Subtopic: Bio-fuels and their use in farm mechanization
Question Statement:
Which of the following statements regarding the production and fuel properties of biodiesel (Fatty Acid Methyl Esters - FAME) derived from non-edible vegetable oils (such as Jatropha curcas or Pongamia pinnata) is/are CORRECT?
Options:
(A) Transesterification converts high-viscosity triglycerides into methyl esters and glycerol by reaction with methanol in the presence of an alkali catalyst
(B) Biodiesel exhibits a higher cetane number than standard petroleum diesel, resulting in shorter ignition delay in compression-ignition engines
(C) Neat biodiesel (B100) has a significantly lower kinematic viscosity than straight vegetable oil, reducing fuel injector spray coking
(D) The gross calorific value of neat biodiesel is approximately $20\text{--}25\%$ higher than that of fossil diesel fuel
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
- **Statement A is correct:** Transesterification reacts $1\text{ mole}$ triglyceride with $3\text{ moles}$ methanol yielding $3\text{ moles}$ FAME and $1\text{ mole}$ byproduct glycerol.
- **Statement B is correct:** Biodiesel typically has a cetane number of $52\text{--}58$ compared to $45\text{--}48$ for regular petrodiesel, accelerating auto-ignition.
- **Statement C is correct:** Raw vegetable oil has a viscosity of $35\text{--}50\text{ cSt}$ at $40^\circ\text{C}$ (causing severe gumming and injector carbonization), while transesterified biodiesel has a viscosity of $4\text{--}6\text{ cSt}$, very close to diesel ($2\text{--}4.5\text{ cSt}$).
- **Statement D is incorrect:** Biodiesel contains $\approx 10\text{--}11\%$ bound oxygen, resulting in a lower energy density ($37\text{--}38\text{ MJ/kg}$) compared to fossil diesel ($42.5\text{--}44\text{ MJ/kg}$), which is about $10\text{--}12\%$ lower, not higher.