Boric acid as a lubricating fuel additive - Simplified lab experiments to understand fuel consumption reduction in field test

In field tests, a boric acid based fuel additive has led to reduced fuel consumption. The reduction was substantial, an average of 6 and 10% in passenger cars and diesel generators respectively. Aiming towards improved understanding of mechanisms behind the fuel saving, three methods to mimic the effect of the additive in the piston-ring/cylinder contact have been evaluated. A reciprocating cylinder/flat configuration with ball bearing steel against grey cast iron was used, and it was lubricated with base oil. The different methods were as following: A) repeated spraying of a small amount of the boric acid solution onto the surfaces, B) predeposition of a boric acid layer on the flat surface and C) a combination of method A) and B). The three methods all showed effects of the additive, spanning from about 20% to 50% reductions (in the latter case, from roughly 0.1 to 0.05 in coefficient of friction averaged over the stroke). The greatest potential of the additive was seen with local coefficient of frictions lower than 0.020 in tests at room temperature with Method C. This means a reduction of around 75% compared to the lowest levels measured for the reference tests run without the additive. The most stable friction test was Method A, where a small amount of boric acid solution was repeatedly sprayed onto the lubricated sliding surfaces. In this type of test, friction reductions of roughly 20% and 40% were found at 100 °C and room temperature respectively. The tribological and chemical mechanisms of boric acid in this test configuration are yet not fully understood and more studies are needed. However, the observed poor stability of the tribofilms containing boron and oxygen complicates such activities.