## 1 Introduction
The current delay in replacing fossil fuels with biofuels in the diesel fleet is primarily due to the high economic costs of these processes. As a result, alternative methods that focus on reducing the viscosity of triglycerides to make them viable for use in existing C.I. engines are being explored for economic feasibility [9]. Various ongoing investigations aim to reduce the production costs of biodiesel using SVOs as a renewable fuel in current C.I. engines, which are traditionally operated with fossil diesel. One promising research direction involves reducing the viscosity of SVOs by blending them with low-viscosity organic solvents until the mixture falls within the range of 2.5 to 4.0 cSt, similar to that of fossil diesel. These low-viscosity solvents, ideally renewable, can be mixed in suitable proportions to achieve the desired viscosity, making them compatible with current C.I. engines. The organic solvents studied so far have a relatively low viscosity because they consist of short-oxygenated hydrocarbon chains. However, these short chains result in relatively low cetane numbers, leading to the classification of these solvents as LVLC (low viscosity and low cetane) solvents [10]. Over the past decade, numerous studies have explored the use of short-chain renewable alcohols as LVLC solvents for reducing the viscosity of various SVOs to levels acceptable for C.I. engines. These mixtures generally produce suitable biofuels with a relatively low cetane number due to the lower calorific value of these alcohols [11; 12; 13; 14; 15]. Additionally, other organic compounds with higher calorific values, more comparable to fossil diesel, have also been investigated as LVLC solvents. Their mixtures with SVOsexhibit better combustion characteristics and performance than short-chain alcohols, but they are typically more expensive. Oils such as Melaleuca cajuputi (MCO) [16], pine oil [17], eucalyptus oil [12; 16], orange oil [12; 18], and camphor oil [19] have all been evaluated as LVLC solvents. However, the high cost of these compounds means that short-chain alcohol remains the most viable option since they can be produced from a wide range of biomass transformation procedures, giving them the advantage of producing economical and renewable biofuels. Moreover, this method eliminates the need for chemical transformation to reduce the viscosity and allows the complete utilization of the oil. Consequently, this is the easiest and most economical method described to use vegetable oils as biofuels without generating any type of waste and reducing the cost to that of the SVO and the LVLC solvent used in the mixture. These optimized SVO/LVLC blends can also be used in triple blends with conventional fossil diesel to improve the cetane number to the levels required for optimal diesel engine performance. While these triple blends do not completely eliminate anthropogenic CO\({}_{2}\) emissions, they offer a significant reduction and represent a major step forward in the transition away from fossil fuels in the current diesel engine fleet. Ternary blends of SVO, diesel, and LVLC solvents have been shown to reduce smoke, CO, NOx, and unburned hydrocarbon emissions, particularly at high loads, highlighting their potential as a renewable energy source to partially or fully replace diesel fuel [20]. Consequently, considering the technical and economic feasibility of this approach, which enables the use of various vegetable oils and LVLC solvents as renewable fuels in current diesel engines, several studies have been conducted. Nevertheless, the selection of feedstocks for renewable fuel applications focuses on oils that do not compete with food supply and are feasible for large-scale industrial production. Castor oil, a non-edible vegetable oil, is particularly promising due to its established use in chemical industries and its global annual production of approximately 220,000 tons [21]. Its non-edible nature ensures no competition with the food chain, and its adaptability to grow in marginal lands further enhances its sustainability.