CN113710778B

CN113710778B - Method for reducing low speed pre-ignition

Info

Publication number: CN113710778B
Application number: CN202080026383.3A
Authority: CN
Inventors: A·加; A·普拉卡什; A·A·阿拉迪; R·F·克拉克内尔
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2019-04-01
Filing date: 2020-03-27
Publication date: 2023-05-23
Anticipated expiration: 2040-03-27
Also published as: CN113710778A; EP3947608B1; JP2022526585A; US20220356409A1; EP3947608A1; WO2020201104A1

Abstract

Use of a gasoline fuel composition for reducing the occurrence of low speed pre-ignition (LSPI) in a spark-ignition internal combustion engine, wherein the gasoline fuel composition comprises a gasoline base fuel and has a PM index of 1.4 or less.

Description

Method for reducing low speed pre-ignition

Technical Field

The present invention relates to a method for reducing low speed pre-ignition in a spark ignition internal combustion engine.

Background

Under ideal conditions, normal combustion occurs in a conventional spark-ignition engine when a mixture of fuel and air in a combustion chamber in a cylinder is ignited by the generation of a spark from a spark plug. Such normal combustion is generally characterized by the flame front expanding in an orderly and controlled manner in the combustion chamber.

However, in some cases, the fuel/air mixture may ignite prematurely before the spark plug ignites, or after ignition thereof, with the consequent flame front compressing and heating the unburned terminal gases, resulting in a phenomenon known as pre-ignition. Pre-ignition is undesirable because it typically causes a substantial increase in temperature and pressure within the combustion chamber, which can have a significant negative impact on the overall efficiency and performance of the engine. Pre-ignition may cause "mega-knock," which may damage cylinders, pistons, and valves in the engine, and may even cause engine failure in some cases.

Recently, low speed pre-ignition ("LSPI") has been recognized by many original equipment manufacturers ("OEMs") as a potential problem for high boost small spark ignition engines, particularly high compression ratio direct injection spark ignition engines. LSPI generally occurs at low speeds and high loads, as opposed to the pre-ignition phenomenon observed at high speeds later in the 50 s. LSPI is a constraint that limits torque improvement at low engine speeds, which can affect fuel economy and drivability. The occurrence of LSPI may eventually cause so-called "monster knock" or "mega-knock", where potentially damaging pressure waves may cause serious damage to the piston and/or cylinder. Thus, any technique that can mitigate the risk of pre-ignition, including LSPI, is highly desirable.

There are a number of mechanisms to trigger LSPI events discussed in the literature. One of these mechanisms involves ignition of the flaking deposits that are present in the combustion chamber (e.g., the injector and cooler regions around the piston gap region or behind the spark plug) that initiate the LSPI event, while the other mechanism is based on ignition of oil droplets in the combustion chamber. It may be a combination of these two mechanisms (sediment and oil droplets) that cause LSPI, or it may be a yet to be established mechanism.

LSPI has been found to be more common in engines operating with motor oils having high calcium content and average market value gasoline fuels, such as modern small turbocharged spark ignition engines. Most commercial engine oils currently available on the market have high calcium levels, typically ranging from 1200ppm to 3000ppm. As noted above, this LSPI phenomenon is typically common under high torque, low speed operating conditions. Most Original Equipment Manufacturers (OEMs) calibrate their engine management systems to limit engine operation under these conditions to prevent LSPI from occurring. However, operating under these conditions may potentially give the OEM additional opportunities to reduce fuel consumption.

One solution to the LSPI problem is to formulate the engine oil so that it has a new composition. Examples of such methods can be found in WO2015/171978A1, WO2016/087379A1, WO2015/042341A 1. One such solution is to formulate engine oils with very low calcium content (< 500 ppm). The effect of lower calcium levels in engine oils on reducing LSPI incidence is described in SAE 2016-01-2275. Such a formulation potentially alters the chemical pathway in terms of priming the oil droplets of LSPI. However, most commercially available motor oils currently have a medium to high calcium content, and thus, it is desirable to propose an alternative to the problem of LSPI without having to reformulate the motor oil formulation.

U.S. serial No. 62/573723 relates to a method of reducing low speed pre-ignition by using a gasoline formulation that includes some type of detergent additive package and/or some detergent additive ingredients, particularly in the case of engines for lubrication with engine oils having a high calcium content.

SAE international paper SAE-2010-01-2115 published at 10 and 25 2010 relates to a survey of the relationship between gasoline characteristics and vehicle particulate emissions. In the investigation described therein, various chemical species were mixed with indoline base fuels, respectively, and the solid Particle Number (PN) emissions of each mixture were measured in a New European Driving Cycle (NEDC). Based on the weight fraction of each component in the fuel, the vapor pressure, and the Double Bond Equivalent (DBE) value, a predictive model, referred to as the "PM index", was constructed. It has been demonstrated that the PM index can accurately predict not only the total PN trend, but also the total Particulate Matter (PM) mass, regardless of engine type or test period.

The inventors have now found that by using a gasoline formulation with a certain maximum Particulate Matter (PM) index (as calculated according to the PM index equation set forth in SAE international paper 2010-01-2115), an unexpected reduction of LSPI events can be achieved, especially when used in engines that are lubricated with engine oils having high levels of calcium.

Disclosure of Invention

In accordance with the present invention, there is provided a gasoline fuel composition for reducing the occurrence of low speed pre-ignition (LSPI) in a spark-ignition internal combustion engine, wherein the gasoline fuel composition has a PM index of 1.4 or less.

In accordance with the present invention, there is further provided a method of reducing the occurrence of low speed pre-ignition (LSPI) in a spark-ignition internal combustion engine, the method comprising providing the engine with a gasoline fuel composition having a PM index of 1.4 or less.

The features and advantages of the present invention will be apparent to those skilled in the art. Although many variations may be made by those skilled in the art, such variations are within the spirit of the invention.

Drawings

The drawings illustrate certain aspects of some embodiments of the invention and should not be used to limit or define the invention.

Fig. 1 shows a test procedure for engine testing in the following example.

FIG. 2 is a graph of the results of Table 6 below.

FIG. 3 is a graph of the results of Table 7 below.

Detailed Description

The fuel compositions used herein generally comprise a gasoline base fuel and optionally one or more fuel additives. Thus, the fuel composition comprising the gasoline base fuel is a gasoline fuel composition. The gasoline fuel compositions herein have the greatest PM index.

The PM index of a gasoline fuel composition may be calculated herein using equation (1) below (as disclosed in SAE-2010-01-2115):

in equation (1), each gasoline component in the gasoline composition is assigned a number, or i, DBE _i Is the double bond equivalent value of component i, V.P (443K) _i Is the vapor pressure at 443K of component i, wt _i Is the weight fraction of component i in the gasoline component.

More details on this equation for calculating PM index can be found in SAE paper SAE-2010-01-2115, which is incorporated by reference in its entirety.

The PM index of the gasoline fuel composition used in the present invention is 1.4 or less, preferably 1.3 or less, more preferably 1.2 or less, even more preferably 1.1 or less, particularly 1.0 or less. In preferred embodiments herein, the fuel composition has a PM index of 0.9 or less, preferably 0.8 or less, more preferably 0.7 or less, even more preferably 0.6 or less, especially 0.5 or less.

In one embodiment herein, the fuel composition has a PM index between 0.4 and 1.4.

Any suitable method may be used to evaluate the level of incidence of pre-ignition in a spark-ignition engine. Such methods may involve operating a spark-ignition engine using an associated fuel and/or lubricant composition and monitoring changes in engine pressure, i.e., changes in pressure relative to crank angle, during its combustion cycle. The pre-ignition event will result in an increase in engine pressure before or even after ignition, in which case the advancing flame front within the cylinder over compresses and heats the unburned exhaust gases to the auto-ignition point: this may occur in some engine cycles, but not others. Alternatively, or in addition, the position of the crankshaft angle may also be monitored, for example, at the start of an early combustion cycle before spark, or at the start of combustion (SOC). Alternatively or additionally, changes in engine performance may be monitored, for example, by maximum available brake torque, engine speed, intake air pressure, and/or exhaust gas temperature. Alternatively or additionally, a suitably experienced driver may test driving a vehicle driven by a spark-ignition engine to assess the impact of a particular fuel and/or lubricant composition on, for example, the extent of engine knock or other aspects of engine performance. Alternatively or additionally, the level of engine damage due to pre-ignition, e.g., due to associated engine knock, may be monitored during periods of time when the spark-ignition engine is operating with the associated fuel and/or lubricant composition.

The reduction in the incidence of pre-ignition may be a reduction in the number of engine cycles in which the pre-ignition event occurs, or may be a reduction in the rate at which the pre-ignition event occurs and/or a reduction in the severity of the pre-ignition event that occurs (e.g., the extent of the pressure change they cause) within the engine. This may be indicated by one or more of the effects that pre-ignition may have on engine performance, such as a weakening of the braking torque or a reduction in engine speed. This may be indicated by a reduction in the number or severity of engine knocks, particularly by a reduction or elimination of "giant knocks". Preferably, in the present invention, the reduction in the incidence of pre-ignition is a reduction in the number of engine cycles in which a pre-ignition event occurs.

Since pre-ignition, particularly if pre-ignition occurs frequently and results in "giant knock", can cause significant engine damage, the fuel compositions disclosed herein can also be used for the purpose of reducing engine damage and/or for the purpose of increasing engine life.

The uses and methods of the present invention may be used to achieve any degree of reduction in the incidence of pre-ignition in an engine, including reducing to zero (i.e., eliminating pre-ignition). Which may be used to achieve any degree of reduction in the side effects of pre-ignition, such as engine damage. Which may be used for the purpose of achieving the desired incidence of target levels or side effects. The methods and uses herein preferably achieve a reduction in the incidence of pre-ignition in an engine of 5% or more, more preferably a reduction in the incidence of pre-ignition in an engine of 10% or more, even more preferably a reduction in the incidence of pre-ignition in an engine of 15% or more, and in particular a reduction in the incidence of pre-ignition in an engine of 30% or more. In particularly preferred embodiments, the methods and uses of the present invention achieve a 50% or more reduction in the incidence of pre-ignition in an engine. In another particularly preferred embodiment, the methods and uses herein completely eliminate the occurrence of pre-ignition in an engine.

Examples of suitable methods for measuring low speed pre-ignition events can be found in the following SAE papers: SAE 2014-01-1226, SAE 2011-01-0340, SAE 2011-01-0339 and SAE 2011-01-0342. Another example of a suitable method for measuring a low speed pre-ignition event is the test method described in the examples below.

The gasoline fuel composition herein includes a gasoline base fuel. The gasoline base fuel may be any gasoline base fuel suitable for use in spark ignition (gasoline) type internal combustion engines known in the art, including automotive engines, as well as other types of engines, such as, for example, off-road and aeroengines. The gasoline used as the base fuel in the liquid fuel composition of the present invention may also be conveniently referred to as "base gasoline".

Gasoline typically comprises a hydrocarbon mixture (EN-ISO 3405) boiling in the range 25 to 230 ℃, the optimal range and distillation curve typically varying according to climate and season of the year. The hydrocarbons in the gasoline may be derived by any method known in the art, conveniently the hydrocarbons may be derived in any known manner from straight run gasoline, synthetically produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbons, hydrocracked, hydroisomerized petroleum fractions, catalytically reformed hydrocarbons or mixtures thereof. The sulfur and nitrogen content of the final gasoline should be minimized, for example, by judicious hydrotreating, so that it does not exceed the specifications of the respective local market. All of these gasoline components may come from fossil carbon or renewable resources.

The specific distillation curve of the gasoline, hydrocarbon composition, research Octane Number (RON) and Motor Octane Number (MON) are not critical.

Conveniently, the Research Octane Number (RON) of the gasoline may be at least 80, for example in the range of 80 to 110, preferably the RON of the gasoline will be at least 90, for example in the range of 90 to 110, more preferably the RON of the gasoline will be at least 91, for example in the range of 91 to 105, even more preferably the RON of the gasoline will be at least 92, for example in the range of 92 to 103, even more preferably the RON of the gasoline will be at least 93, for example in the range of 93 to 102, and most preferably the RON of the gasoline will be at least 94, for example in the range of 94 to 100 (EN 25164). The Motor Octane Number (MON) of the gasoline may conveniently be at least 70, for example in the range of 70 to 110, preferably the MON of the gasoline will be at least 75, for example in the range of 75 to 105, more preferably the MON of the gasoline will be at least 80, for example in the range of 80 to 100, most preferably the MON of the gasoline will be at least 82, for example in the range of 82 to 95 (EN 25163).

Typically, gasoline comprises components selected from one or more of the following groups: saturated hydrocarbons, olefins, aromatic hydrocarbons, and oxygenated hydrocarbons. Conveniently, the gasoline may comprise a mixture of saturated hydrocarbons, olefins, aromatic hydrocarbons and optionally oxygenated hydrocarbons.

Typically, the olefin content of the gasoline is in the range of 0 to 40% by volume based on the gasoline (ASTM D1319); preferably, the olefin content of the gasoline is in the range of 0 to 30% by volume based on the gasoline, more preferably, the olefin content of the gasoline is in the range of 0 to 20% by volume based on the gasoline.

Typically, the aromatic content in gasoline is in the range of 0 to 70% by volume based on gasoline (ASTM D1319), e.g., the aromatic content in gasoline is in the range of 10 to 60% by volume based on gasoline; preferably, the aromatic hydrocarbon content in the gasoline is in the range of 0 to 50% by volume based on the gasoline, for example, the aromatic hydrocarbon content in the gasoline is 10 to 50% by volume.

The benzene content of the gasoline is at most 2% by volume based on the gasoline, more preferably at most 1% by volume.

The gasoline preferably has a low or ultra low sulphur content, for example up to 1000ppmw (parts per million by weight), preferably no more than 500ppmw, more preferably no more than 100, even more preferably no more than 50, and most preferably no more than 10ppmw.

The gasoline also preferably has a low total lead content, such as up to 0.005g/l, most preferably is lead-free, to which no lead compound (i.e. lead-free) is added.

When the gasoline includes oxygenated hydrocarbons, at least a portion of the non-oxygenated hydrocarbons will be substituted for oxygenated hydrocarbons. The oxygen content of the gasoline may be up to 35% by weight (EN 1601) based on the gasoline (e.g., ethanol itself (i.e., pure absolute ethanol)). For example, the oxygen content of the gasoline may be up to 25% by weight, preferably up to 10% by weight. Conveniently, the oxygenate concentration will have a minimum concentration selected from any of 0% to 5% by weight, and a maximum concentration selected from any of 30%, 20%, 10% by weight. Preferably, the oxygenate concentration herein is from 5% to 15% by weight.

Examples of oxygenated hydrocarbons that may be incorporated into gasoline include: alcohols, ethers, esters, ketones, aldehydes, carboxylic acids and derivatives thereof, and oxygen-containing heterocyclic compounds. All of the above oxygenates may comprise a saturated and/or unsaturated hydrocarbon backbone, as well as aromatic molecules. Preferably, the oxygenated hydrocarbon that can be incorporated into the gasoline is selected from alcohols (such as methanol, ethanol, propanol, 2-propanol, butanol, t-butanol, isobutanol, isoprene, isopentyl glycol and 2-butanol), ethers (preferably ethers containing 5 or more carbon atoms per molecule, for example methyl t-butyl ether and ethyl t-butyl ether) and esters (preferably esters containing 5 or more carbon atoms per molecule); a particularly preferred oxygenated hydrocarbon is ethanol.

When oxygenated hydrocarbons are present in gasoline, the amount of oxygenated hydrocarbons in the gasoline may vary over a wide range. For example, gasoline including a large proportion of oxygenated hydrocarbons, such as ethanol itself and E85, and gasoline including a small proportion of oxygenated hydrocarbons, such as E10 and E5, are currently commercially available in countries such as brazil and the united states. Thus, gasoline may contain up to 100% oxygenated hydrocarbons by volume. Also included herein are E100 fuels used in brazil. Preferably, depending on the desired gasoline end-formulation, the amount of oxygenated hydrocarbons present in the gasoline is selected from one of the following amounts: up to 85% by volume; up to 70% by volume; up to 65% by volume; up to 30% by volume; up to 20% by volume; up to 15% by volume; up to 10% by volume. Conveniently, the gasoline may comprise at least 0.5%, 1.0% or 2.0% oxygenated hydrocarbons by volume.

Examples of suitable gasoline include the following: it has an olefin content of 0 to 20% by volume (ASTM D1319), an oxygen content of 0 to 5% by weight (EN 1601), an aromatic content of 0 to 50% by volume (ASTM D1319) and a benzene content of up to 1% by volume.

Gasoline blending components that may be derived from biological sources are also suitable for use herein. Examples of such gasoline blending components can be found in WO2009/077606, WO2010/028206, WO2010/000761, european patent application No.09160983.4, 09176879.6, 09180904.6 and us patent application serial No. 61/312307.

Although not critical to the present invention, the base gasoline or gasoline composition of the present invention may also conveniently contain one or more optional fuel additives. The concentration and nature of the optional fuel additives that may be included in the base gasoline or gasoline composition used in the present invention is not critical. Non-limiting examples of suitable types of fuel additives that may be included in the base gasoline or gasoline composition used in the present invention include: anti-oxidants, corrosion inhibitors, antiwear additives or surface modifiers, flame speed additives, detergents, defogging agents, antiknock additives, metal deactivators, valve-seat recession protectant compounds, dyes, solvents, carrier fluids, diluents and markers. Examples of suitable such additives are generally described in U.S. Pat. No. 5,855,629. Suitable detergents/dispersants for reducing engine and fuel delivery system deposits may be selected from the group consisting of PIB-amine derivatives, mannich, polyetheramines, succinimides, and mixtures thereof.

Conveniently, the fuel additive may be blended with one or more solvents to form an additive concentrate, which may then be blended with the base gasoline or gasoline composition of the present invention.

The (active matter) concentration of any optional additives present in the base gasoline or gasoline composition herein is preferably up to 1% by weight, more preferably in the range of 5 to 2000ppmw, advantageously in the range of 300 to 1500ppmw, such as 300 to 1000ppmw.

The fuel composition may be conveniently prepared by blending one or more base fuels with one or more performance additive packages and/or one or more additive ingredients using conventional formulation techniques.

The lubricant compositions for use in the spark-ignition engines described herein generally comprise a base oil and one or more performance additives and should be suitable for use in spark-ignition internal combustion engines. In some embodiments, the lubricant compositions described herein are particularly useful in turbocharged spark ignition engines, more particularly in turbocharged spark ignition engines where: the turbocharged spark ignition engine is operated at an inlet pressure of at least 1bar, or may be operated at an inlet pressure of at least 1bar, or is intended to be operated at an inlet pressure of at least 1 bar.

The high calcium content of engine oils is often found to exacerbate low speed pre-ignition, and thus the present invention finds particular utility in high calcium engine oil environments, but the present invention is useful in any situation where low speed pre-ignition is likely to occur in an engine, regardless of engine oil calcium content. Thus, the calcium content of the lubricant composition used herein may be 0ppmw or higher, preferably 500ppmw or higher, more preferably 1000ppmw or higher, even more preferably 1200ppmw or higher, but more preferably 1500ppmw or higher, in particular 2000ppmw or higher, measured according to ASTM D5185.

In one embodiment of the invention, the lubricating composition comprises 1200ppmw to 3000ppmw, based on the total lubricating composition. In another embodiment herein, the calcium content of the lubricating oil composition is from 1500ppmw to 2800ppmw, preferably from 2000ppmw to 2800ppmw, more preferably from 2500ppmw to 2800ppmw, based on the total lubricating composition, as measured according to ASTM D5185.

Optional lubricating oil additives that may be included in the lubricating compositions herein include antiwear agents, anti-foaming agents, detergents, dispersants, corrosion inhibitors, rust inhibitors, antioxidants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and the like.

The lubricant composition herein preferably has a magnesium content of from 1 to 1000ppmw, preferably from 200 to 800ppmw, based on the total lubricant composition.

Preferred additives for use in the lubricating oil compositions herein are zinc-based antiwear additives such as zinc dithiophosphate compounds. Zinc-based antiwear additives are well known in the art of lubricating compositions. Preferably, the zinc content in the lubricant composition is between 0 and 1200ppmw, preferably between 600 and 1200ppmw, based on the total lubricant composition.

Another preferred lubricating oil additive for use herein is a molybdenum-based friction reducing additive, such as molybdenum dithiocarbamate. Molybdenum-based friction reducing additives are well known in the art of lubricating compositions. Preferably, the molybdenum content in the lubricant composition herein is in the range of 0 to 1000ppmw, preferably in the range of 0 to 900ppmw, more preferably in the range of 0 to 500ppmw, based on the total lubricant composition.

In order to facilitate a better understanding of the present invention, examples of certain aspects of some embodiments are given below. The following examples should in no way be construed as limiting or defining the full scope of the invention.

Examples

Three different fuels (fuel a, fuel B, and fuel C) were used in this example. The chemical compositions and properties of these fuels are shown in table 1 below. All fuels were mixed to have the same RON, MON and ethanol content, and fuels B and C were mixed to have the same aromatic content. The PM index for each fuel is calculated according to equation (1) above (as disclosed by SAE 2010-01-2115 published at 10/25/2010).

TABLE 1

	Fuel A	Fuel B	Fuel C
				T90,℃	123.20	149.50	185.20
FBP,℃	170.20	194.00	208.70
				Density of kg/m ³	730.90	758.40	759.10
RON	97.60	97.70	97.60
				MON	87.10	87.10	87.10
Ethanol, vol%	10.7	10.2	10.2
				Aromatic hydrocarbon, vol%	9.8	31.1	31.1
Aromatic hydrocarbon, C8vol%	8.0	24.1	6.1
				Aromatic, C9/9+vol%	1.2	6.4	24.1
n-Paraffin, vol%	1.1	5.6	8.0
				i-Paraffin, vol%	52.1	41.9	40.0
Naphthene, vol%	20.3	5.8	5.5
				Olefins, vol%	4.9	4.4	4.7
ASVP,kPa	61.10	50.40	73.10
				DVPE,kPa	55.20	44.90	66.80
PM index	0.49	1.36	2.83

The type of lubricant used in this example was GF-5 certified 5W-30 viscosity grade high calcium lubricant having a calcium content of 2763ppm as determined by ASTM D5185. The chemical and physical properties of the lubricants are listed in table 2 below.

TABLE 2

Oil grade	SAE 5W-30
		Viscosity modifier	Comb
Friction modifiers	MoDTC
		Ca,ppm	2763
Mg,ppm	8
		Molybdenum, ppm	88
P,ppm	848
		S,ppm	2369
Zn,ppm	1021
		HTHS 150℃	3.12
Vk100(cSt)	10.39
		Vk40(cSt)	60.11
Viscosity index	163

The following test methods were performed on fuels A, B and C to measure LSPI events and their frequencies.

Test method for measuring LSPI

The test protocol for measuring LSPI events in this embodiment is described below. The engine used was a GEM-T4 engine.

Common variables for LSPI detection are:

(1) Crank angle position at the start of the early combustion cycle before spark, i.e. 2% Mass Fraction Burn (MFB).

(2) Peak pressures during pre-ignition and combustion (up to or exceeding 100 mpa, or greater than the sum of the average peak pressure and 4.7 times the standard peak pressure).

(3) The angular position of the crankshaft (SOC) at the start of combustion is processed by the post-processing software of the FEV using the LSPI detection algorithm (see Haenel et al, SAE int.J. fuels Lubr., volume 10, stage 1 (month 4 of 2017), entitled "Influence of Ethanol Blends on Low Speed Pre-Ignition in Turbocharged, direct-Injection Gasoline Engines"; SAE 2019-01-0256 entitled "Analysis of the Impact of Production Lubricant Composition and Fuel Dilution on Stochastic Pre-Ignition in Turbocharged, direct-Injection Gasoline Engines"; US9869262B2 and US10208691B 2). These pressure levels are implicit to the LSPI detection algorithm and they need to be outside of normal combustion pressure conditions.

The variables used for LSPI detection in this method are the crank angle position at the beginning of combustion (method number (3) above).

In summary, the step-wise method of detecting LSPI is:

-calculating an average combustion cycle without pre-ignition to determine a pressure trajectory and SOC.

Definition of cycle SOC: taking into account the combustion delay, before the spark is set to the trigger, it is +/-2% higher than the average pressure (shown by Pmax).

-calculating LSPI and tap characteristics from the inputs of the two factors and continuously preserving pressure traces.

These experiments used a multiple engine dynamometer. The steady state (i.e., constant speed and constant load) test procedure in fig. 1a is used for the engine test herein unless other test procedures are explicitly mentioned. Steady state testing involved running the engine 160,000 times over a period of 4 hours and 30 minutes and after each 4000 engine cycles, coasting at the same speed but with a lower load for 2 minutes to cool the engine to ambient conditions. 10 repetitions of the cycle shown in fig. 1 constitute one engine test. LSPI events were initially counted for 160,000 cycles, then scaled to one million cycles, and finally reported in parts per million (ppm) units (or events per million (ep)).

Transient tests are incorporated into the test program to reflect real life driving conditions.

Where applicable, the load ladder method was incorporated into a long steady state test procedure. Figures 1b and 1c show a load ladder method as a fast "screener" for the response to various lubricants and calibration changes at very high loads (typically exceeding 21bar BMEP). The test procedure involves running a steady state LSPI test at each load point for half the number of engine cycles (i.e., 80,000) and then shifting to higher loads. This process helps to determine the effect of changes in engine conditions or operating fluid on the LSPI response in a relatively short period of time without subjecting the engine to pressure at very high loads, where LSPI events may result in high and potentially damaging in-cylinder pressure values (P _max ). Load step procedures are used when the goal is to explore the maximum BMEP at a minimum LSPI event amount under specific engine conditions. A few tests have also been performed under transient conditions in order to understand the ability of the engine to react to rapid fluctuations in the speed-load operating strategy (i.e. approaching real driving conditions). As shown in fig. 1d, these conditions involve a rapid increase in load within a few seconds, followed by a coasting. These cycles were repeated for about 5-10 seconds for a total of 50,000 cycles.

An important aspect of the test method is also the oil flushing procedure, consisting of four oil changes and filter changes, with 30 minutes of engine operation in between to circulate the flushing oil.

LSPI measurement program

An LSPI event is typically followed by a large "aftershock" (or subsequent) event, which may be either a pre-ignition event caused by a hot spot or a knock event. However, these aftershock events cannot generally be considered independent LSPI events because they are generated due to pressure wave reflections in the cylinder caused by the initial pre-ignition event. To distinguish these events from the LSPI period, the aftershock event is defined as the pre-ignition event three periods after the leading pre-ignition event. If the follow-up event occurs within three cycles, the window for the second follow-up event is again three cycles after the first follow-up event, and so on. Thus, independent events need to be separated by at least four cycles. Table 3 illustrates how each LSPI event is reported in this experiment.

TABLE 3 LSPI count examples for 17 Combustion cycles

The engine specifications used in this example are set forth in table 4 below.

TABLE 4 Table 4

Table 5 below sets forth the test conditions sensitive to PM/PN formation and LSPI for this engine. PM/PN was recorded using an AVL Microsoft sensor.

TABLE 5

Table 6 below shows the particle count (PN), number of LSPI events, and PM index (determined according to SAE paper SAE-2010-01-2115) for each of fuels A-C. FIG. 2 is a graph of the results in Table 6.

TABLE 6

Table 7 below sets forth the number of LSPI events per test for fuels A, B and C, as well as the PM (as defined by SAE-2010-01-2115) and PM index for each of fuels A-C. FIG. 3 is a graphical plot of the results shown in Table 7 below.

TABLE 7

Fuel and its production process	A	B	C
				PM(mg/cm ³ ) -cycle average	1.8	7.7	50
PM peak (mg/cm) ³ )-@LSPI	1.8	75	75
				PN(mg/cm ³ ) Average value- @ LSPI	1	15	45
LSPI(ppm event), x10 ¹	0.00	23.1	145.6
				PM(mg/cm ³ ) - @ operating condition 5	5.20	14.70	19.80
PM index	0.49	1.36	2.83

Discussion of

The results in tables 6 and 7 and in fig. 2 and 3 show that the fuel with the highest PM index (fuel C) also has the highest LSPI event number. In addition, the fuel with the lowest PM index (Fuel A) has the lowest number of LSPI events. Fuel C (PM index 2.83) exhibited significantly higher LSPI event levels compared to PM indices of fuel B and fuel a of 1.36 and 0.49, respectively.

Claims

1. Use of a gasoline fuel composition for reducing the occurrence of low speed pre-ignition, LSPI, in a spark-ignition internal combustion engine, wherein the gasoline fuel composition comprises a gasoline base fuel and has a particulate matter PM index of 1.4 or less, wherein the particulate matter PM index is calculated using the following equation (1):

in equation (1), DBE _i Is the double bond equivalent value of component i, V.P (443K) _i Is the steaming of component i at 443KThe pressure of the steam is high, and the pressure of the steam is high,

Wt _i is the weight fraction of component i in the gasoline component.

2. Use according to claim 1, wherein the spark-ignition internal combustion engine is a direct injection spark-ignition internal combustion engine.

3. The use according to claim 1 or 2, wherein the gasoline fuel composition has a particulate PM index of 1.0 or less.

4. The use according to claim 1 or 2, wherein the gasoline fuel composition has a particulate PM index of 0.8 or less.

5. Use according to claim 1 or 2, wherein the spark-ignition internal combustion engine is lubricated with a lubricant composition containing 500ppmw or more of calcium, based on the total amount of lubricant composition.

6. The use of claim 5, wherein the lubricant composition comprises 1000ppmw or more calcium, based on the total lubricant composition.

7. The use of claim 5, wherein the lubricant composition comprises 1500ppmw or more calcium, based on the total lubricant composition.

8. The use according to claim 5, wherein the lubricant composition comprises 1000ppm or less magnesium based on the total amount of lubricant composition.

9. The use of claim 5, wherein the lubricant composition comprises 1200ppmw or less zinc-based antiwear additive, based on the total amount of lubricant composition.

10. The use of claim 5, wherein the lubricant composition comprises 1000ppmw or less molybdenum-based friction reducer, based on the total lubricant composition.

11. A method of reducing the occurrence of low speed pre-ignition in a spark-ignition internal combustion engine, the method comprising providing to the internal combustion engine a gasoline fuel composition comprising a gasoline base fuel and having a particulate matter PM index of 1.4 or less, wherein the particulate matter PM index is calculated using the following equation (1):

in equation (1), DBE _i Is the double bond equivalent value of component i, V.P (443K) _i Is the vapor pressure at 443K of component i, wt _i Is the weight fraction of component i in the gasoline component.