U.S. patent application number 11/760031 was filed with the patent office on 2008-12-11 for evaporative emission control system with new adsorbents.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Sam R. Reddy.
Application Number | 20080302341 11/760031 |
Document ID | / |
Family ID | 40076195 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080302341 |
Kind Code |
A1 |
Reddy; Sam R. |
December 11, 2008 |
EVAPORATIVE EMISSION CONTROL SYSTEM WITH NEW ADSORBENTS
Abstract
One embodiment of the invention includes an adsorbent canister
in a vehicle and an adsorbent having a nearly linear isotherm
provided in the adsorbent canister.
Inventors: |
Reddy; Sam R.; (West
Bloomfield, MI) |
Correspondence
Address: |
GENERAL MOTORS CORPORATION;LEGAL STAFF
MAIL CODE 482-C23-B21, P O BOX 300
DETROIT
MI
48265-3000
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
40076195 |
Appl. No.: |
11/760031 |
Filed: |
June 8, 2007 |
Current U.S.
Class: |
123/520 ;
123/519; 510/403; 903/902 |
Current CPC
Class: |
Y02T 10/62 20130101;
F02M 25/089 20130101; F02M 33/04 20130101; Y02T 10/6221 20130101;
B60K 6/48 20130101 |
Class at
Publication: |
123/520 ;
123/519; 510/403; 903/902 |
International
Class: |
F02M 33/02 20060101
F02M033/02; B60K 6/00 20071001 B60K006/00; C11D 17/00 20060101
C11D017/00 |
Claims
1. An evaporative emissions control system for a vehicle,
comprising: a fuel tank for storing a volatile fuel; an engine
having an air induction system; at least one canister containing an
adsorbent material, wherein the adsorbent material has a nearly
linear isotherm; a vapor inlet on the canister coupled to the fuel
tank; a purge outlet on the canister coupled to the air induction
system; a first vent opening on the canister for allowing fuel
vapor to enter and exit said canister; a scrubber canister
fluidically coupled to canister through said first vent opening,
said scrubber canister including an activated carbon adsorbent
material; wherein the adsorbent material and said activated carbon
adsorbent material adsorbs fuel vapors when the engine is not
running and desorbs fuel vapors when the engine is running.
2. An evaporative emissions control system for a vehicle as set
forth in claim 1 wherein the adsorbent material consists
essentially of an alumino-silicate gel comprising 97 weight %
SiO.sub.2 and .sub.3 weight % Al.sub.2O.sub.3.
3. An evaporative emissions control system for a vehicle as set
forth in claim 1 wherein the engine is integrated with a hybrid
powertrain.
4. An evaporative emissions control system for a vehicle as set
forth in claim 1 wherein the canister has a volume of about 800 cc
to about 1200 cc.
5. (canceled)
6. An evaporative emission control system for a vehicle as set
forth in claim 1 wherein the adsorbent material has a surface area
of at least 750 m.sup.2/g.
7. An evaporative emission control system for a vehicle as set
forth in claim 1 wherein the adsorbent material has a pore volume
of at least 0.5 cm.sup.3/g.
8. An evaporative emission control system for a vehicle as set
forth in claim 1 wherein the adsorbent material has an attrition
rate less than 0.05 wt %.
9. A method for reducing purge air flow requirements of an
evaporative emissions control system for a vehicle comprising:
storing a volatile fuel in a fuel tank; providing at least one
canister containing an adsorbent material and including a first
vent opening, wherein the adsorbent material has a nearly linear
isotherm; coupling a vapor inlet of the canister to the fuel tank;
coupling a purge outlet of the canister to an air induction system
of an engine of the vehicle; fluidically coupling a scrubber
canister having an activated carbon adsorbent material to the
canister through said first vent opening; adsorbing fuel vapors
when the engine is not running using the adsorbent material and the
activated carbon adsorbent material; and desorbing fuel vapors from
the adsorbent material and from the activated carbon adsorbent
material when the engine is running.
10. (canceled)
11. A method for reducing purge air flow requirements of an
evaporative emissions control system for a vehicle as set forth at
claim 9 wherein the canister has a volume of about 800 cc to about
1200 cc.
12. A method for reducing purge air flow requirements of an
evaporative emissions control system for a vehicle as set forth at
claim 9 wherein the adsorbent material consists essentially of an
alumino-silicate gel comprising 97 weight % SiO.sub.2 and 3 weight
% Al.sub.2O.sub.3.
13. A method for reducing purge air flow requirements of an
evaporative emissions control system for a vehicle as set forth at
claim 9 wherein the engine is integrated with a hybrid
powertrain.
14. A hybrid vehicle comprising an internal combustion engine and
an electric motor, the hybrid vehicle further comprising: a fuel
tank for storing a volatile fuel; an engine having an air induction
system; at least one canister containing an adsorbent material,
wherein the adsorbent material has a nearly linear isotherm; a
vapor inlet coupled to the fuel tank; a purge outlet coupled to the
air induction system; a first vent opening on the canister; a
scrubber canister fluidically coupled to the canister through said
first vent opening, said scrubber canister including an activated
carbon adsorbent material; wherein the adsorbent material and said
activated carbon adsorbent material adsorbs fuel vapors when the
engine is not running and desorbs fuel vapors fuel vapors when the
engine is running.
15. A hybrid vehicle as set forth in claim 14 wherein the adsorbent
material consists essentially of an alumino-silicate gel comprising
97 weight % SiO.sub.2 and 3 weight % Al.sub.2O.sub.3.
16. A hybrid vehicle as set forth in claim 14 wherein the canister
has a volume of about 800 cc to about 1200 cc.
17. (canceled)
18. (canceled)
Description
TECHNICAL FIELD
[0001] The field to which the disclosure generally relates includes
methods and systems for evaporative emission control for hybrid and
non-hybrid vehicles, and more specifically to methods and systems
for reducing and preventing vapor emissions from fuel tanks of such
vehicles.
BACKGROUND
[0002] Gasoline typically includes a mixture of hydrocarbons
ranging from higher volatility butanes (C.sub.4-) to lower
volatility hydrocarbons (C.sub.8 to C.sub.10). When vapor pressure
increases in the fuel tank due to conditions such as higher ambient
temperature or displacement of vapor during filling of the tank,
fuel vapor flows through openings in the fuel tank. To prevent fuel
vapor loss into the atmosphere, the fuel tank is vented into a
canister (known as an evaporative canister or adsorbent canister)
that contains an adsorbent material such as activated carbon
granules or pellets. The evaporative canister is part of a system
directed to controlling the emission of fuel vapors generated by
fuel carried in the vehicle's fuel system. These evaporative
emission control systems ("EVAP" systems) are implemented as a
collateral system to the fuel system.
[0003] When the gasoline tank is filled, fuel vapor accumulates in
the canister. The fuel vapor is a mixture of gasoline vapor
(referred to in this description also by its main component,
hydrocarbon vapor) and air. The initial loading may be at the inlet
end of the canister, but over time the fuel vapor is gradually
distributed along the entire bed of the adsorbent material. As the
fuel vapor enters an inlet of the canister, the hydrocarbon vapor
is adsorbed onto activated carbon granules and the air escapes into
the atmosphere. The size of the canister and the volume of the
adsorbent activated carbon are selected to accommodate the expected
gasoline vapor generation.
[0004] After the engine is started, the control system uses engine
intake vacuum to draw air through the adsorbent to desorb the fuel.
A purge valve between the vehicle's engine and the EVAP system
opens and air is drawn through the canister. The air removes fuel
vapor that is stored in the adsorbent material. The desorbed fuel
vapor is directed into an air induction system of the engine as a
secondary air/fuel mixture to be consumed in the normal combustion
process.
[0005] In a hybrid vehicle including both an internal combustion
(IC) engine and an electric motor, the IC engine is turned off
nearly half of the time during vehicle operation. Because the
purging takes place only during operation of the IC engine when the
desorbed vapor can be consumed in engine combustion, in a hybrid
vehicle the adsorbent canister purging with fresh air occurs less
than half of the time. A hybrid vehicle generates nearly the same
amount of evaporative fuel vapor as does a conventional vehicle
having an IC engine. Therefore, the lower purge rate of the hybrid
vehicle is not sufficient to clean the adsorbed fuel out of the
adsorbent canister.
SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0006] One embodiment of the invention includes an adsorbent
canister in a vehicle and an adsorbent having a nearly linear
isotherm provided in the adsorbent canister.
[0007] Other exemplary embodiments of the invention will become
apparent from the detailed description of exemplary embodiments
provided hereinafter. It should be understood that the detailed
description and specific examples, while indicating the exemplary
embodiments of the invention, are intended for purposes of
illustration only and are not intended to limit the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Exemplary embodiments of the invention will become more
fully understood from the detailed description and the accompanying
drawings.
[0009] FIG. 1 illustrates an evaporative control system for a
vehicle according to one embodiment of the invention;
[0010] FIG. 2 illustrates an evaporative control system for a
vehicle according to one embodiment of the invention;
[0011] FIG. 3 illustrates an evaporative control system for a
vehicle according to one embodiment of the invention;
[0012] FIG. 4 illustrates the isotherms for activated carbon and an
adsorbent having a nearly linear or linear isotherm;
[0013] FIG. 5 illustrates hydrocarbon purging for activated carbon
and an adsorbent having a nearly linear or linear isotherm;
[0014] FIG. 6 illustrates hydrocarbon storage capacities for
activated carbon and an adsorbent having a nearly linear or linear
isotherm; and
[0015] FIG. 7 is a view of a vehicle containing an evaporative
control system according to one embodiment of the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0016] The following description of the embodiments is merely
exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0017] According to one embodiment of the invention, an adsorbent
canister is provided in a vehicle. Evaporative fuel vapors (mainly
diurnal and refueling) are stored in the adsorbent canister where
the adsorbent traps the hydrocarbons from the fuel vapors. The
evaporative fuel vapors are purged from the canister with ambient
air and consumed in the engine combustion. An adsorbent with a
nearly linear isotherm is provided in the adsorbent canister. The
term "nearly linear isotherm" as used herein means that the amount
of absorbed vapor in a given volume of the absorption material does
not deviate more than 40% from a straight line for a pretrial
pressure from 0-0.5 atm at a given temperature (e.g. 25.degree. C.
in FIG. 4). Fuel vapor generation in a typical vehicle may be, for
example, about 30 g/day for diurnal, 80 g/fill for refueling, and
10 g/trip for running loss.
[0018] Referring now to FIG. 1, an evaporative control system 10
for a hybrid vehicle including an IC engine 12 and an electric
motor (not shown) according to one embodiment of the invention is
illustrated. Hybrid vehicles combine a gasoline fueled IC engine
and an electric motor to provide a hybrid powertrain with improved
fuel economy. Frequent on-off engine operation results in much
smaller canister purge air volume for a hybrid vehicle. Because the
IC engine does not operate nearly 50% of the time, canister purging
with fresh air occurs less than 50% of the time during vehicle
operation. In one embodiment, the IC engine 12 is controlled by a
controller 14. The controller 14 may be a separate controller or
may form part of an engine control module (ECM), a powertrain
control module (PCM), or any other vehicle controller. In various
embodiments, the IC engine 12 may burn gasoline, ethanol, or other
volatile hydrocarbon-based fuels.
[0019] When the IC engine 12 is started, the controller 14 may
receive signals from one or more engine sensors, transmission
control devices, and/or emissions control devices. Line 16 from the
engine 12 to the controller 14 schematically depicts the flow of
sensor signals. During operation of the IC engine 12, gasoline is
delivered from a fuel tank 18 by a fuel pump (not shown) through a
fuel line (not shown) to a fuel rail (not shown). Fuel injectors
(not shown) inject gasoline into cylinders of the IC engine 12 or
to ports that supply groups of cylinders. The timing and operation
of the fuel injectors and the amount of fuel injected are managed
by the controller 14.
[0020] The fuel tank 18 is typically a closed container except for
a first vent line 20. The fuel tank 18 is often made of blow
molded, high density polyethylene provided with one or more
gasoline impermeable interior layer(s). The fuel tank 18 is
connected to a fill tube 22. A gas cap 24 closes a gas fill end 26
of the fill tube 22. The outlet end 28 of the fill tube 22 is
located inside of the fuel tank 18. A one-way valve 30 prevents
gasoline 32 from splashing out of the fill tube 22. An upper
surface of the gasoline is identified at 34. A float-type fuel
level indicator 36 provides a fuel level signal at 38 to the
controller 14. In various embodiments, a pressure sensor 40 and a
temperature sensor 42 optionally provide pressure and temperature
signals 44 and 46 to the controller 14.
[0021] The fuel tank 18 includes a first vent line 20 that extends
from a seal 48 on the fuel tank 18 to a canister 50. A float valve
52 within the fuel tank 18 prevents liquid gasoline from entering
the vapor first vent line 20. Fuel vapor pressure increases as the
temperature of the gasoline increases. Vapor flows under pressure
through the first vent line 20 to the vapor inlet of the canister
50. The vapor enters a canister vapor inlet 54, flows past a
retainer element (not shown), and diffuses into the canister 50.
The canister 50 contains an adsorbent material 56 having a nearly
linear or linear isotherm. The adsorbent material 56 may be a weak
adsorbent, may have a high saturation capacity (for example greater
than 20 g/100 cc), have a large pore volume (for example greater
than 600 cubic centimeters (cc) per liter compared to activated
carbon pore volume of 400 cc per liter), may have a slightly
favorable isotherm (for example nearly linear compared to highly
nonlinear isotherm of activated carbon), and may have a low
interaction energy (for example less than half of that of
carbon).
[0022] The canister 50 may be formed of any suitable material, for
example, molded thermoplastic polymers such as nylon. In one
embodiment, the canister 50 may have separate chambers of adsorbent
material 56 defined by a vertical internal wall 64 and a horizontal
internal wall 92. The walls 64 and 92 may be porous to allow vapor
to pass through. The vapor may pass through all chambers of the
adsorbent material 56, with the air exiting through a first vent
opening 68 at the top of the canister 50. The first vent opening 68
also serves as an inlet for the flow of air past a retainer element
(not shown) during purging of adsorbed fuel vapor from the
adsorbent material 56. A purge outlet 70 is also formed in the top
of the canister 50 through which a stream of purge air and purged
fuel vapor can exit the canister 50.
[0023] Connected to vent opening 68 may be a second vent line 72
and a solenoid actuated vent valve 74. The vent valve 74 is
normally open as shown, but upon actuation of a solenoid 76, the
solenoid 76 moves a stopper 78 to cover a second vent opening 80.
The solenoid 76 is actuated by a controller 14 through a signal
lead 79. The vent valve 74 is usually closed for diagnostic
purposes only. As an air/fuel mixture flows from the fuel tank 18
through first vent line 20 and through the canister vapor inlet 54
into canister 50, fuel vapor will be absorbed onto the adsorbent
material 56 in the canister. When vent valve 74 is open and the
adsorbent material 56 becomes saturated with vapor, then vapor will
accompany air exiting the canister at the first vent outlet 68 and
pass through second vent line 72 and through the open
solenoid-actuated valve 74.
[0024] The purge outlet 70 is connected by a purge line 82 through
a solenoid actuated purge valve 84 to the IC engine 12. The purge
valve 84 includes a solenoid 86 and a stopper 88 that selectively
close a third vent opening 90. Purge valve 84 is operated by the
controller 14 through a signal lead 91 when the IC engine 12 is
running and can accommodate a fuel-laden air stream drawn through
canister 50. When the engine is operating, the controller 14 opens
the purge valve 84 to allow air to be drawn past the vent valve 74.
The air flows through the second vent line 72 and into the vent
opening inlet 68. In the canister 50, the air becomes laden with
desorbed fuel vapor and exits the purge outlet 70. The fuel-laden
air is drawn through the purge line 82 and the purge valve 84 into
the engine 12.
[0025] Referring now to FIG. 2, in another embodiment, an optional
scrubber 95 containing a carbon material 98 is coupled to the first
vent opening 68. The carbon material 98 may be, for example,
activated carbon fiber material or carbon monolith. The scrubber
may be made of any suitable material, for example molded
thermoplastic polymers such as nylon or polycarbonate. Air leaving
the canister 50 may flow through the scrubber. The carbon material
98 adsorbs emissions contained in the air. At the other end from
the canister 50, the scrubber 95 is connected through a third vent
opening 96 to the second vent line 72 and the solenoid actuated
vent valve 74.
[0026] In the embodiment shown in FIG. 2, as an air/fuel mixture
flows from the fuel tank 18 through the first vent line 20 and the
canister vapor inlet 54 into the canister 50, hydrocarbons from the
vapor are adsorbed by the adsorbent material 56 in the canister 50.
Lower molecular weight hydrocarbons, such as butanes and pentanes,
due to being smaller in size and more volatile, may be lost as
bleed emissions. The air and bleed emissions passing through the
first vent opening 68 pass through the scrubber canister 95, where
the bleed emissions are adsorbed by the carbon material 98.
[0027] In one embodiment of the invention including the optional
scrubber 95, while the hybrid vehicle's IC engine 12 is operating,
purge air is drawn through scrubber 95 to draw desorbed vapor into
engine 12 for combustion. During purging, controller 14 opens the
purge valve 84 to allow air to be drawn past the vent valve 74. The
air flows through the second vent line 72, scrubber 95, first vent
opening 68, and canister 50. In other words, air is drawn through
the carbon material 98 and the adsorbent material 56. The air
becomes laden with desorbed hydrocarbons and exits through the
purge outlet 70. The fuel-laden air is drawn through the purge line
82 and the purge valve 84 into the IC engine 12.
[0028] Referring now to FIG. 3, in another embodiment a passive
purge system provides a simple and inexpensive way to control
emissions. When a vehicle's fuel tank temperature decreases when
the engine is not running, for example while the vehicle is parked,
the pressure in the tank 18 decreases. The pressure in the tank
decreases due to the thermal contraction of the gas phase and due
to the decrease in the vapor pressure of fuel in the tank. The
decrease in fuel tank pressure causes some air to flow from the
canister 50 into the fuel tank, which results in canister
back-purge. The back-purged hydrocarbons may condense in the fuel
tank. The amount of canister back-purge may depend on the amount of
vapors in the canister, the tank vapor space volume, the Reid Vapor
Pressure (RVP) of the tank fuel, and the decrease in tank
temperature. When the ambient temperature increases, the fuel tank
18 may expel fuel vapors which are then stored in the canister
50.
[0029] Passive purge may result in partial emissions control, for
example about 50%. The adsorbent material 56 may increase the
effectiveness of passive purge by increasing the amount of vapor
back-purged with the same amount of purge air. The passive canister
purge may be used, for example, in lawn mower engines and
off-highway recreational vehicles which do not have any vapor
emission control systems.
[0030] The adsorbent material 56 may result in improvements to the
evaporative emission control system by reducing the size of the
canister by more than 50% and reducing the purge air flow
requirement by more than 75%. Adsorption/desorption and load/purge
characteristics of an adsorbent may be described by its isotherm.
The adsorbent material 56 has a nearly linear or linear
isotherm.
[0031] Referring now to FIG. 4, the isotherms of a commonly used
adsorbent (activated carbon) and the adsorbent material 56 are
provided. Because the adsorbent material 56 has a nearly linear or
linear isotherm, it can adsorb an increasing amount of fuel vapors
as the partial pressure of adsorbing fuel vapor increases at a
constant temperature. The adsorbent material 56 may be, for
example, Sorbead H, available from Engelhard Corporation (Iselin,
N.J.). Sorbead H is an alumino-silicate gel formed into hard,
spherical beads. Sorbead H includes 97 weight % SiO.sub.2 and 3
weight % Al.sub.2O.sub.3. Sorbead H has a surface area of 750
m.sup.2/g; a pore volume of 0.5 cm.sup.3/g; a packed bulk density
of 44 lb/ft.sup.3; a crushing strength of >200 N; and an
attrition rate of <0.05 wt %. Adsorbents which meet the
characteristics of the adsorbent material 56 may also be
commercially available from other companies such as Air
Products.
[0032] The adsorbent material 56 may have some or all of the
following properties: high pore volume; low interaction energy with
hydrocarbons; high saturation capacity; weak adsorbent; and a
nearly linear or linear isotherm, which is a slightly favorable
isotherm. Due to these properties, the adsorbent material 56 purges
easily and results in very little or no heel, which is the residual
hydrocarbons remaining on the adsorbent and requiring large volumes
of purge air to purge. Reducing the purge air volume may improve
the engine air/fuel control problem, for example in hybrid
vehicles, which operate with reduced purge due to engine on-off
operation.
[0033] Mathematical models were used to predict the performance of
a canister with the adsorbent material 56 in vehicle evaporative
emission control. Referring now to FIG. 4, the hydrocarbon storage
capacities of the activated carbon and the adsorbent material 56
are compared. Referring now to FIG. 5, the hydrocarbon purging
capacities of the activated carbon and the adsorbent material 56
are compared. The activated carbon builds heel, but the use of the
adsorbent material 56 results in little or no heel build up.
Therefore, the volume of an adsorbent canister needed for a typical
vehicle evaporative system is very small for the adsorbent material
56, for example 800 cc, compared to a canister volume of 1850 cc
for activated carbon. For example, for a 15 gallon fuel tank 800 cc
of Sorbead H in a canister may be sufficient to adsorb emissions
from the tank. FIG. 6 compares the adsorption or vapor storage
characteristics of the same two adsorbent canisters by loading to
2-g breakthrough with butane containing 50% air. Both adsorbents
adsorbed about the same amount of vapor. As shown in FIG. 5,
however, the adsorbent canister with the adsorbent material 56
purges very rapidly, and it takes less than 4 cubic feet of air to
purge 10 g of butane. The adsorbent canister with the activated
carbon purges slowly and requires more than 15 cubic feet of purge
air to purge 100 g of butane.
[0034] Referring now to FIG. 7, in one embodiment, the evaporative
emission control system is used in a vehicle 100. The evaporative
control system includes the fuel tank 18 connected by the first
vent line 20 to the canister 56, the canister 56 is connected to
the IC engine 12 by purge line 82, and the second vent line 72. In
one embodiment, the vehicle 100 is a hybrid vehicle. In another
embodiment, the vehicle 100 is a Partial Zero Emissions Vehicle
(PZEV). In yet another embodiment, the vehicle 100 is a
conventional gasoline vehicle.
[0035] The above description of embodiments of the invention is
merely exemplary in nature and, thus, variations thereof are not to
be regarded as a departure from the spirit and scope of the
invention.
* * * * *