Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2002-08-01
2003-11-25
Kwon, John (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S676000, C123S568210, C123S690000
Reexamination Certificate
active
06651623
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to methods and systems for measuring air-fuel ratios and more particularly to methods and systems for measuring air-fuel ratios in hydrogen fueled internal combustion engines.
BACKGROUND AND SUMMARY OF THE INVENTION
As is known in the art, it is frequently required to measure the air-fuel ratio in internal combustion engines. In gasoline-fueled engines, it is common practice to employ an Exhaust Gas Oxygen (EGO) sensor to measure the fuel-to-air ratio. The EGO sensor is disposed in the exhaust gas flow produced by the engine. The EGO sensor is well developed for use in engines that operate at a stoichiometric proportion of fuel to air, i.e., a proportion at which the fuel and the oxygen in the air would be completely consumed if the reaction went to completion.
As is also known in the art, excess air combustion potentially provides higher fuel efficiency than stoichiometric combustion. However, for lean mixtures, a conventional EGO sensor provides limited information. In the lean case, a wide range or Universal EGO (UEGO) sensor is used instead of an EGO sensor. UEGO sensors are capable of measuring fuel-to-air ratio for rich (excess fuel) and lean mixtures as well as stoichiometric mixtures. One disadvantage is that a UEGO sensor is more costly, and less well developed, than the conventional EGO sensor.
As is also known, both EGO and UEGO sensors have a precious metal coating on the sensor surface exposed to the exhaust gas stream. A catalytic reaction occurs on the surface of the sensor causing excess fuel to react with excess oxygen. It is well known in the art that combustion efficiency in a stoichiometric gasoline engine, for example, is less than 100%, typically 97%. Thus, the gases emanating from the engine contain some unburned fuel and oxygen. Depending on the stoichiometry of the exhaust gases, one or the other of the fuel or oxygen is depleted prior to the other. An EGO sensor provides a signal essentially indicating whether there is excess fuel or excess oxygen existing in the exhaust gases after the reaction on the surface of the sensor. A UEGO sensor provides a signal proportional to the amount of excess fuel or excess oxygen.
As is also known in the art, a fuel, which combusts at extremely lean fuel-to-air ratios, and thus delivers high fuel efficiency, is hydrogen. A well-known issue using an EGO sensor or UEGO sensor to determine fuel-to-air ratio from hydrogen combustion is that a biased measurement is produced due to the unequal diffusion rates of hydrogen compared to other species in the exhaust. More particularly, hydrogen, being an extremely small molecule, diffuses more readily than other constituents (i.e., N
2
, O
2
, and H
2
O) also in the exhaust gases. Thus, at the precious metal surface of an EGO or UEGO sensor, unburned hydrogen is catalytically reacted with oxygen, thereby depleting the hydrogen in the exhaust in the vicinity of the EGO or UEGO sensor, while also diminishing the quantity of oxygen in such exhaust. The lower concentration of these two species occurring at the sensor surface compared to the bulk gas concentration causes diffusion of H
2
and O
2
from the bulk gas toward the sensor surface. due to its high diffusivity, arrives at the surface more rapidly than O
2
, thereby biasing the EGO or UEGO signal. More particularly, the effect is that the EGO or UEGO sensor indicates a richer mixture than what actually exists in the bulk exhaust gases.
The inventors of the present invention have recognized a need for an inexpensive and reliable alternative to an EGO or UEGO sensor for measuring fuel-to-air ratio in a lean-burning, hydrogen-fueled engine.
In accordance with the present invention, a method is provided wherein hydrogen is introduced into an internal combustion engine along with an oxidizer. The hydrogen and the oxidizer are combusted in the internal combustion engine with products of such combustion being removed from the engine as an exhaust gas stream. The method determines the mass ratio based on said temperature independent of engine operating power.
Thus, the inventors have discovered that while engine power along with temperature may be used to determine the air-fuel ratio with a gasoline fueled engine, with a hydrogen fuel engine, the oxidizer-hydrogen ratio may be determined independent of engine operating power.
More particularly, while the relationship between exhaust temperature and stoichiometry has been exploited previously in gasoline powered aircraft and racing applications, the inventors have discovered that with a hydrogen fuel engine, the oxidizer-hydrogen ratio may be determined independent of engine operating power. In the prior art, the fuel-to-air ratio is manually adjusted until the exhaust temperature is at a maximum. Then, the fuel-to-air ratio is increased (made richer). The purpose of increasing the fuel-to-air ratio beyond the stoichiometric ratio is to avoid overheating exhaust valves. Essentially, the fuel provides a cooling effect. The method, according to the present invention, is different than prior uses for a number of reasons. Firstly, the present method applies to hydrogen fuel only because of the unique relationship between stoichiometry and exhaust temperature recognized by the inventors of the present invention. Specifically, the fuel-to-air ratio to exhaust temperature relationship does not depend on engine speed, engine torque, or the product of the two, engine power, for hydrogen fuel. Secondly, because there is a unique relationship between exhaust temperature and stoichiometry for hydrogen fuel combustion, the present invention relies on the relationship to provide a measure of fuel-to-air ratio, as opposed to prior methods which use temperature only in a relative sense to determine an operating condition rich of stoichiometric which is not deleterious to the engine components.
Other disadvantages of prior methods are overcome by a method for determining a mass ratio of a fuel to an oxidizer being combusted in an internal combustion engine including the steps of determining the temperature of an exhaust gas stream from the engine and computing the mass ratio based on said temperature. The fuel contains greater than 90% hydrogen, on a mass basis. The mass ratio is adjusted depending on the composition of the fuel, composition of the oxidizer, and an exhaust gas recirculation amount. The temperature may be determined by a thermocouple, a thermistor, a thermopile, an optical measuring device, or any combination these temperature measuring devices.
An advantage of the present invention is that the mass ratio is determined independently of engine rpm and torque.
An advantage of the present invention is a reliable, unbiased measure of fuel-to air ratio in a hydrogen-fueled engine. Basing the measure of fuel-to-air ratio on temperature overcomes the problem of signal bias of EGO and UEGO sensors.
A further advantage is that robust, inexpensive, well-developed temperature measuring hardware can be used to determine air-fuel ratio in a hydrogen-fueled engine.
Yet another advantage of the present invention is that if a UEGO sensor is provided in the engine's exhaust, the fuel-to-air ratio, as determined by the present invention, can be compared with that determined by the UEGO. These two measures can be used to determine a fault in either the temperature measuring device or the UEGO. Alternatively, the two measures can be used to update calibration constants within the engine computer to refine the computed fuel-to-air ratio determination.
Other advantages, as well as objects and features of the present invention, will become apparent to the reader of this specification.
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patent: 3982591 (1976-09-01), Hamrick et al.
patent: 4901525 (1990-02-01), Beveridge et al.
patent: 5558783 (1996-09-01), McGuinness
patent: 5707593 (1998-01-01), Wang
patent: 6000384 (1999-12-01), Brown et al.
patent: 6427639 (2002-08-01), Andrews et al.
Hashemi Siamak
Kotwicki Allan Joseph
Tang Xiaoguo
Brehob Diana D.
Ford Global Technologies LLC
Kwon John
LandOfFree
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