I noticed some dust in the funnel when I filled my car's tank in a an emergency. Is this dust harmful to the engine? Will the fuel filter remove it?
All modern engines -gasoline or diesel- use fuel injection systems to inject fuel into the cylinder. A single high-pressure pump or two-stage low- and high-pressure pumps are used to bring fuel pressure up to a given level, at which it can be sprayed into the chamber or cylinder through a nozzle.
The presence of any type of particle within the fuel can be detrimental at two points of the system:
- The high-pressure pump. This is built to exacting tolerances, so any particles that could get between the moving surfaces will in time cause deterioration through friction. Furthermore, dust particles can contain some silicates (stone), which can be particularly abrasive.
- The injector nozzle. This may be considered simply as a very small hole, through which fuel passes. In this reference Injector Nozzle Geometry nozzle diameter is given as 0.090mm, meaning that hard particles above this diameter may cause blocking. Even smaller particles, in sufficient quantity could theoretically clog the output.
So, yes, the fuel filter should be built to eliminate such particles, at least those larger than the maximum size the injector nozzle can handle. This has most surely been taken into account by the manufacturer when designing the vehicle, so if you are using the original type of fuel filter you should be OK.
Actually, I would be more concerned by the presence of water in the fuel than dust particles - water sensors are present in some 4x4 vehicles, but are not usually found in passenger cars.