Sensors and Instrumentation and Nondestructive Evaluation
Energy System Applications
DOE Office of Transportation Technologies
Ion-mobility Spectrometry Based NOx Sensor
Real-time measurement of NOx content in the exhaust gas can provide the needed control parameter for the diesel-engine combustion management system. Such a NOx sensor must be sensitive (ppm), fast response (ms), robust, and low cost. Furthermore, the NOx sensor must be able to function under the environment of the exhaust gas recirculation line or the after-treatment catalyst stream. To date, available NOx sensors are mostly solid-state electrochemical sensors such as Yttria-stabilized zirconia (YSZ) sensors. Poor accuracy, slow response (in minutes), cross sensitivity, and aging problems are the main shortcomings of the YSZ sensors. Argonne has recently developed a practical fast-response NOx sensor based on ion-mobility spectrometry (IMS) technique. The sensor uses a corona/spark-discharge ionization source replacing the conventional radioactive ion source. The sensor is expected to function in a hostile exhaust-line environment with long-term stability and at low cost.
This development project is a collaborative effort between Argonne and Cummins, Inc. under a CRADA agreement. For further information, please visit: Ion-mobility Spectrometry Based NOx Sensor
NDE for Ceramic Valves for Diesel Engines
Figure 1: Photograph of automated laser-scattering system for scanning full ceramic valves. Click on image to view larger image.
As part of the Heavy Vehicle Propulsion System Materials Program, DOE Office of FreedomCAR and Vehicle
Technologies, NDE technologies
are being developed for inspection/evaluation of ceramic valves. This program is a cooperative program
with the Caterpillar Technical Center. In this program, silicon-nitride ceramic valves are being machined
and evaluated under rig/engine test conditions by Caterpillar. The Argonne effort is to develop NDE technologies
that will detect and quantify processing- and operation-induced surface/subsurface damage in the ceramic
valves. Laser scattering is the primary NDE method. A fast, automated laser-scatter NDE system
(photograph below) was developed to scan entire valves. This system has two rotation and two translation
stages to align and focus the laser beam on the valve surface during the scan, and the resulting two-dimensional
scattering image is used to identify the location, size, and relative severity of subsurface defects/damage.
Laser-scattering images were obtained for several bench-tested silicon-nitride valves. The NDE results
established the detection sensitivity for two types of defect/damage: (1) surface contact damage and
(2) subsurface porosity and pre-spallation due to valve processing.
Diesel Fuel Reformer
This program is a joint effort between NE and the Chemical Sciences and Engineering Division. The objective is to develop a device that will convert diesel fuel into hydrogen-rich gas on board a heavy-duty vehicle in a small fuel processor. The technical approach consists mainly of (1) evaluation of various engineering issues that need to be addressed with regard to diesel fuel reforming and (2) development of a fuel/exhaust-gas mixing device that will optimize diesel-fuel reforming. The main engineering issues are how to avoid pre-ignition and coke formation and how to achieve catalyst stability.
In FY 2003, we completed the test facility design and started construction. The facility, shown in the schematic diagram below, consists of a fuel-injection assembly, simulated exhaust-gas-generating system, and fuel-exhaust-gas mixing apparatus. The proposed sensors and instrumentation for process measurement and control have been identified. We have also established a collaboration with International Truck and Engine Corp., which will provide Argonne with diesel-fuel injectors and a fuel-injection controlling system. Fuel/exhaust-gas mixing tests were conducted in FY 2004 to optimize the design of the mixing device. Numerical simulation will also be performed.
Figure
2: Schematic diagram of the diesel-fuel/air/steam mixing test facility.
Click on photo to view a larger image.
Acoustic Fuel Vapor Sensor
This program, completed in FY 2002, was a joint effort among Argonne, Ford Motor Co., and Northwestern University. The objective of the Argonne effort was to develop a low-cost, fast-response, acoustic-based fuel-vapor sensor that could be used in the harsh automotive environment to measure or monitor the fuel-vapor mass flow rate and to detect variations in fuel-vapor composition.
We initially focused on evaluating the use of the (1) speed of sound (SOS) to estimate the fuel gas composition and (2) acoustic relaxation spectra to characterize the fuel-gas composition. A laboratory prototype of the sensor was built and tested with methane gas. The basic design consists of two 0.5 MHz transducers operating in a pitch-catch mode. Gated sine waves of a fixed frequency (0.5 MHz or its harmonics) are propagated in a narrow flow channel, and their reflections are analyzed for variations in amplitude and time of flight, from which attenuation and speed of sound are measured. The prototype uses a high-pressure vessel to house the transducers and the flow cavity. To obtain the acoustic relaxation spectra, we vary the gas pressure because the attenuation in a gas depends on the ratio of acoustic frequency over the gas pressure.
Figure 3: Speed of sound in methane/nitrogen mixtures (solid line calculated using isentropic model). Click on image to view larger image.
Figure 3 shows the SOS in
methane/nitrogen mixtures. The solid line represents the calculated values based on an isentropic model.
Although the measured SOS values
(circles) are higher than the calculated curve, we concluded that the SOS can
be used to predict the methane concentration in nitrogen gas. This conclusion is justified as long
as the carrier gas mixture has a fixed composition so that the mixture of methane and carrier gas can
be considered as a binary gas.
Figure 4: Dimensionless attenuation versus frequency/pressure in 50% methane in nitrogen. Click on image to view larger image.
Acoustic relaxation spectra of methane and methane/nitrogen mixtures were predicted by a theoretical
model developed by Northwestern. We confirmed the model prediction qualitatively. Figure 4 shows
the dimensionless attenuation (attenuation times wavelength, al) versus the frequency/pressure ratio
(f/P) for 50% methane in nitrogen. The solid line represents the best-fit curve to the data. Clearly,
a relaxation peak exists around f/P = 0.07 MHz/atm under ambient conditions, which is somewhat
lower than the model prediction (>0.1 MHz).
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