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January/February 2002 Excerpt

Testing on Diesel Engine Test Facility Helps Effort to Lower Emissions



By Joseph Smith

PHILADELPHIA—The Diesel Engine and Power Transmission Branch (932) has represented U.S. Navy interest in the area of diesel exhaust emissions since 1998. It is anticipated that global demand for emissions reduction technologies, test facilities, as well as monitoring systems will continue to increase in the coming years. The branch vision for the emissions program is to maintain resources (including personnel and facilities) to continue to represent the U.S. Navy’s best interests as regulations become more restrictive and also to establish expert emissions test capabilities as the demand for these technologies increases. In support of this vision, NSWCCD-SSES is teaming with private industry to improve NOx emissions from diesel-electric locomotives, while improving fuel economy.

The Diesel Engine and Power Transmission Branch (932), specifically Codes 9325 and Code 9324, has an emission bench installed on a Fairbanks Morse Opposed Piston 2-Stroke diesel engine in the Diesel Engine Test Facility (DETF), located in the Richard C. Cunningham Engineering Complex. The emission bench contains Rosemount analyzers which can detect CO, CO2, NO, NOx, O2, SO2, and total hydrocarbons. A private company, Scentczar, utilized the DETF to compare their prototype NOx analyzer, which uses ion mobility spectrometry (IMS), to our NO/NOX analyzer, which uses chemiluminescence. Code 932’s chemiluminescence analyzer is highly accurate and considered to be the industry standard for NOX detection.

Scentczar is developing a control system for improving or at least maintaining NOX emissions from diesel-electric locomotives while improving fuel economy. Engine settings are adjusted based on NOX sensor inputs to maintain Environmental Protection Agency (EPA) requirements while maximizing fuel economy. Although they are focusing their work on diesel-electric locomotives, they intend to broaden it to include gas turbines and smaller diesel engines used on trucks. Scentczar is developing a NOX sensor that uses IMS because IMS sensors are very accurate, compact, lightweight, and have a fast response and clear-down time. However, until the testing at the DETF was started, Scentczar’s IMS sensor had never been used on actual diesel engine exhaust.

On November 14, preliminary testing was done at the DETF to determine if the IMS responded at all to diesel exhaust, which it did. Exhaust samples were also taken and stored in “Tedlar” bags so that Scentczar could bring the exhaust samples back to their laboratory and make adjustments to their analyzer before further testing.

After the adjustments were made, four test sequences were run during the week of December 10 at the DETF. Each test sequence procedure consisted of running the diesel engine at various load points, allowing the temperatures to stabilize, recording chemiluminescence analyzer output data (which is assumed to be the actual concentration of NOX), and recording IMS output data at the same time. The purpose of Test 1 was to determine if IMS can respond correctly to NOX in diesel exhaust or if there are materials in diesel exhaust that falsely inhibit or increase IMS response.

Once it had been established that IMS seemed to work from the results based on Test 1, the performance of IMS in diesel exhaust was evaluated in Test 2. The performance of the IMS analyzer was evaluated by measuring the following parameters:

• Response Time—the time delay from when gas is applied to the sensor until the sensor reads 90% of the actual concentration.

• Limit of Detection—the lowest level of NOx that can be detected.

• Accuracy—the worst-case difference (expressed in percent) between the IMS reading and the actual concentration.

• Saturation—the highest concentration that the IMS readings match the actual concentration.

• Clear Down Time—the time between when the NOX is removed from the IMS inlet stream and the time that the IMS reading goes below 10% of the value of its last reading.

The purpose of Test 3 was to determine if IMS is a practical sensor for Scentczar’s diesel engine emission control system. This was done by demonstrating repeatability of the estimated value of the NOx concentration from IMS data. Test 3 was also used for developing a response curve for data spikes in NOX concentration.

The purpose of Test 4 was to show that the NO converter in the IMS will accurately convert NO in the diesel exhaust to NO2. This is crucial because the IMS does not respond to NO, and it must be converted to NO2 to give an overall NOX reading.

On the last day of testing, a representative from Hughes Research Laboratories (HRL) performed comparative tests on an alternate design prototype NOx analyzer.

The results of the tests are still being analyzed by Scentczar and HRL. It is expected that further refinements will be made to each analyzer and future testing at the DETF may be conducted.


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