Greener and Scalable E-fuels for Decarbonization of Transport

Electro fuels or e-fuels are produced by using renewable electricity. They are an emerging class of carbon-neutral drop-in fuels for the transport sector. E-fuels family is large and covers both gaseous and liquid fuels such as hydrogen (H₂), methane (CH₄), methanol (CH₃OH), DME (CH₃-O-CH₃), ammonia (NH₃), synthetic petrol, diesel etc. These E-fuels powered vehicles are superior to battery electric vehicles (BEVs) in overall greenhouse gas (GHG) emissions. E-fuels can be delivered from existing fuel outlets without significant modifications, which is not the case for BEVs. Developing infrastructure for charging the BEVs requires huge investments; therefore, policymakers of the European Union (EU) have shown interest in the large-scale implementation of the E-fuels. Also, a significant advantage of E-fuels is their energy efficiency. The electricity used to power the battery electric vehicles (BEVs) and Hydrogen fuel cells is ~4–6 times and two times higher, respectively than the e-fuels used to power the internal combustion engines (ICEs). This book covers several ways to use these E-fuels in existing engines and their effects on tailpipe emissions. Calibration and optimisation procedures for the adaptation of these fuels are covered in this book. Also, the economics of these fuels is covered.

E-fuels are synthetic fuels, that can be considered greener as they are produced from green hydrogen. Green hydrogen is generally produced by sustainable process like gasification of biomass. The objective of the present chapter is to provide an overview of the alternate fuels utilization and global efforts towards decarbonization of the transport sector by promoting e-fuels. A detailed summary of articles including the gradual efforts for implementation of greener scalable E-fuels is reported. This chapter also discusses the potential alternatives available to decrease the greenhouse gas emissions for cleaner road transportation in brief. This chapter includes a brief discussion on fossil carbon energy carriers such as biofuels, e-fuels and renewable electricity. Further, some barriers in the way of implementation of renewable, greener scalable e-fuels for decarbonization are reported with the possible solutions. This chapter should provide a quick understanding of the present state of the art on E-Fuels.

Despite having a valuable resource like biomass, India has constantly failed to tap its potential. For instance, out of a total annual potential of 29–48 billion m³, the Indian biogas sector only produces 2.07 billion m³ per year. A similar situation has been there with the other biofuel sectors like bioethanol and biodiesel, where we have consistently failed to achieve the set blending targets. This points out the constant mismatch between the previous policies formed in the sector and the actual output received. The chapter analyzes the key factors that have played a major role in shaping the biofuel policies in India after independence. The timeline between 1947 and 2021 is analyzed to understand the processes that went through in the backdrop of biofuel policy formulation. This helps us in getting a micro picture of why these policies have not been able to deploy biofuels as a substitute in the Indian automobile sector at a mass scale. Majorly depending on limited number of first-generation feedstocks hindered the policies to achieve blending targets. It was found that issues like—opting for a top-down approach in initial policies, not scaling up the research and development in the initial stages, lack of coordination between stakeholders, etc., are also the main reasons for not achieving the expected goals. The work can potentially help to formulate a robust way of defining biofuel development pathways in the upcoming renewable boom, which can improve the share of biofuels in the overall renewable sector.

Shipping is the most energy-efficient way for the transportation of goods and it has a substantial role in the global economy. The vast majority of the ships are addicted to fossil fuels as an energy source due to economic advantages, strong bunkering nets, and well-experienced operations of marine diesel engines. However, environmental concerns drive the industry to take precautions on the ship-sourced greenhouse gas emissions, and the International Maritime Organization (IMO), the ruler of the maritime industry, is bringing strict rules to regulate the emissions under The International Convention for the Prevention of Pollution from Ships—Annex VI (MARPOL). On the way of decarbonization and emission-free shipping, marine alternative fuels may draw a framework for the future of the maritime industry. In this perspective, hydrogen is a promising alternative for maritime transportation with its carbon-free structure. Furthermore, green hydrogen is one of the electrofuels for maritime transportation to solve the issue to achieve full decarbonization. The use of hydrogen for ships is still under investigation at the level of research projects. Therefore, elaboration of the feasibility from different points of view for the commercial fleet is necessary to enlighten the future of the industry. This chapter includes information about the status of maritime transportation, recent international maritime emission rules and regulations, and hydrogen compliance with the International Code of Safety for Ships Using Gas or Other Low-flashpoint Fuels (IGF Code). Furthermore, hydrogen production technologies, onboard hydrogen storage methods, hydrogen combustion concepts on marine diesel engines, and fuel cells are reviewed. Lastly, the conclusion section comprises the chapter discussion.

Increasing concerns over environmental issues and traditional resource depletion have heightened the motivation to use clean and alternative fuels. Biodiesel is an alternate renewable fuel to be used in diesel engines. On the other hand, expert studies designate hydrogen as the fuel of the longer term. Ideally, it is possible to possess both zero-greenhouse gas (GHG) emissions, and zero regulated emissions, carbon monoxide (CO), particulate matter (PM), hydrocarbon (HC) and nitrogen oxides (NO_x) from IC engines powered by hydrogen. A dual-fuel combustion system that burns hydrogen as the primary fuel and biodiesel as a pilot fuel is the main focus of this work. Use of diesel in dual-fuel combustion is typical. To completely replace diesel with biodiesel, improvement of cold flow properties (CFPs) of biodiesel is an absolute necessity. Cold flow properties indicate the low-temperature operation ability of any fuel. To render biodiesel usable during winter, biodiesel requires urea fractionation, which is discussed in this study. The most challenges with a hydrogen-operated dual-fuel engine are the power output almost like that of diesel engines, and to sustain stable engine operation at lean engine running conditions. Supercharging can address the power output issue, but it increases the likelihood of premature ignition and knock tendency unless the equivalence ratio and other parameters are properly adjusted. A hydrogen-diesel supercharged dual-fuel engine results are presented in this study. The charge dilution (by N₂) that helps to lower NO_x emissions is also presented. Furthermore, a detailed engine conditions and engine parameters are suggested to make near-zero emissions from hydrogen-biodiesel dual-fuel engine.

The rapid depletion of fossil fuels has prompted the upcoming generations to adopt alternative resources which are similarly efficient and could meet the soaring energy demand. Furthermore, being non-renewable in nature, having an adverse effect on the environment while burning and mining, the replacement of this outdated means of energy supplies will be the future challenge in addressing the environmental and economic issues in a sustainable manner. However, among the practiced alternative sources, the most popular sources are renewable energy (solar, wind, geothermal, biomass energy), nuclear energy, or hybrid nuclear energy. Although the energy demand is somehow getting fulfilled, these are not able to contribute enough to fulfilling energy demand for having some drawbacks and inconsistencies. For instance, the insufficient power generation capacity, relatively lower efficiency, necessitating the huge upfront capital, and dependency on geographical conditions and locations impede their potential in covering the energy demand on a large scale. Besides, nuclear energy poses a security risk and generates radioactive waste. Similarly, biomass energy sources can lead to serious deforestation. On the contrary, hydrogen is getting popularity as an alternative fuel because of its cleaner production, non-toxicity, economic feasibility, and having a satisfactory efficiency than most other energy sources. It’s nonpolluting production from electrolysis and renewable sources, and wide range of flammability implies its scalability and greener solution for transportation. Considering these aspects, hydrogen as fuel may be a promising solution in the future. In this study the evaluation of hydrogen as a fuel over other alternative energy resources has been evaluated in terms of performance and emission characterization. Moreover, the economical assessment carried out in this chapter will make a comprehensive demonstration of the feasibility and prospect of hydrogen over the other sources. Further, this study also identifies some challenges and limitations and their possible solutions regarding the production and use of hydrogen.

Eucalyptus biodiesel (EB) powered CI engine was characterized by low brake thermal efficiency (BTE) and more smoke emission. The inherent oxygen content of nanoparticles could be added with EB leading to improve the oxidation of hydrocarbon that results in low smoke emission. The present study was initially carried out on a compression ignition engine powered by EB considered as reference fuel. Further, this experiment was assessed with the same modified CI engine fuelled with hydrogen enrichment in EB blends. The high energy density of hydrogen may results better combustion efficiency and drastically reduce global emissions. The hydrogen flow rate was fixed at 5 lpm throughout engine operation for enrichment of air. In this experiment, the different combination of fuel blends were used such as Eucalyptus biodiesel 15% + diesel 85% (EB15), neat Eucalyptus biodiesel 100% (EB100), Eucalyptus biodiesel 15% + diesel 85% + Alumina nanoparticle 50 ppm (EB15-A), Eucalyptus biodiesel 15% + diesel 85% + Alumina nanoparticle (Al₂O₃) 50 ppm + hydrogen enrichment (EB15-A-H), neat Eucalyptus biodiesel 100% + Al₂O₃ 50 ppm (EB100-A), neat Eucalyptus biodiesel 100% + Al₂O₃ 50 ppm + hydrogen enrichment (EB100-A-H). The results indicated that EB15-A-H showed 6.6% increase in the thermal efficiency whereas it was 2.5% lower fuel consumption as compared to diesel operation. EB100 powered CI engine indicated 17% lower combustion efficiency as compared to diesel in CI mode. The results also showed that the emission value of CO, HC, and smoke for fuel EB15-A-H were 9.5%, 12.6%, and 15.9% lower when compared to neat diesel in CI mode operation. However, the emission of NOx was slightly higher for the fuel EB15-A-H than other blends. Overall, it was concluded that EB15-A-H as a potential alternative fuel for CI engine application.

The continuous depletion of the earth’s natural reserves has spurred recent research towards searching for alternative fuels. In addition, it is common knowledge that the conventional gasoline from fossils is associated with high gaseous emissions owing to its hydrocarbon content and high flammability when in contact with air in automobile engines. In recent times, fuels sourced from other sources/biomass such as hydrogen and natural gas have also gained considerable attention as alternative fuels. This has also led to the era of electro/e-fuels which are an emerging class of carbon neutral replacement fuels that have the ability to store electrical energy from renewable sources in inherent chemical bonds of liquid/gaseous fuels. However, the major problem associated with their being commercialized for use in their unblended forms is that of high relative volatilities, very low viscosities, high oxidative instabilities, low engine compatibilities etc. hence, the reason they are adopted as additives in gasoline, also it is important to note that biofuels are currently being exploited for use in diesel engines whereas, their use in spark ignition engines is still currently being exploited due to the fact that they also lack some basic properties listed for hydrogen and natural gas but have higher viscosities and give low carbon emissions. This then implies that the world can begin to look towards adopting biofuels in modified forms by blending them with gasoline/natural gas and hydrogen as done for diesel engines so as to further reduce the carbon emissions, as well as improve the ignition potentials, oxidative stability, viscosities etc. of the fuels towards improving the tendencies for their application in compression ignition engines (ICEs). In modern-day research, the role of hydrogen and compressed natural gas in biofuel cannot be over emphasized owing to the high degree of atomization, improved break thermal efficiency, heat release rate, low carbon emissions as well as moderate peak pressures induced in the fuels. Hence, this chapter will focus on the role of hydrogen and natural gas in biofuels, the blending techniques adopted in mixing NG and H₂ with biofuels, their measures of compatibility/property-variations as well as their spray characteristics, and how they related to the carbon contents of these fuel-blends when used in ICEs.

Governments worldwide have imposed strict emission regulations to control GHG emissions from the road transport sector. The industry is under stress to find alternative fuels and technologies to cope with these stringent emission regulations. E-Fuels are the kind of alternative fuels whose production aim towards storing electrical energy from renewable energy sources in the form of chemical bonds of fuels. Soot and NOx emissions are the main problems in diesel-fuelled compression ignition (CI) engines. Using alternative fuels alone can solve the issues related to conventional Fuel, but it has its challenges. Optimization of fuel injection strategies along with the use of alternative fuels has been explored as a solution. The dual-fuel mode has shown superior control over the combustion and simultaneous reduction of soot-NOx in several studies. DME is one of the most promising ultra-clean, alternate CI engine fuels. DME is considered as an e-fuel if production occurs from renewable energy sources. Its superior atomization characteristics result in the homogeneous fuel–air mixture formation. Its higher cetane number (CN) and oxygenated nature help to achieve efficient in-cylinder combustion. This results in lower PM, soot, hydrocarbons (HC), and carbon monoxide (CO) emissions than baseline diesel. However, nitrogen oxides (NOx) and unregulated emissions are higher in DME direct injection (DI) engines. The operating range of DME homogeneous charge compression ignition (HCCI) engines is limited due to knock intensity; however, it can be widened using the dual-fuel mode. DME has ultra-low viscosity, high vapour pressure, and negligible self-lubrication characteristics, which create difficulties in the conventional fuel injection systems to handle the DME. These challenges can be overcome by using high octane number (ON) fuel as an ignition suppressor to reduce the chances of knocking and coefficient of variance (COV) of engine performance parameters with DME used in CI engines. This chapter explores different injection strategies and fuels in dual-fuel mode by considering DME as an E-Fuel. The combustion and emission characteristics of the DME dual-fuel engine are discussed.

The ever-increasing demand for energy, the exhaustible nature of conventional fuels, and increasing pollution have led to an immediate search for clean, sustainable, and renewable alternative energy sources. DME is one such alternative fuel that is quite promising for internal combustion (IC) engines because of several advantages over conventional fuels. DME is the ultimate next-generation e-fuel since it can be produced from renewable feedstocks such as agricultural, municipal sewage waste, and many kinds of biomass fuels by direct and indirect synthesis. However, DME-fueled IC engines have few limitations, e.g., high NO_x emissions, which need to be overcome to expand their usage in production-grade engines. In addition to environment-friendly fuel, there is also a need to investigate emerging, innovative combustion technologies capable of meeting fuel economy targets and complying with the prevailing stringent emission norms. Engines with low-temperature combustion (LTC) concepts are highly efficient and environmentally friendly and offer promising alternatives to conventional combustion engine technologies. Homogeneous charge compression ignition (HCCI), partially premixed charge compression ignition (PCCI), Reactivity controlled compression ignition (RCCI), and gasoline compression ignition (GCI) are a few of the LTC variant technologies, which should be investigated for DME to combine both cleaner and efficient engine technology and environment-friendly alternative fuel. HCCI engine technology is an ideal LTC engine technology with higher efficiency. However, there are some limitations of HCCI engine technology, such as limited operational range. Hence, other LTC engine technologies are being widely investigated. PCCI engine technology is one of them. Factors such as lean premixed charge, high compression ratio, and multi-point spontaneous ignition lead to excellent fuel economy and low NO_x emissions. Another LTC engine technology is the RCCI, which uses two different fuel reactivities to achieve excellent engine efficiencies. Low reactivity fuels such as natural gas can be used along with high reactivity fuels such as DME, yielding lower NO_x and PM emissions, reducing heat transfer loss, and increasing engine efficiency. Moreover, the RCCI technology leads to an elimination of the need for expensive exhaust gas after-treatment systems. This chapter examines the concepts of various LTC engine technologies and their performance and emission characteristics, underlying challenges, and way forward for using DME as a fuel in IC engines.

Fossil fuels are seized or stored underground for millions of years and are all non-sustainable resources. They are derived from non-renewable resources that cause irreversible degradation to the environment. Fossil fuel related prominent drawback of limited petroleum reserves, the concentration of global warming, harmful emissions and stores in specific areas. This has led to a situation where the use of alternative fuels such as natural gas, biodiesel, hydrogen, alcohol and dimethyl ether is under intense scrutiny. Compared to other candidates, DME (CH₃–O–CH₃) appears to have great potential and should be examined as fuel of choice for eliminating the dependency on petroleum. In particular, DME can be used as a clean, high-efficiency fuel for the diesel engines and exhibits minimum environmental impact due to its molecular structure which has no carbon–carbon bonds and much oxygen with respect to diesel fuel. Good burning characteristics, high thermal efficiency, non-toxicity, renewability and high cetane content make it a superior clean, green and scalable fuel as compare to that of fossil fuel. Sustainable application of DMEs requires critical evaluation of performance, efficiency, fuel injection characteristics, combustion and exhaust emission characteristics. Both pure and blended DME fuel is tested in combustion engine to acquire the optimal conditions of various parameters for extracting out maximum and efficient output. Hence, to maximize the sustainability of DMEs, the effects of fuel injection parameters and in-cylinder air motion, such as the pump plunger diameter, nozzle type, fuel injection timing, nozzle tip protrusion, nozzle opening pressure, fuel delivery angle, vapor pressure and swirl ratio on emissions and performance of the DME engine must be critically evaluated and compared with those of diesel engine. The present chapter focuses on adopting suitable changes in fuel injection strategies to enhance the emission and performance characteristics of DMEs fueled engine. Advance methods to sustain DME in the preexisting diesel engine system are discussed by modifying some effective improvements in the engine for getting maximum optimal output. Due to distinguished characteristics of DME from the diesel, the effects of fuel compressibility on compression work spray pattern, atomization characteristics are also compared, which may pave way for maximum exploration of DME as fuel for combustion engine through manipulation of fuel injection strategies.

Energy demand for the transport sector is continuously increasing along with the implementation of stricter emission norms. It is necessary to find alternatives for conventional petroleum fuels. Methanol has emerged as a promising replacement for conventional petroleum fuels in the transport sector. It can be produced using renewable and non-renewable feedstocks. Also, it is considered an E-fuel as it can be produced using renewable electricity. The physicochemical properties of methanol are more suitable for its use in spark-ignition engines. Out of all the technologies, port fuel injection technology is one of the best ways for methanol utilization in existing electronic fuel injection (EFI) engines with minimal structural changes in the engine. The typical properties of methanol like lower calorific value, higher latent heat of vaporization, low volatility, higher laminar flame speed and higher octane number warrants modifications in the injection and ignition strategies in the conventional gasoline engines. For better performance, these strategies must be optimized for corresponding engine operating conditions. The combustion of EFI engines is primarily governed by Electronic Control Unit (ECU), which contains pre-calibrated maps to decide optimum injection and ignition strategy. ECU calibration is the process of determining the optimal calibration tables for an engine. In this chapter, the methodology of ECU calibration for methanol-fueled SI engine equipped vehicles is discussed at length.

To exploit the potential benefits of reactivity controlled combustion (RCCI) of methanol induced diesel dual fuel operation under split injection strategy, the present study has adopted data driven surrogate modelling technique in contrast to the computationally expensive computational fluid dynamics (CFD) platform. For the partial replacement of conventional diesel fuel, port premixed methanol has been introduced in this study as a renewable alternative energy resource considering its renewability and sustainability perspectives [E-fuel]. To explore the challenges and opportunities of RCCI operation the response parameters of nitrogen oxides (NO_x), soot, unburned hydrocarbon (UHC), carbon-dioxide (CO₂), exergy efficiency and co-efficient of variation of indicated mean effective pressure (COV_IMEP) have been studied considering pilot (PIA) and main injection timings (MIA), overall reactivity (R0) and pilot injection mass percentage (PIM) of diesel fuel as the control parameters. A constrained optimization study has been carried out in this investigation based on the response surface methodology under the respective constraints of emission elements as per the EPA Tier-4 emission mandates and operational stability. The study also incorporated a novel customized design of experiment (DoE) for the multivariate exploration of design space followed by a thorough analysis of the robustness of design space, which has been characterized through the measures of fraction of design space (FDS) metric, D-optimality criteria, G-efficiency and condition number (CoN). Further, desirability based multi-criteria decision making approach has been undertaken wherein, the highest desirability was observed as 0.832. Subsequently the optimization results revealed that the footprints of NO_x, soot, UHC, CO₂ and COV_IMEP were improved by 3.59%, 96.2%, 49.3%, 2.5% and 15.95% respectively compared to the experimental investigation. Besides, with respect to the limits for emission elements specified in the EPA Tier 4 norms, the study yielded 77 and 73.33% lower footprint of NHC and PM compared to the limits specified as constraints. The study further revealed that the CO₂ emission is 42.3% less than the amount of CO₂ consumed in the process of methanol production, which eventually displays the potential of such RCCI operational regime in addressing the carbon emissions crisis.

Fuel requirement for the transport sector is a function of population growth. Currently, the automotive industry is powered extensively by fossil fuels. Diesel and gasoline-powered vehicles contribute heavily to environmental pollution by emitting carbon dioxides (CO₂) and other pollutant species. Greenhouse gas (GHG) emissions from fossil fuel combustion are significantly increasing since 1900. Fossil fuels depletion depends on discoveries of new petroleum reserves; however, the use of fossil fuels won’t be feasible in the foreseeable future due to GHG emissions and other environmental concerns. To tackle these, several researchers have focused on developing alternative fuels. Although low carbon fuels (energy) are being explored for internal combustion engines (ICEs), nitrogen-based fuels are also beginning to attract researchers worldwide. Ammonia has potential as a low carbon fuel since it has a high-octane number and is carbon-free; therefore, it doesn’t produce soot. Other nitrogen-based fuels are not viable low GHG alternatives for vehicles. Despite higher NOx emissions, ammonia has potential for heavy-duty power generation and the marine sector. This is because, in these applications, the implementation of exhaust gas after-treatment is feasible. Significant challenges that hinder ammonia’s growth in the automotive sector as fuel are (i) narrow flammability limits, (ii) high ignition temperature, and (iii) low flame speed. Also, ammonia’s higher heat of vaporization reduces the temperature when ammonia makes a phase transition from liquid to gas, reducing the in-cylinder temperature. Currently, vehicles are not operated using ammonia as fuel because its production involves extensive use of natural gas, which is not a zero-carbon fuel. Biogas is a sustainable carbon-free feedstock for producing ammonia, which uses a carbon-free path from well-to-tank (WTT). Ammonia can be produced from hydrogen, obtained from electrolysis of water and nitrogen obtained from air. Since, the electricity could be generated from renewable energy sources, ammonia can be considered as E-fuel. This chapter covers production methods, properties, environmental and health aspects, storage and transportation, and the potential of ammonia as a transport fuel in compression-ignition (CI) and spark-ignition (SI) engines. Pure Ammonia operation and dual-fuel modes are extensively discussed for both CI and SI engines. Hydrogen as a combustion improver is also covered towards the end of this chapter. However, for realizing the potential of ammonia as fuel, it is important to determine feasible Ammonia induction and combustion techniques applicable to ICEs, which would enhance engine performance in the entire operating range.