METHOD FOR DETERMINING THE PROPENSITY OF AN ENGINE OIL TO CAUSE PRE-IGNITION OF A VEHICLE ENGINE

Abstract

The present invention relates to a method for determining the propensity of an engine oil to generate pre-ignition in an internal combustion engine of a vehicle, in particular a motor vehicle, said engine oil being intended to be introduced into said internal combustion engine of the vehicle, said method comprising: - a step (p1) of aging said engine oil for a predetermined aging time, - after said predetermined aging time, a step (e11) of evaluating an auto-ignition temperature of the engine oil at high pressure, - a step (e12) of comparing said auto-ignition temperature of the engine oil with a predetermined temperature, and if the auto-ignition temperature of the engine oil is lower than the predetermined temperature this oil is judged to have a propensity to generate pre-ignition.

Description

[0001] The invention relates, in general, to the field of pre-ignition of a thermal engine, in particular installed in a motor vehicle.

[0002] The invention relates more specifically to a method for determining the propensity of an engine oil to lead to pre-ignition of a motor vehicle engine during its aging.

[0003] As is well known, a vehicle's internal combustion engine consists of hollow cylinders, called combustion chambers, into which a mixture of air and fuel is injected. This mixture is compressed by a piston sliding within each combustion chamber. The expansion of the mixture generates the thrust of the piston, driving the rotation of a crankshaft, which in turn drives the rotation of the vehicle's wheels. Thus, the internal combustion engine transforms the thermal energy released by the combustion of the mixture into mechanical energy, propelling the vehicle forward.

[0004] In the case of a gasoline engine, a spark plug is mounted in the engine to generate a spark in the combustion chamber in order to trigger the combustion of the air and fuel mixture at a predetermined time to optimize engine operation.

[0005] However, it is a known phenomenon that combustion can sometimes occur before the predetermined time; this is called pre-ignition of the fuel-air mixture in the combustion chamber. Pre-ignition occurs particularly when the engine speed is low; this phenomenon is referred to as low-speed pre-ignition, or LSPI. Low-speed pre-ignition affects engines operating at low engine speeds (low crankshaft revolutions per minute) and under high loads. Engine load is the ratio between the work done by the engine at a given engine speed and the maximum work the engine can do at that speed. For example, a high load is representative of a vehicle traveling uphill or a vehicle towing a trailer or caravan.

[0006] As is known, low-speed pre-ignition occurs, for example, in the presence of high levels of oil vapor or hot spots in the combustion chamber, and can also be caused by the presence of engine oil droplets during the compression phase of the air / fuel mixture preceding the ignition spark. Such pre-ignition can damage the engine by causing a sudden increase in combustion chamber temperature and a loss of driving pleasure for the driver.

[0007] According to current technology, several solutions exist to prevent pre-ignition, such as the use of specific spark plugs, adjusting the air / fuel mixture, or periodically cleaning the combustion chambers. However, these solutions can be complex to implement. State-of-the-art technology also includes solutions for recirculating cooled exhaust gases into the combustion chamber, but these technologies are expensive and also introduce materials into the combustion chamber, increasing the risk of pre-ignition under certain engine operating conditions.

[0008] We are also familiar with the article "engine oil development for preventing pre-ignition in turbocharged gasoline engine", SAE International Journal Of Fuels and Lubricants, vol.7, no.3, April 15, 2014, pp869-874, corresponding to the preamble of claim 1.

[0009] The invention therefore aims to overcome at least some of these drawbacks by proposing a simple, reliable and effective test method, making it possible to reduce the risks of pre-ignition of a vehicle internal combustion engine.

[0010] More specifically, to achieve this objective, the present invention relates to a method for determining the propensity of an engine oil to generate pre-ignition in an internal combustion engine of a vehicle, in particular a motor vehicle, said engine oil being intended to be introduced into said internal combustion engine of the vehicle, said method comprising: a step of aging said engine oil for a predetermined aging time, after said predetermined aging time, a step of evaluating an auto-ignition temperature of the engine oil carried out at high pressure, and a step of comparing said auto-ignition temperature of the engine oil with a predetermined temperature, and if the auto-ignition temperature of the engine oil is lower than the predetermined temperature this oil is judged to have a propensity to generate pre-ignition.

[0011] Such a process makes it advantageous to evaluate the auto-ignition temperature of an engine oil in order to anticipate the risk of pre-ignition of a vehicle engine when using aged engine oil.

[0012] Advantageously, the process includes, after comparing the auto-ignition temperature of the oil with the predetermined temperature, a step of evaluating the distance the vehicle can travel, under predetermined conditions, without the engine oil posing a risk of pre-ignition of the vehicle's engine, based on said auto-ignition temperature. This step of the process makes it possible to determine the engine oil's propensity to pre-ignite the vehicle's engine, with the aim of advantageously eliminating the risk of pre-ignition over a given driving distance.

[0013] Such a process makes it possible to classify engine oils in order to prevent the risk of pre-ignition, allowing for the further development of small turbocharged gasoline engines, which are particularly prone to the problem of pre-ignition at low speeds.

[0014] Advantageously, the engine oil aging step is carried out for a plurality of predetermined aging times, preferably 72h and / or 96h and / or 120h and / or 144h, in order to carry out a plurality of tests allowing a comparison according to the aging of the engine oil.

[0015] Preferably, the process includes a plurality of steps for evaluating an auto-ignition temperature, each auto-ignition temperature being evaluated after a different predetermined aging time, enabling the realization of ranges for an oil exhibiting different auto-ignition temperatures depending on the stage of aging of the oil.

[0016] Advantageously, the method comprises multiple evaluation steps for multiple distances that the vehicle can travel, under predetermined conditions, without the engine oil posing a risk of pre-ignition of the vehicle's engine. Each distance is evaluated for a different predetermined aging time of the engine oil, based on the corresponding auto-ignition temperature. This plurality of distance evaluation steps allows, in particular, for the validation of the method by confirming the results obtained.

[0017] Advantageously, the process includes, prior to the step of evaluating the auto-ignition temperature of the engine oil, a step of measuring an oxidation induction time, allowing the time required for the oxidation of the oil to be determined for a given oil.

[0018] Advantageously, the step of evaluating the auto-ignition temperature of the engine oil is carried out using a differential scanning calorimetry method, allowing the use of a calorimeter whose results are recognized.

[0019] Advantageously, the process includes, prior to the step of evaluating the auto-ignition temperature of the engine oil, a step of increasing the temperature of the engine oil, preferably following a gradual evolution up to a predetermined maximum temperature, allowing the triggering of the oxidation of the oil.

[0020] Preferably, the engine oil auto-ignition temperature evaluation step is carried out at a high pressure of 10.13 bar, enabling a standardized high-pressure test to recreate average conditions similar to the pressure conditions in a combustion chamber, outside of combustion.

[0021] Advantageously, the evaluation of the auto-ignition temperature is carried out using computer software dedicated to the analysis of thermal data, allowing for a reliable measurement.

[0022] Other features and advantages of the invention will become apparent upon reading the detailed description of embodiments of the invention, given by way of example only, and with reference to the drawings which show: there figure 1 a schematic representation of the steps in a process for determining the propensity of an engine oil to cause pre-ignition of a vehicle's engine as it ages, the figure 2 , a graph of the evolution of engine oil temperature controlled by a calorimeter during the process according to a preferred embodiment of the invention, and the figure 3 , a graph, allowing the evaluation of the auto-ignition temperature of an engine oil.

[0023] In what follows, the invention is described in particular, without this being interpreted restrictively, with a view to the evaluation of an oil intended to be introduced into a motor vehicle engine.

[0024] As described previously, a motor vehicle equipped with an internal combustion engine comprises a plurality of combustion chambers, into which a mixture of air and fuel is injected. The combustion of this mixture generates thrust from pistons mounted to slide within the combustion chambers, enabling the rotation of the engine shaft and thus the wheels of the vehicle.

[0025] In a gasoline engine, the combustion of the air / fuel mixture is generally initiated by a spark plug located in each combustion chamber of the engine, which generates a spark. This spark occurs at a precise moment to optimize engine operation.

[0026] However, sometimes the mixture ignites spontaneously before the spark plug generates a spark. This phenomenon, known as engine pre-ignition, occurs particularly when the engine speed is low; this is referred to as low-speed pre-ignition, or LPSI, as described previously. Low-speed pre-ignition is especially common when using oils that are not stable with age.

[0027] Indeed, the engine includes a lubrication system, containing oil, which lubricates various engine components to reduce friction and wear during their movement. The oil circulates, in particular, around the pistons, on the outside of the combustion chamber, to lubricate the piston as it moves within the engine cylinder. However, under certain engine operating conditions, oil can enter the combustion chamber, leading to a risk of pre-ignition at low speeds. This is because, under the influence of heat and oxygen, oil tends to oxidize; this is known as oil aging. Such oil aging results in the formation of deposits and therefore fouling of the combustion chambers, a source of pre-ignition risk.

[0028] The invention described in this document proposes to limit the risk of pre-ignition in a low-speed engine by specifying a pre-ignition criterion for aged oil in a vehicle engine. To this end, a method for determining the propensity of an oil to cause pre-ignition in a motor vehicle engine as it ages will now be presented.

[0029] With reference to the figure 1 According to a preferred embodiment, the process according to the invention comprises a step designated first phase P1 of aging the oil to be tested followed by a step designated second phase P2 of determining the propensity of the oil to lead to a pre-ignition of the engine.

[0030] The first phase P1 of oil aging preferably follows the procedure designated "Aging by oxidation of diesel engine oils in the presence of biofuel", developed by the French Coordination Group for the development of performance tests of Fuels, Lubricants and other fluids in Transport (reference of the test method: GFC Lu-43-A-11 ind2).

[0031] The GFC Lu-43-A-11 ind2 procedure describes aging by catalyzed oxidation, that is, by adding a catalyst solution to an engine oil, in order to generate oxidation of the oil representative of its aging. To enable its implementation, the first phase P1 of the process according to the invention requires a container, designated a test cell, and includes a first step E1 of preparing such a test cell. In this step E1, the test cell is cleaned and disinfected using a solvent such as perchloroethylene or petroleum ether, for example, and then with heptane, in order to remove any residue.

[0032] A test solution, containing the oil to be tested, for example 150 g of oil, is then prepared in step E2. During this same step E2, a catalyst solution is also prepared. Such a catalyst solution comprises, for example, 1.9023 g of anhydrous Fe(III) acetylacetonate introduced into a 100 mL volumetric flask, to which chloroform is added.

[0033] In this example, 5mL of the catalyst solution are then mixed in the test cell with 150g of oil, with the aim of obtaining in step E3 a homogenization of the oil / catalyst mixture.

[0034] The test cell, containing the mixture of the test solution and the catalyst solution, is then placed in a heating bath in step E4. A silicone tube is then put in place to connect the test cell to a flow meter, set for example to a flow rate of 10 liters / hour (plus or minus 0.5 liters / hour), in order to avoid a boiling of the chloroform which could lead to the expulsion of the plug from the test cell.

[0035] In this example, the heating bath is activated in step E5 and set to a temperature of 170°C (plus or minus 1°C). The temperature of the test cell containing the oil sample is then regularly monitored using a thermocouple or a temperature probe, for example. The heating bath is then maintained at 170°C for a period of 144 hours, for example, after which the heating bath is switched off and the oil is sampled in step E6. In this example, three intermediate samples can also be taken after 72 hours, 96 hours, and 120 hours at 170°C.

[0036] The first phase P1 of the process according to the invention is described in this document by way of an exemplary embodiment; however, it is understood that any variant described in the GFC Lu-43-A-11 ind2 procedure can be implemented to obtain at least one sample of aged oil. Similarly, this aging procedure can also be modified by including a pre-dilution of the oil, for example by 8%, or even conditioning for several days at a moderate temperature, for example 30°C.

[0037] Step E6 of the first aging phase P1 thus results in a plurality of aged oil samples, ready for use in the second phase P2 of the process according to the invention. Each HX oil sample is subsequently designated according to its number X of aging hours; thus, an HX oil aged for 144 hours during the first phase P1 will be designated H144, and similarly, an oil aged for 96 hours will be designated H96.

[0038] The second phase P2 of the process according to the invention allows for the evaluation of the auto-ignition temperature of the aged HX oil during the first phase P1. To this end, a method known as differential scanning calorimetry, also called DSC, is adapted and performed at high pressure. High pressure is defined here as a pressure representative of that which can exist in the combustion chamber of an internal combustion engine at the end of the compression stroke, before combustion. This pressure is generally greater than 1 bar and less than 25 bar.

[0039] Differential scanning calorimetry (DSC), commonly used to determine the thermal transitions of a polymer, studies the evolution and changes of state of polymers when heated to high temperatures. In DSC, two test cells are placed in a calorimeter: one containing a sample to be tested and the other empty. As the calorimeter heats up, the sample absorbs heat, requiring additional energy for the cell containing the sample to reach the same temperature as the empty cell. This additional heat is measured by the calorimeter using thermocouples or thermoprobes connected to the cells.

[0040] This process is carried out under so-called inert conditions, meaning that the cells introduced into the calorimeter are purged, for example, with nitrogen. During the temperature increase, a chemical reaction occurs, transforming the nitrogen gas into oxygen. This reaction takes place over a period of time known as the oxidation induction time (OIT), which corresponds to the time required between the gas change and the onset of oxidation. When the oxidation induction time is long, the material is said to have good oxidation stability.

[0041] According to one embodiment of the invention, such a measurement of the oxidation induction time allows for the evaluation of the auto-ignition temperature of an aged oil under test. The auto-ignition temperature is evaluated on a curve, as shown in the figure 3 , by the tangent rule generally applied during differential scanning calorimetry analyses and commonly implemented by the person skilled in the art.

[0042] Thus, in order to study aged HX oil, the process requires a differential scanning calorimetry apparatus and the use of two test cells. The second phase P2 of the process according to the invention therefore includes a step E7 of cleaning the cells using one or more solvent(s), preferably n-Heptane and acetone.

[0043] In this example, two cells are required to carry out the process as described previously. The first cell is kept empty, and the second cell is filled with aged HX oil, for example, 2 milligrams (plus or minus 0.05 mg), in step E8. Both cells are then placed in the calorimeter, which is then sealed. Nitrogen is then introduced to create the inert conditions described earlier. The calorimeter is then configured to control the temperature rise of both cells in step E9. A pressure, for example, 10.13 bar, is also applied to reproduce the pressure conditions inside a combustion chamber of a motor vehicle's internal combustion engine, when combustion is not occurring.

[0044] With reference to the figure 2 The temperature rise inside the calorimeter is gradual. In this example, the calorimeter controls a rapid temperature increase up to an initial plateau of 50°C, at which temperature is maintained for 5 minutes. The temperature then increases gradually to a second plateau, for example, by 40°C per minute up to 120°C. The temperature increase is then controlled more gradually, for example, by 1°C per minute until a temperature of 250°C is reached.

[0045] Such a high temperature allows the change of nitrogen into oxygen, thus enabling the measurement of the oxidation induction time, in a step E10. The oxidation induction time is measured at the onset of oxidation preferably using computer software connected to the calorimeter, for example STARe-Software.

[0046] Once the oxidation induction time of the cell containing the aged oil to be tested has been measured, the software determines the energy produced by the cell to reach the required temperature of 250°C. The software then allows, in step E11, the evaluation of the auto-ignition temperature under pressure of such an oil. figure 3 illustrates a graph plotted by the STARe-Software representing the evolution of the energy produced so that the oil reaches the desired temperature as a function of time and showing the evaluation of the auto-ignition temperature of the oil by the tangent method.

[0047] The auto-ignition temperature of an oil, as a function of its age, determines the oil's propensity to cause engine pre-ignition. If the engine oil's auto-ignition temperature is lower than a predetermined temperature, the oil is considered to have a propensity to generate pre-ignition. In step E12, the oil's auto-ignition temperature is compared to a predetermined temperature, for example, 205°C. This comparison then allows for the evaluation, in step E13, of the distance a vehicle can travel in a temperate climate, using fuel that does not affect oil stability, before the oil presents a risk of engine pre-ignition, based on the corresponding auto-ignition temperature assessed in step E11.

[0048] In this example, an oil can be tested under several aging conditions as described previously. Thus, the procedure described in this document can be repeated for the same oil with multiple samples taken at different stages of aging, for example, after 72, 96, or 120 hours of aging.

[0049] For example, after 144 hours of aging, if the auto-ignition temperature is above 205°C, then H144 oil is considered unlikely to cause pre-ignition at low speeds for 30,000 km in a temperate climate and with a fuel that does not affect its stability. Similarly, after 72 hours of aging, if the auto-ignition temperature is above 205°C, then H72 oil is considered unlikely to cause pre-ignition at low speeds for 10,000 km in a temperate climate and with a fuel that does not affect its stability.

[0050] This method of determining an oil's propensity to cause engine pre-ignition allows for the creation of oil ranges intended for use in engine lubrication systems. These ranges advantageously classify oils according to their propensity to generate pre-ignition based on their auto-ignition temperature.

Claims

1. A method for determining the propensity of an engine oil to generate a pre-ignition of an internal combustion engine of a vehicle, in particular a motor vehicle, said engine oil is intended to be introduced into the said engine combustion internal of u vehicle, said method comprising a step (P1) aging said oil motor for a predetermined aging time, characterized in that it further comprises : - after said predetermined aging time, a step (E11) for evaluating an auto-ignition temperature of the engine oil carried out at high pressure, - a step (E12) comparing said temperature of self-ignition of the engine oil with a predetermined temperature, and if the temperature of self-ignition oil engine is lower than the predetermined temperature the oil is deemed to have a propensity to generate pre-ignition.

2. Method according to the preceding claim, comprising, after step (E12) of comparing the self -ignition temperature of the oil with the predetermined temperature, a step (E13) of evaluating a distance that the vehicle is able to travel, under predetermined conditions, without the engine oil presenting a risk of generating a pre-ignition of the vehicle engine, as a function of said auto-ignition temperature.

3. Method according to one of the preceding claims, in which the step (P1) of aging the engine oil is carried out for a plurality of predetermined aging times.

4. Method according to the preceding claim, comprising a plurality of steps (E11) for evaluating an auto-ignition temperature, each auto-ignition temperature being evaluated after a different predetermined aging time.

5. Method according to the preceding claim, comprising a plurality of steps (E13) for evaluating a plurality of distances that the vehicle is able to cover, under predetermined conditions, without the engine oil presenting a risk to generate a pre-ignition of the engine of the vehicle, each distance being evaluated for a predetermined aging time different from the engine oil, as a function of the corresponding auto-ignition temperature.

6. Method according to one of the preceding claims, comprising, previously in step (E11) of evaluating the auto-ignition temperature of the engine oil, a step (E10) of measuring an induction time to the oxidation of oil.

7. Method according to one of the preceding claims, in which the evaluation of the auto-ignition temperature of the engine oil is carried out by means of a differential scanning calorimetry method.

8. Method according to one of the preceding claims, comprising, previously in step (E11) of evaluating the auto-ignition temperature of the engine oil, a step (E9) of increasing the temperature of the engine oil. engine oil, preferably following a gradual evolution up to a predetermined maximum temperature.

9. Method according to one of the preceding claims, in which the evaluation of the auto-ignition temperature of the engine oil is carried out at a high pressure of 10, 13 bar.

10. Method according to one of the preceding claims, in which the evaluation of the auto-ignition temperature is carried out by means of computer software dedicated to the analysis of thermal data.