Biodiesel-Based Ternary Fuel Blends in Compression Ignition Engines: A Comprehensive Review of Combustion, Performance, and Emission Characteristics

Abstract

The increasing dependence on fossil diesel fuel and the associated environmental and energy security concerns have intensified research efforts toward sustainable and renewable alternatives for compression ignition (CI) engines. Biodiesel derived from non-edible oils and waste cooking oil has emerged as a promising substitute due to its renewable nature, biodegradability, and favorable combustion characteristics. However, the widespread application of biodiesel is constrained by inherent drawbacks such as higher viscosity, lower calorific value, increased brake-specific fuel consumption, and a tendency to elevate nitrogen oxide emissions. To overcome these limitations, the present research investigates the performance, combustion, and emission characteristics of ternary fuel blends comprising diesel, biodiesel, and higher alcohols. In this study, biodiesel produced from selected non-edible and waste-based feedstocks is blended with diesel and higher alcohols such as butanol, pentanol, hexanol and n-octanol in varying proportions. Experimental investigations are conducted on a single-cylinder, four-stroke, water-cooled compression ignition engine under different load conditions. Key performance parameters, including brake thermal efficiency and brake-specific fuel consumption, are evaluated alongside detailed combustion analysis involving in-cylinder pressure, ignition delay, and heat release rate. Exhaust emissions such as carbon monoxide, unburned hydrocarbons, nitrogen oxides, and smoke opacity are also analyzed and compared with baseline diesel operation. Furthermore, statistical optimization techniques such as the Taguchi method and Response Surface Methodology are employed to identify optimal blend compositions that achieve a balanced trade-off between engine performance, combustion stability, and emission reduction. The outcomes of this research are expected to provide comprehensive experimental insights into the feasibility of ternary biofuel blends and contribute to the development of cleaner and more efficient CI engine fuel strategies.

Introduction

Rising global energy demand, depletion of fossil fuels, price volatility of crude oil, and environmental concerns have intensified the search for renewable alternatives to diesel, especially for compression ignition (CI) engines that dominate transportation, agriculture, and power generation. Diesel engines, while efficient and durable, contribute significantly to air pollution and greenhouse gas emissions. Although advanced after-treatment systems reduce emissions, their high cost and complexity have shifted research interest toward fuel-based emission reduction strategies using renewable fuels.

Biodiesel has emerged as a prominent alternative due to its renewability, biodegradability, higher cetane number, and inherent oxygen content, which improve combustion and reduce carbon monoxide, hydrocarbons, and particulate matter emissions. However, its higher viscosity, lower calorific value, cold-flow issues, and tendency to increase nitrogen oxide (NO?) emissions limit its use at higher blend ratios. Alcohol fuels such as ethanol, butanol, and higher alcohols offer high oxygen content and volatility, improving atomization and air–fuel mixing, but suffer from low cetane number, ignition instability, and miscibility issues with diesel when used alone or in binary blends.

Because no single alternative fuel satisfies all performance, emission, and compatibility requirements, research has increasingly focused on ternary fuel blends combining diesel, biodiesel, and alcohols. In these systems, biodiesel acts as a bridging agent that enhances miscibility between diesel and alcohols, reduces viscosity, and balances ignition characteristics. Optimized ternary blends have been shown to deliver brake thermal efficiency comparable to conventional diesel, with improved combustion stability, smoother pressure rise, and significant reductions in CO, HC, and particulate emissions. While brake-specific fuel consumption may increase slightly due to lower energy content, overall performance–emission trade-offs are favorable.

Combustion studies indicate that biodiesel’s higher cetane number compensates for the ignition-retarding effects of alcohols, while volatility differences promote secondary atomization and micro-explosions that enhance combustion efficiency. Emission trends generally show reduced smoke and unburned emissions, with NO? effects varying depending on blend composition and operating conditions.

Conclusion

In this review, the literature on the use of bio-diesel and alcohol fuels as well as ternary mixtures as fuels in compression ignition (CI) engines have been thoroughly reviewed, with special focus on fuel properties, combustion behavior, engine performance, emission properties and optimization strategies. According to the big results, non-edible and waste products as feedstocks to biodiesel have an immense contribution to the environment by reducing carbon monoxide, unburned hydrocarbons, and particulate matter emissions, and engine performance, when blended with petrol, was as good as conventional diesel. Alcohol fuels and, in particular, higher alcohols, including butanol and pentanol, also increase the quality of combustion (by improving atomization and mixing of air and fuel) but have low cetane number and low calorific value that negatively impact ignition stability and fuel consumption in pure form. Consensus Ternary fuel blends that incorporate diesel, biodiesel, and alcohols have become a good option in that fuel characteristics are well balanced to ensure the desired effects of fuel efficiency, lowering smoke emission, and satisfactory level of performance when optimized accordingly. Although these developments are made, a critical evaluation of the literature produced has shown that there are various shortcomings that prevent ternary blends to be used widely in CI engines. Numerous research has been focused on small-scale blend mixtures and operating conditions, and less attention has been paid to finer combustion diagnostics, long-term engine performance, and scalability across engines. Also, variation in experimental approaches, engine designs, and standards of reporting makes it difficult to compare and generalize results of different studies. The use of statistical and data-driven optimization methods like Taguchi method, Response Surface Methodology and artificial neural networks have been applied but their implementation has been in isolated cases without unified multi-objective optimization models to cater to performance, emissions and combustion stability at a given time. Moreover, studies that are region-specific, especially those based on Indian non-edible feedstock, and region-specific operating conditions are relatively few, restricting the practical usefulness of available results. Considering the above gaps, the current experimental studies are highly warranted, as it will be intended to investigate in a systematic fashion the biodiesel-based ternary fuel blends under controlled experimental conditions, detailed combustion analysis, and rigorous optimization tools. The target of the proposed study to produce credible, application-oriented findings by ensuring the engine performance is tested under a significant range of load conditions using non-edible and waste-based biodiesel feeds is expected to provide solutions to the technical and environmental issues. It is hoped that the results of this study will be helpful in the future of optimized, sustainable fuel policies to CI engines contributing to a cleaner burn, greater energy security and knowledgeable policy and engineering decisions.

References

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Copyright

Copyright © 2026 Rajinder Kumar, Dr. Basant Lal, Dr. Sunil Mahla. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.