Application of Clean Fuels in Combustion Engines

Energy and the environment are the primary concerns for the transportation sector. Besides, the rapidly shrinking petroleum reserves are already alarming. All these, push the governments to find solutions for alternatives able to reduce the carbon footprint and pollutant emissions. Indeed, recent directives push toward carbon–neutral mobility by 2050. The electrification of the propulsion systems represents the priority. However, the research community has demonstrated as the application of cleaner fuels or zero-carbon fuels in the transport sector represents a valid medium-term alternative for decarbonizing the sector. This accelerates the alternative fuels requirements. In this context, renewable fuels, such as bio-alcohols, biogases are considered promising solutions. In this regard, the chapters of this book are based on aspects related to the technologies, methodologies for improving the combustion process and emissions trends applying cleaner fuels to internal combustion engines.

The increasing concern of global warming due to the ever-increasing amount of greenhouse gases (GHG) such as carbon dioxide (CO₂) and pollutant emissions induces regulatory authorities to stricter emission legislation in the transportation sector. In this context, renewable fuels, such as methanol and ethanol, are considered a promising solution to mitigate the carbon footprint and reduce engine-out emissions. Based on the several studies published in the specific literature, this work aims to summarise and normalize the main outcomes, highlighting the pro and cons of exerting alcohol fuels in compression ignition engines through a critical literature review for helping the researchers, who start to work on these applications. Both dual-fuel and direct-injection fuelling concepts of diesel and alcohol (ethanol and methanol) in compression ignition engines are discussed. Analyses on the combustion, emissions and performance and CO₂ are carried out. Depending on the fuel supply method and the engine type, the use of alcohol fuels performs differently in terms of emissions and engine performance. Dual Fuel combustion mode, port fuel injected alcohol, and direct-injected diesel emits higher HC and CO, while diesel-alcohol blends perform as diesel. Generally, the blends characterized by lower alcohol concentration than dual-fuel perform higher indicated thermal efficiencies. Significant benefits on NOx-soot trade-offs are observed, independently on the fuelling mode, NOx concentration, and engine type by using alcohols. The soot reduction reaches values up to 70%, and the lower carbon content of alcohols fuel reduces the CO₂ up to 15%.

Carbon dioxide (CO₂), nitrogen oxides (NOx) and soot emissions are primary concerns and the most investigated topics in the automotive sector. Indeed, recent governments directives push toward carbon–neutral mobility by 2050. In this framework, zero-carbon fuels, as hydrogen, or renewable low carbon alcohol fuels, play a fundamental role. To this aim, in this chapter, the main results on largely used alcohol fuels application in spark-ignition (SI) engines are discussed. Aspects inherent ethanol and methanol production processes, chemical-physical properties and their application in SI engines are presented. Different engine fuelling strategies, dual fuel and blend are analysed. Alcohols have higher enthalpies of vaporisation and research octane number (RON) values as well as excellent anti-knock ability compared to gasoline. This effect enhances in dual fuel mode. Ethanol and methanol have higher thermodynamic conversion efficiencies than gasoline combustion. Cycle to cycle variation is in line with gasoline values. In general, NOx decreases with alcohol fuels, and the best results are achieved in blend mode with a reduction of up to 30% with methanol compared to gasoline. Independently of the fuelling mode, significant benefits on particle number emissions are observed by using alcohol fuels. Carbon monoxide (CO) and hydrocarbons (HC) emission trends strongly depend on fuelling mode and engine operating conditions. Additionally, the lower carbon content of alcohol fuels reduces the CO₂ emissions up to 10% compared to reference gasoline.

Engine research community and automobile manufacturers are making considerable effort to look for the alternative solutions of conventional diesel and gasoline for internal combustion engines (ICEs) and power production. Several developing technologies including electric vehicles (EVs), fuel cells, hydrogen powered engines, and other technologies are being employed as an alternative to ICEs. Studies suggest that the use of alcohol fuel provides substantial advantages over traditional fuels with lower modifications in existing engine technology. Use of alcohol fuel in ICE is possible through various ways, each has its own advantages over the other alternatives. In this book chapter a thorough review has been conducted of the various strategies for utilization of alcohols in ICEs, their effect on combustion characteristics and emissions formations has been presented and discussed.

Degradation of air quality, rising overall temperature of the earth, dependency on fossil fuels, and energy security are among the primary reasons driving the alternative fuel initiatives worldwide. Methanol is considered by many researchers as one of the relatively cleaner, carbon neutrally producible alternatives to traditional internal combustion (IC) engine fuels. Methanol being liquid at standard conditions can allow the pre-existing infrastructure for storage and transportation of traditional fuel to be used with minimal modifications. However, there are challenges with methanol when used as IC engine fuel compared to conventional fuels such as diesel or gasoline. This chapter begins with a summary of methanol utilization in the market and IC engines, followed by methanol characteristics, and then the comparison of methanol with traditional fuels is presented. The challenges in the design of fuel injection systems for methanol are discussed in detail. Methanol and diesel have a substantial difference in their properties, therefore, modifications in fuel injection systems are required in the diesel engines to use methanol fuel. A summary of injection strategies for methanol in CI engines, including recent studies and their engine performance along with engine modifications is presented. The challenges in the design of fuel injection systems for methanol are discussed in detail. An overview of methanol injection strategies in compression ignition engines, including recent research and its engine performance and engine improvements. Low temperature combustion has been known to reduce soot and nitrogen oxide emissions. The studies related to performance of methanol or methanol-diesel in LTC mode are also reviewed. Finally, an overall perspective is provided, emphasizing the performance of methanol in IC engines. The study concluded that methanol has better LTC characteristics. It is very promising in limiting engine soot and nitrogen oxide to an ultra-low level.

Butanol is actively being researched by scientists for its suitability as a renewable fuel for internal combustion engines. Physical and chemical properties of butanol motivate researchers to use it as a fuel in internal combustion engine. Butanol is a four-carbon alcohol and has five isomeric structures. Butanol has a comparatively higher energy density and lesser vapor pressure compared to other alcohol such as ethanol, which makes it more attractive as fuel or blending agent. The objective of this chapter is to examine the potential of bio-butanol as a replacement for conventional fuels such as diesel/gasoline in internal combustion engine. To fulfill this objective, a literature review was performed and some important results were highlighted. In addition to literature review, experiments were performed in a single cylinder diesel engine to investigate the impact of diesel fuel blended in small proportion with butanol. In this regard, DB15 (15% v/v blend of butanol with diesel) was selected as a test fuel and results were compared with baseline diesel. Results pertaining to performance characteristics such as brake specific fuel consumption, brake thermal efficiency and brake specific energy consumption are discussed. The novelty in the current study is that numerous current and upcoming research directions are outlined in chapter. Research in ethanol/methanol fuel has increased since past few decades, but research on butanol is still limited.

Soot emission or carbon black is considered as a major challenge recently. Generally, internal combustion engines have been introduced as the main source of these materials specially in urban areas. Different methods are proposed to control soot emission of diesel engine such as DPF (Diesel Particulate Filter) which is attached to the engine exhaust line and the microstructure and size of NPs were introduced as important parameters on its efficiency. In addition, biodiesel has become widely accepted as an appropriate substitution for diesel fuel, however, the using of biodiesel fuel may change the structural characteristics of soot emission. It is observed that biofuel has higher soot oxidative reactivity, and it is more reactive than diesel fuel, which is an advantage for DPF regeneration. Smaller size of particles in biodiesel fuel soot compared to diesel fuel is mentioned as a reason for this phenomenon. For instance, it is reported that the fractal dimension of micro algae, cotton seed, waste cooking oil, eucalyptus oil, tea tree oil and diesel fuel is 2.02, 1.97, 1.85, 1.75, 1.80, 1.73, 1.69 (nm) respectively. Filtration efficiency which is a crucial characteristic of the DPFs for biodiesel fuel and diesel fuel was found to be much different. These differences are attributed to the morphology of the produced soot of the fuel burning. The source of the biodiesel fuel is introduced as an impactful parameter on engine NPs morphology and size. For example, the primary diameter of the soot emission from the above fuels is 20.1, 14.8, 14.8, 15.5, 14.5, 15, 17.5 and 20.75 nm, respectively. The result of these study reveals that structure and morphology of soot emission come from biofuel combustion is different from diesel fuel and these properties should be investigated for any unique biofuel resource individually. However, the smaller size of the biofuel combustion generated soot is an advantage of these fuels to enhance their oxidation reactivity.

Recycling waste products is necessary to sustain the environment without being polluted. This chapter includes the recycling of vegetable waste, fruit waste, plastic waste and engine oil waste to produce alcohol, pyrolysis plastic oil and treated waste engine oil. Various proportions of these fuels are blended with diesel and tested for solubility. The properties of the fuel blends are found as per the guidelines of ASTM standards. By comparing the properties such as cetane number, energy content and kinematic viscosity considering diesel fuel as base, competent blends are chosen. Performance, combustion and emissions of fully instrumented CI engine is performed by fueling the chosen blends under various brake powers. Results of the properties test indicates that the blends containing 15% bioethanol, 85% of diesel along with pyrolised plastic oil of 20% (BE15RPO20); pyrolised plastic oil of 75% along with 25% of biobutanol (RPO75BB25); treated waste engine oil 20% along with 15% of bioethanol and 85% of diesel (BE15PWEO20); treated waste engine oil 75 and 25% biobutanol (PWEO75BB25) are found to be competent. Out of the four, the two blends containing 15% bioethanol are found to be producing 5.6% higher thermal efficiency. Other two blends are producing 0.7 and 1.7% higher thermal efficiencies. All the four blends produce 6–10% low emissions of oxides of nitrogen at higher brake power higher than 70%. However, the emissions at lowest brake power are found to be marginally higher. This replaces around 80% of diesel fuel for fueling CI engines, thereby decreases pollution to environment.

The European Union (EU) ambitious targets planned for 2050, are demanding for zero greenhouse gas (GHG) emissions. In this context, member countries governments, large companies and SMEs are working to meet their products, services and goods to these new requirements. EU has emphasized measures to mitigate emissions in the transport sector, which represents a quarter of GHG emissions. Therefore, the development of vehicles powered by alternative fuels such as natural gas, liquefied petroleum gas and electricity, has been spectacular in recent years. However, alternative second-generation fuels are being developed. They are called renewable gases such as biomethane, hydrogen and syngas which further reduce GHG emissions. The aim of renewable gases is to remove CO₂ from the feedstock and/or the production processes, which presents a wide range of R&D opportunities. There are still many barriers such as the high price of vehicles, the availability of refuelling points in large cities and transport corridors, the confidence of all stakeholders in these technologies, the development of low emissions policies and the Administration’s support for fleet renew. Therefore, it is essential to develop R&D projects to minimize emissions and try to reduce the overall costs (production, transport and supply) of renewable gases. Currently, the price of natural gas for vehicles is 60% lower than gasoline 95 and 40% lower than diesel per 100 km. These trade margin are a firm argument for the development of renewable gases for sustainable mobility and for their injection into the grid. This Chapter analyses the state of the art and the necessary lines of research in order to efficiently apply renewable gases to sustainable mobility.

In the present world, there is a huge demand for spark ignition (SI) engines in transportation sector as there is an increase in population of light commercial vehicles such as motorcycles and cars. Petrol powered SI engine produces less noise and vibration with high thermal efficiency as compared with diesel engines. Utilization of hydrogen as fuel in SI engines has found to improve the combustion and performance characteristics of engines. The primary fuel petrol and secondary fuel hydrogen are induced in the inlet manifold. The various percentage of hydrogen used in the SI engines include 5, 10, 15, 20 and 25%, together with different ratios of petrol fuel. Whenever hydrogen induced in the SI or compression ignition (CI) engines for safety purpose a flame arrester is used. This current was assessed to calculate the combustion, performance and emission characteristics of a high-speed single cylinder SI engine operating with different hydrogen–petrol blends. The various percentage of hydrogen was inducted along with petrol fuel to reduce the tailpipe emissions. The hydrogen was mixed with base fuels such as P95H5 (95% petrol, 5% of hydrogen), P90H10 (90% petrol, 10% of hydrogen), P85H15 (85% petrol, 15% of hydrogen), P80H20 (80% petrol, 20% of hydrogen) and P75H25 (75% petrol, 25% of hydrogen). About 20% of hydrogen blend showed greater brake thermal efficiency of 26.8% when compared with base fuel. Furthermore, 25% of hydrogen mixed with petrol drastically reduced the hydrocarbon content, carbon monoxide content and exhaust gas temperature petrol by 22.8%, 40.26% and 15.61%, respectively, when compared with base fuel at full load condition.

In order to reduce the use of fossil fuels in the transportation sector, various alternatives have been explored in the past. Biogas is an interesting candidate in this context with its large potential in countries like India, which can be utilized for vehicular as well as decentralized power generation applications. Biogas is a renewable fuel that is produced from organic waste materials through anaerobic digestion process. The produced raw biogas contains methane as the fuel; however, carbon dioxide is also present in considerable amount. This inert gas reduces the flame speed and heating value of biogas and eventually deteriorates engine performances. The auto-ignition temperature of biogas is high enough that it cannot be directly utilized in the diesel engines. One of the easiest and flexible ways to utilize biogas in diesel engines is through ‘Dual Fuel (DF)’ technique. In this technique biogas is used as the main gaseous fuel and another liquid fuel (commonly diesel) is used as the pilot fuel. In this way, existing diesel engines can use biogas as the fuel with minimum engine modifications. Nevertheless, the performance of biogas DF engine has been found to be much poor than the standard diesel engine, especially at the low loads. It has been shown that there are many engine parameters, e.g. engine load, type and quantity of biogas, injection timing of the pilot fuel etc., which can affect the performance and emission characteristics of a DF engine. This article presents an overview of these effects on a biogas operated DF engine and suggests various techniques to enhance the performance of the engine.