SEP> 170 <SEP> 23.1 <SEP> with
<tb><SEP> 4000 <SEQ> 431 <SEP> 383 * <SEP> 1.6 <SEP> 1060 <SEP> 10.9 <SEP> 8 <SEP> 0.8 <SEP> 220 <SEP> 46 , 8 <SEP> with
<Tb>
TABLE 7
VACUUM TESTS WITH SALT OF LANTHANE

<tb><SEP> T. <SEP> ech. <SEP> T. <SEP> SMB <SEP> dp <SEP> 02 <SEP> HC <SEP> CO <SEP> with <SEP> or <SEP> without
<tb> REGIME <SEP> upstream <SEP> FAP <SEP> additive
<tb><SEP> FAP
<tb><SEP> rpm <SEP>'C<SEP> C <SEP> bar <SEP> mbar <SEP>% <SEP> ppm <SEP> glh <SEP> ppm <SEP> glh <SEP>
<tb><SEP> 1500 <SEQ> 498 <SEP> 124 <SEP> 0 <SEP> 705 <SEP> 17.5 <SEP> 46 <SEP> 2.00 <SEP> 265 <SEG> 23.0 <SEP> with
<tb><SEP> 0
<tb><SEP> 1500 <SEP> 189 <SEP> 161 <SEP> 0 <SEP> 892 <SEP> 16.8 <SEP> 410 <SEP> 16.8 <SEP> 660 <SE> 54.8 <SEP> with
<tb><SEP> AI <SEP> = 0 <SEP>
<tb> no regeneration

<tb> 1500 <SEP> 170 <SEP> 145 * <SEP> 0 <SEP> 1020 <SEP> 17 <SEP> 82 <SEP> 3.5 <SE> 240 <SE> 20.5 <SEP> with
<tb> * Spontaneous regeneration

Claims (10)

 1. A method for reducing the emission of soot from an internal combustion engine in which the exhaust gas is passed through a particulate filter, characterized in that an additive containing lanthanum. 2. A treatment method according to claim 1 characterized in that the lanthanum is added to the fuel in the form of a salt or a stable soil in said fuel. 3. Method according to claim 1, characterized in that the lanthanum-containing compound is introduced directly into the engine. 4. Method according to one of claims 1 and 2, characterized in that the lanthanum fuel content is between 10 and 1000 ppm, preferably between 20 and 200 ppm, preferably between 50 and 150 ppm. 5. Method according to one of claims 1, 2 and 4, characterized in that the soil and / or salt are introduced so as to form aggregates of crystallites whose largest dimension is between 20 and 10 000 angstroms (2 and 1000 nm) and whose crystallite size is between 20 and 250 angstroms (2 and 25 nm). 6 Process according to claim 1, characterized in that the lanthanum is introduced into the engine via air. 7. Method according to claim 1, characterized in that it comprises the following operations:  - introducing into the fuel a derivative of lanthanum at a concentration of  between 10 ppm and 500 ppm (by weight);  - collect sw a filter the soot produced by the internal combustion motew, the  the temperature of the gases entering the filter being chosen in the range 100 to 400 ° C .;  - Soot bead accumulate until reaching a diet where a noticeable fraction  incoming soot is offset by burning soot in the cake  soot on the filter and do not provide any regeneration as long as the pressure loss  caused by swelling of the soot remains below a value chosen at  ravance. 8. Adjuvant for internal combustion engine fuel, characterized in that it comprises:  a) a lanthanum compound,  (b) a compound with at least one transition element or other  rare earth. 9. Adjuvant according to claim 8, characterized in that the lanthanum content based on the sum of the metal elements contained in the adjuvant is at least 50%, preferably 80%. 10. Lanthanum-based compound, characterized in that it can be obtained by combustion in an internal combustion engine bun fuel containing an adjuvant according to claims 8 and 9.