Published: Nov 2012
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Diesel engine fuel pump and fuel injection system components rely for lubrication on the fuels that are generally not good lubricants. Diesel fuels have low viscosities and are composed almost entirely of nonpolar hydrocarbons with intrinsically poor boundary lubricating properties. To achieve relatively complete combustion to reduce exhaust emissions, fuel injection pressures in diesel engines of recent manufacture are becoming very high (~200 MPa) to achieve fine atomization of the fuel. The tolerances between the plungers and the bores in fuel injectors (e.g., Figure 23.1) must be extremely tight, typically 2–4 μm, to seal the pressure between the top and bottom ends . The combination of the low fuel lubricity and tight geometric clearance makes the diesel fuel injector operate at boundary lubrication and vulnerable to scuffing damage that would cause the injector plunger to stick or seize, leading to an engine failure.
Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN