Bulk Fuel Filtration for Off-Road Applications

  Richard Douglas, Caterpillar |  2013

How evolution of modern High Pressure Common Rail engine (off-road) drove the need for cleaner fuel; and a discussion on the need for and value of bulk fuel filtration (for off-road use)

  • Review of fuel cleanliness problems in the mining world and the efficacy of bulk fuel filtration to fix those problems
  • 90% of all problems with diesel fuel systems caused by dirt and water (has not changed), but what has changed is the power density of engines and resultant injection pressures of the fuel systems
  • Believes increased engine problems related to fuel cleanliness caused by Tier 4 Emission Standards – “new high pressure fuel systems simply cannot provide adequate performance and service life without very clean fuel”
  • Minimum ISO cleanly recommendation for diesel fuel is ISO 16/13/11 or better; free water is 500 ppm or less
  • New Caterpillar systems use 3 stage filtration to guarantee extra clean fuel: 10 micron primary, 4 micron secondary and 4 micron tertiary
  • Only reliable way to determine fuel cleanliness is by sampling in dynamic flow with laser particle counter
  • Comparison of old engine technology to modern common rail systems and why newer engines have more problems than older ones
    • Engines used to be much simpler and much less sensitive to dirt – injection pressures were typically 15,000 psi or less; emissions regulations were limited or non-existent
    • Mechanical unit injectors (early to mid-90s); injector pressures were 18,000-20,000 psi; emissions regulations were reasonable and easily met
    • Electronic unit injectors (mid 90s to 2007); injection pressures were 22,000-30,000 psi; on-highway emissions got tougher and deterioration of fuel system components impact on emissions was better understood – became understood that microscopic abrasive particles in the fuel were the major source of injector wear
    • Modern High Pressure Common Rail Engines: injector pressures of 30,000 psi; faster start and end of injection, and injection rate shaping capability; emissions regulations continue to get tougher
      • Engines/combustion design alone no longer capable of meeting emission standards without significant after-treatment (catalytic converters, particulate traps, and exhaust gas recirculation systems);
      • Pressurized fuel becomes very hot and remains hot for extended period of time, causing it to cook in the fuel rail (especially in large engines); no return flow (fuel pressurized to 30,000 psi flows very slowly from pump to injector nozzles) – temperature of pressurized fuel is increased about 125– 150°F above ambient due to the heat of pressurization and it has time to soak up additional heat from engine – “In high ambient temperature environments, this provides much more time, temperature and opportunity for asphaltines to form in the fuel than an EUI fuel.”
      • High temperatures also mean lower fuel viscosity, which reduces critical size of wear particles and makes very clean fuel essential
  • Review of success of bulk filter filtration installation in CAT mining equipment – drastic reduction (90%) in need to replace injectors & unscheduled fuel filters
  • Fuel analysis shows plugging of coalescer elements (which causes injector failures) is caused by corrosion inhibitors added to fuel by pipelines – coalescing elements in bulk filtration units effectively remove corrosion inhibitors and prevent injector failures

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