阅读说明：本技术 用于减少低速提前点火的方法 (Method for reducing low speed pre-ignition ) 是由 A·加 A·普拉卡什 A·A·阿拉迪 R·F·克拉克内尔 于 2020-03-27 设计创作，主要内容包括：汽油燃料组合物用于减少火花点火式内燃机中低速提前点火(LSPI)发生的用途,其中汽油燃料组合物包含汽油基础燃料并具有1.4或更低PM指数。(Use of a gasoline fuel composition for reducing the occurrence of low speed pre-ignition (LSPI) in a spark-ignited internal combustion engine, wherein the gasoline fuel composition comprises a gasoline base fuel and has a PM index of 1.4 or less.)

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

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

3. Use according to claim 1 or 2, wherein the PM index of the gasoline fuel composition is 1.0 or less.

4. Use according to any one of claims 1 to 3, wherein the PM index of the gasoline fuel composition is 0.8 or lower.

5. The use according to any one of claims 1 to 4, wherein the spark-ignited internal combustion engine is lubricated with a lubricating oil composition containing 500ppmw or more of calcium, based on the total lubricating oil composition.

6. Use according to claim 5, wherein the lubricant composition comprises 1000ppmw or more calcium based on total lubricant composition.

7. Use according to claim 5 or 6, wherein the lubricant composition comprises 1500ppmw or more calcium based on the total amount of lubricant composition.

8. Use according to any one of claims 5 to 7, wherein the lubricant composition comprises 1000ppm or less magnesium based on total lubricant composition.

9. The use of any one of claims 5 to 8, wherein the lubricant composition comprises 1200ppmw or less of a zinc-based antiwear additive, based on the total lubricant composition.

10. Use according to any one of claims 5 to 9, wherein the lubricant composition comprises 1000ppmw or less of a 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-ignited internal combustion engine, said method comprising providing to said engine a gasoline fuel composition comprising a gasoline base fuel and having a PM index of 1.4 or less.

Technical Field

The invention relates to a method for reducing low speed pre-ignition in a spark-ignited 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 a flame front that expands in the combustion chamber in an orderly and controlled manner.

However, in some cases, the fuel/air mixture may ignite prematurely before the spark plug ignites, or after it ignites, the consequent flame front compresses and heats the unburned end gases, resulting in a phenomenon known as pre-ignition. Pre-ignition is undesirable because it typically causes a large 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 lead to "mega-knock", damage to the cylinders, pistons, and valves in the engine, and in some cases may even lead to engine failure.

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

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

It has been found that LSPI is more common in engines that run on motor oils with high calcium content and average commercial gasoline fuels, such as modern small turbocharged spark-ignition engines. Most commercial engine oils currently available on the market have high calcium content, typically ranging from 1200ppm to 3000 ppm. As noted above, in general, this LSPI phenomenon is 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 provide OEMs with 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 levels (<500 ppm). The effect of lower calcium levels in motor oils on reducing the incidence of LSPI is described in SAE 2016-01-2275. Such formulations potentially alter the chemical pathway in eliciting the oil droplets of LSPI. However, most current commercial engine oils have moderate to high calcium levels, and therefore, it is desirable to come up with alternatives to the LSPI problem without having to reformulate the engine 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 composition, particularly in the case of engines that are used to lubricate with engine oils having a high calcium content.

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

The present inventors have now found that by using a gasoline formulation having 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 in LSPI events can be achieved, especially when used in engines lubricated with engine oils having high levels of calcium.

Disclosure of Invention

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

According to the present invention, there is further provided a method of reducing the occurrence of low speed pre-ignition (LSPI) in a spark-ignited internal combustion engine, the method comprising providing to the engine 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. While numerous changes may be made by those skilled in the art, such changes 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, a fuel composition comprising a gasoline base fuel is a gasoline fuel composition. The gasoline fuel compositions herein have the largest 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_iIs the double bond equivalent value of component i, V.P (443K)_iIs the vapor pressure of component i at 443K, Wt_iIs the weight fraction of component i in the gasoline component.

More details on this equation for calculating the PM index can be found in SAE paper SAE-2010-01-2115, which is incorporated herein 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 a preferred embodiment herein, the PM index of the fuel composition is 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 PM index of the fuel composition is between 0.4 and 1.4.

Any suitable method may be used to assess the level of occurrence of pre-ignition in a spark-ignition engine. Such methods may involve operating a spark-ignition engine with 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. A pre-ignition event will result in an increase in engine pressure before ignition or even after ignition, in which case the flame advancing in the cylinder will over compress and heat the unburned exhaust gas 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 early combustion cycle initiation prior to 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 pressure, and/or exhaust temperature. Alternatively or additionally, a suitably experienced driver may try a vehicle driven by a spark ignition engine to assess the effect of a particular fuel and/or lubricant composition on, for example, the degree of engine knock or other aspects of engine performance. Alternatively or additionally, the level of engine damage due to pre-ignition, for example due to associated engine knock, may be monitored over a period of time during which the spark-ignition engine is operating with the relevant fuel and/or lubricant composition.

The reduction in the rate of occurrence of pre-ignition may be a reduction in the number of engine cycles over which pre-ignition events occur, or may be a reduction in the rate at which pre-ignition events occur within the engine and/or a reduction in the severity of the pre-ignition events that occur (e.g., the degree of pressure changes they cause). This may be indicated by one or more of the effects that pre-ignition may have on engine performance, such as a reduction in brake torque or a reduction in engine speed suppression. This may be indicated by a reduction in the amount or severity of engine knock, particularly by a reduction or elimination of "giant knock". Preferably, in the present invention, the reduction in the rate of occurrence of pre-ignition is a reduction in the number of engine cycles in which a pre-ignition event occurs.

Since pre-ignition, particularly if it occurs frequently and leads to "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 use and method of the present invention may be used to achieve any degree of reduction in the incidence of pre-ignition in an engine, including reduction to zero (i.e. elimination of 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 a desired target level of incidence or side effects. The methods and uses herein preferably achieve a 5% or greater reduction in the rate of occurrence of pre-ignition in an engine, more preferably achieve a 10% or greater reduction in the rate of occurrence of pre-ignition in an engine, even more preferably achieve a 15% or greater reduction in the rate of occurrence of pre-ignition in an engine, and particularly achieve a 30% or greater reduction in the rate of occurrence of pre-ignition in an engine. In particularly preferred embodiments, the methods and uses of the present invention achieve a 50% or greater 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 the engine.

An example of a suitable method for measuring low speed pre-ignition events can be found in the following SAE paper: 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 low speed pre-ignition events is the test method described in the examples below.

The gasoline fuel composition herein comprises 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 aviation engines. 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 mixture of hydrocarbons boiling in the range of 25 to 230 ℃ (EN-ISO 3405), the optimum 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 regulatory specifications of the respective regional market. All of these gasoline components may be derived from fossil carbon or renewable resources.

The specific distillation profile, hydrocarbon composition, Research Octane Number (RON), and Motor Octane Number (MON) of the gasoline 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 70 to 110, preferably the MON of the gasoline will be at least 75, for example in the range 75 to 105, more preferably the MON of the gasoline will be at least 80, for example in the range 80 to 100, most preferably the MON of the gasoline will be at least 82, for example in the range 82 to 95(EN 25163).

Typically, the gasoline includes ingredients 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 gasoline is in the range of 0 to 40% by volume based on 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 aromatics content in gasoline is in the range of 0 to 70% by volume based on gasoline (ASTM D1319), for example, the aromatics content in gasoline is in the range of 10 to 60% by volume based on gasoline; preferably, the aromatic content in the gasoline is in the range of 0 to 50% by volume based on the gasoline, for example, the aromatic 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 at most 1000ppmw (parts per million by weight), preferably not more than 500ppmw, more preferably not more than 100, even more preferably not more than 50, and most preferably not more than even 10 ppmw.

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

When the gasoline includes oxygenated hydrocarbons, at least a portion of the non-oxygenated hydrocarbons will be substituted with oxygenated hydrocarbons. The oxygen content of gasoline may be up to 35% by weight based on gasoline (EN 1601) (e.g., ethanol itself (i.e., pure anhydrous ethanol)). For example, the oxygen content of 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 their derivatives, and oxygen-containing heterocyclic compounds. All of the above oxygenates may contain a saturated and/or unsaturated hydrocarbon backbone, as well as aromatic molecules. Preferably, the oxygenated hydrocarbons that can be incorporated into gasoline are selected from the group consisting of alcohols (such as methanol, ethanol, propanol, 2-propanol, butanol, t-butanol, isobutanol, isoprene and 2-butanol), ethers (preferably ethers containing 5 or more carbon atoms per molecule, such as 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 the gasoline, the amount of oxygenated hydrocarbons in the gasoline can 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% by volume of oxygenated hydrocarbons. Also included herein is the E100 fuel 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; and up to 10% by volume. Conveniently, the gasoline may comprise at least 0.5%, 1.0% or 2.0% by volume of oxygenated hydrocarbons.

Examples of suitable gasolines include the following gasolines: 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 at most 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 nos. 09160983.4, 09176879.6, 09180904.6, and U.S. 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, anti-wear additives or surface modifiers, flame speed additives, detergents, dehazers, anti-knock 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 derivatives of PIB-amine, mannich, polyetheramine, succinimide, 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 from 5 to 2000ppmw, advantageously in the range of from 300 to 1500ppmw, such as from 300 to 1000 ppmw.

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

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

In one embodiment of the invention, the lubricating composition comprises from 1200ppmw to 3000ppmw, based on the total lubricating composition. In another embodiment herein, the lubricating oil composition has a calcium content of 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-foam agents, detergents, dispersants, corrosion inhibitors, anti-rust additives, antioxidants, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, and the like.

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

Preferred additives for use in the lubricating oil compositions herein are zinc-based anti-wear 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 from 0 to 1000ppmw, preferably from 0 to 900ppmw, more preferably from 0 to 500ppmw, based on the total lubricant composition.

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

Examples

Three different fuels (fuel a, fuel B and fuel C) were used in this example. The chemical composition and properties of these fuels are shown in table 1 below. All fuels were blended to have the same RON, MON and ethanol content, and fuels B and C were blended to have the same aromatics content. The PM index for each fuel was calculated according to equation (1) above (as disclosed in SAE 2010-01-2115 published on 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, kg/m3	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
				Arene, vol%	9.8	31.1	31.1
Aromatic hydrocarbons, C8 vol%	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
Cycloalkane, vol%	20.3	5.8	5.5
				Olefin, 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 lubricating oil used in this example was a GF-5 certified high calcium lubricating oil of 5W-30 viscosity grade having a calcium content of 2763ppm as determined according to ASTM D5185. The chemical and physical properties of the lubricants are set forth 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 method was performed on fuels A, B and C to measure LSPI events and their frequency.

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 crank angle position (SOC) at the start of combustion is processed by FEV post-processing software using the LSPI detection algorithm (see Haenel et al, SAE int. J. Fuels Lung., Vol. 10, No. 1 (4.2017), entitled "underfluence of Ethanol Blends on Low Speed Pre-Ignition in turbo charged, Direct-Injection Gasoline Engines"; SAE paper 2019-01-0256, entitled "Analysis of the Impact of Production lubricating Composition and Fuel Injection on storage Pre-Ignition in turbo charged, Direct-Injection Gasoline Engines"; US9869262B2 and US10208691B2 for further details). These pressure levels are implicit to the LSPI detection algorithm and they need to be outside of normal combustion pressure conditions.

The variable used for LSPI detection in this method is the crank angle position at the start of combustion (method number: (3) or more).

In summary, the step-by-step method for detecting LSPI is:

-calculating the average combustion period without pre-ignition to determine the pressure trace and the SOC.

Definition of the cycle SOC: the mean pressure is +/-2% higher (denoted Pmax in the figure) before the spark is set to the trigger, taking into account combustion delays.

-calculating LSPI and tap characteristics based on the input of the two factors and continuously saving the pressure trace.

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 engine testing herein, unless other test procedures are explicitly mentioned. The steady state test involves 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 lower load for 2 minutes, with the engine cooling to ambient conditions. 10 repetitions of the cycle shown in FIG. 1 constitute one engine test. The LSPI events are 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 (epm)).

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

Where applicable, the load step method was incorporated into the long steady state test procedure. Fig. 1b and 1c show the load step method as a rapid "screener" in response to various lubricant and calibration changes at very high loads (typically in excess of 21bar BMEP). The test procedure involved running the 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 determine the effect of changes in engine conditions or operating fluids on the LSPI reaction in a relatively short period of time without subjecting the engine to very high loads, where an LSPI event may result in high and potentially damaging in-cylinder pressure values (pspi)_max). The load step routine is used when the goal is to explore the maximum BMEP achieved with the minimum number of LSPI events under specific engine conditions. A few tests were also performed during transient conditions in order to understand the engine's ability to react to rapid fluctuations in speed-load operating strategy (i.e., approaching true driving conditions). These conditions involve a rapid increase in load within a few seconds, followed by coasting, as shown in figure 1 d. 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 flush procedure, consisting of four changes of oil and filter changes, with 30 minutes of engine operation in the middle to cycle flush oil.

LSPI measurement program

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

TABLE 3, LSPI count example for 17 Combustion cycles

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

TABLE 4

Table 5 below sets forth test conditions sensitive to PM/PN formation and LSPI for this engine. The AVL Microboot sensor was used to record PM/PN.

TABLE 5

Table 6 below shows the number of Particles (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	A	B	C
				PM(mg/cm3) -cyclic mean value	1.8	7.7	50
PM Peak (mg/cm)3)[email protected]	1.8	75	75
				PN(mg/cm3) Mean value- @ LSPI	1	15	45
LSPI (ppm event), x101	0.00	23.1	145.6
				PM(mg/cm3) - @ operating conditions 5	5.20	14.70	19.80
PM index	0.49	1.36	2.83

Discussion of the invention

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