Gaseous, Particulate, and Smoke Emissions from a Heavy Duty Automotive Gas Turbine Engine T. Shih, G. Smith, and G. Springer* Department of Mechanical Engineering, The University of Michigan, Ann Arbor, Mich. 48109 ??
Gaseous, particulate, and smoke emissions were studied in the exhaust of a heavy duty automotive gas turbine engine. The effects of brake horsepower, gasifier rotor angular speed, overall mass air-fuel ratio, and combustor exit temperature were evaluated a t engine loads ranging from 136 to 542 N.m and a t constant output shaft angular speeds ranging from 1500 to 2700 rpm. ThLe results were compared to emissions previously reported for a heavy duty spark ignition engine and a heavy duty compression ignition engine, both of which had platinum oxidation catalysts and EGR. T h e hydrocarbon emissions from the gas turbine engine were lower, while the NO, and CO emissions were comparable to the emissions from the spark and the compression ignition engines. Under all test conditions, the amount of particulate matter emitted was less than 0.001 gabhp-l-h-' (bhp is brake horsepower), and the smoke opacity of the exhaust gas was less than 0.3 Bosch unit. The brake specific fuel consumption of the gas turbine engine was also measured and was 4040% higher than the consumption of a heavy duty spark and a heavy duty compression ignition engine operating a t corresponding conditions.
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Figure 1. Schematic of gas turbine engine, dynamometer, and exhaust system set up. Open circles represent thermocouple and sampling ports
Gaseous and particulate emissions from spark and compression ignition engines have been investigated extensively in recent years. Less attention has been directed to emissions from gas turbine engines, and most of the previous studies have been on aircraft and industrial gas turbines and turbine combustors. Relatively few investigators have studied emissions from automotive gas turbine engines. T h e major parameters studied thus far on emissions from automotive gas turbines include driving cycles (1-7), cold and hot start ( 2 ) , fuel type ( 2 , 6, 8, 91, combustor design (3, 5 , 6, I I ) , gasifier rotor speed (5,6, 8-10), water injection (6, 11), and overall air fuel ratio (6, 11). Data have not yet been reported showing the direct effects of engine speed and load on gaseous, particulate, and smoke emissions. The objective of this investigation was to evaluate the emissions and fuel consumption characteristics of a heavy duty automotive gas turbine engine operating a t different steady speeds and loads, with particular attention directed to the NO,, CO, C02, and HC concentrations in the exhaust, to the mass and size distribution of the emitted particulates, and to the exhaust gas smoke opacity.
ExpcrimPntal The gas turbine engine investigated was a Ford 360 M-2000 two-shaft regenerative gas turbine engine with a reverse-flow can-type combustor equipped with a fuel atomizing nozzle (12).The engine was mounted on a Midwest Dynamatic eddy current dynamometer (Figure 1). The engine and dynamometer were instrumented to monitor the gasifier rotor angular speed, the output shaft angular speed and torque, the combustor exit temperature, and the engine exhaust temperature. Of these parameters, only the engine output shaft angular speed and torque and the gasifier rotor angular speed could be varied independently. The air flow rate into the engine was measured with a pitot tube mounted inside the air inlet duct. T h e fuel consumption was measured by a rotameter. The test cell temperature, pressure, and relative humidity were also monitored. The tests were conducted using number 2 diesel fuel supplied by the Amoco Oil Co. T h e physical and chemical prop0013-936X/79/0913-0855$01.00/0
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@ 1979 American Chemical Society
erties of the fuel were given by Laresgoiti and Springer (13). T h e engine was lubricated with Stauffer J e t I1 lubricating oil. The exhaust system consisted of two 25.4 cm diameter, 7.31 m long ducts coupled to the two engine exhaust openings (Figure 1).These ducts exhausted into an exhaust tunnel. There were five sets of sampling ports in each of the two ducts for thermocouples and sampling probes. Exhaust samples for gaseous and particulate analyses were collected by stainless steel probes with 3.98 (0.75 mm wall thickness) and 2.39 mm i.d. (0.3 mm wall thickness), respectively. T h e probes were located a t the center of the exhaust ducts 1 m downstream from the engine exhaust and faced in the direction of oncoming flow. Measurements were also made a t different positions along and across the exhaust ducts. The variation in the gaseous and particulate emissions with probe position was found to be negligible. The exhaust sample for gaseous analyses was passed through a Dwyer flow meter and was drawn into the gas analyzers by a vacuum pump. The probe and the instruments were connected by 4.8 mm i.d. nylon tubing. The flow rate through the probe was controlled by a needle valve built into the Dwyer flow meter. The flow rate was maintained a t 0.566 m3-h-' (0 "C, 0.101 MPa) for all measurements and calibrations. Before each measurement, the sampling line was flushed with nitrogen. The NO, concentration was measured by a Thermoelectron Corp. Series 10 chemiluminescent NO, analyzer, the CO concentration by a Horiba AIA-21 ( A S . ) nondispersive infrared analyzer, the COz concentration by a Horiba AIA-21 nondispersive infrared analyzer, and the unburned hydrocarbon concentration by a Beckman Model 109A flame ionization hydrocarbon analyzer. All of these instruments as well as the sampling lines leading to them were a t room temperature. Although the exhaust sample was undiluted, water vapor condensation did not occur in the sampling line. The infrared analyzers were tested for water vapor interference. T h e tests showed water vapor did not affect measurably the readings. Gaseous products react inside the sampling lines. These reactions may affect the measured values of NO,, CO, COz, and unburned hydrocarbons. Approximate calculations indicated that the effects of these reactions on the measured concentrations were less than about 0.1%. Particulate matter was collected on Gelman 47-mm diameter type A glass fiber filters placed in a modified Gelman 2220 filter holder. The entire filter unit was surrounded with beaded heaters and Kaowool insulation (Figure 2). The flow rate through the sampling probe was adjusted to the proper Volume 13, Number 7 , July 1979
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Figure 2. Schematic of particulate sampling trains: (left) unit housinc filter for collecting total particulate matter; (right) unit used in conjunction with the Royco particle counter; (open circles) thermocouple locations
700 0
20 40 60 80 100 120 140 160 180 200 220 BRAKE HORSEPOWER
Figure 4. Brake specific emissions as a function of brake horsepower and output shaft angular speed: ( 0 )Ford 360 M-2000 gas turbine engine (present study; range: 1500-2700 rpm, 136-542 N-m); (solid lines) fit to data
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Figure 3. NO, CO, and C 0 2 emissions as a function of output shaft angular speed and torque: ( 0 )Ford 360 M-2000 gas turbine engine (present study; range: 1500-2700 rpm, 136-542 N-m); (solid lines) fit to data
value for isokinetic sampling. The flow rate through the probe was measured by a Dwyer flow meter installed after the filter and was controlled by an "on-off'' toggle valve placed before the filter and by a needle valve built into the Dwyer flow meter. The flow rate was adjusted continuously by the needle valve on the Dwyer flow meter to compensate for the increased filter resistance with time. A high vacuum pump provided the flow through the sampling line. The filters were placed in an air-tight container containing CaC12 as a desiccant for 24 h before and after each test. T h e filters were then weighed and the difference in mass was taken as the total particulate mass emitted during the filtering period. The particulate size distribution was measured with a Model 225 Royco particle counter. The flow rate through the probe was measured with a 2.77-mm diameter sharp-edged orifice and controlled by two stainless steel metering valves. T h e flow rate through the probe was adjusted t o the proper value for isokinetic sampling. T o prevent condensation in the sampling line, the probe, orifice, and metering valve were wrapped with beaded heaters and Kaowool insulation (Figure 2). The exhaust sample was diluted with filtered ambient air. 856
Environmental Science & Technology
The exhaust sample-air mixture was then fed through a 11.4-L dilution chamber to reduce the temperature of the sample below 49 "C and the particulate concentration below 120 particles per cm3. These values were dictated by the specifications of the Royco particle counter. T h e dilution air flow rate was adjusted by a bleed valve and measured with a sharp-edged orifice. The dilution ratio was always maintained a t 8:l. A portion of the diluted exhaust sample was drawn into the Royco particle counter through a 9.5 mm i.d., 3 m long tygon tube. The flow rate through the Royco particle counter was measured with a Kontes metering tube and ranged from 1800 to 2600 cm3-min-l. This was about 6% of the exhaust sample-air mixture flow rate. Particulate sizes were recorded in five size ranges yielding the number of particulates of diameters greater than 0.3,0.7, 1.4, 3.0, and 5.0 pm. T h e smoke opacity was measured by a Bosch EFAW 68A Smoke Meter which includes a standard sampling probe. The probe was inserted 25.4 cm from the ends of the exhaust ducts with the tip of the probe a t the center of the duct and facing in the direction of the oncoming flow. The gaseous, particulate, and smoke emissions from the two exhaust ducts differed slightly (
