US2206594A - Diesel fuel - Google Patents

Description

Patented July 2, 1940 UNITED STATES PATENT OFFICE M; Nygaard, Woodbury, N. J

., assignors. to

Socony-Vacnum Oil Company, Incorporated New York, N. Y., a corporation of New York No Drawing.

Application November 8, 1938,

Serial No. 239,506

Claims.

This invention has to do in a general way with fuels for internal combustion engines of the Diesel or compression ignition type and is more particularly concerned with the improvement of such fuels by the admixture therewith of a characterizing ingredient. In an internal combustion engine operating on the Diesel cycle it is important to the attainment of maximum efliciency that the delay period between the injection of the fuel and its ignition in the cylinder be short. Improperly delayed ignition gives'rise to the phenomenon known as knocking because of improper coordination between the combustion and cylinder conditions. By decreasing the ignition delay period of a Diesel fuel it is possible to lower the compression pressure at which ignition of the fuel mixture takes place, thus insuring spontaneous ignition without comoustion shock. This increases the ease of start- Lug and the smoothness with which combustion takes place, and in addition it permits less weight )1 mass in the engine design, which makes for lower cost per unit of power output. It will be ieen, therefore, that enhanced speed of ignition Ls a characteristic highly desirable in fuels for ise in Diesel engines.

It has been found that the ignition quality of 1 Diesel or compression ignition fuel can be improved by the addition thereto of small amounts if certain compounds which act as ignition ac- :elerators. This offers a means for improving ;he better grades of Diesel fuels and also permits widening the range of available fuels by raising ;he ignition quality of the low grade fuels.

The present invention is directed to Diesel ;ype fuels which have been improved in ignition uality by the addition of novel compounds which )romote rapidity of combustion and so give the iesired control over the fuels combustion charicteristics. More specifically our invention has LS its object the provision of an improved method if accelerating the ignition of liquid hydrocarion fuels in compression ignition engines which s} characterized by the admixture with the fuel If a reaction product which we will hereinafter 'efer to as a material predominantly comprised f hydrogen persulfides.

As a material predominantly comprised of hy-- lrogen persulfides our invention comprehends the rude reaction products to be hereinafter decribed, which are comprised of hydrogen perulfides containing sulfur in solution; also those materials obtained as distillates from this crude eaction product, which are considered to be a mixture of hydrogen persulfldes and in addition our invention contemplates materials which are obtained as the residue from such distillation, such residue being a mixture of hydrogen persulfides and sulfur.

Materials of the type just referred to above 5 may be conveniently prepared by the method described by Walton and Parsons (J. Am. Chem. Soc., 1921, 43, 2539). This procedure involves the steps of preparing a solution of sodium persulfides by dissolving and digesting elementary l0 sulfur in a sodium sulfide solution and then acidifying this solution to liberate the hydrogen persulfides. The hydrogen persulfide mixture obtained from this reaction may be separated from the aqueous solution, and such crude mixture can be used as an improving agent forv Diesel fuels. This crude persulfide mixture may be distilled under vacuum to obtain what we may term purified hydrogen persulfides, which also are effective improving agents for Diesel fuels, and the residue from such distillation may also be employed as an improving agent.

Walton and Parsons report that the crude product of the reaction described above is believed to be a solution of sulfur in equilibrium with various sulfides of hydrogen and not a.

definite compound and for this reason we have chosen to define such product herein in general chemical terms or by its method of preparation rather than attempting to definitely identify the various constituent compounds.

The details in one illustrative procedure which may be followed in preparing the ignition accelerators for Diesel fuel contemplated by this invention will be best understood from the following specific example:

The sodium sulfide-sulfur, solution was prepared by dissolving 667 grams of crystalline sodium sulfide and 100 grams of flowers of sulfur in 267 cc. of distilled water. This solution was 40 prepared in a stoppcred flask equipped with a Bunsen valve by heating on a water bath for three hours. The contents of the flask were then slowly added with constant stirring below the surface of two liters of concentrated hydrochloric acid,-whichwas maintained at a temperature between -4 and l0 C. The crude hydrogen persulfide mixture thus formed was at first largely present as an emulsion but settled to, the bottom of the container over night. This crude liquid was then separated, washed several timeswith water, and dried by allowing it to stand in contact with phosphorus pentoxide for. two days. The phosphorus pentoxide was removed by filtration and a portion of the crude hydrogen persulfide filtrate, hereinafter referred to as product A, was used in preparing a Diesel fuel blend.

The product herein referred to as the purified hydrogen persulfides was obtained by vacuumdistilling the crudeproduct described above at a liquid temperature of C. and under pressure of 5 mm. The distillate was collected in two portions, as hydrogen trisulfide and hydro- .gen disulfide,but these two portions were com-.

bined and tested as the product hereinafter referred to as product B.

The residue left after this distillation, which was comprised of a mixture of the persulfides and elementary sulfur, was also tested as an ignition accelerator for Diesel fuel and is hereinafter identified as product C.

To demonstrate the effectiveness of the products contemplated by this invention as ignition accelerators for Diesel fuels we have prepared fuel blends containing the products A, B, and C described above and have determined the ignition quality of such blended fuel by comparison with a standard reference fuel in a converted C. F. R. engine, using the ignition delay method. The results obtained are expressed as Cetane numbers, which represent the percent by volume of cetane in a blend of cetane and alpha methyl naphthalene having the same combustion characteristics as the sample under test (see Proc. Am. Soc. Testing Materials, vol. 36 I p. 416, (1936)). An increase in cetane number indicates an improvement in the combustion characteristics of the fuel.

The results of these'tests, which are indicated in the table, below, were obtained with blends prepared from a Diesel fuel oil having the following characteristics:

The amount of the persulfide product (A,.B or C) in the blend in each case is indicated by the percentage of sulfur in the blended oil.

Table I Material blended with 56 PercentS Cetane No. Increase in cetane No. fuel 7 in blend of blend cetane No.

Product A 0. 57 59. 5 3. 5 Product Bl 0.47 61 5 Product 0 1.02 62 6 It will be apparent from the foregoing table that all of the products contemplated by this invention, which we have broadly characterized as being predominantly comprised of hydrogen persulfides, are effective when admixed with a fuel oil refined for use in a compression ignition engine to materially improve the ignition quality of the fuel.

It is to be understood that the terms Diesel fuel, Diesel type fuel, hydrocarbon fuel oil," eto., as used-herein are inclusive of any and all .types of hydrocarbon products intended for use in any engine operating according to the Diesel cycle.

We claim:

1. An improved Diesel fuel comprising: a hydrocarbon fuel oil and in admixture therewith a minor proportion of hydrogen persulfides and elementary sulfur in an amount suflicient to decrease the ignition delay period of the fuel.

2. An improved Diesel fuel comprising: a hydrocarbon fuel oil and in admixture therewith a minor proportion of hydrogen persulfides in an amount sufficient to decrease the ignition delay period of the fuel.

4 3. An improved Diesel fuel comprising: a hydrocarbon fuel oil and in admixture therewith a minor proportion of a crude hydrogen persulfide-sulfur mixture obtained by digesting a water solution of sodium sulfide and elementary sulfur at an elevated temperature; acidifying the reaction mixture with hydrochloric acid to form the hydrogen persulfide-sulfur mixture; and separating said mixture from the aqueous solution, said mixture being present in the oil in an amount sufficient to decrease the ignition delay period of the fuel.

4. An improved Diesel fuel comprising: a hydrocarbon fuel oil and in admixture therewith a minor proportion of purified hydrogen persulfides obtained by digesting a water solution of sodium sulfide and elementary sulfur at an elevated temperature, acidifying the reaction mixture with hydrochloric acid to form crude hydrogen persulfides, separating the crude hydrogen persulfides from the aqueous solution, washing and drying the crude hydrogenpersulfides, and distilling the crude hydrogen persulfides under vacuum at a liquid temperature in the neighborhood of 120 C.- to obtain the purified hydrogen persulfides, said purified hydrogen persulfides being present in the oil in sufficient amount to decrease the ignition delayperiod of the fuel.

5. An improved Diesel fuel comprising: a hydrocarbonv fuel oil and in admixture therewitl". a minor proportion of the residue obtained from the distillation under vacuum at a liquid temperature in the neighborhood of 120 C. of th( reaction product obtained by digesting a watei solution of sodium sulfide and elementary sulfur at an elevated temperature, acidifying thl product thus obtained with'hydrochloric acid anc then separating the aqueous solution from tht crude product to be distilled, said residue being present in the oil in an amount sufiicient to decrease the ignition delay period of the fuel.

6. An improved Diesel fuel comprising: a hy drocarbon fuel oil and in admixture therewith minor proportion of a crude hydrogen per-sulfide sulfur mixture obtained by digesting a water so lution of about 6.7 parts of sodium sulfide am about one part of elementary sulfur at an elevatei temperature; acidifying the reaction mixture wit] hydrochloric acid to form the hydrogen persul fide-sulfur mixture; and separating said mix ture from the aqueous solution, said mixture bein present in the oil in an amount sufficient to de crease the ignition delay period of the fuel.

7. An improved Diesel fuel comprising: a hy drocarbon fuel oil and in admixture therewith minor proportion of purified hydrogen persul fides obtained by digesting a water solution c about 6.7 parts of sodium sulfide and about on part of elementary sulfur at elevated tempera ture, acidifying the reaction mixture with by drochloric acid to form crude hydrogen persui fides, separating the crude hydrogen persulfide from the aqueous solution; washing and drying the crude hydrogen persulfides; and distilling the crude hydrogen persulfides under vacuum, at a liquidtemperature in the neighborhood of 120 C. to obtain the purified hydrogen persulfides, said purified hydrogen persulfides being present in the oil in sufficient amount to decrease the ignition delay period of the fuel.

8. The method of accelerating the ignition of liquid fuels for internal combustion engines of the type wherein ignition o1 the fuel is spontaneously effected by injection into the compressed air in the engine cylinder which comprises admixing with the fuel prior to ignition a minor proportion of a material predominantly comprised of hydrogen persulfides.

9. The method oiacceleratlng the ignition oi liquid fuels for internal combustion engines of the type wherein ignition 01' the jtuel is spontaneously effected by injection into the compressed air in the engine cylinder which comprises admixing with the fuel prior to ignition a minor proportion of a material comprised of hydrogen persulfldes and sulfur.

10. The method of accelerating the ignition of liquid fuels for internal combustion engines of.

the type whereineignition of the fuel is spontaneously effected by injection into the compressed air in the engine cylinder which comprises admixing with the fuel prior to ignition a minor proportion of hydrogen persulfides.

HENRY G. BERGER.

RICHARD S. GEORGE. EDWIN M.- NYGAARD.