Quantification of the Impacts of Vibration and Flow Fluctuation on Automotive Air Filter Performance, 08-R8058

Principal Investigator
Martin Treuhaft
 

Inclusive Dates:  04/01/09 – 09/30/10

Background - Diesel and gasoline internal combustion engines are the primary sources of motive power for automobiles and heavy-duty vehicles. In spite of efforts to find alternatives, these engines will likely retain this role well into the foreseeable future. Air induction is a primary process in the operation of an internal combustion engine. A key component of the air induction system is the air cleaner, and more specifically, the air filter element, which protects the engine from becoming dirty, and therefore, susceptible to wear. The burden placed on the air filter has significantly increased as engine designers have been forced to use more aggressive combustion control strategies and sophisticated after-treatments to meet increasingly stringent emission standards worldwide. Previously, the consequences of wear were mostly related to engine performance and longevity. Now, major concerns include the impacts of wear-induced blow-by on downstream emission control components, such as exhaust catalysts and diesel engine particulate traps. It is well known that atmospheric dust particles, especially in highly dusty environments, can contribute significantly to ring and liner wear if the particles are not adequately removed from the incoming air. Furthermore, the buildup of deposits on the mass air flow sensor can affect sensitivity and greatly distort performance, resulting in power loss and increased fuel consumption and exhaust emissions.

Modern air filters are expected to meet specific performance values given in industry and government specifications when tested to specific protocols typically given in organizational standards, developed and upgraded over time by a committee of interested members. All of these standardized tests evaluate air filter performance under static mechanical conditions that ignore vibration and vibration plus flow fluctuation. As such, despite technical advances in filter design and materials technology, laboratory proven air cleaner systems and filter elements sometimes perform poorly in real-world environments. This not only demonstrates that there can be a significant difference between testing conditions and working conditions, but also that it is a mistake to assume that laboratory performance will automatically translate directly to performance in the field. To ensure that vehicle propulsion system components are adequately protected from airborne dust, realistic air filter testing must be performed. It is conjectured that vibration, and specifically vibration combined with flow fluctuation, are important parameters that should not be excluded from such tests, as they are now.

Approach - The purpose of this project was to lay the groundwork for correcting this situation. The approach was to (1) develop vibration data through field testing and then conduct laboratory experiments to examine the extent to which filter performance is impacted by flow fluctuation, vibration and vibration plus simultaneous flow fluctuation, and to (2) increase SwRI's knowledge to provide enough scientific evidence, if the data corroborated the project's contentions, to show the automotive and air filter industries that a closer look at how air filters are specified and tested is warranted. As such, field testing of instrumented vehicles was conducted to measure vibration spectra encountered by many air filter systems under real-world conditions. These spectra were used to design test matrices for combined dust and vibration testing of air filters for specific vehicle classes (passenger cars, light duty trucks, and on and off-road heavy duty trucks and construction equipment, for example). Laboratory testing was conducted on selected air filter systems with and without vibration, with and without flow fluctuation, and with combined flow fluctuation and vibration. For the most part, this testing was conducted in accordance with the standard test procedures given in ISO 5011, with the addition of downstream particle sizing. Data for many of the filter subsets were analyzed, although time did not allow full analysis for all of the filter performance data sets. Further data analysis and, for some cases additional testing, are needed to fully define the nature of the problem.

Accomplishments - Because not all data sets were analyzed, it is not possible to fully quantify the extent to which vibration and flow fluctuation universally impact filter performance. What can be said is as follows:

• Vibration and flow fluctuation significantly degraded filtration performance for some systems, while the impact of these parameters on other systems appears to be less evident. Further data analysis and, for some cases additional testing, are needed to fully define the nature of the problem.

• This result is not necessarily surprising. Even if all of the data had been analyzed and if additional testing had been completed, variations in systems design and media selection would be expected to produce variable results. This was a major consideration during system selection and a primary reason why multiple system designs and media types were chosen for testing.

• Sufficient results were obtained to strongly indicate that vibration and flow fluctuation, especially when combined, as is the case in almost all pertinent applications, provide sufficient risk to filter performance to warrant earnest consideration by the filtration industry and air filtration standards committees.

• Another important reason to take a second look at the vibration issue is the need for better filtration required by new engine technologies and combustion and emissions control strategies that would be easily compromised by engine wear. This is recognized by SAE and ISO, and is a major reason why they are working to add upstream and downstream particle sizing to their current air filtration test standards so that they can more accurately measure filter performance by providing fractional efficiency data as a function of test time (dust loading).

• Vehicle and air cleaner manufacturers do a reasonably good job in reducing the amount of engine and vehicle vibration that is transferred to the air cleaner and filter element. Nevertheless, sufficient vibration is transferred in many cases to make air cleaner vibration a concern.

Supporting data for an automotive panel filter (Figures 1 and 2) and for a heavy-duty, axial seal air filter system (Figures 3 to 5) are shown below. The data shown in Figures 1 and 2 for mass efficiency and mass penetration show decreasing cumulative mass efficiency and increasing cumulative mass penetration under vibration and vibration plus flow fluctuation. The particle size data shown in Figures 3 to 5 show increasing downstream particle concentrations with flow fluctuation and with flow fluctuation plus vibration as a function of test time (dust loading).

2010 Program Home