Method for increasing the maximum operating speed of an internal combustion engine operated in a low temperature combustion mode

Abstract

Disclosed herein is a method for increasing the maximum operating speed of an internal combustion engine operated in a low temperature combustion ignition mode, the method comprising operating the engine with a fuel composition comprising (a) gasoline having a Research Octane Number (RON) greater than 85 and (b) one or more cetane improvers.

Claims

1. A method for increasing a maximum operating speed of an internal combustion engine operated in a low temperature combustion mode, the method comprising operating the internal combustion engine in the low temperature combustion mode with a fuel composition comprising (a) a gasoline having a Research Octane Number (RON) greater than 85 and (b) one or more cetane improver additives, wherein the fuel composition allows the internal combustion engine to operate at a higher maximum operating speed.

2. The method of claim 1, wherein the internal combustion engine is operated in a premixed compression ignition combustion mode.

3. The method of claim 1, wherein the internal combustion engine is operated in a homogeneous charge compression ignition mode.

4. The method of claim 1, wherein the RON of the gasoline is greater than 85 and up to about 120.

5. The method of claim 1, wherein the RON of the gasoline is greater than 85 and up to about 100.

6. The method of claim 1, wherein the gasoline contains ethanol.

7. The method of claim 1, wherein the gasoline contains from about 0.5 up to about 20 vol. % ethanol.

8. The method of claim 1, wherein the one or more cetane improver additives are selected from the group consisting of nitrogen-containing cetane improver additives, nitrogen-free cetane improver additives, and mixtures thereof.

9. The method of claim 8, wherein the nitrogen-containing cetane improver additives are nitrate-containing cetane improver additives.

10. The method of claim 9, wherein the nitrate-containing cetane improver additives are selected from the group consisting of substituted or unsubstituted alkyl nitrates, substituted or unsubstituted cycloalkyl nitrates, nitrate esters of alkoxy substituted aliphatic alcohols, and mixtures thereof.

11. The method of claim 10, wherein the nitrate-containing cetane improver additives are selected from the group consisting of methyl nitrate, ethyl nitrate, n-propyl nitrate, isopropyl nitrate, allyl nitrate, n-butyl nitrate, isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, n-amyl nitrate, isoamyl nitrate, 2-amyi nitrate, 3-amyl nitrate, tert-amyl nitrate, n-hexyl nitrate, 2-ethylhexyl nitrate, n-heptyl nitrate, sec-heptyl nitrate, n-octyl nitrate, sec-octyl nitrate, n-nonyl nitrate, n-decyl nitrate, n-dodecyl nitrate, isomers thereof and mixtures thereof.

12. The method of claim 10, wherein the nitrate-containing cetane improver additives are selected from the group consisting of cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate, cyclododecyl nitrate, isomers thereof and mixtures thereof.

13. The method of claim 10, wherein the nitrate esters of alkoxy substituted aliphatic alcohols are selected from the group consisting of 1-methoxypropyl-2-nitrate, 1-ethoxpropyl-2 nitrate, 1-isopropoxy-butyl nitrate, 1-ethoxylbutyl nitrate and mixtures thereof.

14. The method of claim 8, wherein the nitrogen-free cetane improver additives are selected from the group consisting of alkyl peroxides, aryl peroxides, alky aryl peroxides, acyl peroxides, peroxy esters, peroxy ketones, per acids, hydroperoxides and mixtures thereof.

15. The method of claim 8, wherein the nitrogen-free cetane improver additives are selected from the group consisting of di-tert-butyl peroxide, cumyl peroxide, 2,5-dimethyl-2,5-di(tertiary butylperoxy) hexane, tertiary butyl amyl peroxide, benzoyl peroxide, tertiary butyl peracetate, 3,6,9-triethyl-3,9-trimethyl-1,4,7-triperoxononan, 2,2- di(teriary butyl) butane, peroxy acetic acid, tertiary butyl hydroperoxide and mixtures thereof.

16. The method of claim 1, wherein the one or more cetane improver additives is 2-ethylhexyl nitrate.

17. The method of claim 1, wherein the one or more cetane improver additives is di-tert-butyl peroxide.

18. The method of claim 1, wherein the one or more cetane improver additives are present in the fuel composition in an amount ranging from about 0.1 to about 5.0 wt. %.

19. The method of claim 16, wherein the 2-ethylhexyl nitrate is present in the fuel composition in an amount ranging from about 0.1 to about 5.0 wt. %.

20. The method of claim 16, wherein the 2-ethylhexyl nitrate is present in the fuel composition in an amount ranging from 0.25 to about 5 wt. %.

21. The method of claim 17, wherein di-tert-butyl peroxide is present in the fuel composition in an amount ranging from about 0.1 to about 5.0 wt. %.

22. The method of claim 17, wherein di-tert-butylperoxide is present in the fuel composition in an amount ranging from about 0.25 to about 5.0 wt. %.

23. The method of claim 1, wherein an amount of the one or more cetane improver additives added to the fuel composition during engine operation is dependent on one or more of engine speed, power output (load), boost level, or % EGR.

24. The method of claim 1, wherein the internal combustion engine is operated at an intake pressure of 100 kPa.

25. The method of claim 1, wherein the internal combustion engine is operated at an intake pressure of about 100 kPa to about 400 kPa.

26. The method of claim 1, wherein the one or more cetane improver additives are nitrate-containing cetane improver additives.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph illustrating the load versus engine speed for the fuel compositions of Examples 1-5 and Comparative Example A.

(2) FIG. 2 is a graph illustrating the load versus engine speed, for the fuel compositions of Examples 6-9 and Comparative Example A.

(3) FIG. 3 is a graph illustrating the maximum speed obtained for the various concentrations of the cetane improvers 2-EHN and DTBP in the fuel compositions of Examples 1-9 and the fuel composition of Comparative Example A containing no cetane improver.

(4) FIG. 4 is a graph illustrating the load versus engine speed for the fuel compositions of Examples 4 and 9.

(5) FIG. 5 is a graph illustrating the CA50 point for the fuel compositions of Examples 2-4 and 7-9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) To facilitate the understanding of the subject matter disclosed herein, a number of terms, abbreviations or other shorthand as used herein are defined below. Any term, abbreviation or shorthand not defined is understood to have the ordinary meaning used by a skilled artisan contemporaneous with the submission of this application.

(7) RONThe Research Octane Number is measured in a specially designed single cylinder CFR engine at an engine speed of 600 rpm and a specified intake air temperature that depends on barometric pressure. It reportedly simulates fuel performance under low severity engine operation.

(8) Advanced Combustion Engines are defined as engines that produce ultra low NO.sub.x or low soot or both. An example of an Advanced Combustion Engine is an internal combustion engine operated in a homogeneous charge compression ignition mode.

(9) Maximum Operating Speed is defined as the maximum engine speed that is achievable for an internal combustion engine operating in one of a low temperature combustion mode, a premixed compression ignition combustion mode or a homogeneous charge compression ignition mode. The maximum operating speed is generally limited by high combustion variance, due to inadequate fuel reactivity. This results when gasoline with a RON greater than 85 is used.

(10) Fuel Composition

(11) The fuel compositions for use in the method of the present invention advantageously increase the maximum operating speed of an internal combustion engine operated in a low temperature combustion mode such as a homogeneous charge compression ignition mode. Preferably, the fuel composition is a gasoline-type fuel composition that is employed in a diesel-type engine. Furthermore, for certain fuel compositions of the present invention, reasonable maximum pressure rise rates can be obtained, thus significantly expanding the range where the engine can be run under advanced combustion conditions satisfactorily.

(12) The fuel composition employed in the present invention includes (a) gasoline having a Research Octane Number (RON) greater than 85 and (b) one or more cetane improvers. In one embodiment, the gasoline employed in the fuel composition has a RON greater than 85 and up to about 120. In another embodiment, the gasoline employed in the fuel composition has a RON greater than 85 and up to about 100. If desired, the gasoline can contain other components such as, for example, ethanol in amount up to about 85 vol. %. In one embodiment, the gasoline contains from about 0.5 up to about 20 vol. % ethanol.

(13) Method of Making the Fuel Composition

(14) The gasoline employed in the presently claimed invention was taken from a commercial refinery. Information about typical processes and conditions for making these fuels can be found in Petroleum Refining by William Leffler (PennWell Corp, 2000).

(15) Suitable cetane improvers include, but are not limited to, nitrogen-containing cetane improvers, nitrogen-free cetane improvers, and the like and mixtures thereof. Useful nitrogen-containing cetane improvers include nitrate-containing cetane improvers such as, for example, substituted or unsubstituted alkyl or cycloalkyl nitrates having up to about 12 carbon atoms, or from 2 to 10 carbon atoms, nitrate esters of alkoxy substituted aliphatic alcohols, and the like and mixtures thereof. The alkyl group may be either linear or branched.

(16) Representative examples of alkyl nitrate compounds include, but are not limited to, methyl nitrate, ethyl nitrate, n-propyl nitrate, isopropyl nitrate, allyl nitrate, n-butyl nitrate, isobutyl nitrate, sec-butyl nitrate, tert-butyl nitrate, n-amyl nitrate, isoamyl nitrate, 2-amyl nitrate, 3-amyl nitrate, tert-amyl nitrate, n-hexyl nitrate, 2-ethylhexyl nitrate, n-heptyl nitrate, sec-heptyl nitrate, n-octyl nitrate, sec-octyl nitrate, n-nonyl nitrate, n-decyl nitrate, n-dodecyl nitrate, isomers thereof, and the like and mixtures thereof.

(17) Representative examples of cycloalkyl nitrate compounds include, but are not limited to, cyclopentyl nitrate, cyclohexyl nitrate, methylcyclohexyl nitrate, cyclododecyl nitrate, isomers thereof and the like and mixtures thereof.

(18) Representative examples of nitrate esters of alkoxy substituted aliphatic alcohols include, but are not limited to, 1-methoxypropyl-2-nitrate, 1-ethoxpropyl-2 nitrate, 1-isopropoxy-butyl nitrate, 1-ethoxylbutyl nitrate and the like and mixtures thereof. Preparation of the nitrate esters may be accomplished by any of the commonly used methods: such as, for example, esterification of the appropriate alcohol, or reaction of a suitable alkyl halide with silver nitrate.

(19) Useful nitrogen-free cetane improvers include organic compounds containing oxygen-oxygen bonds, such as alkyl peroxides, aryl peroxides, alky aryl peroxides, acyl peroxides, peroxy esters, peroxy ketones, per acids, hydroperoxides, and the like and mixtures thereof. Representative examples of nitrogen-free cetane improvers include, but are not limited to, di-tert-butyl peroxide, cumyl peroxide, 2,5-dimethyl-2,5-di(tertiary butylperoxy) hexane, tertiary butyl cumyl peroxide, benzoyl peroxide, tertiary butyl peracetate, 3,6,9-triethyl-3,9-trimethyl-1,4,7-triperoxononan, 2,2-di(teriary butyl) butane, peroxy acetic acid, tertiary butyl hydroperoxide and the like and mixtures thereof.

(20) In general, the one or more cetane improvers will be added to the fuel composition in an amount ranging from about 0.1 to about 5.0 wt. %. In another embodiment, the one or more cetane improvers will be added to the fuel composition in an amount ranging from about 0.25 to about 50 wt. %.

(21) In one embodiment, the cetane improver and gasoline are contained in separate storage vessels onboard the vehicle and the amount of cetane improver added to the fuel is varied, depending on the specific engine operating parameters such as speed, power level, boost pressure, and % EGR.

(22) Engine

(23) In the case of the low temperature combustion process such as the HCCI combustion process, during the homogeneous charge compression ignition mode of operation, the ignition takes place in the entire combustion chamber almost simultaneously by an auto-ignition of the combustion mixture. The combustion is therefore not initiated by a locally limited ignition source (for example, a spark plug) but is determined only by the ignition conditions in the combustion chamber. The ignition conditions required for this purpose are ensured, for example, by the return of hot residual gas. Outside the homogeneous charge compression ignition mode, the combustion mixture is not ignited by auto-ignition, but by an active (external) igniting by means of an ignition system. The internal combustion engine for use herein can be any internal combustion engine which can operate in the homogeneous charge compression ignition mode. Engines not equipped with turbochargers or superchargers will typically operate at intake pressures of 100 kPa (unboosted, naturally aspirated operation). Engines equipped with single or multi-stage turbochargers and/or superchargers will operate from about 100 kPa to about 400 kPa, depending on the type and number of stages. The higher the boost pressure, the more expensive the engine system. In one embodiment, the engine will operate at an intake pressure of 100 kPa. In another embodiment, the engine will operate at an intake pressure ranging from about 100 kPa to about 400 kPa.

(24) The methods of the present invention advantageously increase the maximum operating speed of an internal combustion engine operated in a low temperature combustion process such as the HCCI combustion process by employing a fuel composition comprising (a) gasoline having a RON greater than 85 and (b) one or more cetane improvers, more than 2.5 times as compared to an internal combustion engine operated in a homogeneous charge compression ignition mode employing a fuel composition comprising gasoline having a RON greater than 85 in. the absence of one or more cetane improvers. In another embodiment, the methods of the present invention advantageously increases the maximum operating speed of an internal combustion engine operated in a homogeneous charge compression ignition mode employing a fuel composition comprising (a) gasoline having a RON greater than 85 and (b) one or more cetane improvers, from about 2.5 times to about 6 times as compared to an internal combustion engine operated in a homogeneous charge compression ignition mode employing a fuel composition comprising gasoline having a RON greater than 85 in the absence of one or more cetane improvers.

(25) The following non-limiting examples are illustrative of the present invention.

COMPARATIVE EXAMPLE A

(26) A pump gasoline was used as a control. The main properties of the pump gasoline are listed in Table 1 below.

(27) TABLE-US-00001 TABLE I Specific Gravity (15 C.) Net Heating Value, MJ/kg Carbon, wt % 85.0 Hydrogen, wt % 15.0 Oxygen, wt % 0.0 RON 88.4 MON 82.7 Antiknock Index (R + M)/2 85.5

EXAMPLE 1

(28) To the pump gasoline of Comparative Example A was added 0.25 wt. % of 2-ethyhexyl nitrate (EHN).

EXAMPLE 2

(29) To the pump gasoline of Comparative Example A was added 0.50 wt. % of EHN.

EXAMPLE 3

(30) To the pump gasoline of Comparative Example A was added 1 wt. % of EHN.

EXAMPLE 4

(31) To the pump gasoline of Comparative Example A was added 2 wt. % of EHN.

EXAMPLE 5

(32) To the pump gasoline of Comparative Example A was added 5 wt. % of EHN.

EXAMPLE 6

(33) To the pump gasoline of Comparative Example A was added 0.50 wt. % of di-tert butyl peroxide (DTBP).

EXAMPLE 7

(34) To the pump gasoline of Comparative Example A was added 1 wt. % of DTBP.

EXAMPLE 8

(35) To the pump gasoline of Comparative Example A was added 2 wt. % of DTBP.

EXAMPLE 9

(36) To the pump gasoline of Comparative Example A was added 5 wt. % of DTBP.

(37) Testing

(38) The fuel compositions of Examples 1-9 and Comparative Example A were tested to determine whether the speed-high load limit can be increased using the Chevron ETC advanced combustion AVL single cylinder research engine. The engine consists of direct fuel injection and a compression ratio of 15:1. For the purpose of this test, the intake temperature was held constant at 40 C. and the intake pressure was held at atmospheric conditions (about 100 kPa).

(39) The load and speed range for each test fuel was then determined as follows. At each speed, the load tested ranged from the low load limit (limited by engine variance of 10%) to the high load limit (limited by engine knock, kept below 3 MW/m). The speed was then increased, and the load range was then tested again at the given speed. The speed was continuously increased until the engine could not operate under a stable condition (limited by engine variance of 10%). This would then represent the maximum speed range.

(40) FIG. 1 shows the operating map using a range of 2-EHN concentrations for the fuel compositions of Examples 1-5. The output load of the engine is shown on the vertical axis, and is represented by the Indicated Mean Effective Pressure (IMEP). The operating engine speed is shown on the horizontal axis. The open points shown on the graph are the actual operating points tested, while the lines represent the maximum operating load (limited by knock at 3 MW/am) for each test fuel and engine speed.

(41) As can be seen, FIG. 1 shows that the maximum speed the engine can operate at with the base fuel of Comparative Example A was 1200 rpm (with a 200 rpm error bar). The speed increased to 3000 rpm (the upper speed limit of the engine used for this test procedure) with the fuel compositions of Examples 4 and 5 containing 2 vol % and 5 vol % of 2-EHN, respectively. A higher maximum operating speed would have been achievable with unrelated modifications to the experimental apparatus (to accommodate the additional vibration). The fuel compositions of Examples 1-3 also had a positive effect, with the engine speed increasing to 1.600 rpm, 1800 rpm, and 2400 rpm, respectively. In addition, as the amount of 2-EHN increased, the engine was able to operate at lower loads.

(42) FIG. 2 shows the operating map using a range of DTBP concentrations for the fuel compositions of Examples 6-9. Similar to FIG. 1, the output load is shown on the vertical axis, and the operating engine speed is shown on the horizontal axis. As can be seen, the fuel composition of Example 9 containing 5 vol % DTBP increased the engine speed from 1200 rpm to 3000 rpm, while the fuel composition of Example 8 containing 2 vol % DTBP increased the engine speed to 2000 rpm.

(43) FIG. 3 summarizes the maximum operating engine speeds for the various concentrations of 2-EHN and DTBP in pump gasoline. It can be seen that at a constant concentration, 2-EHN can generally result in a higher engine speed. FIG. 4 shows that the fuel compositions of Examples 4 and 9 containing 2 vol % 2-EHN and 5 vol % DTBP, respectively, have very similar operating maps.

(44) Finally, a good measure of the impact of the cetane improver is to determine the location of the piston when 50% of the fuel in the engine burns (with a constant amount of fuel, constant intake temperature, and constant engine speed). This is known as the combustion phasing, or CA50 point. FIG. 5 shows that the CA50 point occurs later (i.e., takes longer to ignite) when comparing DTBP to 2-EHN at the same concentration.

(45) It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. For example, the functions described above and implemented as the best mode for operating the present invention are for illustration purposes only. Other arrangements and methods may be implemented by those skilled in the art without departing from the scope and spirit of this invention. Moreover, those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.