FR2936809A1 - Diesel fuel formulation, useful for motor functioning according to homogeneous or quasi-homogeneous low temperature combustion mode, comprises mixture of fuel base with olefin charge obtained from light olefin oligomerization process - Google Patents

Abstract

Diesel fuel formulation (I) comprises a mixture of at least a fuel base with olefin charge obtained from light olefin oligomerization catalytic process.

Description

FIELD OF THE INVENTION

The present invention provides a novel diesel engine fuel formulation operating in a low temperature combustion mode, also commonly referred to as LTC (Low Temperature Combustion) combustion mode.

PRIOR ART

In a general context of controlling the emission of greenhouse gases and mainly CO2 emissions, the diesel engine is naturally placed as a good energy converter. However, the problem in terms of depollution on diesel engines is currently to reduce the emissions of NOx fumes and nitrogen oxides, to meet the Euro 5 pollution standards in 2009. To achieve this objective, various solutions are possible: It is possible to modify the engine technology, the post-processing or to search for new fuel formulations. It is within the framework of this latter possibility that the present invention is included.

In all existing conventional diesel injection systems, the fuel is sprayed into the combustion chamber just prior to ignition. However, this combustion leaves little time for mixing the fuel with the air. Thus the fuel does not burn optimally and pollutants are created. Many studies have recently been conducted on low temperature combustions, such as HCCI (Homogeneous Charge Compression Ignition) combustion, or homogeneous or partially homogeneous combustion. It is important to note that there are many nuances of applications that are associated with as many denominations in the literature. Examples include Low Temperature Combustion (LTC) combustion, Low-Nox combustion, Premixed Controlled Compression Ignition (PCCI), Partially Premixed Compression Ignition (PPCI), Highy Premixed Combustion (HPC), Partially Premixed Combustion (PPC) combustion. Combustion), HCLI (Homogeneous Charge Late Injection) combustion, Highly Premixed Late Injection (HPLI) combustion, mild-HCCI combustion.

The HCCI (Homogeneous Charge Compression Ignition) combustion mode is fundamentally based on the combination of a perfectly premixed fuel with air heavily diluted by flue gas and mass self-ignition throughout the entire fuel cell. combustion chamber. To achieve a homogeneous premix 1, the fuel is introduced very early during the compression phase. The goal is to increase the self-ignition delay. Added to this is the admission of high levels of flue gases which also contribute to the slowing down of chemical reactions and therefore to an increase in the auto-ignition delay.

The large concentration of flue gases in the admitted mixture reduces the oxygen concentration by dilution and increases the heat capacity of the enclosed mixture. The resulting reduction in combustion temperature has the advantage of drastically reducing the production of nitrogen oxides. On the other hand, this combustion does not form particles by removing fuel-rich areas and lowering the local combustion temperature by dilution. Thus, it appears that the emissions of NOx and particles are reduced by a factor of 10 to 100.

The disadvantage of this type of low temperature combustion is the operating range (regime, load) which remains limited. It is indeed difficult to meet this homogeneous combustion mode HCCI throughout the operating range of the engine. There is therefore a degradation of the purely homogeneous mode, with the objective of being able to carry out low-NOx combustions over a larger part of the motor field.

Research is currently being conducted to try to improve this operating range.

The patent application WO2005 / 059063 describes a fuel formulation suitable for HCCI combustion comprising n-paraffins and iso-paraffins of 7 to 14 carbon atoms. It is demonstrated in this application that with such a formulation the ignition time becomes less than 7 ms (according to ASTM D6890 measurement method).

Patent application WO2007 / 123832 proposes a method of selecting a fuel, from among a plurality of fuel formulations, to optimize the operation of an HCCI engine. This method consists in determining a cetane number derived for each of the fuel formulations to be tested, in order to be able to compare them, then to test the different formulations to determine the autoignition properties in relation to the cetane number derivatives and then to adapt the self-ignition of the fuel formulation to the compression ratio so as to have HCCI operation in the widest range of speed and load possible for a given compression ratio.

In general, conventional diesel is not known to be an optimized candidate in low temperature combustion (LTC) mode.

The inventors have now discovered a new formulation of diesel fuel for low temperature combustion engine comprising reactive compounds, to significantly reduce the emissions of nitrogen oxides and fumes.

SUMMARY OF THE INVENTION The subject of the present invention is a diesel fuel formulation operating in a homogeneous or quasi-homogeneous low temperature combustion mode comprising a mixture of at least one fuel base with an olefinic feedstock derived from a catalytic process. oligomerization of light olefins. SUMMARY DESCRIPTION OF THE FIGURES FIG. 1 shows combustion time measurements for a motor operating point 2500 rpm-6 bar for two fuel formulations.

Figure 2 shows the maximum engine load (PMI) at low temperature combustion obtained at 2500 rpm for two fuel formulations.

Figure 3 gives the maximum load at low temperature combustion for different regimes depending on the content of olefinic compounds.

DETAILED DESCRIPTION OF THE INVENTION

The diesel fuel formulation according to the present invention is intended to be used for an engine operating in a homogeneous or near-homogeneous low temperature combustion mode. Said formulation consists in incorporating into an fuel base an olefinic feedstock derived from a light olefin oligomerization process. A conventional EN 590 gas oil is composed of 50 to 65% by volume of paraffins, 20 to 30% by volume of naphthenes and 10 to 30% by volume of aromatics. It does not contain olefins, unlike gasoline which can contain up to 20% volume.

Indeed, olefins generally have lower cetane numbers than corresponding paraffins.

Olefins, by the presence of a carbon-carbon double bond are reactive compounds. Thus, the incorporation of such compounds in a fuel base advantageously makes it possible to increase the reaction rate, which in the context of a low temperature combustion makes it possible to reduce the smoke emissions.

The addition of reactive compounds allows an acceleration of the combustion and therefore a widening of the operating range (regime / load) for a targeted level of fumes.

The fuel base used in the formulation according to the present invention may be a gas oil base, a jet fuel or a Fischer-Trcpsch cut. The formulation according to the present invention of using an olefinic feedstock in a diesel fuel makes it possible in particular to recover gasoline cuts towards the diesel fuel pool, when the fuel base used is a diesel fuel.

The jet fuel used in the present invention may be, for example, a Jet A or a Jet B. Preferably, the jet fuel is a jet B.

The olefinic cut added to the fuel base is a cut resulting from light olefin oligomerization processes involving a Ziegler type catalyst system composed of a transition metal derivative associated with an organometallic compound, or processes still known as Dimersol.

This oligomerization process uses a homogeneous catalysis process involving nickel activated by an organoaluminum compound, as described in patents FR 2 443877, FR 2464 243 or FR 2555 570 for example. The reaction involved is as follows: ## STR2 ## The groups R 1 chosen from hydrogen and the organic radicals may be identical or different.

This method comprises a liquid phase reactor whose temperature is regulated by an external circulation of the cooled liquid phase in an exchanger. The catalytic system, which is liquid under normal conditions of temperature and pressure, is injected continuously into the reactor. The product obtained is subjected to fractionation and the catalyst is removed by an injection of ammonia and a washing with sodium hydroxide. The process conventionally operates under the following conditions: -temperature between 40 and 60 ° C, pressure between 10 and 30 bar, residence time of 1 to 5 hours.

In general, this type of oligomerization process of olefins in homogeneous catalysis (Dimersol) is known not to allow the formation of oligomers with a high degree of polymerization. The length of the chains (before transfer) is thus limited to n + m <_ 4 and each monomer can integrate the chain in head-to-head mode but also in head-tail mode, which gives a very large variety of structures for the same number of carbon atoms.

Advantageously, the olefinic cut added to the fuel base is derived from a process known as Dimersol G, corresponding to a catalytic oligomerization process of propylene. The effluent from the Dimersol G process is known to be used as it is in the gasoline pool. It consists of at least 75% by weight of hexenes (dimers), nonenes and dodecenes.

The olefinic cut added to the fuel base may be derived from a Dimersol X process, corresponding to the catalytic oligomerization of butene. The effluent resulting from such a process is composed of at least 85% by weight of octenes, dodecenes and hexadecenes. n + m \ / R CH = CH Ni ++ EADC

The olefinic cut added to the fuel base can be a so-called crude Dimate cut, originating from a Dimersol X process, thus from a catalytic oligomerization process of butene before distillation. It is a charge consisting of 6 ° by weight of linear octenes, 58% by weight of methylheptenes and 34% by weight of dimethylhexenes.

Preferably, the olefinic cut used in the present invention and resulting from these oligomerization processes has a density of about 0.803 and its distillation curve extends from 186 to 319 ° C. It is therefore in the distillation range of a conventional diesel which is in general 180-360 ° C.

The diesel fuel formulation according to the present invention comprises at most 45% by volume of olefin feedstock derived from light olefin oligomerization processes.

Preferably, when the fuel base is a diesel fuel type EN590, the olefinic filler content is between 12 and 37% by volume.

Preferably, when the fuel base is a jet fuel, the olefinic filler content is between 2 and 15% by volume, and very preferably is around 8% by volume.

Preferably, when the fuel base is a Fischer-Tropsch cut, the olefinic filler content is between 10 and 40% by volume, and very preferably is around 20% by volume.

The following examples illustrate the invention, without limitation. EXAMPLES

EXAMPLE 1 Improvement of LTC Combustion Performance by Adding Olefins to a Diesel Base

Measurements of burning time and average pressure indicated (MIP) were performed for two fuels. The first is a conventional diesel EN590 and the second is a fuel formulation according to the present invention consisting of EN590 gas oil and 36% by volume of an olefinic cut from a light olefin oligomerization process. The olefinic section has a density of 0.803 and a distillation curve which ranges from 186 to 319 ° C. The results of the combustion time measurements for a motor operating point 2500 rpm to 6 bar are given in FIG. 1. It can be seen that the addition of the olefinic feed makes it possible to reduce the burning time.

On the other hand, the results presented in FIG. 2 correspond to the PMI measurements and therefore to the maximum engine load obtained at low temperature combustion at 2500 rpm and meeting the limit criteria for smoke emissions, NOx, and noise. The fuel formulation according to the present invention makes it possible to widen the low temperature combustion operating range. EXAMPLE 2 Improvement of LTC Combustion Performance by Adding an Olefinic Charge to a Jet B Jet Fuel

Olefins from the Dimate process were added to a Jet B type jet fuel at 8 and 16% v.

Figure 3 gives the maximum charge at low temperature combustion for different regimes as a function of the olefinic compounds content.

Figure 3 shows that the addition of reactive compounds such as olefins improves the low temperature combustion, but to a certain extent: 8% seems the optimum content in our case. Indeed it is not necessary to increase the reactivity of a fuel too much since the curve has an optimum.

EXAMPLE 3 Comparison of the Impact of the Addition of Model Molecules (Octene and Octadiene) Relative to a Petroleum Cut Resulting from a Dimersol-type Oligomerization Process in a Conventional Diesel Base on the Performance of Low Temperature Combustion Comparative Tests were made by adding to a conventional diesel base different types of olefins. Thus, the performance of the formulation according to the present invention can be compared with those of formulations in which the olefinic cut is replaced by "model" olefins, and in particular with 1-octene and dioctadiene. For these two molecules, the boiling points are of the order of 122 ° C, therefore outside the range of distillation of a conventional diesel which is in general 180-360 ° C. The results are shown in Table 1.

NOx levels are little different with the addition of olefins in a diesel base whether pure molecules or an olefinic cut from the Dimersol process. On the other hand, the smoke emissions are much lower in the formulation according to the present invention, which therefore comprises a particular olefinic cut, since a reduction of more than 69% is noted with respect to a conventional diesel fuel. Gain in% relative to G0 + 10% v octene GO + 10% v octadiene GO + 36% v oligo to GO base NOx - - - Smoke -13.20 -9.90 -69.5 Table 1: Gain in% compared to base diesel on the smoke and NOx levels when octene, octadiene and cuts from oligomerization in diesel fuel are added for an operating point of 2500 rpm and 6 bar.

Claims (10)

REVENDICATIONS1. A diesel fuel formulation for an engine operating in a homogeneous or near-homogeneous low temperature combustion mode comprising a mixture of at least one fuel base with an olefinic feedstock derived from a light olefin oligomerization catalytic process. 2. The formulation of claim 1 wherein the fuel base is a gas oil base or a jet fuel or a Fischer-Tropsch cut. 3. Formulation according to one of claims 1 or 2 wherein the olefinic feedstock is derived from a catalytic process for oligomerization of propylene and consists of at least 75% by weight of hexenes, nonenes and dodecenes. 4. Formulation according to one of claims 1 or 2 wherein the olefinic feedstock is derived from the catalytic oligomerization process of butene and is composed of at least 85% by weight of octenes, dodecenes and hexadecenes. 20 5. Formulation according to one of claims 1 or 2 wherein the olefinic feedstock is a cut from a catalytic oligomerization process of butene before distillation and consists of 6% by weight of linear octenes, 58% by weight. of methylheptenes and 34% by weight of dimethylhexenes. 25 The formulation according to one of the preceding claims wherein the olefinic feedstock has a density of about 0.803 and a distillation curve ranging from 186 to 319 ° C. 7. Formulation according to one of the preceding claims comprising not more than 45% by volume of olefinic feedstock from oligomerization processes of light olefins. 8. The formulation of claim 7 wherein the fuel base is a diesel fuel type EN590, and the olefinic filler content is from 12 to 37% by volume. 15 The formulation of claim 7 wherein the fuel base is a jet fuel and the olefinic filler content is from 2 to 15% by volume. The formulation of claim 7 wherein the fuel base is a Fischer-Tropsch cut and the olefinic filler content is between 10 and 40% by volume.