Intake and Exhaust Systems
The function of air cleaners is to hinder dust contained in the intake air from entering the engine and thus to prevent premature engine wear. Air cleaners are additionally employed to damp intake noise.
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Intake and Exhaust Systems Oswald Parr, Jan Kru¨ger, and Leonhard Vilser
13.1
Air Cleaners
13.1.1
Requirements
The function of air cleaners is to hinder dust contained in the intake air from entering the engine and thus to prevent premature engine wear. Air cleaners are additionally employed to damp intake noise. The air’s dust content depends on the application and road conditions. Table 13-1 presents an overview of mean dust concentrations and Fig. 13-1 particle size distributions of various real dusts in the field. Two standardized test dusts employed in lab air cleaner tests have also been entered for comparison [13-1]. The dust concentrations and particle size distributions differ from one another by orders of magnitude depending on the applications. This data is important when designing air cleaners for different cases of application and enables estimating their expected service life. Dust that enters an engine with the intake air causes abrasive wear in sliding systems. Cylinder liners, pistons and piston rings, crankshafts and connecting rod bearings, valves and gaskets are critical points. Wear in these components affects an engine’s service life adversely. Figure 13-2 presents the percentage of wear in three of an engine’s different critical points measured with a dust test rig, once without an air cleaner, once with an older type of air cleaner, an oil wetted air bath cleaner, and once with a paper dry type air cleaner. Significantly reducing wear, paper dry type air cleaners provide the most effective wear protection. Along with basic knowledge of various types of air cleaners’ ability to reduce wear, the influence of particle sizes is also important for design. Taking a piston ring in a diesel engine as an example, Fig. 13-3 presents percentages of wear from different particle size ranges as a ratio of dust wear to basic wear without the influence of dust. The intake air’s dust concentration is 2.3 mg/m3. The 5–10 mm fraction causes the strongest
L. Vilser (*) J. Eberspa¨cher GmbH & Co. KG, Esslingen, Germany e-mail: [email protected]
increase of wear over basic wear without the addition of dust, followed by the 10–20 mm fraction. Therefore, an air cleaner must reliably filter these fractions out of the intake air. In addition to the abrasive wear caused by dust particles, deposits of fine particulate matter can also form on the compressor walls in exhaust gas turbocharged engines. This reduces compressor efficiency [13-4]. Space and cost normally preclude implementing the very fine filtration that is quite possible technically. The injection of fluids during operation constitutes an effective measure to clean compressor surfaces of deposited fine particulate matter. Yielding good protection against wear and sufficient hours of operation, recommended values for filtration efficiency and service life gathered from years of practical experience are applied as the basis of cleaner design. Failure to adhere to these values results in reduced filtration efficiencies and insufficient du
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