Core Challenges and Prospects of Methanol Utilization, Prediction and Optimization for Sustainable Environment

Abstract

The transportation sector stands at the forefront of global challenges, where its significant contribution to greenhouse gas emissions and air pollution has become an urgent matter demanding immediate attention. For addressing these compelling concerns and leading the automotive industry toward a sustainable future, it is, therefore, imperative to explore the realm of alternative fuel that can effectively mitigate the environmental impact of automobiles. Methanol, a renewable alternative fuel, has gathered quite an attention due to its potential to be used as a wonderful alternative to neat gasoline in spark ignition engines. However, there are some core challenges that must be addressed to utilize methanol on a commercial scale in the transport sector. These core challenges include cold start issues, enhanced NOx emissions, 100% methanol utilization, transportation concerns and lubricant oil deterioration. In this chapter, these challenges along with their potential solutions have been discussed in detail. Moreover, different techniques such as artificial neural network and response surface methodology have been discussed to predict and optimize the usage of methanol in SI engines. The adoption of methanol, as an alternative to gasoline, will help us achieve some important sustainable development goals, thus fulfilling the promise of a sustainable future for the upcoming world.

1. Introduction

The desire for a luxurious lifestyle has forced mankind to deploy energy resources at a very fast rate. With each passing day, fossil fuels are getting consumed immensely to fulfill this particular desire. Non-renewable fossil fuels are being majorly employed in two sectors: Power Generation and Transportation [1]. In 2017, it was reported that the global crude oil production had reached approximately 4700 million tons as shown in Figure 1. The transportation sector performs a significant role in the socioeconomic development of any country around the world. Currently, the primary concerns for transportation sector include the oscillation in the fuel prices, vehicular exhaust emissions and constantly depleting fossil fuels [2].

Figure 1.

World energy consumption (y-axis) in million tons.

As per reports of EIA, in terms of years, the predicted lifespan of fossil fuel reserves left is only about 50.7 years [3]. Moreover, the present oil reserves of world approximated about 1342 billion barrels in the year 2009 [4]. Moreover, the EIA has also notified that the worldwide oil production in the year 2007 reached approximately 85 million barrels [5]. Dr. Colin Campbell, an American biochemist, proposed that the total fuel reserves of world will be exhausted in upcoming four decades if the oil production stays at present rate. The unpredictable fluctuation in fuel prices has also become a major concern for both developed and developing countries [6]. The main reason for this sudden fluctuation in fuel prices is the continuous depletion of fossil fuels along with the increase in world population and the corresponding energy demand [7]. Most of the developing countries are spending a large proportion of their budgets for importing the petroleum products to meet the ongoing energy demand that greatly affects the economic stability and social development of these countries [8].

The immense usage of fossil fuels is not only responsible for its depletion but also results in various socioenvironmental impacts including global warming, tempered air quality, extreme weather events, ecological disruptions, traffic congestion and noise pollution [9]. The major sources of greenhouse gases (GHG) are industries and the constant increase in the usage of comforting vehicles. It has been proposed that by the year 2050, the number of vehicles including busses, cars and trucks will increase to approximately 2.5 billion if the production and use of these particular automotive continue at the constantly increasing rate [10]. This makes the automotive sector the largest contributor of the total GHG emissions which ranges up to 60% of the total emissions. According to EIA, total global energy consumption is projected to increase by approximately 56% by the year 2040 in contrast with year 2010 [11]. This alarming increase in energy consumption indicates an astounding amount of greenhouse gases (GHGs) emissions, comprising at least 80% of carbon emissions being discharged into the atmosphere causing environmental deterioration and abrupt climate change.

The consequences of the combustion of fossil fuels include global warming resulting due to considerable emissions of CO2, NOx and mainly SOx, reported deadly for mankind and wildlife. It was reported, by IEA in 2015, that the total final consumption of coal from 1973 to 2014 increased from 631 MTOE to 1075 MTOE [11], as shown in Figure 2(a) and (b). Shares of world coal consumption in various sectors in 1973 and 2013 can be predicted from the given pie charts.

Figure 2.

(a) and (b). Coal consumption in 1973 and 2013.

On the other hand, sector wise consumption of oil had reached an amount of 2252 MTOE by the end of 1973 and by the end of 2013, this sector wise oil consumption had reached an amount of 3716 MTOE which can be observed in Figure 3.

Figure 3.

Overall sector wise oil consumption in MTOE from the year 1971 to 2013.

The overall sector wise consumption of natural gas in 1973 and 2013 was 652 MTOE and 1401 MTOE, respectively, which can be seen in Figure 4(a) and (b). According to a review by the World Bank in year 2000, these deleterious gases have resulted in more than 70,000 deaths annually [12]. Several nitrous and sulfur oxides are the key emissions of the road-based transport sector. These gases are not just irritant but also responsible for acidic rain which has hazardous impacts on the crops as well as the aquatic life. The major cause of sulfur oxide emissions is the combustion of coal in the industrial sector for the purpose of power generation. One-third of the total carbon emissions are also directly linked to the industrial division. These carbon emissions are responsible for the increase in the average temperature of earth. It has been reported via a survey that global earth temperature has been amplified at the rate of 0.6 degrees Celsius. The USA Department of Energy predicted that the earth’s average temperature would be expected to increase 1.7–4.9 degree Celsius by the year 2015 due to 54% increased carbon emissions when compared with the year 1990 [13].

Figure 4.

(a) and (b). Natural gas consumption in 1973 and 2013.

The transport sector has served as a major contributor to the increase in CO₂ emissions which resulted in global warming. As per Figure 5, it can be seen that transport sector contributes 23% global anthropogenic CO₂ emissions out of which about 73.9% of the total carbon emissions in this sector is mainly due to road-based vehicles [14].

Figure 5.

Global anthropogenic CO₂ emissions from the transport sector.

The dwindling of fossil fuels around the globe has been a hot topic of discussion in world monetary and political circles in preceding decades, especially in developed consumer nations like Europe and America. The central focus of this conversation revolves around alternative sources of energy once the fossil fuel reserves are depleted [15]. Undoubtedly, the key variables in formulating and making informed decisions regarding alternative energy sources lie in their financial viability and how they can be effectively utilized to meet the needs and preferences of consumers. During recent decades, the energy mix of consumer countries shifted toward renewable resources like hydro, nuclear, biomass, wind and solar instead being dependent on conventional fuels [16]. An immense effort has been incorporated for the advancement of renewable technologies but still, these technologies have not been commercialized on massive scale because the calorific value or energy content in petrol or diesel cannot be matched by these renewable energy sources and high initial capital investment is a major barrier toward the development of these renewable sources as complete alternative to fossil fuels. But still the modern area of research is to improve the effectiveness of turbomachinery and to look at alternatives of fossil fuels which are not only renewable in nature but can also be easily available so that they can be produced on small scale easily, therefore resulting in reduction of dependence on fossil fuels [17]. Therefore, there is need to look for renewable fuel sources which can not only reduce emissions but also lessen reliance on fossil fuels. If the utilization of fossil fuels is continued at a present rate, no sincere effort will be made to explore new oil reserves or fuel alternatives, then there will be a time when all the present fossil fuel reserves will drain out and no more fuel resources will be left to generate energy and run the engines [18].

The basic operating principle of automobiles involves the burning of fuel to produce heat energy that is subsequently converted into mechanical energy for the propulsion of vehicle. Consequently, the emissions get exhaled into the atmosphere and deteriorate the environment so badly. Spark Ignition (SI) engines operate on rich conditions, and they generate more carbon emissions when compared to the diesel engines [19]. SI engines are widely used in automotive, lawn mowers, portable small generators and other low power applications due to their lower maintenance cost and lower initial investment. Whereas the substantial depletion of fossil fuel resources, alarming environmental risks and fluctuations in fuel costs are the paramount concerns. Developed countries have two challenges, first, they are releasing more carbon emissions into the air, causing climate change and secondly, they are running out of fossil fuels like oil and coal [20]. The modern area of research is focused on looking for green fuel sources which are not only compatible to this particular type of engines but also produce less emissions and give higher thermal efficiencies, so that they can be served as good alternative of fossil fuels. Alcohol is considered renewable in nature and presents excess oxygen which plays a significant role in reducing emissions and ensuring complete combustion with minimal losses, when compared to gasoline. Among many members in the alcohol family, methanol and ethanol proved to be more desirable due to affordability and reduced emissions [21].

Expansion of cities and advancements in industrial segments prompted environmental concerns. Petroleum-based products play a pivotal role in meeting the energy needs across various sectors crucial for a country’s development, including industrial, power and transport segments. But emissions from the combustion of such fuels promote environmental issues [22]. A drawn-out resolution for these issues is required for a maintainable turn of events.

In this manner, sustainable power sources are emerging as productive and successful resolutions for ecological issues [23]. Bioenergy from biomass has been attracting countries in recent years to attain benefits from bioenergy and utilize this energy as substitute of these fossil fuels. The major beneficial outcomes of bioenergy are listed below [24].

• Reduction in emissions

• Renewable in nature

• Responsible for economic growth

• Enhances agriculture

• Diminishes landfills

• Energy security

• Decreases necessity on fossil fuels

• Many products can be produced like ethanol and methanol from bioenergy

2. Overview of methanol

Methanol, CH₃OH, is the simplest hydrocarbon with oxygen. It stands among the five most widely used chemicals in the world [25]. In the past, methanol was mainly used for the production of adhesives, paints, silicones, LCD screens and pharmaceutical products. It has also been used in the wood and automotive industry on commercial scale. During recent years, methanol has been largely employed for power purposes, with approximately 0.020 billion tonnes of methanol being generated annually [26]. Its major uses, which are constantly increasing day by day, include its usage as a fuel as well as a fuel blend component.

One prime reason to investigate methanol as a transportation fuel is its scalability. The simplicity in its making and a wider choice of raw feedstocks presents methanol a convincing entrant for a sustainable alternative energy source with the ability to immensely diminish the carbon footprint of fossil fuels used in transportation sector [27]. The better efficiency with which it can be produced as compared to its fellow alcohols (ethanol, propanol and butanol), coupled with the increased brake thermal efficiency it generates in the internal combustion engines, means that it generates a combined impact on enhancing primary power utilization. Although methanol produces hydrocarbon emissions at the same level to gasoline, its particulate matter contents are substantially lower when compared to the complex synthetic hydrocarbon fuels [28]. The reason for this is its better burning attributes and mono carbon in a molecule by nature. Thus, it can be concluded that methanol has certain potential advantages when it comes to energy security, sustainability and air quality [29].

Methanol is majorly extracted from reforming of natural gas with steam, which transforms this gaseous mixture into methanol through distillation under high temperature and pressure circumstances in manifestation of nickel catalyst [30]. In consequence, methanol is obtained as organic and biodegradable liquid. Another way to produce methanol is to allow the reaction between coal and oxygen in gasifier for generation of synthesis gas incorporating, H₂, CO, CO₂ and minute traces of inert gases like N₂, Ar, CH₃. The reaction in gasifier served as reason to generate syngas, which is the blend of CO, CO₂ and H₂ under conditions of 50–100 bar pressure and 250–300°C temperature, employing copper and zinc-based catalyst to speed up the reaction. These catalysts remain active at 200°C temperature and selective for the production of H₂ and CO₂ [31].

Methanol is extracted from the synergetic response of CO, CO₂ and H₂ in the manifestation of catalyst. The combination of the gases mentioned above is known to be synthesis gas which is usually extracted from gasification of biomass at high temperature and pressure [32]. Then, Syngas is treated to remove impurities like tar and to adjust the carbon-to-hydrogen ratio. Methanol can also be produced from pyrolysis of wood. Biomass can serve as good option in production of methanol. As Pakistan is an agricultural country and has lot of biomass potential, it should be harnessed in order to provide relief to economy by reducing imports of fossil fuels and by increasing production of methanol through biomass [33]. When the production cost of methanol is estimated in terms of equivalence energy and compared to the production cost of gasoline, then still production cost of methanol is lower as compared to gasoline production cost. The basic alcohol can be created by the hydrogenation of carbon monoxide, the natural gas steam reforming, destructive refinement of biomass and wood [34].

There are numerous desirable attributes of methanol which make it an exceptional fuel for spark ignition engines. These include,

• Lower theoretical air-fuel ratio

• Higher latent heat

• Higher specific energy per unit of fuel-air mixture

• Lower combustion temperature

• Higher hydrogen-to-carbon ratio

Out of all these properties, the most important property of methanol is that it can provide clean ignition. It is used in the automotive sector as an alternative to gasoline for air quality goals. With a single carbon atom, methanol cannot easily produce the carbonaceous particulate matter which is common for long-chair hydrocarbon fuels [35]. Another advantage is lesser vehicular tailpipe pollutants when energized with gasoline-methanol mixtures as methanol carries a low boiling point, that is, 65°C which aids burning of fuel within the expansion stroke of the engine working cycle. Complete combustion is responsible for lower hydrocarbon emissions. The more oxygen percentage (50 percent by volume) of methanol along with its simpler composition led to less carbon monoxide emissions. These characteristics increase its significance to be utilized as substitute to gasoline fuel or additive to gasoline fuel in spark ignition engines [36]. Furthermore, methanol possesses inferior vapor pressure and higher latent heat, which confines its usage as fuel in automotive owing to cold start issues in winter. This cold start problem could be resolved by utilizing mixtures of methanol and gasoline. Numerous strategies have been implemented like blended fuel, reforming and heating of fuel along with induction air heating to use methanol as alternate to fossil fuels [37]. Interestingly, these fuel bends having various proportions of methanol in gasoline fuel allow SI engine to run at more compression ratios due to increased octane number [38].

2.1 Physical and chemical properties of methanol

In this section, the physical and chemical properties of methanol are discussed in detail. Furthermore, these properties will be linked to expected consequences of engine design and engine’s performance and emission parameters. Tables 1 and 2 present the physical and chemical properties of methanol and gasoline. A qualitative analysis will be performed, in this section, between these two fuels in order to identify the reliability of methanol as a sustainable alternative fuel.

Property	Gasoline	Methanol
Vapor density (STP) [kg/m^3]	388	142
Dynamic viscosity (20°C) [mPas]	0.56	0.61
Surface tension (20°C) [mN/m]	21.6	22.1
Heat of vaporization [kJ/kg]	190–350	1100
Boiling point at 1 bar [°C]	25–215	65
Density (STP) [kg/m^3]	740	790

Table 1.

Physical attributes of methanol and gasoline [39].

Property	Gasoline	Methanol
Chemical formula	Various	CH3OH
Adiabatic Flame Temperature [K]	2275	2143
Autoignition temperature [K]	465–743	738
Stoichiometric AFR [kg/kg]	14.7	6.5
Hydrogen Content by mass [%]	14	12.58
Volumetric Energy Content [MJ/m^3]	31,746	15,871
Higher heating value [MJ/kg]	48	22.88
Lower heating value [MJ/kg]	42.9	20.09
Carbon Content by mass [%]	86	37.48
Oxygen Content by mass [%]	0	49.93
Molecular weight [kg/kmol]	107	32.04

Table 2.

Chemical aspects of methanol and gasoline [39].

3. Core challenges in methanol utilization

As the search for sustainable alternative to conventional fuels continues, methanol has emerged as one of the potential solutions for internal combustion engines, especially spark ignition engines. However, there are several challenges that need to be addressed before the deployment of methanol fuel as an alternative to neat gasoline in spark ignition engines. These challenges include cold start issues, lubricant oil deterioration, increased NOx emissions, 100% methanol usage and transportation concerns. Methanol, itself, has excellent properties to be used as an optimum alternative fuel but without properly discussing the above-mentioned issues, its uses will be limited in the automotive sector and, hence, cannot reach its complete potential in this particular sector. The details of these issues and their predicted solutions have been mentioned in the later sections.

3.1 Cold start issue

Cold start still exists as one of the core challenges encountered while using methanol in SI engines. The major reasons due to which this issue arises in SI engines are the physio-chemical properties of methanol fuel, which differ greatly from the conventional gasoline. During the cold start, the components of the SI engine are cooler, thereby demanding an efficient vaporization process in order to propagate complete combustion of the fuel [40]. However, the high heat of vaporization of methanol presents a formidable obstacle, restraining the required atomization and vaporization for optimal fuel-air mixing in the early stages of the engine operation.

This particular issue of cold start gets worsened by lower volatility of methanol fuel, when compared to that of gasoline. This lessened volatility of methanol hinders the fuel’s ability to readily evaporate at decreased temperatures, thus, obstructing the generation of a homogeneous and combustible fuel-air mixture. As a result, the spark ignition engines struggle to attain a complete and efficient combustion in the crucial ignition phase, therefore, resulting in the suboptimal engine performance, enhanced emissions and heightened fuel consumption [41]. Furthermore, the issue of cold start also gets worse by the presence of water in methanol fuel, whether as a contaminant or through condensation. This presence of water particles in methanol serves as an additional hindrance and thus slows down the fuel’s vaporization process. This results in decreasing the engine’s ability to obtain the required air-fuel mixture, therefore generating a negative impact on the overall efficiency and the effectiveness of the entire combustion process [42].

The cold start issue results in the consequences that reverberate throughout the engine processes. The incomplete combustion due to the cold starts leads to decreased power output, compromised efficiency of fuel and increased emissions, which act as a counter to the objective of achieving sustainable transportation [43]. The SI engines, as a result, may experience rough idling, misfires or hesitation till reaching the desired operating temperature, thereby, leading to discomfort for the driver as well as significant wear on the engine components.

In order to address the challenge of cold start for methanol fuel in SI engines, there is a need for effective and innovative solutions. One of the solutions that the researchers have suggested in recent years is engine modification for employing methanol fuel in SI engines. Various types of engine modifications have been identified to optimize the vaporization process of the fuel. The fuel vaporization and atomization can be enhanced by using high-pressure fuel injection systems. These systems will ensure the improved air-fuel mixing during the cold starts [44]. Moreover, electrically heated injectors can be used as an additional heat source, aiding the vaporization process and thus resulting in smoother ignition of engine in cold starts. Another modification is to utilize the preheated intake air for the combustion process which will elevate the fuel’s temperature, therefore, strengthening the fuel’s ability to vaporize efficiently and allowing the combustion process to be more effective during the cold starts.

Furthermore, the utilization of fuel additives can also serve as a potential remedy for this particular problem. The ignition enhancers, such as small amounts of gasoline and ether, can aid in starting the combustion process in cold starts, thereby facilitating easier ignition of the SI engines. The temperature of the methanol fuel can also be increased by the application of fuel heaters, engine coolant-heated systems as well as electrically powered heated systems, thus, enhancing its vaporization and improving the combustion efficiency from the very outset [45].

3.2 Enhanced NOx emissions

The implication of methanol as a sustainable alternative fuel for SI engines has gathered considerable attention because of its potential to significantly reduce the GHG emissions and reliance on conventional fossil fuels. However, a major concern linked with methanol’s usage for SI engines lies in the enhanced nitrogen oxide (NOx) emissions.

There are several reasons for the heightened NOx emissions while utilizing methanol as a fuel in SI engines, out of which the primary reason is the contrasting physio-chemical properties of methanol when compared to conventional gasoline. For complete and efficient combustion process in SI engines, methanol requires a longer duration than gasoline because of its high latent heat of vaporization [46]. As a result, the extended combustion process leads to enhanced residence time of nitrogen molecules in the combustion chamber, thus, facilitating the generation of nitrogen oxides. Moreover, characterized by the excess air in the air-fuel mixture, the combustion of methanol exhibits a lean-burn tendency. While this condition of lean combustions illustrates the potential to increase fuel efficiency and reduce CO₂ emissions, it consequently promotes the formation of NOx emissions. Under these lean conditions, the availability of excess oxygen favors the generation of thermal NOx, where the molecules of nitrogen and oxygen react at increased temperatures to produce complex NOx compounds [47].

Apart from the intrinsic nature of the methanol, the combustion process also plays an important role when it comes to the NOx emissions. The formation of nitrogen oxides is exacerbated due to the high flame temperature associated with methanol combustion in spark ignition engines. The pathway for the formation of thermal NOx gets intensified due to the elevated temperatures as this enhanced temperature acts as a catalyst for the reaction between nitrogen and oxygen molecules. Consequently, the combustion of methanol in SI engines tends to produce substantially higher NOx emissions as compared to the neat gasoline [48].

To address this issue of enhanced NOx emissions when using methanol in SI engines, several mitigation strategies can be adopted. One of the strategies involves the application of catalytic converters equipped with selective catalytic reduction (SCR) systems [49]. These specific types of systems use a catalyst, mostly a metal such as platinum or palladium, for the conversion of NOx compounds into water and nitrogen via reduction reaction [50]. A promised reduction in NOx emissions has been shown by this technology and thus can be adapted for utilizing methanol in SI engines.

Another potential approach involves the optimization of combustion process for minimizing the formation of NOx. Various advanced management techniques such as timing adjustment of fuel injection and exhaust gas recirculation (EGR) can be used for controlling the temperature within the combustion chamber, thereby reducing the generation of NOx compounds [51].

3.3 100% pure methanol utilization

The utilization of 100% methanol in spark ignition engines presents one of the core challenges that emerges from a multitude of technical and logistical considerations. Methanol, a colorless volatile alcohol, has physio-chemical properties that differ significantly when compared to that of gasoline. The core challenge lies in reconciling the unique characteristics of methanol with the intricate requirements of SI engines, demanding innovative engineering and adaptation.

One of the primary hurdles in using 100% pure methanol in SI engines is its dissimilar combustion behavior compared to the neat gasoline. Methanol, as a fuel, possesses high octane rating, which is advantageous when it comes to knocking and resistance to pre-ignition. However, the downside of methanol is its slow flame propagation speed which generates the need for modifications for engine’s injection and combustion systems [52]. With methanol, ensuring efficient combustion and effective power delivery requires precise calibration as well as fine tuning because the modified combustion attributes have significant impact on the several factors including, air-fuel ratio, ignition timing and injection strategy.

Furthermore, the low energy density of methanol as compared to gasoline has a direct negative impact on the overall efficiency of the engine. In order to maintain the power output, there is a need to increase the fuel’s flow rate during ignition, which consequently results in enhanced fuel consumption. Thus, in order to provide the unaffected engine performance, large quantities of methanol are required which pose a challenge in terms of fuel storage and transport. As a result, the automotive engineers and engine manufacturers must tackle the challenge of fuel efficiency optimization while maintaining sufficient range and refueling infrastructure [53].

One of the many challenges that occurs in utilizing 100% pure methanol as a sustainable alternative fuel is its corrosive nature of properties. This corrosive nature of methanol damages certain metals, rubbers and polymers that are commonly used in several components of engines. This necessitates comprehensive material compatibility studies and careful selection of materials for manufacturing engine components [54]. Due to this particular nature of methanol, it is imperative for engine manufacturers to develop corrosion alloys as well as compatible seals and gaskets for mitigation of potential damage, thereby ensuring the durability of engine [55].

Moreover, the extensive usage of 100% pure methanol as a fuel, alternative to conventional gasoline, requires a comprehensive infrastructure overhaul. Due to the difference in distinctive handling, storage and transportation requirements of methanol, the currently employed gasoline distribution network is ill-suited to accommodate pure methanol [56]. The construction of such distribution network for the purpose of utilizing 100% pure methanol would require significant investments and time, thereby hindering its adoption on commercial scale [57]. Furthermore, in order to ensure the availability of methanol on refueling stations for consumers poses a substantial logistical challenge, demanding extensive cooperation and collaboration between fuel providers, vehicle manufacturers and regulatory authorities.

3.4 Transportations concerns

Various transportation issues also need to be addressed before the usage of methanol in SI engines on commercial scale. Methanol, possessing the potential of a renewable and clean-burning fuel, provides significant benefits when it comes to reduced emissions and reliance on conventional fossil fuels. However, there are several challenges associated with the distribution and transportation of methanol, which present quite a hindrance in its utilization in SI engines. The later sections will present the details of these challenges as well as the predicted solutions for overcoming them.

One of the major concerns lies in the infrastructure that is required for the transportation and storage of methanol. Methanol has contrasting properties when compared to the conventional fuels like gasoline and diesel, including its enhanced flammability and corrosiveness. Thus, the implementation of special materials and safety measures in transportation infrastructure seems imperative, including the pipeline tanker and other storage facilities [58]. This will not only ensure the safe handling and transport of methanol but also make the transportation faster than usual. However, such an advancement in infrastructure requires substantial capitals and comprehensive planning in order to support the ubiquitous adoption of methanol as an alternative to gasoline.

Another important transportation challenge involves the accessibility and availability of refueling stations of methanol. As of now, there is a limited access of consumers to methanol in terms of fuel stations as compared to that of neat gasoline. This creates the necessity of infrastructure development in order to facilitate the users of methanol-fueled applications, i.e., SI engines. Currently, they may be finding it very difficult to reach the methanol refueling stations, especially in remote or less populated regions [59]. Thus, the solution in this case will be expansion of methanol refueling stations network which will promote the widespread utilization of methanol as a renewable alternative fuel in SI engines.

In addition to above-mentioned challenges, methanol’s transportation as well as its distribution on large scale also involves serious logistical considerations [60]. The production of methanol is mainly from sources such as natural gas or biomass and due to this particular reason, the production facilities are typically found in specific regions to ensure the availability of raw materials for methanol [61]. Transporting the generated methanol from these production facilities to different regions needs efficient as well as effective logistical planning, including the modes of transportation, routes and last but not least, storage facilities. For this particular challenge, the solution involves the development of robust supply chains and optimization of ongoing logistics. This will be very crucial to ensure the reliability and cost-effectiveness of methanol distribution to the end-users.

Moreover, methanol’s energy density is less when compared to conventional gasoline. This means that more quantity of methanol is required to obtain the same energy content as that of gasoline, consequently, necessitating the need of large containers or tanks and specialized equipment for the accommodation of larger volumes of methanol [62]. To address this specific issue, there is a need of innovative solutions such as increasing the methanol’s energy content via blending with some other conventional but high energy fuels or by exploring sophisticated means of storage and technological advancements related to delivery of methanol. When transporting such kind of corrosive and highly flammable, one significant concern is the safety factor involved. As it is mentioned previously that methanol is less flammable than gasoline, its higher flammability as compared to diesel originates certain safety challenges. Proper safety protocols as well as regulations are needed to be established and abided throughout the process of transportation, including, handling, loading, unloading and storage of methanol. The education and training of personnel involved in this entire procedure of transportation and distribution is necessary for ensuring safe practices as well as minimizing the risk of tragic accidents.

3.5 Lubricant oil deterioration

In the world of automotive engineering, the selection of fuel for a vehicle or any transport plays a very keen role in delivering optimized engine performance as well as engine longevity. As the entire world is shifting from conventional fossil fuel toward alternative fuels, such as methanol, it becomes imperative to understand the potential impacts of such fuels on lubricant oil degradation. The later sections have explained many parameters such as kinematic viscosity, total acid number, specific gravity and flash point of lubricant oil in order to determine the feasibility of methanol for engine’s durability.

3.5.1 Kinematic viscosity

Kinematic viscosity is an important parameter which measures the resistance of lubricant to flow and thus plays a very crucial role in evaluating its effectiveness. Methanol demonstrates lower viscosity as compared to gasoline when it comes to the utilization of methanol as an alternative to gasoline in SI engines. This lessened viscosity is due to the unique molecular structure and contrasting physio-chemical properties of methanol [63, 64]. Methanol, as compared to gasoline, is a smaller molecule and, hence, possesses weaker intermolecular forces as well as lower molecular weight. The lower viscosity of methanol can be attributed to these previously mentioned properties. This decreased viscosity has a drastic impact on the lubricant oil, being used in SI engines, thereby, resulting in compromising the lubricating film thickness that is formed between the engine’s moving parts. This reduced thickness of lubricating film eventually results in reduced lubrication, enhanced friction and heightened wear and tear between the moving components [64]. The consequences of this enhanced wear and increased friction can prove detrimental for the engine’s performance and its durability. For addressing the challenges resulted due to reduced kinematic viscosity, specialized lubricants must be employed that are formulated to meet the specific requirements of utilizing methanol as a fuel in spark ignition engines. These specific properties will include enhanced film-formation and involvement of anti-wear additives for compensating the lower viscosity.

3.5.2 Total acid number

The total acid number (TAN) is an important property of lubricant oil and thus plays a key role in identifying the acid content present within the oil. When methanol is burnt in spark ignition engines, its combustion can produce several acidic compounds. These acidic by-products of methanol’s combustion can infiltrate the lubricant oil through various channels and pipelines such as blow-by gases. Consequently, the TAN of the oil will increase, thereby indicating an increase in acidification. This availability of acidic compounds within the lubricant oil can lead to detrimental effects on components of engine. One of the major concerns is the enhanced corrosion, which eventually promotes the degradation of critical engine parts and lessened engine lifespan [65]. The corrosive nature of these acidic compounds can erode surfaces, impair proper functioning and sub-optimal engine performance. In order to reduce the impact of acidification, continuous monitoring of TAN and implementation of proper maintenance schedules are imperative [66]. This includes timely oil changes and the utilization of high-quality lubricants with suitable additives to neutralize the effect of acidic compounds, thus, maintaining a favorable environment for engine operation.

3.5.3 Specific gravity

Specific gravity refers to the density of a substance compared to the density of water. The specific gravity of methanol is lower when compared to traditional gasoline. This particular characteristic of methanol can have detrimental impacts on the performance of SI engines during methanol usage. The major consequence of this lower specific gravity is the reduction in oil film thickness which results in increased metal-to-metal contact inside the engine [67]. This enhances contact between the components of engine results in heightened friction and wear. This increased friction and wear can contribute to premature component deterioration, reduced engine efficiency and a shorter lifespan for critical engine parts. The lessened oil film thickness becomes a hindrance in lubrication effectiveness, allowing for direct metal contact and heightened friction between the moving parts [68]. These deleterious impacts of thinned oil film mark the importance of usage of special lubricants which are formulated in such a way that they can contribute for the lower specific gravity of methanol during its utilization in SI engines as a fuel. These measures will help maintain optimum lubrication between the components, reduce friction between them and thus mitigate the significant negative effects on the engine performance and lifespan.

3.5.4 Flash point

The flash point is an important property of lubricant oil, which indicates the minimum temperature at which sufficient vapor gets released from it, in order to ignite when exposed to an open flame or spark. When methanol is used in the SI engines instead of neat gasoline, the lubricant oil after designated hours of running exhibits lower flash point as compared to the traditional gasoline. Thus, the utilization of methanol enhances the potential for heightened operating temperature, thereby resulting in increased incidents of flash points that can occur within the lubricant oil [69]. This reduction in flash points can create significant impact on the chemical stability of oil, leading to unfortunate consequences [70]. One of its major consequences is the enhanced formation of deposits and sludge. The occurrence of flash points at higher frequencies can result in lubricant oil degradation, thus, formulating the by-products that promote the production of sludge and deposits. This accumulation of sludge and other deposits can generate overall negative impact on the engine’s performance and durability by hindering the circulation of oil, inhibiting proper lubrication and lessening the effectiveness of several crucial components of engine [71]. To lessen the effects of frequent flash points, the use of special lubricant oils, which are formed to withstand increased temperatures and maintain their chemical stability, is imperative. These special oils much possess better resistance to thermal degradation and must be equipped with increased detergency and dispersant properties for the purpose of minimizing the formulation as well accumulation of sludge and deposits in lubricant oil.

4. Artificial neural network-based prediction

Techniques like artificial neural network (ANN) have risen as powerful tools for the prediction and analysis of complex patterns in different fields [72]. This technique can be employed to predict the utilization of gasoline-methanol blends in SI engines. Methanol can be described as a renewable and environmentally friendly fuel, which has garnered quite an attention as a wonderful alternative to conventional gasoline because of its reduced carbon footprint. However, for the purpose of its successful integration into the currently used SI engines, the accurate predictions of various engine characteristics including performance, emissions and combustion seem imperative. This is the space which can be filled with the application of ANN in a wonderful manner.

ANNs can be defined as computational models which are inspired and generated by the human brain’s neural network structure [73]. They comprise of interconnected neurons (artificial) that can process and, hence, transmit information. The historical data acts as a raw material in training an ANN and it can learn to identify several patterns and relationships within the data, allowing it to predict the future data. In this particular context of utilizing gasoline-methanol blends in SI engines, based on various factors, ANNs can be trained to predict the behavior of various engine characteristics. In the beginning, ANN can be provided with the historical data about the chemical composition of gasoline-methanol blends which includes the percentage of methanol in the entire blend [74]. Other important parameters, including, ignition timing, engine speed, air-fuel ratio and engine load can also serve the purpose of input parameters. With the help of historical data that can provide information on the above-mentioned parameters, ANNs can learn to determine patterns and correlations. This enables the ANNs to create multiple predictions about the engine’s performance and emissions when provided with the updated values of input parameters [75]. Figure 6 demonstrates the development of ANN model for various fuel blends. The input parameters include engine load, engine speed and fuel blends, of which the effects have been observed on output parameters such as performance and emission characteristics. The ability to capture nonlinear relationships between input and output variables can be described as one of the key advantages of using ANN techniques. It is often difficult for traditional mathematical models to identify the complex interaction within the engine system. Rather than this, ANNs excel at determining complicated relationships between multiple input and output variables, and hence can precisely provide the predictions about the impact of various gasoline-methanol blends composition on the engine performance, emissions and combustion parameters [76, 77].

Figure 6.

Development of ANN model for gasoline-methanol blends.

By using this special technique, named ANN, researchers and engineers can discover a vast range of scenarios, without any particular need for comprehensive practical experimentation. They can easily analyze the effect of various ratios of gasoline-methanol blends on critical output parameters including the fuel efficiency, power output, generated torque as well as emission of several pollutants such as carbon monoxide (CO), oxides of nitrogen (NOx) and unburned hydrocarbons (HC). This predictive capability of this technique develops a model for efficient optimization of engine performance while ensuring compliance with emissions regulations [78]. Moreover, ANN can assist real-time forecasts, thereby, making them valuable in onboard control systems of engines. With the help of continuous surveillance on input variables and utilizing the modified ANN model, the operating conditions of engine can be adjusted by the system dynamically for optimize the performance as well as emissions, based on the desired composition of gasoline-methanol blend [79].

4.1 Comparison with other prediction techniques

In addition to artificial neural network (ANN), several other deep learning architectures such as convolutional artificial network (CNN) and recurrent artificial network (RNN) can also be used for the prediction analysis of gasoline-methanol blends. ANN can be defined as a foundational model that comprises of interconnected nodes or neurons, arranged in the form of layers. Each neuron has the capability to process input data and via iterative learning as well as past records, ANN can optimize its weights to capture intricate patterns in the provided data. However, despite being a wonderful technique, ANN lacks spatial awareness, which makes it less suitable for tasks including, grid-like data such as images.

Unlike ANN, convolutional neural network (CNN) is particularly designed for image processing tasks. Its basic function involves employment of multiple convolutional layers to identify spatial patterns and features in the provided data. These layers use versatile filters in order to scan the input and thus acquire the local information, thereby allowing the CNNs to effectively extract the meaningful information about the features and recognize objects inside the images. In comparison with ANN, CNN’s architecture enhances the weight sharing, as well as lessens the model’s memory demands and increases its capability to handle more intricate visual data. In comparison, recurrent artificial network (RNN) can be used effectively for sequential data, including the time series data. It comprises of a recurrent collection that generates feedback loops, thus enabling the RNN to capture information from previous time steps. The prediction analysis based on the sequential dependencies can be easily handled by this temporary memory of RNN. The ability of RNN to model dynamic patterns makes it an ideal candidate for forecasting tasks including temporal data such as prediction of gasoline-methanol blends over time.

To conclude, it can be said that a versatile model like ANN is best suited for complicated relationships. CNNs excel in image-processing tasks, whereas RNN can be used proficiently for capturing temporal dependencies. Combining these different models can allow us to have a comprehensive approach to forecasting analysis of gasoline-methanol blends, leveraging their individual strengths for addressing various aspects of the data.

5. Optimization

Determining the optimized conditions for the utilization of gasoline-methanol blends in SI engines is a complex task which requires a comprehensive and systematic approach. One method that is quite effective and has been widely used for this purpose is response surface methodology (RSM). RSM can be defined as a statistical and mathematical tool that can be employed for modeling and optimization of the relationships between multiple input variables and a response or output variable [80]. One of the basic steps in using RSM is the selection of input variables that creates an impact on the performance characteristics of methanol-gasoline blends [81]. The examples of such factors can include blend ratio of gasoline to methanol, ignition timing, engine speed, load, compression ratio, air-fuel ratio and other several associated parameters. The factors that are chosen in the first stage should cover a wide range of values for the purpose of capturing the full spectrum of engine processes. In the next step, a set of experiments is performed for collecting data on the chosen input variables and the corresponding output variable(s) [82]. The response variables can be any of the engine’s performance characteristics including torque, brake power, brake-specific fuel consumption, brake thermal efficiency as well as the corresponding emissions of the engine. The design of experiment must be planned carefully so that it can ensure enough number of data points that can easily cover the design space as well as give reliable information for modeling. After the collection of the data attained via experimentation, RSM will generate a mathematical model using the regression analysis for describing the relationship between input and output variables [83].

Now, with the availability of mathematical model, the next step is the optimization of conditions for using gasoline-methanol blends in SI engines. RSM employs optimization algorithms, including the desirability function approach, to find the combination of input variables that can either maximize the required response variables or minimize the undesirable ones. The values of desirability function range from 1, representing the best, to 0, signifying the worst [84]. In RSM, the optimization process includes adjustment of values of the input variables iteratively, that is based on the generated mathematical model and the required optimization criteria. Repeated evaluations of the model are done, and it gets updated until the optimization of desired response [85]. This procedure of iterations helps researchers to systematically explore the design space and evaluate the optimal conditions for using gasoline-methanol blends in SI engines. Figure 7 shows an example of optimization process for fuel blends. The desirability chart of optimization has been generated by RSM for showing the contribution of each response variable in developing the optimized model for the engine.

Figure 7.

Desirability chart.

There are several significant benefits that researchers will get by using RSM for optimizing the conditions of gasoline-methanol blends. First of all, with a relatively limited number of experimentations, RSM can provide the efficient exploration of a large parameter space. This saves time, resources and cost compared to conducting a large number of exhaustive experiments. Secondly, a systematic as well as a structured approach can be generated with the help of RSM, which allows the understanding of complex relationships between input and response variables (engine performance and emissions) [86].

5.1 Comparison with other optimization techniques

Besides response surface methodology (RSM), several other distinct techniques including the Taguchi Method and Genetic Algorithm can also be used in an effective manner for the purpose of optimization of gasoline-methanol blends. RSM can be defined as a statistical approach that strives for modeling and optimizing the relation between multiple input variables (engine speed, load, blend ratio) and the response variables (performance and emission characteristics). RSM helps in capturing the interaction between different variables and thus aids in locating the optimal operating conditions for the superior gasoline-methanol blends. The Taguchi Method, developed by Genichi Taguchi, emphasizes on reliable optimization by lessening the effects of noise and variations in manufacturing or experimental processes. This particular method uses an orthogonal array for efficiently conducting the experiments with a limited set of trials, thereby, making it less time-consuming as well as cost-effective. The major purpose of Taguchi Method is to find the optimal variable settings that lead to minimizing the sensitivity of responses to external variations, thus, enhancing the reliability and sensitivity of the gasoline-methanol blends. On the other hand, genetic algorithm (GA) can be defined as an evolutionary optimization technique which is inspired by the laws of natural selection and genetics. It initiates with a set of potential solutions, termed as chromosomes, which represent different combinations of input variables as defined above. With the help of successive generations, GA implements selection, cross-over and mutation techniques to evolve innovative solutions over time. GA is mostly useful when dealing with the intricate, nonlinear and multi-dimension optimization problems. This makes it a suitable candidate for deriving optimal gasoline-methanol blends in a vast parameter space.

To conclude, it can be said that RSM focuses majorly on statistical modeling for deriving the optimal settings of input variables. On the other hand, the Taguchi Method emphasizes on robust, stable and least sensitive optimization. In comparison, GA utilizes evolutionary principles in order to search for solutions in complex and multi-dimensional spaces, considering nonlinear relationships. With complete understanding about the strengths as well as limitations of above-mentioned methods, engineers and researchers can make better decisions about which approach is the most suitable one for gasoline-methanol optimization objectives.

6. Environment and sustainable development goals (SDGs)

The sustainable development goals (SDGs) emphasize the importance of maintaining balance between social involvement, economic growth and environment protection for ensuring the development of a sustainable era. These goals provide a roadmap for different governing bodies, institution and individuals to work cooperatively toward a most inclusive, just and sustainable world. Utilization of methanol in SI engines as a fuel, instead of neat gasoline, allows us to achieve some important sustainable development goals which include, good health and well-being, climate action, clean and affordable energy and responsible consumption and production.

First of all, an alternative fuel like methanol has the potential of substantially reducing GHG emission when compared to traditional gasoline. The combustion of methanol in SI engines will produce lower levels of CO₂ and other hazardous pollutants including the oxides of nitrogen (NOx) and particulate matter (PM). With the utilization of methanol as a fuel in SI engines, we can surely and actively contribute to sustainable development goal of climate action, by lessening the effect of climate change and reducing the carbon footprint in transportation sector. Secondly, the usage of methanol in SI engines can generate a positive impact on another sustainable development goal, i.e., good health and well-being. The usage of traditional gasoline in SI engines emits large number of hazardous pollutants which have deleterious effects on human health, thereby, contributing to the increase in respiratory diseases and other diseases. The utilization of methanol not only produces less harmful emissions but can also lead to improved air quality. This will eventually lead to lessened health risks linked with vehicular emissions. Thus, by using methanol as a fuel, a healthier and safer environment can be created for upcoming generations and communities.

Moreover, since methanol is a renewable, clean and cost-effective source, this aligns with the sustainable goal of clean and affordable energy. Various kinds of feedstocks, including renewable resources such as captured carbon dioxide and biomass, can be used for the production of methanol. This versatility in feedstocks allows for sustainable and clean production as well as helps in the integration into the existing energy platforms. Thus, by utilizing methanol in SI engines, we can make our energy resources more versatile and reduce reliance on conventional fossil fuels, thereby contributing to the cleaner and renewable energy future.

In addition to the above-mentioned SGDs, the adoption of methanol as an alternative to gasoline promotes the sustainable development goal of responsible consumption and production. Methanol can be easily produced via environmentally sensible methods and feedstocks, which lessen their impact on the ecosystems and thus support sustainable practices. Moreover, the efficiency of methanol’s combustion properties and its compatibility with current engine infrastructure promote responsible consumption and its effective resource utilization. By using methanol as a fuel, the sustainable responsible consumption patterns can be encouraged, and this will lead to more environmentally friendly production practices.

7. Conclusions

Methanol, a promising alternative to neat gasoline, has been under observation for quite some time. Its physio-chemical properties have made it quite an attention-grabbing fuel for the research to address the issue of energy demands as well as environmental deterioration. However, there are certain core challenges that must be addressed before the utilization of methanol on commercial scale in the transportation sector.

Cold start issue stands as a prominent challenge when it comes to its utilization in SI engines as a fuel. Methanol’s high heat of vaporization, lower volatility and the presence of water impede the fuel’s atomization, vaporization and combustion during engine ignition phase. These particular attributes of methanol serve as an obstruction because they lead to reduced engine performance, intensified emissions and compromise fuel efficiency. However, with the application of fuel additives, the issue of cold start can be mitigated. Also, by increasing the fuel vaporization and enabling optimal air-fuel mixing, these innovative solutions can pave the way for an effective and sustainable utilization of the methanol in spark ignition engines.

The enhanced emissions of nitrogen oxides (NOx) also present a notable challenge in its usage as an alternative fuel in SI engines. The formation of NOx can be resulted due to peculiar combustion attributes of methanol, which includes elevated flame temperatures, extended combustion duration and lean-burn tendencies. However, by the application of several strategies like catalytic converters, it seems possible to address the issue of enhanced NOx emissions.

The utilization of 100% pure methanol in spark ignition engines seems quite impossible. However, the modification of engine’s fuel delivery and ignition systems in order to accommodate the unique attributes of methanol, including its lower energy content and bizarre combustion characteristics can be favorable. Moreover, another solution is the application of fuel blending techniques for the preparation of ideal methanol-gasoline blends. This approach will not only enhance the combustion efficiency of methanol but also improve its energy content. In addition, modern engine technologies including direct injection and variable valve timing, can be utilized for the purpose of optimizing the performance of 100% pure methanol.

For commercial-scale utilization of methanol in spark ignition engines, the transportation sector needs to focus on infrastructure development, expansion of refueling station network, optimization of logistical section, ensuring safety and addressing of issues related to energy density. The collaboration among the industry stakeholders, policy makers and researchers will play an essential role in addressing the very issue. This will direct the full potential of methanol as a clean-burning, sustainable and efficient fuel for SI engines, thereby contributing to a cleaner and more sustainable transportation sector.

For the issue of lubricant oil deterioration, there is need of more research and development for formulating specialized lubricant oils which can significantly lessen their deterioration during the utilization of methanol in spark ignition engines. These specialized lubricant oils must possess enhanced film-formation properties, suitable additives to neutralize the effect of acidic compounds and better resistance to thermal degradation.

With the use of ANN techniques, a marvelous potential for predicting the utilization of gasoline-methanol blends in SI engines can be identified. ANNs can encompass intricate relationships, ensuring the accuracy of predictions about the several engine characteristics, based on the input variables. With the advancements in ANN techniques, it will surely play a very vital role in the development of sustainable and efficient engine systems for the upcoming generations. Moreover, RSM can be considered as a powerful tool in determining the optimal conditions for the utilization of methanol-gasoline blends in SI engines. This is achieved through systematic exploration of the design space and the utilization of mathematical models derived from the experimental data.

The utilization of methanol in SI engines provides an optimistic pathway for addressing the multiple sustainable development goals. By reducing the impact of climate change, ameliorating the air quality, making the energy resources more versatile and promoting the reliable consumption and maintaining the renewable production, methanol contributes to SGDs of climate action, good health and well-being, clean and affordable energy and responsible consumption and production. However, it is essential to make sure of sustainable production methods, effective distribution platforms and suitable waste management for maximizing the environmental and social perks of methanol usage. Thus, embracement of methanol as an alternative to gasoline in SI engines can promote a more sustainable and greener future.

Acknowledgments

The authors extend their appreciation to the Researchers Supporting Project number (RSPD2023R698), King Saud University, Riyadh, Saudi Arabia, for funding this work.