Method for increasing the high load (knock) limit of an internal combustion engine operated in a low temperature combustion mode

Abstract

Disclosed herein is a method for increasing the high load (knock) limit 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 the high load (knock) limit of an internal combustion engine operated in a low temperature combustion 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.

2. The method of claim 1, wherein the internal combustion engine is operated in a premixed charge compression ignition 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 gasoline has a RON greater than 85 and up to about 120.

5. The method of claim 1, wherein the gasoline has a RON greater than 89.

6. The method of claim 1, wherein the gasoline contains ethanol up to 85 vol.

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 improvers are selected from the group consisting of nitrogen-containing octane, improvers, nitrogen-free cetane improvers, and mixtures thereof.

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

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

11. The method of claim 10, wherein the alkyl nitrate compounds 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-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 mixtures thereof.

12. The method of claim 11, wherein the cycloalkyl nitrate compounds 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 11, wherein the nitrate esters of alkoxy substituted aliphatic alcohols are selected from the group consisting of 1-methoxypropyl-2-nitrate, ethoxpropyl-2 nitrate, 1-isopropoxy-butyl nitrate, 1-ethoxylbutyl nitrate and mixtures thereof.

14. The method of claim 8, wherein the nitrogen-free cetane improvers 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 improvers are selected from the group consisting of 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(tertiary butyl) butane, peroxy acetic acid, tertiary butyl hydroperoxide and mixtures thereof.

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

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

18. The method of claim 1, wherein the one or more octane improvers are present in the fuel composition in an amount ranging from about 0.05 to about 5 wt. %.

19. The method of claim 16, wherein 2-ethylhexyl nitrate is present in the fuel composition in an amount ranging from about 0.05 to about 1 wt. %.

20. The method of claim 16, wherein 2-ethylhexyl nitrate is present in the fuel composition in an amount ranging from 0.1 to about 0.5 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 wt. %.

22. The method of claim 17, wherein di-tert-butylperoxide is present in the fuel composition in an amount ranging from about 0.1 to about 2 wt. %.

23. The method of claim 1, wherein the amount of the one or more cetane improvers added to the fuel 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 130 kPa.

26. The method of claim 1, wherein the gasoline has a RON greater than 92.5.

27. The method of claim 1, wherein the gasoline has a RON greater than 925 and up to about 120.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph illustrating the effect of a cetane improver to the intake temperature when added to a convention pump gasoline.

(2) FIG. 2 is a graph illustrating the effect of a cetane improver on the high load limit (expressed in terms of maximum gross Indicated Mean Effective Pressure (IMEPg) vs. Intake Pressure) when added to a convention pump gasoline.

(3) FIGS. 3a and 3b is a graph illustrating the effect of a cetane improver on the engine-out NOx emissions at 100 kPa intake pressure and 130 kPa intake pressure, respectively, when added to a convention pump gasoline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) 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.

(5) 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.

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

(7) Knock Limit is set as a safety margin to prevent the formation of severe pressure waves/oscillations in the engine cylinder, which typically results from high heat release and pressure rise rates. The knock limit is specified to ensure minimal engine vibration and noise levels (typically referred to as noise, vibration, and harshness, or NVH). Several different metrics are used to establish knock limits, including acoustic energy flux (in units of MW/m.sup.2) and maximum pressure rise rate (in units of pressure/Crank Angle Degree). (See, e.g., SAE Technical Paper 2013-01-1658 by Maria et. al.).

(8) Fuel Composition

(9) The fuel compositions for use in the methods of present invention advantageously increase the knock limit when employed in 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 under partially premixed combustion conditions. Furthermore, for certain fuel compositions of the present invention, reasonable maximum pressure rise rates are obtained, thus significantly expanding the range where the engine can be run under advanced combustion conditions satisfactorily.

(10) 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 89. In another embodiment, the gasoline employed in the fuel composition has a RON greater than 89 and up to about 120. If desired, the gasoline can contain other components such as, for example, ethanol in an amount up to about 85 vol. %. In one embodiment, the gasoline contains from about 0.5 up to about 20 vol. % ethanol.

(11) Method of Making the Fuel Composition

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

(13) 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.

(14) 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.

(15) 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.

(16) 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, I-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.

(17) 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.

(18) 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 wt. %. In another embodiment, the one or more cetane improvers will be added to the fuel composition in an amount ranging from about 0.1 to about 1 wt. %.

(19) In one embodiment, 2-ethylhexyl nitrate is present in the fuel composition in an amount ranging from about 0.05 to about 1 wt. %. In another embodiment. 2-ethylhexyl nitrate is present in the fuel composition in an amount ranging from 0.1 to about 0.5 wt. %.

(20) In one embodiment, di-tert-butyl peroxide is present in the fuel composition in an amount ranging from about 0.1 to about 5 wt. %. In another embodiment, di-tert-butylperoxide is present in the fuel composition in an amount ranging from about 0.1 to about 2 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 (load), 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 the 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 of 130 kPa.

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

COMPARATIVE EXAMPLE A

(25) A pump gasoline containing 10 vol. % ethanol was used as a control. The main properties of the pump gasoline are listed in Table 1 below.

(26) TABLE-US-00001 TABLE 1 Specific Gravity (15 C.) 0.7238 Net Heating Value, MJ/kg 41.74 Carbon, wt. % 81.67 Hydrogen, wt. % 14.72 Oxygen, wt. % 4.06 RON 92.5 MON 84.6 Antiknock Index (R + M)/2 88.6

EXAMPLE 1

(27) To the pump gasoline of Comparative Example A was added 0.15 wt. % of 2-ethylhexyl nitrate (EHN).

EXAMPLE 2

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

EXAMPLE 3

(29) To the pump gasoline of Comparative Example A was added 0.40 wt. % of EHN.

EXAMPLE 4

(30) To the pump gasoline of Comparative Example A was added 0.35 wt. % of di-tert butyl peroxide (DTBP).

EXAMPLE 5

(31) To the pump gasoline of Comparative Example A was added 0.60 wt. % of DTBP.

(32) Engine Test

(33) The fuel compositions of Examples 1-5 and Comparative Example A were tested to determine their high load limit in engines operated under advanced combustion conditions. The engine used was a single cylinder version of a 6-cylinder medium duty diesel engine in which 5 of the 6 cylinders were deactivated. The engine compression ratio was 14/1, and the engine speed was held constant at 1200 rpm. The fuel compositions of Examples 1-5 and Comparative Example A were each first premixed with air and then injected into the engine using a port fuel injector. Intake pressures ranged from 100 kPa (naturally aspirated conditions that are representative of most engines on the road) to 130 kPa (representative of some mildly boosted engines having turbochargers).

(34) The effects of the cetane improver's concentration and type are shown in FIG. 1. As can be seen, the fuel composition of Comparative Example A required a relatively high intake temperature of 140 C. to initiate combustion. The high intake temperature is an indicator of its resistance to combust. For the fuel compositions of Examples 1-4, as the cetane improver concentration was increased, the intake temperature required to initiate combustion decreased significantly, indicating a significant improvement in reactivity. In particular, for EHN: (1) 0.15 wt. % EHN reduced the intake temperature to 95 C.; (2) 0.25 wt. % EHN reduced the intake temperature to about 78 C.; and (3) 0.40 wt. % EHN reduced the intake temperature to 60 C. (the lowest desirable intake temperature to ensure that the water in the recycled exhaust gas does not condense). For DTBP, (1) 0.35 wt. % DTBP reduced the intake temperature to 95 C. and (2) 0.6 wt. % DTBP reduced the intake temperature to about 78 C. Thus, EHN was more effective than DTBP for improving the gasoline reactivity.

(35) The impact of the cetane improvers on the high load knock limits of the engine were determined by increasing the fueling rate until the knocking of the engine exceeded acceptable ringing intensity limits of 3 MW/m.sup.2 at 100 kPa intake pressure and 5 MW/m.sup.2 at 130 kPa intake pressure. The results are shown in FIG. 2 where the high load knock limit (expressed in terms of maximum gross Indicated Mean Effective Pressure (IMEPg) vs. Intake Pressure) for the fuel compositions of Examples 1, 3 and 4 (i.e., 0.25 wt. % and 0.4 wt. % EHN and 0.35 wt. % DTBP (equivalent to EHN at 0.15 wt. %)) and Comparative Example A. At both 100 and 130 kPa, the high load knock limits of the fuel compositions of Examples 1, 3 and 4 were increased relative to the fuel composition of Comparative Example A (demonstrated by the lower values of Max. IMEPg for the fuel composition of Comparative Example A shown by the squares). Furthermore, the fuel composition of Comparative Example A required a high intake temperature of 130 C. just to have any combustion reactivity, while the fuel compositions of Examples 1, 3 and 4 only required an intake temperature of about 60 C.

(36) As shown in FIG. 2, at 130 kPa, the reactivity of the fuel composition of Comparative Example A increased (as shown by a lower intake temperature requirement of 93 C.) and the high load limit increased. However, the fuel compositions of Examples 1, 3 and 4 continued to be more reactive and still have higher high load knock limits. The high load knock limits of the fuel compositions of Examples 1 and 3 having 0.25 and 0.4 wt. % EHN, respectively, were more than 28% higher than that of the fuel composition of Comparative Example A. The high load knock limit of the fuel composition of Example 4 having 0.35 wt. % DTBP (0.15% EHN equivalent) was intermediate between that of the fuels containing 0.25 and 0.4 wt. % EHN.

(37) The NOx emissions were plotted in FIGS. 3a (100 kPa) and 3b (130 kPa) along with a line for the current US NO.sub.x limit (0.27 g/kWhr). For the fuel compositions of Examples 1-5 and Comparative Example A, the engine-out NO.sub.x emissions were each significantly lower than the requirements. This was achieved without the use of any NOx aftertreatment equipment and demonstrates that advanced combustion has been attained. As EHN concentration increased, the amount of NOx increased (most likely due to the presence of NO in the chemical structure of EHN). However, even at the highest EHN concentration, the NOx was still well below the US emission specifications. For DTBP, which does not contain NO in its chemical structure, the NOx did not increase with concentration.

(38) The results of this invention clearly demonstrate the use of cetane improvers such as EHN and DTBP at relatively low concentrations can significantly increase the engine high load limits of pump gasoline and thus allows for the feasibility of the use of pump gasoline in advanced combustion engines.

(39) 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.