Advancement in Oxygenated Fuels for Sustainable Development: Feedstocks and Precursors for Catalysts Synthesis

By Niraj Kumar

Advances in Oxygenated Fuels for Sustainable Development: Feedstocks and Precursors for Catalysts Synthesis provides a roadmap to the sustainable implementation of oxygenated fuels in internal combustion engines through sustainable production, smart distribution and effective utilization. Focusing on the sustainability of feedstocks, the book assesses availability, emissions impact and reduction potential, and biodiversity and land utilization impact. Existing technologies and supply chains are reviewed, and recommendations are provided on how to sustainably implement or update these technologies, including for rural communities.

Furthermore, effective supply and distribution network designs are provided alongside methods for monitoring and assessing their sustainability, accounting for social, economic, environmental and ecological factors. This book guides readers through every aspect of the production and commercialization of sustainable oxygenated fuels for internal combustion engines and their implementation across the global transport industry.

• Provides multilevel perspectives on how to facilitate the sustainable production of oxygenated fuel and develop new indices for measuring the effectiveness and sustainability of implementation
• Recommends a framework and criteria for assessing the suitability, sustainability, and environmental benefits of oxygenated biofuels
• Describes the fuel properties of all oxygenated fuels and their performance in unmodified and enhanced CI and SI engines

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 9, 2022
• ISBN: 9780323908764

Book preview

Chapter 1

Climate change and the energy sector

Ashok K. Das and Ayushi Sharma,    SunMoksha Power Pvt. Ltd., Bangalore, Karnataka, India

Abstract

Since the 20th century, the climate changes observed are primarily caused by human activities driven by the burning of fossil fuels. The current human contribution to the GHG emission into the atmosphere stands at 9.5 billion metric tons from fossil fuels and 1.5 billion from deforestation and changes in land cover. In 2016, the energy sector alone contributed 73.2% out of 49.4 billion tons of CO2eq GHG emission. With the growing population and increasing economic activities, as per EIA, the energy consumption is projected to grow by approximately 50% between 2018 and 2050. While the major renewable energy interventions can be observed in building and industry (two of the major CO2eq GHG emission contributors through energy consumption), transportation continues to rely heavily on fossil fuels at 96.7%. With the projection of exhausting all of the remaining oil by 2067, incorporation of alternative fuels is becoming more cardinal. This chapter explains in detail the causes and impacts of fossil fuel consumption over the past century, the current alternative measures, specifically in the transportation sector that have been developed and a brief technical introduction to the oxygenated fuels.

Keywords

IPCC report; GHG emissions; natural and human factors; planet; fossil fuels; climate change

1.1 Introduction

The 2021 IPCC Report (IPCC, 2021) highlights that the temperature on the earth’s surface has increased by about 1.07°C for the decade 2010–19 from the 1850–1900 baseline. The report also estimates that by 2081–2100, the global temperature will rise by 1.0°C to 1.8°C under very low GHG emissions scenario, by 2.1°C to 3.5°C in the intermediate scenario and by 3.3°C to 5.7°C under the very high GHG emissions scenario. Over millions of years, this process of warming up and cooling down of the earth has been continual. However, the planet is warming much faster today than it has over the whole of human history. Most of the warming has occurred in the past 40 years, and the 7 most recent years have been the warmest. The years 2016 and 2020 are tied for the warmest year on record (NASA Global Climate Change). According to the IPCC report, the last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago (IPCC, 2021). This change of temperature has had great impacts on the planet (Denchak, 2019).

Over time, both natural and human factors have influenced the earth’s climate system. The climate change that have been observed in the past century are caused primarily by the human activities driven by the burning of fossil fuels. The burning increased the levels of greenhouse gases (GHGs), which trapped more heat in the earth’s atmosphere and caused a rise in the earth’s surface temperature. Natural causes that contribute to the climate change are cyclical ocean patterns, such as El Niño, La Niña, and the Pacific decadal oscillation; volcanic activity; changes in the sun’s energy output; and variations in the earth’s orbit (NASA Global Climate Change). The human impact on climate during this era greatly exceeds that due to known changes in natural processes.

The IPCC (2021) reinforces that GHGs contributed by human activities have been the main drivers in the rising global temperatures. For most of the past 800,000 years, the concentration of GHGs in the atmosphere was between 200 and 280 parts per million. But over the last century, that concentration has exceeded 400 parts per million. The largest known contribution comes from the burning of fossil fuels, emission of GHGs into the atmosphere, and deforestation (Denchak, 2019). The current human contribution to this emission into the atmosphere stands at 9.5 billion metric tons from fossil fuels and 1.5 billion from deforestation and changes in land cover (Herring, 2020). There are two major sinks of GHGs on the earth, namely, the forests and oceans, that absorb about 3.2 billion metric tons per year and 2.5 billion metric tons per year, respectively. However, this amount of absorption falls short of human-produced emission by a net 5 billion metric tons per year (Herring, 2020).

1.2 Human contribution to climate change

Humans have contributed almost 49% of the CO2 emissions over the past 171 years, far exceeding the amount contributed by natural phenomena over 20,000 years, as seen in Fig. 1.1 (NASA Global Climate Change).

Figure 1.1 Global variation of the concentration of CO2 (NASA Global Climate Change). NOAA.

The high GHG emissions due to human activities take place are the result of energy generation via fossil fuels, running the inefficient appliances and devices, and the activity of sectors such as industry, waste and agriculture, and forestry and land use. In 2016 the energy sector alone contributed 73.2% of the 49.4 billion tons of CO2eq GHG emission (Sector by sector, 2020).

The GHG emissions from the energy sector mainly result from energy use in industries, which account for 33% of GHG emissions from the total energy sector, energy use in transport is at 22%, and energy use in buildings is around 24%, all of which depend heavily on fossil fuels, as shown in Fig. 1.2. Table 1.1 provides a summary from the Renewables 2021 Global Status Report on the dependency on fossil fuels in each subsector at a global level (Renewables, 2020).

Figure 1.2 Global greenhouse gas emissions by energy sector (Sector by sector, 2020).

Table 1.1

With the growing population of the world and increasing economic activities, energy consumption is projected to grow by approximately 50% between 2018 and 2050 (EIA, 2019; International Energy Outlook, 2021). As of 2018, 79.9% of total final energy consumption was coming from fossil fuels (Renewables, 2020). In the Business as Usual scenario, in 2050 the primary energy consumption from fossil fuels will be approximately 70% (Energy Outlook, 2020). If fossil fuel consumption continues to be a major source of energy supply, two major issues will arise: (1) GHG emissions will not undergo the reduction required to prevent global temperatures to rise, and (2) fossil fuel reserves, which are already being depleting, will be even less available to support the demand for energy. According to a report on fossil fuels from Our World in Data (Fossil Fuels), coal, natural gas, and oil are expected to be fully depleted within 114, 53, and 51 years, respectively, from 2016. However, the depletion rate is subject to change with time based on the discovery of new reserves and changes in annual production.

1.3 Alternatives

Since GHG emissions come from several sectors and subsectors, sustainable alternative sources of energy are needed to address the forecasted demand for energy. Additionally, interventions are needed to increase the efficiency of appliances and devices that consume energy. As can be seen from Table 1.1, renewable energy–based solutions have started to be part of the energy mix in each subsector. Between 2013 and 2018, global growth in renewable energy was 21.5%, whereas fossil fuels, traditional biomass, and nuclear combined saw growth of only 5.7% (Renewables, 2020).

While major renewable energy interventions can be observed in building and industry subsectors, transportation continues to rely heavily on fossil fuels at 96.7% (Table 1.1) (Renewables, 2020). Between 2000 and 2015 the total energy consumption by transport increased by around 44%. However, the total emissions from transportation increased by only 31%, reflecting some growth in efficiency. Nonetheless, transport remains extremely dependent on oil. In 2015, transportation accounted for around two-thirds of global oil consumption, out of which road transport accounted for half of the oil consumption. Oil demand in the transport sector increased by around 25% between 2000 to 2015 (Everything, 2019).

The GHG emissions from transportation accounted for 16.2% of 49 billion tons carbon dioxide equivalent (CO2eq) in 2016 (EIA, 2019). With the potential for all remaining oil to be exhausted by 2067 (Fossil Fuels), incorporation of alternative fuels is becoming more urgent. Electric vehicles (EVs) are emerging as a promising alternative, such that EVs will shift the energy burden in the transportation sector from oil to electricity. Furthermore, electricity from renewable energy sources can help to reduce the GHG emissions associated with power generation for EVs. There are three types of EVs: all-electric vehicles (AEVs), hybrid electrical vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) (All-Electric Vehicles; Plug-in Hybrid).

AEVs convert 77% of the electrical energy from the energy sources, whereas conventional gasoline vehicles convert about 12%–30% of the energy stored in the gasoline. Therefore EVs are more efficient and economic operationally. EVs also provide a smooth ride, are easy to operate, have stronger acceleration, and require less maintenance than internal combustion engines. The two major drawbacks of EVs are the limited driving range and long recharge time (All-Electric Vehicles). However, both of these issues are being addressed through better batteries and fast charging technologies.

Both HEVs and PHEVs use a combination of electricity and gasoline to operate. HEVs charge batteries while the vehicle is running on gasoline. PHEVs do the same but have an added feature to recharge the batteries with an electrical outlet. HEVs and PHEVs provide better mileage in comparison to AEVs, as the vehicles run on both electricity and gasoline. Since gasoline is used in addition to electricity, GHG emissions from HEVs and PHEVs are less than those from conventional vehicles but not near zero, as in the case of AEVs. The operation cost of HEVs and PHEVs is less than that of vehicles that run on only gasoline. There is not much difference in maintenance costs of HEVs and PHEVs and conventional vehicles (Plug-in Hybrid). Overall, the technologies for electric vehicles are still evolving.

Apart from the AEVs, HEVs, and PHEVs, the transportation sector is also adapting to oxygenated fuel. The ingredients and additives (oxygenates) in oxygenated fuels increase the oxygen content to offset the carbon monoxide that is created from burning the fuel (Oxygenated, 2018). These oxygenates are alcohols and ethers, such as ethanol fuel, methyl tertiary butyl ether, ethyl tertiary butyl ether, and tertiary amyl methyl ether (Fuel Oxygenates Market, 2027). These can be produced from several sources, such as locally available conventional biomass resources. This makes oxygenated fuel biodegradable, reliable, affordable, and eco-friendly (Awad et al., 2018). The production of oxygenated fuel can also be achieved locally, reducing the cost of fuel transportation and its corresponding impact on the environment.

When alcohols are blended with gasoline, there is an increase in octane rating, which helps to reduce issues related to air emission (Awad et al., 2018). According to a study on the impacts of ethanol-gasoline on the engine emissions by Rong-Horng et al. (Chen et al., 2011), if the ethanol amount is between 20% and 30%, it significantly reduces the hydrocarbon and carbon monoxide (CO) emissions. Moreover, increasing the ethanol concentration in gasoline by 10% leads up to 30% decreased in CO emission (Awad et al., 2018).

There are a few disadvantages associated with oxygenated fuels. Owing to higher vapor pressures and low heating value, alcohol fuels lead to higher evaporative emissions that drops the performance of the engine. One of the critical properties of a few alcohols, such as hydroethanol (4%–7%) and fusel oil (5%–20%), is that they have a high moisture content. With high moisture and ash contents in biofuels, there can be problems related to ignition and combustion within an engine (Awad et al., 2018).

References

All-Electric Vehicles All-Electric Vehicles. Fuel Economy, U.S. Department of Energy. https://www.fueleconomy.gov/feg/evtech.shtml.

Awad et al., 2018 Awad, O.I., Mamat, R., Ibrahim, T.K., Thaeer Hammid, A., Yusri, I.M., Adnin Hamidi, M., Humada, A.M., Yusop, A.F. (2018). Overview of the oxygenated fuels in spark ignition engine: Environmental and performance. ELSEVIER, Science Direct. https://www.sciencedirect.com/science/article/abs/pii/S1364032118302065.

Chen et al., 2011 Chen R-H, Chiang L-B, Chen C-N, Lin T-H. Cold-start emissions of an SI engine using ethanol–gasoline blended fuel. Applied Thermal Engineering. 2011;31:1463–1467.

Denchak, 2019 Denchak, M. (2019, July 16). Greenhouse Effect 101. NRDC. https://www.nrdc.org/stories/greenhouse-effect-101.

EIA, 2019 EIA projects nearly 50% increase in world energy use by 2050, led by growth in Asia. (2019, September 24). https://www.eia.gov/todayinenergy/detail.php?id=41433.

Energy Outlook., 2020 Energy Outlook. (2020). Edition, BP. https://www.bp.com/content/dam/bp/business-sites/en/global/corporate/pdfs/energy-economics/energy-outlook/bp-energy-outlook-2020.pdf.

Everything, 2019 Everything You Need to Know about the Fastest Growing Source of Global Emissions: Transportation. (2019, October 16). https://www.wri.org/blog/2019/10/everything-you-need-know-about-fastest-growing-source-global-emissions-transport.

Fossil Fuels Fossil Fuels. Our World in Data. https://ourworldindata.org/fossil-fuels.

Fuel Oxygenates Market, 2027 Fuel Oxygenates Market - Global industry analysis, size, share, growth, trends, and forecast 2019–2027. Transparency market research. https://www.transparencymarketresearch.com/fuel-oxygenates-market.html.

Herring, 2020 Herring, D. (2020, October 29). Are humans causing or contributing to global warming? https://www.climate.gov/news-features/climate-qa/are-humans-causing-or-contributing-global-warming.

International Energy Outlook., 2021 International Energy Outlook. (2021). (IEO2021). https://www.eia.gov/outlooks/ieo/pdf/IEO2021_ReleasePresentation.pdf.

IPCC, 2021 IPCC. (2021). Summary for policymakers. In: Climate change 2021: The physical science basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf.

NASA Global Climate Change NASA Global Climate Change. Evidence: Climate change: How do we know? https://climate.nasa.gov/evidence.

NASA Global Climate Change NASA Global Climate Change. Vital signs: Carbon dioxide. https://climate.nasa.gov/vital-signs/carbon-dioxide.

NASA Global Climate Change NASA Global Climate Change. Overview: Weather, global warming and climate change. https://climate.nasa.gov/resources/global-warming-vs-climate-change.

Oxygenated, 2018 Oxygenated vs Unoxygenated Fuels, SA Oil Directing Energy.(2018, November 30). https://saoil.co.za/oxygenated-vs-unoxygenated-fuel.

Plug-in Hybrid Plug-in Hybrid Advantages and Disadvantages, Cars Direct. https://www.carsdirect.com/green-cars/plug-in-hybrid-advantages-and-disadvantages.

Renewables, 2020 Renewables. (2020). Global Status Report, Ren21. https://www.ren21.net/wp-content/uploads/2019/05/gsr_2020_full_report_en.pdf.

Sector by sector, 2020 Sector by sector: Where do global greenhouse gas emissions come from? Hannah Ritchie. (2020, September 18). Our World in Data. https://ourworldindata.org/ghg-emissions-by-sector.

Chapter 2

Comparative investigation of the suitability of fuel properties of oxygenated biofuels in internal combustion engines

M.A. Mujtaba¹, ², Md.Abul Kalam³, H.H. Masjuki¹, ⁴, M. Gul¹, ⁵, Waqar Ahmed⁶, Manzoore Elahi M. Soudagar⁷ and Luqman Razzaq⁸,    ¹Centre for Energy Sciences, Department of Mechanical Engineering, Universiti Malaya, Kuala Lumpur, Malaysia,    ²Department of Mechanical Engineering, University of Engineering and Technology, New Campus Lahore, Lahore, Pakistan,    ³School of Civil and Environmental Engineering, University of Technology Sydney, Australia,    ⁴Department of Mechanical Engineering, Faculty of Engineering, IIUM, Kuala Lumpur, Malaysia,    ⁵Department of Mechanical Engineering, Faculty of Engineering and Technology, Bahauddin Zakariya University, Multan, Punjab, Pakistan,    ⁶Takasago i-Kohza, Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Kuala Lumpur, Malaysia,    ⁷Department of Mechanical Engineering and University Centre for Research & Development, Chandigarh University, Mohali, Punjab, India,    ⁸Department of Mechanical Engineering Technology, University of Gujrat, Gujrat, Pakistan

Abstract

This chapter discusses all types of oxygenated alcohols used in the automotive industry for internal combustion engines to improve diesel engine characteristics. Biodiesel is a type of biofuel used in diesel engines as an alternative fuel. The physicochemical properties of biodiesel are discussed in detail to analyze the effect on diesel engine performance and emission characteristics. Different oxygenated alcohol properties are discussed. Diesel engine characteristics for oxygenated alcohol–diesel fuel blends are reviewed and summarized. More focus is given to study the effects of oxygen content present in oxygenated alcohols on diesel engine characteristics.

Keywords

Biodiesel; oxygenated alcohols; diesel engine; engine performance; engine emissions

2.1 Introduction

Fossil fuels are being depleted by excessive consumption of fuels in different sectors. In the future, the degradation of fossil fuels represents a serious threat to the energy demand of oil and gas companies in all sectors (Mujtaba et al., 2020). In general, diesel engines are better, owing to high thermal efficiency, durability and reliability, less fuel consumption, and lower CO2 emissions than gasoline engines (Şahin et al., 2014). Biofuels have the potential to provide a viable solution to the global petroleum crisis. Because of their durability and increased fuel efficiency, diesel compression ignition engines are the principal prime movers in transportation, agriculture, mining, the military, and energy (Alagumalai et al., 2020). One of the intriguing alternative fuel sources for diesel engines is biodiesel. The major advantages of biodiesel are nontoxicity, renewability, biodegradability, inherent lubricity, low or no levels of sulfur, a high flash point, and domestic origin (Sajjadi et al., 2016). Biodiesel commercialization is questionable in different regions, owing to its poor physicochemical properties (viscosity, cold flow properties, and oxidative stability). Different research improved these properties to make this biodiesel a potential fuel source for the automotive industry by blending with different oils and alcohols. Biodiesel is produced from edible oils (palm, canola, sunflower, coconut, soybean), nonedible oils (Moringa oleifera, Jatropha curcas, Croton megalocarpus, Calophyllum inophyllum), recycled or waste oil, animal fats (poultry fat, pork lard, chicken fat, beef tallow), and algae (Mofijur et al., 2013). Around the globe, different feedstocks are used as a main potential source for biodiesel production. Examples are sunflower and rapeseed in France; waste oil, soybean, and peanut in the United States; sunflower and rapeseed in Italy; yellow grease and tallow, rapeseed, flax, animal fat, mustard, and soybean in Canada; rapeseed in Germany; waste oil and animal fat in Mexico; rapeseed in Sweden; sunflower and linseed oil in Spain; waste cooking oil and rapeseed in the United Kingdom; cottonseed in Greece; coconut, palm oil, and jatropha in Indonesia; animal fats and frying oil in Ireland; palm oil in Malaysia; karanja, rapeseed, peanut, jatropha, and sunflower in India; tallow and waste cooking oil in New Zealand; palm oil in Singapore; waste cooking oil in Japan; jatropha and coconut in the Philippines; soybean in Argentina; coconut, palm, and jatropha in Thailand; castor, soybean, cotton oil, and palm oil in Brazil; and rapeseed, jatropha, and waste cooking oil in China (Atabani et al., 2012).

According to the survey, 80% of published articles on the effect of biodiesel on diesel engine characteristics (engine performance and emission) reported a reduction in carbon emissions (hydrocarbons and carbon monoxide) and particulate matter (PM) after the year 2000. The main reason behind this reduction is the presence of higher oxygen content in biodiesel. In the literature survey, many researchers reported that biodiesel reduced carbon monoxide (CO) emissions due to higher oxygen content and lower hydrogen/carbon ratio compared to petroleum diesel (Khalife et al., 2017; Xue et al., 2011). On the other hand, many researchers reported an increase in nitrogen oxide (NOx) emissions with the addition of biodiesel in diesel engines as a fuel additive (Elahi et al., 2019; Soudagar et al., 2018, 2020). The major reasons that were proposed for the increase in NOx emissions of biodiesel combustion are radiative heat loss, ignition delay, higher combustion temperature, and oxygen content (Hoekman & Robbins, 2012). Few researchers emphasized that the faster combustion rate of biodiesel was a key factor for higher NOx emissions. The lower heating value of biodiesel may be a reason for high NOx emissions, resulting in higher fuel consumption (Demirbaş, 2000). These shortcomings of biodiesel can be overcome by launching a modern electronic fuel injection system, retarding fuel injection timing, new diesel engine technologies, and additives for improving biodiesel characteristics (Hoekman & Robbins, 2012).

Various oxygenated additives (biodiesel, oxygenated alcohols, bioalcohols, etc.) are added as a fuel additives with petroleum diesel in a diesel engine. In addition, other additives (cold flow additives, detergents, water, metal-based additives, polymer wastes, and carbon nanotubes) can also be used to improve diesel engine characteristics (Khalife et al., 2017). This chapter focused on studying oxygenated fuel additives used with petroleum diesel in diesel engines to improve diesel engine characteristics.

2.2 Effect of diesel engine emissions on the environment and human health

The burning of petroleum fuel has contributed to environmental issues such as climate change, global warming, and human health concerns. Various pollutant gases (e.g., unburned hydrocarbons, NOx, minute PM, CO) released from the burning of fossil fuel in diesel engines pollutes the air, which is harmful to human health (Mujtaba et al., 2021). Several medical diseases (asthma, allergies, etc.) can be triggered by PM in the air. PM can cause cardiopulmonary disease and lung cancer. Formaldehyde causes shortness of breath, nose irritation, nausea, and coughing. NOx emissions cause edema, pneumonia, bronchitis, and irritation in the lungs. Hydrocarbon (HC) emissions cause lung disease, drowsiness, coughing, sneezing, and eye irritation. CO emission cause respiratory or circulatory issues and affects the development and growth of the fetus in pregnant women (Mofijur et al., 2013).

2.3 Types of oxygenated additives for diesel engines

Combustion characteristics should be monitored and controlled for better engine emissions. It is a complicated process and is affected mainly by incomplete combustion due to the lack of oxygen in combustible fuel. The addition of an oxygenated additive with petroleum diesel assisted in the complete combustion process due to oxygenated oxygen in the chemical composition of oxygenated additive. Oxygenated additives increase the oxygen amount in fuel to overcome this incomplete combustion process (Dec, 1997). Many oxygenated fuel additives are used in the automotive industry to improve diesel engine performance and emission characteristics. The major oxygenated additives are biodiesel (Habibullah et al., 2014), acetone (Chang et al., 2013), diethylene glycol diethyl ether (Herreros et al., 2015), dimethyl carbonate (Kumar & Saravanan, 2016), n-butanol (Doğan, 2011), ethyl tert-butyl ether (Górski et al., 2010), ethylene glycol monoacetate (Wang & Liu, 2008), methyl butanoate (Gaïl et al., 2007), poly ethoxy-ester (Yang et al., 2013), glycerin triacetate, methanol (Yilmaz, 2012), triacetin (Rao & Rao, 2011), di-n-pentyl ether (Happonen et al., 2013), ethanol (Shi et al., 2005), dimethoxyethane (Balasubramaniyan et al., 2013), butanol (Rakopoulos et al., 2010), dimethyl ether (Patil & Taji, 2013), and diethylene glycol dimethyl ether (Nabi & Chowdhury, 2006). Physicochemical characteristics of different oxygenated additives for diesel engine application are listed in Table 2.1.

Table 2.1

These oxygenated additives with petroleum diesel resulted in cleaner combustion and reduced carbon emissions (Nuszkowski, 2008). The heating value of oxygenated additives is lower than that of petroleum diesel, leading to dilution of the energy content of diesel-oxygenated additive blends (Farkade & Pathre, 2012). The ignition temperature could be lowered with oxygenated additives with fuel, owing to oxygen concentration in the fuel blends. Fuels ignite earlier, owing to shorter ignition delays because of low heat release, higher cetane numbers (CNs), and lower temperature reactivity with higher amounts of compounds (Coniglio et al., 2013).

Different important properties should be considered in the selection of suitable oxygenated additives for diesel engine application, namely, kinematic viscosity (<4 mm²/s), boiling point (>60°C), energy density, flash point (>50°C), self-ignition temperature, and oxygen content. For the particular reduction of particulate matter emissions, CN and density may also be considered for oxygenated additives (Bertola & Boulouchos, 2000). Ethanol is less corrosive and toxic than methanol (Berglund, 2004). Oxygenated additives mentioned in Table 2.1 are well miscible with gasoline, but most are not miscible with petroleum diesel. Different surfactants and emulsifiers (ethyl acetate, fatty acid methyl ester, tetrahydrofuran (used for diesel and ethanol blend), sodium dodecyl sulfate, and NP-9 (used for a blend of poly ethoxy ester+water+diesel and glycerin)) can be used to improve the stability of diesel-oxygenated additive blends and to prevent phase separation (De Caro et al., 2001; Lei et al., 2012; Pidol et al., 2012; Wang et al., 2012).

2.4 The effect of oxygenated additives on diesel engine characteristics

The effect of different oxygenated alcohols on diesel engine characteristics is summarized in Table 2.2. The addition of oxygenated additives with diesel fuel blends increased the BSFC, owing to the lower energy content and heating value of diesel-oxygenated fuel blends, which required more fuel to be injected to obtain the same output power (Fang et al., 2013). Mujtaba et al. (2021) investigated the effect of oxygenated alcohols (hexanol, butanol, pentanol, ethanol, and propanol) (10% volume) with palm biodiesel-diesel fuel blends (70% diesel+20% biodiesel). Results predicted that engine performance [brake thermal efficiency (BTE) and brake-specific fuel consumption (BSFC)] improved in comparison to P20 biodiesel. The addition of alcoholic additives improved the performance characteristics compared to P20 instead of petroleum diesel. The energy content and calorific value of fuel decreased with an increase in oxygen content, which resulted in higher BSFC (Atmanli & Yilmaz, 2018). P20Pe10 exhibited less BSFC among tested fuel blends, owing to lower oxygen content (18.15%) compared to P20E10 (34.8%), P20Pr10 (26.7%), and P20B10 (21.59%).

Table 2.2