Is it feasible to blend isobutanol and diesel?

Context

• Biofuel under consideration: Isobutanol – an alcohol compound with inflammable properties.
• Agency: Automotive Research Association of India (ARAI) exploring blending with diesel.
• Motivation: Ethanol blending with diesel was unsuccessful; isobutanol blends better with diesel.
• Pilot Project: Expected duration ~18 months; if successful, India may become the first country to blend isobutanol with diesel.

Relevance:

• GS3 (Economy / Energy / Environment): Alternative fuels, emission reduction, import substitution.
• GS3 (Science & Technology): Biofuel production, fermentation technology, engine performance studies.

Production & Raw Material

• Raw materials: Sugarcane syrup, molasses, grains, and other biomass sources used for ethanol production.
• Production process:
  • Specially engineered microbes ferment natural sugars under sterile conditions.
  • Unlike conventional yeast for ethanol, these microbes are designed to produce isobutanol.
• Infrastructure requirements:
  • Existing ethanol plants can be retrofitted:
    • Fermentation tanks slightly modified.
    • Distillation tanks to separate ethanol from isobutanol.
  • Example: 150 klp/d plant → 125 klp/d ethanol + 20 klp/d isobutanol with minimal changes.

Why Ethanol Was Discarded

• Miscibility: Ethanol blends poorly with diesel.
• Flash point concerns: Ethanol has a lower flash point → higher volatility → greater fire risk.
• Surplus issue: Ethanol is already in surplus; government targets 20% blending with petrol.

Advantages of Isobutanol

• Better blending with diesel: No need for efficiency complements.
• Higher flash point than ethanol: Safer for storage and transport.
• Emission benefits: Reduces pollutants and aids India’s net-zero targets.
• Import substitution: Reduces dependence on fossil diesel imports.
• Utilization of surplus biomass: Offers an alternative use for sugarcane molasses/syrup.

Challenges / Cons

• Cetane number: Significantly lower than diesel → may reduce ignition quality and combustion efficiency.
• Diesel knock risk: Uneven/premature combustion can damage engines and reduce power.
• Miscibility issues with diesel: Requires blending with biodiesel to stabilize mixture.
• Cost implications: Cetane-enhancing additives needed → incremental cost.
• Blending limit: No more than 10% isobutanol recommended in diesel to avoid engine issues.
• Further testing needed: Impacts vary by vehicle type and class; pilot studies essential.

Impact on Engine Performance

• Potential positive: Reduced emissions, better environmental outcomes.
• Potential negative:
  • Lower cetane → slower ignition, reduced power, risk of engine knock.
  • Proper additives required to restore performance.
• Pilot study essential to determine optimal blending ratios and effects on different engines.