US2405560A - Fuel - Google Patents

Description

Patented Aug. 13, 1946 UNITED STATES PATENT OFFICE General Motors Corporation, Detroit, Mich, a

corporation .of Delaware No Drawing. Application February 6, 1943, Serial No. 475,003

1 Claim. --l

This invention relates generally to fuels for high-compression. spark-ignition engines and more particularly to fuels in which there is less tendency to cause preignition when high compression internal combustion engines are operated thereon than is the .case when present wellknown fuels are used under similar operating conditions.

:It has longbeen recognizedthatth'ere are two distinguishable but related combustion-phenomena that act as barriers to the utilization of higher compression ratios in internal combustion spark-ignition engines. By preventing the use of higher compression ratios or higher pressures attainedby other 'means, these two barriers preent the attainment of fuel economy and emciency that would otherwise be possible.

These two barriers are: first, knock and second, preignition. Substantial progress has been made in the control of knock through the discovery of the antiknock effect of lead alkylssuch as tetraethyl lead and through progress in the-manufacture of hydrocarbon fuels having high antiknock value. c 1 The present invention has as its principal object the control .of the second barrier, namely, preignition in gasolinef-carbureted spark-ignition engines. In accordance with this invention, this object is accomplished by the use of fuels containing addition agents which afiectthe i nition characteristics of the combustion chamber deposits.

In order to make clear the object of this invention it'is necessary to distinguish between the phenomena of preignition and knock which are often confused. Preignition, as the name implies, is an ignition of the mixture in advance of the regular, timed spark ignition. 'When preignition occurs in its most objectionable form, the observerhears a loud knock similar to that which mightrbe expected if the sparkhad been advanced far beyond itsnormal timing. During preignition the observer will often find that the electric spark ignition switch can be shut offend the ,.preignition'willcontinue unaffected. This is because,

Knock is a phenomenon associatedwith the compressiomignition of an unburned mixture .of .fuel and .air ahead of .the normal name front.

: .Ifh'e phenomena associated withknock can occur 55 ject the reduction or suppression of preignition in spark ignition engines. In accordance with the invention, this object is accomplished by the use .of fuels or gasolines containing addition agents which affect the chemical composition and oxidation characteristics andto some extent the weight and other .mechanical characteristics of I the combustion chamber deposits.

Acting upon the aforesaid conceptof the causes .ofpreignition, namely, an uncontrolled ignition ahead of the spark ignition caused by incandesic'eiit particles of engine deposits-an investigationihas been made of theoxidation characteristics iofivarious combustionchamber deposits and ofivarious mixtures of inorganic compounds with carbon. Of particular significance, it has been .foundthat certain compounds of leadcommonly iound'incombustion chamber deposits have an unusualand unexpected effect upon the igni- Jti'onand burning characteristics of carbon.

Gasolines used today in, automobile engines com- .monlyncontaina small amount of ,lead alkyl an- I tiknock compound, tetraethyl lead being employed commercially. Common automotive fuels may contain up to about 3 cc. of tetraethyl lead per gallon of gasoline. Along with the tetraethyl lead lvarious volatile alkyl halides arecommonly employed, for exampe bromides and chlorides such as ethylene dibromide andethylene dichloride. Whe'n'a 'gasolinecontaining lead tetraethyl, and the bromide and/or chloride compounds are used as a fuel in internal combustion engines it is found that the deposits on the walls of the combustion chamber contain carbon and various lead compounds such as lead bromide, basic lead bromide, lead chloride, basic lead-chioride lead sulfateIand basic lead sulfate. Lead compounds such as these and also engine deposits from leadedgasolines exert a catalytic elfect and not only lower the ignition temperature of carbon, but they impart to the mixture an ability to continue to burn after the primary source of heat is removed that isnot had by carbon alone.

vThe effect of several lead compounds on ignition temperature is given in Table I below in which the ignition temperatures of I mixture I containing 10 per cent of various substances and ,90 per cent of carbon, in the form of carbonv black, were determined under'certain controlled conditions: u

first test, Car No. 1 was operated on ethyl gaso- TABLE I.

I Chemical for- I ition tem- Material tested mu 3 0 Pure carbon C Over 1200 Combustion chamber deposit from engine operated on gasoline con taining Ethyl fluid 680-750 Individual lead compounds known to exist in combustion chamber deposits: Lead bromide PbBI: 1 720 I Basic lead bromide.-. PbO.PbB1,. 1 727 Lead chloride l; 1 727 Basic lead chlor1de.- PbO.PbCl, 727.. Lead sulphate PbSO.; 1 939 Basic lead sulphate Pb0.PbSO4 1 950 presence of these compounds in combustion chamber deposits will tend to produce, preignition when other conditions are favorable- I have found that the activating effect of lead on ignition of carbon can be inhibited and even prevented altogether by-the presence of phosphorus compounds. In accordance with. the present invention,.thereor,.I propose a fuel for internal combustion, spark-ignition engines containing'a small peroentagegusually'less thanone per cent by volume, of a liquid phosphorus-containing compound in addition to the other ingredients which have normally been used in leadedgasolines heretofore. The phosphorus-containing compound should be soluble in the gasoline and of sufficient volatility. asto vaporize with the hydrocarbonv constituents of the gasoline.

For example, tributyl phosphite is illustrative of a readily available liquid, organic, compound of phosphorus of suitable-volatility andsolubility in gasoline which I have found. to be efiective in concentrations less than one-tenth of one per cent by volume. Tests indicate that the ignition temperatures of deposits from. the combustion chambers of internal combustion engines which,- have been run on leaded-fuels containing relatively small amounts of tributyl .phosphiteare increased substantially as compared with deposits obtained from similar fuels containing none of the phosphorus compound. An analysis of, the deposits indicates appreciably lesslead, bromine, chlorine and sulphur in engine deposits obtainedfrom engines run on leaded-fuels containing the organic phosphorus compound than Engine conditions maintained while using the fuels:

Speed 2000 R. P. M.

Spark advance Air-fuel ratio Ranged between 13 and 14 to 1 Compression ratio- 8.5 to 1 r l M. E. P 90 lbs. per sq. in.

Table III given below shows data obtained from tests on late model test cars. During the line and Car No. 2 on ethyl gasoline containing 1- cc. per gallon of tributyl phosphite; otherwise, the experimental conditions were substantially the same. In the second test, Car No. 2 ran on ethyl gasoline containing 2 cc. per gallon of tri- .butyl phosphite, while Car No. 1 was running on wheretheorganic phosphorus compound is ab-- sent. These results are indicated in Table .11

below which is based on combustion chamber deposits of a single-cylinder test engine.

TABLE II Errscrs or THE Us]: or TRIBUTYL PHOSPHI'I'E IN THE FUEL ON THE COMPOSITION or LEAD DEPosi'rs'rN THE COMBUSTION CHAMBER or A SINGLE-CYLINDER Tns'r ENGINE Fuel used in producing engine deposit u 3 cc. tributyl ethyl gasoline alone. At the end of each test the engine deposits were removed, weighed and analyzed. The results of the tests are tabulated in Table III. These two tests demonstrate clearly the effect of the phosphorus additive on the weights and chemical compositions of the engine deposits, namely, a reduction in the lead, bromine, chlorine and sulphur in engine deposits from engines run on leaded-fuels.

TABLE III EFFECT or TRIBUTYL Pnospnrrn 'ON ENGINE .Ds-

POSITS or MULTICYLINDER ENGINES WHEN IT IS Usnn IN THE FUEL TO INHIBIT PREIGmrroN End of first 3,000-mile test r izg l Car No. 1 Y y gaso' line+l.o cc.- per Fuel-Ethyl gasoline Properties of deposits mb-utylphos' phite Heads Pistons Heads Pistons Weight grams 54.7 30.5 I 48.8. I 19.9 Chemical analysis: 7

. Brominauper centu l6. 1 15. 7 6. 2 7. 4 Chlorine do 7. 9 2. 9 6.3 3. 1 Sulphur .do. 1.4 1.5 1.3 1.3 Phosphorus do 0.5 0.2 3. 2 A I 2.5 Lead do 55. 0 51. 0 52. l 48. 2

End ofsecondmow-nzile'test r i iit i 1 y gaso' Car No. 2 P 11 gij l Fuelallthyl gasoline ropertesoi deposits phospmte I w H I Heads Pistons Heads Pistons Weight --grams 58. 5 20.1v f 73.2 28.2 Chemical analysis:

Bromine. per cent 9.8 7.2 15.8 9.1 Chlorine -do 4.4 2.8 8. 5 8.7 Sulphur; d0.- 1. 1 1. 2 '0. 9 1. 0 Phosphorus; do 2.9" 1.9 Trace "Trace Lead .d 54.7 47.9. 57.5 54.1

-It is equallyimportant to note in Table IV below the relative effects of these engine deposits on the preignition tendencies of the two testcars. There; the preignition tendency is express'edin termsof octane number of the fuel Which is-required to suppress preignition at a series of differentspeeds. At 15 miles per hour, for" example, 1 cc. per gallon of tributyl phosphite' in ethyl'gasoline is equivalent to an in'creaseoi 4 octane numbers in the fuel rating. and 2 cc. per

gallon of tributyl phosphitein ethyl gasoline is "e uivalent to an increase of 13--o ctane numbers in the fuel rating. Similar difierences may fbe I observed .at the other speeds listed i n Table bustion chambers were clean, no preignition could be observed in these cars even though they were run under severe knocking conditions on 40- octane-number gasoline.

TABLE IV EFFECT or TRIBUTYL PHOSPHITE ON THE PREIGNI- TIoN TENDENCIES OF TEST CARS AFTER 3,000 MILES OF AVERAGE OPERATION End of first 8,000-mile test Car No. 2 Octane number of fuel required to stop preignition,

Car No. l Octane number of fuel required to stop preignition,

Speed, miles per hour- No'rE.-Neither one of these cars would preignite on gasoline of 4% oeililane speeds below 40 miles per hour with clean combustion 0 am ers.

'Ifributyl phosphite is readily available commercially and is illustrative of a phosphoruscontaining compound that has proven effective in greatly reducing preignition in using leadedgasolines as a fuel in spark-ignition internal combustion engines. Other phosphorus-containing compounds have been tested and found to be effective. It is contemplated that any phosphorus compound having sufiicient solubility and being sufiiciently volatile will accomplish the desired result. I believe that I am the first to have discovered the effect of phosphorus-containing compounds in leaded-gasolines in order to prevent or suppress preignition in spark ignition engines and it is desired to cover such discovery in broad terms.

The invention is useful, also, in combating preignition in gasolines which have not been treated with lead but which may preignite due to the presence of lead compounds in the combustion chamber acquired previous to the use of the nonleaded fuel.

I claim:

A leaded-gasoline for use in spark-ignition in ternal combustion engines containing a small amount of a tributyl phosphite, said small amount being not greater than about .1% of the fuel by volume.

JOHN M. CAMPBELL.