PROCEDURE FOR REDUCING THE EMISSIONS OF DIESEL ENGINES

The present invention relates to a procedure for reducing the emissions, in particular NO _x and particulate, of diesel cycle engines.

One of the problems of diesel engines consists in the harmful _. emissions, in particular NO _x and particulate.

A solution suggested by the prior art consists in the addition of water to the fuel. This solution has proved to be beneficial as it reduces the harmful components. A typical example of technology which uses the addition of water is represented by the so-called "white gas oil", an emulsion of water (about 10%) in gas oil, produced by the addition of suitable emulsiflers. The beneficial effect of water can be attributed to the reduced temperature in the combustion chamber, which lowers the NO _x level, and also a better combustion due to the pulverization of gas oil into droplets caused by the explosion of the water drops contained in the emulsion, during the compression phase. This technology, however, has the disadvantage that said emulsion has a low time stability, in particular with variations in the environmental conditions. It is also known in the art that alcohols having a low molecular weight (for example methanol and ethanol), are successfully used, as a result of their high octane number, as octane-improver additives of fuels for driven ignition engines (Otto cycle) and are negative, however, for gas oil engines (diesel cycle) as they have poor self-ignition qualities (low cetane number). A low cetane number corresponds to a high octane number. Their direct use in considerable quantities in a blend with gas oil causes a deterioration in the self-ignition qualities, which leads to non-optimal driving due to the considerable noise, the difficulty of ignition under cool conditions, and the high smoke emission, both at the start-up (white smoke) and under regime conditions (black smoke). The use of low mo-

lecular weight alcohols which can be obtained from renewable sources, on the other hand, allows a reduction in carbon dioxide emissions, which represent one of the highest contributions to the green-house effect.

It has now been found, and this represents the object of the present invention, that it is possible to use hydro-alcoholic blends in addition to the hydrocarbon portion, obtaining considerable benefits in the combustion quality and, consequently, in the emission quality, without having the negative effects of the alcohols mentioned above, obtaining, on the contrary, synergetic effects which could not have been envisaged on the basis of the known art.

In accordance with this, the present invention relates to a procedure for reducing the emissions of diesel engines, characterized in that said diesel- engines are fed by means of two separate feedings, a first feeding consisting of gas oil and a second feeding consisting of a hydro-alcoholic blend comprising water and alcohols from C ₁ to C ₄ . Diesel engines which can be used in the procedure of the present invention include, as an example, engines for light road transport (cars), engines for heavy road transport (lorries, buses, tractors) motors for electricity generators. The term diesel engine means any kind of diesel cycle engine, preferably turbojet and turbo-diesel engines. "Hydro-alcoholic blend" means an aqueous solution Of C ₁ - C ₄ alcohols, preferably Ci - C ₂ , even more preferably C ₁ . It is essential, however, for the alcohols to be present in an amount and with a number of carbon atoms such as to assure the formation of a perfectly homogeneous and limpid aqueous solution. Therefore the ratio alcohols C ₃ -C ₄ / alcohols Ci-C ₂ is usually low due to the scarce water solubility of the C ₃ -C ₄ alcohols. In the experimental part, tests related to a homogeneous mixture of 50% by volume demineralized water and 50% by volume, of an alcohol blend consisting of 97% by volume of methanol and 3% by volume of iso-butanol are described.

The above alcohols can be obtained from petrochemical productions, or, preferably, from renewable sources.

The water content of these hydro-alcoholic blends can vary from 5 to 95% by volume. Preferred compositions are within the range of 40 to 60% of water. When required by the current regulation for Public Health protection, a denaturing agent can be added, completely miscible with the above hydro-alcoholic solutions, said denaturing agent not being easily removable from the hydro-alcoholic solutions and having such characteristics as to avoid the improper use of the above blends. Non-limiting examples of said denaturing agents are ethers (for example MTBE, i.e. methyl tert-butyl ether, ETBE ₅ i.e. ethyl tert-butyl ether) and higher alcohols, for example C ₄ -C ₅ alcohols. Should a C ₄ alcohol be present in the hydro-alcoholic solution, the denaturing agent cannot be a C ₄ alcohol. The addition of the denaturing agent can be effected within a range of 1 to 6% by volume. As a further guarantee of the above, a suitable dye can be added still within the scope of the invention.

As specified above, the present invention requires the separate feeding of gas oil and the hydro-alcoholic blend. The volumetric ratio between the hydro-alcoholic blend and the gas oil ranges from 2/98 to 80/20, preferably 5/95 to 75/25. The above ratio mainly depends on the type of engine and regime at which it runs.

As far as gas oil for road vehicles is concerned, its characteristics and properties are well-known to experts in the field. We would like to indicate, in particular, a typical evaporation curve of gas oil for road vehicles: at 150°C, 2% by volume evaporates, at 250 ⁰ C, 64.5% by volume, at 350°C, 85% by volume, at 370°C, 95% by volume. Other important characteristics of the gas oil for road vehicles are density at 15°C (from 820 to 845 Kg/m ³ ) and viscosity at 40°C (from 2.00 to 4.5 mm ² /sec). The feeding to the diesel engine can be effected by means of the usual means suitable

for this purpose, for example by injectors. The only restriction consists of the material of the means which feeds the hydro-alcoholic solution; this in fact must be resistant to water and also to alcohols. A typical commercial injector which can be used for the hydro-alcoholic solutions of the present invention is known as Aquamist ^® of E.R.L. Ltd. The procedure of the present invention, in addition to allowing a reduction in the NO _x and particulate (PM), also has the advantage of increasing the engine power. The reduction in emissions can be mainly ascribed to the presence of water, whose environmental advantages in diesel engines are already described in the known art. The increase in power, on the contrary, is mainly due to the introduction of alcohols into diesel engines. In the procedure of the present invention, the alcohol acts as a complement to gas oil for the purpose of improving the power yield.

These two advantages, the improvement in the emissions and power, cannot be obtained with any other procedure of the known art.

Furthermore, the procedure of the present invention does not have the drawbacks mentioned above for "white gas oil". The procedure of the present invention does not, obviously, have storage problems typical of gas oil/water emulsions, due to its nature. The system of the present invention does not require the presence of surface-active agents (necessary for preparing emulsions of white gas oil) which could create problems in gas oil engines.

These and other advantages will be clearly shown in the experimental part. The following examples are provided for a better understanding of the present invention.

EXAMPLES ^•

For illustrative and non-limiting purposes, the results of a comparison in bench tests between a commercial Fiat Punto 1.3 MJ engine (see table below) are indicated here-.

under.

Vehicle characteristics

The above engine is fed, for comparative purposes, with commercial gas oil only, of the EN 590 Agip Bludiesel type and, according to the present invention, with the same gas oil and with a second feeding consisting of a hydro-alcoholic blend consisting of:

• 50% by volume : demineralized water;

• 50% by volume blend consisting of 97% by volume of methanol and 3% by volume of iso-butanol.

The tests were carried out following the ECE 15 cycle, at the Experimental Fuel Station of S. Donato Milanese.

The test cycle ECE 15 consists in driving the vehicle in a simulated run on a dynamom- etric bench on suitably calibrated rolls in order to consider the inertia and passive resistances according to the Extra-Urban Cycle EUDC.

Results of the ECE 15 test

The results of the ECE 15 test clearly show the advantages which can be obtained by means of the procedure of the present invention, which includes two different feedings, with respect to a normal feeding with gas oil alone. In particular, it can be seen that the procedure of the present invention allows a more than halved emission of PM into the atmosphere and a considerable reduction in NO _x .

Finally, it should be pointed out that the emission/power ratio is considerably reduced with respect to feeding with gas oil alone.

Tables Ia-Ic show the properties and the compositions of the mixture used in these tests (48.5% methanol, 1.5% iso-butanol, 50% demineralized water) at three different temperatures, i.e. 15°C (minimum operating temperature), 32°C (maximum operating temperature) and 78°C (flash point temperature).

It is important to underline that this mixture is flameproof at 15 ⁰ C and 32 ⁰ C. Furthermore the vaporization of said mixture begins at 78°C.

Table Ia (15 ⁰ C) CONDITIONS

Table la (cont) COMPOSITION

Overall Phase Vapour Fraction 0.0000

Table Ib (32 ⁰ C) CONDITIONS

Table Ib (cont.) COMPOSITION

Overall Phase Vapour Fraction 0.0000

Table Ic (78 ⁰ C) CONDITIONS

Table Ic (cont.) COMPOSITION

Overall Phase Vapour Fraction 0.0334