Dual Fuel Engine System

Abstract

The present invention provides a process for improving the sustainability of a dual fuel engine system operated with a first liquid fuel and a second gaseous fuel, the process comprising providing the engine system with an EN15940 compliant paraffinic gas oil as the first liquid fuel and a gaseous fuel selected from ammonia, methanol, hydrogen and methane based gases as the second gaseous fuel, and combusting the fuels in an internal combustion engine system, wherein exhaust gases from combustion of the fuels are contacted with a methane oxidation catalyst provided in the exhaust system of the internal combustion engine system.

Description

[Technical field]

[0001] The present invention relates to a method for improving the sustainability of a dual fuel engine system. [Background technology]

[0002] Natural gas, which is primarily composed of methane, has a more pronounced CO emission rate than crude oil-based fuels. 2 It has the advantage of being cleaner burning and has higher CO 2 The benefits come from methane from biogas production (biomethane) and methane from power-to-gas (power-to-methane) plants. This renewable methane production is attractive because it can be done with high efficiency compared to other renewable fuel production routes.

[0003] Methane (typically in the form of liquefied natural gas - LNG) has been investigated as a fuel in applications such as heavy trucks, inland waterways and ocean-going vessels, locomotives, rockets, other heavy machinery, distributed island mode power generation, and potentially aircraft. However, the internal combustion engines and fuel systems used in these applications have traditionally been designed primarily for diesel-like fuels.

[0004] Pure methane offers a high mass specific energy content (about 15% higher than gasoline and diesel), but it is not easy to ignite without custom complex fuel injection systems, and therefore pure methane cannot be easily used in today's compression ignition engines used in energy efficient vehicles (such as trucks, ships, locomotives, etc., as mentioned above) because methane autoignition occurs at too high a temperature and the ignition delay time is too long.

[0005] Thus, so-called "dual fuel" engine systems have been developed to allow existing or new heavy duty engines to operate at lower cost and / or lower emissions. Typically, dual fuel engines are operated with a first liquid fuel in combination with a second gaseous fuel. The first liquid fuel is generally a self-ignitable fuel, and combustion ignition of that fuel is used to ignite the second gaseous fuel.

[0006] Many methane-based dual fuel systems have been described in the prior art, including those in WO 2017069120(A1), U.S. Patent Application No. 2016160791(A1), WO 2016052256(A1), U.S. Patent Application No. 2011259290(A1), JP 2007239600(A2) and GB 200601617(A). Although such dual fuel engine systems have the potential to reduce costs and emissions, several problems remain to be overcome.

[0007] Methane itself is a greenhouse gas, and incompletely combusted methane can be emitted from dual fuel engine systems via the exhaust. 2 The higher level of warming potential from methane compared to CO obtained by using methane instead of crude oil-based fuels 2 Methane is also commonly derived from natural gas, a fossil fuel, and the ignitable liquid fuels typically used in dual fuel systems are also typically derived from fossil fuels.

[0008] Therefore, improved dual fuel engine systems with better sustainability are a desirable goal. Summary of the Invention

[0009] The present invention provides a process for improving the sustainability of a dual fuel engine system operated with a first liquid fuel and a second gaseous fuel, the process comprising providing to the engine system an EN15940 compliant paraffinic gas oil as the first liquid fuel and a gaseous fuel selected from ammonia, methanol and a methane based gas as the second gaseous fuel, and combusting the fuels in an internal combustion engine system, wherein exhaust gases from the combustion of the fuels are contacted with a methane oxidation catalyst provided in the exhaust system of the internal combustion engine system. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating a dual fuel system of the type that may be used in the present invention. [Diagram 2] 1 is a graph showing the results of an example. [Diagram 3] 1 is a graph showing the results of an example. [Figure 4] 1 is a graph showing the results of an example. [Diagram 5] 1 is a graph showing the results of an example. [Figure 6] 1 is a graph showing the results of an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An improved process has been determined for operating a dual fuel engine system that runs on a first liquid fuel and a second gaseous fuel. The use of a paraffinic gas oil as the first liquid fuel has been demonstrated to provide improved combustion efficiency (i.e., the extent to which the fuel is completely combusted). The combination of a specific fuel type and the use of a methane oxidation catalyst in the exhaust system of the dual fuel engine system provides an even more effective method of reducing methane emissions.

[0012] The process of the present invention requires a paraffinic gas oil as a first liquid fuel, which is a self-ignitable fuel, the combustion ignition of which is used to ignite a second gaseous fuel.

[0013] The operation of a dual fuel engine is such that the ratio of the two fuels can be changed during operation. In general, it is possible to run the engine entirely on liquid fuel. This is necessary under some circumstances, for example to ensure compliance with emission regulations during cold start. The invention presented herein also provides a means to maximize the amount of gaseous fuel that can be used during the operation of the vehicle while remaining compliant with emission regulations. The use of paraffinic fuel improves the completeness of combustion, thereby reducing the amount of methane that is exhausted from the engine uncombusted. Furthermore, the presence of a methane oxidation catalyst serves to oxidize any methane exhausted from the engine. In contrast to a general oxidation catalyst, the use of a dedicated methane oxidation catalyst recognizes the specific challenges in oxidizing methane.

[0014] The paraffinic gas oil is preferably selected from Fischer-Tropsch derived paraffinic gas oils, renewable paraffinic gas oils, and mixtures thereof.

[0015] Renewable paraffinic gas oils are gas oils obtained from biological sources or biomass through processes such as, but not limited to, hydrotreating, thermal conversion and biomass to liquids (BTL). A preferred renewable paraffinic gas oil is hydrotreated vegetable oil (HVO) derived paraffinic gas oil.

[0016] The HVO process is based on oil refining technology. In this process, hydrogen is used to remove oxygen from triglyceride vegetable oil molecules, splitting the triglycerides into three separate chains to produce paraffinic hydrocarbons. The HVO process is described, for example, in U.S. Patent No. 1,0941,349 and U.S. Patent No. 8,809,610.

[0017] The paraffinic nature of gas oils derived from hydrotreated vegetable oils is very similar to Fischer-Tropsch derived gas oils.

[0018] "Fischer-Tropsch derived" means that the fuel or base oil is or is derived from the synthesis product of a Fischer-Tropsch condensation process. The term "non-Fischer-Tropsch derived" may be interpreted accordingly. Fischer-Tropsch derived products are sometimes referred to as GTL (gas-to-liquids) fuels. However, the term also encompasses such products as biomass-to-liquids and power-to-liquids products.

[0019] The Fischer-Tropsch reaction converts carbon monoxide and hydrogen into longer chain, usually paraffinic, hydrocarbons, i.e. In the presence of a suitable catalyst, typically at elevated temperature (e.g., 125-300° C., preferably 175-250° C.) and / or elevated pressure (e.g., 5-100 bar, preferably 12-50 bar), n(CO+2H 2 )=(-CH 2 -) n +nH 2 O + heat. Hydrogen:carbon monoxide ratios other than 2:1 may be used if desired.

[0020] The carbon monoxide and hydrogen themselves can be derived from either organic or inorganic, natural or synthetic sources, typically natural gas or organically derived methane. More recently, techniques have been investigated and used to derive carbon monoxide and hydrogen from other sources, including more sustainable sources. For example, starting with carbon dioxide and water, the water can be electrolyzed, typically using electricity from a sustainable source, to produce free hydrogen. This hydrogen can be reacted with carbon dioxide in a "reverse water shift reaction" to produce a source of carbon monoxide. This carbon monoxide can then be reacted with the remaining hydrogen in a typical Fischer-Tropsch synthesis process. Due to the use of electrolysis, some of these production processes are referred to as "power-to-liquids".

[0021] The gas oil, kerosene fuel and base oil products can be obtained directly from the Fischer-Tropsch reaction or indirectly, for example, by fractionation of the Fischer-Tropsch synthesis product or from a hydrotreated Fischer-Tropsch synthesis product. Hydrotreating can involve hydrocracking to adjust the boiling range (see, for example, GB 2077289 and EP 0147873) and / or hydroisomerization, which can improve cold flow properties by increasing the proportion of branched paraffins. EP 0583836 describes a two-stage hydrotreating process in which the Fischer-Tropsch synthesis product is first subjected to hydroconversion under conditions such that it does not undergo substantial isomerization or hydrocracking (which hydrogenates olefins and oxygen-containing components), and then at least a portion of the resulting product is hydroconverted under conditions such that hydrocracking and isomerization occur to obtain a substantially paraffinic hydrocarbon fuel or oil. The desired diesel fuel fraction may then be isolated, for example, by distillation.

[0022] Other post-synthetic treatments, such as polymerization, alkylation, distillation, cracking-decarboxylation, isomerization and hydromodification, may be used to modify the properties of the Fischer-Tropsch condensation products, as described, for example, in U.S. Pat. No. 4,125,566(A) and U.S. Pat. No. 4,478,955(A).

[0023] Typical catalysts for the Fischer-Tropsch synthesis of paraffinic hydrocarbons contain as catalytically active component a metal from group VIII of the periodic table, in particular ruthenium, iron, cobalt or nickel. Suitable such catalysts are described, for example, in EP 0 583 836.

[0024] An example of a Fischer-Tropsch based process is the Shell Middle Distillate Synthesis (SMDS), described in van der Burgt et al., "The Shell Middle Distillate Synthesis Process" (see above). This process (sometimes referred to as Shell "Gas-to-Liquid" or "GTL" technology) produces diesel range products by converting natural gas (mainly methane) derived synthesis gas into heavy long-chain hydrocarbon (paraffin) waxes, which can then be hydroconverted and fractionated to produce liquid transportation fuels and other fuels such as gas oil and kerosene. A version of the SMDS process, which utilizes fixed-bed reactors for the catalytic conversion step, is currently used in Pearl GTL at Bintulu, Malaysia, and Ras Laffan, Qatar. Kerosene and (gas) oil prepared by the SMDS process are commercially available, for example, from the Royal Dutch / Shell Group of Companies.

[0025] Due to the Fischer-Tropsch process, Fischer-Tropsch derived gas oil contains essentially no or undetectable levels of sulfur and nitrogen. Compounds containing these heteroatoms tend to act as poisons for the Fischer-Tropsch catalyst and are therefore removed from the synthesis gas feed. Furthermore, normally operated processes produce no or substantially no aromatic compounds.

[0026] Paraffinic gas oils, including Fischer-Tropsch derived paraffinic gas oils and renewable paraffinic gas oils, for use in the present invention must meet the European EN 15940 standard.

[0027] The paraffinic gas oil preferably comprises at least 95 w / w%, more preferably at least 98 w / w%, even more preferably at least 99.5 w / w%, most preferably up to 100 w / w% paraffinic components, preferably isoparaffins and normal paraffins, preferably 80 w / w% or more isoparaffins.

[0028] For example, the aromatics content of a paraffinic gas oil is typically less than 1 w / w%, preferably less than 0.5 w / w%, more preferably less than 0.1 w / w%, for example as measured by ASTM D4629.

[0029] Generally speaking, paraffinic gas oils have relatively low levels of polar components, especially polar surfactants, compared to, for example, petroleum derived fuels. It is believed that this may contribute to improved antifoam and haze elimination performance. Such polar components may include, for example, oxygenates, as well as sulfur and nitrogen containing compounds. Low levels of sulfur in Fischer-Tropsch derived fuels generally indicate low levels of both oxygenates and nitrogen containing compounds, since all are removed by the same treatment process.

[0030] Preferred paraffinic gas oils for use herein are liquid hydrocarbon middle distillate fuels having a distillation range similar to that of petroleum derived diesel, typically in the range of 160°C to 400°C, preferably having a T95 of 360°C or less.

[0031] Preferred paraffinic gas oils for use herein have a viscosity at 15°C of typically from 0.76 to 0.80, preferably from 0.77 to 0.79, more preferably from 0.775 to 0.785 g / cm 3 It has a density (measured according to EN ISO 12185).

[0032] Preferred paraffinic gas oils for use herein have a cetane number (ASTM D613) greater than 70, preferably 70-85, most preferably 70-77.

[0033] The preferred paraffinic gas oil for use herein is 2.0 mm 2 / sec~5.0mm 2 / sec, preferably 2.5mm 2 / sec~4.0mm 2 3 / sec. / s (measured according to ASTM D445).

[0034] Preferred paraffinic gas oils for use herein have a sulphur content (ASTM D2622) of not more than 5 ppmw (parts per million by weight), preferably not more than 2 ppmw.

[0035] As used herein, a paraffinic gas oil preferably contains not more than 3 w / w% cycloparaffins (naphthenes) by weight of the paraffinic gas oil, more preferably not more than 2 w / w%, even more preferably not more than 1 w / w%.

[0036] As used herein, a paraffinic gas oil preferably contains not more than 1 w / w%, more preferably not more than 0.5 w / w% olefins based on the weight of the paraffinic gas oil present.

[0037] In a particularly preferred embodiment of the present invention the paraffinic gas oil comprises, or more preferably consists essentially of, one or more hydrotreated vegetable oil (HVO) derived paraffinic gas oils.

[0038] In the process of the present invention, the second gaseous fuel is selected from ammonia, methanol, hydrogen and methane-based gas. Preferably, the second gaseous fuel is a methane-based gas. As used herein, the term "methane-based gas" refers to a substance that is gaseous at ambient temperature and pressure and contains a majority of methane. As used herein, the term "ambient temperature and pressure" refers to a temperature of 25°C (298.15K) and a pressure of 1.01325 bar. As used herein, the term "majority of methane" refers to a content of methane of preferably more than 70% by volume, more preferably more than 80% by volume, and most preferably more than 90% by volume, based on the total amount of methane-based gas.

[0039] Methane-based gases for use herein are preferably selected from natural gas, renewable methane gases such as biomass-derived methane, synthetic methane from methanation processes, and mixtures thereof. In order to maximize the sustainability of the dual fuel engine system, it is preferred that the methane-based gas is derived from a renewable process.

[0040] Alternatively, the methane-based gas may comprise a mixture of any amount of natural gas and hydrogen where the natural gas is present at a level where a methane oxidation catalyst is required to prevent methane emissions. The total combined percentage of methane and hydrogen in the mixture means a combined methane / hydrogen content of preferably greater than 70% by volume, more preferably greater than 80% by volume, and most preferably greater than 90% by volume, based on the total amount of methane-based gas.

[0041] In the process of the present invention, the methane based gas may be supplied as a compressed gas, such as compressed natural gas (CNG), or a liquefied gas, such as liquefied natural gas (LNG).

[0042] In particularly preferred embodiments of the invention, both the first liquid fuel and the second gaseous fuel are produced from renewable resources. For example, in one embodiment, the first liquid fuel comprises HVO-derived paraffinic gas oil and the second gaseous fuel comprises biomass-derived methane.

[0043] Other additives may be added to either the first liquid fuel or the second gaseous fuel, or both, or combinations thereof, to improve the process of operating the dual fuel engine system. Such additives are well known to those skilled in the art and include, but are not limited to, detergents, corrosion inhibitors, viscosity index improvers, antifoam agents, dispersants, friction modifiers, fragrances, colorants, and the like.

[0044] The fuel combination is combusted in an internal combustion engine system. Such combustion engines may be of the standard type used in road transportation, marine, mining, rail, and aviation applications. Modifications can be made to the engine system to facilitate the use of dual fuels.

[0045] In the present invention, further improvements in the sustainability of dual fuel engine systems are obtained by providing a methane oxidation catalyst in the exhaust system of the internal combustion engine system. Such a catalyst may be any suitable catalyst capable of converting low levels of methane in the exhaust gas into carbon dioxide and hydrogen. Such a catalyst may be made from precious metals and zirconia, for example according to US20190022625 or WO2018041630.

[0046] Typically, the exhaust gas treated by the exhaust system of a dual fuel engine system contains a methane concentration of 10,000 ppm by volume (ppmv) or less, preferably in the range of 25 ppmv to 10,000 ppmv, more preferably 50 to 5000 ppmv, and even more preferably 100 to 3000 ppmv.

[0047] Methane in the exhaust gas is contacted with oxygen in the presence of a methane oxidation catalyst to convert the methane to carbon dioxide and water. Preferably, the methane and oxygen are in an O:O ratio of at least 2:1, more preferably at least 10:1, even more preferably at least 30:1, even more preferably at least 50:1, even more preferably at least 100:1. 2 :CH 4Preferably, the methane and oxygen are contacted with a methane oxidation catalyst in a ratio of 0.5 to 1.0. 2 The methane:CH4 ratio is in the range of 2:1 to 200:1, more preferably 10:1 to 200:1, even more preferably 30:1 to 200:1, even more preferably 50:1 to 200:1, and even more preferably 100:1 to 200:1.

[0048] Preferably, the methane and oxygen are contacted with the methane oxidation catalyst at a temperature in the range of 120 to 650°C, more preferably 250 to 650°C, and even more preferably 300 to 600°C.

[0049] The oxygen used to oxidize the methane may be supplied as part of the exhaust gas and / or from an external source such as air, oxygen-enriched air, pure oxygen, or a mixture of oxygen and one or more other, preferably inert, gases. Optionally, when some or all of the oxygen is supplied from a source other than the exhaust gas, it may be advantageous to preheat the oxygen before contacting it with the methane.

[0050] The combination of features provided by the present invention provides the CO2 reduction potential of using methane instead of crude oil based fuels in a standard internal combustion engine. 2 This allows for the full benefit of

[0051] Detailed Description of the Drawings 1 provides a schematic diagram of a dual fuel engine system operated by the process according to the present invention. This diagram is illustrative and is not intended to be limiting of the present invention in any way.

[0052] Compressed natural gas (1) is fed to a natural gas injector (3) via a pressure regulator (2). Natural gas (4) is then injected into the purified air stream via an air filter (5) to form a natural gas / air mixture (6). The natural gas / air mixture (6) is then fed to a combustion chamber (7) of an engine (8) where it is mixed with a diesel stream (9) from diesel injectors (10). The engine (8) may also be fitted with an angle encoder (11), a combustion analyzer (12), and a dynamometer (13) to track the combustion of the air / diesel / natural gas mixture and the operation of the engine (8). Exhaust gases (14) from the combustion chamber (7) are then sent to an exhaust system (15). The exhaust system (15) contains a methane oxidation catalyst (16) and is typically equipped with an emissions analyzer (17). The exhaust (18) of the system contains very low levels of methane.

[0053] 2 to 6 are described in the following examples.

[0054] The invention will now be further described by reference to the following non-limiting examples. EXAMPLES

[0055] The examples were carried out using various fuel combinations of methane and diesel fuel. Both mineral diesel fuel and EN 15940 compliant paraffinic diesel gas oil were tested. The test engine used was a model 2010 Euro 5 4 cylinder 2.2 liter Ford Puma diesel with common rail direct fuel injection, variable geometry turbocharger and cooled external exhaust gas recirculation (EGR). The main engine specifications are given in Table 1 below. The engine was equipped with gas port fuel injection and associated controls.

[0056] [Table 1]

[0057] The test rig incorporated a DC dynamometer for speed and load control, with standard industry settings for coolant fluid control and primary measurements of torque, fuel consumption, engine performance, and emissions.

[0058] The dual fuel experimental work implemented premixed dual fuel combustion (PDFC) with two pilot injections, the first premixed in a 50 / 50 ratio by volume before the second injection. PDFC tests were performed at 1200 rpm / 5.3 bar BMEP. 99.95% methane by volume was stored in a gas cylinder with a maximum pressure of 200 bar, fed through a gaseous fuel delivery system and injected into the intake manifold inlet. The diesel rail pressure was fixed at 600 bar and the average pressure in the intake manifold was again kept at 1.3 bar. PDFC tests were performed under a natural gas displacement rate (by energy) of 58% (±2). The interval between the start of injection (SOI) of the pilot fuel and the main injection of the second pilot fuel was maintained at -3°A ATDC ("crank angle after top dead center"), and the start of injection (SOI) of the first pilot fuel was varied to 40°, 50°, and 60° A prior. Table 2 shows the properties of the test fuels used in the experiments.

[0059] [Table 2]

[0060] To test the exhaust gases, samples were taken at the post-turbine exhaust port by two sampling probes, one for the gas analyzer and one for the smoke meter. Details of the gas analyzer and smoke measurement equipment are listed in Table 3.

[0061] [Table 3]

[0062] Figures 2-5 show exhaust gas emissions during EN15940 paraffinic diesel-PDFC and diesel PDFC, and Figure 6 shows combustion efficiency during EN15940 paraffinic diesel-PDFC and diesel PDFC tests. The x-axis of each of these figures is labeled Pilot Separation and is measured in °C A. EN15940 paraffinic diesel gas oil and diesel are called pilot fuels. Pilot Separation refers to the difference in °C A between the combustion of the pilot fuel and the combustion of the premixed gas fuel. The y-axes of Figures 2, 3 and 4 show net carbon monoxide (BSCO), net hydrocarbons (BSHC) and net oxides of nitrogen (BSNO), respectively. x ) and are all measured in g / kWh. The y-axis in Figure 5 is labeled Filter Smoke Number (FSN) and the y-axis in Figure 6 is labeled Combustion Efficiency and is measured in %.

[0063] Figures 2-5 show that using EN15940 paraffinic diesel as pilot fuel generally results in lower emissions compared to using diesel. The lower CO and THC emissions for EN15940 paraffinic diesel-PDFC indicate higher combustion efficiency compared to diesel-PDFC due to less unburned CO and hydrocarbons. These figures show that 40°C A pilot separation is the optimal operating condition as it results in the lowest CO, THC, NOx and FSN values ​​for both EN15940 paraffinic diesel and diesel as pilot fuel. Better fuel atomization and attraction of the injected pilot fuel into the premixed gaseous fuel provided more ignition sources for the surrounding gaseous fuel, thus improving flame propagation and resulting in improved emissions and combustion efficiency.

[0064] FIG. 6 shows that using EN15940 paraffinic diesel gas oil as the pilot fuel results in higher combustion efficiency compared to using diesel.

[0065] This increase in combustion efficiency, when combined with a methane oxidation catalyst, results in a significant overall reduction in emissions and increased sustainability for dual fuel engine systems. Further sustainability improvements are obtained if such systems also use bio-derived fuels.

[0066] 1. A process for improving the sustainability of a dual fuel engine system operated with a first liquid fuel and a second gaseous fuel, the process comprising supplying the engine system with a paraffinic gas oil conforming to EN15940 as a first liquid fuel and a gaseous fuel selected from ammonia, methanol and a methane based gas as a second gaseous fuel, combusting the fuels in an internal combustion engine system, and contacting exhaust gases from the combustion of the fuels with a methane oxidation catalyst provided in an exhaust system of the internal combustion engine system.

[0067] 2. The process of claim 1, wherein the EN15940 compliant paraffinic gas oil comprises either a fossil derived Fischer-Tropsch derived paraffinic gas oil, a renewable paraffinic gas oil, or a mixture thereof.

[0068] 3. The process of claim 2, wherein the EN15940 compliant paraffinic gas oil comprises a hydrotreated vegetable oil derived paraffinic gas oil.

[0069] 4. EN15940 Compliant Paraffinic Gas Oil The process of claim 3, wherein the renewable paraffinic gas oil consists essentially of one or more hydrotreated vegetable oil derived paraffinic gas oils.

[0070] 5. The process of any one of claims 1 to 4, wherein the second gaseous fuel is a methane-based gas.

[0071] 6. The process of claim 5, wherein the methane-based gas is supplied by methane from a biogas production or power-to-gas plant.

[0072] 7. The process of any one of claims 1 to 6, wherein the first liquid fuel comprises hydrotreated vegetable oil-derived paraffinic gas oil and the second gaseous fuel comprises biomass-derived methane.

[0073] 8. The process of any one of claims 1 to 7, wherein the methane oxidation catalyst is prepared from a precious metal and zirconia.

[0074] 9. The ratio of methane and oxygen in the exhaust gas is at least 2:1. 22 :CH 4 9. The process of claim 1, wherein the exhaust gas is contacted with a methane oxidation catalyst such that the methane is present in a ratio of 0.1 to 0.5.

[0075] 10. Use of one or more hydrotreated vegetable oil derived paraffinic gas oils complying with EN 15940 as liquid fuel in a dual fuel engine system, wherein methane based gas is used as the gaseous fuel and a methane oxidation catalyst is provided in the exhaust system of the engine system to reduce emissions of methane from the engine system.

Claims

1. 1. A process for improving the sustainability of a dual fuel engine system operating on a first liquid fuel and a second gaseous fuel, the process comprising providing said engine system with an EN 15940 compliant paraffinic gas oil as the first liquid fuel and a methane based gas as the second gaseous fuel, and combusting said fuels in an internal combustion engine system, wherein exhaust gas from combustion of the fuels is contacted with a methane oxidation catalyst provided in an exhaust system of the internal combustion engine system, and a ratio of methane and oxygen present in the exhaust gas is at least 2:1 O ２ :CH ４ wherein the exhaust gas is contacted with the methane oxidation catalyst such that:

2. 2. The process of claim 1, wherein the EN15940 compliant paraffinic gas oil comprises a Fischer-Tropsch derived paraffinic gas oil, a renewable paraffinic gas oil, or a mixture thereof.

3. 3. The process of claim 2, wherein the EN15940 compliant paraffinic gas oil comprises a hydrotreated vegetable oil derived paraffinic gas oil.

4. 4. The process of claim 3, wherein the EN 15940 compliant paraffinic gas oil consists essentially of one or more hydrotreated vegetable oil derived paraffinic gas oils.

5. 5. The process according to any one of claims 1 to 4, wherein the methane-based gas is supplied by methane from a biogas production or power-to-gas plant.

6. 6. The process of any one of claims 1 to 5, wherein the first liquid fuel comprises a hydrotreated vegetable oil derived paraffinic gas oil and the second gaseous fuel comprises biomass derived methane.

7. The process of any one of claims 1 to 6, wherein the methane oxidation catalyst is made from a precious metal and zirconia.

8. 1. Use of one or more EN 15940 compliant paraffinic gas oils derived from hydrotreated vegetable oils as liquid fuel in a dual fuel engine system, wherein a methane based gas is used as the gaseous fuel and a methane oxidation catalyst is provided in an exhaust system of said engine system to reduce said emissions of methane from said engine system.

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