Emission Characteristics of a Diesel Engine Fueled with Fish Oil Biodiesel Blends Using EGR and Cetane Improver

Abstract

This study examines the emission characteristics of a single-cylinder, four-stroke diesel engine operating on fish oil biodiesel blends (B20, B30, B40) containing 0.5% ethylhexyl nitrate (EHN) as a cetane improver. Exhaust gas recirculation (EGR) was applied at rates of 0%, 10%, and 20%. Results indicate a notable reduction in nitrogen oxide (NOx) emissions—B40E0.5 with 20% EGR reduced NOx by 34.89% (1112 ppm) compared to diesel (1500 ppm) at full load. Carbon monoxide (CO) and hydrocarbon (HC) emissions were lower with biodiesel blends but showed slight increases with higher EGR due to oxygen deficiency. Smoke opacity increased with both biodiesel proportion and EGR, a result of shorter ignition delays caused by EHN. A B40 blend with 15% EGR provided the most balanced emission profile, minimizing NOx while managing CO, HC, and smoke levels.

Introduction

Fish oil biodiesel, derived from waste fish processing, is a renewable fuel that reduces emissions like carbon monoxide (CO), hydrocarbons (HC), and smoke. However, its high oxygen content can increase nitrogen oxides (NOx). This study explores how combining Exhaust Gas Recirculation (EGR) and a cetane improver (ethylhexyl nitrate or EHN) can reduce NOx without compromising engine performance.

Methodology:

• Engine Setup: Single-cylinder, 4-stroke diesel engine at constant 1500 rpm, tested with 0%, 10%, and 20% EGR rates.

• Emission Measurement: NOx, CO, HC via AVL gas analyzer; smoke via AVL 437 smoke meter.

• Test Fuels: Diesel blended with 20%, 30%, and 40% fish oil biodiesel (B20, B30, B40) + 0.5% EHN (cetane improver).

Key Findings:

• CO Emissions:

  • All biodiesel-EHN blends (B20E0.5, B30E0.5, B40E0.5) showed lower CO emissions than pure diesel.

  • EHN improves ignition by shortening ignition delay, promoting more complete combustion, and reducing CO from incomplete burn zones.

  • Higher biodiesel content combined with EHN leads to enhanced carbon oxidation and cleaner combustion.

Conclusion

The use of fish oil biodiesel blends, combined with 0.5% ethylhexyl nitrate (EHN) and moderate exhaust gas recirculation (EGR) at 15%, has proven to be an effective strategy for reducing emissions in diesel engines. The incorporation of EGR plays a crucial role in lowering NOx emissions by recirculating a portion of the exhaust gases back into the intake, thereby reducing peak combustion temperatures. In particular, the B40E0.5 blend (40% fish oil biodiesel with 0.5% EHN) achieved a significant 34.89% reduction in NOx emissions at 20% EGR compared to baseline diesel operation. This demonstrates the strong potential of this combination in addressing stringent NOx regulations. In addition to NOx reduction, the oxygenated nature of biodiesel contributes positively to the reduction of carbon monoxide (CO) and unburned hydrocarbons (HC). The inherent oxygen in the biodiesel promotes more complete combustion, thereby lowering CO and HC formation. However, the introduction of EGR, while beneficial for NOx control, tends to slightly increase CO and HC emissions due to the dilution of the intake charge and the consequent reduction in oxygen availability for combustion. Smoke opacity—a key indicator of particulate emissions—also reflects the complex interplay between blend composition and EGR rate. While biodiesel\'s cleaner-burning characteristics help reduce smoke under certain conditions, excessive EGR or suboptimal blend ratios can lead to increased soot formation. Therefore, achieving minimal smoke levels requires careful optimization of both EGR rate and biodiesel blend percentage to ensure the right balance between temperature control and oxygen availability. Overall, the combination of fish oil biodiesel, EHN additive, and moderate EGR (15%) offers a practical and sustainable approach for reducing harmful emissions in diesel engines without significantly compromising performance. This strategy not only helps in meeting environmental regulations but also supports the transition towards cleaner, renewable fuel alternatives. Future work should aim to fine-tune these parameters under varying load and speed conditions, and explore advanced EGR technologies (e.g., cold EGR) to further enhance the emission reduction potential.

References

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Copyright

Copyright © 2025 Samudrala Rama, Banka Hemasunder. 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.