FR2720441A1 - 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

A FILTRATION AND COMBUSTION PROCESS
OF CARBON MATERIALS FROM INTERNAL COMBUSTION ENGINE
The present invention relates to a method for filtering and combustion of carbonaceous materials from internal combustion engines. The invention relates more particularly to the regulation of the pressure drop caused in the filters by the accumulation of soot in the filters.

During the combustion of fuels in internal combustion engines and in particular diesel fuel in the diesel engine, carbonaceous materials are formed, hereinafter referred to as "soot", which are considered harmful for the health of the higher mammals. only for the environment.

These soot are particularly abundant in the case of diesel engines and constitute a handicap for this type of engine. Most of the solutions envisaged to change the engine speed or its operating parameters face another constraint, that of not increasing the emission of carbon monoxide and / or gases deemed toxic and mutagenic such as nitrogen oxides. .

Given the foregoing, the most efficient technique seems to be the adaptation to the exhaust pipe of a filter capable of stopping all or at least most of the soot formed by the combustion of various fuels.

It has thus succeeded in making filters, especially cordierite, which can reduce by at least 85% by mass soot emissions.

The problem to be solved lies in the accumulation of these soot in the filters which initially causes an increase in pressure drop and, in a second step, a start of shutter which leads to a loss of efficiency of the combustion engine. internal.

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 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 ignition ( temperature of the order of 500 ° C).

It has also been proposed to introduce ignition catalyst precursors in the various fuels, so as to lower the temperature of the soot ignition. These techniques, in particular that of the combination of the increase of the soot temperature by means of a suitable and transient circuit of the exhaust gases with the addition of oxidation catalyst precursors, made it possible to solve the problem. less partially the problem.

However, on the one hand the soot ignition temperature remains relatively high (of the order of 500 ° C) and on the other hand the intermittent and brutal combustions may cause a significant alteration of the filter and its cooling capacities. filtration, either by cracking due to thermal shock, or even by fusion.

Therefore, it is an object of the present invention to provide a soot burning process that is as continuous as possible.

Another object of the present invention is to provide a soot combustion process which does not result in sudden, violent and sudden ignitions leading to damage to the filter. To achieve such a result, it should be avoided that during the ignition phase, at any point in the filter the temperature does not reach 1000 ° C, preferably 900 ° C, preferably 700 ° C.

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

These and other objects which will become apparent are achieved by a gas filtration process of an internal combustion engine, which method comprises:
introducing into the combustion chamber at least one rare earth derivative
or rare earth mixture at a concentration of between 10 ppm and 500
ppm (by mass), preferably between 20 ppm and 200 ppm;
collect on a filter the soot produced by the internal combustion engine,
the temperature of the gases entering the filter being chosen in the range 100 ° C
350 "C (position zeros are not significant digits), and
let the soot accumulate until reaching a diet or a fraction
noticeable soot is compensated for by the burning of soot in the
soot cake on the filter and do not expect any regeneration as long as the loss of
charge caused by soot does not exceed a value chosen in advance and
not exceeding 400 millibar.

Surprisingly it was found that there was, in general, no need to cause regeneration when the above conditions were respected
Allogenic (or exogenous) regeneration can only be considered when it is desired to maintain a particularly low level of pressure drop. As allogeneic regeneration it is then necessary to consider regenerations carried out by a single overheating, and not global over the entire filter; this possibility is only interesting because, according to the invention, an overheating point does not result in a complete and complete regeneration of the filter.

Spot overheating can be achieved by any means known to those skilled in the art, such as micro-resistances distributed over the surface of the filter, metal particles heated by eddy current, mini-arc or equivalent.

The filtration mode according to the invention generally only works during a part of the engine speeds, because some of the regimes generate gas temperature of the order of 5000C ipso facto performs a gradual regeneration and often complete filter .

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

Preferred rare earths are cerium, lanthanum and mixtures containing cerium and lanthanum. The most common content of the REE fuel (metal) content is between 50 and 150 ppm.

According to the present invention, the rare earth content of the fuel can be selected so as to adjust the pressure drop to a value chosen in advance. One can also play on the filtering surface, and while remaining in the above specified temperature range.

This value chosen in advance is preferably between 100 and 400 millibar, preferably between 150 and 300 millibar.

To obtain such results, it is preferable that the rare earths present in the soot have a concentration between 500 ppm and 10%, preferably between at least 1000 ppm (mass of metal contained relative to the total mass of the soot, y including the compounds they adsorbed) and at most 5% on average.

In most of the engines marketed to date, it is advantageous to introduce the rare earth, or the rare earth mixture, with its procession of impurity (s) and adjuvant (s), at a content of between 10. and 1000 ppm in fuel These values are expressed as 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 desired (and not the general improvement of the combustion), this makes it possible to reduce the quantities of rare earth or rare earth mixture 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 content of rare earth, or the mixture of rare earths in soot.

 It is advantageous that the form in which the rare earth or rare earth mixture is introduced induces the formation of aggregates of rare earth oxide crystallites, or rare earth mixtures, where the largest dimension of said aggregate is between 20 angstroms and 10,000 angstroms, preferably between 100 and 5,000 angstroms, for which the size of the crystallites is between 20 and 250 angstroms, preferably between 50 and 200 angstroms.

The introduction of compounds based on rare earths, alone or in mixture, can be achieved in particular by the introduction of rare earth compounds, alone or in mixture, in the fuel to be introduced into the engine.

Another possibility is to introduce the rare earths, alone or mixed, in various forms via the air, including air when it is mixed with engine exhaust, when a fraction of the exhaust gas is recycled to the engine. In this case, the rare earth compounds, alone or in mixture, incorporated into the recycled soot are introduced into the engine.

One of the most practical ways to introduce the rare earth, alone or in mixture, into the engine circuit is to introduce it into the fuel either in the form of salt or in the form of 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 last acids have the disadvantage of increasing the sulfur content of the fuel.

In general, for the rare earths having valence lil as the highest valency, the carboxylic acid salts of C 2 to C 20, preferably C 4 to C 15, are among the most suitable for this purpose.

For cerium, cerium IV derivatives are preferred because of their stability and ability to make fewer particles.

 It is preferred that the rare earth oxides or rare earth oxide mixtures be stable in the fuel. Cerium is the favorite rare earth, alone; or in combination. In fuels, cerium can be introduced either in the form of sols or in the form of various salts provided that the latter are sufficiently stable in the medium. The salts that are the subject of the European patent application filed under the number 93 / 304760.7 and published under the number 057 5189 are particularly noteworthy.

Indeed, completely surprisingly, it has been found that when using additives based on transition metals (that is to say metals which one of the underlays d is being filled ) Low temperature regenerations were either non-existent or gave rise to sudden inflammations leading to high temperatures that could damage the filters.

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

 This results in weak athermal effects as well as much lower variations in pressure drop.

Thus, it has been shown that the use of additives based on rare earth elements leads to a double advantage:
- in the first place, the limitation of thermal excursions makes it possible to keep
material filtering all of its properties and in particular its efficiency of
filtration; the system has a more sustainable and better efficiency;
- secondly, the behavior in the presence of additives based on the elements of
rare earths allows a more flexible management of the phenomena of loss of
charge; indeed, in the case of additives based on the elements of
transition (in particular copper and iron), the regenerations are random, violent and
brutal, the losses of charge evolve in a very sudden way. This causes
variations in engine power and undermines the safety and comfort of
driving and the proper operation of the engine; on the other hand, in the case
additives based on the elements of the rare earth elements, the regenerations are
low amplitude which reduces the effects on the pressure loss and the effects
thermal. The pressure loss due to the filter stabilizes and can be managed without
penalize safety and driving pleasure.

The elements promoting this low temperature regeneration are the content of
oxygen 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 particulate matter, the content of volatile hydrocarbon compounds in the soot is at least 10%, preferably one 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 following nonlimiting examples illustrate the invention.

EXAMPLES:
A - Description of the experimental conditions
The engine used is an atmospheric diesel engine with four cylinders, indirect injection, of 1.696 liters of displacement and developing 50 kilowatts at 4400 revolutions per minute. This engine is sold under the Volkswagen brand.

The filters used are cordierite filters produced by the company Coming, type Ex 47 (5.66 inches in diameter, 6 inches in length, with a cell density of 100 cpi / 17 mil). Each additive has been tested on a new filter. We measure continuously during tests:
- the pressure drop associated with the filter (pressure drop between filter inlet and outlet);
- the temperature of the gases at the inlet of the filter
- the temperature of the gases at the outlet of the filter
- carbon monoxide emissions.

The tests are conducted at 2,000 rpm keeping the temperature of the gas at the filter inlet constant over time. The tests conducted at a temperature of 250 ° C. are reported hereinafter, but similar results have been obtained at other temperatures.

The tests were carried out in particular with:
an iron-based additive whose content in the fuel oil is 20 ppm (mass);
- a copper-based additive; the copper content in the fuel oil is 20 ppm;
- two additives based on cerium and rare earths; the content of land elements
rare (cerium) in the fuel oil is 50 ppm.

Given the respective molar masses of the elements, the molar contents, or more exactly atomic, are of substantially the same order for all the additives, namely: iron: 0.36 mol / 1000 kg of copper fuel oil: 0.32 mol / 1000 kg of fuel oil: 0.36 moles / 1000 kg of fuel oil.

B - Results
Example 1: Case of the iron-based additive
The results are reported in FIG. 1. This figure gives, firstly, the evolution of the pressure drop as a function of time as well as the carbon monoxide content in the gas leaving the filter, as well as the evolution of the gas temperature at the outlet of the filter as a function of time. It can be seen that the accumulation periods can reach a duration of 35,000 seconds. The pressure drop easily reaches 300 millibar. During regenerations that correspond to the sudden decrease in back pressure, there is a sharp increase in the carbon monoxide content for the gases at the outlet of the filter. At the same time as these carbon monoxide content variations, there is a very sharp increase in the temperature of the gases at the outlet of the filter, with temperatures of up to 700 ° C or 800 ° C, whereas the temperature of the gases at filter input is only 250 ° C. The variation of the backpressure is very brutal.You can lose 250 millibar very quickly during these regeneration phases, and the duration of the accumulation zones as the amplitude Backpressure variations seem to vary randomly.These graphs highlight the random and brutal behavior of the regenerations, which suggests that the motor will probably be affected by these sudden downstream counterpressure variations.

In this example, the iron additive is ferrocene.

Example 2: Case of the copper-based additive
The copper used is a cupric carboxylate. The results are shown in Figure 2.

This figure gives, on the one hand, the evolution of the backpressure as a function of time as well as the carbon monoxide content in the gas leaving the filter, and the evolution of the temperature of the gas at the outlet of the filter and this according to the time.

It can be seen that the periods of accumulation can reach 54000 seconds, that is to say nearly 20 hours. There is a loss of load, or back pressure, up to 350 millibar. During regenerations that correspond to the sudden decrease in the pressure drop, there is a sharp increase in the carbon monoxide content in the gases at the outlet of the filter. Parallel to these variations in the carbon monoxide content, there is a very sharp increase in the temperature of the gases at the outlet of the filter with temperatures that can reach more than 800 ° C., whereas the temperature of the gases at the inlet of the filter is only 250 "C. The variation of the back pressure is very brutal. It can lose 300 millibar very quickly during these regeneration phases. The duration of the accumulation zones as well as the amplitude of the backpressure variations seem to vary randomly. These graphs highlight the random and brutal behavior of these regenerations, which suggests that the engine will be affected by these sudden downstream counterpressure variations.

Example 3: Case of a cerium-based additive (compound described in the European patent application filed under the number 93 / 304760.7 and published under the number 0575189)
The results are shown in FIG. 3. This figure gives, on the one hand, the evolution of the back pressure as a function of time as well as the CO content in the gas leaving the filter, and the evolution of the temperature of the gas output filter as a function of time. There is a filter loading period of 25,000 seconds. Beyond this, it can be seen that the back pressure is practically stable. This back pressure stabilizes at around 200 millibar. At the time of the regenerations which correspond to very small decreases in the back pressure (less than 50 millibar), there are variations in the carbon monoxide content in the gases at the outlet of the filter. These variations reflect a constant regeneration activity over time.

In parallel with these variations in the carbon monoxide content, there is a moderate increase in the temperature of the gases at the outlet of the filter with temperatures that can reach at most 400 ° C., and this for a temperature of the gases at the inlet of the filter 250 "C. These graphs demonstrate the behavior of both moderate and permanent regenerations which suggests that the engine and therefore the violent conduct will not be altered.

Example 4: Example of an additive based on cerium sol.

These results are reported in FIG. 4. This figure gives, on the one hand, the evolution of the back pressure as a function of time as well as the carbon monoxide content in the gas leaving the filter, and the evolution of the gas temperature at the outlet of the filter as a function of time. There is a filter loading period of 45,000 seconds. Beyond this, it can be seen that the back pressure is practically stable. This back pressure stabilizes at around 200 millibar. At the time of the regenerations which correspond to very small decreases in the back pressure (less than 50 millibar), there are variations in the carbon monoxide content in the gases at the outlet of the filter. These variations reflect a constant regeneration activity over time. Parallel to these variations in the carbon monoxide content, there is a moderate increase in the temperature of the gases at the outlet of the filter with temperatures that can reach at most 350 ° C., and this for a temperature of the gases at the inlet of the filter 250 "C. These graphs show the moderate and permanent behavior of the regenerations, which suggests that the engine, the safety and the pleasure of driving are not in any way impaired.

The number of fine particles formed is significantly lower than that of the previous examples.

EXAMPLE 5: Engine bench tests in isoegime
Tests have been carried out on a new engine of the F8Q 706 type, and the particle filter used is an EBERSPACHER particle filter number 2626000415. This filter is equipped with two thermocouples, one upstream and 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 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:
BOARD .

ESsais 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> FAP <SEP> additive
<tb><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 <SEP> 503 <SEP> 4.15 <SEP> 769 <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><SEP> TEST <SEP> A <SEP> EMPTY
<tb><SEP> with <SEP> 150 <SEP> ppm <SEP> of <SEP> salt <SEP> of <SEP> cerium <SEP> (octoate <SEP> cerous)
<tb><SEP> with
<tb> REGIME <SEP> T. <SEP> ech. <SEP> T. <SEP> SMB <SEP> dp <SEP> 02 <SEP> HC <SEP> CO <SEP> or
<tb><SEP> upstream <SEP> FAP <SEP> without
<tb><SEP> FAP <SEP> ad
<tb><SEP> ditif <SEP>
<tb><SEP> rpm <SEP> C <SEP> C <SEP> bar <SEP> mbar <SEP>% <SEP> ppm <SEP> g / h <SEP> ppm <SEP> g / h <September>
<tb><SEP> 800 <SEP> 98 <SEP> 79 <SEP> 0 <SEP> 240 <SEP> 17.50 <SEP> 138 <SEP> 2.8 <SEP> 300 <SEP> 12.3 <SEP> with
<tb><SEP> 1000 <SEP> 104 <SEP> 87 <SEP> 0 <SEP> 258 <SEP> 17.45 <SEP> 62 <SEP> 1.5 <SEP> 230 <SEP> 11.5 <SEP> with
<tb><SEP> 1500 <SEP> 126 <SEP> 114 * <SEP> 0 <SEP> 360 <SEP> 17.70 <SEP> 38 <SEP> 1.60 <SEP> 250 <SEP> 21.7 <SEP> with
<tb><SEP> 0
<tb><SEP> 1500 <SEP> 125 <SEP> 119 * <SEP> 0 <SEP> 426 <SEP> 17.55 <SEP> 27 <SEP> 1.1 <SEP> 240 <SEP> 1.2 <SEP> with
<tb><SEP> 2500 <SEP> 239 <SEP> 227 * <SEP> 0 <SEP> 1156 <SEP> 15.55 <SEP> 58 <SEP> 3.8 <SEP> 320 <SEP> 42.6 <SEP > with
<tb><SEP> 4000 <SEP> 362 <SEP> 336 * <SEP> 0 <SEP> 1133 <SEP> 13.45 <SEP> 46 <SEP> 4.6 <SEP> 220 <SEP> 44.7 <SEP> with
<Tb>

Claims (1)

1. A method for filtering and combustion of soot produced by an internal combustion engine, characterized in that it comprises the following provisions: introduce into the combustion chamber at least one derivative of rare earth or rare earth mixture at a concentration of between 10 ppm and 500 ppm (by weight), preferably between 20 ppm and 200 ppm; collect on a filter the soot produced by the internal combustion engine, the temperature of the gases entering the filter being chosen in the range 100 "C-  350 C; and  let the soot accumulate until reaching a diet or a fraction  significant amount of incoming soot is offset by the burning of soot in the  soot cake on the filter and do not expect any regeneration as long as the waste  charge caused by soot does not exceed a value chosen in advance and  not exceeding 400 millibar. 2- Process according to claim 1, characterized in that the temperature at which the gases are filtered is between 200 and 350 ° C. 3. Method according to one of claims 1 and 2, characterized in that the rare earth content of said fuel is between 50 and 150 ppm. 4- Method according to one of claims 1 to 3, characterized in that said rare earth is cerium or a cerium compound. 5. Method according to one of claims 1 to 4, characterized in that one chooses the surface of the filter so as to maintain the pressure drop in said filter to a value at most equal to 300 millibar, preferably 200 millibar.  Process according to one of Claims 1 to 5, characterized in that the temperature of the gases in contact with the filter is chosen so as to maintain the pressure drop in said filter at a value not exceeding 300 millibar, advantageously 200 millibar. 7- Method according to one of claims 1 to 4, characterized in that the rare earth content in the fuel is chosen so as to maintain the pressure drop in said filter to a value at most equal to 300 millibar advantageously at 200 millibar.