Systems and methods for rotating coalescers maintaining positive recirculation through a dynamic seal

Abstract

Rotating coalescer crankcase ventilation (CV) systems are described. The described CV systems utilize a pumping pressure created by the porous media of the rotating coalescer to maintain positive recirculation of filtered blowby gases through a potential leak gap between a static housing inlet and a spinning component of the rotating coalescer. In some arrangements, the porous media is fibrous media. The filter media may be pleated or non-pleated. The positive recirculation caused by the pressure balance prevents unfiltered blowby gases from bypassing the media of the rotating coalescer from the upstream side to the downstream side of the filter media through the gap. During operation, the pressure balance between the upstream side and downstream side of the filter media maintains the positive recirculation, which in turn maintains a high filtration efficiency.

Description

TECHNICAL FIELD

The present application relates to crankcase ventilation (CV) systems that utilize rotating coalescing devices. In particular, the field of the invention relates to CV systems employing rotating coalescing devices that create a positive recirculation effect.

BACKGROUND

During operation of an internal combustion engine, a fraction of combustion gases can flow out of the combustion cylinder and into the crankcase of the engine. These gases are often called “blowby” gases. Typically, the blowby gases are routed out of the crankcase via a CV system. The CV system passes the blowby gases through a coalescer (i.e., a coalescing filter element) to remove a majority of the aerosols and oils contained in the blowby gases. The filtered blowby gases are then either vented to the ambient (in open CV systems) or routed back to the air intake for the internal combustion engine for further combustion (in closed CV systems).

Many CV systems utilize rotating coalescers. Rotating coalescers may include fibrous filters as well as centrifugal separation devices. Performance attributes of rotating coalescer devices may be measured in terms of pressure drop (or rise) through the device and efficiency of oil removal. In rotating coalescers, the oil droplets (e.g., aerosol) suspended and transported by the blowby gases are separated inside the coalescer media through the particle capture mechanisms of inertial impaction, interception, and diffusion onto the fibers. By rotating the media, inertial impaction is enhanced by the additional centrifugal force. In addition to this aspect, after the oil droplets coalesce to form larger drops, the centrifugal force removes the larger drops by overcoming the surface drag force of the media fibers. This aspect increases the collection of and the discharge of oil from the coalescer by providing improved drainage compared to a stationary coalescer. In turn, the improved drainage from the rotating coalescing filter aids in improving the filtration efficiency as well as greatly reducing the pressure drop across the filter.

Because a rotating coalescer is positioned within a static filter housing, there is typically a slight gap between the rotating components and the stationary housing. For example, a gap may exist between the static inlet of the housing and the rotating inlet opening of the rotating coalescer. This gap can allow unfiltered aerosol contained in the blowby gases to bypass the rotating coalescer if the downstream pressure on the clean side of the rotating media in the radial vicinity of the gap is lower than the upstream pressure on the dirty side of the rotating media in the radial vicinity of the gap. Example gaps are shown, for example, in U.S. Pat. No. 4,189,310, entitled “APPARATUS FOR REMOVING OIL MIST,” by Hotta (see, e.g., the gaps in FIG. 4). The bypass of unfiltered blowby gases can be detrimental to the efficiency of the CV system, particularly at larger aerosol sizes for which the filtering medium is highly efficient at removing.

SUMMARY

One example embodiment relates to a CV system. The CV system includes a housing, an inlet configured to receive blowby gases from an internal combustion engine and to provide the blowby gases to the housing, and an outlet configured to provide filtered blowby gases from the housing and to at least one of an intake of the internal combustion engine and the surrounding ambient. The CV system further includes a rotating coalescer positioned within the housing such that a gap exists between the rotating coalescer and the housing. The rotating coalescer includes a first endcap and a filter media. The gap permits gas flow between a clean side of the filter media and a dirty side of the filter media. The CV system includes a central shaft coupled to the rotating coalescer. The central shaft is rotatable such that when the central shaft rotates, the rotating coalescer rotates and creates a pumping pressure that causes a high pressure within the housing on the clean side of the filter media and a low pressure on the dirty side of the filter media. The pressure differential causes a positive recirculation of the blowby gases in which a portion of already filtered blowby gas from the clean side of the filter media returns through the gap to the dirty side of the filter media.

Another example embodiment relates to a CV system. The CV system includes a housing, an inlet configured to receive blowby gases from an internal combustion engine and to provide the blowby gases to the housing, and an outlet configured to provide filtered blowby gases from the housing and to at least one of an intake of the internal combustion engine and the surrounding ambient. The CV system further includes a rotating separating element positioned within the housing such that a gap exists between the rotating separating element and the housing. The gap permits gas flow between a clean side of the rotating separating element and a dirty side of the rotating separating element. The CV system includes a central shaft coupled to the rotating separating element. The central shaft is rotatable such that when the central shaft rotates, the rotating separating element rotates and creates a pumping pressure that causes a high pressure within the housing on the clean side of the rotating separating element and a low pressure on the dirty side of the rotating separating element. The pressure differential causes a positive recirculation of the blowby gases in which a portion of already filtered blowby gas from the clean side of the rotating separating element returns through the gap to the dirty side of the rotating separating element.

These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of a CV system 100 according to an example embodiment.

FIG. 2 is a close-up cross-sectional view of a portion of the CV system of FIG. 1.

FIG. 3 is a simplified cross-sectional view of the CV system of FIG. 1.

FIG. 4 is a cross-sectional view of a pleated annular filter element is shown according to an example embodiment.

FIG. 5 is a computational fluid dynamics diagram of the CV system of FIG. 1.

DETAILED DESCRIPTION

Referring to the figures generally, rotating coalescer CV systems are described. The described CV systems utilize a pumping pressure created by the porous media and/or internal radial ribs or spiral vanes of a rotating separating element, such as a rotating coalescer, to maintain positive recirculation of filtered blowby gases through a potential leak gap between a static housing inlet and a spinning component of the rotating coalescer. In some arrangements, the porous media is fibrous media. The filter media may be pleated or non-pleated. The positive recirculation caused by the pressure balance prevents unfiltered blowby gases from bypassing the media of the rotating coalescer from the upstream side to the downstream side of the filter media through the gap. During operation, the pressure balance between the upstream side and downstream side of the filter media maintains the positive recirculation, which in turn maintains a high filtration efficiency.

Referring to FIG. 1, a cross-sectional view of a CV system 100 is shown according to an example embodiment. The CV system 100 includes a blowby gas inlet 102 that receives blowby 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 blowby gas outlet 106 that outputs filtered blowby gas during operation of the CV system 100. The outlet 106 is coupled to the housing 104. The outlet 106 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 ambient (e.g., in an open CV system arrangement). The CV system includes a rotating coalescer 108 positioned within the housing. The rotating coalescer 108 is a rotating separating element. The rotating coalescer 108 includes a first endcap 110 and a second endcap 112. It should be understood, however, that the rotating coalescer could also have only single endcap, instead of both a first endcap 110 and a second endcap 112, in certain alternative embodiments. A filter media 114 is positioned between the first and second endcaps 110 and 112. In some arrangements, a frame 116 surrounds an outside surface of the filter media 114 to provided structural support to the filter media 114 when the rotating coalescer 108 is rotating. The frame 116 includes a plurality of vanes 117. The vanes 117 act as centrifugal fan blades so as to contribute to a pumping pressure created by the rotating coalescer 108. The vanes 117 may be arranged as radial ribs or spiral vanes. The creation of the pumping pressure by the rotating coalescer 108 is described in further detail below.

During operation, the rotating coalescer 108 is rotated along its central axis 118 by a central shaft 120 coupled to the rotating coalescer. The first and second endcaps 110 and 112 are secured to the central shaft 120 such that when the central shaft 120 rotates, the filter media 114 rotates. As shown in FIG. 1, the central shaft is rotated by a pelton wheel 122 that is spun by a pressurized stream of fluid (e.g., engine oil, hydraulic fluid, etc.). In alternative arrangements, the central shaft 120 is rotated by a separate electric motor, a chain drive system, or a belt drive system. As the rotating coalescer 108 rotates, blowby gas flows along flow path 124. The flow path 124 directs the blowby gas into the inlet, 102, through the second endplate 112 and into a central area surrounded by the filter media 114, through the filter media 114, and out of the housing 104 via the outlet 106. As the blowby gas passes through the filter media 114, oil suspended in the blowby gas, such as aerosols, are separated. The separated oil is collected in a drain pan 126 and drained back to the crankcase. The drain pain 126 may be a stationary part coupled to the housing 104 or integral with the housing 104.

Referring to FIG. 2, a close-up cross-sectional view of portion A of the CV system 100 is shown. As shown in FIG. 2, a gap 202 exists between the drain pan 126 and the central shaft 120 or the second endplate 112 of the rotating coalescer 108. The gap 202 potentially permits a potential leak path that allows the blowby gases entering the CV system 100 to bypass the rotating coalescer 108. However, the rotating coalescer 108 is designed to create a pumping pressure that causes a high pressure within the housing 104 on a clean side of the filter media 114, and a low pressure on a dirty side of the filter media 114 (e.g., in the central area of the rotating coalescer 108). Accordingly, a portion of the already filtered blowby gas flows from the high pressure area of the housing 104, through the gap 202, and back into the rotating coalescer 108 for further filtration. The recirculation of the blowby gas is described in further detail below with respect to FIG. 3.

FIG. 3 shows a simplified cross-sectional view of the CV system 100. As shown in FIG. 3, blowby gas follows the flow path 124 into the inlet 102. The flow of blowby gas pass through either the filter media 114 or the gap 202 (as shown in FIG. 2). The flow split between the flow going thought the gap and filter media depends on pressure drop across gap 202 and filter media 114. When the rotating coalescer 108 is rotating, the filter media 114 creates centrifugal “pumping” pressure due to its rotational velocity “ω”, which creates higher pressure P2 at the outer (downstream or clean) side of the rotating coalescer 108 than P1 at the inner (upstream or dirty) side of the filter media 114 and at the inlet of the gap 202 at diameter D₀. In some arrangements, the radial 117 also contribute to the pumping pressure. This pressure situation exists when certain design criteria of the CV system 100 are met. The design criteria relates to the magnitude of rotational velocity “ω”, flowrate “Q”, dimensions D₀, D₁, D₂, D₃, and the average intrinsic permeability of filter media 114 “κ” in the approximately direction of gas flow through the filter media 114.

The rotating coalescer 108 can have filter media arrangements that include a single layer or multiplayer construction, in which different physical properties (e.g., fiber diameter, porosity, etc.) are combined in a series. For arrangements that utilize a single layer of media, the intrinsic permeability of the filter media 114 is defined below in equation 1.

$\begin{array}{cc}\kappa =\frac{v·\mu ·t}{\Delta P}& \left(1\right)\end{array}$

In equation 1, κ has dimensional units of length squared, V is the superficial fluid velocity through the media 114, μ is the fluid viscosity, t is the media thickness, and ΔP is the pressure drop across the media 114 from an upstream position to a downstream position.

For single and multilayer media constructions, the average intrinsic permeability through the media 114 is defined by equation 2.

$\begin{array}{cc}\frac{\sum _i^n{t}_i}{\sum _i^n\left(\frac{t_i}{{\kappa }_i}\right)}& \left(2\right)\end{array}$

In equation 2, n is the number of layers of media, t_i is the thickness of layer “i”, and κ_i is the intrinsic permeability of layer “i”.

A simple numeric example of the average intrinsic permeability calculation for a three layer multilayer media construction is shown below in Table 1.

	TABLE 1
		Layer	Layer	Thickness/
	Layer “n”	Thickness	Intrinsic Perm.	Permeability
	layer 1	0.2	5	0.04
	layer 2	1	10	0.1
	layer 3	5	20	0.25
	Total	6.2	Total	0.39
	Thickness:		Thickness/
			Permeability:
	Average composite intrinsic permeability: 15.9

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

As illustrated in FIG. 3, if pressure P2>P1, then “positive” recirculation exists, whereby a portion of filtered gas from the clean side of the filter media 114 returns through the rotating gap to the upstream, dirty side of the filter media 114, thus recirculating and causing no loss in filtration efficiency. Alternatively, it can be said that if pressure P2<P1, then “negative” recirculation exists whereby a meaningful percentage of the aerosol-laden blowby gas can pass to the clean side of the filter media 114 through the gap 202 thereby bypassing the filter media 114, causing a reduction in filtration efficiency.

As noted above, positive recirculation of the blowby gas through the gap 202 is achieved when P2>P1 (alternatively stated as P2/P1>1). This situation can be achieved by intentionally selecting an optimum combination of the following critical parameters for the rotating coalescer 108 and the CV system 100. Table 2 describes the various design parameters that are utilized in calculating the optimal CV system 100 design to achieve the positive recirculation.

TABLE 2
Symbol	Description	Units
ρ	gas density	kg/m3
ω	rotational speed	rad/s
h	media height	m
D0	inside diameter of rotating	m
	annul portion of element
D1	media inner diameter	m
D2	media outer diameter	m
D3	element outer diameter	m
μ	gas viscosity	kg/m · s
ν	gas kinematic viscosity	m2/s
Q	gas flowrate	m3/s
κ	average intrinsic permeability	m2
	of media

As described in further detail below, different design parameter optimizations are utilized depending on whether the filter media 114 is comprised of a pleated porous media or a non-pleated porous media.

In arrangements where the filter media 114 is an annular porous non-pleated media, if the condition of equation 3 is met, P2>P1 is maintained and positive gas recirculation occurs.

$\begin{array}{cc}\frac{\pi ·\kappa ·{\omega }^2·h·\left(D_3^2-D_0^2\right)}{4·Q·v·\ln \left(\frac{D_2}{D_1}\right)}>1& \left(3\right)\end{array}$

In other arrangements, the filter media 114 is an annular porous pleated media. For example, a cross-sectional view of a pleated annular filter element 400 is shown according to an example embodiment. As shown in FIG. 4, the pleats of the pleated annular filter element 400 are arranged within the annular zone defined by the outer diameter D₂ and the inner diameter D₁. The additional terms required for determining the optimized size and arrangement of the pleated annular filter element 400 are the number of pleats (N) and the thickness of the media normal to the flow direction through the media (t, measure in m). The number of pleats must be greater than 2, and typically is greater than 10. Accordingly, for arrangements utilizing the pleated annular filter element 400, positive gas recirculation occurs when the condition of equation 4 is satisfied.

$\begin{array}{cc}\frac{\kappa ·N·h·{\left(D_2^2-2D_1{D}_2\cos \left(\frac{\pi }{N}\right)+D_1^2\right)}^{\frac{1}{2}}·{\omega }^2·\left(D_3^2-D_0^2\right)}{8·Q·v·t}>1& \left(4\right)\end{array}$

As shown in equations 3 and 4, different CV system 100 designs having a widely different sizes, operating speeds, and/or flow rates may require filtering media with significantly different intrinsic characteristics. For example, diesel engine CV applications for on-highway and off-highway equipment are typically constrained by practical considerations such as space available in the vicinity of the engine, energy available for inducing rotation of the rotating coalescer, and the strength of economically available materials of construction. Accordingly, it is preferable to design rotating porous or fibrous medium coalescers that may be utilized across multiple different applications and that share a range of common filtering medium properties across a very broad range of engine sizes and rotating coalescer operating speeds and sizes.

A narrower range of values for preferred arrangements of rotating porous medium coalescers can be defined utilizing a dimensionless parameter of

$N_{\mathrm{hyd}}=\frac{t}{\sqrt{\kappa }},$ 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 coalescers are set forth below in tables 3 through 6.

	TABLE 3
	Exemplary		ID of
Exemplary		Design	Media				Rotating	Maximum # of Hydraulic Radii
Engine	Nominal	Blow-by	Rotation	Element	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Flow Rate,	Speed,	OD,	OD,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	liters/min	RPM	mm	mm	mm	mm	Media Thickness, mm
Relatively High Speed Media Elements with Height to OD Aspect Ratio ~= 1	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	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	135	127	159	60	512	880	1560	2282

	TABLE 4
	Exemplary		ID of
Exemplary		Design	Media				Rotating	Maximum # of Hydraulic Radii
Engine	Nominal	Blow-by	Rotation	Element	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Flow Rate,	Speed,	OD,	OD,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	liters/min	RPM	mm	mm	mm	mm	Media Thickness, mm
Moderate Speed Elements with Aspect Ratios < 1	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
	Exemplary		ID of
Exemplary		Design	Media				Rotating	Maximum # of Hydraulic Radii
Engine	Nominal	Blow-by	Rotation	Element	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Flow Rate,	Speed,	OD,	OD,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	liters/min	RPM	mm	mm	mm	mm	Media Thickness, mm
Lower Speed, Larger Media Elements with Aspect Ratios = 1	1	3	10	25
3	45	75	4500	87	81	81	30	369	631	1095	1485
4	60	100	4500	87	81	81	30	319	546	948	1286
5	75	125	4500	98	92	92	35	369	632	1104	1544
6.7	101	168	4500	98	92	92	35	319	546	954	1333
8.9	134	223	4500	93	92	92	35	276	473	828	1157
11	165	275	4500	112	106	105	45	320	549	965	1381
13	195	325	4500	112	106	106	45	294	505	888	1271
15	225	375	4500	135	127	127	52	397	683	1209	1768
19	285	475	4000	146	138	138	52	377	647	1150	1696
30	450	750	3500	158	150	150	60	303	522	929	1379

	TABLE 6
	Exemplary		ID of
Exemplary		Design	Media				Rotating	Maximum # of Hydraulic Radii
Engine	Nominal	Blow-by	Rotation	Element	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Flow Rate,	Speed,	OD,	OD,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	liters/min	RPM	mm	mm	mm	mm	Media Thickness, mm
Higher Speed, Compact Size Media Elements with Aspect Ratios = 1	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	155	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

Example design parameters and approximate maximum preferred values of N_hyd for annular pleated coalescers are set forth below in tables 7 through 10.

	TABLE 7
	Exemplary		ID of
Exemplary	Design	Media					Rotating	Number of Pleats and Maximum Hydraulic Radii
Engine	Blow-by	Rotation	Element	Media	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Speed,	OD,	OD,	ID,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	RPM	mm	mm	mm	mm	mm	Media Thickness, mm
Relatively High Speed Media Elements with Height to OD Aspect Ratio ~= 1	# Plts	0.5	# Plts	1	# Plts	2	# Plts	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	97	159	60	46	685	44	805	30	1139	19	1332

	TABLE 8
	Exemplary		ID of
Exemplary	Design	Media					Rotating	Number of Pleats and Maximum Hydraulic Radii
Engine	Blow-by	Rotation	Element	Media	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Speed,	OD,	OD,	ID,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	RPM	mm	mm	mm	mm	mm	Media Thickness, mm
Moderate Speed Elements with Aspect Ratios < 1	# Plts	0.5	# Plts	1	# Plts	2	# Plts	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
	Exemplary		ID of
Exemplary	Design	Media					Rotating	Number of Pleats and Maximum Hydraulic Radii
Engine	Blow-by	Rotation	Element	Media	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Speed,	OD,	OD,	ID,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	RPM	mm	mm	mm	mm	mm	Media Thickness, mm
Lower Speed, Larger Media Elements with Aspect Ratios = 1	# Plts	0.5	# Plts	1	# Plts	2	# Plts	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
	Exemplary		ID of
Exemplary	Design	Media					Rotating	Number of Pleats and Maximum Hydraulic Radii
Engine	Blow-by	Rotation	Element	Media	Media	Media	Element	for Different Media Thickness,
Displacement,	Flow Rate,	Speed,	OD,	OD,	ID,	Height,	Annul,	at Design Blowby Flow Rate
liters	liters/min	RPM	mm	mm	mm	mm	mm	Media Thickness, mm
Higher Speed, Compact Size Media Elements with Aspect Ratios = 1	# Plts	0.5	# Plts	1	# Plts	2	# Plts	4
3	75	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	27	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

As shown above in Tables 3-10, particular embodiments of rotating coalescers for diesel engine crankcase ventilation applications generally indicate that values of N_hyd less than approximately 3000 are required to avoid bypassing unfiltered flow though the clearance seal, with several cases requiring lesser values than 3000. These embodiments, listed for engine displacements ranging from 3-30 liters and blowby flowrates of 75-750, respectively, are applicable across a wide range of commercial gasoline, diesel, natural gas, or other alternatively fueled engine applications.

Preferred values of N_hyd tend to depend on the thickness of the employed media. In many arrangements of annular non-pleated media, preferential maximum values for N_hyd include: 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, preferential maximum values for N_hyd include: 800 for media with 0-0.5 mm thickness, 950 for 0.5-1 mm thick media, 1400 for 1-2 mm thick media, 1700 for 2-4 mm thick media, and 2000 for 4-8 mm thick media, and somewhat larger values for media thicker than 8 mm. Nevertheless, it is possible that certain applications with very different amount of physical installation space available and other competing design objectives would maintain the efficiency benefits from positive recirculation at higher or lower values than those taught above, thus it can be beneficial to simply maintain adherence to criteria for maximum number of hydraulic radii for annular non-pleated porous filter elements and pleated porous filter elements, respectively, such that recirculation flow is maintained.

Equation 5 defines the criteria for maximum number of hydraulic radii for annular non-pleated porous filter elements, and equation 6 defines the criteria for maximum number of hydraulic radii for annular pleated porous filter elements, above which unfiltered gas would be expected to bypass the dynamic clearance seal.

$\begin{array}{cc}{N}_{\mathrm{hyd}\left(\mathrm{annular}\right)}<\sqrt{\frac{\pi ·h·{\left(D_2-D_1\right)}^2·{\omega }^2·\left(D_3^2-D_0^2\right)}{16·Q·v·\ln \left(\frac{D_2}{D_3}\right)}}& \left(5\right)\\ N_{\mathrm{hyd}\left(\mathrm{pleated}\right)}<\sqrt{\frac{N·h·{\left(D_2^2-2D_1{D}_2\cos \left(\frac{\pi }{N}\right)+D_1^2\right)}^{\frac{1}{2}}·t·{\omega }^2·\left(D_3^2-D_0^2\right)}{8·Q·v}}& \left(6\right)\end{array}$

Furthermore, fibrous coalescing filtering efficiency is typically higher for elements with media having greater total hydraulic radii count in the flow direction, due to smallness of pore or fiber, or number of opportunities for aerosol droplets and particulate matter to become captured within the medium as flow proceeds through the media from upstream to downstream. Thus, optimum designs for overall aerosol filtering efficiency can be found in the vicinity of the aforementioned maximum hydraulic radii count values. However, allowance for variation in application conditions (e.g., engine wear resulting in blow-by flow rate increases, solid or semi-solid contaminants becoming captured by the filtering medium that further restricts flow through the media, etc.) suggest that optimum values of hydraulic radii count may be less than the maximum values listed above. While designs with filter media having significantly lower hydraulic radii count values, such as 10, will almost certainly result in positive recirculation, their overall aerosol filtering efficiencies are not as high as those optimized according to the above-described methodologies. Thus, for certain products that are designed primarily for the objective of highest efficiency, a range of suitable values for the N_hyd can be defined. In many arrangements, preferential ranges of the parameter for annular non-pleated media elements include: 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, preferential ranges of values for N_hyd include: 120-800 for media with 0-0.5 mm thickness, 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 somewhat larger values for media thicker than 8 mm. These ranges establish values where there exists an optimum tradeoff 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 coalescing filter system overall due to potential bypass of flow, unfiltered through the dynamic clearance seal.

The relationships set forth in equations 5 and 6 are derived by considering the positive pumping pressure versus the negative pressure drop (dP) across the filter element as set forth below in equations 7 through 11. In equations 7-11, R corresponds to the radius of the noted diameter as defined above.

$\begin{array}{cc}{P}_{\mathrm{rise}}=\rho ·\frac{{\omega }^2}{2}·\left({\left(\frac{D_3}{2}\right)}^2-{\left(\frac{D_0}{2}\right)}^2\right)& \left(7\right)\\ \Delta P_{\mathrm{media}}=\frac{\mu ·Q}{2·\pi ·h·\kappa }·\ln \left(\frac{D_2}{D_1}\right)& \left(8\right)\\ \frac{P_{\mathrm{rise}}}{\Delta P_{\mathrm{media}}}>1& \left(9\right)\\ \frac{\rho ·\frac{{\omega }^2}{8}·\left(D_3^2-D_0^2\right)}{\frac{\mu ·Q}{2·\pi ·h·\kappa }·\ln \left(\frac{D_2}{D_1}\right)}>1,\mathrm{and}\mathrm{by}\mathrm{definition}\text{:}\frac{\mu }{\rho }=v& \left(10\right)\\ \frac{\pi ·\kappa ·{\omega }^2·h·\left(D_3^2-D_0^2\right)}{4·Q·v·\ln \left(\frac{D_2}{D_1}\right)}>1& \left(11\right)\end{array}$

Accordingly, the objective for annular media rotating CV systems is to maintain the relationship set forth above in equation 11.

Referring to FIG. 5, a computational fluid dynamics diagram 500 is shown of CV system 100. As shown in the diagram 500, a higher pressure (P2) exists at location 1 than the lower pressure (P1) at location 2. Location 1 is on the clean side of the filter media 114, and location 2 is on the dirty side of the filter media 114. The higher pressure at location 1 is caused by the pumping pressure of the rotating coalescer 108. Preferred values for the pressure ratio of P2:P1 are 0.8 to 5, depending on the depth and type of filter media utilized in the CV system 100. In addition to causing a positive recirculation effect within the CV system, the P2>P1 condition also provides the additional benefit of pushing the separated oil back to the crankcase. Accordingly, oil drains from the high pressure at location 1 to the low pressure of location 2. In some arrangements, the draining of the oil is facilitated through weep holes in the drain pan 126.

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

In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible.

It should be noted that any use of the term “example” herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).

The use of the term “approximately” in relation to numbers, values, and ranges thereof refers to plus or minus five percent of the stated of numbers, values, and ranges thereof.

The terms “coupled” and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,” “above,” “below,” etc.) are merely used to describe the orientation of various elements in the FIGURES. It should be noted that the orientation of various elements may differ according to other example embodiments, and that such variations are intended to be encompassed by the present disclosure.

It is important to note that the construction and arrangement of the various example embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions 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 of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments, and elements from different embodiments may be combined in a manner understood to one of ordinary skill in the art. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various example embodiments without departing from the scope of the present invention.

Claims

1. A crankcase ventilation system, comprising: a housing;an inlet configured to receive blowby gases from an internal combustion engine and to provide the blowby gases to the housing;an outlet configured to provide filtered blowby gases from the housing and to at least one of an intake of the internal combustion engine and a surrounding ambient;a rotating coalescer positioned within the housing such that a gap exists between the rotating coalescer and the housing, D0 is an inside diameter of a rotating portion of the rotating coalescer, the rotating portion representing an outer diameter of the gap, the rotating coalescer including: a first endcap,a filter media, wherein the gap permits gas flow between a clean side of the filter media and a dirty side of the filter media, anda frame surrounding an outside surface of the filter media, the frame comprising a plurality of vanes disposed radially outward of the filter media; anda central shaft coupled to the rotating coalescer, the central shaft rotatable such that when the central shaft rotates, the rotating coalescer rotates and creates a pumping pressure that causes a high pressure within the housing on the clean side of the filter media and a low pressure on the dirty side of the filter media and at an inlet in the gap at the inside diameter D0, thereby causing a positive recirculation of the blowby gases in which a portion of already filtered blowby gas from the clean side of the filter media returns through the gap to the dirty side of the filter media.

2. The crankcase ventilation system of claim 1, wherein the filter media is non-pleated.

3. The crankcase ventilation system of claim 2, wherein the filter media is selected such that

4. The crankcase ventilation system of claim 2, wherein the filter media possesses a value of Nhyd of less than or equal to 3000, where

5. The crankcase ventilation system of claim 4, wherein the filter media has a thickness of less than 0.0005 m and possesses a value of Nhyd of 75 to 500.

6. The crankcase ventilation system of claim 4, wherein the filter media has a thickness between 0.0005 m and 0.001 m and possesses a value of Nhyd of 100 to 700.

7. The crankcase ventilation system of claim 4, wherein the filter media has a thickness between 0.001 m and 0.002 m and possesses a value of Nhyd of 130 to 1000.

8. The crankcase ventilation system of claim 4, wherein the filter media has a thickness between 0.002 m and 0.004 m and possesses a value of Nhyd of 160 to 1300.

9. The crankcase ventilation system of claim 4, wherein the filter media has a thickness between 0.004 m and 0.008 m and possesses a value of Nhyd of 200 to 1800.

10. The crankcase ventilation system of claim 4, wherein the filter media has a thickness between 0.008 m and 0.015 m and possesses a value of Nhyd of 300 to 2200.

11. The crankcase ventilation system of claim 4, wherein the filter media has a thickness between 0.015 m and 0.03 m and possesses a value of Nhyd of 400 to 3000.

12. The crankcase ventilation system of claim 1, wherein the filter media is pleated.

13. The crankcase ventilation system of claim 12, wherein the filter media is selected such that

14. The crankcase ventilation system of claim 13, wherein the filter media possesses a value of Nhyd of less than or equal to 2000, where

15. The crankcase ventilation system of claim 14, wherein the filter media has a thickness of less than 0.0005 m and possesses a value of Nhyd of 120 to 800.

16. The crankcase ventilation system of claim 14, wherein the filter media has a thickness between 0.0005 m and 0.001 m and possesses a value of Nhyd of 140 to 950.

17. The crankcase ventilation system of claim 14, wherein the filter media has a thickness between 0.001 m and 0.002 m and possesses a value of Nhyd of 180 to 1400.

18. The crankcase ventilation system of claim 14, wherein the filter media has a thickness between 0.002 m and 0.004 m and possesses a value of Nhyd of 240 to 1700.

19. The crankcase ventilation system of claim 14, wherein the filter media has a thickness between 0.004 m and 0.008 m and possesses a value of Nhyd of 300 to 2000.

20. The crankcase ventilation system of claim 1, wherein the plurality of vanes, when rotated by the central shaft, contribute in creating the pumping pressure.