The diameter of sticks from the same species of wood (we use Douglas fir at ARC for testing) seems to have a dramatic effect on emissions and thermal efficiency. We used to use small diameter sticks of wood and experienced high thermal efficiency, low CO and high PM2.5. Small sticks make a lot of flame as the wood burns quickly and minimizes the burning of charcoal. Charcoal is known to make lots of CO but little PM2.5. Lots of flame may result in high temperature gases that increase thermal efficiency.

Trying to decrease PM2.5 in a wood burning stove has pushed us to try burning bigger diameter sticks. Maybe more charcoal is then burning, which reduces PM2.5 but increases CO?  It also seems harder to achieve 50% thermal efficiency. 

It’s beginning to look like one of the most effective strategies to achieve project goals is to adjust the diameter of the burning sticks.

It is great to do standardized testing! CO was never a problem when we used small sticks. Now, using bigger sticks (1” by 1.5” in diameter) we struggle to get Tier 3 for CO but PM2.5 seems to be lot better. Without standardized testing, the influence of changes like the diameter of sticks might escape unnoticed.

Some days I love science!