Measuring and testing – Gas analysis – Gas of combustion
Patent
1994-06-06
1995-12-19
Chilcot, Richard
Measuring and testing
Gas analysis
Gas of combustion
731181, G01N 27417, G01N 2712, F02D 4114
Patent
active
054760011
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention proceeds from a sensor for determining gas components and/or gas concentrations in gas mixtures according to the generic concept of the main claim.
Sensors and Actuators B 9(1992), pages 233-239 discloses a sensor of the generic type for determining the CO concentration, in which a pump cell pumps oxygen to a measuring element. It has been found in this case that in the case of CO in air having 21% O.sub.2 the resistance value of an SnO.sub.2 semiconductor gas sensor is more than three orders of magnitude higher than in the case of CO in N.sub.2. In this case, the measuring element is arranged in a measuring chamber without a defined reference to the pump cell or to the gas mixture. All that is required is for an adequate oxygen concentration to be present at the measuring element. The gas components to be measured in the gas mixture are designated below as pollutant components.
Furthermore, DE-OS 27 52 530 discloses a method for measuring the sum of all the combustible constituents in a total fuel atmosphere, in which method an electrochemical measuring cell and a pump cell are provided. The measuring cell sets the pumping potential to a level such that sufficient oxygen is pumped into the inner chamber in order in this way to cause a depletion in combustible constituents. Precisely as much oxygen is pumped in for a stoichiometric mixture always to be present at the measuring cell. The pumped flow is used in this case as a measure of the proportion of combustible constituents, the pumped flow being proportional to the rate of diffusion of the combustible constituents through the diffusion opening due to the conversion of the combustible constituents at the pump electrode. Because of the cross sensitivity with respect to oxygen, the reaction rate at the pump electrode provides no direct conclusion on the concentration of the combustible constituents in the exhaust gas.
ADVANTAGES OF THE INVENTION
The invention utilizes the fact that given over-occupancy of the grain surfaces of the sensitive region of the measuring element with oxygen, even large changes in oxygen concentration have a negligibly small influence on the sensor signal. This dependence follows, for example, from FIG. 1a. The sensor according to the invention for determining gas components and/or gas concentrations in gas mixtures, in particular of CO, NO.sub.x and HC in exhaust gases of internal combustion engines, basically includes a measuring element which has a sensitive region, a pump cell with pump electrodes which are arranged on a solid electrolyte and cause a transfer of oxygen to the measuring element, and a diffusion path, in which a concentration gradient of the gas component to be determined and an concentration oxygen gradient are formed, provided between the pump cell and the gas mixture, and wherein the measuring element is positioned relative to the diffusion path such that an excess of oxygen is present in the sensitive region of the measuring element. Along the diffusion path, the two above mentioned gradients run counter to one another.
The sensor according to the invention has the advantage that it is possible to determine pollutant components and/or pollutant concentrations in gas mixtures independently of the oxygen partial pressure or of the lambda value of the gas mixture. The O.sub.2 cross sensitivity is largely eliminated. A further advantage consists in that the sensor has a simple design and manages using measuring elements known per se. The measuring element is designed with a conventional pump cell in such a way that there is always an excess of oxygen at the measuring element.
Advantageous developments and improvements of the sensor specified above are possible and are described basic. It is particularly advantageous to set the pollutant concentration to a value at which the measuring element has a high sensitivity. This is performed in the case of a semiconductor gas sensor and of an electrochemical measuring cell by setting the pollutant concentration in such a way that a change in
REFERENCES:
patent: 4158166 (1979-06-01), Isenberg
patent: 4543273 (1985-09-01), Handa et al.
patent: 4553424 (1985-11-01), Sakurai et al.
patent: 4750353 (1988-06-01), Wright et al.
patent: 4927517 (1990-05-01), Mizutani et al.
patent: 4961341 (1990-10-01), Tanaka et al.
patent: 5071626 (1991-12-01), Tuller
patent: 5223783 (1993-06-01), Willis
patent: 5248617 (1993-09-01), De Haan
patent: 5270009 (1993-12-01), Nakamori et al.
J. H. Visser et al.: "Sensors for measuring combustibles in the absence of oxygen", vol. 9, 1992, pp. 233-239.
Logothetis et al, "Chemical and Physical Sensors based on oxygen pumping with solid state electrochemical cells," Sensors and Actuators, vol. 9, 1992, pp. 183-189.
Friese Karl-Hermann
Gruenwald Werner
Hoetzel Gerhard
Neumann Harald
Riegel Johann
Chilcot Richard
Dombroske George M.
Robert & Bosch GmbH
LandOfFree
Sensor for determining gas components and/or gas concentrations does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensor for determining gas components and/or gas concentrations , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensor for determining gas components and/or gas concentrations will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-986513