Mohazzam Saeed Consider the burning of a fuel in an engine. The rate of burning is controlled by access of oxygen to to surface of the petroleum. Smaller particles/droplets increase the burning in relation to their surface area. Generally as the size decreases the reactivity increases by a squared factor as surface is proportional to 1/d2.

Alan F Rawle Thank you for your answer,

Could you elaborate (particularly for pyrolysis) on the concept of reactivity , increasing by a squared factor as the particle size decreases? How is this relationship determined or measured?

Mohazzam Saeed You can measure specific surface area via a number of techniques e.g. BET, porosimetry. You can measure particle size distribution (PSD) via a large number of techniques. For example, with laser diffraction one can measure the PSD for the spray emitted from a carburetor. Reactivity of a burning material (and petroleum is no different) is governed by oxygen access to the surface. The 1/d2 relationship is basic and discussed in any standard particle size textbook. Take a look at these webinars (free registration required). References to basic texts are provided within these:

Particle Size Masterclass: Why Measure Particle Size?

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W181002PSMasterclass.html

How to measure particle size distribution

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W181023HowisPSmeasured.html

Basic Principles of Particle Size Analysis

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W170216BasicsParticleSize

Good luck with your research.