A 3D CFD Combustion Evaluation of Hydrotreated Vegetable Oil (HVO) as a Potential Alternate Fuel for the Future CI Engines

Transportation industry is facing the growing challenge to reduce its carbon footprint and utilize the carbon neutral, more environmentally sustainable fuels to comply with the goal of carbon neutrality. Implementation of carbon free fuels such as Hydrogen, Ammonia and low carbon fuels such as Methanol, Ethanol can significantly reduce the greenhouse gas emissions, but these fuels are suitable for SI engine architecture due to their high-octane ratings. Hydrotreated Vegetable Oil (HVO) is one of the few fuel solutions available today with a high Cetane rating (70-80), that can be used as a drop-in fuel in the existing CI engines, with minimal modifications. The main constituent of HVO is pure alkane and it can be produced from feedstocks such as vegetable oils, animal fats and various wastes and by-products. A closed cycle 3-D CFD combustion simulation using a detailed chemistry-based solver was conducted with the HVO, on a three cylinder, naturally aspirated water-cooled CI engine at its full load, rated rpm. Chemical kinetics file with 92 species and 1240 reactions was used as a surrogate for the HVO to conduct the combustion simulation. The peak firing pressure was observed to be lower by 3% and SoC was advanced by 1o CA for HVO as compared to the baseline diesel. HVO combustion manifested the same thermal efficiency with respect to its diesel counterpart. Soot emission was 35.3% lower for HVO due to the absence of unsaturated hydrocarbons and the NOx emission was lowered by 31.7% for HVO, as a consequence of a lowered in-cylinder temperature. Simultaneously, a 12.8% reduction in CO, 77.2% reduction in UHC and 72.7% reduction in VOC was observed for HVO as compared to diesel. Additionally, the CO2 emissions were almost equal for HVO and diesel, and a meticulous monitoring of unregulated emissions proved that the HVO exhaust is devoid of their presence. The 3D CFD combustion exploration unveils that the HVO indeed holds the potential to be a promising drop-in alternate fuel for the next generation CI engines.