US2031497A - Fuel - Google Patents

Description

Patented Feb. 18, 1936 uNrrru v STATES ea-Tear OFFICE Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing.

, pression ignition fuels and it particularly relates to the use of novel ignition accelerators for the said fuels.

One'object of this invention relates to improvements in Diesel engine fuels, and particularly in fuels adapted for use in high-speed compression ignition engines whereby to obtain reduction of the delay period between the injection and the ignitionof the fuel oil, a reduction in the ignition temperature of the fuel oil and/or a lowering of the compression ratio of the engine. A more specific object relates to compression ignition fuels containing as an ignition accelerator an alkyl nitrate containing a branched carbon chain and corresponding to the nitrates of the 1 higher alcohols produced by the catalytic hydrogenation of carbon monoxide. Other objects of the invention will become apparent i'romthe following description.

In accordance with the present invention, it

- has been found thatwhen the nitrates of branched chain alcohols obtainable by carbon monoxide hydrogenation are added to the fuel oil there is obtained a reduction in the delay period between injection and ignition of the fuel oil. This phenomenon is accomplished by a lowering of the ignition temperature of the-fuel oil and/or a lowering of the compression ratio in the compression engine required to ignite the fuel. Alkyl nitrates of the character described have a substantial solubility in fuel oil.

The following table illustrates the effect of the use of these alkyl nitrates on the fuel oil characteristics. The properties of the doped and modified fuel oil are compared with those of the unmodified fuel oil:

sisted in injecting the fuel oil into air at atmospheric pressure into a heated. chamber. The ignition delay is the elapsed time betweeninjection and ignition of the fuel. The minimum ignition temperature is the lowest temperature at Application January 21, 1933, Serial No. 652,937

' comm. (01. 44-9) which a majority of a series of samples injected into the chamber ignite. The minimum compression ratio was determined according to the method described by Pope and Murdock in the Society of Automotive Engineers Journal, Transactions pages 136-142for March, 1932.

Tertiary butyl nitrate may be .used in lieu of isobutyl nitrate but the latter is preferred due to the fact that isobutyl alcohol is available in large quantities as a product of carbon monoxide hydrogenation.

In general, I have found that the nitrates of the branch chain alcohols produced by the hydrogenation of carbon monoxide are considerably superior to the ethyl and methyl nitrates which have hitherto been proposed as Diesel fuel accelerators in that they are less volatile and consequently reducethe hazards involved.

In addition to the branch chain butyl nitrates which can be used in accordance with the present invention, other useful compounds comprise the nitrates of alcohols other than isobutyl and likewise obtainable by the catalytic hydrogenation of carbon monoxide. Those nitrates of branched chain alcohols having at least six carbon atoms are particularly suitable since the use of these compounds in fuel oils involves substantially no hazard because of the fact that they have very low vapor pressures'and also because of the fact that they are completely miscible in the oil and W consequently can be stored and transported in concentrated solutions in the 011 without danger of having them separate out during cold weather. In accordance with the present invention, I may use either the secondary or the primary alcohols or a mixture of these alcohols as formed in the hydrogenation of carbon monoxide.

The following illustrates one mode of preparing a nitrated product capable of use in accordance with the present invention:

Example A fraction of alcohols obtained by the hydrogenation of carbon monoxide and boiling above C. was nitrated by using a mixed acid containing 49.3% nitric acid and 51.44% sulfuric acid. The temperature was maintained at 8-l0 C. The alcohol was added cautiously to the nitrating mixture and when the reaction mixture began to fume off it was drowned in water and given the usual water and soda washes. The product was thus obtained as a dark greenish oil.

I prefer however to separate the primary alcohols and nitrate them separately inasmuch as the nitration of the individualprlmary alcohols on proceeds more smoothly. As specific examples of the primary branched chain'alcohols other than isobutyl which are eminently suited forthe prep aration of nitrate accelerators, the following are mentioned: Z-methyl-l-pentanol, 2, 4-dimethyll-pentanol, 4-methyl-1-hexanol, 2, d-dimethyl one per cent up to the limit of solubility in the fuel,

but the preferred amount of accelerator ranges from one to five per cent of the fuel.

The branched chain aliphatic nitrates comin within the scope of the present invention in-- clude those having four or more carbon atoms, but preferably containing at least six carbons, the hydrocarbon content conferring on the compoundsa high boiling point which increases generally with increased carbon content.

The advantages of the use of these accelerators in fuel oil for compression ignition engines are:

l. Elimination of knocking and rough-running by decreasing the ignition lag.

2. Reduction of engine wear by removing the cause of knocking and roughness.

3. Easier starting. The reduced spontaneous ignition temperatures of the doped oil enables it to ignite much more easily when starting from cold.

4. Improved exhaust. Owing to the more complete combustion the exhaust is cleaner especially at higher speeds. No harmful constituents are introduced into the exhaust gases by the combustion of the dope.

5. Possibility of use of inferior fuels. By the addition of dope, low grade fuels, at present quite unsuitable for compression ignition engines, can be rendered equal or superior to high grade undoped fuels.

6. Naturev of dope. The dope has a neutral reaction, is non-toxic and soluble in the oil.

'7. Improvements in engine design. Reduced engine stresses, resultingfrom the more gradually applied piston pressures, should make for lighter scantlings while the more readily ignited and rapidly burning fuel should render' possible the construction of smaller and faster running engines.

8. Increased power and reduced fuel consumption. The improved combustion resulting from the explosive action of the dope enables a greater proportion of the air charge to be burnt, and

further, as ignition takes place at once, the fuel .can be injected during the compression stroke at a smaller crank angle near top dead center.

The specific utility of the present invention results from the higher boiling points and lower vapor pressures of the branched ,chain alkyl nitrates as compared with the ni described in the prior art. The boiling point of isobutyl primary nitrate (isopropyl methyl nitrate) is compared with the boiling points of straight chain lower alkyl nitrates:

Boiling Dope point C Methyl "mu. Ethyl nitrat 87 Propy trots 110.6 Isobutyl primary nitrate 125 Further advantages are: l. The increased boiling point prevents the formation of vapor locks in the fuel system of the engine.

dopes also decreases the physiological effects,

such as headaches, which constitute an objection to lower alkyl nitrates.

The above description and examples are to be taken as illustrative only and not as limiting the scope of. the invention. Any modification or variation therefrom which conforms to the spirit of the invention is intended to be included within the scope of the claims.

I claim:

1. A compression ignition fuel comprising a fuel oil boiling above the gasoline range containing the nitrates of the mixture of open branched chainaliphatic monohydric alcohols obtainable by the catalytic hydrogenation of carbon monoxide and having at least four carbon atoms and containing isobutyl alcohol.

2. A compression ignition fuel comprising a fuel oil boiling above the gasoline range containing isobutyl nitrate obtainable by the nitration of isobutyl alcohol, said alcohol being obtainable by the catalytic hydrogenation of carbon monoxide.

CARL S. MARVEL.