• In 4 stroke engines firing order 1-3-4-2 is most commonly used than other orders because it delivers more smooth and efficient power output.
• The reason is that, lets divide the flywheel into 4 equal parts.
• Means from 0^o to 90^o power is generated by cylindernumber1 and likewise upto 360^o or 0^o by 4 cylinders.

Hence, the correct option is (D).

&Key Points:-