Crankcase ventilation systems that use rotating droplet separators

Abstract

Crankcase ventilation system (200, 400, 500), which includes the following: a case (104); an inlet (102) designed to receive leakage gases from an internal combustion engine and to direct the leakage gases to the housing (104); an outlet designed to provide filtered leakage gases from the housing (104) to at least one inlet of the internal combustion engine and an environment; a rotating droplet separator (106) arranged in the housing (104), wherein the rotating droplet separator (106) comprises the following: an end cap (110) and a filter medium (112) and an oil inlet (204, 404) that directs oil to a gap (202, 414, 502) between a stationary section of the housing (104) and the end cap (110), such that the oil arranged in the gap (202, 414, 502) during an operating condition of the rotating droplet separator (106) forms a hydrodynamic seal, wherein the hydrodynamic seal prevents negative recirculation of the leakage gases, in which a significant percentage of the aerosol-laden leakage gases can pass through the gap (202, 414, 502) to the clean side of the filter medium (112), wherein when the rotating droplet separator (106) rotates at more than a threshold rotational speed and generates a pumping pressure that results in a high pressure inside the housing (104) on a clean side of the filter medium (112) and a low pressure on a dirty side side of the filter medium (112) causes a positive recirculation of the leakage gases,wherein part of the already filtered leakage gas flows back from the clean side of the filter medium (112) through the gap to the dirty side of the filter medium (112), thus breaking the hydrodynamic seal.

Description

[0001] The present application relates to crankcase ventilation (CV) systems that use rotating droplet eliminators. BACKGROUND

[0002] During operation of an internal combustion engine, a portion of the combustion gases can flow from the combustion cylinder into the engine crankcase. These gases are often referred to as "bleed-by." Typically, the blow-by gases are vented from the crankcase via a CV system. The CV system directs the blow-by gases through a drift eliminator (i.e., a drift eliminator filter element) to remove most of the aerosols and oils contained in the blow-by gases. The filtered blow-by gases are then either vented to the atmosphere (in open CV systems) or redirected back to the engine air intake for further combustion (in closed CV systems).

[0003] Many CV systems use rotating drift eliminators. Rotating drift eliminators can incorporate fabric filters as well as centrifugal separation devices. Performance characteristics of rotating drift eliminators can be measured in terms of the pressure drop (or rise) through the device and the efficiency of oil removal. In rotating drift eliminators, the oil droplets (e.g., aerosol) suspended and carried by the bypass gases are separated in the drift eliminator media by the particle capture mechanisms of inertial impaction, interception, and diffusion onto the fibers. By rotating the media, the inertial impaction is amplified by the additional centrifugal force. In addition to this aspect, after the oil droplets coalesce to form larger droplets, the centrifugal force removes the larger droplets by overcoming the drag friction of the media fibers.This aspect increases the collection and separation of oil from the droplet separator by providing improved drainage compared to a stationary droplet separator. The improved drainage from the rotating droplet separator filter, in turn, contributes to improved filtration efficiency and a significant reduction in pressure drop across the filter.

[0004] Because the rotating mist eliminator is arranged within a static filter housing, a small gap is usually present between the rotating components and the stationary housing. For example, a gap may be present between the static inlet of the housing and the rotating inlet opening of the rotating mist eliminator. This gap may allow unfiltered aerosol contained in the bypass gases to bypass the rotating mist eliminator if the downstream pressure on the clean side of the rotating medium in the radial vicinity of the gap is lower than the upstream pressure on the dirty side of the rotating medium in the radial vicinity of the gap. Exemplary gaps are shown, for example, in US Patent No. 4,189,310 entitled "APPARATUS FOR REMOVING OIL MIST" to Hotta (see, for example, the gap in Fig.4). The bypassing of unfiltered bypass gases can adversely affect the efficiency of the CV system, especially for larger aerosol sizes for which the filter media is very efficient at removing them. One solution is the use of a high-speed rotating mist eliminator, which generates the necessary pumping pressure to effect positive recirculation through the gap (i.e., the recirculation of already filtered bypass gases from the clean side of the filter media to the dirty side of the filter media through the gap). However, the increased mechanical stresses caused by high-speed rotating mist eliminators can reduce reliability and / or increase costs.Additionally, certain internal combustion engines may not be equipped with the necessary components to rotate the rotating drift eliminator at the required high speed while maintaining adequate media permeability and thickness.

[0005] DE 10 2007 054 922 A1 discloses a separator for separating oil mist from the crankcase ventilation gas of an internal combustion engine, comprising a gas cleaning chamber in which a rotatably mounted centrifugal rotor is arranged, wherein the gas cleaning chamber has a raw gas inlet, a clean gas outlet and an oil outlet, wherein the crankcase ventilation gas can be introduced into a radially inner region of the centrifugal rotor, wherein clean gas freed from oil mist can be discharged from the gas cleaning chamber and wherein oil separated from the gas can be discharged from the gas cleaning chamber, and comprising a rotary drive for the centrifugal rotor, wherein the rotary drive is arranged in a drive chamber separate from the gas cleaning chamber and is operable with pressurized lubricating oil of the internal combustion engine and is connected to the centrifugal rotor via a shaft.The separator is characterized in that the rotary drive is formed by a thrust nozzle connected to the shaft and feedable with the pressurized lubricating oil of the internal combustion engine. US 6,517,612 B1 discloses a continuously cleanable centrifugal filtration device with radial inflow, comprising a tubular filter element located in a chamber and rotatably connected to an outlet for the filtered liquid in a bulkhead adjacent to the chamber. The side walls of the filter element contain a filter medium rotatably connected to the outlet for the filtered liquid. This is achieved by a seal capable of maintaining the seal during rotation of the filter element.US 5 056 935 A discloses a squeeze film damper using spaced-apart, diagonally cross-sectional piston ring seals in diagonal cross-sectional grooves, whose cross-sections match and align with each other, with the diagonal surfaces directly exposed to the squeeze film space between the rings. DE 19 41 194 U discloses a sealing or decorative strip that can be slid onto a flange. SUMMARY

[0006] One embodiment relates to a CV system. The CV system includes a housing having an inlet and an outlet. The inlet is configured to receive blow-by gases from an internal combustion engine and to provide the blow-by gases to the housing. The outlet is configured to provide filtered blow-by gases from the housing to at least one of an inlet of the internal combustion engine and the environment. The CV system includes a rotating drift eliminator disposed within the housing. The rotating drift eliminator includes an end cap and a filter media. The CV system further includes an oil inlet. The oil inlet provides oil to a gap between a stationary portion of the housing and the end cap such that a hydrodynamic seal is formed by the oil disposed within the gap during an operating condition of the rotating drift eliminator.wherein the hydrodynamic seal prevents negative recirculation of the leakage gases, in which a significant percentage of the aerosol-laden leakage gases can pass through the gap to the clean side of the filter medium, wherein, when the rotating droplet eliminator rotates at more than a threshold rotational speed and generates a pumping pressure that causes high pressure within the housing on a clean side of the filter medium and low pressure on a dirty side of the filter medium, this causes positive recirculation of the leakage gases, with a portion of the already filtered leakage gas flowing back from the clean side of the filter medium through the gap to the dirty side of the filter medium, thus breaking the hydrodynamic seal.

[0007] Another embodiment relates to a CV system. The CV system includes a housing having an inlet and an outlet. The inlet is designed to receive blow-by gases from an internal combustion engine and provide the blow-by gases to the housing. The outlet is designed to provide filtered blow-by gases from the housing to at least one of an inlet of the internal combustion engine and an ambient environment. The CV system further includes a rotating drift eliminator including a filter media (112) disposed within the housing such that a gap exists between a portion of the rotating drift eliminator and a stationary portion of the housing. The CV system includes an elastomeric seal providing a seal between the rotating drift eliminator and the stationary portion of the housing.The rotating drift eliminator may include an end cap and a filter media, wherein when the rotating drift eliminator rotates at more than a threshold rotational speed and creates a pumping pressure that causes high pressure within the housing on a clean side of the filter media and low pressure on a dirty side of the filter media, positive recirculation of the bypass gases collapses a portion of the elastomer seal, providing passage of a portion of the already filtered bypass gas from the clean side of the filter media through the gap to the dirty side of the filter media, thus breaking the seal.

[0008] These and other features, as well as the organization and manner of operation, will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which like elements have like reference numerals throughout the various drawings described below. BRIEF DESCRIPTION OF THE CHARACTERS Fig. 1 is a cross-sectional view of a CV system 100 according to one embodiment. Fig. 2 and Fig. 3 are close-up views of a cross-section of sections of a CV system with a hydrodynamic soft seal. Fig. 4 is a close-up view of a cross-section of portions of a CV system according to another embodiment. Fig. Figure 5 is a simplified cross-sectional view of the CV system of the Fig. 1 to Fig. 4. Fig.6 is a cross-sectional view of a pleated annular filter element according to one embodiment. DETAILED DESCRIPTION

[0009] With general reference to the figures, CV systems with rotating mist eliminators are described. The described CV systems use a contact seal to seal a gap between a static side of a housing and a rotating mist eliminator inlet. The rotating mist eliminator can be driven mechanically, electrically, hydraulically, or similarly. The contact seal can be formed by a soft solid or an oil-generated liquid film. Accordingly, the contact seal is a hydrodynamic seal or soft seal. The contact seal prevents leakage gases from bypassing the filter element of the rotating mist eliminator. The hydrodynamic seal or soft seal can act as a low-friction bearing for the rotating mist eliminator.The hydrodynamic seal, or soft seal, is effective for rotating drift eliminator applications where positive recirculation through the gap where the seal is formed cannot otherwise be ensured. Such situations can arise, for example, when the input power (i.e., rotational power) for the rotating drift eliminator is limited to small amounts. At the same time, because the contact seal is a hydrodynamic soft seal, the contact seal can be disrupted under circumstances of positive leakage gas recirculation (e.g., caused by a pumping force generated by a rotating drift eliminator and / or internal radial vanes). In some situations, the contact seal can be disrupted by a centrifugal force acting on the seal itself, thus eliminating the drag torque when speeds are high enough to maintain positive recirculation.

[0010] Referring to Fig.1 shows a cross-sectional view of a CV system 100 according to one embodiment. The CV system 100 includes a blow-by inlet 102 that receives blow-by gas from a crankcase of an internal combustion engine to a housing 104 of the CV system 100. The inlet 102 is coupled to the housing 104. The housing 104 is a stationary or static housing. The CV system 100 includes a blow-by outlet (not shown) that discharges filtered blow-by gas during operation of the CV system 100. The outlet is coupled to the housing 104. The outlet may be coupled to an air intake of the internal combustion engine (e.g., in a closed CV system arrangement) or may vent to the atmosphere (e.g., in an open CV system arrangement). The CV system 100 includes a rotating mist eliminator 106 disposed within the housing. The rotating mist eliminator 106 includes a first end cap 108 and a second end cap 110.However, it should be understood that in certain alternative embodiments, the rotating drift eliminator 106 could also include a single end cap. A filter media 112 is disposed between the first and second end caps 108 and 110. In some arrangements, a frame 114 surrounds an outer surface of the filter media 112 to provide structural support to the filter media 112 as the rotating drift eliminator 106 rotates. The frame 114 includes a plurality of radial vanes 115. The radial vanes 115 act as centrifugal fan blades to contribute to a pumping pressure generated by the rotating drift eliminator 106. The generation of the pumping pressure by the rotating drift eliminator 106 is described in more detail below.In some arrangements, the CV system 100 includes a flexible seal 116 disposed between a rotating inlet portion of the second end cap 110 and the inlet 102 of the static housing 104. The flexible seal 116 has a V-shape or a U-shape. The flexible seal 116 is an elastomeric seal. In some arrangements, the flexible seal 116 is stiffened by molding the flexible seal 116 over a metallic support ring. In other arrangements, the flexible seal 116 is stiffened by including a helical coil spring, which helps increase and / or maintain the sealing force of the flexible seal 116 over extended periods and / or high temperatures. The flexible seal 116 forms a bushing between the rotating inlet portion of the second end cap 110 and the inlet 102 of the static housing 104.The flexible seal 116 may form a contact seal between the rotating inlet portion of the second end cap 110 and the inlet 102 of the static housing 104. The flexible seal 116 may be pressed into or attached to the rotating second end cap 110 or pressed onto the stationary portion of the static housing 104 (e.g., the stationary shaft). In arrangements where the flexible seal 116 is pressed into or attached to the rotating second end cap 110, centrifugal forces on the flexible seal 116 help reduce the drag torque caused by the flexible seal 116.

[0016] During operation, the rotating drift eliminator 106 is rotated along its central axis 120 by a central shaft 122 coupled to the rotating drift eliminator 106.The first and second end caps 108 and 110 are attached to the central shaft 122 such that the filter media 112 rotates as the central shaft 122 rotates. As shown in FIG. Fig. 1, the central shaft 122 is rotated by an electric motor 124. In alternative arrangements, the central shaft 122 is rotated by a fluid-driven Pelton wheel (e.g., as shown in Fig.2), a chain drive system, or a belt drive system. As the rotating drift eliminator 106 rotates, bypass gas flows along flow path 126. Flow path 126 directs the bypass gas into inlet 102, through filter media 112 (as shown by arrows 126), and out the outlet from housing 104. As the bypass gases flow through filter media 112, oil suspended in the bypass gas, such as aerosols, is separated. The separated oil is collected at the bottom of housing 104 and returned to the crankcase via a drain 128. In some arrangements, the separated oil is collected in a drain pan 130 disposed in a bottom portion of housing 104. The drain pan 130 may be a stationary part coupled to the housing 104 or may be formed integrally with the housing 104.In such arrangements, the flexible seal 116 may be disposed between the stationary drain pan 130 and the rotating inlet portion of the second end cap 110.

[0011] Still with reference to Fig.1, the flexible seal 116 rotates during operation with the second end cap 110. As the flexible seal 116 rotates, the seal created between the flexible seal 116 and the inlet 102 may be breached under certain circumstances. For example, if the pressure on the dirty side of the filter media 112 (P1) is greater than the pressure on the clean side of the filter element (P2), leakage gases may cause the seal to rupture, and the leakage gases may bypass the filter media 112, creating negative recirculation of the leakage gas. Negative recirculation reduces the overall filtration efficiency of the CV system 100. Furthermore, the centrifugal forces acting on the flexible seal 116 contribute to the flexible seal 116 flexing outward (i.e.,collapses) and loses contact with the static housing 104 when velocities are sufficiently high to achieve positive recirculation pumping of the filtered bypass gases. As another example, if the pressure on the dirty side of the filter media 112 (P1) is less than the pressure on the clean side of the filter media 112 (P2), bypass gases can break the seal, and the bypass gases can positively recirculate from the clean side of the filter media 112. In this example, the downstream side of the rotating drift eliminator 106 will not be contaminated with dirty bypass gas because the higher P2 than P1 eliminates negative recirculation. A higher rotational speed of the rotating drift eliminator 106 is required to maintain P2 greater than P1 (positive recirculation).The ratio of the contact pressure of the flexible seal 116 and the pressure difference (P2 - P1) across the gap is preferably greater than or equal to 1. Accordingly, when the pumping ratio (i.e., P2 / P1) is less than 1, the contact pressure of the flexible seal 116 is greater than 1.

[0012] In an alternative arrangement, a lip seal can be used instead of the V-shaped or U-shaped flexible seal 116. In such arrangements, the rotation speed of the rotating drift eliminator 106 can be reduced compared to arrangements using the flexible seal 116 because the lip seal can seal a higher pressure differential between P1 and P2 with a lower contact pressure than the flexible seal 116. The higher pressure differential allows the use of thicker, less porous, and more efficient filter media than in arrangements using the flexible seal 116.

[0013] As explained below with reference to the Fig. 2 and Fig. 3, a CV system 200 may utilize a hydrodynamic soft seal in addition to or instead of the flexible seal 116 of the CV system 100. The described hydrodynamic soft seal of the CV system 200 prevents the leakage gases from bypassing the filter medium 112 under negative recirculation conditions. Additionally, the hydrodynamic soft seal is formed by oil and provides additional lubrication of the rotating parts in the contact area of ​​the hydrodynamic soft seal. Thus, the hydrodynamic soft seal enables a non-contact and wear-free seal between the rotating droplet eliminator and the static housing 104.

[0014] Referring to Fig. 2, a close-up view of a cross-section of a bottom portion of a CV system 200 according to one embodiment is shown. The CV system 200 is similar to the CV system 100 of Fig.1. The primary difference between the CV system 200 and the CV system 100 is that the CV system 200 does not include a flexible seal (e.g., flexible seal 116 of the CV system 100). Instead, the CV system 200 uses a soft hydrodynamic seal. Accordingly, the same reference numerals are used when describing the overlapping parts of the CV system 200 and the CV system 100. The hydrodynamic seal is described in more detail below.

[0015] As in Fig. 2, there is a gap 202 between the stationary drain pan 130 of the housing and the second end cap 110 of the rotating drift eliminator 106. An additional close-up view of a cross-section of the area of ​​the CV system 200 near the gap 202 is shown in Fig.3. In some arrangements, the gap 202 is approximately one millimeter in size. If unsealed, leakage gas flowing through the CV system 200 can bypass the filter media 112 of the rotating drift eliminator 106 by flowing through the gap 202 during operation of the CV system 200. To prevent this, a hydrodynamic seal is formed to seal the gap 202 under negative recirculation conditions.

[0016] The hydrodynamic seal is formed by oil. Accordingly, the drain pan 130 includes an oil inlet 204. The oil inlet is coupled to a supply line 206, which is coupled to a pressurized oil supply 208. In some arrangements, the supply line 206 is a flexible hose that passes through an opening in the bottom of the housing 104. The pressurized oil supply 208 provides pressurized oil to the oil inlet 204 via the supply line 206. In some arrangements, the pressurized oil supply 208 also drives the rotation of the rotating drift eliminator 106 (e.g., by rotating a Pelton wheel 210). The oil may be lubricating oil from a lubrication system of the internal combustion engine. The oil inlet 204 supplies oil to the gap 202. The oil supplied through the oil inlet 204 is distributed in a substantially uniform manner throughout the gap as the rotating droplet 106 rotates.The circumferential distribution of the oil can be achieved by incorporating a circumferential groove (e.g., the circumferential groove 302 as shown in . Fig. 3). The oil in the gap 202 forms a hydrodynamic film of liquid oil, creating a soft, hydrodynamic seal between the drain pan 130 and the rotating inlet portion of the second end cap 110. The oil in the gap 202 essentially forms a bushing between the rotating inlet portion of the rotating drift eliminator 106 and the inlet 102 of the static housing 104. Excess oil is collected in the drain pan 130 and returned to the crankcase in the same manner as separated oil from the blow-by gases processed by the CV system 200.

[0017] In some arrangements, a circumferential groove 302 in the vertical component of the drain pan 130 helps facilitate the formation of the hydrodynamic seal. The circumferential groove 302 completely circumscribes the vertical component of the drain pan 130. In arrangements where the circumferential groove 302 is formed in a plastic drain pan 130, special design considerations are required. In some arrangements, the opening of the inlet 204 is located above a bottom portion 304 of the gap 202, which allows a short core pin to be used in creating the inlet 204 during injection molding of the drain pan 130. Additionally, a length of the mold pin 306 should remain short to prevent distortion of the pin 306 and the oil inlet 204 during high injection pressures. The pin 306 includes barbs 308 that secure the supply line 206 to the pin 306 and the oil inlet 204.

[0018] The hydrodynamic seal formed by the oil in the gap 202 has different properties that depend at least in part on the temperature of the oil. The warmer the oil, the less viscous the oil becomes. In arrangements where the oil is cold and more viscous (e.g., when the internal combustion engine is cold), the oil causes a higher drag force on the rotating drift eliminator 106 than when less viscous (i.e., warmer) oil fills the gap 202. The higher drag force causes the rotating drift eliminator 106 to rotate at a slower speed than if the warmer, less viscous oil were used. Because the rotating drift eliminator 106 rotates at a slower speed, the pumping pressure is reduced, potentially creating a leak-bypass situation with negative recirculation through the gap 202. However, the more viscous oil forms a stronger hydrodynamic seal than warmer, less viscous oil.Thus, even if the pumping pressure is lower, resulting in a lower P2, the stronger hydrodynamic seal effectively seals the gap 202 and prevents leakage gases from bypassing the filter media 112. In arrangements where the oil is warm and less viscous than the cold oil, the oil creates less drag on the rotating drift eliminator 106, and the rotating drift eliminator 106 can rotate at a higher speed. Because the rotating drift eliminator 106 rotates at a higher speed, the pumping pressure is increased, which reduces the likelihood of leakage gas bypassing through the gap 202 due to a positive recirculation effect. Accordingly, although the warmer oil forms a weaker hydrodynamic seal, leakage gas does not bypass the filter media 112 by flowing through the gap 202.In some arrangements, when using the warmer oil, the rotation of the rotating drift eliminator 106 breaks the hydrodynamic seal, but this is not necessary because of the positive recirculation caused by the pumping effect created by the rotating drift eliminator 106. As explained above, the hydrodynamic seal is formed by oil flowing through the circumferential groove 302 and sealing against the second end cap 110. In other arrangements, the hydrodynamic seal may be formed by a labyrinthine groove (i.e., a groove that also includes axial components) or an axial cross-offset (e.g., as discussed below with reference to FIG. Fig. 4 described).

[0019] Referring to Fig. 4 shows a close-up view of a cross-section of a CV system 400 with a hydrodynamic seal according to one embodiment. The CV system 400 is similar to the CV system 200 of Fig. 2 and Fig.3. The CV system 400 differs from the CV system 200 in the manner in which the hydrodynamic seal is formed. Accordingly, the same reference numerals are used when describing the overlapping portions of the CV system 400 and the CV system 200. The CV system 400 includes a drain pan 402. The drain pan 402 includes an oil inlet 404 and a pin 406 with barbs 408. The oil inlet 404 and the pin 406 are coupled to a pressurized oil supply (e.g., in the same manner as described above with respect to the CV system 200). The oil inlet 404 provides oil to a groove 410 formed in the extension portion 402. The second end cap 110 of the rotating droplet eliminator 106 includes a tongue 412. The tongue 412 extends partially into the groove 410. A gap 414 exists between and is defined by the tongue 412 and the groove 410.The oil supplied into the groove 410 via the oil inlet 404 forms a hydrodynamic seal between the groove 410 and the tongue 412, effectively sealing the gap 414 in the same manner as described above with respect to the CV system 200. The tongue and groove design of the CV system 400 offers the additional benefit of providing axial vibration dampening of the rotating drift eliminator relative to the housing. However, the hydrodynamic seal formed by the tongue and groove system may cause a higher drag torque on the rotating drift eliminator than in the CV system 200. In addition, the CV system 400 requires less oil to form the hydrodynamic seal because the oil is retained in the groove 410 rather than flowing down the side of the drain pan 402 as in the CV system 200.

[0020] In the CV systems described above (CV System 100, CV System 200, and CV System 400), the seal can be located on the inner diameter of the stationary part (e.g., the drain pan 130), the outer diameter of the stationary part, the inner diameter of the rotating part (e.g., the second end cap 110), or the outer diameter of the rotating part. The hydrodynamic seal generally reduces the energy consumption required to rotate the rotating drift eliminator compared to a conventional rotating shaft seal (e.g., flexible seal 116), resulting in CV systems with higher overall efficiency despite lower energy consumption.

[0021] Referring to Fig.5, a schematic view of a CV system 500 is shown. The CV system 500 is representative of the CV systems 100, 200, and 400. The CV system 500 uses similar reference numerals to describe the same components as shown in the CV systems 100, 200, and 400. The CV system includes a gap 502. The gap 502 is representative of the gap 202, the gap 414, and the gap sealed by the flexible seal 116. As discussed above with respect to the CV systems 100, 200, and 400, the bypass gas flow passes through either the filter media 112 or the gap 502. The flow distribution between the flow through the gap 502 and the filter media 112 depends on the pressure drop across the gap, the filter media 112, and any seal disposed within the gap (e.g., the hydrodynamic seal discussed above, flexible seal 116, etc.).

[0022] As the rotating droplet eliminator 106 rotates, the filter media 112 generates a centrifugal "pumping" pressure due to its rotational speed "ω," which under certain circumstances can generate a higher pressure P2 on the outer (downstream or clean) side of the filter media 112 than P1 on the inner (upstream or dirty) side of the filter media 112. This pressure situation occurs when certain design criteria of the CV system 500 are met. The design criteria relate to the magnitude of the rotational speed "ω," the flow rate "Q," the dimensions D0, D1, D2, D3, and the average intrinsic permeability of the filter media 112 "κ" in the approximate direction of gas flow through the filter media 112. As shown in Fig.As illustrated in Figure 3, when pressure P2 > P1, "positive" recirculation occurs, whereby a portion of the filtered gas from the clean side of the filter media 112 returns through the rotating gap 502 to the upstream, dirty side of the filter media 112 and thus recirculates, causing no loss of filtration efficiency. In some arrangements, the radial vanes 115 also contribute to the pumping pressure. Alternatively, when pressure P2 < P1, "negative" recirculation occurs, whereby a significant percentage of the aerosol-laden blowout gas can pass through the gap 502 to the clean side of the filter media 112, thereby bypassing the filter media 112 and causing a reduction in filtration efficiency. During negative recirculation situations, the hydrodynamic seal or soft seal described above and the flexible seal 116 prevent negative circulation.However, under sufficiently strong positive recirculation conditions, the hydrodynamic seal or soft seal can be broken, thus enabling positive recirculation of leakage gas through the rotating droplet eliminator 106.

[0023] With reference to the negative recirculation situations, where the various contact seals prevent negative recirculation over a sufficiently wide range of differential pressure P1 to P2, it is desirable to use filter media with high efficiency properties. For example, for media with a larger number of hydraulic radii, as defined by the dimensionless parameter of NHyd=tκ defined, they can be expected to have higher aerosol removal efficiency because physical properties of the media that result in a larger number of hydraulic radii, such as smaller fiber diameter, lower porosity, or greater thickness, also result in rotating porous mist eliminator devices having higher aerosol removal efficiency. Therefore, the conditions consistent with operation at the lowest possible pressure drop or within a allowable pressure drop with high efficiency can be defined. For example, this is described when Equation 1 is satisfied (Equation 1 refers to annular, non-pleated media), and the resulting value for pressure, P1, does not exceed an allowable value specified by the engine manufacturer incorporating the system. π⋅κ⋅ω2⋅h⋅(D32−D02)4⋅Q⋅v⋅In(D2D1)<1

[0024] This pressure value varies for different engine applications, but for commercial diesel engines it is often between approximately -1 kPa and 7 kPa. For annular pleated elements, the following equation applies similarly: κ⋅N⋅h⋅(D22−2D1D2cos(κN)+D12)12⋅ω2⋅(D32−D02)8⋅Q⋅v⋅t<1

[0025] Equation 2 should be satisfied and the resulting value for pressure, P1, should not exceed a permissible value specified by the engine manufacturer installing the system.

[0026] The rotating drift eliminator 106 may include filter media assemblies comprising a single-layer or multi-layer construction in which different physical properties (e.g., fiber diameter, porosity, etc.) are combined in a series. For assemblies using a single layer of media, the intrinsic permeability of the filter media 112 is defined below in Equation 3. K=V⋅μ⋅tΔP

[0027] In equation 3, κ has the unit of dimension of a length squared, V is the surface fluid velocity through the medium 112, µ is the fluid viscosity, t is the media thickness, and ΔP is the pressure drop across the medium 112 from an upstream position to a downstream position.

[0028] For single and multi-layer media constructions, the average intrinsic permeability through the medium 112 is defined by Equation 4. ∑inti∑in(tiκi)

[0029] In equation 4, n represents the number of media layers, t i for the thickness of layer “i” and κ i stands for the intrinsic permeability of layer “i”.

[0030] A simple numerical example of the average intrinsic permeability calculation for a three-layer multilayer media construction is shown below in Table 1. Table 1 Layer "n" Layer thickness Intrinsic Perm. of the layer Thickness / permeability Layer 1 0,2 5 0,04 Layer 2 1 10 0,1 Layer 3 5 20 0,25 Total thickness: 6,2 Total thickness / permeability: 0,39 Average composite intrinsic permeability: 15.9

[0031] Experimentally, the average intrinsic permeability can be easily measured by maintaining air flow through a flat sample of the multilayer porous medium under controlled conditions of gas viscosity (µ) and superficial velocity (V) while measuring the pressure drop from the upstream side of the medium to the downstream side. The average intrinsic permeability is calculated using Equation 1 above.

[0032] As mentioned above, positive recirculation of the blow-by gas through the gaps of the CV systems described above is achieved when P2 > P1 (alternatively expressed as P2 / P1 > 1). When P2 > P1, the seal is non-contact. This situation can be achieved by deliberately selecting an optimal combination of the following critical parameters for the rotating drift eliminator 106 and the CV system 100. Table 2 describes the various design parameters used in calculating the optimal CV system design to achieve positive recirculation. Table 2 symbol Description units ρ Gas density kg / m3 ω rotation speed rad / s h Media height m D0 Inner diameter of the rotating annular section of the element m D1 Media inner diameter m D2 Media / rotor outer diameter m D3 Element outer diameter m µ Gas viscosity kg / (m s) v kinematic gas viscosity m 2 / s Q Gas volume flow m 3 / s K average intrinsic permeability of the media m 2

[0033] As described in more detail below, different optimizations of the design parameters are used depending on whether the filter media 112 is a pleated porous media or a non-pleated porous media.

[0034] In arrangements where the filter media 112 is an annular porous, non-pleated media, P2 > P1 is maintained when the condition of Equation 5 is met, and the seal is non-contact, resulting in positive gas recirculation through the gap.

[0035] In other arrangements, the filter media 112 is an annular porous pleated media. For example, a cross-sectional view of a pleated annular filter element 600 is shown according to one embodiment. As shown in Fig.As shown in Figure 6, the pleats of the pleated annular filter element 600 are arranged within the annular zone determined by the outer diameter D2 and the inner diameter D1. The additional terms required to determine the optimized size and arrangement of the pleated annular filter element 600 are the number of pleats (N) and the thickness of the media perpendicular to the direction of flow through the media (t, measured in m). The number of pleats must be greater than 2 and is typically greater than 10. Accordingly, for arrangements employing the pleated annular filter element 600, positive gas recirculation occurs when the condition of Equation 6 is met and the seal is non-contact. κ⋅N⋅h⋅(D22−2D1D2cos(πN)+D12)12⋅ω2⋅(D32−D02)8⋅Q⋅v⋅t>1

[0036] As shown in equations 5 and 6, different CV system designs with widely varying sizes, operating speeds, and / or flow rates may require filter media with substantially different intrinsic properties. For example, diesel engine CV applications for on- and off-highway vehicles are typically limited by practical considerations such as space near the engine, available energy to induce rotation of the rotating drift eliminator, and the strength of commercially available materials of construction. Accordingly, it is preferable to design rotating porous or fibrous media drift eliminators that can be used for several different applications and that share a range of common filter media properties over a very wide range of engine sizes and rotating drift eliminator operating speeds and sizes.

[0037] A narrower range of values ​​for preferred arrangements of rotating droplet eliminators with porous media can be calculated using a dimensionless parameter of NHyd=tκ which represents the average number of hydraulic radii through the thickness of the media in the flow direction. Example design parameters and approximate maximum preferred values ​​of N Hyd for annular, non-pleated droplet eliminators in operation with non-contacting of the seal are given below in Tables 3 to 6. Table 3 Example displacement, liters Nominal flow rate, liters / min Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Media OD, mm Media height, mm ID of the rotating annular element, mm Maximum number of hydraulic radii for different media thickness at design leakage gas flow rate Relatively high-speed media elements with a height to AD aspect ratio ~ = 1 Media thickness, mm 1 3 10 25 3 45 75 11000 73 67 67 30 615 1048 1798 2285 4 60 100 11000 73 67 67 30 533 908 1557 1979 5 75 125 10000 83 77 77 35 563 963 1666 2232 6,7 101 168 10000 83 77 77 35 487 831 1439 1928 8,9 134 223 10000 83 77 77 35 422 721 1249 1673 11 165 275 10000 95 89 89 45 488 836 1 1460 2027 13 195 325 10000 95 89 89 45 449 769 1343 1864 15 225 375 9000 115 107 107 52 555 953 1677 2403 19 285 475 8500 125 117 117 52 565 970 1713 2484 30 450 750 7500 127 127 159 60 512 880 1560 2282 Table 4 Example displacement, liters Nominal flow rate, liters / min Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Media OD, mm Media height, mm ID of the rotating annular element, mm Maximum number of hydraulic radii for different media thickness at design leakage gas flow rate Moderate speed elements with aspect ratios < 1 Media thickness, mm 1 3 10 25 3 45 75 6000 100 94 45 30 466 798 1397 1961 4 60 100 6000 100 94 45 30 404 691 1210 1698 5 75 125 6000 113 107 51 35 465 .798 1405 2013 6,7 101 168 6000 113 107 51 35 402 689 1214 1739 8,9 134 223 6000 113 107 51 35 349 598 1053 1509 11 165 275 5000 131 123 59 45 343 590 1044 1521 13 195 325 5000 131 123 59 45 316 543 960 1400 15 225 375 5000 154 146 71 52 416 716 1274 1888 19 285 475 5000 167 159 78 52 442 761 1357 2024 30 450 750 4200 180 172 106 60 383 659 1178 1767 Table 5 Example displacement, liters Nominal flow rate, liters / min Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Media OD, mm Media height, mm ID of the rotating annular element, mm Maximum number of hydraulic radii for different media thickness at design leakage gas flow rate Larger media elements with lower speed with aspect ratios = 1 Media thickness, mm 1 3 10 25 3 45 75 4500 87 81 81 30 466 631 1095 1485 4 60 100 4500 87 81 81 30 404 546 948 1286 5 75 125 4500 98 92 92 35 465 632 1104 1544 6,7 101 168 4500 98 92 92 35 402 546 954 1333 8,9 134 223 4500 98 92 92 35 349 473 828 1157 11 165 275 4500 112 106 106 45 343 549 965 1381 13 195 325 4500 112 106 106 45 316 505 888 1271 15 225 375 4500 135 127 127 52 416 683 1209 1768 19 285 475 4000 146 138 138 52 442 647 1150 1696 30 450 750 3500 158 158 158 60 383 522 929 1379 Table 6 Example displacement, liters Nominal flow rate, liters / min Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Media OD, mm Media height, mm ID of the rotating annular element, mm Maximum number of hydraulic radii for different media thickness at design leakage gas flow rate Higher speed compact media elements with aspect ratios = 1 Media thickness, mm 1 3 10 25 3 45 75 12000 60 54 54 30 413 701 1178 1220 4 60 100 12000 60 54 54 30 357 607 1020 1056 5 75 125 12000 68 62 62 35 421 717 1221 1487 6,7 101 168 12000 68 62 62 35 364 619 1055 1285 8,9 134 223 11000 68 62 62 35 289 492 839 1022 11 165 275 11000 78 72 72 45 333 568 979 1284 13 195 325 10000 78 72 72 45 278 475 819 1074 15 225 375 10000 94 88 88 52 382 654 1140 1577 19 285 475 9000 102 96 96 52 379 649 1136 1601 30 450 750 8000 113 105 105 60 316 542 954 1362

[0038] Example design parameters and approximate maximum preferred values ​​of N Hydfor annular pleated droplet eliminators in operation with non-contacting seal are given below in Tables 7 to 10. Table 7 Example displacement, liters Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Media OD, mm Media ID, mm Media height, mm ID of the rotating annular element, mm Number of folds and maximum hydraulic radii for different media thickness at design leakage gas flow rate Relatively high-speed media elements with a height to AD aspect ratio ~ = 1 Media thickness, mm Number of mines 0,5 Number of mines 1 Number of mines 2 Number of mines 4 3 75 11000 73 67 47 67 30 22 659 21 792 15 1120 9 1363 4 100 11000 73 67 47 67 30 22 571 21 686 15 970 9 1180 5 125 10000 83 77 57 77 35 27 619 26 742 18 1049 11 1273 6,7 168 10000 83 77 57 77 35 27 534 26 641 18 906 11 1100 8,9 223 10000 83 77 57 77 35 27 464 26 556 18 786 11 955 11 275 10000 95 89 59 89 45 28 611 26 720 19 1018 12 1197 13 325 10000 95 89 59 89 45 28 562 26 662 19 936 12 1101 15 375 9000 115 107 77 107 52 36 722 35 850 24 1202 15 1408 19 475 8500 125 117 87 117 52 41 746 39 877 27 1241 17 1452 30 750 7500 135 127 197 159 60 46 685 44 805 30 1139 19 1332 Table 8 Example displacement, liters Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Media OD, mm Media ID, mm Media height, mm ID of the rotating annular element, mm Number of folds and maximum hydraulic radii for different media thickness at design leakage gas flow rate Moderate speed elements with aspect ratios < 1 Media thickness, mm Number of mines 0,5 Number of mines 1 Number of mines 2 Number of pits 4 3 75 6000 100 94 74 45 30 35 526 33 630 23 890 15 1078 4 100 6000 100 94 74 45 30 35 456 33 545 23 771 15 933 5 125 6000 113 107 77 51 35 36 605 35 712 24 1007 15 1180 6,7 168 6000 113 107 77 51 35 36 522 35 615 24 870 15 1019 8,9 223 6000 113 107 77 51 35 36 453 35 534 24 755 15 884 11 275 5000 131 123 93 59 45 44 457 42 537 29 760 18 889 13 325 5000 131 123 93 59 45 44 420 42 494 29 699 18 818 15 375 5000 154 146 116 71 52 55 567 52 666 36 942 23 1101 19 475 5000 167 159 129 78 52 61 608 58 714 41 1010 25 1179 30 750 4200 180 172 142 106 60 67 531 64 624 45 882 28 1029 Table 9 Example displacement, liters Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Medi en-AD, mm Media ID, mm Media height, mm ID of the rotating annular element, mm Number of folds and maximum hydraulic radii for different media thickness at design leakage gas flow rate Larger media elements with lower speed with aspect ratios = 1 Media thickness, mm Number of mines 0,5 Number of mines 1 Number of mines 2 Number of mines 4 3 75 4500 87 81 61 81 30 29 408 27 489 19 691 12 839 4 100 4500 87 81 61 81 30 29 353 27 423 19 599 12 726 5 125 4500 98 92 72 92 35 34 415 32 497 23 703 14 851 6,7 168 4500 98 92 62 92 35 29 401 28 473 19 669 12 786 8,9 223 4500 98 92 62 92 35 29 348 28 410 19 580 12 682 11 275 4500 112 106 76 106 45 36 415 34 488 24 691 15 810 13 325 4500 112 106 76 106 45 36 382 34 449 24 635 15 745 15 375 4500 135 127 97 127 52 45 531 43 624 30 883 19 1032 19 475 4000 146 138 108 138 52 51 509 48 599 34 847 21 989 30 750 3500 158 150 120 150 60 56 414 54 487 38 688 23 804 Table 10 Example displacement, liters Exemplary design, leak gas flow rate, liters / min Media rotation speed, rpm Element OD, mm Medi en-AD, mm Media ID, mm Media height, mm ID of the rotating annular element, mm Number of folds and maximum hydraulic radii for different media thickness at design leakage gas flow rate Higher speed compact media elements with aspect ratios = 1 Media thickness, mm Number of mines 0,5 Number of mines 1 Number of mines 2 Number of mines 4 3 175 12000 60 54 34 54 30 16 421 15 507 11 717 7 877 4 100 12000 60 54 34 54 30 16 364 15 439 11 621 7 759 5 125 12000 68 62 42 62 35 20 444 19 534 13 755 8 921 6,7 168 12000 68 62 42 62 35 20 384 19 461 13 652 8 796 8,9 223 11000 68 62 42 62 35 20 305 19 367 13 519 8 633 11 275 11000 78 72 52 72 45 25 362 23 434 16 613 10 746 13 325 10000 78 72 52 72 45 25 302 23 363 16 513 10 624 15 375 10000 94 88 58 88 52 25 475 26 561 18 793 11 932 19 475 9000 102 96 66 96 52 31 481 30 567 21 802 13 942 30 750 8000 113 105 75 105 60 35 409 33 482 23 681 15 799

[0039] As shown above in Tables 3-10, specific embodiments of rotating droplet eliminators for diesel engine crankcase ventilation applications generally show that values ​​for N Hydof less than approximately 3000 are required to avoid bypassing the unfiltered flow through the clearance that exists when the seal is not in contact (i.e., the seal does not prevent negative recirculation), with values ​​less than 3000 being required in some cases. These embodiments, listed for engine displacements in the range 3-30 liters and blow-by flow rates of 75-750, are applicable over a wide range of commercial gasoline, diesel, natural gas, or other alternatively fueled engine applications. In situations where the seal remains in contact during operation, the number of hydraulic radii specified in Tables 3 through 10 will be greater than the values ​​listed in Tables 3 through 10.

[0040] Preferred values ​​of N Hydtend to depend on the thickness of the media used. For many arrangements of annular, non-pleated media in non-contact seal situations, preferred maximum values ​​for N Hyd the following: 500 for media with 0-0.5 mm thickness, 700 for 0.5-1 mm thick media, 1000 for 1-2 mm thick media, 1300 for 2-4 mm thick media, 1800 for 4-8 mm thick media, 2300 for 8-15 mm thick media, 3000 for 15-30 mm thick media and 4000 for > 30 mm thick media. In many arrangements of annular pleated media, preferred maximum values ​​for N include HydDuring operation with a non-contact seal, use the following values: 800 for media 0-0.5 mm thick, 950 for 0.5-1 mm thick, 1400 for 1-2 mm thick, 1700 for 2-4 mm thick, and 2000 for 4-8 mm thick, and slightly larger values ​​for media thicker than 8 mm. Nevertheless, it is possible that certain applications with widely varying physical space requirements and other competing design objectives may retain the efficiency benefits of positive recirculation at higher or lower values ​​than those taught above, so it may be advantageous to simply maintain compliance with the maximum number of hydraulic radii criteria for annular non-pleated porous filter elements and pleated porous filter elements, respectively, so that recirculation flow is maintained.

[0041] Equation 7 defines the criteria for the maximum number of hydraulic radii for annular non-pleated porous filter elements, and Equation 8 defines the criteria for the maximum number of hydraulic radii for annular pleated porous filter elements, and above these values ​​it would be expected that unfiltered gas would flow past in the case of non-contact seals. NHyd(ring-shaped)<π⋅h⋅(D2−D1)2⋅ω2⋅(D32−D02)16⋅Q⋅v⋅In(D2D1) NHyd(pleated) <N⋅h⋅(D22−2D1D2cos(πN)+D12)12⋅t⋅ω2⋅(D32−D02)8⋅Q⋅v

[0042] Furthermore, the filtration efficiency of the fibrous mist eliminator is typically higher for elements with media that have a larger total number of hydraulic radii in the flow direction. This is because the pores or fibers are small, or the number of opportunities for aerosol droplets and particulate matter to be trapped in the media is greater when the flow is from top to bottom through the media. Thus, optimal designs for overall aerosol filtration efficiency can be found near the aforementioned maximum numbers of hydraulic radii. Considering variations in application conditions (e.g., engine wear leading to an increase in bypass gas flow rates, solid or semi-solid contaminants trapped by the filter media that further restrict flow through the media, etc.)) suggest that optimal values ​​may be fewer hydraulic radii than the values ​​specified above for non-contact seals. While designs using filter media with significantly lower numbers of hydraulic radii, such as 10, are likely to result in positive recirculation, their overall aerosol filtration efficiency will not be as high as that of those optimized according to the methods described above. Therefore, for specific products designed primarily for the highest efficiency goal, a range of suitable values ​​for N may be established. Hydbe defined. In many arrangements, preferred ranges of the parameter for annular, non-pleated media elements include the following: 75-500 for 0-0.5 mm thick media, 100-700 for 0.5-1 mm thick media, 130-1000 for 1-2 mm thick media, 160-1300 for 2-4 mm thick media, 200-1800 for 4-8 mm thick media, 300-2200 for 8-15 mm thick media, 400-3000 for 15-30 mm thick media, and 600-4000 for > 30 mm thick media. For annular pleated media elements, preferred value ranges for Nhyd include the following: 120-800 for media 0-0.5 mm thick, 140-950 for 0.5-1 mm thick media, 180-1400 for 1-2 mm thick media, 240-1700 for 2-4 mm thick media and 300-2000 for 4-8 mm thick media and slightly larger values ​​for media thicker than 8 mm.These ranges define values ​​where an optimal compromise exists between: (a) the inefficiency of porous media due to small aerosol size, excessive size of pores or fibers, or excessive porosity, and (b) the inefficiency of the rotating mist eliminator filtration system as a whole due to potential bypassing of the unfiltered flow through the gap created by the non-contact seal clearance.

[0043] The relationships set forth in equations 7 and 8 are derived by considering the positive pumping pressure against the negative pressure drop (dP) across the filter element, as set forth below in equations 9 to 13. In equations 9-13, R corresponds to the radius of the specified diameter as defined above. PArise=ρ⋅ω22⋅((D32)2−(D02)2) ΔPMedia=μ⋅Q2⋅π⋅h⋅κ⋅ln(D2D1) PIncreaseΔPMedia>1 ρ⋅ω28⋅(D32−D02)μ⋅Q2⋅π⋅h⋅κ⋅ln(D2D1)>1 and by definition: π⋅κ⋅ω2⋅h⋅(D32−D02)4⋅Q⋅v⋅ln(D2D1)>1

[0044] Accordingly, for rotating CV systems with annular media where the seal is non-contact (e.g., as described above), the goal is to maintain the relationship set forth above in Equation 13.

[0045] The systems and methods described above are not limited to separating oil and aerosols from crankcase leakage gases. The same or similar arrangements and principles can be used in other filtration systems that utilize porous drift eliminator technology to separate liquid from a gas-liquid mixture.

[0046] In the foregoing description, certain terms are used for brevity, clarity, and understandability. This does not imply unnecessary limitations beyond the requirements of the prior art, as such terms are used for descriptive purposes and are to be broadly construed. The various configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems, and method steps. Various equivalents, alternatives, and modifications are expected to be possible.

[0047] It should be noted that the term "exemplary" as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and / or illustrations of possible embodiments (and that such term is not necessarily intended to imply that such embodiments are exceptional or excellent examples).

[0048] As used herein, the term "connected" and similar terms means the direct or indirect connection of two elements to one another. This connection can be stationary (e.g., permanent) or movable (e.g., removable or detachable). This connection can be achieved by the two elements, or the two elements and any other intermediate elements, being integrally formed as a unitary body, or by the two elements, or the two elements and any other intermediate elements, being fastened to one another.

[0049] References herein to the positions of elements (e.g., "top," "bottom," "upper," "bottom," etc.) merely describe the orientation of the various elements in the figures. It should be noted that the orientation of various elements may vary depending on other exemplary embodiments, and such variations are intended to be covered by the present disclosure.

[0050] It should be understood that the construction and arrangement of the various exemplary embodiments are for illustrative purposes only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art will readily recognize upon reading this disclosure that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes, and portions of the various elements, values ​​of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be constructed from multiple parts or elements, the position of the elements may be reversed or otherwise varied, and the nature or number of separate elements or positions may be changed or varied.The order or sequence of a process or method steps may be altered or rearranged according to alternative embodiments, and elements from different embodiments may be combined in a manner understandable to one of ordinary skill in the art. Other substitutions, modifications, changes, and omissions may also be made in the construction, operating conditions, and arrangement of the various exemplary embodiments without departing from the scope of the present invention.

Claims

[1] Crankcase ventilation system (200, 400, 500) comprising: a housing (104); an inlet (102) designed to receive blow-by gases from an internal combustion engine and to direct the blow-by gases to the housing (104); an outlet designed to provide filtered blow-by gases from the housing (104) to at least one of an inlet of the internal combustion engine and an environment; a rotating droplet separator (106) disposed in the housing (104), the rotating droplet separator (106) including: an end cap (110) and a filter medium (112) and an oil inlet (204, 404) directing oil to a gap (202, 414, 502) between a stationary portion of the housing (104) and the end cap (110) such that a hydrodynamic seal is formed by the oil disposed in the gap (202, 414, 502) during an operating condition of the rotating mist eliminator (106), the hydrodynamic seal preventing negative recirculation of the leakage gases in which a significant percentage of the aerosol-laden leakage gases can pass through the gap (202, 414, 502) to the clean side of the filter medium (112), wherein when the rotating mist eliminator (106) rotates at more than a threshold rotational speed and generates a pumping pressure that creates a high pressure within the housing (104) on a clean side of the filter medium (112) and a low pressure on a dirty side of the filter medium (112), thereby causing a positive recirculation of the leakage gases,wherein a portion of the already filtered leakage gas flows back from the clean side of the filter medium (112) through the gap to the dirty side of the filter medium (112), so that the hydrodynamic seal is broken. [2] Crankcase ventilation system according to claim 1, wherein the oil inlet supplies oil to a groove (410) defining the gap. [3] The crankcase ventilation system of claim 2, wherein the end cap (110) includes a tongue (412) extending partially into the groove (410) and further defining the gap. [4] The crankcase ventilation system of claim 3, wherein the tongue (412) is structured to provide axial vibration damping of the rotating droplet eliminator (106) with respect to the housing (104). [5] The crankcase ventilation system of claim 1, wherein the hydrodynamic seal is formed in part by a radial oil groove around a circumference of the stationary portion of the housing (104). [6] Crankcase ventilation system according to claim 1, wherein the filter medium (112) is non-pleated. [7] Crankcase ventilation system according to claim 6, wherein the filter medium (112) is selected such that π⋅κ⋅ω2⋅h⋅(D32−D02)4⋅Q⋅v⋅ln(D2D1)<1 is fulfilled, where: ω, measured in rad / s, is the rotational speed of the rotating droplet separator (106), h, measured in m, stands for a media height of the filter medium (112), D0, measured in m, represents an inner diameter of a rotating annular portion of the rotating droplet separator (106), the rotating annular portion representing the outer diameter of the gap, D1, measured in m, represents an inner diameter of the filter medium (112), D2, measured in m, represents an outer diameter of the filter medium (112), D3, measured in m, represents an outer diameter of the rotating droplet separator (106), v, measured in m 2 / s, stands for a kinematic viscosity of the leakage gases, Q, measured in m 3 / s, stands for a volume flow of the leakage gases and κ, measured in m 2 , stands for a permeability of the filter medium (112). [8] Crankcase ventilation system according to claim 6, wherein the filter media (112) comprises multiple layers of filter media. [9] Crankcase ventilation system according to claim 1, wherein the filter medium (112) is pleated. [10] Crankcase ventilation system according to claim 9, wherein the filter medium (112) is selected such that κ⋅N⋅h⋅(D22−2D1D2cos(πN)+D12)12⋅ω2⋅(D32−D02)8⋅Q⋅v⋅t<1 is fulfilled, where: ω, measured in rad / s, is the rotational speed of the rotating droplet separator (106), h, measured in m, stands for a media height of the filter medium (112), t, measured in m, represents a thickness of the filter medium (112) which is perpendicular to a flow direction through the filter medium (112), N stands for a number of folds of the filter medium (112), D0, measured in m, represents an inner diameter of a rotating annular portion of the rotating droplet separator (106), the rotating annular portion representing the outer diameter of the gap, D1, measured in m, represents an inner diameter of the filter medium (112), D2, measured in m, represents an outer diameter of the filter medium (112), D3, measured in m, represents an outer diameter of the rotating droplet separator (106), v, measured in m 2 / s, stands for a kinematic viscosity of the leakage gases, Q, measured in m 3 / s, stands for a volume flow of the leakage gases and κ, measured in m 2 , stands for a permeability of the filter medium (112). [11] Crankcase ventilation system according to claim 1, wherein the stationary portion is a drain pan of the housing (104). [12] Crankcase ventilation system (100, 500) comprising: a housing (104); an inlet (102) designed to receive blow-by gases from an internal combustion engine and to direct the blow-by gases to the housing (104); an outlet designed to provide filtered blow-by gases from the housing (104) to at least one of an inlet of the internal combustion engine and an environment; a rotating droplet separator (106) containing a filter medium (112) arranged in the housing (104) such that a gap (202, 414, 502) exists between a portion of the rotating droplet separator (106) and a stationary portion of the housing (104); and an elastomer seal forming a seal between the rotating droplet eliminator (106) and the stationary portion of the housing (104), wherein, when the rotating droplet eliminator (106) rotates at more than a threshold rotational speed and creates a pumping pressure that causes high pressure within the housing (104) on a clean side of the filter media (112) and low pressure on a dirty side of the filter media (112), positive recirculation of the bypass gases causes a portion of the elastomeric seal (116) to collapse, thereby providing passage of a portion of the already filtered bypass gas from the clean side of the filter media (112) through the gap (202, 414, 502) to the dirty side of the filter media (112), thus breaking the seal. [13] Crankcase ventilation system according to claim 12, wherein the rotating droplet eliminator (106) includes: an end cap (110) and a filter medium (112). [14] Crankcase ventilation system according to claim 12, wherein the elastomer seal is V-shaped. [15] Crankcase ventilation system according to claim 12, wherein the elastomer seal is U-shaped. [16] Crankcase ventilation system according to claim 12, wherein the elastomer seal is a lip seal. [17] The crankcase ventilation system of claim 12, wherein the elastomeric seal includes a metallic stiffening component. [18] The crankcase ventilation system of claim 17, wherein the metallic stiffening component includes a spring that increases a sealing force of the elastomer seal.

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