EP2145940A1

EP2145940A1 - Use and vehicle

Info

Publication number: EP2145940A1
Application number: EP08252407A
Authority: EP
Inventors: John Stuart Rogerson; Julie Ellen Dawson
Original assignee: BP Oil International Ltd
Current assignee: BP Oil International Ltd
Priority date: 2008-07-15
Filing date: 2008-07-15
Publication date: 2010-01-20

Abstract

The present invention relates to the use of a water-gasoline microemulsion fuel composition to fuel a gasoline direct injection engine, the use of a water-gasoline microemulsion fuel composition to reduce engine deposit formation in a gasoline direct injection engine and to a gasoline direct injection engined vehicle which comprises a water-gasoline microemulsion fuel composition in its fuel tank.

Description

The present invention relates to the use of an emulsion fuel in a gasoline direct injection engine, usually referred to as a GDi engine.
Gasoline direct injection engine technology can provide improved gasoline engine efficiency compared to conventional multi-point fuel injection. In GDi engines ultra-lean burn operation is employed to give lower fuel consumption and CO₂ emissions than conventional multi-point injection engines.
Despite providing improved (lower) fuel consumption, however, GDi engines also suffer from a number of drawbacks when compared to conventional multi-point injection engines. One of these is that GDi engines tend to produce higher levels of nitrogen oxides (usually referred to as NOx). The NOx produced may be reduced by use of after-treatment systems that utilise unburned hydrocarbons to selectively reduce the NOx to nitrogen in the presence of excess molecular oxygen. However, such systems are generally not completely effective and post treatment exhaust NOx emissions can still be a problem.
GDi engines also suffer from fuel injector nozzle deposit formation, which is attributed to pyrolysis of certain species, especially olefins and aromatics, in the fuel and/or lubricating oil. This occurs because the fuel is subjected to much higher injection pressures e.g. 5-20 atmospheres, than in conventional engines and very much higher temperatures at the injection nozzle than in conventional engines because the nozzles are in the combustion zone. These extreme conditions promote thermal cracking of the fuel and deposition of soot on and around the injection nozzle. The presence of the soot tends to produce uneven combustion. The GDi engine manufacturers have tried to overcome the problem by treating the nozzle to resist solids deposition.
Thus, there remains a need for a fuel which avoids or at least mitigates the problems identified above with use of gasoline in a GDi engine.
The addition of water to transport fuels has long been known to improve engine efficiency and reduce emissions. The presence of water is believed to lower combustion temperature and hence inhibit NOx formation. In addition, rapid vaporisation of the water leads to better fuel dispersion in the combustion chamber of the engine leading to reduced soot and particulate formation.
Although water may be injected directly into an engine, use of a homogeneous emulsion containing very finely dispersed water-in-fuel is considered to have advantages over direct water injection to the engine, including reduced fuel flammability, due to higher vaporisation temperature; elimination of the need for a separate water tank; reduced air pollution through lower hydrocarbon vapour losses from the tank; improved atomisation; providing greater and more uniform cooling; and safer transportation and storage, due to low volatility.
This has led to attempts to produce homogeneous water-fuel emulsions for use in engines, especially petrol and diesel engines. For the fuel to prove suitable for use it should exhibit the following qualities: assured storage stability, adequate lubricity, corrosion resistance, engine compatibility, mixture stability over minimum pressure and temperature ranges, and acceptable driveability. Many of these features can be provided by water-fuel microemulsions. A microemulsion is a transparent, thermodynamically stable system wherein the water droplets are nanometres in size. The droplets are too small to scatter light; giving the micro-emulsion a similar appearance to conventional homogeneous hydrocarbon fuel. The extremely low surface tension of the very finely dispersed water droplets makes such microemulsions inherently stable.
Water-gasoline microemulsions are known, and are described, for example, in US 6,068,670 , US 4,599,088 , US 4,465,494 , US 4,158,551 , US 4,046,519 and US 3,876,391 .
In particular, US 6,068,670 relates to water-fuel microemulsions comprising water, at least one hydrocarbon and an emulsifying system comprising at least one sorbitol ester, at least one fatty acid ester and at least one polyalkoxylated alkylphenol. The fuel is said to offer an advantage of two different types of carrier for additives: a lipophilic continuous hydrocarbon phase and a hydrophilic aqueous phase. Among the additives which are said to be useful are those that improve octane, inhibit soot, confer biocidal or bactericidal properties, provide detergency, inhibit NOx formation and/or provide antifreeze properties.
US 3,876,391 relates to a process for preparing water-petroleum microemulsions comprising water, gasoline, at least one gasoline-soluble surfactant, at least one water-soluble surfactant, and a selected water-soluble insufficiently gasoline-soluble additive. The process is said to increase the quantity of water soluble additives that can be incorporated into petroleum fractions.
It has now been found that water-gasoline microemulsions can advantageously be used with GDi engines to provide improved performance compared to use of non-emulsion gasoline fuels.
In particular, in addition to the benefits expected for water-fuel emulsions, it has now been found that use of a water-gasoline microemulsion in a GDi engine leads to reduced fuel injector nozzle deposit formation, and may actually "clean-up" deposits that are already present. Further, it has also been found that the use of a water-gasoline microemulsion fuel composition in a GDi engine leads to reduced piston crown deposit formation.
Thus, in a first embodiment, the present invention provides for use of a water-gasoline microemulsion fuel composition to fuel a gasoline direct injection engine.
The present invention also provides for use of a water-gasoline microemulsion fuel composition to reduce engine deposit formation in a gasoline direct injection engine, especially when compared to the use of the fuel without water. In particular, such use may reduce fuel injector nozzle deposit formation and/or piston crown deposit formation.
The present invention also provides a gasoline direct injection engined vehicle which comprises a water-gasoline microemulsion fuel composition in its fuel tank.
As noted above, the use of a water-gasoline microemulsion fuel composition in a GDi engine has been found to lead to reduced engine deposit formation, especially when compared to the use of the fuel without water.
Although reduction of emissions, including NOx and particulates, are known benefits of water-fuel emulsions in diesel and gasoline engines, these are combustion and post-combustion (exhaust) emissions, and are not related to fuel injector nozzle or piston crown deposits: In particular, the benefit of water on combustion emissions is generally attributed to the cooling effect of water during combustion. In contrast, fuel injector nozzle deposit formation and piston crown deposit formation are generally attributed to pre-combustion pyrolysis of olefins and aromatics present in the fuel composition.
Thus, the reduction in engine deposit formation by use of water-gasoline microemulsions in a GDi engine is surprising.
The use of a water-gasoline microemulsion fuel in a gasoline direct injection engine also reduces the NOx emissions from the GDi engine, which has significant advantages since increased NOx emissions are one of the drawbacks of GDi engines using conventional fuels.
The water-gasoline microemulsion fuels have also been found to have higher octane numbers than the base gasolines, even without the addition of octane improving additives.
The water-gasoline microemulsion fuels preferably comprise 0.5% by weight to 20% by weight water, for example, 2 to 10% by weight water.
The water-gasoline microemulsion fuels preferably comprise 75 to 98% by weight of a gasoline base fuel, for example, 80 to 95% by weight gasoline base fuel.
Suitably, a surfactant is present to facilitate the dispersion of water in gasoline. The water-gasoline microemulsion fuels preferably comprise 2 to 15 % by weight of a surfactant, for example, 5 to 9 % by weight surfactant.
The water-gasoline microemulsion fuels may also comprise other additives typically found in the gasoline fuels. Such additives may be present in the gasoline base fuel before formulation of the water-gasoline microemulsion fuel, or may be added separately to the microemulsion fuel.
Further, the presence of water allows the addition of water soluble additives to the microemulsion fuel which are not soluble in the gasoline alone.
Typical motor gasoline additives are described, for example, in "Gasoline and Diesel Fuel Additives Ed. K Owen, Publ. J Wiley 1989 or as listed in ASTM D-4814, and include antioxidants, corrosion inhibitors, stabilisers, pour point depressants, demulsifiers, antifoams, cetane improvers, lubricity additives, anti-static additives, dehazers, lubricity additives package compatibilisers and dispersant/detergent additives. Such additives may typically each be present in the water-gasoline microemulsion fuel in amounts of 1-1000ppm, for example, 20-200ppm by weight.
The gasoline base fuel may comprise a mixture of liquid saturated hydrocarbons, for example, a distillation product e.g. naphtha or straight run gasoline, or a reaction product from a refinery reaction e.g. an alkylate including aviation alkylate (bp 30-190°C), an isomerate (bp 25-80°C), a light reformate (bp 20-79°C) or a light hydrocrackate.
The gasoline base fuel typically contains at least 60% by weight, for example, 70-90% by weight liquid saturated aliphatic hydrocarbon.
The gasoline base fuel also preferably contains at least one olefin, in particular which is a liquid alkene of 5-10 carbons, for example, pentene, isopentene, hexene, isohexene or heptene or 2 methyl 2 pentene, or a mixture comprising alkenes which may be made by cracking. For example, the mixture may be made by catalytically or thermally cracking a residue from crude oil, e.g. atmospheric or vacuum residue. The mixture may be heavy or light catalytically cracked spirit (or a mixture there of).
The volume amount of olefin(s) in total in the gasoline base fuel is typically 0-30% by weight, for example, 5-30% by weight.
The gasoline base fuel preferably also contains at least one aromatic compound, preferably an alkyl aromatic compound such as toluene or o-, m-, or p-xylene or a mixture thereof or a trimethyl benzene. The aromatics may have been added as single compounds or may be added as an aromatics mixture containing at least 30% by weight aromatic compounds. Such mixtures may be made from catalytically reformed or cracked gasoline obtained from heavy naphtha. Examples of such mixtures are catalytic reformate and heavy reformate.
The volume amount of aromatic(s) in total in the gasoline base fuel is typically 5-40% by weight, for example, 10-35% by weight.
The gasoline base fuel compositions may also contain at least one oxygenate octane booster, usually an ether, usually of Motor Octane Number of at least 96-105 e.g. 98-103. The ether octane booster is usually a dialkyl ether. Examples of such oxygenates include methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether and methyl tertiary amyl ether. The oxygenate may also be an alcohol of 1-6 carbons e.g. ethanol and/or butanol.
The volume amount of the oxygenate in the base fuel composition may be 0-25% by weight, for example, 1-5% by weight.
The gasoline base fuel compositions usually have a Motor Octane Number (MON) value of at least 80 e.g. 80 to 98. The gasoline base fuel compositions usually have a Research Octane Number (RON) of 90-120 e.g. 90-100.
The gasoline base fuel usually has a boiling range (ASTM D86) of 20-225°C.
The water-gasoline microemulsion fuel compositions usually have a Motor Octane Number (MON) value of at least 85 e.g. 85 to 105. The water-gasoline microemulsion fuel compositions usually have a Research Octane Number (RON) of 95-125 e.g. 95-105.
The surfactant is preferably a non-ionic surfactant with a C₈-C₂₀ backbone. Preferred surfactants are selected from one or more non-ionic ethoxylates, especially alkyl phenol ethoxylates, linear alcohol ethoxylates, sorbitan ester ethoxylates and mixtures thereof. Suitable alkyl phenol ethoxylates include nonyl phenol ethoxylates.
The microemulsions employed in the present invention are stable dispersions of water droplets in a continuous gasoline phase. The water droplets of the water-gasoline microemulsion fuels are generally too small to scatter light, and hence the microemulsions usually appear transparent. Typically, the water droplets have a droplet size of the order of nanometres, for example less than 1000nm.
The surfactants in the water-gasoline microemulsion fuels preferably have a hydrophilic : lipophilic balance (HLB) of 8 to 14, preferably 10 to 13.
The hydrophilic : lipophilic balance (HLB) is a classification of the relative simultaneous attraction that a surfactant possesses for water and hydrocarbon, and for non-ionic surfactants, is normally calculated from its ratio of ethoxylated : hydrocarbon molecular weights. Surfactants having a high HLB of above 12, are highly hydrophilic (and predominantly water soluble) whilst substances having a low HLB below 8 are lipophilic and predominantly oil-soluble. Those with HLB values between 8 and 12 have intermediate properties.
Suitably, microemulsions for use in the present invention may be made by blending together water, gasoline and a suitable surfactant.
Alternatively, microemulsions for use in the present invention may be formed as the "middle phase" of a three-phase system.
The phase-behaviour of microemulsions is described, for example, in "Microemulsions in Technical Processes", Chemical Reviews, 1995, Vol. 95, No.4, p.849-864. Within certain, and definable, compositional and temperature ranges, a ternary water, gasoline and surfactant mixture will form three-phases with a surfactant-rich middle phase.
Thus, the water-gasoline microemulsion fuels can be prepared by mixing the required components at ambient temperature and pressure, typically in the percent weight ratio range of 1 - 20 : 75 - 98 : 2 -15 of water : gasoline base fuel : surfactant, respectively. In certain cases, the mixture will separate into three phases, and the middle phase of the three phases, which is the desired water-gasoline microemulsion phase, may be separated, for example by decantation.
The present invention will now be described with reference to the following examples.

Comparative Gasoline Base Fuel

An ultra-low sulphur 2005 specification gasoline was used as a reference fuel. The base fuel comprised 26% by weight aromatics, less than 1% by weight benzene, less than 20ppm sulphur, and had a density of 0.74 g/ml.
The base fuel has a research octane number (RON) of 96.0, and a motor octane number (MON) of 85.6.

Emulsion A

Emulsion A was prepared by mixing the base fuel with 8.8% by weight of a nonyl phenol ethoxylate surfactant and subsequently adding 6.9% by weight of water. The density was 0.78 g/ml.
Emulsion A was found to have a RON of 98.7 and a MON of 92.0.
This octane number benefit was not observed by addition of 8.8% by weight nonyl phenol ethoxylate to the base fuel in the absence of water.

Engine testing

A Mitsubishi Carisma, 1.8L, 4 cylinder, GDi engine was used for the testing.
The vehicle was run on a EURO Stage 2 test cycle, with 40 second idle, and at an ambient temperature of 25°C +/-2°C.
The vehicle was also run under steady-state conditions of lean partial burn mode (air/fuel ratio λ = 1.7) at engine speeds of 90kph and 120kph.
Particulate emissions total hydrocarbons (THC), CO, NOx, CO₂, non-methane hydrocarbons and fuel consumption were all monitored.
The majority of the emissions were unaffected, within statistical ranges. However, some NOx reduction and some fuel consumption increases were observed for Emulsion A under steady-state conditions. In particular, for Emulsion A under steady-state conditions at 90kph the NOx emissions were observed to be reduced by 85%, and under steady-state conditions at 120kph, the fuel consumption was increased by 6.6% compared to the base fuel, consistent with the water content of the emulsion (6.9% by weight water).

Engine deposits

After the engine testing, the engine manifold and spark plugs were removed and engine deposits measured. After operation with Emulsion A it was noted that the piston crown areas and fuel injector nozzles showed significantly less carbonaceous deposit than after operation with the base fuel.

Claims

Use of a water-gasoline microemulsion fuel composition to fuel a gasoline direct injection engine.
Use of a water-gasoline microemulsion fuel composition to reduce engine deposit formation in a gasoline direct injection engine.
Use as claimed in claim 2 wherein fuel injector nozzle deposit formation is reduced.
Use as claimed in claim 2 wherein piston crown deposit formation is reduced.
Use as claimed in any preceding claim wherein the water-gasoline microemulsion comprises 1 to 20 % by weight water.
Use as claimed in any preceding claim wherein the water-gasoline microemulsion comprises 75 to 98 % by weight of a gasoline base fuel.
Use as claimed in any preceding claim wherein the water-gasoline microemulsion comprises one or more additives selected from the group consisting of antioxidants, corrosion inhibitors, stabilisers, pour point depressants, demulsifiers, antifoams, cetane improvers, lubricity additives, anti-static additives, dehazers, lubricity additives package compatibilisers and dispersant/detergent additives.
Use as claimed in any preceding claim wherein the water-gasoline microemulsion comprises 2 to 15 % by weight of a surfactant.
Use as claimed in claim 8 wherein the surfactant is a non-ionic surfactant with a C₈ to C₂₀ backbone.
Use as claimed in claim 8 or claim 9 wherein the surfactant is selected from one or more of non-ionic ethoxylates.
Use as claimed in any of claims 8 to 10 wherein the surfactant has a hydrophilic : lipophilic balance (HLB) of 8 to 14.
A gasoline direct injection engined vehicle which comprises a water-gasoline microemulsion fuel composition in its fuel tank.
A gasoline direct injection engined vehicle as claimed in claim 12 in which the water-gasoline microemulsion fuel composition is a water-gasoline microemulsion as defined in any one of claims 5 to 11.