Test Parameters Being Set for Crankcase Ventilation Filters
Nelson's EcoVent Recirculators Remove Particulate and Oil Mist from Engine Crankcase Breather Vents. Exhibit 99% Efficiency, 100% System Effectiveness (Reprinted from second Quarter 1996 CompressorTech)
Some 20 years ago, Nelson Division of Nelson Industries developed its crankcase ventilation filters for marine and stationary power applications where engines were confined in limited spaces. The filters contributed a great measure of safety and cleanliness to engine room environment. They also prevented air intake filters from becoming prematurely clogged because the vent filters eliminated oil mist being vented to engine rooms through the crankcase breather vent.
The Nelson product name was changed over the past year to EcoVent Recirculator, to reflect an additional major function - to keep products of combustion and oil mist from contaminating the atmosphere and contributing substantially to an ecologically clean environment.
According to Bob Ring, product manager for the EcoVent Recirculator, the effectiveness is derived from the fact that after the recirculator takes out 99% of the oil mist droplets, the remaining crankcase fumes can be directed through the air intake filter of the engine. The system, in effect, is closed loop so that no products of combustion or oil mist ever find their way into the engine room or the atmosphere via the engine crankcase vent.
During operation, the fine oil droplets are removed from the crankcase gases by an absorbent depth media. The droplets then coalesce and can be drained from the housing into the separate oil collection resevoir at the operator's convenience. Filtered crankcase gases can be redirected back into the engine either before or after the air intake filter.
"Though the EcoVent recirculator has been around for some time," Ring said, "recognized standards for crankcase emission filter testing are needed. Over this past year, our research division has taken giant steps to remedy this situation."
According to Nelson's research personnel, Chris Holm senior research engineer and Brian Schwandt, senior research scientist, public awareness and regulations governing air quality (1990 Clean Air Act), are influencing engine users to consider methods to reduce crankcase emissions. Applications where this is becoming an issue include engine crankcase emissions, air compressors, air brakes, and air industrial work settings. Several types of oil mist separators such as inertial separators, electrostatic precipitators, and cartridge filters are used in industry with varying degrees of success. Each applications challenging because of the relatively small size of oil mist particles (0.1 to 10 um in diameter) and customer needs for smaller, finer, less expensive filter systems.
The research team has developed dedicated test equipment for evaluating new and existing crankcase emission filters to assist in further development of the EcoVent Recirculator and to measure performance of both the Nelson product and others. The computer automated test temperature, flow rate, filter pressure drop, filter contaminant holding capacity, and reports filter efficiency both gravimetrically and by size using particle counters. The test bench is also used for testing crankcase pressure regulation devices.
The crankcase emission filter test bench includes an upstream HEPA (high efficiency air) filter to provide particle free air for testing, a programmable, controlled heater to select and maintain constant test temperatures and an oil mist generator to create an oil mist with or without solid contaminant, such as soot, to challenge the test filter. The size distribution of the oil mist itself can be controlled in the range of less than 0.1 um to about 10 um.
Also included is a mixing chamber to ensure proper, even mixing of the oil mist/contaminant with the air, a test filter holder for developing and evaluating sheets of filter media or for testing entire filter assemblies, upstream and downstream optical particle counters and condensation nuclei conters to measure and count particles as small as 0.01 um to 7 um. The particle size distribution data is used to determine filter efficiency by size and to characterize the oil mist being generated.
Upstream and downstream pressure ports are included to monitor both filter assembly and element pressure drop during testing. An absolute filter captures all oil mist and/or contaminant that may pass through the test filter. This mass is used to determine the filters gravimetric efficiency. An electronically controlled, variable-speed blower generates flow rates that would simulate blowby rates from a wide variety of engine sizes (1-50cfm). The research team developed custom software to control and record all aspects of test bench operation.
In addition to the crankcase emission filter test bench, Nelson performs full scale, computer-controlled engine tests. A well-equipped analytical laboratory, including a scanning electron microscope with energy dispersive X-ray analysis, is also available for filter materials development.