A liquid fuel

Abstract

The invention relates to utilising methane as a main part of a liquid fuel for compression ignition engines with part ignition enhancers. These ignition enhancers were dimethyl ether (DME) and hydroge

Description

Technical Field The present invention relates to the replacement of carbon heavy fuel in compression ignition engines with a zero-emission alternative - methane (CH4). Methane generates significantly less pollutants and has a smaller carbon footprint, while maintaining the cycle efficiency within compression ignition engines. Disclosure is provided of methane blended fuel for use in compression ignition engine for zero carbon combustion. The methane blended fuel may, for example, comprise biogenic methane. Background Following the Paris Agreement, the world has committed to move towards a low-carbon economy. Many countries are now implementing policies to facilitate transition to cleaner economies. The European Commission have developed the Green Deal, to deliver a package of policy initiatives, which aims to achieve the ultimate goal of reaching climate neutrality by 2050. Equally the USA, India and majority of all other world powers are working towards climate neutrality by 2050. China being the exception as they are looking to 2060. In relation to transport, the Green Deal sets an ambitious target: by 2050, transport emissions will have to be reduced by 90 percent, compared to 1990. In addition, the recent COP28 which was the 28th Conference of Parties to the UN Framework Convention on Climate Change had extensive deliberations and action points on transport emissions. These action points include the various commitments made by various transportation stakeholders. Currently, transport represents almost a quarter of Europe’s greenhouse gas emissions and is the main cause of air pollution in cities. CO2 emissions from transport have been consistently increasing over the past years, in stark contrast with the trend in other sectors such as electricity generation. This is critical as the transport sector is responsible for almost a quarter of global energy related CO2 emission (not just Europe) in 2021. The decarbonisation of transport would present a lot of essential challenges such as the high upfront costs that alternatives like clean transportation technologies and electric vehicles presents. Also, the extreme dependence on fossil fuels and the transportation sectors of maritime, aviation and long-distance trucking seeming aversion to adapting new technologies in attaining appreciable emission reductions. Although these transportation sectors had made commitments in the just concluded COP28 of a revised target of 70 to 80% emissions reductions by 2040 while cargo owners also committed to utilising only zero-emission freight services by 2040 the plan towards actualisation of these commitments is more important and seems to lack distinct clarity of the inherent requirements and steps of such plan. The United States Energy Information Administration (US EI A) estimates that about 29% of the total U.S energy consumption was used by the transportation industry (EIA, 2017). While for the UK it is estimated that the transportation industry consumption is slightly above 33% of the total UK energy consumption for 2021 as stated by Energy Consumption UK (2024). The demand for petroleum-based fuels for transportation continues to escalate with increases in both movements of people and goods. Gasoline and diesel account for 76% of the total energy consumed by the transportation industry. But also, other pollutant emissions from transport need to be drastically reduced without delay. Emissions of air pollutants such as nitrogen dioxide, NOX and particulate matter, are the most significant causes of premature deaths in the EU, with estimates of more than 400,000 premature deaths each year, including 76,000 directly linked to nitrogen dioxide (NO2). Inventions that attempt to reduce these air pollutants for petroleum-based fuels for transportation are exemplified by WO2007140261 A3, AU2008320578B2 and AU2008200024A1. Wherein WO2007140261 A3 presents an integrated capture of fossil fuel gas pollutants including CO2 with energy recovery while AU2008320578B2 provides an exhaust system for a dual fuel engine and AU2008200024A1 avail methods and systems for reducing NOX emissions in industrial combustion systems. Changing the fuel base to low-and zero-emission alternative fuels is a major element of reaching the 2050 goal. Biofuels play a particularly important role in decarbonising transport by providing a low-carbon solution for existing technologies, such as light-duty vehicles in the near term and heavy-duty trucks, ships and aircraft with few alternative and cost-effective solutions in the long-term. Ethanol is a renewable fuel that can be produced from various feedstocks, such as sugar cane, corn, wheat, and cellulosic biomass. Its use as an alternative fuel has been growing steadily in recent years. Majority of ethanol is blended with gasoline to create a fuel known as ethanol-blended gasoline, which can be used in conventional gasoline engines without any modifications. It has also been blended with diesel for use in compression ignition engines as opposed to spark ignition engines. Further work has been undertaken to develop compression ignition engine that does not use diesel at all but ethanol makes up 95% of the fuel. Inventions that illustrate this particular work or similar are exemplified by GB202400880D0, EP2604833A3, GB202214048D0, CN101037970A and EP2407654A2. Wherein GB202400880D0 provides method of operating an internal combustion engine powered with gaseous fuel, while EP2604833A3 presents a system and method for controlling a variable ignition diesel gasoline dual fuel powered combustion engine, then GB202214048D0 offers a method for controlling operation of an internal combustion engine which runs on a fuel mixture of hydrogen and natural gas. Moreover, CN101037970A proposes a method for controlling the combustion phase of an internal combustion engine, in particular of a supercharged, direct injection gasoline engine. Furthermore, EP2407654A2 suggests a method for controlling the combustion of a fuel-air mixture for a turbocharged internal combustion engine with controlled ignition, in particular a petrol engine. These preponderance of patents highlights the pull exerted by inventor and researchers to assist in the decarbonisation drive through low-and zero-emission alternative fuels amongst others. Brazil was the world's first nation to run a large-scale program for using ethanol as fuel. Eventually, the United States also developed large-scale production of ethanol which has predominantly mixed with gasoline. Other countries, such as Canada, China, and various European nations, are also moving in this direction though at present it is at small scale. However, the global use of ethanol for decarbonising transport faces some challenges. One significant issue is the availability of feedstocks for ethanol production. The use of food crops, such as corn and sugarcane, can raise concerns about food security and land use competition. To address these concerns, many countries are exploring the use of waste biomass e.g., food waste, farm slurries, crop residues etc. This is exemplified by Rietzler Johann patent application WO2010003397A2 that sort to provide a method of producing methane from process water and biogenic material. Other similar patent applications are CN106995236A and DE102014101838A1. Although the other predominant challenge to utilising ethanol for decarbonization is government policy which cannot be tackled by patents nor innovations but patents such as WO2010003397A2, CN106995236A and DE102014101838A1 could help provide the infrastructure that would nudge government towards considering policy reviews. Anaerobic digestion is a process whereby biogenic material is broken down using a bacterial culture to produce biogas (50% methane). This can then be easily upgraded to 98% methane for direct injection into the gas grid or used in other ways for example in the transport system. Methane production technology is low-risk and has been used in the waster sector for over 100 years. Furthermore, almost every community in the developed world has a local waste water treatment plant that breaks down organic matter as part of the water cleaning process to produce methane, in other words there is an existing infrastructure of methane production sites across many parts of the world. It is estimated that there are 150,000 largescale plants worldwide as well as some 50 million small-scale digesters. Currently most of methane is still used directly to produce electricity or heat but there is a growing trend to upgrade the gas to by taking out the CO2 and other components and producing a 98% purified methane can then be used for transport or injected into the gas grid. The USA and Europe are the major markets for methane in transport, and there is growing interest and activity in other areas, notably in China and India. Thus, marketable means of getting methane for transports can be highlighted by inventions such as WO2024036187A1, US20230381841A1, AU2023219849A1 and JP2024001259A. Wherein WO2024036187A1 affirms carbon sequestration in soils with production of chemical products, also, US20230381841A1 presents systems and methods for processing mixed solid waste, while AU2023219849A1 provides method and system for synthesising fuel from dilute carbon dioxide source and JP2024001259A gives compositions and methods for reducing atmospheric methane and nitrogen oxide emissions. In terms of methane’s use in combustion engines, it shows an immediate advantage over other hydrocarbon fuels because of the lower C / H ratio, which produces reduced CO2 (carbon dioxide) emissions. Methane has no carbon-carbon bonds and the lowest carbon-to-hydrogen ratio among abundantly available hydrocarbons. These chemical properties make methane a clean and promising fuel for internal combustion engines. Methane-enriched fuel-powered vehicles have lower life cycles of greenhouse gas emissions compared to those of traditional diesel fuels. Methane, is also economical, at 45% relative to diesel, 65% relative to petrol, and 30% relative to LPG; CO2 emission is reduced by 25% compared to petrol-powered vehicles; methane does not emit large-sized particulate matter, benzene, and aromatic hydrocarbon; the emissions of CO, NOX, and SO2 are reduced compared to those of traditional fuel. At present, methane is mainly used as fuel in homogeneous charge spark ignition (SI) engines because of its high auto-ignition temperature. Although presently, patents such as US7669578B2 which highlights ‘method of operating an internal combustion engine’ and CN1075879308 which highlights ‘method for starting an internal combustion engine’ are working to address this stated challenge. However, the low density and slow flame propagation speed of the methane fuel results in low volumetric efficiency and the problem of a limited engine size. This highlighted challenge of a limited engine size has had resolution attempts been made through patents such as CN116804398A, KR20220009355A and US6386152BI, with these patents, all suggesting ‘internal combustion engine’. Furthermore, to overcome the high autoignition temperature of methane, a dual-fuel direct-injection engine was developed. This was exemplified in patents such as US20060219213A1 that proposes an ‘opposed piston, homogeneous charge pilot ignition engine’ and US9482168B2 that offers a ‘midcycle fuel injection strategies.’ The advantages being reduced pollutant emissions and high thermal efficiency could be attained. However, these methods require expensive fuel injection system for both fuels and did not take full advantage of the high efficiency and low emission potential of methane when it is used as the major constituent of fuel to power a CI engine. Methane single-fueled compression ignition engines have not gained acceptance for the following reasons: 1) the higher compression ratio; 2) the need for significant modifications to the ignition system and cylinder designs; 3) the higher auto-ignition temperature and the lower reactivity of methane 4) the higher specific heat capacity; and 5) the slower burning rate. Methane dual-fuel engines have the potential to solve these problems by supplementing methane with other fuels that can compensate for the poor combustion properties of methane. This was evidenced in the patent RU2682465C1 which highlights ‘multi-fuel system for preparation of fuel gas for feeding gas internal combustion engine’. Moreover, methane as a biofuel with its known efficient combustion process is an essential component to the solution for achieving sustainability while mitigating climate change as earlier stated. This is because carbon heavy fuels use can critically impact climate change, cause heat in the atmosphere from trapped CO2 which could result to growing global temperatures, ruffled weather patterns, increasing sea levels amongst others. Furthermore, the extraction and processing of these carbon heavy fuels can result to spills causing water and air pollution. The compression ignition engines have the critical attributes of being fuel efficient, high compression ratio, lower fuel volatility, higher torque output, durability, lower flammability and multiMuel capability while having the constraints of emissions (example higher emission of NOX and particular matter), cold starts and noise. These critical attributes and constraints have evolved as areas of research leading to advancements and inventions. Consequently, there are inventions and patents in the area of high compression ratio for compression ignition engines such as patent US7370626B2 that highlights ‘High compression spark ignition engine with throttle control, externally supplied ignition, and direct fuel injection into a precombustion chamber’, while patent US5603298A highlights ‘High compression ratio internal combustion engine’ also patent US4444166A which highlights ‘Method and apparatus for reducing the operating compression ratios of compression ignition engines’. Subsequently, some essential patents and inventions in the area higher torque output for compression ignition engines such as patent US9133758B2 which highlights ‘Split-cycle airhybrid engine with air expander and firing mode’, whereas patents US7556014B2, CA2693521C which highlights ‘Split-cycle engine with early crossover compression valve opening’ for the later while ‘reciprocating machines’ for the former. While patent US10428863B2 highlight ‘Variable compression ratio engine’ which attempted to address the areas of higher torque output and high compression ratio concurrently. The patent US10428863B2 approach to addressing these areas was visible and both areas were predominant as none was addressed minimally to the other. Then, some essential patents and inventions that attempted to extend durability for compression ignition engines such as patent WO2005084344A3 which highlights ‘compression ignition engine by air injection from air-only cylinder to adjacent air-fuel cylinder’ while patent CN111164285B that highlights ‘internal combustion engine for a motor vehicle’ also patent US20110283688A1 which highlights ‘operation control device and operation control method for multi-cylinder internal combustion engine’. Moreover, patent US7063064B1 highlights ‘progressive combustion engine’ which attempted to address fuel efficiency, decreases emissions and power output. Furthermore, outlining essential patents and inventions that attempted to address lower flammability for compression ignition engines such as patent RU2541346C2 that highlights ‘method of ice operation’ while patent US20070084428A1 highlights ‘homogeneous charge compression ignition engine and method of operating’ in addition patent WO2009130777A1 which highlights ‘multifuel internal-combustion engine’ However, ethanol faced similar issues before it was widely taken up in Brazil and USA. Ethanol’s autoignition temperature is 400°C at ambient conditions, but this falls with increasing temperature and pressure. The way in which this was achieved was by adding ignition improvers to ethanol in varying percentages. This had the effect of reducing the autoignition temperature and pressure and facilitating the development of the single fuel ethanol solution. Scania is a world leading provider of transport solutions. Scania launched its compression ignition ethanol fueled engine in 1989. The 9-1 itre unit has been adopted in buses and 600 units have been sold to date. A 13-litre engine debuted in 2019. The engine adopts a higher than usual 28:1 compression ratio but also uses 5% ignition improvers to amend the properties and performance of the ethanol - both to avoid the need for an even higher compression ratio (with a resulting higher temperature and pressure at the end of the compression stroke) and to amend the rate of combustion of the ethanol. Patents of Scania such as variable valve timing internal combustion engine (US20220112847A1) also the method and control arrangement for controlling a four-stroke internal combustion engine (DE102023114379A1). Scania, though a leading provider of transport solution still has to be mindful of competitions from Caterpillar and Cummins. Presently, Cummins does not have any compression ignition ethanol fueled engine but Caterpillar has researched extensively on ethanol diesel blends in compression ignition engines. In this research Caterpillar has modified existing compression ignition engines to cater for the different combustion characteristics of ethanol with respect to diesel. Furthermore, Delphi technologies though not a main or known competitor of Scania has been responsible for patents in ignition ethanol fueled engine such as US8006672B2 which suggest ‘method for cold starting ethanol-fueled engines’. Other related Delphi patents are EP2188517B1 that offers ‘fuel injector and fuel injection system’ and US5405280A which highlights ‘integrated molding and inking process for forming a torch jet spark plug’. In addition, Ford Global Technologies also has a patent that could cater for an ethanol fuel though not invented strictly for it, this is evidenced in the patents such as US7234440B2, US20070233354A1, US8820049B2 and US9624823B2. In detail patent US7234440B2 offers ‘fuel injection strategy for reduced cold start emission from direct injection gasoline engines’. While patent US20070233354A1 suggest ‘transition strategy for engine operation with spark ignition and homogeneous charge compression ignition modes. Also, US8820049B2 propose ‘method to reduce engine emissions for an engine capable of multi-stroke operation and having a catalyst. In addition, US9624823B2 highlights ‘internal combustion engine with deactivatable cylinder, and method for operating an internal combustion engine of said type’. Summary Aspects of the present invention are set out by the claims. Further aspects are also described. Autoignition is an important factor for fuels used in Compression Ignition (CI) engines. The parameters influencing autoignition delay time are fuel composition, mixture pressure, and mixture temperature. Too short or too long an autoignition delay time of a fuel makes it inappropriate to be used in CI engines. There is no single definition for autoignition delay time. Ethanol suffered similar barriers to methane and to overcome these Ethanol was blended with low percentages of ignition enhances / improvers. This invention takes a very similar approach to overcome the barriers associated with methane as a single fuel for CI engines. Autoignition reactivity improvers have qualities that provide a mechanism for catalytic cracking of hydrocarbon bonds in fuels with low ignition quality. Autoignition reactivity improvers also provide a promising pathway to tune the ignition quality for advanced compression ignition. Blending methane with specific autoignition reactivity improvers at differing percentages prior to being injected into an engine compression chamber has proven to significantly improve methane’s autoignition properties and as such position methane as a single use fuel in CI engines. Brief Description of the Drawings Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: • FIG. 1 shows the four-stock cycle of a compression ignition engine; • FIG. 2 shows the in-cylinder pressure profile for a typical diesel fuel combustion event; • FIG. 3 shows the blends ratios of methane / n-butane / air mixture, at intake temperatures of 380K to providing for enhanced autoignition; and • FIG. 4 shows various blend ratios that deliver over 80% combustion efficiently while also reducing the autoignition properties of the fuel / air mix. Detailed Description Various exemplary embodiments, features, and aspects are described in detail below with reference to the drawings. Compression ignition engines, a.k.a. (Rudolf) Diesel engines operate using the principle of compression autoignition of hydrocarbons with 12 to 20 carbon atoms per molecule. Note that this carbon atoms per molecule connotes a typical diesel fuel which can mildly vary based on the refining process and the source. If it is a higher carbon atoms per molecule (longer carbon chains), higher boiling points are expected and compatibility with the high compression of compression ignition engine is improved. In addition, it is desired that the compression ignition engine has a higher cetane number (mainly above 40) essentially for an efficient and smooth operation. The general process begins with the introduction of a charge of fresh air which is then compressed by the piston. This is sometimes referred to as “intake stroke” which results in a visible increase in temperature based on the principle of adiabatic compression wherein pressure increases, volume decreases and temperature rises. Diesel engines typically have compression ratios between 14:1 to 25:1. This compression ratios are desired to be high to ensure that autoignition of the fuel is achieved and an efficient combustion without spark plugs is enabled. At the end of the compression stroke the air charge reaches around between 30 to 45 bar between 500 and 600 degrees Celsius. Towards the end of the compression stroke, the diesel fuel is injected. After a delay called the ignition delay, the fuel starts to react with the air a.k.a. combustion. Combustion takes place in two phases. First the pre-mixed phase i.e., diesel and air which is already mixed together starts to react or combust. Moreover, based on the high turbulence created by the swirling air motion, a small portion of the fuel mixes with the hot, high-pressure air around the injector nozzle. Furthermore, this pre-mixed fuel-air mixture gets to the autoignition point as a result of the high temperature and pressure, causing a gradual initial combustion event. The gradual burning contributes essentially to the power output of the engine. The second phase is diffusion-controlled combustion, controlled by the rate of further fuel and air mixing. The fuel injection event also continues alongside and beyond the start of combustion. This is critical to certify a sustained supply of fuel for ongoing combustion throughout the power stroke. The injection timing that is used and the properties of the diesel fuel means that the combustion event occurs in-phase with the piston moving downwards from Top Dead Centre ( (TDC) is the maximum height of the piston in the cylinder) during the power stroke. This guarantees that power generation is maximised as the burning force acts on the piston as it travels downwards. Additionally, the rate of fuel bum needs to be neither too far nor too slow in order to optimally push the piston downwards on the power stroke and also that the combustion event finished by the time the exhaust valve opens. Note that an early injection can result to uncontrolled preignition and excessive pressure which can increase the wear and tear on the engine while a late injection can lead to an incomplete combustion and a loss of power output. This invention deals with lowering the ignition thresholds of methane in a compression ignition engine. Similar to diesel engines methane is injected into the chamber but with an autoignition point of 540 degrees the methane will not respond in the required manor. However, if mixed with ignition enhancers the required reaction will take place in the appropriate manor. A homogenous charge of methane, and a percentage of ignition enhancer is injected into the chamber during the compression stroke. This is combined with an air intake which is preheated using exhaust gas. The combination of the preheated air and the rise in temperature due to compression reaches a point to ignite the methane blend (methane and ignition enhancers), the details of which are listed below. 1. Methane / n-butane / air - various blend ratios of and butane auto ignition temperatures and auto ignition pressure were constant at n-butane blend of 0% to 2%. At a blend ratio of n-butane of more than 2% autoignition temperatures and autoignition pressures decrease. With increasing blend ratio of n-butane auto ignition temperature is 25K lower and auto ignition pressure is 0.8 MPA lower. Moreover, it is important to state that n-butane improves the cold-starting challenge of methanol. This is due to it being a gas at room temperature, then when mixed with methanol, it improves its volatility and vaporisation. Also, it may improve flame propagation characteristics for complete combustion as methanol is slower than diesel &gasoline. In addition, it assists in reducing emissions from methanol combustion. This is because methanol mixed with n-butane has a reduced CO and NOX emissions. Though it has the downsides of increased Hydrogen emissions (HC), reducing the overall octane rating of the resulting fuel mixture or blend, mixing challenges at room temperature, lower energy density and it may require special engine modifications or cofeeding systems. 2. Methane / hydrogen peroxide (H2O2) / air - By injecting a mix of methane with 5% hydrogen peroxide (H2O2) an incremental improvement in a lower autoignition point is achieved. Moreover, the addition of even 7% by volume of H2O2 could ignite a mixture at an intake temperature of 350 K. It is essential to note that H2O2 is relatively inexpensive, readily available as diluted solutions and improve combustion in most situations by providing oxygen. This has the accompanying downside of being corrosive to engine components and should be handled expertly in highly concentrated solutions. 3. Methane / dimethyl ether (DME) or formaldehyde (CH2O) / air mixture - Blend ratios of DME or CH2O were found to reduce autoignition thresholds but these additives need to constitute larger percentages of the fuel air mix. fractions of 12.5% and 35% by volume were needed for dimethyl ether (DME), and formaldehyde (CH2O), respectively. It is critical to emphasise that dimethyl ether (DME) has a high cetane number which is important for selfignition. This improves the ignition of methanol, ensure better operation and reduction of emissions. Note that the cetane number of methanol is low so the mix or blend with DME is essential as its significantly impacts the autoignition of methanol. As methanol fuelled combustion ignition engines were known to have the challenge of cold-starting. DME improves cold-starting in methanol fuelled combustion ignition engine. Although, DME is not cost effective in comparison with other ignition enhancers and there is a scarcity of its production infrastructure. Moreover, at n-butane blend ratios ranging from 2% to 10% a combustion efficiency of over 80% is achieved. Overall, the enhanced reactivity of methane in the presence of varying amounts of ignition enhancers could be used in IC engines fuelled with methane to alleviate the high intake temperature requirement. 5 Although the disclosed subject matter has been described using specific terminology relating to apparatus features and / or method features, it is to be understood that the claimed subject matter is not necessarily limited to the examples disclosed. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. The advantages disclosed may relate to several of the 10 examples that are disclosed.

Claims

1. A Liquid fuel for compression ignition engines that is characterised by being majority part methane and part ignition enhancer.

2. A Liquid fuel of claim 1 that is characterised by being majority part methane with n-butane constituting at least 10% of the fuel mix.

3. A Liquid fuel for compression ignition engines that is characterised by being majority part methane and hydrogen peroxide (H2O2) constituting at least 7% of the fuel mix.

4. A Liquid fuel f of claim 1 that is characterised by being majority part methane with formaldehyde (CH2O) constituting of at least 5% to 15% of the fuel mix.

5. A Liquid fuel of claim 1 that is characterised by being majority part methane with dimethyl ether (DME) constituting of at least 5% to 15% of the fuel mix.

6. The liquid fuel of claim 1, wherein said, liquid fuel is classified as zero carbon if produced from biogenic sources.

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