High Lubricity Coatings for High Pressure Fuel Pumps

Direct-injection (DI) fuel pumps operate on petroleum-based hydrocarbons that have inherent lubricating properties. DI fuel pumps that inject clean-burning liquid fuels with no lubricating properties (such as methanol or dimethyl ether) induce a major wear problem at the interface of the plunger and cylinder wall. Addition of a sacrificial liquid lubricant to reduce this wear would defeat the object of using clean-burning fuels. To alleviate this problem, this proposal outlines the development of corrosion and abrasion-resistant DI pumps with lubricity incorporated into the contacting and sliding surfaces of the pump. The proposed technique utilizes the well-established expertise of the Inframat Corporation in the area of thermal spray and describes the plasma spray of functionally graded nanostructured coatings that incorporate solid-state lubricity components into the plunger coatings. The grading is such that the lubricity component is concentrated at or near the sliding surfaces, while the corrosion and abrasion-resistant ceramic is concentrated at the underlying metal surface. This proposal describes plasma spray of corrosion/abrasion resistant ceramics (titania-alumina and/or yttria-stabilized zirconia) with functionally graded solid-state lubricating components (iron sulfide and/or iron oxide). Coatings will be plasma sprayed onto test coupons, characterized, tested for corrosion/abrasion performance, and the coefficient of friction will be determined to select the best coating materials for use with alcohol and ether-based fuels. Following fine tuning, a plan will be proposed in the final report to plasma spray coatings of the best composite materials onto DI fuel pump plungers to provide further test data on devices representative of the actual application. Included in the plan will be an outline of an automated pilot manufacturing line for coating DI fuel pump plungers.