FUEL COMPOSITIONS

Abstract: Coking in and around the injector nozzles of indirect injection compression ignition engines is reduced by means of distillate fuel with which has been blended suitable concentrations of (i) organic nitrate ignition accelerator, and (ii) an alkoxyalkanol. Also described are additive mixtures of (i) and (ii) for use in distillate fuels in amounts sufficient to reduce the coking tendencies of such fuels when used in the operation of indirect injection compression ignition engines.

Description: This invention relates to compression ignition fuel compositions and additive mixtures therefor comprising organic nitrate ignition accelerator and an alkoxyalkanol. The mixture is added to the fuel in amounts sufficient to Control the coking tendencies of the compression ignition fuel composition when used in the operation of indirect injection diesel engines. Throttling diesel nozzles have recently come into wide-spread use in indirect injection automotive and light-duty diesel truck engined, i.e., compression ignition engines in which the fuel is injected into and ignited in a prechamber or swirl chamber. In this way, the flame front proceeds from the prechamber into the larger compression chamber where the combustion is com­ pleted. Engines designed in this manner allow for quieter and smoother operation. The Figure of the Drawing illustrates the geometry of the typical throttling diesel nozzle (often referred to as the "pintle nozzle"). Unfortunately, the advent of such engines has given rise to a new problem, that of excessive coking on the critical surfaces of the injectors that inject fuel into the prechamber or swirl chamber of the engine. In par­ ticular and with reference to the Figure, the carbon tends to fill in all of the available corners and surfaces of the obturator 10 and the form 12 until a smooth profile is achieved. The carbon also tends to block the drilled orifice 14 in the injector body 16 and fill up to the seat 18. In severe cases, carbon builds up on the form 12 and the obturator 10 to such an extent that it interferes with the spray pattern of the fuel issuing from around the perimeter of orifice 14. Such carbon build-up or coking often results in such undesirable consequences as delayed fuel ignition, decreased rate of fuel injection, increased rate of combustion chamber pressure rise, increased engine noise, and can also result in an excessive increase in emission from the engine of unburned hydrocarbons. While the composition of the low cetane number fuel is believed to be a major contributing factor to the coking problem, it is not the only relevant factor. Thermal and oxidative stability (lacquering tendencies), fuel aromaticity, and such fuel characteristics as viscosity, surface tension and relative density have also been indicated to play a role in the coking problem. Thus, an important contribution to the art would be a fuel composition which has enhanced resistance to coking tendencies when employed in the operation of indirect injection diesel engines. We have now discovered that the coking problem can be ameliorated by the addition to the fuel of a mixture of an organic nitrate and an alkoxyalkanol. The alkoxyl­ alkanols contemplated for use in the invention are diverse and can be any alkoxyalkanol which, when added to distillate fuel in combination with an organic nitrate ignition accelerator, reduced, minimizes or inhibits coking in the prechambers or swirl chambers of an indirect injection compression ignition engine operated on such a fuel. Thus, broadly stated, the present invention is directed to distillate fuel composition for indirect injection compression ignition engines containing, in an amount sufficient to control coking, especially throttling nozzle coking, in the prechambers or swirl chambers of indirect injection compression ignition engines operated on such fuel, at least the combination of (i) organic nitrate ignition accelerator and (ii) an alkoxyalkanol. Since the invention also embodies the operation of an indirect injection compression ignition engine in a manner which results in reduced coking, a further embodiment of the present invention is a method of inhibiting coking, especially throttling nozzle coking, in the prechambers or swirl chambers of an indirect injection compression ignition engine, which method comprises sup­ plying said engine with a distillate fuel composition containing a least the combination of (i) organic nitrate ignition accelerator and (ii) an alkoxyalkanol capable of inhibit­ ing said coking. A feature of this invention is the combination of additives that is capable of suppressing coking tendencies of fuels used to operate indirect injection compression ignition engines. A wide variety of organic nitrate ignition accel­ erators may be employed in the fuels of this invention. Preferred nitrate esters are the aliphatic or cycloali­ phatic nitrates in which the aliphatic or cycloaliphatic group is saturated, contains up to about 12 carbon carbons and, optionally, may be substituted with one or more oxygen atoms. Typical organic nitrates that may be used are methyl nitrate, ethyl nitrate, propyl nitrate, isopropyl nitrate, allyl nitrate, butyl nitrate, isobutyl nitrate, sec -butyl nitrate, tert -butyl nitrate, amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, hexyl nitrate, heptyl nitrate, 2-heptyl nitrate, octyl nitrate, isooctyl nitrate, 2-ethylhexyl nitrate, nonyl nitrate, decyl nitrate, undecyl nitrate, dodecyl nitrate, cyclo­ pentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate, cyclododecyl nitrate, 2-ethoxyethyl nitrate, 2-(2-ethoxy-ethoxy)-ethyl nitrate and tetrahydrofufuryl nitrate, for example. Mixtures of such materials may also be used. The preferred ignition accelerator for use in the fuels of this invention is a mixture of octyl nitrates available as an article of commerce from Ethyl Corporation under the designation DII-3 Ignition Improver. As previously mentioned, the alkoxyalkanol compounds of the invention are diverse. They include any alkoxyalkanol compound or mixture of alkoxyalkanol compounds which, when combined with an organic nitrate ignition accelerator or mixtures of organic nitrate ignition accelerators, in a distillate fuel, minimizes and/or reduces coking in the prechambers or swirl chambers of indirect injection compression ignition engines operated on such fuel. Especially useful alkoxyalkanols are those having the structure R′ OR″ OH wherein R′ is an alkyl group containing 1-12 carbon atoms, R″ is a divalent aliphatic hydrocarbon group containing 2-4 carbon atoms and n is an integer from 1-4, including mixtures of such alkoxyalkanols. They are readily made by reacting C 2-4 alkylene oxides with C 1-12 alcohols. Typical alkoxyalkanols are 2-methoxy ethanol, 2-ethoxy-1-propanol and 2-decyloxy-1-butanol for example. A most preferred alkoxyalkanol is 2-ethoxy ethanol. It will be appreciated from the foregoing that the alkoxyalkanols of the invention may be (polyalkoxy)alkanols. Thus, in a more preferred embodiment of the present invention there is provided distillate fuel composition for indirect injection compression ignition engines containing, in an amount sufficient to control coking, especially throt­ tling nozzle coking, in the prechambers or swirl chambers of indirect injection compression ignition engined oper­ ated on such fuel, at least the combination of (i) organic nitrate ignition accelerator, and (ii) an alkoxyalkanol having the structure R′ OR″ OH wherein R′ is an alkyl group containing 1-12 carbon atoms, R″ is a divalent aliphatic hydrocarbon group containing 2-4 carbon atoms and n is an integer from 1-4. The alkoxyalkanol components of the invention should usually be used at a concentration of at least about 20 PTB (pounds per thousand barrels) of the base feed to insure that the finished blend contains an adequate quantity of the foregoing ingredient although smaller amounts may be successfully employed. The nitrate ignition accelerator, component (i), should usually be present in an amount of at least 100 to 1000 PTB (pounds per thousand barrels) of the base fuel. Prefer­ ably, the concentration of the ignition accelerator is 400 to 600 PTB. It is not believed that there is anything critical as regards the maximum amount of components (i) and (ii) used in the fuel. Thus, the maximum amount of these com­ ponents will probably be governed in any given situation by matters of choice and economics. The coking-inhibiting components (i) and (ii) of the invention can be added to the fuels by any means known in the art for incorporating small quantities of additives into distillate fuels. Components (i) and (ii) can be added separately or they can be combined and added together. It is convenient to utilize additive fluid mixtures which consist of organic nitrate ignition accelerator and the alkoxyalkanol components of the invention. In other words, part of the present invention is coking inhibiting fluids which comprise organic nitrate ignition accelerator and alkoxyalkanol compounds. Such fluids in addition to resulting in great convenience in storage, handling, transportation, and blending with fuels, also are potent concentrates which serve the function of inhibiting or minimizing the coking charac­ teristics of compression ignition distillate fuels used to operate indirect compression ignition engines. In these fluid compositions, the amount of com­ ponents (i) and (ii) can vary widely. In general, the fluid compositions contain 5 to 95% by weight of the organic nitrate ignition accelerator component and 95 to 5% by weight of the alkoxyalkanol component. Typically, from .01% by weight up to 1% by weight of the combina­ tion will be sufficient to provide good coking-inhibiting properties to the distillate fuel. A preferred distillate fuel composition contains from 0.1 to 0.5% by weight of the combination containing from 25% to 95% by weight of the organic nitrate ignition accelerator and from 75% to 5% by weight of the alkoxyalkanol component. The additive fluids, as well as the distillate fuel compositions of the present invention may also contain other additives such as corrosion inhibitors, antioxi­ dants, metal deactivators, detergents, cold flow improvers, inert solvents or diluents, and the like. EXAMPLE 1 In order to determine the effect of the fuel com­ positions of the present invention on the coking tendencies of diesel injectors in indirect injection compression ignition engines, use was made of a diesel fuel injector test apparatus developed for the purpose of screening chemical agents for use as anticoking, anti­ deposit and antivarnish agents. The design of the apparatus allows it to accommodate any type of conven­ tional automotive diesel fuel injector used in diesel engines such as the Bosch injectors used in turbocharged XD2S engines and the Lucas pencil-type or mini-fuel injectors used in 6.2 liter or 350 cu. in. diesel engines. The apparatus comprises a diesel fuel injector nozzle assembly attached to and extending into an aluminum cylinder 2.5 inches in width and 5.0 inches in diameter. Attached to and extending into the opposite side of the aluminum block is a 1-inch pipe assembly consisting of a connector nipple and tee which acts as a combustion chamber into which diesel fuel is injected by the injector assembly. The chamber is coupled to a flash arrestor and exhaust-gas assembly. Also coupled to the combustion chamber is a serpentine-gas/air heater, 0.5 inches in diameter and 6.5 inches in length. The heater controls the temperature of the air entering the combustion chamber. If desired, air temperatures up to 750°C. can be produced. Under normal testing conditions, air tempera­ ture is maintained at a range between 470°C. and 525°C. Air flow rate, which is critical to the operation and replication of the test, is maintained by a mass flow controller to within 0.1 liter per minute at flow volumed of 20 to 50 liters per minute. A standard single cylinder diesel engine Bosch fuel pump is used to develop pressure and fuel volume passing into the injector. A 1-horsepower motor directly connected to the fuel pump is operated at 1750 RPM providing approximately 875 injections of fuel per minute. The fuel pump can be adjusted to provide fuel flow rates ranging from 35 milliliters to 3000 milliliters per hour. Standard operating fuel flow rates used for testing generally range between 80 and 120 milliliters per hour. Under the standard operating conditions of air flow and fuel flow, incipient combustion of injected fuel occurs. Tests are carried out using 1-quart samples of fuel, with or without additives. The length of each test is four hours. After the test operation, the injectors are carefully removed from the apparatus so as not to disturb the deposits formed thereon. After the test, the amount of deposit, coke or varnish on various areas of the injector external or internal parts are rated. Visual differences in amounts of deposits between a non-additive test and one with an additive are used to distinguish and establish the effect of the chemical agent being tested as an anticoking additive. The areas of the injector parts which are rated for deposits include (i) the external area of the nozzle face, (ii) an area around the injector orifice extending one millimeter in diameter from the center of the orifice, (iii) the rim of the nozzle orifice, (iv) the exterior pintle tip, (v) the pintle obturator, and (vi) the nozzle face. To demonstrate the anticoking effects of the present additives, a base fuel was prepared consisting of a commercially available diesel fuel having a nominal cetane rating of 37. Fluorescence Indicator Adsorption (FIA) analysis indicated that the fuel was composed by volume of 41% aromatics, 2.0% olefins and 57% saturates. The base fuel also contained 140 pounds per thousand barrels (PTB) of mixed octyl nitrates (a commercial prod­ uct available from Ethyl Corporation under the designation DII-3 Ignition Improver). Test blends were prepared from this base fuel, and were designated Fuels A, B, and C. Fuel A contained, in addition to 140 PTB of mixed octyl nitrates, 50 PTB of 2-methoxy ethanol. Fuel B contained, in addition to 140 PTB of mixed octyl nitrates, 50 PTB of 2-ethoxy ethanol. Fuel C contained, in addition to 140 PTB of mixed octyl nitrates, 50 PTB of 2-(2-ethoxyethoxy)ethanol. The diesel fuel injection test apparatus was operated for four hours on the base fuel followed by operation for four hours on the test blends (1-quart samples of each). Operating conditions for all tests were as follows: Air Temperature . . . 510 °C. to 520°C. Air Flow Rate . . . . 32.5 liters per minute RPM . . . . . . . . . 1750 Fuel Flow Rate . . . 135 cubic centimeter/hour Before each test, a new Bosch DNOSD-251 nozzle was installed in the apparatus. After the tests, the injectors were carefully removed from the apparatus so as not to disturb the de­ posits formed thereon. Visual ratings of injector depos­ its were made with a deposit rating system in which 1 = clean and 5 = extreme deposit build-up. The test results are given in Table I below:

Claims: 1. A distillate fuel composition for indirect injection compression ignition engines containing, in an amount sufficient to control coking, especially throttling nozzle coking in the prechambers or swirl chambers of indirect injection compression ignition engines operated on such fuel, a combination of (i) an organic nitrate ignition accelerator and (ii) an alkoxyalkanol. 2. A composition as claimed in claim 1 in which the ignition accelerator is a mixture of octyl nitrates. 3. A composition as claimed in claim 1 or claim 2 in which the alkoxyalkanol has the structure R′ OR″ OH wherein R′ is an alkyl group containing 1-12 carbon atoms, R″ is a divalent aliphatic hydrocarbon group containing 2-4 carbon atoms and n is an integer from 1-4. 4. A composition as claimed in claim 3 in which the alkoxyalkanol is 2-methoxy ethanol or 2-ethoxy ethanol. 5. A composition as claimed in any one of the preceding claims in which nitrate ignition accelerator is present in an amount of 100 to 1000 PTB (0.29 to 2.9 kg/m³) of base fuel and alkoxyalkanol is present in an amount of at least 20 PTB (0.06 kg/m³) of base fuel. 6. A method of inhibiting coking, especially throttling nozzle coking, in the prechambers or swirl chambers of an indirect injection compression ignition engine, which method comprises supplying the engine with a distillate fuel composition as claimed in any of the preceding claims. 7. An additive fluid concentrate for use in distillate fuels, comprising a combination of (i) an organic nitrate ignition accelerator and (ii) an alkoxyalkanol. 8. A concentrate as claimed in claim 7 in which the ignition accelerator and/or the alkoxyalkanol are as defined in any one of claims 2 to 4. 9. A concentrate as claimed in claim 7 or claim 8 which contains 5 to 95 percent by weight of the organic nitrate ignition accelerator and 95 to 5 percent by weight of the alkoxyalkanol. 10. The use of a mixture of organic nitrate ignition accelerator and an alkoxyalkanol as an anti-coking agent, or the use of organic nitrate ignition accelerator and an alkoxyalkanol in the formulation of additive fluid concentrate or distillate fuel composition. AUSTRIAN CLAIMS 1. A method of inhibiting coking, especially throttling nozzle coking, in the prechambers or swirl chambers of an indirect injection compression ignition engine, which method comprises supplying the engine which a distillate fuel composition containing a combination of (i) organic nitrate ignition accelerator and (ii) an alkoxyalkanol, the combination being present in an amount sufficient to control the coking characteristics of the fuel. 2. A method as claimed in claim 1 in which the ignition accelerator is a mixture of octyl nitrates. 3. A method as claimed in claim 1 or claim 2 in which the alkoxyalkanol has the formula: R′ OR″ OH wherein R′ is a C₁ to C₁₂ alkyl group, R″ is a C₂-C₄ divalent aliphatic hydrocarbon group and n is an integer from 1 to 4. 4. A method as claimed in claim 3 in which the alkoxyalkanol is 2-methoxy ethanol or 2-ethoxy ethanol. 5. A method as claimed in any one of the preceding claims, in which nitrate ignition accelerator is present in the fuel in an amount of 100 to 1000 PTB (0.29 to 2.9 kg/m³) of the base fuel and alkoxyalkanol is present in an amount of at least 20 PTB (0.06 kg/m³ of base fuel. 6. The use of a mixture of organic nitrate accelerator and an alkoxyalkanol as an anti-coking agent. 7. A method of inhibiting coking, especially throttling nozzle coking, in the prechambers or swirl chambers of a vehicle indirect injection compression ignition engine, which method comprises combining a base fuel, organic nitrate ignition accelerator and an alkoxyalkanol, the nitrate ignition accelerator and the alkoxyalkanol being present in amounts sufficient to control the coking characteristics of the fuel, and supplying the vehicle with the resultant fuel mixture. 8. The use of organic nitrate ignition accelerator and an alkoxyalkanol in the formulation of additive fuel concentrates or distillate fuel compositions, the concentrates preferably comprising from 5 to 95% by weight of organic nitrate ignition accelerator and from 95 to 5% by weight of alkoxyalkanol. 9. A method of formulating a distillate fuel composition, comprising combining a base fuel, organic nitrate ignition accelerator and an alkoxyalkanol, the nitrate ignition accelerator and the alkoxyalkanol being used in amounts sufficient to control the coking characteristics of the base fuel in the prechambers or swirl chambers of an indirect injection compression ignition engine. 10. A use as claimed in claim 6 or claim 8 or a method as claimed in claim 7 or claim 9 wherein the nitrate ignition accelerator or the alkoxyalkanol or both are as defined in any one of claims 2 to 4.

Inventors: NIEBYLSKI, LEONARD MARTIN, ZAWESKI, EDWARD FELIX
Applicants: ETHYL CORPORATION
Application year: 1986
Main classification: C10L1
IPC codes: C10L1