Energy Sources, Part A: Recovery, Utilization, and Environmental Effects ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/ueso20 Effect of alcohol additives on diesel engine performance: a review Tan Trung Truong, Xuan Phuong Nguyen, Van Viet Pham, Van Vang Le, Anh Tuan Le & Van Tam Bui To cite this article: Tan Trung Truong, Xuan Phuong Nguyen, Van Viet Pham, Van Vang Le, Anh Tuan Le & Van Tam Bui (2021): Effect of alcohol additives on diesel engine performance: a review, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, DOI: 10.1080/15567036.2021.2011490 To link to this article: https://doi.org/10.1080/15567036.2021.2011490 Published online: 14 Dec 2021 Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=ueso20 ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS https://doi.org/10.1080/15567036.2021.2011490 Effect of alcohol additives on diesel engine performance: a review Tan Trung Truong and Van Tam Buie a , Xuan Phuong Nguyenb, Van Viet Pham b , Van Vang Lec, Anh Tuan Led, a Institute of Research and Applied Technological Science (IRATS), Dong Nai Technology University, Dong Nai, Vietnam; PATET Research Group, Ho Chi Minh City University of Transport, Ho Chi Minh city, Vietnam; cInstitute of Maritime, Ho Chi Minh City University of Transport, Ho Chi Minh, Vietnam; dSchool of Mechanical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam; eInstitute of Engineering, HUTECH University, Ho Chi Minh city, Vietnam b ABSTRACT ARTICLE HISTORY Environmental hazards are peaking as carbon dioxide emissions have exceeded critical levels Therefore, finding and applying renewable and clean energy sources to compensate for energy needs is extremely urgent Alcohol compounds such as methanol, ethanol, butanol, etc emerging as renewable fuel sources with the potential to replace diesel fuel used in internal combustion engines With properties favourable to conventional fuels such as high oxygen content, high latent heat, low viscosity and density, alcohol-based chemicals are greatly interested in researchers on internal combustion engines The use of alcohol-based biofuels with low blending ratios in pure diesel or/and biodiesel fuel is seen as the alcohol additive used in compression ignition engines In this work, a wide assess ment was made of the properties of alcohol additives as well as their effect on their ability to improve combustion characteristics and engine perfor mance when alcohol additives are used in diesel engines By in-depth discussion and analysis of recently surveyed results on the potential to improve and double impact on brake thermal efficiency, specific fuel con sumption, and exhaust gas temperature, some prospects on the application of alcohol-based additives in CI engines were also given in the conclusion Received July 2021 Revised 17 November 2021 Accepted 20 November 2021 KEYWORDS Alcohol additives; diesel engine; renewable energy; specific fuel consumption; brake thermal efficiency; exhaust gas temperature Introduction Rapid exhaustion of fossil fuels and contamination of the environment caused by emission become serious troubles globally It is difficult to carry out simultaneous improvement of engine performance and emission management (Hoang, Nižetić, and Pham 2020)(Nguyen et al 2021) Combining additives in different concentrations may enhance the properties of diesel fuel substantially to reduce emission to a standard level without deterioration of the engine performance (Atarod et al 2021) (Pourhoseini and Ghodrat 2021)(Hoang and Pham 2021) However, the trend of applying bio-based alternative fuels is still a test of time Indeed, fossil fuels including gasoline and diesel accounted for over 92% of the total fuel supply for the global road transport sector (Zhang, Lin, and Qiu 2021)(Yaïci and Longo 2021), while alternative fuels contributed nearly 8% in 2018 (Figure 1a) (Daphné and Anne 2020)(Vinayagam et al 2021) The growth rates of biofuels such as Hydrotreated Vegetable Oil (HVO), Fatty Acid Methyl Ester (FAME) biodiesel and ethanol are depicted in Figure 1b Indeed, fossil fuels can be conserved by renewable fuels such as biodiesels (ElKelawy et al 2019) (Hoang et al 2021d), vegetable oils (Hoang 2019), biogas (Bui et al 2021), hydrogen (Sok and Kusaka 2021)(Murugesan et al 2021), producer gas originated from biomass waste (Le et al 2022), and CNG CONTACT Xuan Phuong Nguyen phuong@ut.edu.vn Institute of Research and Applied Technological Science (IRATS), PATET Research Group, Ho Chi Minh City University of Transport, Ho Chi Minh city, Vietnam; Anh Tuan Le tuan.leanh@hust.edu School of Mechanical Engineering, Hanoi University of Science and Technology, Vietnam; Van Tam Bui bv.tam@hutech edu.vn Institute of Engineering, HUTECH University, Ho Chi Minh city, Vietnam © 2021 Taylor & Francis Group, LLC T T TRUONG ET AL Figure Global energy (a) and biofuel (b) consumption in the road transport sector (Daphné and Anne 2020) (Le et al 2020) The application of biodiesel can improve the efficiency of the engine but it is impossible to reduce significantly exhaust emission, especially, emission of nitrogen oxide (NOx) can sometimes increase to some extent (Huang et al 2016)(Ong et al 2021) Indeed, oxygen content and cetane number of fuel can affect higher combustion temperature that is mainly responsible for the growth rate of nitrogen oxide emissions (Hoang 2021) In this context, from an economic and environmental perspective, biodiesel is seen as the most promising alternative in the coming decades to diesel fuel The use of biodiesel for vehicles can shorten the life cycle of carbon dioxide that contributes to effective control of global warming However, the benefits of biofuels still not outweigh the disadvantages of their properties The first is that higher values of viscosity and density compared to diesel fuel can cause many problems with injection characteristics (Gülüm and Bilgin 2017)(Hoang 2018), combustion chamber deposit formation (Liaquat et al 2014)(Pham, Le, and Hoang 2019), and lubricating oil degradation (Hoang and Pham 2019) In addition, the stubborn disadvantage of biodiesel, in compression ignition (CI) engines, are out of control for NOx emissions (Ganesan et al., 2021)(Nayaka et al 2021) Meanwhile, economic treatment solutions to reduce NOx emissions are still limited when applied commercially (Żółtowski and Żółtowski 2015)(Pham 2019) Therefore, it is vital to search for chemical additives to blend with biodiesel to improve properties as well as engine performance Being components of fuel, very small concentrations of additives are mixed with automotive fuel, which is the aim of improving, maintaining, or imparting advantaged based-fuel properties The classification of additives can be broadly divided into inorganic and organic Organic additives consisting of the hydrogen-carbon chain have been used popularly by ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS various researchers (P Berg, Berg, and Berg 2019)(Soudagar et al 2020b) Ethanol and methanol are the most widely studied lower alcohols in IC engines In the decade of 1980s, alcohol-based additives were used in initial researches in this field (Hansen, Zhang, and Lyne 2005)(Labeckas et al 2018) and conclusions obtained from these researches showed that the use of ethanol-diesel blends in diesel engines was accepted technically (Qi et al 2020) Alcohol-based additives are impressive additives in terms of higher oxygen content addition and stronger volatility which promote a cooling effect to lower the combustion temperature as well as cleaner-burning (Yilmaz and Atmanli 2017)(Kumar et al 2020)(Kowalski 2015) However, in the last decade, a considerable amount of research on higher alcohols has been recorded along with the advancement of higher alcohol production by modern microbial-based fermentation technologies (Saggi and Dey 2019) Furthermore, a trend of producing alcohol-based second or third-generation biofuels from biomass feedstocks by sustainable pathways is very promising It is apparent that most of the researches were published used alcohol-based additives and among them, the highest contribution belongs to n-butanol, which is about 22% (Sharma 2021) More importantly, in comparison with lower alcohols, higher alcohols have higher energy density, higher cetane number, better mixing stability, less hygroscopic nature and longer carbon chain which is contributes to the improvement of the ignition quality of the alcohol molecules (Koivisto, Ladommatos, and Gold 2015) In the context, higher alcohol-based additives are attracting much interest from researchers because their production and use meet new environmental and specification standards However, in recent years, reviews of alcohol-based additives in CI engines have often focused on the first homologous serries of saturated alcohols (methanol and ethanol) (Zaharin et al 2017) or only on higher alcohols (propanol and butanol) (Kumar and Saravanan 2016) Therefore, a comprehensive review of the relevant literature of production and application on CI engines of the entire range of saturated alcohol homologues from methanol to phytol can add illuminating insights into the remaining gap This work is carried out on the effect assessments of all alcohol additives (methanol-to-phytol) blending with diesel, biodiesel and their blends on combustion characteristics and engine perfor mance Also, this review briefly discusses the production process and the physicochemical and combustion properties of the variety of additives to answer the question of whether additives are suitable for diesel and/or biodiesel or not Last but not least, future research direction and enhance ment in this field will be drawn based on a comprehensive review in which pros and cons and opportunities of the alcohol additive application concerning to performance of engine and combus tion were discussed Production process of alcohol additives Methanol is an important chemical that can be used as a hydrogen carrier, fuel, or feedstock in organic synthesis processes Furthermore, methanol is used in fuel cells that run electric cars (Zhen and Wang 2015) People produce methanol from natural gas, coal, biomass, or CO2 (in the exhaust from cement plants, fossil fuel power plants, or from the atmosphere) Currently, 75% of the world’s methanol is produced from natural gas (Li et al 2018) The process of producing methanol from natural gas includes the following steps: natural gas reforming to produce syngas, converting syngas to crude methanol, then distillation of crude methanol to obtain the required purity of methanol In addition, the process of producing methanol from coal or biomass also includes gasification to produce syngas, synthesis of crude methanol, and refining of crude methanol In industry, methanol is produced mainly from syngas (a mixture of CO, H2, and a small amount of CO2) (Blumberg, Morosuk, and Tsatsaronis 2017) However, with fossil fuel resources increasingly depleted, the option of producing methanol from natural gas and coal needs to be gradually replaced in the future In addition to the problem of raw materials, the production of methanol from fossil fuels also releases a large amount of CO2 emissions into the environment, causing climate change Therefore, the direction of methanol synthesis directly from CO2 and H2 is of particular interest In which, the reaction to generate CH3OH is exothermic and reduces the volume, so reducing the temperature and increasing the pressure of the T T TRUONG ET AL reaction will shift the equilibrium to form CH3OH (Li and Tsang 2018) The technology to convert CO2/H2 into methanol has the advantage of reducing the cost of methanol production by 28% compared with the traditional technology from syngas Besides, the application of membrane reactor technology can also reduce production costs by about 20% (Giuliano, Freda, and Catizzone 2020) In addition to the economic benefits, this research direction also has great environmental implications Ethanol is produced by hydrolysis and fermentation of lignocellulose-containing agricultural wastes (such as rice straw, corn stalks, etc.), from energy grasses or other energy crops (Hoang et al 2021c)(Hoang et al 2019)(Chen et al 2021) The end product is the same as conventional bioethanol, for blending with gasoline and diesel Cellulose ethanol has the same properties as corn ethanol, but because it is created from the residue left on the ground after corn is harvested, this production cycle reduces carbon dioxide emissions by about 210,000 tons annually (Liu et al 2019) Moreover, the second generation of ethanol has escaped competition with the food industry because it uses only agricultural waste and huge sources of wood waste (Bharj, Singh, and Kumar 2020)(Pham, Tran, and Hoang 2018) Indeed, there are three types of ethanol fermentation from lignocellulose including separate hydrolysis and fermentation, simultaneous hydrolysis and fermentation, and consolidated bioprocessing, shown in Figure Separated fermentation and hydrolysis was the first type of fermentation in ethanol production from lignocellulose (Tavva et al 2016) In which hydrolysis and fermentation are operated under favourable conditions, the efficiency of both processes is high On the other hand, for the second method, hydrolysis and fermentation are carried out at the same time in the same apparatus Therefore, the hydrolysis here is usually performed by commercial enzymes, and enzymes are introduced into the apparatus when microbial culture for fermentation (Harris et al 2014) However, because enzymatic hydrolysis and both hydrolysis and enzymatic processes not take place under optimal conditions, the yield is lower and more time-consuming than hydrolysis and separate fermentation Finally, the process of ethanol production from lignocellulose that has attracted Figure Pathway for ethanol and butanol production from lignocellulose biomass (Hoang et al 2021b)(Satari, Karimi, and Kumar 2019) ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS much recent interest is consolidated bioprocessing It is a low-cost, environmentally friendly process because the processes take place in the same device and only microorganisms are used to carry out these processes However, because of its multi-tasking nature, almost no microorganism can effec tively fulfill the tasks of an integrated biological process (Jin et al 2016)(Gełesz et al 2017) Even so, this is a promising trend of the future Production of butanol can take advantage of the existing infrastructure of ethanol production The oxo petrochemical process is the most feasible for the cheaper production of butanol from different biomass sources (Nanda et al 2017) The fermentation to produce butanol uses bacteria, while the fermentation to produce ethanol is mainly yeast Butanol fermentation requires less energy, but the product separation scheme is more complex Currently, in the world, there is a lot of infrastructure and many ethanol production plants from cane sugar and grass It would be political and economic to abandon all previous fundamental investments to recreate a new system for new fuel production In the first half of the 20th century, the production of butanol as a solvent, and other chemical applications, mainly used the microbial fermentation of acetone-butanol-ethanol (ABE bacterial fermentation process) In 2015, a joint venture project between BP and Dupont on bio-butanol production by ABE process in China was implemented, which has brought many prospects to promote this new fuel consumption market (Jiang et al 2015) Besides the current process like ABE or oxo synthesis for biomass, they all announced their pursuit of improved diversification of biomass sources for biorefineries Compared with other pre-feasibility projects such as the production of ethanol from cellulose, hydrocarbons from biomass, and diesel from algae, bio-butanol production from different biomass sources is the most feasible (Nanda et al 2017) With the advantage of the inherently low-cost oxo synthesis (Kazemi Shariat Panahi et al 2019), when successful in commercializing butanol production from diverse biomass sources, the cost will be lower and will help the market have a more abundant fuel supply in the future Furthermore, alcohols with a high carbon structure can be produced from coal-derived syngas They can be prepared at bior efineries with a combination of structural ethanol thanks to the ageing process For example, new biocatalyst-assisted conversion technologies have improved the yield of pentanol production from glucose or glycerol (King et al 2015) Properties of alcohol additives The exhaustive information of physicochemical and combustion behaviour of additives has a contribution to understanding the typical properties of blends It will be straightforward to under stand the quality of mixture and characteristics of combustion during the burning process of fuel blend with supporting to outstanding properties of oxygenated chemicals The detailed physicochem ical properties of different alcohol-based additives are given in Table All properties of fuel additives not only have the role of great importance but also affect to consider the fuel blend combustion process Hence, the following suggestions are recommended in choosing alcohol-based additives for blending with pure diesel fuel or/and biodiesel (Heywood 2011)(Ganesan 2012)(Hadiyanto et al 2020) Viscosity and density of alcohol additives are lower than that of diesel fuel, which preserves these blends in stable and soluble conditions as well as improves additive-fuel blends pumping In blending with diesel fuel, the boiling point of the blended additive plays an essential role in uniform combustion Cetane number and oxygen content of alcohol additives are desired as high as possible to reduce the ignition delays as well as minimize knock chance, resulting in complete combustion of fuel (Hoang et al 2021a) Additives with lower latent heat can support the combustion process of the blend to happen better and quickly Nevertheless, most alcohol additives have a higher value of latent heat compared to diesel fuel Some of the recommendations from engine manufactures reported that a lower heat value of additives is not lower than diesel fuel because specific fuel consumption can rise if the value of this parameter is low Therefore, cost parameters should be considered when selecting an additive Additives with a lower auto-ignition temperature should be kept in mind for proper fuel blend combustion T T TRUONG ET AL Table Physico-chemical and combustion properties various alcohol additives Density Latent Boiling Oxygen Molecular (kg/ Viscosity heat point Cetane content Additive formula m3) (cSt) (kJ/kg) (°C) number (%) Methanol CH3OH 729 0.54 1178 64 05 50 Ethanol Lower heating value (MJ/ kg) 20 C2H5OH 792 1.04 840 78 07 34 27 Propanol C3H7OH n-Butanol C4H9OH 804 810 1.74 2.20 728 585 97 118 12 25 26.6 22 30.6 33 Pentanol C5H11OH 814 2.89 308 138 20 18.2 34.7 Hexanol C6H13OH 822 5.32 486 157 23 15.7 39.1 Octanol C8H17OH 827 - - 195 39 12.3 52.9 Decanol C9H19OH 830 6.5 - 233 50 10.1 - Phytol C20H39OH 851 63.5 - 204 45.9 5.4 43.6 Autoignition temperature (°C) Ref 470 (Mujtaba et al 2020) 434 (de Menezes et al 2006) 350 (Şen 2019) 385 (Sukjit et al 2012) 300 (Yilmaz, Atmanli, and Trujillo 2017) 285 (Ramesh et al 2019) 270 (Soudagar et al 2020a) 255 (Rami Reddy, Murali, and Dhana Raju 2020) (Nanthagopal et al 2020) The oxygen content in alcohol additives plays a significant role in improving the oxygen content of the fuel The increase in the atomic oxygen content of an alcohol additive fuel enhances the combus tion quality in the combustion chamber It is believed that the increase in ignition capacity and the decrease in ignition delay are a consequence of the decrease in ignition temperature caused by the presence of oxygenated additives in the fuel (Fayyazbakhsh and Pirouzfar 2017)(Wang and Yao 2020) The degree of influence of alcohol additives depends on the atomic oxygen concentration in the compound as well as in the overall blends It is clear that the lower alcohols have significantly higher oxygen content than the higher alcohols, while the low calorific value sees the inverse Moreover, the low calorific value of alcohol additives is lower than that of biodiesel fuels (Le et al 2022) That makes the energy value of the alcohol additive mixture lower in comparison to pure fuel As a result, more amount of fuel with alcohol additives is required to meet the energy balance More clearly, the properties of the fuel such as density, flash point, kinematic viscosity, surface tension, and acidity index, are significantly affected by the content of alcohol additives (Kumar et al 2018) For example, in a study on adding ethanol to the sesame oil-based biofuel, Khalife et al (Khalife et al 2017) noticed a decrease in density, viscosity, and flashpoint in the modified blends On the other hand, with the addition of more OH radicals, there was an increase in the acidity index of the fuel In addition, (Qi et al 2020) combined two main fuels including biodiesel based on castor oil and pure diesel with two saturated alcohol additives including ethanol and n-butanol, resulting in improving key biofuel properties such as density, viscosity, oxygen content and latent heat of tertiary and quaternary fuels Specifically, the oxygen content in the blended fuels was recorded as 6.86%, 8.08% and 12.9% for DC80B20, DC80B10E10 and DC60B20E20 respectively, while the latent heat of vaporization was significantly increased because alcohol additives had a higher latent heat of vapor ization (585 kJ/kg for n-butanol and 840 kJ/kg for ethanol) Higher alcohols with a high-carbon structure consist of to 20 carbons, with a high cetane number and high density very close to that of diesel fuel Furthermore, the calorific value of the higher alcohols is higher than that of methanol and ethanol With hexanol, alcohol is not as water-soluble as n-butanol, so it can be mixed with diesel by the splash method Besides, it can be safer to use hexanol because it is less volatile than n-butanol The oxygen content of hexanol is about 15.7% when mixed ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS with diesel can promote combustion (Ramesh et al 2019) The disadvantage of hexanol and higher alcohols is the high viscosity Therefore, the choice of blending ratio of long-carbon alcohols up to 20% with diesel should be considered and studied more Combustion characteristics of blends with alcohol additives The presence of alcohol additives in quadratic or tertiary or quaternary blends has changed their properties as well as the combustion characteristics in CI engines The addition of homologous saturating alcohols into diesel and/or biodiesel fuel has reduced the maximum cylinder temperature In a study by Datta and Mandal (Datta and Mandal 2017), it was shown that methanol and ethanol with the latent heat of vaporization were 1110 kJ/kg and 920 kJ/kg, respectively, higher than pure diesel and biodiesel That created a cooling effect for the fuel-air mixture and resulted in a decrease in cylinder temperature Latent heat of vaporization has been recorded as 410 kJ/kg of PE15, 437 kJ/kg of PM15, and 320 kJ/kg of B100 The maximum temperatures found were 1637.5 K, 1601.6 K, and 1596.8 K for B100, PE15, and PM15 respectively The above results are also recorded and explained similarly by (Zhu et al 2011) and (Cheng et al 2008) The higher latent heat of vaporization of the saturated alcohol additives also explains the maximum pressure drop and the moving tendency for the peak pressure to the right of the top dead centre with PE15 and PM15 blends In addition, the lower cetane number of the blends resulted in a reduced ignition delay as well as a slower initiation of combustion (Hoang, Nieti, and I.ệlỗerc 2020)(Le et al 2021) These results were similarly reflected in the study by Jamrozik (Jamrozik 2017), the maximum in-cylinder pressure with Diesel-Methanol (DM) and Diesel-Ethanol (DE) blends both revealed a slight reduction compared to pure diesel The reason given by them is the lower calorific value of both methanol and ethanol compared to diesel fuel, the corresponding values are 20 MJ/kg and 27 MJ/kg Moreover, when increasing the content of methanol involved in the DM blends beyond 30%, a disorder of the combustion process was recorded as well as a sharp decrease in combustion pressure in the cylinder However, no decrease in peak pressure was observed when increasing ethanol contributed to diesel fuel This proved that the addition of ethanol at high rates still maintains a stable combustion quality The addition of alcohol lengthened the ignition delay and increased the heat release rate Furthermore, the rate of cylinder pressure rise is also strongly influenced by saturated alcoholbased additives The pressure rise ratio is in the range of 3–8 bar/degree, it is noted that the engine is “soft,” while the ratio of reaching or exceeding 10 bar/degree, the noise and vibration level of the engine is alarming The pressure rise rate of DM15, DM20, and DM25 has been higher than 10 bar/ degree, while DE20 has recorded 12 bar/degree, which was over the allowable limit (Jamrozik 2017) The resulting increase in knock in the engine is thought to stem from the energy density when ethanol is added Furthermore, the heat release rate for the blends with alcohol-based additives was also similar to the trend of change in maximum pressure When the ethanol content was higher than 15%, the heat release rate (HRR) of the DE blends was found to be higher than the blends of lower ethanol and pure diesel In terms of ignition delay and burn time in diesel engines, the addition of methanol and ethanol to diesel fuel has resulted in an increase in ignition delay due to alcohol’s higher latent heat of vaporization with an increased cooling effect and lower ignition temperature Furthermore, saturated alcohols have very low cetane numbers, making them unsuitable for the use of diesel-alcohol blends with an alcohol content higher than 30–40% (Tutak et al 2015) The role of ethanol and n-butanol additives in tertiary and quaternary blends in improving combustion behaviour in cylinders is prominently shown in the study of (Qi et al 2020) on a 4-stroke, 6-cylinder CRDI engine with a dual injection strategy Results on the evolution of cylinder pressure and heat release rate revealed that in comparison with pure diesel fuel, the reduction in cetane number extended the ignition delay and shortened the burn duration (BD) with the greater presence of alcohol-based additives in the blends, resulting in significantly rise peak in-cylinder pressure and HRR Figure depicts the changes in-cylinder pressure and HRR for the four fuels tested Regarding the maximum pressure in the cylinder, at a speed of 1000 rpm and a load of 0.64 MPa, DC60B20E20 T T TRUONG ET AL Figure Change in in-cylinder pressure and HRR with different blends at 1000 rpm and 0.64 MPa (Qi et al 2020) recorded the largest value (8.7 MPa) compared to the remaining fuels, while pure diesel was the lowest (8.15 MPa) The trend of HRR change in Figure revealed the role of calorific value and cetane number in HRR behaviour Indeed, fuel components have an impact on atomization, vaporization and mixing through blend properties such as viscosity, density, vaporization temperature and physicalchemical ignition delay mechanism Therefore, the HRR of tertiary and quaternary blends revealed great growth in comparison with neat diesel fuel In addition, the contribution of fatty acid unsatu rated substances in biodiesel has adversely affected evaporation The time required for vaporization was longer and caused the ignition delay to be prolonged More interestingly, ethanol and n-butanol have higher autoignition and latent heat of vaporization while the cetane number is much lower than that of diesel fuel, leading to further prolongation of the ignition delay However, alcohol-based chemicals have brought with them interesting properties of lower viscosity and density, which stimulate better atomization and mixing, resulting in faster combustion and HRR is higher The results and interpretation of HRR were also consistent with viewpoints in a study by (Labeckas et al 2018) and (Hurtado et al 2019) A study by (Imdadul et al 2016) carried out on TF120M engines with biofuel blends added 10%, 15% and 20% (vol.) pentanol revealed the lower viscosity and higher volatility of pentanol resulted in an increase in the fuel-air mixture in the premixed combustion phase As a result, for modified blends, the start of combustion is delayed and the peak pressure in the cylinder is higher Thus, the combustion attributes were significantly improved with the participation of pentanol in the modified blends In summary, the significant positive effects of alcohol additives on combustion have shown that they can be a promising choice in the search for alternative fuels using CI engines As a result, an improvement in combustion performance can have beneficial effects on engine performance The impact of alcohol-based additives in diesel/biodiesel blends on combustion characteristics and engine performance are discussed in this review, these contents have been summarized and described in Figure Effect of alcohol additives on engine performance Various alcohol additives with different physicochemical properties and combustion which consider able influences on the operating parameters of the engine and characteristics of emission Concerning the purpose of improving the engine performance, the recent studies incorporated diesel/biodiesel fuel with different types of additives at various fuel blending ratios (Subramanian, Chandrasekaran, and Rajesh 2009) Alcohol additives are mainly associated with diesel or biodiesel fuels (Kumar et al 2013) ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS Figure Effects of alcohol-based additives’ physicochemical properties on combustion and engine performance They are more especially attractive for purposes of optimization of engine performance, minimization of emissions, mileage increase, combustion rate improvement, operating as anti-oxidants, allowing fuels to work under extreme operating conditions, environmental preservation, etc (Hoang, ệlỗer, and Nieti 2020) It is fact that alcohol additives have paid special attention because as they are compared to diesel fuel, they have better combustion behaviour as well as their molecular structure has high available oxygen content (Table 1) The improved combustion characteristics of the blend between additives and diesel lead to engine performance improvement (BTE, BSFC, etc.) and reduc tion of emissions characteristics (Geng et al 2017) Methanol is considered the most promising alcohol-based additive candidate because of its highest oxygen content at 50% by weight which promotes a cleaner and more stable combustion Furthermore, the production of methanol can come from renewable and inexpensive sources such as biomass Therefore, methanol has been piloted on both SI and CI engines On CI engines, methanol can be injected into the cylinders through solutions such as dual injection, mixing, and emulsification (Valera and Agarwal 2019) However, the dissolution of methanol in diesel fuel has encountered many difficulties because the OH group has a large degree of polarity in solutions that not use co-solvents such as diesel fuel In a study by Jamrozik (Jamrozik 2017), the ability to improve engine performance when increasing the addition of ethanol and methanol to diesel fuel was concluded The indicated thermal efficiency (ITE) of the methanol-diesel blend (DM25) has been increased by about 14.5% compared to pure diesel fuel However, if the increase in the amount of methanol continues, ITE has recorded a sharp decrease, with DM40, ITE has only reached 20%, which is 12% lower than diesel Meanwhile, the increase in ITE of the ethanol-diesel blend was proportional to the increase of ethanol The reason for the decrease in the ITE of the methanol-diesel blend was a significant reduction of the combustion pressure and heat release rate due to the very low cetane number and lower calorific value in comparison with ethanol Thus, the addition of methanol of no more than 30% had very positive effects on the ITE of the CI engine Another study by (Agarwal et al 2019) demonstrated a suitable combination of diesel-methanol blend with 1-Dodecanol additive to improve stability of blends as well as BTE, BSEC, and EGT The BTEs of the MD10 and MD15 blends have seen higher values than pure diesel fuels Obviously, the ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS 11 Figure Change in BSFC of biodiesel blends with methanol (a) and ethanol (b) (Datta and Mandal 2017) and BE15 have more pronounced adverse effects on engine performance than Bu5, Bu10, and Bu15 In general, the BSFC of fuels with alcohol-based additives increased with the increase in the proportion of the additive The main reason has also been confirmed that their calorific value is lower while latent heat is higher Regarding BTE, compared with biofuels, both BE and Bu have shown slight reductions under different loading conditions An experimental study to optimize the parameters of brake specific fuel consumption and thermal efficiency (TE) for 4-stroke, 4-cylinder diesel engines using different fuels including pure diesel and blended fuels of diesel, biodiesel, and ethanol (Krishna et al 2019) The blending ratios of ethanol were 5%, 6%, 7%, 8%, 9% and 10%, respectively, in the BDE fuels The BSFC at full load showed that BDE9 had the largest value, 13.4% higher than diesel The increase in BSFC was observed to be proportional to the increase in ethanol Meanwhile, in terms of TE, BDE6 saw a slight increase compared to BDEopt, however, the rise of ethanol from 7% to 9%, there was a decrease compared to both BDE6 and diesel (Tran, Le, and Hoang 2020) The review of (Khalife et al 2017) indicated that values of BTE and BSFC are enhanced by adding alcohols (< 10% vol.) into diesel Adelman 1979 and (Wagner et al 1979) presented the reasons for benefit of blending alcohols into the pure fuel deal with the performance such as (1) Due to its viscosity 12 T T TRUONG ET AL are lower than diesel fuel, it has better atomization, injection, and mixing; (2) Its laminar flame propagation velocity is around 0.45 to 0.55 m/s, which is faster than that of diesel (about 0.45 m/s) at an equivalence ratio of 1.0, which results in the early combustion process and improvement of BTE (Chong and Hochgreb 2011); (3) Engine performance has been improved with conditioned reactions of the compression ignition process, which was influenced by the cooling mechanism during vapor ization and compression process caused by the higher latent heat of the oxygenated additives (Pan et al 2017) Furthermore, a by-product of the fermentation and distillation of ethyl alcohol that has attracted a lot of interest in the search for an alternative fuel is fusel In the study of (Akcay and Ozer 2019), pure diesel fuel and four blends of diesel and fusel were fed to a DICI engine to investigate engine performance such as BSEC and EGT under variable load conditions BSEC data has revealed that it increased with the fusel addition ratio Compared to pure diesel fuel, the BSEC of DF5, DF10, DF15 and DF20 increased by 10.1%, 13.5%, 18.4% and 23.7%, respectively Suitable reasons for those results came from the calorific value and latent heat of the fusel Specifically, with a calorific value Figure Change in EGT (a) and BSFC (b) along with various loads (Bencheikh et al 2019) ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS 13 about 33% lower than neat diesel, lead to produce the same power it is necessary to supply more fuel into the combustion chamber In addition, the higher latent heat of the fusel reduced the combustion temperature by the cooling effect of the mixture, resulting in a rise in BSEC Furthermore, ETG has recorded a decrease in all loads for blended fuels In comparison with pure diesel fuel, the biggest reduction of EGT made up with 22.1% of DF20 at 2.5 Nm and 7.5 Nm This is also reflected in a study of (Ağbulut, Sarıdemir, and Karagöz 2020), increasing the fusel ratio has significantly reduced the density, cetane number and calorific value of the modified fuels Propanol has also been seen as a good candidate for improving engine combustion characteristics A study on the tertiary fuel blend formed from waste cooking oil biodiesel, diesel, and propanol was investigated on diesel engines to evaluate the influence of the physicochemical properties of blends on BTE, BSFC, and EGT (Bencheikh et al 2019) Prominent benefits in BSFC and EGT reduction of propanol addition were revealed in Figure The highest mean EGT was recorded for D80B5Pro15, while the lowest mean was D80Pro20 The reduction in EGT of the D80B5Pro15, D80B10Pro10, D80B15Pro5 and D80Pro20 compared to D100 was 0.78%, 13.39%, 19.5% and 53.93% respectively Clearly, the increase of oxygen content in the blends with biodiesel and propanol explained the changing trend of EGT In addition, a consensus on the trend of BSFC and BSEC was observed The results revealed that there was an increase in BSFC of D80B15Pro5, D80B10Pro10, D80B5Pro15, and D80Pro20 compared to D100 by 4.95%, 8.07%, 8.33%, and 11.65% respectively The main reasons include the higher viscosity and density of biodiesel which made the injected fuel particle diameter larger and more difficult to evaporate, also the calorific value of B100 was significantly lower than that of D100 Furthermore, propanol has a greatly lower calorific value compared to both B100 and D100, while its oxygen content is higher Therefore, with the same power value, it is necessary to feed more fuel into the cylinder A study by (Ganesh et al 2019) on a DICI engine using diesel fuels, Rice bran biodiesel (R100), and blends of R100 with 10% and 20%vol propanol Regarding EGT, the added oxygen content in propanol, lower viscosity, the cetane number of R90P10 and R80P20 promoted fuel oxidation, more over, the reduction in ignition delay time resulted in earlier combustion Therefore, the ETG of biodiesel with the addition of propanol was found to be lower than that of R100 and pure diesel On the other hand, compared with pure diesel fuel, the BTE value of biofuels has been reported to be lower Clearly, the higher viscosity of biofuels resulting in much amount of injected fuel and poorer miscibility can be explained However, with its low volatility and low viscosity, the addition of propanol to biofuels has also helped improve BTE Thus, in comparison with R100, the BTE of Figure Change in BTE of binary and ternary fuel blends compared in diesel fuel (Thakkar et al 2020) 14 T T TRUONG ET AL R90P10 and R80P20 was slightly increased with the increase of propanol Another study on the role of propanol in improving the fuel properties of the waste plastic pyrolysis oil blends as well as the engine performance has yielded a lot of useful information (Ravi and Karthikeyan 2019) Indeed, 5% to 15% propanol addition gradually improved BTE, typically, the BTE of D70-WPO20-P15 was recorded higher than pure diesel at higher loading conditions Propanol with lower viscosity and cetane number, resulting in the rise of the ignition delay time, promoting uniformity of the fuel-air mixture, leading to improved thermal efficiency In addition, its rich oxygen content stimulated complete oxidation, leading to an improved BSFC of propanol-containing fuels compared with WPO, even though the BSFC of WPO and diesel blends was reported higher than pure diesel fuel due to the lower calorific value of WPO N-butanol also has beneficial properties for diesel and biodiesel blends to improve engine performance (Goga et al 2019) surveyed a 4-stroke, single-cylinder diesel engine using blended fuels of diesel, rice bran biodiesel, and n-butanol to analyze the effects of blends’ properties on BTE and BSFC The results showed that all biodiesel blends recorded an increase in BSFC Increased n-butanol content in rice bran biodiesel revealed higher BSFC Viscosity and calorific value are the two factors that contribute to these changes Indeed, the viscosity of biodiesel is higher while the calorific value is lower for both biodiesel and n-butanol These factors have also adversely affected the BTE of blended fuels BTE was found to be lower as the ratio of biodiesel as well as n-butanol increased Another study by (Singh, Singh, and Kumar 2020) investigated the effect of the properties of fuels blended from eucalyptus-based biodiesel, diesel fuel, and n-butanol additives on brake power (BP), BSFC, and BTE in the Kirloskar TV1 diesel engine under variable load and constant speed Regarding BSFC, the experimental report has revealed that with significantly higher calorific value, viscosity, and density for B100, fuel injection, and combustion quality are not good, leading to the BSFC being recorded at the highest level compared to modified fuels More interestingly, the blends of eucalyptus oil-based biodiesel and diesel fuel were added n-butanol, some properties beneficial to combustion were signifi cantly improved, including higher oxygen content, lower viscosity, and density As a result, BSFC recorded a clear reduction compared to B20, specifically, the reduction was 1% for B20-5Bu, 2% for B20-10Bu, and 6% for B20-15Bu Regarding BTE, in comparison with pure diesel fuel, the average BTE has witnessed a decrease of 2.1% for B100, 1.7% for B20, 1.2% for B20-5Bu, 0.8% for B20-10Bu, and except B20-15Bu was higher than 0.5% Obviously, with the addition of n-butanol to the biodiesel blend fuels, the BTE of the blends approached that of the diesel fuel In a comprehensive survey of secondary and tertiary fuels, n-butanol was blended with castor oil-based biodiesel and neat diesel to supply a direct-injection diesel engine(Thakkar et al 2020) Figure Change in BTE and BSFC with pure diesel and two ternary blends (Nour, Attia, and Nada 2018) PSME, PM5, PM10, PM15 PSME, PE5, PE10, PE15 Diesel-ethanol-THF: RE0, RE10, RE30 Diesel, ethanol, E + 10% EGR, E + 20%EGR D100, Pe10E10D80, Oc10E10D80 Diesel, NCO, NCO60D30E10, NCO50D30E20, NCO40D30E30 Diesel, B100, B90D5E5, B85D5E10, B80D5E15 Diesel, P100 + D, P100+ B10, P100+ B20, P100+ B30 Diesel, R100, R90P10, R80P20 Diesel, D80WPO20, D75WPO20P5, D70WPO20P10, D65WPO20P15 D100, D80Pro20, D80B5Pro15, D80B10Pro10, D80B15Pro5 Diesel, B10, B20, B10nB10, B20nB20 Methanol Methanol Ethanol Ethanol Ethanol Ethanol n-Butanol Propanol Propanol Propanol Propanol Ethanol Ethanol Fuel/Blends Diesel, MD10, MD15 Additive Single-cylinder diesel engine Loads: 0, 20%,40%,60%,80%,100% Speed: 1550rpm Loads: 500, 750, 1000, 1250 W Speed: 3000 rpm Loads: 0–100% Speed: 1500 rpm Loads: 0–100% Speed: 1500 rpm 4-stroke single-cylinder diesel engine Loads: 0, 1.25, 2.5, 3.8, 5.0 bar BMEP Speed: 1500rpm Simulation by Diesel RK; Loads: 0.5 ÷ 3.5 kW Speed: 1500rpm 4-stroke 6-cylinder diesel engine Loads: 0,3 MPa, 0,6 MPa, 1,0 MPa, 1,4 MPa and 1,9 MPa IMEP Speed: 1415rpm 4-stroke single-cylinder diesel engine Loads: various Speed: 1500rpm Single-cylinder diesel engine Loads: 0,150,300,450 kPa Speed: 1500rpm 4-stroke single-cylinder diesel engine Loads: various Speed: 1500rpm Loads: 0, 25, 50, 75, 100% Speed: 1500 rpm Loads: 0–100% Speed: 1500 rpm Test Condition BTE B10> Diesel> B20> B10nB10> B20nB20 Diesel> B90D5E5> B85D5E10> B90D5E5> B100 Diesel> P100 + D> P100+ B10> P100+ B20> P100+ B30 Diesel> R80P20> R90P10> R100 D65WPO20P15> D70WPO20P10> D75WPO20P5> D80WPO20> Diesel NA Diesel> NCO40D30E30> NCO50D30E20> NCO60D30E10> NCO Oc10E10D80> D100> Pe10E10D80 Ethanol> E + 10%EGR> E + 20%EGR> Diesel Diesel> RE30> RE10> RE0 PM15 > PM10 > PM5 > PSME PE15 > PE10 > PE5 ~ PSME MD15> MD10> Diesel Table Changing of diesel engine performance using alcohol additives SFC B20nB20> B10nB10> B20> B10> Diesel D80Pro20> D80B5Pro15> D80B10Pro10> D80B15Pro5> Diesel D80WPO20> Diesel> D75WPO20P5> D70WPO20P10> D65WPO20P15 R100> R90P10> R80P20> Diesel B100> B80D5E15> B85D5E10> B90D5E5> Diesel NA NCO> NCO60D30E10> NCO50D30E20> NCO40D30E30> Diesel Pe10E10D80> D100> Oc10E10D80 Ethanol> E + 10%EGR> Diesel > E + 20%EGR RE30> RE10> RE0> Diesel PM15 > PM10 > PM5 > PSME PE15 > PE10 > PE5 > PSME Diesel> MD10> MD15 EGT NA D80B5Pro15> Diesel> D80B10Pro10> D80B15Pro5> D80Pro20 NA R100> R90P10> R80P20> Diesel Diesel> P100 + D> P100+ B10> P100+ B20> P100+ B30 NA NCO> NCO60D30E10> NCO50D30E20> NCO40D30E30> Diesel NA Ethanol> E + 10%EGR> Diesel > E + 20%EGR NA PSME > PM5 > PM10 > PM15 PSME > PE5 > PE10 > PE15 Diesel> MD10> MD15 Reference (Goga et al 2019) (Bencheikh et al 2019) (Continued) (Ravi and Karthikeyan 2019) (Ganesh et al 2019) (Gawale and Naga Srinivasulu 2020) (Ramalingam and Mahalakshmi 2020) (Prakash et al 2018) (Nour, Attia, and Nada 2018) (Saravanan et al 2020) (Wu et al 2020) (Datta and Mandal 2017) (Datta and Mandal 2017) (Agarwal et al 2019) ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS 15 Diesel, But10,But20 D100, B20, B20P5, B20P10, B20P15, B20P20 100D, P10D90, P20D80, P30D70 D100, B100, B50D50, DBOP10, DBOP20, DBOP30, DBOP40 P0, P25, P50 n-Butanol Butanol Pentanol Diesel, CIME, CI90O10, CI80O20, CI70O30, CI60O40, CI50O50 n-Octanol Octanol Diesel, D70L30, D70L20D10, D70L20DNBE10 Diesel, OCT30 Diesel, CNSBD1000, CNSBD900H100, CNSBD800H200 Diesel, WPO, D50-W40H10, D50-W30-H20, D50-W20-H30 100D, 10H90D, 20H80D, 30H70D, 40H60D Diesel, B10, B20 Diesel, B100, B90D5H5, B85D5H10, B80D5H15 1-decanol n-hexanol Hexanol 1-hexanol n-hexanol Hexanol Heptanol Pentanol n-Pentanol Pentanol Diesel, D85P15, D75P25, D65P35 Diesel,Hep10, Hep20 Diesel, DB1, DB2, DB3, DB4 Butanol n-Pentanol Fuel/Blends D100, B100, B20, B20-5Bu, B20-10Bu, B20-15Bu Additive Table (Continued) Test Condition EGR: 10, 20, 30% Speed: 1500 rpm Loads: 500, 750, 1000, 1250 W Speed: 1500 rpm Loads: 4.16 bar BMEP Speed: 1500 rpm Loads: 20, 40, 60, 80% Speed: 2000 rpm DI diesel engine Loads: 0, 25, 50, 75, 100% Speed: 1500 rpm Loads: 6.2 bar BMEP Speed: 1500 rpm Loads: 0.4–1.2 Mpa Speed: 1400 rpm Loads: 1–5 kW Speed: 1400 rpm Loads: 0, 25%,50%,75%,100% Speed: 900rpm Loads: 0, 25, 50, 75, 100% Speed: 1300 rpm Single-cylinder diesel engine Loads: various Speed: 1500 rpm Single-cylinder diesel engine Loads: various Speed: 1500 rpm Single-cylinder diesel engine Loads: 0, 25%,50%,75%,100% Speed: 900rpm Loads: 0, 25, 50, 100% Speed: 3000 rpm Loads: 20, 40, 60, 80% Speed: 2000 rpm Loads: 20–100% Speed: 1500 rpm BTE CI70O30> CI50O50> CI60O40> Diesel> CI80O20> CI90O10> CIME OCT30> Diesel Diesel> CNSBD800H200> CNSBD900H100> CNSBD1000 Diesel> D50-W40-H10> D50W30-H20> D50-W20H30> WPO 100D> 10H90D> 20H80D> 30H70D> 40H60D B20> B10> Diesel Diesel> B90D5H5> B85D5H10> B90D5H5> B100 D70L20DNBE10> Diesel> D70L30> D70L20D10 Diesel> D65P35> D75P25> D85P15 Hep10> D100> Hep20 D100> B20> B20P5> B20P10> B20P15> B20P20 100D> P10D90> P20D80> P30D70 D100> DBOP40> DBOP30> DBOP20> DBOP10> B50D50> B100 P0> P25> P50 But20> But10> D100 Diesel> DB1> DB2> DB3> DB4 D100> B20-15Bu> B20-10Bu> B20-5Bu> B20> B100 SFC NA OCT30> Diesel NA 40H60D> 30H70D> 20H80D> 10H90D> 100D NA B100> B80D5H15> B85D5H10> B90D5H5> Diesel WPO> D50-W20-H30> D50-W30H20> D50-W40-H10> Diesel CNSBD1000> CNSBD800H200> CNSBD900H100> Diesel Hep20> Hep10> D100 D85P15> D75P25> D65P35> Diesel P50> P25> P0 B100> B50D50> DBOP10> DBOP20> DBOP30> DBOP40> D100 B20P20> B20P15> B20P10> B20P5> B20> D100 NA D100> But20> But10 DB4> DB3> DB2> DB1> Diesel B100> B20> B20-5Bu> B20-10Bu> D100> B20-15Bu EGT NA NA NA 100D> 20H80D> 10H90D> 30H70D> 40H60D NA NA WPO> D50-W40-H10> D50-W30H20> Diesel> > D50-W20-H30 NA D100> Hep10> Hep20 NA NA NA B20> D100> B20P5> B20P10> B20P15> B20P20 NA D100> But10> But20 Diesel> DB1> DB2> DB3> DB4 NA Reference (Li, Yu, and Yang 2021) (Ganesan et al 2021) (Rajasekaran et al 2020) (Duraisamy, et al.,) (Ramalingam and Mahalakshmi 2020) (Santhosh and Kumar 2020) (Nour et al 2021) (Pandian et al 2018) (Nour, Attia, and Nada 2019) (Prabhu and Venkata Ramanan 2020) (Pan et al 2019) (Appavu, Ramanan, and Venu 2019) (Santhosh et al 2019) (Yesilyurt, Yilbasi, and Aydin 2020) (Nour, Attia, and Nada 2019) (Satsangi and Tiwari 2018) (Singh, Singh, and Kumar 2020) 16 T T TRUONG ET AL ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS 17 Engine performance results were reported with the most significant increase of BTE in B20Bu10 and B15Bu15 while BTE of B30 recorded a decrease of up to 3% compared to pure diesel The difference in BTE of fuels B30, B20Bu10, B10Bu20, and B15Bu15 compared with pure diesel under different loads is depicted in Figure Higher alcohols such as pentanol, hexanol, and octanol with higher cetane numbers and higher oxygen content can give diesel engines more advantages compared to low alcohols In the study on the DICI engine of (Dillikannan et al 2020), the possibility of using waste plastic oil mixed with n-hexanol and diesel was investigated with blends including D50-W40-H10, D50-W30-H20, and D50-W20-H30 in different load modes of BMEP and fixed at 1500rpm Regarding BTE, the highest values were recorded at 34.82% for D50-W20-H30, 39.4% for D50-W30-H20, 40.5% for D50-W40-H10, 38.7% for WPO, and 35.9% for diesel Thus, in blended fuels, the BTE of D50W40-H10 is the best, specifically, 13.1% higher than WOP, but still lower than pure diesel by 2.7% However, the property of n-hexanol with higher latent heat increased the cooling effect, further more increasing n-hexanol decreased the cetane number Therefore, BTE was found a reduction in the growth of n-hexanol addition D50-W20-H30 was recorded with the lowest BTE, but still 7.6% higher than that of WPO In a comparative study of diesel engine performance using biodieseldiesel-n-hexanol and biodiesel-diesel-ethanol blends, it was revealed that B90-D5-H5 has a very good BSFC (Ramalingam and Mahalakshmi 2020a) Specifically, the BSFC of B90-D5-H5 was lower by 5% with pure diesel, 10% with B80-D5-E15, and 12% with B100 Furthermore, in terms of BTE, the n-hexanol supplemented fuel revealed a higher BTE than the ethanol supplemented fuel An emerging potential alcohol candidate is n-octanol Compared with diesel fuel, octanol carries properties such as significant cetane number, oxygen content about 12.3%, higher flash point, lower vapour pressure In addition, the use of octanol may be safer for the system because it is completely hydrophobic and non-corrosive to metals Studies on combustion and engine performance when using n-octanol as an additive for diesel fuel and biodiesel are increasing gradually A recent study was performed by Pouresa et al (De Poures et al 2019) to evaluate the substitution potential of n-octanol in 4-stroke, 1-cylinder, and direct-injection diesel engines BSFC for 30% n-octanol blend has been reported higher than pure diesel The main reason comes from the lower cetane number and higher viscosity of Oct30 More strikingly, despite using more EGR ratio, the BTE for Oct30 recorded better This means that the increase of BSFC is less than the decrease of the low calorific value of Oct30 An evaluation study on the potential for improving the engine characteristics of pentanol and octanol in ethanol and diesel tertiary fuel blends was investigated in a single-cylinder 4-stroke diesel engine under variable load BMEP (Nour, Attia, and Nada 2018) The results on BTE and BSFC were depicted in Figure Compared with D100, the BTE of Oc10E10D80 was 4.9% higher at 50% load, while that of Pe10E10D80 was 3% lower at the same load The reason for this change is due to the calorific value of the two tertiary fuels, in addition, the intensely added oxygen content promotes combustion for those two blends In general, alcohol additives can be considered as a new promising alternative biofuel, showing significant improvement in combustion characteristics without seriously affecting diesel engine performance Table depicts how various alcohol additives affect the engine performance This study also discusses the influences of alcohol additives blended with diesel or biodiesel on combustion behaviours in CI engines Conclusions and prospects Our work has generalized the production process of Bio-alcohol fuels to clarify current alcohol additive manufacturing concepts and technologies Analysis of the physicochemical properties and discussion of the relationship between various alcohol additives and engine performance of diesel engines accompanying their advantages and disadvantages are reviewed in this work Base on the wide 18 T T TRUONG ET AL review of published scientific papers, this review studied the combustion characteristics and engine performance of alcohol additives-diesel/biodiesel blends regarding diesel and biodiesel fuel, remark able conclusions have been drawn: ● Today’s bio-alcohol fuel production entails new requirements for decarbonization Therefore, technologies for producing 2nd and 3rd generation alcohol biofuels from lignocellulosic biomass and microalgae have been promoted in biorefineries ● The combination of alcohol additives with diesel or biodiesel gained significant improvement in engine performance and a minimum rise of brake-specific fuel consumption in the majority of the literature ● Most of the literature review utilized methanol, ethanol, and propanol additives-diesel blends indicated the upward trend of exhaust gas temperature because of the high content of oxygen existing in the burning region In contrast, higher alcohol-based additives may have brought about the reduction in EGT in some of the literature ● All alcohol additives with high available oxygen content enrich possibly the blends with oxygen Blend of diesel fuel and/or biodiesel with an appropriate proportion of alcohol additives could improve the engine performance because of proper combustion characteristics A problem arises when adding alcohol additives at certain temperatures can form a two-phase composition Therefore, an effective solution is to add active additives to the composition to form an interface between pure diesel/biodiesel fuel and alcohol and prevents the formation of a two-phase fuel at any temperature Moreover, higher alcohol additives (from C4 and above) with higher cetane numbers are added to pure diesel or biodiesel without forming a two-phase fuel Therefore, the benefits of higher alcohol additives are potential for use on CI engines Tertiary or quaternary fuel blends with the participation of both low and high alcohol can improve output parameters in terms of engine characteristics and emissions In the next study, the positive effect of alcohol additives on emission characteristics will be presented to fill the shortcomings in the evaluation of the application of alcohol additives in CI engines Finally, the innovation around alcohol additives has a broader impact of being able to change or enhance specific attributes of a fuel Generally, alcohol additives should enhance some proper ties without deterioration of other properties of fuels Optimization of performance and emission characteristics of additives-biodiesel-diesel ternary blends become a potential future scope, as comparatively less work has been done on the maximization of performance and minimization of emission Analogous changes of compression ratio, injection pressure, and injection timing which are engine parameters, are suggested to perform for greater optimization of combustion Disclosure statement No potential conflict of interest was reported by the author(s) ORCID Tan Trung Truong http://orcid.org/0000-0001-7974-638X http://orcid.org/0000-0003-4996-3732 Van Viet Pham ENERGY SOURCES, PART A: RECOVERY, UTILIZATION, AND ENVIRONMENTAL EFFECTS 19 Abbreviations ABE B-Bu BD BDE B-D-H BP BSEC BSFC BTE CI CNG CRDI DE DF DICI DM D-Pro D-W-H D-WPO-P Acetone-Butanol-Ethanol Biodiesel-Butanol Burn Duration Biodiesel-Ethanol blend Biodiesel-Diesel-Hexanol Blend Brake Power Brake Specific Energy consumption Brake specific fuel consumption Brake Thermal Efficiency Compression ignition Compressed natural gas Common Rail Diesel Injection Diesel-Ethanol blend Diesel-Fusel blend Direct-Injection Compression Ignition Diesel-Methanol blend Diesel-Propanol Blend Diesel-Waste Plastic Oil-Hexanol Blend Diesel- Waste Plastic 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