Researchers investigated this, along with fuel consumption and chip size distribution.
Buyers of forest fuels require chip size distribution to be within their specifications. However, the chip size distribution also affects chipping contractors due to its influence on fuel consumption and chipper productivity. With open drum chippers, chip length is partly controlled by the mesh size of the sieve. In order to determine how sieve size affects productivity and fuel consumption, researchers investigated two open drum machines in northern Sweden for the professional chipping of forest fuels. Small chippers were represented by a Kesla 645 powered by a 270 kW (367 hp) farm tractor, and larger ones by an Eschlbock Biber 92 powered by a 358 kW (487 hp) farm tractor. The chippers were processing biomass from a first thinning operation.
The Kesla chipper was studied with 25, 50 and 100 mm (1.0, 2.0 and 3.9 in) sieves, while the Biber was studied with 35, 50 and 100 mm (1.4, 2.0 and 3.9 in) sieves. The results showed that with a 100 mm (3.9 in) sieve, the Kesla chipper was able to produce 14.5 oven dry tons of chips per productive machine hour, while the Biber chipper could produce 30 oven dry tons per productive machine hour. The fuel consumption per oven dry ton was 3 litres (0.79 gal) for the Kesla and 2.1 litres (0.55 gal) for the Biber. Reducing the mesh size decreased the size of chips produced by the Kesla, but not the Biber. This was due to the sieve on the Biber mainly serving to reduce oversize chips, while chip length is mostly controlled by the cut length of the knives.
The research was titled “Effects of chipper size on chipper productivity, fuel consumption and chip size distribution for open drum chippers”. It was published in the Croatian Journal of Forest Engineering, Vol 36(1), 2015. The authors were L Eliasson, H von Hofsten, T Johannesson, R Spinelli and T Thierfelder. Source: http://www.crojfe.com/articles-861#864