EP1726793B1 - Device for reduction of fuel quantity in oil of a combustion engine - Google Patents

Abstract

The system has an engine (1) with an exhaust outlet (2) associated to a portion of a turbocharger (4) integrated with an exhaust line (5) of the engine. The line has a depollution unit (6) with a nitrogen oxide catalyst (7) associated to a particle filter (8). The engine is associated to a lubrication oil basin (17) and a diesel fuel/oil separation condenser (18) with a recirculation pipe (19) for evacuating diesel fuel vapor in the engine and an oil filter. A porous membrane (22) with an inlet size of 0.5 nanometers is associated to one or more aerosol particle traps (21).

Description

The present invention relates to a system for reducing the amount of diesel fuel in the lubricating oil of a motor vehicle diesel engine.

More particularly, the invention relates to such a diesel engine whose exhaust line is provided with depollution means associated with regeneration means implementing fuel post-injections in the cylinders thereof and wherein the engine is also associated with an oil tank and a diesel / oil separation condenser provided with means of evacuation of diesel vapors.

It is known that motor vehicle diesel engines are associated with means for treating their polluting emissions, these treatment means comprising, for example, NOx traps, particulate filters, oxidation catalysts, etc.

These different systems have been developed to allow these vehicles, and more particularly these engines, to operate in compliance with increasingly stringent pollution control standards.

For example, exhaust gas pollution control systems comprising means of NOx trap type are currently very promising.

However, the management of their efficiency requires generating an alternately poor and rich gas atmosphere to purge gaseous species NOx and SO present in the exhaust line and they adsorb in their structure.

For this purpose, one or more diesel injections are used in the combustion chambers of the engine. This results in almost total consumption of the oxygen in the exhaust gas, thus making it possible to increase the richness of these exhaust gases passing through the trap, beyond 1, but also a gradual dilution of the lubricating oil. engine with diesel.

This phenomenon of dilution of the lubricating oil is essentially due to the late phasing of the post-injection or post-injections to be used, to pass in richness greater than 1, and the condensation of gas oil in the gas phase on the cylinder walls.

The diesel jets then reach the walls of the combustion chambers and dilute the film of oil present thereon. The resulting oil / diesel mixture then easily passes through the sealing segmentation of the pistons and thus reaches the engine oil tank.

This dilution phenomenon is similar to that which is the consequence of the engine control strategies implemented to allow for example the regeneration of particulate filters, since post-injection is also required to heat the exhaust gases to a level of temperature sufficient to achieve the combustion temperature of the carbon soot retained on such a particulate filter.

After 20000 kilometers, the dilution rate measured on serial applications in vehicles, is generally between 4 and 6%.

A motor vehicle engine comprising a particulate filter and a NOx post-treatment system is therefore highly subject to the phenomenon of dilution of its lubricating oil, because of the high NOx purge frequency that it is necessary to put (in relation to the regeneration frequencies of a particulate filter), to maintain the NOx conversion efficiency of the catalyst (on average one purge every 1 to 3 minutes) and the need to add purge phases sulphates.

For the latter, the purge frequencies are less important than those of the regenerations of the particulate filter, but the post-injection levels must both make it possible to mount the exhaust gases at a high temperature (greater than 650.degree. and at a richness greater than 1.

The resultant purging effect of NOx + purges of So + regeneration FAP leads to a dilution of the lubricating oil with diesel which generally exceeds 30% by mass over 30000 kilometers, if no correction is made to reduce it during engine operation, while the acceptable limit for the lubricating oils of diesel engines currently in use is below 9%.

• une baisse de viscosité de l'huile qui a des récupérations sur la pression d'huile (cisaillement de l'huile, grippage moteur ou casse moteur),
• accélération du vieillissement de l'huile (oxydation),
• corrosion des matériaux ayant un impact sur l'étanchéité du circuit d'huile, et
• dilution de la teneur en additifs introduits dans l'huile de lubrification pour accroitre ses performances physiques et chimiques.

These fuel dilution levels in the oil then have several consequences:

• a drop in viscosity of the oil which has recoveries on the oil pressure (oil shear, engine seizure or engine failure),
• accelerated aging of the oil (oxidation),
• corrosion of materials having an impact on the tightness of the oil circuit, and
• dilution of the additive content introduced into the lubricating oil to increase its physical and chemical performance.

The object of the invention is to solve these problems.

The invention is based on the observation that these problems, in particular the drop in the viscosity of the lubricating oil, can be solved by removing the molecules of small bulk from the oil.

The subject of the invention is therefore a system for reducing the amount of diesel fuel in the lubricating oil of a motor vehicle diesel engine, whose exhaust line is provided with depollution means associated with regeneration means in the case of fuel injections into the cylinders thereof and in which the engine is also associated with an oil tank and a diesel / oil separation condenser provided with means for evacuating the diesel fuel vapors, characterized in that it comprises selective separation means for removing volatile linear hydrocarbons from the lubricating oil.

Volatile linear hydrocarbons are intended to denote saturated or unsaturated aliphatic hydrocarbons generally comprising less than 25 and preferably 10 to 20 carbon atoms. These species are small and therefore are the lightest components of diesel. They therefore contribute the most to modify the properties of the lubricating oil, particularly in terms of viscosity.

In general, the separation means will be chosen so that, in addition to the desired selectivity, they also have sufficient permeability.

Suitable means of separation include porous membranes, also known as molecular sieves, which are capable of separating molecules on the basis of their size and molecular form.

The document DE 10318784 has such a device comprising a porous membrane whose surface is in contact with a material having a high affinity with diesel fuel. In this case the gas oil extracted from the oil is stored in this material, which requires a reservoir to contain this material and an additional maintenance operation to drain the reservoir.

The porous membranes will be chosen from an oil-inert material that is robust to sintering. By way of example, mention may be made of metals, metal oxides, organic or inorganic polymers, ceramics, glasses, graphites. Porous membranes can consist of a single or several materials, in which case they are called composite membranes.

Several types of porous membranes are known, in particular porous membranes of the carbon, glass, ceramic and zeolite type.

Carbon membranes are generally prepared by decomposing a polymeric organic compound that produces a carbonaceous layer having a porous structure. Carbon granules have been used commercially for many years for adsorptive molecular separation. However, these membranes have limited resistance to oxidizing atmospheres.

Porous glass membranes can be prepared with pore diameters of 3 to 300 nm, for example by the Vyborg method. Although the thermal resistance of the porous glass is no longer ensured beyond 575 K, it can be used in the present system, the average temperature of the oil being 285K.

The ceramic membranes are essentially composed of metal oxides such as SiO 2, Al 2 O 3, ZrO 2, TiO 2, CAO. These are generally asymmetrical systems comprising a macroporous and soporous multilayer support ensuring the mechanical strength of the assembly, which carries a thin microporous or mesoporous layer. This thin layer is the membrane that will control virtually the transfer of material. In general, the thin layer is obtained by sol-gel type processes, the pores then being constituted by intergranular voids.

Zeolite-based membranes can also be used. Zeolites are hydrated aluminosilicates containing alkaline or alkaline earth ions. The crystalline structure of dehydrated zeolites comprises channels whose diameter is in the range of micropores or even ultra micropores (pore diameter 0.7 nm). The pore diameter distribution is narrow, which makes these membranes more selective and therefore particularly attractive for the described application.

The selectivity of the porous membranes results essentially from their porosity and their chemical affinity.

In fact, apart from convection, material transfers through porous membranes obey the laws of diffusion of gases in porous media. They therefore strongly depend on the shape, size and pore distribution at the membrane texture.

In terms of pore size, macroporous membranes (pore diameter 50 nm), mesoporous (pore diameter 2 to 50 nm) and microporous membranes (pore diameter 2 nm) are distinguished.

The molecules from diesel fuel most affecting the viscosity of the lubricating oil are unbranched linear molecules having an atomic chain of less than 20 carbon atoms. These molecules can be selectively retained in microporous membranes, preferably having an internal pore diameter of less than 0.5 nm, and in particular less than 0.4 nm.

The pore inlet diameter of a material can be reduced, if necessary, by grafting the membrane with bulky molecules, such as chlora-iso pentane. These molecules block by their conformation a part of the pores causing a decrease in the input diameter of the molecules.

Moreover, a surface of the membrane can be treated to modify its molecular affinity, in particular its polarity. Such a treatment may be advantageous in the present system in that it allows for example to prevent the passage of aromatic molecules.

The shape and size of the porous membrane can be adapted by known techniques to the diameter of the lubricating oil circulation pipes.

In order to prolong its lifetime, the porous membrane is preferably associated with a particle filtering means. For this purpose, it is possible for example to have upstream of the porous membrane one or more traps for submicron particles 21.

Advantageously, the separation means do not interfere with the operation of the diesel engine. In particular, the composition of the lubricating oil is not impaired, especially as regards the additives. In this respect, the system advantageously eliminates selectively compounds from diesel without affecting the presence of the other compounds in the lubricating oil.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended figure which represents a block diagram illustrating the structure and operation of a diesel engine of the invention. state of the art.

We have indeed illustrated on the figure 1 , a motorization system of the state of the art, which comprises a motor designated by the general reference 1, which, in the example described, is a four-cylinder diesel engine.

The exhaust outlet 2 of this engine is associated with the turbine portion 3 of a turbocharger 4 integrated in an exhaust line 5 of this engine, this exhaust line being provided with pollution control means 6 comprising for example a NOx 7 catalyst associated with a particulate filter 8.

The compressor portion 9 of the turbocharger 4 is associated at the input with an air filter, for example 10, and at the output at an intake air cooler designated by the general reference 11, the output of which is connected to an air intake manifold. intake of gases at the engine inlet and designated by the general reference 12.

The exhaust outlet of the engine 2 is also associated with a recirculation EGR circuit designated by the general reference 13, comprising an EGR valve designated by the general reference 14, optionally an EGR oxidation catalyst designated by the general reference 15 and a EGR cooler designated by the general reference 16, whose output is also connected to the intake manifold 12.

This allows in a conventional way to ensure a recirculation of a portion of the exhaust gas at the engine inlet.

In addition, the engine is also associated with a lubricating oil tank designated by the general reference 17 in this figure and a diesel fuel / oil separation condenser 18 provided with means for evacuation of diesel vapors, such as for example a conduit 19 for recirculating these vapors in the engine and an oil filter 20.

It will be recalled that the lubricating oils consist of heavy hydrocarbons whose distillation temperatures are generally between 340 and 500 ° C. C. They also contain specific additives whose role is to enhance its antioxidant properties, maintain or increase its viscosity, etc ..., and whose vaporization temperatures are generally located beyond 380 of . vs.

In the system according to the invention, it is intended to separate from the lubricating oil the light linear compounds derived from diesel, so as to maintain the properties of the lubricating oil.

Thus, in the system according to the invention, there are provided means for separating volatile linear compounds to improve the gas oil / oil separation.

Of course, different embodiments of these separation means can be envisaged.

For example, these separation means may be a porous membrane, advantageously associated with one or more traps for submicron particles located upstream to extend the operating time of the membrane.

This will be downstream of the condenser an oil filter and a trap for submicron particles and a porous membrane.

The porous membrane is preferably of zeolite type also called molecular sieve.

The lubricating oil then passes from the condenser through the oil filter, and the trap (s) for submicron particles before reaching the porous membrane.

Molecules having a size smaller than the pore admission size are preferentially adsorbed in the porous membrane. Thus, a porous membrane having an inlet size of 0.5 nm can adsorb molecules of size less than 0.5 nm. The adsorbed molecules can then migrate along the porous system of the porous membrane.

Advantageously, the porous membrane is formed and arranged in such a way that the molecules thus adsorbed can be easily removed from the oil circuit.

The porous membrane 22 is arranged so that one of its surfaces is in contact with the oil circuit and another with the intake air flowing in the conduit connecting the outlet of the EGR cooler. Both surfaces of the porous membrane are connected by pores. The adsorbed molecules are then aspirated through the porous membrane system through the intake air. They then migrate through the porous membrane to be driven by the intake air entering or leaving the intake manifold (common rail system).

It goes without saying of course that other embodiments of these separation means described can be envisaged.

• pas de modification de l'architecture du moteur pour une meilleure vie du groupe motopropulseur en utilisant un piège submicronique ;
• prolongation des caractéristiques physiques et chimiques d'huile ;
• prolongation de la vie du moteur en diminuant l'usure des pièces ;
• facilite d'intégration ;
• pas d'augmentation de la contre pression huile ;
• solution économique avec des matériaux peu coûteux ;
• versatilité en termes de types d'huile ;
• échange des moyens de séparation possible lors d'une vidange d'huile classique ; et
• possibilité d'éliminer certains composes organiques ou organométalliques juges critiques dans le futur.

The described system allows the selective separation of the most important gas oil molecules in the lubricating oil for maintaining the properties of the oil, especially in terms of viscosity. It also has the following advantages:

• no modification of the engine architecture for a better powertrain life by using a submicron trap;
• prolongation of the physical and chemical characteristics of oil;
• prolonging the life of the engine by reducing the wear of parts;
• ease of integration ;
• no increase in the back pressure oil;
• economical solution with inexpensive materials;
• versatility in terms of oil types;
• exchange of separation means possible during a conventional oil change; and
• possibility of eliminating certain critical organic or organometallic compounds in the future.

Claims (7)

1. System for reducing the quantity of diesel in the lubricating oil of a motor vehicle diesel engine in which the exhaust line (5) is provided with pollution control means (6) associated with regeneration means which post-inject fuel into the engine cylinders and wherein the engine (1) is also associated with an oil pan (17) and with a condenser (18) for separating diesel/oil that is provided with means (19) for discharging the diesel vapours, which system comprises a porous membrane for removing the volatile linear hydrocarbons present in the oil, characterized in that the said membrane is arranged in such a way that one of its surfaces is in contact with the oil circuit and another with the air of the engine intake circuit so that the volatile hydrocarbons can be entrained by the intake circuit.
2. System according to Claim 1, characterized in that it additionally comprises, upstream of the separating means, a trap (21) for submicron particles.
3. System according to either of Claims 1 and 2, characterized in that the porous membrane is chosen from a membrane of the carbon, glass, ceramic and zeolite type.
4. System according to any one of Claims 1 to 3, characterized in that the porous membrane is microporous.
5. System according to Claim 4, characterized in that the porous membrane has an internal pore diameter of less than 0.5 nm.
6. System according to one of Claims 1 to 5, characterized in that the porous membrane has bulky particles rafted onto at least one of its faces.
7. System according to one of the preceding claims, characterized in that the porous membrane is treated on at least one of its faces to modify its polarity.

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