**2. Insight to physiochemical traits**

The engine manufacturers are primarily focused on the efficiency of utilization of fuel. But while efficient biofuel is one priority area of research, the development of biofuel-efficient engines is another. Understanding the characteristics of biofuel leads to a vast field of study based on utilization, engine requirements, and efficiency. The criteria used to identify modifications in biofuel properties that either directly or indirectly affect fuel atomization and combustion define the biofuel's quality [17]. Key properties of efficient biofuel are its well to mix nature with air and ability to combust. The volatile nature of fuel is the major aspect of physical property. The volatile nature determines the Reid Vapor Pressure (RVP), measure of propensity of fuel. The ability of SI engine to startup when cold is another important requirement, at that time fuel vaporization signifies the utility and efficiency, as it determines the ease at which engine will start and blending percentage for good ignition. In the context of biofuels, ethanol has more latent heat of vaporization than gasoline fuel, requires more heat to get vaporized [18]. The higher electrical conductivity of biofuels restricts its 100% usage; hence, blending for good ignition is required, which opens up the scope of improvement in terms of ignition properties.

Commercial incorporation of biofuels as a major fuel is still critically overlooked as in case of diesel engines, fuel atomization process is having little time in combustion chamber when fuel is injected; the crucial step is determined by its important physical properties, namely fuel density, viscosity, fuel surface tension, and obviously the quality of biofuel occupies the position and creates huge scope of processing. The quality of the fatty acid profiles of biofuel or biodiesel fuels, with biodiesel having all higher values, significantly influences these physical properties. A sensor in the exhaust of modern engines can also detect changes in mixture, whereas biofuels with higher blends require more engine modifications. The chemical properties of biofuels are strongly affected by their different molecular structures; presence of oxygen is one of them. Whereas, resistance to self-ignition determines its higher octane number, shows it has resistance to knock [19].

The chemical properties of biofuel mixture are simply the sum of chemistries of each of the constituents, When consideration is taken in the context of modeling of biofuels in terms of molecular weight, the example can be used as methyl-butanoate, the approaches can be envisioned for answering the question of whether utilizing methyl-butanoate a model to study the kinetics of qualitative characteristics of long-chain fatty acids combustion. May be this can be used as a prerequisite to address the issues in modeling of ideal biofuel in order to mitigate the negative temperature coefficient behavior that causes ignition delay of biofuels [20]. The oxidative stability of biofuel is another important concern, with reference to canola/rapeseed derived biofuels, which contain unsaturated components in the oil. Presence of small amount of unsaturated fatty acids creates instability and is prone to photo oxidation, etc. [21]; hence, additives for oxidation stability are preferred in plant-derived fuels. Likely the concern is lowered when looking forward toward the oxygenated diesel fuels rather than the conventional ones; the presence of oxygen in biofuels is helpful in reducing the harmful emissions. Therefore, the oxidation of every individual part is critical in

**Figure 1.** *Physiochemical parameters/factors affecting quality of biofuel.*

the context of influencing the oxidation of other components, this result in the scope of determination of detailed chemical and kinetics study. The all physiochemical factors occupy the equivalent position when it comes to the production of efficient biofuel; the summary is shown in **Figure 1.**
