Low pressure EGR system for diesel engines

Details Low pressure EGR system for diesel engines Low pressure EGR system for diesel engines

2000-05-26

2001-10-16

Denion, Thomas (Department: 3748)

Power plants

Fluid motor means driven by waste heat or by exhaust energy...

With supercharging means for engine

C060S599000, C060S309000, C123S563000, C123S585000, C055SDIG003, C165S158000

Reexamination Certificate

active

06301887

ABSTRACT:

This invention relates generally to an exhaust gas re-circulation (EGR) system for diesel engines and more particularly to a low pressure EGR system for diesel engines.
The invention is particularly applicable to and will be described with reference to a passive, low pressure EGR system particularly suited for retrofit applications to vehicles equipped with diesel engines lacking EGR systems. However, those skilled in the art will recognize that the invention has broader applications and may be integrated with the vehicle's ECU to meet current and proposed emission standards for OEM diesel powered vehicles or may be applied to stationary diesel engine applications such as that used in power generators.
INCORPORATION BY REFERENCE
The following United States patents are incorporated by reference herein and made a part hereof so that details relating to engine operation, EGR systems and system components need not be set forth in detail herein:
a) U.S. Pat. No. 5,927,075 to Khair, issued Jul. 27, 1999, entitled “Method and Apparatus for Exhaust Gas Recirculation Control and Power Augmentation in an Internal Combustion Engine”;
b) U.S. Pat. No. 6,003,316 to Baert et al.,issued Dec. 21, 1999, entitled “Exhaust-Gas Recirculation System for a Turbocharged Internal Combustion Engine”;
c) U.S. Pat. No. 5,947,063 to Smith et al., issued Sep. 7, 1999, entitled “Stoichiometric Synthesis, Exhaust, and Natural-gas Combustion Engine”;
d) U.S. Pat. No. 4,702,079 to Saito et al., issued Oct. 27, 1987, entitled “Air-Cooled Type Intercooler for a Supercharged Internal Combustion Engine”; and,
e) U.S. Pat. No. 5,100,632 to Dettling et al., issued Mar. 31, 1992, entitled “Catalyzed Diesel Exhaust Particulate Filter”.
None of the patents incorporated by reference herein form any part of the present invention.
BACKGROUND
Current United States emission standards for heavy-duty vehicles powered by diesel engines require all new engines not to emit more than 4.0 g/bhp-hr (grams per brake horsepower—hour) of NOx (Nitrogen oxides). Engine manufacturers were able to meet this standard via various improvements to the engine design, advancement to the fuel injection equipment, sophisticated engine controls, etc. Tightening emission regulations by the United States Environmental Protection Agency (EPA) will soon require the heavy-duty diesels to produce 2.5 g/bhp-hr or less NOx and particulate matter emissions of 0.10 g/bhp-hr or less by the year 2002. Meeting this new standard will most likely require use of an EGR system.
For almost two decades, EGR systems have been known to reduce NOx emissions and, as now developed, have been successfully applied to modem gasoline engines to meet past and current emission regulations. Because of the tightening NOx standards for diesel engines, EGR systems have been and are currently being investigated for application to diesel engine emission systems for reduction of NOx. However, application of EGR systems to diesel engines present several distinct challenges or problems unique to diesel engines which include the following:
A) An insufficient differential pressure across the EGR line does not allow for a substantial flow rate of exhaust gases through the EGR line. Gasoline engines have a throttle in the air inlet that creates vacuum sufficient to drive a slipstream of exhaust gases through the EGR loop. Diesel engines, particularly heavy-duty diesel engines, do not have such a throttle.
B) The diesel engines can become contaminated with particulate matter present in the EGR gases, primarily soot. Diesel exhaust contains large amount of soot, which is generally not present in the exhaust gases of a gasoline engine.
C) Re-circulation of exhaust gas into the engine inlet increases emissions of unburned fuel components and particulate matter due to deterioration of the combustion process.
To overcome the insufficient differential pressure problem set forth in item (A), a so-called high pressure EGR (also known as “short-route”) system has been developed. This system is schematically diagramed in prior art
FIGS. 1 and 1A
.
FIG. 1
shows an engine
1
equipped with a turbocharger
2
. Ambient air is drawn into the engine through an air filter
3
where it is compressed through a compressor or charger
4
of turbocharger
2
and subsequently cooled through an intercooler
5
before entering into engine
1
. Exhaust gases from engine
1
pass through the turbine
6
(of turbocharger
2
which drives compressor
4
) before passing through an exhaust system to atmosphere. A high pressure EGR loop, shown as dashed line
7
, re-circulates a slip stream of exhaust gases between an inlet end
7
i of EGR loop
7
that is upstream of turbine
6
and an exit end
7
ii of EGR loop
7
that is downstream of boost air intercooler
5
. A small differential pressure naturally exists between inlet and exit ends
7
i,
7
ii of the EGR loop. The differential pressure in EGR loop
7
is artificially enhanced by de-rating turbocharger
2
. On a conventional turbocharger this is achieved through an appropriate internal geometry affecting exhaust and/or airflow conditions. On a modern variable geometry turbocharger (VGT) this is achieved through a control regulated by the engine control unit (ECU). An EGR valve
10
controls EGR flow and is typically vacuum or pressure operated, but can also be controlled through the engine's ECU. As described, the high pressure EGR system of
FIG. 1
will provide sufficient differential pressure through EGR line
7
for exhaust gas flow although de-rating the turbo charger reduces its efficiency. Further, engine contamination is limited to internal components only. That is, because the EGR exit
7
ii is downstream of the intercooler
5
, contamination resulting from the exhaust gases in EGR loop
7
is not present in compressor
4
and intercooler
5
.
However, a high pressure EGR system does not eliminate the contamination problem of items B and C above. In fact, engines equipped with a high-pressure EGR system suffer durability problems caused by the dirty exhaust in EGR line
7
being re-circulated into the engine. Further, the presence of the exhaust in the engine's combustion chamber and the artificially de-rated turbocharger reduce the engine's fuel efficiency.
In addition, there are more subtle problems caused by a high pressure EGR system, which have significant impact on the engine. By positioning the loop inlet (pick-up)
7
i upstream of turbine
6
, the temperature of the EGR gas is higher than what it might otherwise be, and because of the short travel distance to the intercooler and the engine combustion chamber a mixer, usually in the form of a venturi at loop outlet (return)
7
ii is required. Because of high EGR temperature an additional cooler
8
in the EGR line
7
is required. Such an EGR cooler typically utilizes coolant liquid from the engine cooling system and imposes additional load on the system. Alternatively, if an EGR cooler is simply not applied the inlet gas temperature into the engine increases, causing an additional fuel penalty. Significantly, EGR cooler
8
has proven to be an expensive and non-durable component. It is typically a gas-to-water heat exchanger that plugs up quickly due to contamination with particulate matter. It is believed that contamination of the EGR cooler
8
is being addressed by others who are experimenting with inserting a catalyst or a soot filter
9
in EGR line
7
. The belief is that a catalyst/soot filter will clean the EGR gas to avoid plugging or contamination of EGR cooler
8
. However, the successful implementation of such system has not yet been demonstrated. The addition of a catalyst/soot filter into the high-pressure EGR loop will add additional restrictions to the flow of the EGR gas and may necessitate further de-rating of the turbo-charger causing an additional associated fuel penalty. It is to be recognized that in order to achieve maximum NOx removal effective cooling of the EGR gas is required. However, if the EGR gas is cooled below its dew point to achieve maximum

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