MXPA99000273A - High-octopal aviation gasolines without pl - Google Patents

Abstract

Novel aviation fuel compositions containing a substantially positive or synergistic combination of alkyl tertiary butyl ether, an aromatic amine and optionally, a manganese component. The base fuel containing the additive combination can be an alkylate base fuel with a wide range of boiling

Description

GASOLINE FOR AVIATION WITHOUT LEAD WITH HIGH CONTENT OF OCTANO BACKGROUND OF THE INVENTION The invention relates generally to gasoline compositions for aviation (Avgas) and methods for producing and using said compositions. More particularly, the present invention relates to Avgas compositions with a high octane content containing a package of lead-free additives and methods for producing and using said compositions. Gasoline for conventional aviation (Avgas) generally contains an aviation base fuel for aviation and a lead-based additive package. The normal Avgas in the industry known as "100 Low Lead" (100LL) contains the lead additive tetraethyl lead (TEL) to reinforce the anti-knock property of Avgas on the inert antiknock property of its aviation base aviation fuel. Detonation is a condition of piston-driven aviation engines due to autoignition, spontaneous ignition of the final gases (gases trapped between the cylinder wall and the flame approaching the front) in an engine cylinder after that the spark plug ignites. A standard test that is applied to measure the anti-knock property of Avgas based on lead under various conditions, is the engine octane number (NOM) classification test (ASTM D2700). Another standard test applied to lead-based Avgas is the supercharge classification test (performance number) (ASTM D909). Despite the ability of lead-based Avgas to provide good anti-knock property under the severe demands of piston-driven aviation engines, these lead-based compositions are facing stricter standards because of their lead oxide and lead oxide emissions . The standards of E. U.A. The current regulations establish a maximum amount of TEL for aviation fuels at 4.0 ml / gal and refers to the fact that the negative environmental and health impacts of lead and lead oxide emissions may affect additional restrictions. Gaughan (PCT / US94 / 04985, U.S. Patent No. 5,470,358) refers to an unleaded Avgas that contains a base fuel for aviation and an aromatic amine additive. It is reported that the Avgas compositions exemplified in Gaughan contain a base fuel for aviation, (e.g., isopentane, ethylate and toluene) having a NOM of 92.6 and an alkyl or halogen substituted phenylamine which elevates the NOM to less 98. Gaughan also refers to other unleaded octane boosters such as benzene, toluene, xylene, methyl tertiary butyl ether, ethane, ethyl tertiary butyl ether, methylcyclopentadienyl manganese tricarbonyl and iron pentacarbonyl, but does not support its use in combination with aromatic amine because, according to Gaughan, said additives are not capable by themselves of increasing the NOM to the level of 98. Gaughan concludes that there is little economic incentive to combine the aromatic amines with other additives due to that could have only a very slight increasing effect at the level of NOM 98. It might be convenient to find alternative Avgas compositions that avoid the use of aditi They are lead-based and have good performance in aviation engines powered by pistons. It might also be convenient to find Avgas compositions that could use less expensive base fuels. COMPENDIUM OF THE INVENTION The Avgas compositions of the invention contain a combination of lead-free additives (also referred to as the "additive package") including an alkyl tertiary butyl ether and an aromatic amine. The additive package may also include manganese, for example, as provided by methyl cyclopentadienyl manganese tricarbonyl (MMT). In a preferred embodiment, the substantially positive or synergistic additive package is combined with a broad boiling scale of the alkylate base fuel. In a further preferred embodiment, the Avgas composition of the invention is an unleaded Avgas that has good performance in a piston-driven aviation engine as determined by one or more classifications that include NOM, Supercharge Cycles and Detonation / Intensity a the maximum potential detonation conditions of an aviation engine.

The invention is also directed to a method for forming an unleaded Avgas composition wherein the additive package is combined with a base fuel, such as an alkylate with broad boiling scale. The concentration of the additives in the Avgas can be based on a non-linear model, where the combination of additives has a substantially positive or synergistic effect on the performance of the lead-free Avgas composition. The invention is further directed to a method for improving the performance of aviation engines by operating an aviation engine driven by pistons with said Avgas compositions. DESCRIPTION OF THE ILLUSTRATIVE MODALITIES For the purposes of the invention, "Avgas" or "Avgas composition" refers to aviation gasoline. In general, an Avgas is produced from a base fuel and one or more additives. The compositions according to the invention contain a combination of additives including an alkyl tertiary butyl ether and an aromatic amine. The combination may further include a manganese component that is compatible with the other additives and the base fuel, for example, as provided by the addition of methyl cyclopentadienyl manganese tricarbonyl (MMT). The combination of additives is also referred to as "the additive package". The alkyl tertiary butyl ether in the additive package is preferably a tertiary butyl ether of Ci to C5 and more preferably a methyl tertiary butyl ether (MTBE) or an ethyl tertiary butyl ether (ETBE for its acronym in English). This component of the additive package is also widely referred to as the oxygenate. The aromatic amine in the additive package preferably has the formula: wherein R.sub.2 R.sub.2, R.sub.3 and R.sub.4 are individually hydrogen or an alkyl group of C.sub.Cs- In a preferred embodiment, the aromatic amine additive is aniline, n-methyl aniline, n-ethyl aniline, m-toluidine, p-toluidine, 3,5-dimethyl aniline, 4-ethyl aniline or 4-n-butyl aniline. Methyl cyclopentadienyl manganese tricarbonyl (M MT) is also included in the additive package, particularly to provide a magnesium component to the additive package. The Avgas compositions of the invention preferably comprise from 0. 1 to 40% by volume of alkyl tertiary butyl ether, 0.1 to 10% by weight of aromatic amine and 0 to 0.5 of manganese. For example, the composition of the invention may comprise from 15 to 32% by volume methyl tertiary butyl ether, 1.5 to 6% by weight of aniline and 0 to 0. 1 g of manganese. In a preferred embodiment, the additive package has a substantially positive or synergistic effect on the Avgas composition to which it is added. For the purposes of this specification, the term "substantially positive", in the context of the additive package, means that a successive additive that is added to the Avgas composition substantially reinforces the performance of the Avgas composition. In the case of NOM, the "substantially positive" effect means that each successive additive reinforces the Avgas NOM, preferably by 0.5, more preferably by 1.0 and even more preferably by 1.5. For example, an Avgas containing an alkylate with a broad boiling scale having a NOM of 91.5 and an additive of 10% by weight of aniline has a NOM of 97.6. when that Avgas contains also contains an ETBE of 40% in volume, the NOM of Avgas is reinforced to 101.1. Said composition contains a substantially positive combination of additives because the overall NOM of 101.1 is greater than the individual NOM levels of 97.6 (10% by weight of aniline) and 96.2 (40% by volume of ETBE) and the addition of 40% by weight. % by volume of ETBE reinforced the NOM of the base fuel / 10% by weight of aniline composition by 3.5. For the purposes of this specification, the term "synergistic" in the context of the additive package means that the effect of the combined additives is greater than the sum of the yield achieved by the individual additives under the same conditions. In the case of synergistic NOM, it means that the increase in NOM due to the additive package is greater than the sum of the NOM increments for each additive when it is the only additive in the base fuel.

These definitions of the "substantially positive" and "synergistic" effect are further understood in view of the numerous combinations of aditives that result only in antagonistic combinations, where the overall N OM does not increase or decrease with the addition of other additives. The combination of multiple additives in a package that includes an aromatic amine has been seen as an undesirable approach to improving the anti-knock property of an Avgas. (See Antecedes de la Invención, Gaughan). As further shown in the following Table 1, random mixtures of multiple octane booster additives can result in antagonistic octane effects.

As observed in Mix # 4, the combination of base fuel / 10% by weight of aniline / 40% by volume of ETBE / 0.5 g / gal of manganese results in an antagonistic effect where the additive package (40% by weight of ETBE / 0.5 g / gal of Mn / 10% by weight of aniline) does not reinforce the NOM beyond the base fuel to any significant degree. In addition, this package of additives produces the NOM effect of the base fuel composition / 10% by weight of aniline / 40% by volume of ETBE. In a preferred embodiment, the additive package was combined with a base fuel containing a broad boiling scale alkylate. Under this embodiment of the invention, an Avgas can be formed with a base fuel that is not conventionally used for Avgas. Under normal aviation (ASTM Dd-910), the base fuel in an Avgas is an aviation alkylate, which is an especially fractionated hydrocarbon mixture that has a relatively narrow boiling range. The additive package can be added to any sble base fuel where the resulting combination of additive package and base fuel are sble for use as an Avgas, based on performance characteristics and classifications and not necessarily ASTM standards. Such base fuels include conventional aviation alkylates (e.g., within the specifications of ASTM-910, including specifications for boiling points and distillation temperatures) and broad boiling scale base fuels. For the purposes of this specification, the term "broad boiling scale alkylate" is defined as an alkylate containing components that have a boiling point scale that is substantially wider than the scale of boiling points in a base fuel. alkylate for aviation. Preferably, the alkylate with broad boiling scale contains hydrocarbons having a boiling point scale of up to about 176.6 ° C change. More preferably, the boiling scale is from about 29.4 ° C + -12.2 ° C to about 204 ° C + -9.4 ° C (which essentially corresponds to an automotive gasoline base fuel). Table 2 below provides an example of an aviation alkylate and a broad boiling alkylate.

Table 2: Comparison of Alkylate of Am plia Boiling Scale and Combus Alkylate for Boiling Tests Alkylate Alkylate Tests Alkylate Alkylate Tests for Wide for Aviation scale Boiling scale Boiling Boiling Distillation Results API 71.5 73.0 PEI * 31.1 ° C 36.5 ° C 10% 63.8 68.5 PVR 0.53 kg / cm2 0.456 % 81.8 81.3 kg / cm2 % 92.8 91.0 Paraffins 99.2% vol. 99.4% vol. 40% 98.3 96.6 Olefins 0.2% vol. 0.4% vol. 50% 102.2 100.0 Aromatics 0.6% vol. 0.2% vol. 60% 105.7 102.0 70% 109.2 103.6 NOM 91.4 93.9 80% 114.7 105.1 NEI 93.4 97.1 90% 128.2 107.1 PEF * 202.8 111.8 No. Des. 85.4 97.4 Legend: PEI: Initial Boiling Point, PEF = Final Boiling Point, API: API Gravity, PVR = Vapor Pressure @ 37.7 ° C, NOI = Number of Octane Investigated, NOM = Motor Octane Number, No. Des . Performance number (ASTM-D909) Lower octane of broad boiling alkylate compared to aviation alkylate is mainly due to lower amounts of highly inherent octene hydrocarbons, isopentane and isooctane, as well as higher amounts of higher molecular weight, higher boiling paraffins. Table 3 presents gas industry standard 100 Low Lead gas chromatographic analyzes that use aviation alkylate as the primary base raw material (eg, at least 88% by volume) and the wide-scale alkylate of aviation. boiling and demonstrating the lower concentrations of isopentane and the isocyte isomers in broad boiling scale alkylate.

Table 3. Comparison of Boiling Scale Alquilate and 100 Low Lead The temperatures of the distillation curve for the second half of the boiling wide-scale alkylate were considerably higher than those of the aviation alkylate due to the higher molecular weight paraffinic hydrocarbons present in the former. A common result of having a concentration of larger paraffins, particularly with straight or normal chain paraffins, is a lower value of octane content. The larger paraffin molecules present in the wide-boiling alkylate are usually subjected to more chemical isomerization reaction steps and faster during the low-temperature portion of the oxidation chemistry that leads to self-ignition. The steps of isomerization in paraffin chemistry are very fast routes for the propagation of free radicals and subsequent self-ignition. The oxidation steps that lead to auto-ignition between the two alkylate base fuels are different, thus requiring different fuel formulations and additives for optimum performance. The substitution of oxygenates with high octane content for a substantial proportion of the alkylate base fuel reduces the number of rapid isomerization reactions and replaces them with less reactive partial oxidation intermediates, thus increasing the octane value of the fuel. The preferred embodiment of the invention utilizing the wide-boiling alkylate as a base fuel, offers a high-performance, high-quality alternative to the conventional Avgas. These large boiling scale alkylate base fuels offer a greater choice of base raw materials for Avgas formulations and also probably provide a less expensive base fuel for Avgas purchased with the conventional aviation alkylate base fuel. In a preferred embodiment, the compositions according to the invention have good performance in aviation engines driven by pistons. Preferably, this performance is determined by one or more classifications including NOM, supercharge and Cycles / detonation intensity at maximum potential detonation conditions in aircraft engines. The Avgas compositions of the invention preferably have a NOM of at least about 94, more preferably at least about 96 and even more preferably at least Approximately 98. The preferred Avgas compositions additional k have a NOM of at least about 99 or more preferably of at least 1 00. For example, a preferred NOM scale can be from about 96 to about 1 02. The classification of Supercharge is preferably at least minus 1 30. The Avgas compositions of the invention preferably also reduce, or eliminate, detonation in a piston-driven aircraft engine at maximum potential detonation conditions. The Classification of Detonation Cycle preferably is less than (average) 50 times 400 cycles and the Detonation Intensity classification preferably is at least 30 per cycle. The invention is also directed to a method for preparing an Avgas composition which involves combining a base fuel, such as a broad boiling scale alkylate, with an additive package. The content and concentration of the additive package is preferably selected from a non-linear model of the invention that defines the substantially positive or synergistic additive package. The method preferably identifies Avgas compositions that have good performance in piston-driven aviation engines based on NOM, Supercharge and / or Cycle / Detonation Intensity ratings. The invention also addresses a method for operating a piston-driven aircraft which involves operating the piston-driven engine with an Avgas composition made by a composition according to the invention. EXAMPLES A. Determination of NOM A NOM classification test (ASTM D2700) was carried out using a single variable cylinder compression laboratory engine that has been calibrated with reference fuels of defined octane levels. The sample of interest was compared with two reference fuels in normal detonation intensity and the octane number of the sample was determined by the approximation methods or compression ratio (r.c). On the approach, the octane value of the sample is determined by incorporating between two octane reference fuel values. In the method of r. c. , the octane value of the sample was determined by finding the compression ratio that doubles the normal detonation intensity of a reference fuel and the octane number is then found in a table of values. The repetition limits for NOM determination at 95% confidence intervals is 0.3 NOM for NOM 85-90 fuels while the reproduction limits are 0.9 for NOM 85 and 1.1 for NOM 90. B. Determination of OVERCARLOY CLASSIFICATION The OVERCARLOY classification test (ASTM-D909) determines the limited power by detonation, under conditions of rich mixture in supercharge, of fuels to be used in engines of reciprocal aircraft of ignition of sparks. The classification of Supercharge is a standard in the industry to test the severe octane requirements of piston-driven aircraft. For the purposes of this application, "ASTM-D909" is used interchangeably for "supercharge classification" and "performance number". C. Determination of Cycles Classification of Detonation and Intensity For the purposes of this application, "the Classification Test of Cycles / Detonation Intensity "and" Lycoming IO-360 tests "are used interchangeably.The Cycle Classification / Detonation Intensity classification test was carried out with a Textron Lycoming IO-360 engine (" the Lycoming engine ") in a rack for dynamometer tests (See FIG URA 1) Each of the four cylinders of the Lycoming engine was equipped with a piezoelectric transistor Kistier 6061 B. These transducers produce electric charges proportional to the pressures detected in the combustion chambers in the engine Lycoming The charge was then passed on four Kistier 5010 charge mode amplifiers that were calibrated so that the output voltage of the amplifiers was equivalent to 20 atmospheres as read by the detector .The voltage was processed through a board of National Instruments N B-A2000 A / D that of the four channels simultaneously at a rate of 250 samples per second at a resolution of twelve characters. uisition of data was facilitated by a computer sub-program (see FIGURE 2) using the LabVIEW atrium programming environment of National Instruments. The data acquisition program stores the data of the wires to 400 consecutive ignitions of the engine that is normally operated at 2700 rpm, very open steam outlet at a ratio of approximately 1.12 and a maximum cylinder temperature just below 260 ° C. The data is first stored in buffers, after the Random Access Memory of a Macintosh 8100/80 Power PC and finally on the hard disk. Pure data files are protected on optical magnetic disks and processed further using a Labview program. Prior to storage and processing, individual ignition chamber ignition data is passed through a fourth-order Butterworth digital bandpass filter of the 15kHz-45kHz scale. This is done to isolate frequencies that could only be excited significantly within the combustion chamber by a detonation event. The filtered signal was then "vented" for 3 milliseconds near the upper dead center of the piston path (compression / expansion pulse). The filtered filtered signal was then sent through an absolute value function and integrated to obtain a pressure-time-intensity expression of the acoustic energy supplied to the filter in the 15kHz-45kHz band of the frequencies detected by the system. This value was used to create a scale with which the detonation intensity was measured. If it was found that the intensity of the integral is greater than 20 on this scale, it was determined to be a case of detonation and the detonation events were recorded for 200 cycles. D. Determination of Nonlinear Models to Identify Aviation Fuel Compositions with Convenient NOM Classifications The effects of various fuel formulations of NOM classifications were determined using statistically designed experiments. More specifically, the complex relationships between the oxidation chemistry in the cylinder of the octane booster additives and the base fuel were investigated using statistical designs of cubes with centered faces (See, for example, Figure 3). The statistically designed experiments of the centered face cube measured the NOM values of specific fuel formulations that were combinations of three variables (Manganese level, aromatic amine level and oxygenate level) mixed with a broad boiling scale alkylate. The three variables and their respective concentration scales define the axes of x, y and z of the cube. (See Figure 3). The faces (surfaces) of the cube and the space between the cube define all the points of interaction for research. The three test variables were 0-10% by weight of aromatic amine, 0-0.6 g / gal of manganese (Mn) and 0-40% by volume of oxygenate (an alkyl tertiary butyl ether). Manganese may be provided by a corresponding amount of methyl cyclopentadienyl manganese tricarbonyl (MMT). The two oxygenates tested were methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE). Total, four test cubes were designed to measure numerous fuel combinations and, therefore, potentially differentiate chemical oxidation interactions. The four design faces of the cube are listed in Table 4. The aniline and n-methyl aniline were the aromatic amines chosen to complete the statistical analyzes.

Table 4. Design to Test the Independent Variables of the Cube Number of Base fuel Variable 1 Variable 2 Variable 3 Cube 1 Wide boiling scale MT MTBE Aniline 2 Wide boiling scale M MT ETBE Aniline 3 Wide boiling scale MMT MTBE n-Methyl Aniline 4 Wide boiling scale M MT ETBE n-Methyl Aniline The NOM values were measured at specific points along three axes of the cube as well as at the center point of the cube. Multiple measurements were made at the center point to calculate the level of variation of N O M with the assumption that it is a constant over all the design test space, that is, essentially a number scale of NOM, 91 -1 01. The polynomial curves were adapted to the data to define equations that describe the three interactions of variables with respect to N OM over the whole space of the test cube. From these equations, the N OM performance for all variable combinations was predicted within the test space defined by the maximum and minimum concentration scales of the variables. Some of the predicted and measured NOM values have been summarized in Tables 5-8. The rest of the predicted values can be derived from the prediction equations.

Table 5. NOM Previ st against NOM Measured for Oxygenate + Aniline manganese = 0 g / gal Aniline 0% by weight VOL.% NOM NOM NOM NOM NOM NOM NOM NOM NOM MTBE (P) (m) ífil (m) ÍP) (m) (P) (m) 0 91.5 91.1 93.8 94.6 97.1 98.6 98.8 92.8 95.0 98.0 99.3 20 93.8 93.6 95.8 98.6 99.6 30 94.4 96.3 98.8 98.9 99.6 40 94.7 95.2 96.5 97.0 98.7 99.2 99.0 Aniline 0% by weight VOL.% NOM NOM NOM NOM NOM NOM NOM NOM MTBE (P) (m) ífil (m) (P) (m) (P) (m) 0 92.3 91.1 93.8 95.9 96.8 99.7 97.6 94.6 95.9 98.6 101.1 20 96.0 94.0 97.2 99.4 98.8 101.7 30 96.6 97.5 99.4 101.3 40 96.3 96.2 97.0 97.2 98.6 100.1 101.1 Table 6. NOM Previ st against NOM Med do for Oxig < = born + Manganese of Aniline = 0.5 g / g to Aniline 0% by weight VOL.% NOM NOM NOM NOM NOM NOM NOM NOM MTBE ÍP) (m) íel (m) (P) (m) ífil (m) 0 96.0 95.3 97.4 97.7 98.9 98.7 99.1 97.3 98.5 99.8 99.4 20 98.2 99.1 99.4 100.4 99.6 99.7 30 98.9 99.9 100.6 99.7 40 99.2 100.3 100.1 99.6 100.6 89.3 99.8 Aniline 0% by weight VOL.% NOM NOM NOM NOM NOM NOM NOM NOM MTBE ísl (m) (P) (m) ÍP) () (P) (m) 0 95.5 95.5 95.9 96.0 96.8 97.6 97.8 97.8 98.0 98.5 99.0 20 99.2 97.5 99.3 99.4 100.5 99.5 30 99.8 99.6 99.4 99.2 40 99.4 98.4 99.1 100.9 98.6 98.0 97.1 Table 7. NOM Prev st against NOM Med do for Oxygen + Manganese from n-Methyl Aniline = 0.0 g / g to n-Methyl Aniline 0% by weight VOL. % NOM NOM NOM N OM NOM NOM NOM NOM MTB E (P) (m) LP-1 (m) (P) (m) Lsú. ím) 0 92.1 91. 1 93.4 94.0 95.0 95.4 94.7 1 0 92.6 93.7 95.0 95.0 20 93.2 93.6 94. 1 95.0 94.9 94.6 30 93.7 94.5 95.0 94.2 40 94.3 95.2 94.8 94.8 95.0 93.9 94.6 n-Methyl Aniline 0 wt% VOL. % NOM NOM NOM NOM NOM NOM NOM NOM NOM MTBE ÍP) (m) ífil ím) ÍP) ím) P) (m) 0 92.1 91 .1 92.8 93.8 94.1 95.4 95.6 93.3 93.8 94.6 95.5 20 94.5 94.0 94.7 95.2 95.9 95.6 30 95.7 95.7 95.7 95.7 40 96.9 96.2 96.6 96.2 96.2 95.8 96.5 Table 8. NOM Anticipated against NOM Medid or for Oxygenate + Manganese of n- -Methyl A niline = C .5 g / ga n-Methyl 0% in 2% in 6% in 1 0% Aniline weight weight weight in weight VOL. % NOM NOM NOM NOM NOM NOM NOM NOM NOM MTBE ÍP) ím) ÍP) ím) ÍP) ím) ÍP) ím) 0 97.2 97.7 99.4 97.7 96.4 95.9 1 0 97.7 98.0 97.7 96.0 20 98.3 98.4 97.7 97.5 95.6 30 98.8 98.8 97.7 95.3 40 99.4 99.1 98.7 97.7 94.9 95.3 n-Methyl 0% in 2% in 6% in 10% Aniline weight weight weight in weight VOL. % NOM NOM NOM NOM NOM NOM NOM NOM NOM MTBE LEÍ (m) ÍP) (m) ÍP) ím) Lfil ím) 0 96.6 96.3 97.4 95.9 95.5 95.9 1 0 97. 1 96.9 96.4 96.0 20 97.6 97.4 96.9 97.3 96.5 30 98.2 97.9 97.5 97.0 40 98.7 98.5 97.3 98.0 97.5 98.4 The equations that describe the interactions of the three variables (oxygenate, manganese and aromatic amine) and that finally predict the levels of NOM, are listed in Table 8A.

Table 8A. NOM Prediction Equations Test Cube: MTBE / Aniline / Manaanane NOM = 91.54 + (0.1466 x MTBE) + (8.827 x Mn)? - (1 .252 X Aniline) - (0.006492 x MTBE x Aniline) - (0.8673 x Mn x Aniline) - (0.001667 x MTBE2) - (0.05437 x Aniline2) Test Cube: MTBE / n-Methyl Aniline / Manqanese NOM = 92.06 + (0.05563 x MTBE) ) + (10.23 x Mn) + (0.7308 x nMA) - Í0.0069273 x MTBE x nMA) - (0.8220 x Mn x nMA) - (0.04005 x nMA2) Test Cube: ETBE / Aniline / Manqaneso NOM = 92.32 + ( 0.2730 X ETBE) + (6.349 X Mn) + (0.7429 X Aniline) - (0.009016 x ETBE x Aniline) - (1.058 x Mn x Aniline) - (0.004362 x ETBE2) Test Cube: ETBE / n-Methyl Aniline / Manqaneso NOM = 92.12 + (0.1 185 x ETBE) + (17.04 x Mn) + (0.3317 X nMA) - (0.1306 x ETBE x Mn) - (0.01999x ETBE x nMA) - (0.8828 x Mn x nMA) - (0.0218 x ETBE X Mn x nMA) - (16.36 x Mn2) The NOM variability provided for the four design cubes is a combination engine measurement, fuel mixture and variability that fits the equation. Table 9 shows the measurement variability of the NOM engine in terms of normal deviations for the four test cubes.

Table 9. Normal Deviations for the Four Test Cubes MTBE, Aniline, Mn 0.70 NOM ETBE, aniline, Mn 0.28 NOM MTBE, n-Methyl Aniline, 0.60 NOM ETBE, n-Methyl 0.55 NOM Mn Anilina, Mn The combined normal deviations for the four test cubes are 0.614 with 18 degrees of freedom. At the 95% confidence limit this results in a NOM variability of 1.83. variability, as used herein, is defined in ASTM as a NOM D-2700 classification method for two unique NOM measurements, the maximum difference of two numbers can have a maximum difference of two numbers and still be considered equal. However, the variability as used herein is neither repetitive nor reproducible, but it is something between the two definitions. The 168 test fuels were mixed from the same chemical raw materials / refinery and the NOM randomly classified by two operators into two NOM classification engines over a period of 8 weeks. The precision and variability for the process that is adapted to the NOM data equation is shown in Table 10.

Table 10. Variability that Adapts to the Equation Test Cube Root Value of the Error to the Error Rl C Mediated Average MTBE + Aniline 91.0 0.82 0.54 ETBE + Aniline 74.5 1 .29 0.88 MTBE + n-Methyl Aniline 77.3 0.99 0.70 ETBE + n-Methyl Aniline 81.3 0.81 0.61 The values of R2 are the proportion of variability in the NOM that is explained by the model on the scale of ten of the octane number tested. The fuel blending variability was not quantified but is expected to be a major contribution for the global predicted NOM variability. Most NOM results were obtained while the aromatic amines were established in the design of the statistical cube such as aniline and n-methyl aniline. Subsequent work was done to determine other potentially higher octane aromatic amines. (See Tables 1 1 -13). The specific aromatic amines were substituted in two different mixtures; a) 80% by volume of broad-boiling scale alkylate + 20% by volume of MTBE and 2) 80% by volume of broad-boiling alkylate + 20% by volume of ETBE. The substituted aromatic amines were mixed at 2.0% by weight. Manganese was not added to these mixtures. The NOM results listed in Tables 1 1 -13 are average NOM of two tests.

Table 1 1: The NOM Values for Methyl Substitutions in the Aniline ring 80/20% by volume of 80/20% by volume of alkylate scale of boiling wide scale alkylate + MTBE boiling ampile + ETBE amine NOM dNOM * NOM dMON * aromatic Aniline 96.3 97.3 - o-toluidine 94.5 - 1 .8 95.2 -2. 1 m-toloidine 96.8 0.5 97.4 0. 1 p-toluidine 96.8 0.5 96.8 -0.5 * Note: d NOM = delta NOM = difference between the additive of interest and the aniline reference point Table 12: NOM values for di and trimethyl substitutions in the Aniline ring 80/20% vo lumen of 80/20% volume of alkylate scale of a layered scale of boiling wide broad boiling + MTBE + ETBE amine NOM d NOM * NO M dNOM * aromatic Aniline 96.3 - 97.3 - 2, 3-dimethyl 93.8 -2.6 94.2 -3.1 Aniline 2, 4-dimethyl 95.0 -1 .3 95.2 -2.1 Aniline 2,5-dimethyl 93.9 -2.4 95.3 -2. 1 Aniline 2,6-dimethyl 93.3 -3.0 93.4 -3.9 Aniline 3,5-dimethyl 95.7 -0.6 96.7 -0.6 Aniline 2, 4,6-dimethyl 92.6 -3.8 93.7 -3.6 Aniline Table 13: Values of NOM for Substitutions Alkyl in Aniline Amine 80/20% volume of 80/20% volume of alkylate scale of broad-boiling scale alkylate + MTBE boiling amyloid + ETBE amine NOM dNOM * NOM d NOM * aromatic Aniline 96.3 - 97.3 - 4-etiI Aniline 96. 1 -0.3 97.5 0.2 4-n-butyl Aniline 95.7 -0.6 96.9 -0.5 n-Methyl Aniline 95.0 - 1 .3 95.7 - 1 .6 n-ethyl Aniline 91 .9 -4.4 91.9 -5.4 It can be observed from Tables 1 1 -1 3, that the aromatic amines having a methyl substitution in the ortho position (or the 2-position) in the aromatic ring as well as the n-alkyl substitutions in the amine, they are not effective octane booster additives for these two base fuels. However, the meta ring positions (positions 3 and 5) and the position on the ring for (position 4), the methyl substituted aromatic amines are generally more effective octane booster additives for this base fuel with the exception of the -UIDINE TOLL in the case of ETBE / base fuel. The increasing effectiveness of relative NOM of the different alkyl substituted aromatic amines exemplifies the importance of mapping the chemical oxidation reaction pathways for the additives of interest in relation to e! NOM test environment. Additional data from these experiments are shown in FIGU RAS 4-15. E. Determination of Nonlinear Models to Identify Fuel Compositions for Aviation with Desired NOM, Supercharge and Detonation Cycle / Intensity Classifications To better characterize the performance of fuel formulations, the effects of various fuel formulations in NOM, Supercharge and Classification of Cycles / Detonation Intensity, were determined using statistically designed experiments. The fuel compositions present were combinations of MTBE, aniline and manganese components and the same broad-boiling alkylate fuel as the previous designs. The three variable test scales of these experiments had 20-30% by volume of MTBE, 0.6% by weight of aniline and 0 - 0.1 g / gal of manganese. The classifications of NOM anti-knock, Supercharge and Detonation Cycle / Intensity classifications were measured at least in duplicate. Table 14 shows the nonlinear interactions of the fuel composition components in the classification of data of Supercharge and Average Deceleration Cycles and Average Deceleration Intensity for 400 consecutive engine cycles. The eight fuel formulations shown represent the extremes of the tested scales. The statistical analyzes show an interaction between MTBE and manganese terminations in the equations for the supercharge classification but only when the aniline levels are low with respect to the tested domain. There is another significant interaction for the classification of supercharge which is that, as MTBE increases the interaction between manganese and aniline, it becomes antagonistic. Also, the data analysis for Detonation Intensity contains an antagonistic interaction between MTBE and aniline. The Detonation Cycle data demonstrates a three-way interaction between MTBE, manganese and aniline.

Due to the non-linear fuel composition interactions mentioned above, n i the NOM and the supercharging classifications, when considered individually, will always predict the detonation-free operation of the commercial Lycoming IO-360 aviation engine. (See Table 1 5). The Detonation Cycle and Detonation Intensity data in Table 1 5 are the average of the tests of 400 cycles in duplicate.

The values of R2 between NOM, OVERLOAD, Detonation Cycles and Detonation Level are listed in Table 16. Table 16: R2 Values for Detonation Cycle Predictions and Detonation Inertality Combination R2 NOM Values to Predict Detonation Cycles * .44 NOM to Predict Detonation Intensity .38 Supercharge to Predict Detonation .64 Supercharge to Predict Detonation Intensity .82 Notes: (*) points of the salient data that were not representative for the population were removed after statistical analyzes Table 17 includes references to pure isooctane as well as Avgas 1 00 Low Lead with normal lead in the industry. For example, pure isooctane had a NOM value of 1 00 by definition but detonated severely in Lycoming IO-360 in its condition of maximum potential detonation operation. The addition of tetraethyl lead (TEL) to the sooctane is required to reinforce the classification of supercharging high enough to avoid self-ignition in a commercial aircraft engine.

Using the centered and augmented units for the fuel properties for our equation for NOM is NOM is: NOM = 97.75 + 0.575 * MTBE (s) + 0.305 * Mn (s) + 1. 1 35 * Anilines-0.485 * Mn (s) 2. The conversion to a real unit produces: NOM = 92.95 + 0. 1 1 5 * MTBE + 25.5 * Mn + 0.3783 * Aniline- 1 94 * Mn2. The interactions were not statistically significant. Using the centered and augmented units for the fuel properties our equation for supercharge (SC) is: SC = 140.008 + 2.325 * MTBE (s) + 3.9 * Mn (s) + 1 1 .715 * Aniline (s) + 1 .89375 * MTBE (s) * Mn (s) -2.39775 * Mn (s) * Aniline (s) -2.30625 * MTBE (s) * Mn (s) * Aniline (s) -8.643 * Aniline (s) 2. The conversion to real units produces: SC = 122.72 + 0.375 * MTBE (s) + 294.125 * Mn + 6.628 * Aniline + 16.8 * MTBE * Mn-0.15375 * MTBE * Aniline + 60.917 * Mn * Aniline -3.075 * MTBE * Mn * Aniline -0.9614815 * Anilina2 Observing the equation in the centered and augmented units, we observe that the interaction between MTBE and Mn is synergistic (coefficient of the same sign as coefficients for individual effects of MTBE * Mn). But, due to the presence of the 3-way interaction between MTBE, Mn and Aniline, the size of the MTBE * Mn interaction really depends on the level of aniline. At low levels of aniline, the interaction of MTBE * Mn is synergistic, but as the level of aniline increases, the MTBE * Mn interaction becomes less and less synergistic until it becomes basically from zero to high levels of aniline. aniline (if there is none, it is antagonistic at this point). Therefore, there is a synergism between MTBE and Mn, but generally only at low levels of aniline. A similar description can be used for the interaction of Mn * Aniline, where the size of this interaction depends on the level of MTBE. At low levels of MTBE, the interaction of Mn * Aniline is essentially zero, but as the level of MTBE increases the interaction of Mn * Aniline becomes more and more antagonistic. Table 18 below illustrates the previous concepts.

TABLE 18 1 . This is the expected SC value if there was no interaction, ie if the effects of each of the combustion components were additive. Using centered and augmented units for fuel properties our Detonation Intensity (IntN) equation is: I nt = 26.5-2.138719 * MTBE (s) -1 .905819 * Mn (s) -5.877127 * Aniline (s) -2.477696 * MTBE (s) * Aniline (s) +2.71 1 142 * Mn (s) 2+ 2.780729 * Aniline (s) 2 Converting to real units occurs: lntN = 62.9-0.923283 * MTBE-146.56206 * Mn-7.9423549 * Aniline + 0.1651797 * MTBE * Aniline + 1084.4568 * Mn2 + 0.3089699 * Aniline2 Observing again the equation in the Centered and increased units, we observed that the interaction of MTBE * Aniline is antagonistic. Also, it should be noted that this interaction does not depend on the level of Mn because there is no 3-way interaction in the molding. The following Table 19 illustrates this interaction. TABLE 19 1 . This is the expected Detonation Intensity value if there was no interaction, ie if the effects of each of the fuel components were additive. It should be noted that detonation intensity values below 20 can not be distinguished from one another, so that the antagonistic effect of the MTBE * Anil ina interaction can not be as significant as the high level of Mn (since the expected value under the assumption of no interaction is 14.7 and the actual values were 21.00 &19.0). Using centered and augmented units for fuel properties, our number equation of Detonation Cycles (Cycles) is: Y = ln (Cycles-1) = 1 .529878-0.43339 * MTBE (s) -0.376319 * Mn (s) - 1 .469152 * Aniline (s) + 0.368344 * MTBE (s) * Mn (s) * Aniline (s) + 0.732549 * AniJina (s) 2. Converting to real units occurs: Y = ln (Cycles + 1) = 4.4331281 -0.0130092 * MTBE + 29.308018 * Mn- 03641767 * Aniline-1.4733759 * MTBE * Mn-0.0245563 * MTBE * Aniline- 12.278133 * Mn * Aniline + 0.491 1243 * MTBE * Mn * Aniline + 0.0813943 * Anilina2. In any case, the expected number of detonation cycles is equal to e? - 1 . This variable was analyzed in the natural log (In) scale because it was observed that the variability was a mid-level function. Analyzing the data in the scale of I n causes that the variability is more constant through the average levels, which is necessary for the statistical tests to be valid. Also, since some observations had values of zero for number and detonation cycles (the natural log of zero can not be calculated), 1 was added in each observation so that the transformation of In could be used. Therefore, 1 must be subtracted from Y to return to the original units. Due to the presence of the 3-way interaction in the model and that there is no 2-way interaction, the 3-way interaction can be interpreted in 3 ways. We could say that there is a synergistic interaction between MTBE and Mn at low levels of aniline and an antagonistic interaction at high levels of aniline. This description is maintained for all pairs of fuel properties. The following Table 20 describes that the interaction of MTBE * Mn is synergistic in the absence of aniline and is antagonistic at high levels of aniline.

Table 20 1 - . 1 - This is the expected average # of the value of the detonation cycles if there was no interaction, ie if the effects of each fuel component were additive. Note that at the high aniline level, the ratio for the MTBE * Mn antagonist interaction in that number of detonation cycles can not be reduced to a value below zero. Increased Mn to 0.10 decreases the number of detonation cycles and almost zero increasing MTBE to 30 also decreases the number of detonation cycles to almost zero. Therefore, increasing both Mn and MTBE at the same time can not further reduce the number of detonation cycles. Using center and stepped units for fuel properties our equation for # of Detonation Cycles is: Cycles = 4.462241 -9.166427 * MTBE (s) -7.93772 * Mn (s) - 26.077604 * Aniline (s) + 8.742242 * MTBE (s) ) * Aniline (s) + 8.491223 * Mn (s) * Aniline (s) + 5.167309 * MTBE (s) * Mn (s) * Aniline (s) + 24.483337 * Aniline (s) 2. Converting to real units occurs Cycles = 135.2-2.5482718 * MTBE (s) + 188.15204 * Mn- 33.803388 * Aniline-20.669236 * MTBE * Mn + 0.2383288 * MTBE * Aniline-1 15.63548 * Mn * Aniline * 6.8897453 * MTBE * Mn * Aniline + 2.7203708 * Aniline2. In this case, the only synergistic interaction is between MTBE and Mn at low aniline levels. The other interactions are antagonistic. The synergism of MTBE * Mn at low aniline levels and antagonism at high aniline levels are shown below the Table 21 Table 21 1 . This is the expected average number of detonation cycles if there was no interaction, that is, if the effects of each of the fuel compounds were additive. 2. These observations were not included in the analysis. Additional data from these experiments are shown in FIGS. 16-30. The variability of the test and the adaptation of the equation of the second group of cubes designated experimentally is shown in Tables 22 and 23. For the predicted performance parameter listed in Table 22, the 95% total variability is a combination of engine measurement and fuel mixing variabilities. Table 22 also shows the measurement of the performance parameter engine and the combustion mixing variability in terms of normal deviation and the total variability calculated at the 95% confidence limit.

The total variability, as used herein, is defined as the ASTM Methods for two unique measurements, the maximum difference of two numbers may have and still be considered equal. However, the variability as used in the present is neither purely repetitive nor reproducibly, but it is something between the two definitions. The precision and variability for the equation adaptation process of the performance parameters is shown in Table 23.

Other aspects, advantages and embodiments of the invention described herein will be readily apparent to those of ordinary experience after reading the above description. In this regard, while the specific embodiments of the invention have been described in detail, variations and modifications of these embodiments can be made without departing from the spirit and scope of the invention as described and claimed.

Claims (35)

1. R EIVI N D ICAC ION ES 1. A lead-free aviation fuel composition comprises: (1) a boiling wide-scale alkylate base fuel and (2) a substantially positive or synergistic combination of

   (a) an alkyl tertiary butyl ether, and (b) an aromatic amine having the formula

   wherein Ri, R2, R3 and R are hydrogen or a C1-C5 alkyl group.
2. 2. The composition of claim 1, wherein the base fuel is a broad boiling scale alkylate having a boiling scale of 27.7 ° C + -12.2 ° C to 204.4 + -9.4 ° C.
3. 3. The composition of claim 1, wherein the alkyl tertiary butyl ether is methyl tertiary butyl ether.
4. 4. The composition of claim 1, wherein the alkyl tertiary butyl ether is ethyl tertiary butyl ether.
5. The composition of claim 1, wherein the aromatic amine is aniline.
6. 6. The composition of claim 1, wherein R ^ R2, R3 or R4 are methyl.
7. The composition of claim 1, wherein the aromatic amine is n-methyl aniline, n-methyl aniline, m-toluidine, p-toluidine, 3,5-dimethyl aniline, 4-ethyl aniline or 4-n-butyl aniline.
8. The composition of claim 1, wherein the composition further comprises a manganese compound that is soluble in the fuel composition.
9. The composition of claim 8, wherein the manganese is provided by methyl cyclopentadienyl manganese tricarbonyl.
10. The composition of claim 1, wherein the composition comprises from 0.1 to 40% by volume of alkyl tertiary butyl ether, 0.1 to 10% by weight of aromatic amine and 0 to 0.5 g per gallon of manganese.
11. The composition of claim 1, wherein the composition comprises from 15 to 32% by volume of methyl tertiary butyl ether, 1.5 to 6% by weight of aniline and from 0 to 0.1 g per gallon of manganese.
12. The composition of claim 1, wherein the composition comprises from 15 to 32% by volume of ethyl tertiary butyl ether, 1.5 to 6% by weight of amine and from 0 to 0.1 g per gallon of manganese.
13. The composition of claim 1, wherein NOM of the composition is at least 94.
14. 14. The composition of claim 1, wherein NOM of the composition is at least 96.
15. 15. The composition of claim 1, wherein NOM of the composition is at least 98.
16. 16. A method for preparing a composition. Fuel for unleaded aviation comprising: (1) selecting a substantially positive or synergistic group of additives (a) an alkyl tertiary butyl ether, and (b) an aromatic amine having the formula
17. wherein Ri, R2, R3 and R are hydrogen or an alkyl group of C ^ Cs, and (2) combine the additives selected in step (1) with a broad-boiling alkylate base fuel. The method of claim 16, wherein the base fuel is a broad boiling scale alkylate having a boiling scale of 27.7 ° C + -12.2 ° C to 204.4 + -9.4 ° C.
18. 18. The method of claim 16, wherein the alkyl tertiary butyl ether is methyl tertiary butyl ether.
19. The method of claim 16, wherein the alkyl tertiary butyl ether is ethyl tertiary butyl ether.
20. The method of claim 16, wherein the aromatic amine is aniline. twenty-one .
21. The method of claim 16, wherein R1 (R2, R3 or R are methyl
22. 22. The method of claim 16, wherein the aromatic amine is n-methyl aniline, n-methyl aniline, m-toluidine, p- toluidine,

    3, 5-dimethyl aniline, 4-ethyl aniline or 4-n-butyl anil ina.
23. 23. The method of claim 16, wherein the composition further comprises a manganese compound that is soluble in the fuel.
24. The method of claim 23, wherein the manganese is provided by tricarbonyl of methyl cyclopentadienyl manganese.
25. The method of claim 16, wherein the composition comprises from 0.1 to 40% by volume of alkyl tertiary butyl ether, 0.1 to 10% by weight of aromatic amine and 0 to 0.5 g per gallon of manganese.
26. 26. The method of claim 16, wherein the composition comprises from 15 to 32% by volume of methyl tertiary butyl ether, 1.5 to 6% by weight of aniline and 0 to 0.1 g per gallon of manganese.
27. 27. The method of claim 16, wherein the composition comprises from 15 to 32% by volume of ethyl tertiary butyl ether, 1.5 to 6% by weight of amine and 0 to 0.1 g per gallon of manganese.
28. The method of claim 16, wherein NOM of the composition is at least 94.
29. 29. The method of claim 16, wherein NOM of the composition is at least 96.
30. 30. The method of the claim 16, wherein NOM of the composition is at least 98.
31. 31. A method for preparing a composition comprising combining a broad boiling alkylate base fuel and a synergistic amount of tertiary alkyl butyl ether, a aromatic amine and sufficient manganese to raise the octane number of the engine of the composition to at least 94.
32. 32. The method of claim 31, wherein the synergistic amount is sufficient to raise the octane number of the engine of the composition to at least 96.
33. 33. The method of claim 31, wherein the synergistic amount is sufficient to raise the octane number of the engine of the composition to at least 98.
34. 34. A method for operating an av Piston-driven ion which comprises operating the aircraft engine with the aviation fuel composition of claim 1.
35. 35. A method for operating a piston-driven aircraft and which comprises operating the aircraft engine with the aviation fuel composition made by the method of claim 29.

    RESU M EN The novel aviation fuel compositions contain a substantially positive or synergistic combination of an alkyl tertiary butyl ether, an aromatic amine and optionally a manganese component. The base fuel containing the combination of additives can be a broad-boiling alkylate base fuel.