Diesel back-up generator PM ~80% less than EPA thought; new technologies make difference

Newport, R.I. -- A pioneering research project discovered that in the real world, diesel emergency-electric back-up generator ("bug") particulate matter (P[M.sub.2.5]) emissions are about 80% lower than the emissions rates assumed under U.S. EPA's admittedly shaky "AP-42" standard factor.

EPA has long known that its standard PM emissions factor assumption on diesel "bugs"--1.34 grams/kilowatt-hour--is out-of-date, sketchy and dubious. On a scale from "A" (high confidence) to "E" (poor), EPA gives its "bug" emissions confidence factor only a "D."

But it wasn't until this year--when California Energy Commission (CEC) awarded $1.5 million to University of California, Riverside (UCR) for a joint CEC/California Air Resources Board (CARB) study on "bugs"--that the extent of EPA's AP-42 error became clear.

Also sponsoring the UCR studies are EPA, South Coast Air Quality Management District and six diesel gen-set makers.

As UCR researcher Wayne Miller explained to Diesel Engine Emissions Reduction (DEER) conference here (sponsored by U.S. Department of Energy), real-world measurements from a wide variety of older and newer "bugs" (between 300-600 kilowatts) show P[M.sub.2.5], emissions in a range from about 0.1 g/kW-hr to about 0.3 g/kW-hr, not even close to the 1.34 g/kW-hr assumed in EPA "AP-42."

UCR employs a sophisticated, truck-trailer-mounted portable emissions laboratory to determine emissions on a wide variety of stationary and mobile engines. This system makes it possible to check real-world engines under actual operating conditions, without removing the engine from a vehicle or from a power-generation site.

--CARB Verifies Accuracy

CARB has verified the portable lab's measurement accuracy, giving air regulators more confidence in the significance of its findings.

For the field-test program, investigators initially chose 15 engines of 300-750 kW, plus three engines of 1,000 to 2,000-kW. Age ranges include pre-1987, 1987-1996 and post-1996 engines. Test results so far include engines of 300-600 kW, with future tests planned for uncontrolled, >1,000 kW engines, plus tests on older two-strokes using a fuel-borne catalyst/oxidation-catalyst combo, and a fuel-borne catalyst/bare filter combo. Another test will demonstrate the impact of a diesel particulate filter (DPF) combined with selective catalytic reduction (SCR).

Besides measuring engine-out emissions, the UCR investigators also measured the impact of engines running on water-emulsion fuel (Lubrizol "PuriNOx,") diesel oxidation catalysts, passive diesel particulate filters (DPFs) and an "active" DPF using supplemental electric heat for soot oxidation.

Even without exhaust aftertreatment, the newer diesel "bugs" have much lower PM emissions than the older engines, especially at lower loads. It's apparent that today's cleaner highway diesel engines are migrating to generator applications, even without specific regulatory mandates.

Surprisingly, tests of water-emulsion fuel showed a much bigger PM reduction benefit (over 70%) on the newer engines, compared to the older "bugs" (17% PM reduction). While investigators aren't exactly sure why, it's thought that since older "bugs" produce a relatively "wetter" soot (higher in organic carbon, OC) than newer diesels, the "wetter" soot may respond less to emulsions than "dryer" elemental carbon (EC).

Emulsion fuels also did better on PM reduction at the mid-to-high-load points rather than low-load/idle, researchers found. These higher loads are where EC predominates over OC.

This also could explain why diesel oxidation catalysts (DOCs) did far better in engines operated at low load and also in older, two-stroke "bugs" (42% PM reduction). By contrast, a newer "bug" with DOC got only 17% PM reduction benefit--probably not surprising, since newer engines produce less OC, the portion of PM oxidized by a DOC.

Meanwhile, "bugs" with "passive" DPFs achieved 91% PM reduction, while an "active" DPF got 99% PM reduction, researchers found. (Cleaire/Engine Control System's "BUGtrap"--see Diesel Fuel News 7/21/03, p9--is one such system employing electric heat for "off-line" soot oxidation.)

Following the research work on the larger "bugs," the UCR researchers are about to investigate <300-kw>

Ultimately, all the data generated by the research project will be analyzed and reformatted with the help of various state and regional air-quality organizations including NESCAUM, MAP-AMA, NYSERDA and CARB, Miller said. Finally, EPA will help the researchers "shape it into AP-42 format" prior to EPA putting it out for public comment and eventual adoption, he said.

Automated diesel condition monitoring for generator sets

The Canadian Department of National Defense (DND) operates 36 Short Range Radar sites in Canada's far north. Each unmanned site is powered by three Lister-Petter HL-6 diesel engines coupled to Kato Engineering 30 kW brushless generators. Many of these engines have accumulated in excess of 30,000 hours of operation. DND required some means to remotely diagnose/assess the health of these engines in order to determine which gen-set should operate. In addition, there is a need to determine potential maintenance requirements and associated timing of maintenance site visits.

The power contribution of each cylinder of a diesel engine can be used to assess engine condition and assist in locating faults (i.e., fuel rack adjustment, injector fouling, valve seating, ring breakage, etc). In larger diesel engines, cylinder condition is usually assessed by measuring cylinder pressure during operation using permanently installed cylinder pressure access ports. Smaller high-speed diesel engines, such as the Lister-Petter HL-6, are not normally equipped with combustion pressure access ports and the cost of modifying cylinder heads made this approach unattractive to DND.

Advanced Engine Technology Ltd. (AET), has developed an engine condition monitoring system for this application under contract with the North Warning System Office of DND. AET is a research, development and manufacturing company with diesel engine/fuels laboratory facilities located in Nepean, a neighboring city to Ottawa, Ontario, Canada.

The AET Engine Condition Monitor (ECM) can detect any combination of cylinder faults in six-cylinder high-speed diesel generator sets under continually varying loads. The power balance of each cylinder can be predicted to within [+ or -]2 percent RMS and cylinder pressure measurements are not required. Operation of the ECM is fully automated, and engine data can be downloaded from the remote radar sites to a centrally located monitoring station.

The ECM is based on Instantaneous Crankshaft Angular Velocity technology (ICAV), initially developed and patented by the National Research Council of Canada. AET is the worldwide licensee of this technology. Following the initial development of the ICAV technology by NRC, AET has pursued the development and commercialization of this technology for diesel engine applications over the past several years. Current efforts are directed towards engine condition monitoring for generator set applications in both unmanned and manned settings. ICAV measures the periodic variations in crankshaft velocity during each engine cycle. Pattern recognition software compares the crankshaft velocity waveform to a knowledge base for the engine/generator family. AET creates this knowledge base by mapping a typical engine/generator over a range of loads. During mapping, cylinder power balance is perturbed by known amounts. The knowledge base created by mapping one engine/generator can be used on other diesel generator sets of the same family.

Flywheel speed is measured using two rugged, noncontacting Hall-effect sensors mounted on the engine bell housing. Variations in flywheel tooth spacing or tooth wear are taken into account in order to produce accurate results. The ECM can be quickly retrofitted in the field using common tools. Once installed, no further maintenance or periodic calibration is required, according to AET. Flywheel tooth spacing is measured by a custom timer board installed in a personal computer on each site. ICAV software processes this information and calculates the relative power from each cylinder. Data is automatically acquired and stored in a database on the computer at 30 minute intervals. When requested, stored engine data is transferred from each radar site to the central monitoring station via a satellite link.

Figure 2 shows a sample of data downloaded from one radar site. This display format is used to show the current cylinder power balance of all engines running at the radar site. Each bar represents the deviation from nominal power of an individual cylinder: cylinder No. 1 on the left and cylinder No. 6 on the right. An over-balance condition of +20 percent indicates that the cylinder was producing 20 percent more than 1/6th of the total power; no deviation (zero percent) means that the cylinder was producing exactly 1/6th of the total power. As a general rule, it can be assumed that the engine is performing well when the power balance for all cylinders is within [+ or -]10 percent. Both fuel consumption and exhaust emissions are minimized when cylinder balance is optimized.

Tests performed at AET on this engine/generator family showed that at a power setting of 20 kW, a power imbalance of -30 percent in just one cylinder caused an increase in fuel consumption of 2.5 percent, along with significant increases in N[O.sub.x], THC, and particulate emissions. By using the ECM, maintenance staff are now able to balance cylinder power levels during annual maintenance inspections, thereby minimizing fuel consumption and emissions.

Generator Sets are based on 23 L, 6-cylinder diesel engine

Available in 50 and 60 Hz frequencies, Series DQC consists of 600, 750, and 800 kW generator sets intended for standby and prime power use in wide range of applications. Units include PowerCommand[R] digital control system for total system integration, including automatic remote starting/stopping, precise frequency and voltage regulation, alarms and status message display, alternator protection, output metering, and auto-shutdown-at-fault detection.

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MINNEAPOLIS - Cummins Power Generation has introduced a series of 600 kW, 750 kW, and 800 kW generator sets based on a new 23-liter inline 6-cylinder diesel engine that offers low emissions and fast transient response to load changes. The generator sets are available in 50 Hz and 60 Hz frequencies. They are intended for standby and prime power use in a wide range of applications, and are backed by Cummins' global service support.

"The DQC series of generator sets offer low emissions, and 60Hz models are certified to the current U.S. EPA Nonroad Source Emission standards," says Mark Westphal, Product Director, Cummins Power Generation. "In addition, the generator sets are listed to UL2200, which helps expedite the commissioning and inspection process during installation."

he DQC series features PowerCommand[R] digital control system for total system integration, including automatic remote starting/stopping, precise frequency and voltage regulation, alarm and status message display, alternator protection, output metering, and auto-shutdown-at-fault detection. The generator sets are also NFPA 110 compliant for all standby applications.

The DQCA generator set is standby rated at 600 kW (60 Hz) and 545 kW (50 Hz); and prime rated at 545 kW (60 Hz) and 500 kW (50 Hz). The DQCB generator set is standby rated at 750 kW (60 HZ) and 640 kW (50 Hz); and prime rated at 680 kW (60 Hz) and 584 kW (50 Hz). The DQCC is standby rated at 800 kW (60 Hz) and 656 kW (50 Hz); and prime rated at 725 kW (60 Hz) and 656 kW (50 Hz).