Renewable Fuels for Sustainable Mobility

Transportation sector is facing new challenges in terms of stringent vehicle tailpipe emissions and CO₂ emission reduction, moving the sector towards decarbonisation. In this view, research in the automotive industry has been developing alternative solutions for the mid- and long-term timeframe. The main pillars are electrification, energy storage, zero-carbon renewable fuels, etc. In the transition phase towards zero tailpipe emission vehicles, improvements in state-of-the-art propulsion systems are still required. Several studies in combustion development through advanced techniques, alternative fuel applications, and after-treatment systems improvements are still facing challenges. Using alternative fuels for internal combustion engines is a sustainable way to use these devices for transportation and to reduce emissions simultaneously. This book includes a detailed review of renewable fuel solutions for sustainable mobility. It covers various renewable fuels such as hydrotreated vegetable oils, methanol, ethanol, butanol, dimethyl ether, and biodiesels. This book emphasises the role of renewable fuels as one of the solutions for sustainable transportation.

The COP26 goals rapidly accelerate the shift of road transport to electric vehicles (EVs). However, the global transition to EVs should be assessed carefully. A forced transition to electric mobility without tailored solutions for each case can increase greenhouse gas (GHG) emissions. In this context, low-carbon fuels can be considered a promising short-term solution to efficiently reach the carbon neutrality target. This manuscript aims to highlight the competitive advantages of hydrotreated vegetable oil (HVO) over commercial diesel fuel. Recent works on HVO are considered, ranging from exploring the production processes and spray evolution characteristics to the various engine strategies to highlighting the potential. Greater emphasis was placed on environmental impact assessment, considering the results available for Life Cycle Assessment (LCA) and Well-To-Wheel. The main characteristics and influences of HVO in CI engines are assessed on the combustion process, GHGs, and pollutants emissions. The results show the high potential of the HVO to reduce the impact of the road transport sector actively. It is highly compatible with existing engines and fueling systems while ensuring lower CO₂, CO, THC, PM emissions, and combustion noise levels with similar efficiency and fuel consumption. Additionally, the residual feedstock can assure up to 75% GHG over the whole life cycle. Therefore, sustainable fuels, such as HVO, combined with advanced technologies could not only support the reduction of tailpipe emissions but also benefit the overall CO₂ assessment.

Transport sector is one of the largest contributor to global greenhouse gas (GHG) emissions. GHG emissions are the leading cause of global warming.  Various government bodies have imposed strict emission legislation across the worldwide on industries with large carbon footprints. Therefore, the transport sector is greatly strained to meet stringent emission norms. Crude oil refined products such as diesel and gasoline are the primary fuels used in the transport sector. Greener e-fuels with low carbon footprint are suitable alternatives to replace the fossil fuels, which can reduce the life cycle CO₂ emission and meet emission norms. Dimethyl ether (DME) is one such greener alternative to diesel. Diesel-fuelled CI engines are majorly emitting the NO_x  and soot emissions. DME can reduce NO_x and soot emissions simultaneously. The molecule of DME does not contain a C–C bond. Therefore, it resists the formation of soot precursors. High-temperature zones are the ideal zones for NO_x formation in an engine combustion chamber. The high latent heat of vaporisation of DME reduces the in-cylinder temperatures; hence, decreases the NO_x formation. DME also shows a high cetane number (CN), molecular oxygen, shorter ignition delay, and superior atomisation characteristics than baseline mineral diesel. However, lower viscosity, high vapour pressure, longer fuel injection delay due to higher compressibility, and lower lubrication properties of DME makes it difficult to be used by diesel fuel injection equipment (FIE). Certain modifications are required in diesel FIE to operate on DME. This chapter briefly discusses the various modifications required in FIE to utilise DME. The effects of superior properties of DME on various engine parameters are also described.

Environmental pollution from petroleum products for energy generation is of grave concern nowadays. Oxygenated alternative fuels like biodiesels, alcohols, etc., have gained much popularity for internal combustion (IC) engines. Due to their inherent oxygen content, these oxygenated alternative fuels possess lower carbon-to-hydrogen (C/H) ratio for same heating value. Supporting the road map towards decarbonization of mobility, there has been a recent uptick in curiosity about the possibility of alcohols in compression ignition (CI) engines. Biodiesel contains ~10% inherent oxygen (m/m), and alcohols may contains up to 50% oxygen (m/m), affecting the CI engine's combustion, performance, and emission. An overview of CI engines fuelled with oxygenated fuels (biodiesel and alcohol blends) on combustion characteristics, engine performance, and exhaust emissions are presented in this study. Biodiesel and alcohol fuels (methanol, ethanol, and butanol) have been compared to evaluate the impact of different blend ratios, oxygen mass fraction content based on in-cylinder combustion pressure trace, heat release rate, and engine performance as brake thermal efficiency and carbon dioxide (CO₂) emission. Up to 25% lowered CO₂ emission was recorded for oxygenated fuel compared to diesel, with significantly lower particulate emission.

India envisages energy diversification and transition to a cleaner fuel mix for the road transport segment, which contributes to about 75% of the country’s total CO₂ emissions from the transport sector. In this pursuit, electric vehicles are pitted as a ‘one size fits all’ solution to all the problems posed by the current fossil fuel-based transport in the country. The current vehicle fleet running in India is dominated by the Internal Combustion Engine (ICE)-based products (powered by mainly petrol and diesel), and the trend is likely to continue in the near-to-medium term. Therefore, it is necessary to consider alternate fuels for ICE-based vehicles to achieve decarbonization in India’s road transport sector. This study discusses the ICE-based alternate fuel options (natural gas, auto-gas and hydrogen) in the light of 28 identified parameters under the 4A framework of energy security, encompassing technical availability, resource availability, infrastructure accessibility, price affordability, social acceptability and environmental acceptability. The 4A framework analysis is carried out to assess the large-scale deployability of the alternate fuel options. The learnings from a few prominent global experiences (compressed natural gas in Argentina, liquefied natural gas in China, auto-gas in Turkey, ethanol in Brazil, biodiesel in Indonesia and hydrogen research across the globe) have been imbibed in the mapping of the possibilities in the Indian context, keeping in mind the diverse functional uses of different vehicle segments within the road transport sector. Biofuel blends are deployable in the short term for all vehicles running on conventional petrol or diesel, whereas the expansion of natural gas usage is constrained by the lack of availability and accessibility beyond a few nodes. The energy transition in the freight segment would need a complete overhaul of the ecosystem since hydrogen appears to be the most prominent alternate fuel in the medium-to-long term.

The energy crisis, global warming, and air pollution are the major problems of the modern world. Over the last couple of decades, millions of people are suffering due to worsening air pollution. The transportation sector mainly relies on fossil-fueled internal combustion engines, which significantly contribute to GHG emissions. Alternative fuel technologies are promising options for mitigating vehicular emissions. Among the many alternative fuels, methanol is the best contender as dual fuel or dedicated fuel in internal combustion engines. This review chapter presents the efficient use of methanol in CI engines. Many experimental and numerical studies have been conducted using methanol in CI engines. Methanol fueling improves engine performance, and combustion characteristics and simultaneously reduces emissions due to less carbon and higher oxygen content in methanol. Formaldehyde emissions from methanol fueling is a major concern. Although the cetane number of methanol is quite low, chemical properties of methanol make it possible to use it at higher compression ratios, which can be achieved in CI engines, and lead to higher thermal efficiency. The high self-ignition temperature of methanol requires high pressure and temperature for combustion, which can be achieved in a CI engine running at a higher compression ratio. Due to the high LHV of methanol, it can be used in CI engines as a blend with diesel. Methanol acts as the primary fuel in blending, and diesel acts as the pilot fuel for burning the methanol. Without blending, methanol can be introduced with hot boosted air or methanol can be preheated to deal with the cold start problems. There are various methods through which methanol can be introduced in CI engines such as port injection, direct injection, and direct mixture with diesel. In this chapter, we have discussed the effect of methanol on performance, combustion, and emissions (mainly NO_x, SO_x, and carbon-based emissions) in CI engines along with dual-fuel technology.

Among IC engines, diesel vehicles are the major contributors to particulate mass emissions. Renewable fuels play a major role in reducing both gas phase and particulate mass emissions. In addition to renewable fuels, fuel additives are also investigated by scientists to compensate for the limitations of using renewable fuels. In this book chapter, a review of renewable fuels to be used in compression ignition (CI) engine was carried out. In addition to this, an experimental investigation was carried out in a single cylinder, water cooled variable compression ratio (VCR) diesel engine to make a comparative analysis among baseline diesel fuel and diesel + dodecanol (1% v/v) without renewable fuels. Dodecanol was chosen due to its advantages over other fuel additives. Results pertaining to in-cylinder pressure, hydrocarbon (HC) emission, carbon mono-oxide (CO) emission and particulate mass emission are presented. Soot was collected on a 47 mm quartz filter paper using a dilution tunnel and later analysed for soot morphology using scanning electron microscope (SEM). Energy dispersive spectroscope (EDS) analysis was also performed to find out the presence of metals in soot. Gravimetric analysis shows that Diesel + dodecanol (1% v/v) resulted in 2.62 mg of soot deposited on filter paper whereas diesel fuel showed 1.46 mg of soot deposited on filter paper for a duration of 30 min.

A large number of diesel engine applications in the transportation and agriculture sector has become a major concern for environmental pollution. It is quite difficult to improve diesel engine performance and at the same time controlling its emissions effectively. There are various methods to achieve the same e.g., changes in engine design, fuel blending with additives, engine exhaust treatment, etc. The most practical technique for controlling high emissions without degrading engine performance is to modify fuel with additives. Alcohols are the most promising additives which have been used by various researchers worldwide. In the current study, a bibliometric-based study and the role of various alcohol additives in improving combustion, performance, and fumes outflow qualities of CI engines were comprehensively reviewed. Due to higher oxygen levels in the combustion zone, it was found that combining diesel with alcohol reduces the emissions of CO₂, CO, HC, soot, and particle matter.

Liquid transportation fuels from biomass and CO₂ are considered a promising strategic alternative to simultaneously reduce greenhouse gas emissions and fulfill the massive energy demands. Pyrolysis allows the transformation of lignocellulosic biomass into bio-oil (liquid fraction) which can be further upgraded to hydrocarbon fuels by well-known methodologies including catalytic hydrodeoxygenation (HDO) and steam or aqueous phase reforming to transform bio-oil into hydrocarbons and H₂ as promising alternatives to fossil fuels in forthcoming future. The efficient conversion of CO₂ to fuels and useful chemicals is an essential step toward reducing the atmospheric concentration of CO₂. (Electro)chemical catalytic CO₂ reduction is a promising route to convert CO₂ back into valuable chemicals and fuels. The use of carbon materials for biomass and CO₂ transformation has gained impact as an alternative to conventional oxides due to their excellent features including high surface area, electroconductivity, and low cost. This chapter describes the recent works reported in the literature on the use of carbon-based catalysts to convert biomass and CO₂ into sustainable biofuels. An overview of the most promising carbon-based catalysts and processes will be presented, including the main challenges to improve carbon-based catalysts’ performance and to reduce costs to make biomass and CO₂-derived fuels an effective alternative for future mobility.

Global climate change and depletion of resources are crucial issues for modern societies. Moreover, population growth and rapid industrialization result in increased energy demand. To meet ongoing energy demand, developed and developing countries must adopt sustainable waste management methods. In addition to prevention and recycling, waste-to-energy technologies could certainly be beneficial. Except for heat and electricity generation, biofuels can also be produced from waste. Aviation sector is expanding and its greenhouse gas emissions account for about 2% of total global emissions. Aircraft emissions are more persistent in higher altitudes having a greater environmental impact. Hence, decarbonization of the sector is an ongoing challenge. Sustainable aviation fuels comprise a promising solution over the following years. Utilization of waste materials will contribute to the total production of biojet fuels. To date, eight pathways have been certified by the American Society for Testing Materials standards for blending limits up to 50% with conventional jet fuels. The current chapter highlights sustainable waste management methods focused on waste-to-energy conversion technologies for biojet fuel production from waste materials as feedstocks. Current conversion pathways are further analyzed and discussed toward a “greener” and more sustainable future of aviation industry. Hydrotreated esters and fatty acids pathway is the most mature and promising production method fοr oleochemical feedstocks, including waste oils. Thermochemical methods and alcohol-to-jet pathway will contribute to biojet fuel production in the following years.

Due to their great efficiency and fuel economy, gasoline engines, particularly Direct Injection Spark Ignition (DISI) engines, have been extensively developed and employed in passenger vehicles. Stratified and homogeneous modes are the two basic operating modes of the DISI engines. Stratified mode offers superior efficiency at part-load engine operation. Laser ignition coupled with the stratified mode of operation can increase combustion efficiency by enabling multipoint laser ignition. However, there are several challenges associated with optics and laser beam delivery that must be taken into consideration. Since fuel is injected directly, it requires adequate fuel–air mixing, which dictates the combustion characteristics. Hence, spray characterisation is required to assess the potential of laser ignition in the stratified mode operation. For the fundamental spray and combustion investigations, optical techniques such as Shadowgraphy, Schlieren imaging, Laser-Induced Fluorescence (LIF), Mie scattering and Phase Doppler Interferometry (PDI) are used, which are discussed along with their principles. Different spray chamber types are also discussed, along with design considerations and a demonstration of the horizontal cylindrical combustion chamber. This chapter also covers the fundamentals of laser ignition and associated challenges for a stratified mode DISI engine operation.

The combustion in diesel engines is a complex phenomenon involving two-phase flow, fluid–geometry interactions and fluid–fluid interactions. Diesel engines have seen numerous designs of the combustion chamber and injection system over the years since their invention. The initial developments were primarily based on experimental results and predictive theoretical models. However, recent developments in optical diagnostics have enabled researchers to understand in-cylinder combustion in a much more refined way. The hybrid approaches of computational simulations and optical investigations have contributed immensely to developing cleaner and more efficient diesel engines to meet emission norms. However, adopting renewable fuels would require subtle design and strategic changes in modern diesel engines. Extension of current technologies for adopting renewable fuels having significantly different physiochemical properties requires in-depth knowledge of diesel combustion. The chapter overviews the state-of-the-art optical diagnostics for in-cylinder combustion visualisation in diesel engines. The differences between optical and all-metal engines have been highlighted, and various methods to minimise the gaps have been discussed. A comprehensive literature review on the spray flames in diesel engines has been done to summarise the current understanding of diesel combustion. Various parameters affecting flame evolution have been discussed. The effect of fuel properties and the combustion of biodiesel and methanol have been discussed based on flame visualisation studies.