Self-Ignition Temperature of Diesel vs Petrol – SSC JE 2014 (Morning)

Question:

Self-ignition temperature of diesel as compared to petrol:

(a) is higher / उच्चतर होता है
(b) is lower / निम्नतर होता है 
(c) is same / समान रहता है
(d) varies considerably / काफी परिवर्तन रहता है

Correct Answer: (b) is lower

Video Solutions: Click here

Explanation:

• Self-Ignition Temperature (SIT) is the temperature at which a fuel spontaneously ignites without an external ignition source like a spark.

• Diesel: SIT ≈ 210°C

• Petrol: SIT ≈ 247–280°C

• Since diesel has a lower self-ignition temperature, it can ignite just by the heat generated during compression — hence diesel engines use compression ignition.

• Petrol requires a higher temperature to ignite, so petrol engines use spark ignition.

Key Points for Exams:

• Diesel SIT < Petrol SIT

• Diesel engine → Compression Ignition (no spark plug)

• Petrol engine → Spark Ignition (uses spark plug)