WO2008071628A1

WO2008071628A1 - Improvements in or relating to gasoline compositions

Info

Publication number: WO2008071628A1
Application number: PCT/EP2007/063490
Authority: WO
Inventors: Roger Francis Cracknell
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2006-12-11
Filing date: 2007-12-07
Publication date: 2008-06-19
Also published as: EP2126011A1

Abstract

The invention provides a method of increasing the sensitivity (RON - MON) of a gasoline composition comprising admixing with a gasoline base fuel from 1 to 20 vol.%, based on total volume of the gasoline composition, of a nitroalkane selected from the group consisting of nitroethane, nitropropane and mixtures thereof; and use of such a gasoline composition for improved operation of a homogeneous charge compression ignition (HCCI) engine over a range of load conditions.

Description

IMPROVEMENTS IN OR RELATING TO GASOLINE COMPOSITIONS

Field of the Invention

The present invention provides a method of increasing the sensitivity (RON - MON) of a gasoline composition. Background of the Invention

US 3,900,297 A (Michaels, James) discloses fuels for internal combustion engines, providing improved combustion efficiency, resulting in lower fuel consumption, increased horsepower output and cleaner burning, obtained by blending regular petroleum ether, namely gasoline, with certain nitroparaffins, namely nitroalkanes having one or two nitro groups and containing up to four carbon atoms. In particular, US 3,900,297 A discloses fuel compositions comprising a homogeneous blend of

A. 5 to 95 parts by volume of gasoline, and correspondingly

B. 95 to 5 parts by volume of a blend comprising a. 10 to 90 parts by volume of a nitroalkane having one or two nitro groups, and containing up to four carbon atoms, and mixtures thereof, and correspondingly b. 90 to 10 parts by volume of a normally liquid ester lubricant having a viscosity at 100 ⁰F of at least 1 cSt . selected from the group consisting of esters of i. linear primary alcohols and linear dicarboxylic acids, ii. branched chain primary alcohols and linear dicarboxylic acids, iii. branched chain monocarboxylic acids and linear dihydric alcohols and/or polyalkylene glycols, iv. linear primary alcohols and branched chain dicarboxylic acids, v. neopentyl polyols and monocarboxylic acids, straight chain or branched, and vi . mixed complex esters of primary alcohols, straight chain or branched, mono- and dicarboxylic acids, straight chain or branched, and polyalkylene glycols, and mixtures thereof, with the proviso that the proportion of ester lubricant in the fuel composition may not exceed 25 percent by volume. Nowhere in US 3,900,297 A does it mention the effect of nitroalkanes on Motor Octane Number (MON) or Research Octane Number (RON) of fuel compositions.

US 5,316,558 A (Gonzalez, Frank) discloses a catalytic clean-combustion-promoter composition which is used with finished gasoline and diesel fuels in compression ignition engines and spark ignition engines to improve fuel efficiency and reduce air polluting emissions. In particular, the catalytic clean-combustion- promoter composition utilizes the chemical additives in ratio by volume as follows:

1) From 1 to 30 per cent by volume of an aromatic amine selected from the group consisting of N-ethylaniline CsH₁₁N, and N, N-diethylaniline CgH₅N (C2H5) 2 •

2) From 1 to 85 per cent by volume of ketone as a solvent selected from the group consisting of 2- heptanone C7H_]_4θ, and 5-methyl-3-heptanone CgH₁^O.

3) From 1 to 85 per cent by volume of an alcohol as a co-solvent selected from the group consisting of diacetone alcohols and methyl amyl alcohols, 2- pentanone-4-methyl-4-hydrox CgH^C^, and 2-pentanol-

4-methyl C5H14O respectively.

4) From 1 to 45 per cent by volume of a catalytic medium to promote chemical reactions, 1-methyl, 2- pyrrolidone C5H9NO.

5) From 1 to 85 per cent by volume of a nitro-compound selected from the group consisting of 1-nitropropane CH3CH2CH2NO2, 2-nitropropane CH₃CH (NO2 ) CH₃, and nitroethane CH₃CH2Nθ2 used as combustion supporters in gasoline or diesel fuels.

6) From 1 to 85 per cent by volume of an ether selected from the group consisting of methyl tert-butyl ether (MTBE) , ethyl tert-butyl ether (ETBE) , and tert- amyl-methyl-ether (TAME) used as an octane supporter in gasoline fuels. Nowhere in US 5,316,558 A does it mention the effect of nitroalkanes on Motor Octane Number (MON) or Research Octane Number (RON) of fuel compositions . DE 103 59 158 Al (Institut Franςais du Petrol) discloses fuel formulations characterized using a base fuel "Jet B", as defined in the standard ASTM D-1655, and incorporating at least one constituent or combination of constituents selected from paraffins, nitro compounds, peroxides, carbonates, acetals, ethers, alcohols, glycol ethers and glycol esters, to produce a distillation curve behavior representative of a fuel adapted to functioning demands of operating in HCCI mode. Although nitroalkanes are mentioned as a components in the fuel formulations, nowhere in DE 103 59 158 Al does it mention the effect of nitroalkanes on Motor Octane Number (MON) or Research Octane Number (RON) of fuel compositions. - A -

The HCCI internal combustion engine is a hybrid of the well known spark ignition (SI, petrol) and compression ignition (CI, diesel) engines. A homogeneous, typically highly dilute, fuel/air mixture is created in the inlet system, as in a SI engine, but during the compression stroke the mixture auto-ignites as in a CI engine. Potentially, gasoline-fuelled HCCI engines can offer the efficiency of a diesel engine but with cleaner operation (e.g. lower emissions of particulates and nitrogen oxides) and lower cyclic variations.

Various working HCCI engines have been described in the literature (see editor's keynote address (page 1) in "A new generation of engine combustion processes for the future?", Ed. P. Duret, Editions Technip, Paris, 2002, ISBN 2-7108-0812-9) . These include the ATAC (Active

Thermo - Atmospheric Combustion) [Onishi, S. et al, SAE Paper # 790501, SAE (Society of Automotive Engineers) 1979]; TS (Toyota - Soken) ; FDCCP (Fluid Dynamically Controlled Combustion Process); AR (Activated Radicals) [Ishibashi, Y. and Asai, M., SAE Paper # 960742, SAE 1996]; PCCI (Pre-mixed Charge Compression Ignition) [Ayoma, T. et al, SAE Paper # 960081, SAE 1996] and CAI (Controlled Auto-Ignition) [Oakley, A. et al, SAE Paper # 2001-01-1030, SAE 2001] engines. PCCI engines are also described in US 2002/0026926 Al (Loye et al. ) (published 7 March 2002) .

HCCI combustion processes are also currently used in certain commercially available 2-stroke engines, but 4- stroke engines exploiting the advantages of the HCCI technology do not yet appear to be feasible over a wide operating range. One of the main problems with gasoline HCCI engines is that the point at which auto-ignition occurs varies with the load conditions of the engine for standard gasoline fuels. Under low load conditions the point at which auto-ignition occurs is generally after TDC (top dead-centre) and under high load conditions the point at which auto-ignition occurs is generally before TDC. It is therefore desirable to control the point at which auto- ignition occurs within a HCCI engine so that under low load conditions the point of auto-ignition is not too far after TDC and under high load conditions it is not too soon before TDC.

Olsson, Jan-Ola et al [SAE Paper # 2001-01-1031, SAE 2001] describe blending of the easily ignited fuel n- heptane with a gasoline base fuel (iso-octane) to promote auto-ignition in a HCCI engine. The n-heptane and iso- octane are metered separately into the engine under an electronic closed loop control system, so that the overall fuel formulation may be tailored in response to load conditions. This strategy may be used to extend the operating regime of a HCCI engine.

It has been reported that sensitive fuels (Sensitivity = RON - MON) , fuels containing aromatics/olefins/oxygenates, become more resistant to autoignition at higher pressures/lower temperatures when compared to primary reference fuels, and that as the temperature increases, the sensitive fuels become more prone to autoignition [Kalghatgi, Gautam T. and Head, R. A., SAE Paper # 2004-01-1969, SAE 2004]. Subsequently, Kalghatgi, Gautam T. [SAE Paper # 2005-01-0239, SAE 2005] reported that for a given RON, a sensitive fuel will be more flexible and allow a greater range of operation in the HCCI engine. It has now surprisingly been found that certain fuel compositions comprising a gasoline base fuel together with a nitroalkane can exhibit improved auto-ignition properties in a HCCI engine, and thus extend the operating regime of a HCCI engine running on it. Summary of the Invention

The present invention provides a method of increasing the sensitivity (RON - MON) of a gasoline composition comprising admixing with a gasoline base fuel from 1 to 20 vol.%, based on total volume of the gasoline composition, of a nitroalkane selected from the group consisting of nitroethane, nitropropane and mixtures thereof.

The present invention further provides a method of preparing a gasoline composition suitable for use in a homogeneous charge compression ignition (HCCI) engine, which comprises admixing with a gasoline composition suitable for use in a spark-ignition engine from 1 to 20 vol.%, based on total volume of the gasoline composition suitable for use in a HCCI engine, of a nitroalkane selected from nitroethane, nitropropane and mixtures thereof .

The present invention yet further provides a method of operating a homogeneous charge compression ignition engine (HCCI) internal combustion engine, which method involves introducing into a combustion chamber of the engine a gasoline composition prepared by the method of the present invention.

The present invention yet further provides the use of a concentration of from 1 to 20 vol.%, based on total gasoline composition, of a nitroalkane selected from the group consisting of nitroethane, nitropropane and mixtures thereof, in a gasoline composition comprising a major proportion of gasoline base fuel (for increasing the sensitivity (RON - MON) of the gasoline composition) for improved operation of a homogeneous charge compression ignition (HCCI) engine over a range of load conditions.

Detailed Description of the Invention

By the term "for use in a HCCI engine" as used herein, it is meant that the fuel composition is suitable for such use, whether or not it is actually intended for such use. The term "HCCI engine" is intended to encompass any engine which is operating or is operable in the homogeneous charge compression ignition (HCCI) mode, whether or not it is also capable of operating in another mode such as spark ignition or compression ignition. In engines capable of operating in more than one such mode, the present invention can extend the operating regime over which HCCI operation is possible and/or feasible (in particular without undue mis-firing) .

The term "sensitivity", as used herein, refers to a measurement of the difference between RON (Research Octane Number) and MON (Motor Octane Number), i.e. sensitivity = RON - MON.

The gasoline base fuel comprises a liquid hydrocarbon fuel and would normally be suitable for use m an internal combustion engine of the spark ignition (petrol) type. Gasolines typically contain mixtures of hydrocarbons boiling m the range from 25 to 230 ⁰C (EN- ISO 3405) , the optimal ranges and distillation curves typically varying according to climate and season of the year. The hydrocarbons in a gasoline fuel may conveniently be derived m known manner from straight-run gasoline, synthetically-produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbons, hydro-cracked petroleum fractions, catalytically reformed hydrocarbons or mixtures of these.

The research octane number (RON) of the gasoline base fuel may suitably be from 80 to 100, preferably from 90 to 100, more preferably from 94 to 100 (EN 25164). Its motor octane number (MON) may suitably be from 80 to 100, preferably from 84 to 100 (EN 25163) .

It may have an olefin content of for instance from 0 to 20 % v/v (ASTM D1319), an oxygen content of for instance from 0 to 5 % w/w (EN 1601), an aromatics content of for instance from 0 to 50 % v/v (ASTM D1319) and in particular a benzene content of at most 1 % v/v.

The base fuel, and suitably also the overall fuel composition, preferably has a low or ultra low sulphur content, for instance at most 1000 ppmw (parts per million by weight) , preferably no more than 500 ppmw, more preferably no more than 100, even more preferably no more than 50 and most preferably no more than even 10 ppmw. It also preferably has a low total lead content, such as at most 0.005 g/1, most preferably being lead free- having no lead compounds added thereto (i.e. unleaded) .

Oxygenates may be incorporated in the gasoline base fuel; these include alcohols (such as methanol, ethanol, iso-propanol, tert-butanol and iso-butanol) and ethers

(preferably ethers containing 5 or more carbon atoms per molecule, eg, methyl tert-butyl ether) .

Oxygenates may in particular be desirable additives in unleaded gasoline fuels, since they are of use as octane boosters. Particularly preferred gasoline base fuels incorporate from 0 to 10 % v/v of at least one oxygenate selected from methanol, ethanol, iso-propanol and iso- butanol . A gasoline base fuel may include one or more additives such as anti-oxidants, corrosion inhibitors, ashless detergents, dehazers, dyes and synthetic or mineral oil carrier fluids. Examples of suitable such additives are described generally in US Patent No. 5,855,629. They can be added directly to the gasoline or can be blended before addition with one or more diluents, to form an additive concentrate. The (active matter) concentration of any additives present in the base fuel is preferably up to 1 % w/w, more preferably in the range from 5 to 1000 ppmw, advantageously from 75 to 300 ppmw, such as from 95 to 150 ppmw.

By the term "increasing the sensitivity of a gasoline composition", it is meant that the sensitivity value of the gasoline composition produced by the method of the present invention is numerically increased relative to the sensitivity value of the gasoline base fuel used in the preparation of the gasoline composition according to the method of the present invention.

The nitroalkane admixed with the gasoline base fuel in the present invention is selected from the group consisting of nitroethane, nitropropane and mixtures thereof. "Nitropropane" may be 1-nitropropane, 2- nitropropane and mixtures thereof. However, due to the potentially carcinogenic properties of 2-nitropropane, the use of 1-nitropropane is preferred over the use of 2- nitropropane . In one embodiment of the present invention, the nitroalkane is independently selected from nitropropane and nitroethane, preferably the nitroalkane is nitroethane . The nitroalkane composition admixed with the gasoline base fuel in the present invention may be present in a concentration in the range of from 1 vol.% to 20 vol.%, based on the total volume of the gasoline composition. The nitroalkane composition admixed with the gasoline base fuel in the present invention may be present in various concentration ranges having a lower limit of from 1 vol.%, preferably from 2 vol.%, and an upper limit of at most 20 vol.%, preferably 15 vol.%, more preferably 10 vol.%, even more preferably 5 vol.%, based on the total volume of the gasoline composition (e.g. 1 - 20 vol.%, 1 - 15 vol.%, 1 - 10 vol.%, 1 - 5 vol.%, 2 - 20 vol.%, 2 - 15 vol.%, 2 - 10 vol.%, and 2 - 5 vol.%). Examples of preferred concentration ranges of the nitroalkanes in the gasoline composition are from 1 vol.% to 10 vol.%, and from 2 vol.% to 5 vol.%.

Preferably, the sensitivity value (RON - MON) of the gasoline composition of the present invention is increased by a value of at least 3, more preferably at least a value of 5, most preferably a value of at least 7, over the sensitivity value of the gasoline base fuel. Preferably, the sensitivity value of the gasoline composition of the present invention is increased by a value in the range of from 3 to 20, more preferably by a value in the range of from 5 to 15, and most preferably by a value in the range of from 7 to 15, over the sensitivity value of the gasoline base fuel. The present invention also provides a method of preparing a gasoline composition suitable for use in a homogeneous charge compression ignition (HCCI) engine, which comprises admixing with a gasoline composition suitable for use in a spark-ignition (SI) engine from 1 to 20 vol.%, based on total volume of the gasoline composition suitable for use in a HCCI engine, of a nitroalkane selected from nitroethane, nitropropane and mixtures thereof. The sensitivity value of the gasoline composition suitable for use in a HCCI engine is numerically increased relative to the sensitivity value of the gasoline composition suitable for use in a SI engine.

Typically, the gasoline composition suitable for use in a SI engine is as described for the gasoline base fuel above .

The nitroalkane and concentration of the nitroalkane used in the method of preparing a gasoline composition suitable for use in a HCCI engine, which comprises admixing with a gasoline composition suitable for use in a SI engine from 1 to 20 vol.%, based on total volume of the gasoline composition suitable for use in a HCCI engine, of a nitroalkane selected from nitroethane, nitropropane and mixtures thereof, is as described above. Preferably, the sensitivity value of the gasoline composition suitable for use in a HCCI engine is increased by a value of at least 3, more preferably at least a value of 5, most preferably a value of at least 7, over the sensitivity value of the gasoline composition suitable for use in a SI engine. Preferably, the sensitivity value of the gasoline composition suitable for use in a HCCI engine is increased by a value in the range of from 3 to 20, more preferably by a value in the range of from 5 to 15, and most preferably by a value in the range of from 7 to 15, over the sensitivity value of the gasoline composition suitable for use in a SI engine.

The present invention further provides a method of operating a homogeneous charge compression ignition engine (HCCI) internal combustion engine, which method involves introducing into a combustion chamber of the engine a gasoline composition prepared by a method as described above. Since sensitive fuels (Sensitivity = RON - MON) become more resistant to autoignition at higher pressures/lower temperatures when compared to primary reference fuels, and as the temperature increases, the sensitive fuels become more prone to autoignition, the use of gasoline compositions as described above in a HCCI engine can provide benefits in terms of controlling the point of auto-ignition.

In particular, the inlet temperature in a HCCI engine could be varied to control the point of auto- ignition under various engine load conditions. For example, under low load conditions where the point at which auto-ignition occurs is generally after top dead centre (TDC) , increasing the inlet charge temperature would make the fuel more prone to auto-ignition. Conversely, under high load conditions where the point at which auto-ignition occurs is generally before TDC, decreasing the inlet charge temperature would make the fuel less prone to auto-ignition.

Therefore, by varying the inlet charge temperature, it is possible to vary the point of auto-ignition of the fuel described above, and thus allowing HCCI engines to be operated over a range of load conditions. The present invention further provides the use of a concentration of from 1 to 20 vol.%, based on total gasoline composition, of a nitroalkane selected from the group consisting of nitroethane, nitropropane and mixtures thereof, in a gasoline composition comprising a major proportion of gasoline base fuel (for increasing the sensitivity (RON - MON) of the gasoline composition) for improved operation of a homogeneous charge compression ignition (HCCI) engine over a range of load conditions . Examples

Details of the gasoline compositions used in the following examples are given in Table 1 below.

TABLE 1 Gasoline compositions

- Not of the invention.

Gasoline A is an unleaded gasoline base fuel (ULG- 95), having a sulphur content (ASTM D 2622-94) of 7 ppmw, saturated hydrocarbon content of 68.33 % v/v, aromatics content of 27.33% v/v and olefins content of 4.17 % v/v (ASTM D6623-01 (procedure C) ) , density at 15 ⁰C (DIN 51757/V4) 0.7284 kg/1, distillation (ISO 3405/88) IBP 38.3 ⁰C, 10% 53 ⁰C, 50% 90 ⁰C, 90% 414.7 ⁰C and FBP 172.7 ⁰C. The gasoline compositions described above were tested using a RICARDO HYDRA (trade mark) single cylinder research engine fitted with a TYPHON (trade mark) 4-valve head with a pent roof and a raised piston crown. Engine dimensions and valve timings are as indicated in Table 2.

TABLE 2 Engine dimensions and valve timings

Fuel was injected into the inlet manifold (targeted at the rear of the closed valves) at top dead centre (TDC) (i.e. 0° CAD). The temperature of the intake air was controlled and measured. The conditions used in the examples are given below in Table 3.

TABLE 3

Temperature conditions employed

Low temperature 353 K, 0. 20 MPa

High temperature 523 K, 0. 10 MPa

A KISTLER (trade mark) 6121 pressure tranducer was used to measure in-cylinder pressure and pressure signals were analysed using an AVL INDIMASTER 671 (trade mark) running INDICOM (trade mark) software 1.2.

Fuel/air mixture strength was monitored using a HORIBA EXSA-1500 (trade mark) analyser. Examples 1 and 2 and Comparative Examples A to D

The in-cylinder pressure was used to calculate the number of crank angle degrees at which the fuel composition had released 50 % of it heat of combustion (CA50). An average CA50 was calculated for different values of λ (normalised air: fuel ratio, λ = 1 for stochimetric air: fuel mixtures) under the high and low temperature conditions defined in Table 3.

For each fuel, the difference between the average CA50 values for the high and low temperature conditions, at various values of λ, are given in Table 4 below.

TABLE 4

Difference between CA50 at high and low temperature conditions

- Comparative Example.

It can be seen from Table 4 that the fuels containing nitroalkanes (Examples 1 and 2) have the largest difference in CA50 for high and low temperature conditions of the fuels tested. The large difference in CA50 for high and low temperature conditions indicates that the point of auto-ignition for the fuels containing nitroalkanes changes significantly with temperature. Therefore, in HCCI engines, the point of ignition can advantageously be controlled for fuels containing nitroalkanes by controlling the inlet temperature. Examples 3 and 4 and Comparative Examples E to H

The sensitivity of the fuels listed in Table 1 was calculated using the following equation:

Sensitivity (S) = RON - MON

The sensitivity of the fuels is given in Table 5 below.

TABLE 5 Fuel sensitivities

* - Comparative Example.

Examples 5 to 10 and Comparative Examples I to L

The sensitivities of a series of gasoline compositions containing 2, 5 and 10 %vol. of nitromethane

(Comparative Examples J to L) , nitroethane (Examples 5 to 7), 1-nitropropane (Examples 8 to 10) and the gasoline base fuel containing 0 %vol. of nitroalkane (Comparative Example I) are given in Table 6 below. The gasoline base fuel to which the nitroalkane was added is an unleaded gasoline composition (ULG-95), having a sulphur content

(ASTM D 2622-94) of at most 50 ppmw, saturated hydrocarbon content of 51.92% v/v, aromatics content of 30.2% v/v and olefins content of 16.19% v/v (ASTM D6623-

01 (procedure C)), density at 15 ⁰C (DIN 51757/V4) 0.7339 kg/1, distillation (ISO 3405/88) IBP 27.5 ⁰C, 10% 40.5 °C, 50% 92.8 °C, 90% 165.6 ⁰C and FBP 209.2 ⁰C. TABLE 6

Sensitivity of gasoline compositions containing a range of nitroalkanes and concentrations

- Comparative Example.

It can be seen from Table 6 that the fuels containing nitroethane and nitropropane (Examples 5 to 10) have significantly increased sensitivity compared to the gasoline base fuel. It can also be clearly seen that, on a volumetric basis, the sensitivity of the base fuel is increased more with nitroethane and nitropropane than with nitromethane, and that, on a volumetric basis, the sensitivity of the base fuel is increased most with nitroethane .

Claims

C L A I M S

1. A method of increasing the sensitivity (RON - MON) of a gasoline composition comprising admixing with a gasoline base fuel from 1 to 20 vol.%, based on total volume of the gasoline composition, of a nitroalkane selected from the group consisting of nitroethane, nitropropane and mixtures thereof.

2. The method of Claim 1, wherein from 1 to 10 vol.%, based on total volume of the gasoline composition, of a nitroalkane selected from nitroethane, nitropropane and mixtures thereof, are admixed with the base gasoline.

3. The method of Claim 1 or 2, wherein from 2 to 5 vol.%, based on total volume of the gasoline composition, of a nitroalkane selected from nitroethane, nitropropane and mixtures thereof, are admixed with the base gasoline.

4. The method according to any one of Claims 1 to 3, wherein the nitroalkane is independently selected from nitroethane and nitropropane.

5. The method according to Claim 4, wherein the nitroalkane is nitroethane.

6. The method according to any one of Claims 1 to 5, wherein the sensitivity value (RON - MON) of the gasoline composition is increased by at least 5 over the sensitivity value of the gasoline base fuel.

7. A method of preparing a gasoline composition suitable for use in a homogeneous charge compression ignition (HCCI) engine, which comprises admixing with a gasoline composition suitable for use in a spark-ignition engine from 1 to 20 vol.%, based on total volume of the gasoline composition suitable for use in a HCCI engine, of a nitroalkane selected from nitroethane, nitropropane and mixtures thereof.

8. A method of operating a homogeneous charge compression ignition engine (HCCI) internal combustion engine, which method involves introducing into a combustion chamber of the engine a gasoline composition prepared by the method of any one of Claims 1 to 7.

9. Use of a concentration of from 1 to 20 vol.%, based on total gasoline composition, of a nitroalkane selected from the group consisting of nitroethane, nitropropane and mixtures thereof, in a gasoline composition comprising a major proportion of gasoline base fuel (for increasing the sensitivity (RON - MON) of the gasoline composition) for improved operation of a homogeneous charge compression ignition (HCCI) engine over a range of load conditions.