Department of Mechanical Engineering, FEAT, Annamalai University, India
The rising global demand for energy, coupled with the rapid depletion of fossil fuel resources, has intensified the search for clean and renewable alternatives. Among these, biodiesel has attracted considerable attention due to its renewable origin, biodegradability, and potential to reduce harmful exhaust emissions. This review paper examines the performance and emission behavior of biodiesel–diesel blends when used in Common Rail Direct Injection (CRDI) engines. With its ability to precisely regulate injection pressure and timing, CRDI technology is particularly effective in enhancing the combustion of biodiesel blends. The study highlights the influence of biodiesel feedstock, blending ratio, and injection parameters on key performance aspects such as Brake Thermal Efficiency (BTE), Brake Specific Fuel Consumption (BSFC), and combustion characteristics. It also evaluates the effect of biodiesel blends on exhaust emissions, including nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (HC), and particulate matter (PM). In addition, the role of fuel additives and nanotechnology in improving engine efficiency and reducing emissions is discussed. Overall, this review provides a comprehensive understanding of the opportunities and challenges associated with biodiesel use in CRDI engines and identifies future research directions toward cleaner and more efficient diesel technologies.
Energy is the driving force of modern civilization, powering industries, transportation, households, and global economic growth. At present, most of this demand is met through fossil fuels such as coal, petrol, and diesel. However, these resources are depleting rapidly while their excessive use continues to release harmful pollutants including carbon dioxide (CO?), nitrogen oxides (NO?), carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM). Such emissions contribute to global warming, acid rain, air pollution, and severe health problems. This dual challenge of resource depletion and environmental degradation has created a pressing need for alternative, eco-friendly fuels. Biodiesel has emerged as one of the most promising substitutes for conventional diesel. Derived from renewable sources such as vegetable oils, non-edible oils, animal fats, and waste cooking oil, biodiesel is biodegradable, non-toxic, and capable of reducing harmful emissions. It is produced mainly through transesterification, where oils or fats react with alcohol in the presence of a catalyst to yield fatty acid methyl esters (FAME) and glycerol. Since biodiesel shares many physical and chemical properties with diesel, it can be used in existing engines with little or no modification. However, certain differences—such as higher viscosity, lower calorific value, and greater oxygen content—can influence engine performance, combustion characteristics, and emission levels. Parallel to the development of biodiesel, advancements in diesel engine technology have introduced the Common Rail Direct Injection (CRDI) system, which provides precise control of injection timing, pressure, and quantity through electronically operated injectors. This technology enhances fuel atomization, improves combustion, and reduces emissions, making CRDI engines highly suitable for testing biodiesel blends. Recent studies have examined the use of biodiesel–diesel blends (such as B10, B20, etc.) in CRDI engines to evaluate their effect on performance parameters like Brake Thermal Efficiency (BTE), Brake Specific Fuel Consumption (BSFC), and cylinder pressure, as well as emissions including CO, HC, NO?, and smoke. Results indicate that biodiesel blends generally improve combustion efficiency and reduce CO, HC, and PM emissions due to their inherent oxygen content. However, a notable drawback is the increase in NO? emissions, which is often attributed to higher in-cylinder combustion temperatures. Researchers are addressing this challenge through optimized injection strategies, blend ratios, exhaust gas recirculation (EGR), selective catalytic reduction (SCR), and the incorporation of fuel additives. In addition, nanotechnology and alcohol-based additives are being explored to enhance fuel properties, promote cleaner combustion, and reduce harmful exhaust gases. Feedstock selection also plays a key role in biodiesel performance, with options ranging from edible oils like soybean and palm oil to non-edible oils such as jatropha, karanja, and neem, as well as waste oils and animal fats. Each feedstock influences viscosity, energy content, and oxygen levels differently, leading to varied effects on engine behavior and emissions. Despite its advantages, biodiesel faces challenges such as higher production costs, fuel instability during storage, and cold-weather performance issues. Standardization of fuel properties and long-term engine durability are also concerning. Nevertheless, the integration of biodiesel with CRDI technology, along with the use of additives and improved processing methods, provides a promising path forward. This review consolidates research findings on biodiesel blends in CRDI diesel engines, with emphasis on performance, combustion behavior, and emission characteristics. It further explores the impact of additives, feedstocks, and injection parameters while identifying both the benefits and limitations of biodiesel use. By presenting current knowledge and future prospects, this study aims to support ongoing efforts toward cleaner, more efficient, and sustainable diesel engine technologies.
2. Characteristics of Biodiesel
Biodiesel, produced through the transesterification of vegetable oils, non-edible oils, animal fats, and waste cooking oils into fatty acid methyl esters (FAME), has drawn significant interest as an alternative to petroleum diesel. Its fuel characteristics differ considerably from conventional diesel, and these differences strongly influence engine performance, combustion efficiency, and exhaust emissions. Over the years, researchers have examined these variations in detail. Demirbas (2009) observed that the calorific value of biodiesel is lower than that of petroleum diesel, primarily due to its oxygenated molecular structure. This reduction in heating value leads to slightly higher brake specific fuel consumption when biodiesel is used in diesel engines. Supporting this, Oliveira and Da Silva (2013) reported calorific values in the range of 38–40 MJ/kg for biodiesels derived from different feedstocks, in contrast to about 46 MJ/kg for diesel. Sanjid et al. (2014) reached similar conclusions in their work on palm and jatropha biodiesel, noting that reduced heating value was the major factor behind increased fuel usage. Hoekman et al. (2012) added that although biodiesel has less energy per unit mass, the oxygen content present in the fuel enhances combustion efficiency, offsetting some of the energy loss. In agreement, Graboski and McCormick (1998) also linked biodiesel’s lower energy density to marginal reductions in engine power output.
2.1 Density and Viscosity
The physical properties of density and viscosity have received considerable attention. Alptekin and Canakci (2008) showed that biodiesel blends are denser and more viscous than conventional diesel, which can negatively affect fuel spray and atomization. Lapuerta et al. (2008) confirmed this by demonstrating that higher viscosity results in larger droplet formation during injection, ultimately influencing the combustion process. Wan Ghazali et al. (2015) reported that increased viscosity contributed to poor cold-starting characteristics in diesel engines. Similarly, Silitonga et al. (2013) highlighted that viscosity issues could be mitigated by blending biodiesel with diesel to achieve better atomization. Arbab et al. (2013) further emphasized that modern injection technologies, particularly CRDI systems, can counterbalance these shortcomings through precise control of injection pressure. Fig.1 represents the density values of biodiesel blends.
C. Manikandan*, C. Syed Aalam, Performance and Emission Characteristics of Biodiesel-Blend in CRDI Diesel Engine – A Review, Int. J. Sci. R. Tech., 2025, 2 (12), 1-12. https://doi.org/10.5281/zenodo.17774660
10.5281/zenodo.17774660
