Question

For determining the ignition quality of compression ignition engine fuels, the reference fuels used are

1. Iso octane and n heptane
2. Cetane and α methy naphthalene
3. Hexadecane and n heptanes
4. Cetane and iso octane

Answer 1

Correct Answer - Option 2 : Cetane and α methy naphthalene

Explanation:

Rating of CI engine fuels:

• Knock rating of a CI engine fuel is found by comparing it with a reference fuel under prescribed working conditions.
• Reference fuel:
  • Normal Cetane (C16H34) which is assigned a Cetane number of 100 and α-methyl naphthalene (C11H10) which is assigned a Cetane number of zero.

​Cetane Number (CN):

• It is the measure of the combustion quality of diesel oil or it is the measure of the ignition delay.
• Cetane number (cetane rating) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. 
• It is an inverse of the similar octane rating for gasoline.
• The CN is an important factor in determining the quality of diesel fuel, but not the only one; other measurements of diesel’s quality include energy content, density, lubricity, cold-flow properties, and sulfur content.

According to a standard practice, the antiknock value of an SI engine fuel is determined by comparing its antiknock property with a mixture of two reference fuels, normal heptane (C7H18) and iso-octane (C8H18).