# Heat Release Rates of Straight Soybean and Diesel Oil Blends in a Compression Ignition Engine
## 4 Conclusions  
This work was aimed at the applicability analysis of soybean oil blends in compression ignition engines, studying the heat release rate obtained from in-cylinder pressure measurements. Tests on the dynamometric bench were carried out for diesel oil and two blends, 50/50% \(v/v\) and 80/20% \(v/v\) of soybean and diesel oils. The engine was tested at 1800 and 2100 rpm. In-cylinder pressure readings were recorded and processed to calculate the heat release rate using a zero-dimensional approach. The maximum in-cylinder pressure, ignition delay, and spray parameters were also determined. The results evidenced the premixed, nonpermixed (diffusive), and residual combustion phases. The influence of the physicochemical fuel properties was also evidenced in the experimental results. The premixed combustion phase was similar for all fuels tested at 1800 and 2100 rpm. For the blend of 80% soybean oil, the high \(SMD\) (Sauter mean diameter) and the highest fraction of vegetable oil led to a combustion delay, characterized by high diffusive and residual combustion phases. However, the oxygen content, heating, and high engine speeds favored its combustion. Products of vegetable oil degradation may increase or inhibit the ignition, depending on their chemical nature. In the case of the blend of 50% soybean oil, it is suggested that the highest \(SMD\) increased the droplet Reynold number and, therefore, the evaporation constant. Finally, the results allowed us to observe the feasibility of using straight soybean oil and diesel oil blends as alternatives for electricity generation for replacing diesel oil in isolated regions and also small applications demanded by the agro-industrial sector. Additionally, the results will support the development of a specific combustion model for straight vegetable oils in order to model and optimize the diesel engine operation with these biofuels. Conceptualization, N.A.N.G., A.A.M.O. and E.B. ; methodology, N.A.N.G., A.A.M.O. and E.B. ; software, N.A.N.G. ; validation, N.A.N.G. ; data curation, N.A.N.G. ; formal analysis, N.A.N.G., A.A.M.O. and E.B. ; writing--original draft preparation, N.A.N.G. ; writing--review and editing, N.A.N.G., A.A.M.O. and E.B. ; supervision, A.A.M.O. and E.B. All authors have read and agreed to the published version of the manuscript. This research was funded by CNPq (National Council for Scientific and Technological Development, Grant number: 201205451), and by Mechanical Engineering Graduate Program at Federal University of Santa Catarina. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in the study are included in the article, and university library collection at [[https://pergamum.ufsc.br/acervo/352068](https://pergamum.ufsc.br/acervo/352068)]([https://pergamum.ufsc.br/acervo/352068](https://pergamum.ufsc.br/acervo/352068)) (accessed on 23 September 2024). Further inquiries can be directed to the corresponding author. **Acknowledgments:** The authors acknowledge CNPq (National Council for Scientific and Technological Development) for the scholarship for [PERSON], and Mechanical Engineering Graduate Program at Federal University of Santa Catarina. **Conflicts of Interest:** The authors declare no conflicts of interest.