Wear and Friction Effects on Engine Materials of N-Butanol in Ultra-Low Sulfure Diesel Mixtures

Introduction

The lack of sulfur beneficial lubricity in ultra-low sulfur diesel (ULSD) may lead to premature wear and failure of diesel-fuel systems. Mixing of small percentages of, for instance, biodiesels and other biofuels is typically used to add lubricity in ULSD. N-Butanol is a new alternative fuel being researched for either diluting or replacing some of the mineral diesel fuel without significantly sacrificing internal-combustion engine efficiency (Han, 2017).

Since ULSD fuel was made mandatory for some typical engine applications their lubricity became a concern (because sulfur has anti-wear properties); the addition of biodiesels as additives is a typical solution to ULSD poor lubricity (Hu, 2005). There is specifics knowledge on biodiesel tribological effects in engines (for instance, on the addition of relatively small percentages of biodiesels mixed in mineral diesel, because of their beneficial lubricant properties in the diesel-injector conduits). The wider introduction of alternative fuels, typically biodiesels, to partially or fully replace mineral diesel also brought an early interest on the overall anti-wear properties of biofuels in mineral-diesel mixtures (Agarwal, 2005). Early wear testing was carried out by Schumacher et al (1994) in their extensive study on lubricating properties, in particular on wear prevention properties of biodiesel and biodiesel blends. They employed three different tribometer measuring systems to determine the lubricity of diesel fuels: a ball on cylinder lubricity tribometer, a High-Frequency-Reciprocating-Rig (HFRR) tribometer, and a ball-on-three-seats test rig. The tested biodiesels were added (as 0.2%, 2%, 5%, 10%, and 20% of the total blends) to diesel fuel of two types: of low sulfur/low aromatics content, and of low sulfur/high aromatics one. They found that mineral-diesel fuel dilutions by a 5% or a lower fraction of biodiesel led to no measurable lubricity changes as compared to that of pure fuel. But a 20% dilution by biodiesel led to significant lower wear for both tested types of diesel fuel blends. Similar results were observed by Wadumesthrige et al (2009). Sulek et al (2010) employed a HFRR tribometer to test mineral-diesel fuel diluted by a biodiesel derived from rapeseed oil. They found that 5% of added biodiesel led to a 20% reduction of friction coefficient as compared to that for pure mineral diesel, but that further increases of biodiesel fractions to 20%, 25% and 30% significantly increased friction.