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Bureau of Mines Information Circular/1988 
 
 Effectiveness of Catalytic Converters 
 on Diesel Engines Used 
 in Underground Mining 
 
 By B. T. McClure, K. J. Baumgard, and W. F. Watts, Jr. 
 
 ^ tNT 0r '♦ 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 9197 
 
 Effectiveness of Catalytic Converters 
 on Diesel Engines Used 
 in Underground Mining 
 
 By B. T. McClure, K. J. Baumgard, and W. F. Watts, Jr. 
 ii 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 T S Ary, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 McCIure, B. T. (B. Thompson) 
 
 Effectiveness of catalytic converters on diesel engines useu in underground mining. 
 
 (Information circular; 9197) 
 
 Bibliography: p. 10-12. 
 
 Supt. of Docs, no.: I 28.27:9197. 
 
 1. Mining machinery—Catalytic converters. 2. Diesel motor exhaust gas- 
 Purification. I. Baumgard, K. J. (Kirby, J.). II. Watts, W. F. (Winthrop F.). 
 III. Title. IV. Series: Information circular (United States. Bureau of 
 
 Mines); 9197. 
 
 -TN295.U4 
 
 [TN345] 
 
 622 s [6221.8] 
 
 88-600120 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Commercial converters 2 
 
 Oxidizing catalytic converters 2 
 
 Quantitative evaluation of catalytic converters 3 
 
 Engine operation test results 3 
 
 Catalytic converter performance over time 6 
 
 In-mine tests 6 
 
 Discussion 7 
 
 Conclusions and recommendations 10 
 
 References 10 
 
 Appendix. — Abbreviations and symbols used in this report 13 
 
 ILLUSTRATIONS 
 
 1. Carbon monoxide and total hydrocarbon reduction as function of converter 
 
 temperature 4 
 
 2. Nitrogen dioxide emission as function of converter temperature 4 
 
 3. Sulfate and sulfur dioxide emissions as function of converter temperature. . . 5 
 
 TABLES 
 
 1. Exposure limits for diesel exhaust pollutants 2 
 
 2. Catalytic converter emission reductions 7 
 
 3. Effect of catalytic converters on EQI 9 
 

 
 UNIT OF MEASURE ABBREVIATIONS USED 
 
 IN THIS REPORT 
 
 °c 
 
 
 degree Celsius 
 
 m 3 
 
 cubic meter 
 
 ft 
 
 
 foot 
 
 mg/m 3 
 
 milligram per cubic meter 
 
 g 
 
 
 gram 
 
 min 
 
 minute 
 
 g/h 
 
 
 gram per hour 
 
 mm 
 
 millimeter 
 
 g/kW« 
 
 h 
 
 gram per kilowatt hour 
 
 pet 
 
 percent 
 
 h 
 
 
 hour 
 
 ppm 
 
 part per million 
 
 L 
 
 
 liter 
 
 s 
 
 second 
 
EFFECTIVENESS OF CATALYTIC CONVERTERS ON DIESEL ENGINES 
 
 USED IN UNDERGROUND MINING 
 
 By B. T. McClure, 1 K. J. Baumgard, 2 and W. F. Watts, Jr. 3 
 
 ABSTRACT 
 
 Oxidizing catalytic converters are sometimes used by underground mine 
 operators as an emission control device to reduce odor, hydrocarbon 
 (HC), and carbon monoxide (CO) emissions from diesel equipment. The 
 objectives of this report are to quantitatively assess the effects of 
 catalytic converters on diesel exhaust emissions and to make recommenda- 
 tions for their use. Information in this report is from a literature 
 survey and contract research supported by the Bureau of Mines. 
 
 Catalytic converters are effective in reducing CO, HC, and odors when 
 the exhaust temperature is high enough so that the converter remains 
 above 250° C. Converter temperature is dependent upon engine duty cy- 
 cle. Catalytic converters increse sulfate emissions and slightly in- 
 crease oxides of nitrogen (N0 X ) emissions. If low sulfur fuels are not 
 used, the increase in sulfate and nitrogen dioxide (N0 2 ) emissions can 
 offset any advantages of the catalytic converter as measured by the 
 emissions quality index (EQ1). In addition, in vitro bioassays have 
 shown that catalytic converters produce soluble organic compounds, which 
 have increased mutagenic activity with respect to untreated exhaust. 
 
 Based upon criteria recommended by a joint Canadian-United States re- 
 search panel, catalytic converters should only be used in special cir- 
 cumstances in underground mines. Vehicles equipped with catalytic con- 
 verters should operate under moderate to heavy load conditions, and use 
 fuel with a sulfur content less than 0.1 pet. 
 
 ^ Research physicist. 
 ^Mechanical engineer. 
 ■^Industrial hygienist. 
 Twin Cities Research Center, Bureau of Mines, Minneapolis, MN . 
 
INTRODUCTION 
 
 This Bureau of Mines report quantita- 
 tively assesses the effects of catalytic 
 converters on diesel exhaust emissions 
 and makes recommendations for their use. 
 Information in this report is from a lit- 
 erature survey and contract research sup- 
 ported by the Bureau. 
 
 Diesel-powered equipment is widely used 
 in underground metal and nonmetal mines 
 and its use in coal mines is increasing 
 0_). 4 It is widely believed that diesels 
 are more flexible, economical to operate, 
 and are able to boost productivity over 
 that of their electrically powered (bat- 
 tery, tethered, or trolly) counterparts 
 (2). 
 
 However, diesel engines emit pollutants 
 that reduce overall air quality. Pollut- 
 ants emitted in diesel exhaust include 
 CO, carbon dioxide (C0 2 ), HC, nitric 
 oxide (NO), N0 2 , sulfur dioxide (S0 2 ), 
 and diesel particulate matter (DPM). 
 Such pollution is particularly undesir- 
 able in a restricted environment as in an 
 underground mine. Concentrations of CO, 
 C0 2 , NO, N0 2 , and S0 2 are regulated by 
 the Mine Safety and Health Administra- 
 tion. The standards are shown in table 
 1. DPM has no specific standard at this 
 time, however, in coal mines DPM is in- 
 directly regulated under the 2 mg/m 3 re- 
 spirable dust standard. 
 
 TABLE 1. - Exposure limits for diesel 
 exhaust pollutants 
 
 Pollutant 
 
 Noncoal 
 
 Coal 
 
 
 FSEL 
 
 STEL 
 
 FSEL 
 
 STEL 
 
 CO. . . . ppm. . 
 C0 2 • • • ppm. . 
 NO. . . .ppm. . 
 N0 2 . . .ppm. . 
 S0 2 . • .ppm. . 
 
 50 
 
 5,000 
 
 25 
 
 NAp 
 
 5 
 
 400 
 
 15,000 
 
 37.5 
 
 5 
 
 20 
 
 50 
 
 5,000 
 
 25 
 
 3 
 
 2 
 
 400 
 
 30,000 
 
 NAp 
 
 5 
 
 5 
 
 FSEL Full-shift exposure limit. 
 
 NAp Not applicable. 
 
 STEL Short-term exposure limit. 
 
 Because of the usefulness of diesels it 
 is desirable to control their emissions, 
 
 and catalysts are one method. Mine oper- 
 ators have been using catalytic conver- 
 ters in underground mines for more than a 
 decade to reduce CO, HC 03), and odor, 
 which is primarily associated with HC's 
 (4_). Converter use is prohibited in some 
 areas of gassy noncoal mines, and coal 
 mines, because of their high operating 
 temperatures. Examples of these areas 
 include the cutting face and return air- 
 ways where gas and dust concentrations 
 may be high and where permissible equip- 
 ment is required. 
 
 COMMERCIAL CONVERTERS 
 
 Oxidizing catalytic converters are sold 
 commercially for several applications, 
 including wood-burning stoves, natural 
 gas burners, and for heavy-duty diesel 
 engines used in mining. The precious 
 metals that are used as catalysts include 
 platinum, palladium, and others, which 
 are bonded to the surface of a substrate 
 where the chemical reactions take place. 
 
 Converters used on underground diesels 
 in the United States are typically one 
 of two types, monolithic substrate or 
 pellet-type. The monolithic converter 
 uses a ceramic, monolithic honeycomb sub- 
 strate to support the catalyst. The 
 monolith has many small axial passages 
 that extend the length of the honeycomb, 
 and are separated from one another by 
 thin porous walls approximately 0.15- to 
 0.3-mm thick. The monolith is usually 
 cylindrical, sized to accommodate the ex- 
 haust flow of the engine, and enclosed in 
 a stainless steel container adapted to 
 fit the exhaust system. 
 
 The pellet-type converter uses spheri- 
 cal or cylindrical pellets, approximately 
 3 mm in diam which fit into a stain- 
 less steel container sized to fit the ex- 
 haust system. A typical pellet converter 
 is larger and heavier than a monolithic 
 converter. 
 
 OXIDIZING CATALYTIC CONVERTERS 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references 
 preceding the appendix. 
 
 An oxidizing catalytic converter is 
 placed as near as possible to the ex- 
 haust manifold to ensure that hot exhaust 
 
gases pass over the catalyst at maximum 
 temperature. The performance of conver- 
 ters is critically dependent on the ex- 
 haust temperature, which depends upon en- 
 gine operation. If an engine is operated 
 at low load, the low exhaust temperature 
 allows soot to accumulate on the catalyst 
 surface, thereby restricting access of 
 the exhaust to the catalyst and inhibit- 
 ing the desired oxidation. As the hot 
 gases pass over the catalyst, oxidation 
 of CO and HC to C0 2 , water vapor takes 
 place, thus reducing the amount of CO, 
 HC, and offensive odors in the exhaust 
 stream. At high exhaust temperatures the 
 converter also oxidizes S0 2 and NO to 
 more toxic sulfuric acid (H2SO4) and N0 2 
 (5-2)- 
 
 Research conducted by the Engelhard 
 Corp. , Edison, NJ, under a Bureau 
 
 contract (7) demonstrated that converter 
 effectiveness is temperature dependent 
 and that high-temperature operation in- 
 creases N0 2 emissions. Figure 1 shows 
 that greater than 50 pet reductions in 
 CO and HC ems s ions can be achieved 
 when catalyst temperatures exceed 250° C. 
 This temperature is not achieved unless 
 the engine is operated at moderate to 
 high loads. Figure 2 shows that above 
 300° C this particular catalyst signifi- 
 cantly increased the emission of N0 2 . 
 This occurs because at the higher temper- 
 atures the oxidation of NO to N0 2 is 
 enhanced. Figure 3 shows that S0 2 is 
 oxidized to S0 4 at catalyst temperatures 
 above 300° C. S0 4 emissions are depen- 
 dent upon fuel sulfur content and can be 
 minimized by using fuel that has a sulfur 
 content of less than 0.1 pet. 
 
 QUANTITATIVE EVALUATION OF CATALYTIC CONVERTERS 
 
 Laboratory tests have been performed by 
 government agencies, private industry, 
 and others to determine the effective- 
 ness of using converters as an emis- 
 sion control device. These tests can be 
 classified in categories; steady-state, 
 transient, durability, and in-mine. 
 Steady-state tests are performed by oper- 
 ating the engine at constant load and 
 speed conditions and do not include 
 periods of acceleration or deceleration. 
 Transient engine tests, on the other 
 hand, have periods of changing load and 
 speed conditions, and more closely sim- 
 ulate equipment operation. Durability 
 tests evaluate the long-term effective- 
 ness of converters and in-mine tests 
 evaluate the performance under actual 
 working conditions. 
 
 ENGINE OPERATION TEST RESULTS 
 
 Eccleston (8_) tested a monolithic con- 
 verter on a Deutz F6M-212W engine using 
 the Environmental Protection Agency 13- 
 mode heavy-duty test cycle and No. 2 
 diesel fuel containing 0.20 pet sulfur. 
 Emissions were measured before and after 
 the converter. The results show that for 
 the heavy-load conditions the converter 
 decreased HC by 33 pet, CO by 78 pet, 
 while N0 2 increased by 12 pet and S0 4 
 increased from 2.3 ppm to 25 ppm (983 
 
 pet). Under light-load conditions, HC 
 decreased 28 pet, CO decreased 39 pet, 
 SO4 decreased 10 pet, and there was no 
 significant change in N0 2 . The average 
 results over all 13 modes showed, that HC 
 decreased 35 pet, CO 63 pet, N0 2 12 pet, 
 and SO4 increased 455 pet. These tests 
 were repeated for a Deutz F6L-912W engine 
 with similar results. 
 
 Acres (9) evaluated a ceramic substrate 
 platinum catalyst at three different con- 
 ditions; idle, medium, and heavy loads. 
 At idle load and speed the catalyst had 
 no effect on CO emissions, at medium 
 loads the conversion efficiency was 80 
 pet, and at high loads the conversion 
 efficiency was 84 pet. Acres also mea- 
 sured the N0 X concentration and found no 
 significant effects. 
 
 Sercombe (10) tested the effectiveness 
 of two platinum catalysts using a direct- 
 injection diesel engine following the 
 California Air Resources Board 13-mode 
 cycle. Emissions were observed in each 
 mode, and cycle weighted averages were 
 obtained. The results from the first 
 catalyst tested indicate that the HC 
 emissions decreased 68 pet and the CO 
 emissions decreased 90 pet. The tests of 
 a second catalyst showed a reduction of 
 HC emissions of 64 pet and CO emissions 
 of 87 pet. Neither catalyst showed a 
 significant change in N0 2 emissions. 
 
100 
 
 KEY 
 O Carbon monoxide 
 A Total hydrocarbons 
 
 150 
 
 200 250 300 350 400 
 
 CATALYST TEMPERATURE, °C 
 
 450 
 
 500 
 
 550 
 
 FIGURE 1. -Carbon monoxide and total hydrocarbons reduction as function of converter temperature. 
 
 1 40 
 
 1 50 200 250 300 350 400 
 
 CATALYST TEMPERATURE, °C 
 
 450 
 
 500 
 
 550 
 
 FIGURE 2. -Nitrogen dioxide emission as function of converter temperature. 
 
cn 
 
 LU 
 < 
 
 or 
 
 O 
 
 co 
 
 CO 
 
 LU 
 CM 
 
 o 
 
 CO 
 "O 
 
 c 
 o 
 
 O 
 CO 
 
 .2 - 
 
 1.0 - 
 
 .8 - 
 
 .6 - 
 
 .4 - 
 
 .2 - 
 
 
 
 1 1 1 
 
 
 1 
 
 KEY 
 
 l 
 
 1 ° 
 
 S0 4 (sulfate) 
 
 
 1 A 
 
 S0 2 
 
 (sulfur di 
 
 oxide) 
 
 \ 
 
 A 
 
 
 - 
 
 - 
 
 
 A ^* 
 
 ^Sw 
 
 1 1 1 
 
 
 i 
 
 1 
 
 150 200 250 300 350 400 
 
 CATALYST TEMPERATURE, °C 
 
 FIGURE 3. -Sulfate and sulfur dioxide emissions as function of converter temperature. 
 
 450 
 
 Evaluation of catalytic converters op- 
 erated under steady-state engine condi- 
 tions has shown that a high conversion 
 efficiency of CO occurs when the engine 
 is operated at high engine loads, but 
 that the efficiency is significantly less 
 for the lighter loads. Sulfate emissions 
 are greatly increased by the converter 
 for the heavy loads, but not for the 
 light loads. 
 
 Bykowski (11) tested an eight-cylinder, 
 indirect-injection, 5. 7-L diesel engine 
 equipped with a monolithic converter us- 
 ing the transient Federal test procedure 
 and fuel with 0.29 pet sulfur. The cata- 
 lyst decreased the emission of CO by 
 approximately 90 pet and HC by approxi- 
 mately 60 pet. A slight increase in N0 X 
 emissions and a 500-pct increase in 
 
 sulfate emissions were observed. The 
 same data were collected after the vehi- 
 cle had been operated 190 miles. No 
 change in converter operation was de- 
 tected. During the tests, the maximum 
 temperature at the converter inlet was 
 196° C and the minimum temperature was 
 76° C. 
 
 Steady-state data were used to estimate 
 the cycle emissions for a mining load- 
 haul-dump (LHD) vehicle equipped with a 
 Deutz F6L 714 engine and a PTX 623 mono- 
 lithic converter (5). The cycle was 
 divided into six steady-state modes, each 
 of different duration. The total time 
 for one complete cycle was 210 s. The 
 emissions, before and after the conver- 
 ter for each of the six modes, were aver- 
 aged over time to yield integrated values 
 
for each pollutant for the entire cycle. 
 The converter removed 85 pet of the CO 
 and caused a small reduction in NO with a 
 corresponding increase in N0 2 . A small 
 increase in DPM was accompanied by a de- 
 crease in S0 2 with a corresponding 44-pct 
 increase in H 2 S0 4 . 
 
 The efficiency of a clean converter de- 
 pends mainly upon the temperature of the 
 catalyst, which in turn is dependent on 
 the duty cycle. Figure 1 shows 50 pet 
 conversion of CO and HC occurs at about 
 190° and 250° C, respectively. As higher 
 temperatures are attained, the conversion 
 efficiency increases. At low exhaust 
 temperatures, soot and carbon accumulate 
 on the converter substrate and perfor- 
 mance degrades rapidly. 
 
 Tests of catalytic converters operated 
 under transient test conditions resulted 
 in increased N0 2 emissions. DPM emis- 
 sions were increased by the formation 
 of S0 X through oxidation of fuel sulfur. 
 This can be mitigated if low-sulfur fuel 
 is used. 
 
 CATALYTIC CONVERTER PERFORMANCE OVER TIME 
 
 The durability of a monolithic conver- 
 ter was investigated by Fleming (12). 
 Tests were conducted on a naturally aspi- 
 rated, direct-injection, 10.4-L displace- 
 ment diesel engine using fuel with 0.14 
 pet sulfur. During the evaluation NO 
 emissions were reduced by retarding the 
 injection timing by three degrees and by 
 employing exhaust gas recirculation. To 
 reduce CO and HC emissions, a monolithic 
 platinum converter was installed on each 
 bank of cylinders. The injection nozzles 
 were modified to aid in lowering HC emis- 
 sions. At 125-h intervals, the emis- 
 sions of CO, HC, and N0 2 were measured 
 for thirteen 10-min periods and averaged. 
 Samples of the exhaust were taken up- 
 stream of the converter during the first 
 5 min and downstream of the converter for 
 the last 5 min during each period. The 
 results indicated that the converter oxi- 
 dized about 90 pet CO at the beginning of 
 the test and about 88 pet after 1,060 h. 
 Initially, 70 pet of the HC's were con- 
 verted, but after 1,060 h only 60 pet 
 were converted. The converters caused a 
 small increase in fuel consumption, and 
 
 smoke emissions increased slightly with 
 operating time. 
 
 Marshall (13-14) tested several cata- 
 lysts to determine their efficiency in 
 oxidizing CO and HC, and also tested a 
 platinum-based pellet-type converter for 
 durability. For these tests, a duty 
 cycle was chosen to simulate the opera- 
 tion of a utility vehicle with an overall 
 load factor approximately 25 pet. The 
 converter was most effective at reducing 
 CO and HC concentrations when operated 
 above 300° C and maintained a relatively 
 constant conversion efficiency for the 
 first 1,000 h. After that time, the CO 
 and HC emissions increased both before 
 and after the converter. The increase 
 was attributed to fuel-injection nozzle 
 malfunctions, such as a poor spray pat- 
 tern or leakage of the injectors. 
 
 Inadequate engine maintenance can ad- 
 versely affect emissions and degrade cat- 
 alytic converter performance (15). All 
 catalysts tested greatly increased the 
 emissions of SO3 and these increases were 
 related to the fuel sulfur content. Be- 
 cause of these increased emissions, the 
 investigators recognized that other con- 
 trol measures, such as ceramic particle 
 filters or water scrubbers, might have to 
 be used in conjunction with catalyst sys- 
 tems to ensure satisfactory performance. 
 
 These evaluations establish that cata- 
 lytic converters maintain their perfor- 
 mance up to 1,000 h under laboratory con- 
 ditions, proper engine maintenance is 
 required for best performance. 
 
 IN-MINE TESTS 
 
 A West German research group installed 
 PTX-4D and 6D monolithic converters on 
 mining vehicles (16) , which were peri- 
 odically taken out of service and checked 
 for emissions after operation in two 
 drifts. Drift A had eight PTX-4D cata- 
 lysts and a total of 18,500 h of opera- 
 tion were accumulated on the eight 
 converters for an average of 3,083 h 
 each. Two converters failed during this 
 test after 925 and 1,732 h, respectively. 
 In drift B, one PTX-6D failed after 
 1,436 h and two PTX-4D failed after 1,156 
 and 1,432 h, respectively. The engines 
 equipped with PTX-4D converters should 
 
have used the larger PTX-5D, but because 
 of space constraints the 4D's were sub- 
 stituted. This may explain the high 
 failure rate of the 4D's. The remaining 
 eight PTX-6D's accumulated 17,500 h of 
 operation for an average of 2,188 h each. 
 The converters were tested under two 
 conditions, partial load and full load. 
 For the PTX-4D, the initial conversion 
 efficiency was 87 pet for CO, which de- 
 creased to 65 pet after 200 operating h. 
 The efficiency dropped to 30 pet between 
 1,000 to 1,500 operating h at which point 
 the converters were cleaned by burning 
 off the collected soot at high temper- 
 atures, a process called regeneration. 
 Regeneration resulted in improved effi- 
 ciency, but the initial conversion 
 
 efficiency was not restored. The PTX-6D 
 converter tested at full load had an ini- 
 tial CO conversion efficiency of 90 pet, 
 which gradually decreased to 50 pet after 
 2,000 operating h. 
 
 Table 2 summarizes the catalytic con- 
 verter test results reported in the lit- 
 erature. These results were obtained on 
 a variety of engines operated under dif- 
 ferent conditions, with different types 
 of catalytic converters. Specific infor- 
 mation can be obtained from the reference 
 cited. 
 
 The average reduction for CO was 77 pet 
 and 54 pet for HC for all tests summar- 
 ized in table 2. The results for N0 2 and 
 S0 4 indicate an increase in emissions. 
 
 TABLE 2. - Catalytic converter emission reductions, percent 
 
 CO 
 
 HC 
 
 NO- 
 
 SO, 
 
 CO 
 
 HC 
 
 NO- 
 
 SO, 
 
 Reference 4. , 
 Reference 8. . 
 
 Reference 9. . 
 Reference 10. 
 
 85 
 63 
 78 
 39 
 80 
 84 
 90 
 87 
 
 NG 
 35 
 33 
 
 28 
 NG 
 NG 
 68 
 64 
 
 INC 
 12 
 
 + 12 
 NC 
 NC 
 NC 
 NC 
 NC 
 
 '+441 
 
 +455 
 
 + 983 
 
 + 10 
 
 NG 
 
 NG 
 
 NG 
 
 NG 
 
 Reference 11. 
 Reference 12. 
 
 Reference 14. 
 
 Reference 16. 
 
 Reference 17. 
 
 90 
 90 
 88 
 2 752 
 2 802 
 87 
 30 
 90 
 
 60 
 
 70 
 
 60 
 
 2772 
 
 2 452 
 NG 
 NG 
 NG 
 
 NC 
 NG 
 NG 
 NG 
 NG 
 NG 
 NG 
 + 25 
 
 + 500 
 NG 
 NG 
 NG 
 NG 
 NG 
 NG 
 +4,251 
 
 + Percent increase. 
 INC Increased. 
 NC No change. 
 
 NG Not given. 
 1 Measured as H 2 S0 4 . 
 Approximate values. 
 
 DISCUSSION 
 
 Diesel exhaust contains many sub- 
 stances, each of which may be affected 
 by the use of a control device. To 
 ensure that the use of a specific device 
 to control one pollutant does not lead to 
 an overall degradation of emissions, some 
 means to judge the overall effectiveness 
 of a treatment device is required. In 
 1981, three criteria were recommended by 
 a joint Canadian-United States research 
 panel (18). These were (1) an index for 
 ventilation, (2) the Ames bioassay, which 
 tests for mutagenicity, is one indicator 
 of potential carcinogenity , and (3) mea- 
 surement of the concentrations of six 
 polycyclic aromatic HC, some of which 
 are known carcinogens. These criteria 
 are used to evaluate catalytic control 
 systems. 
 
 The air quality index (AQI) was formu- 
 lated (19) to provide a single qualita- 
 tive indicator of the risk associated 
 with exposure to diesel emissions. AQI 
 was defined as, 
 
 AQI - (C0)/TLV for CO 
 
 + (N0)/TLV for NO 
 
 + (RCD)/TLV for RCD 
 
 + 1.5 [(S0 2 )/TLV for S0 2 
 
 + (RCD)/TLV for RCD] 
 
 +1.2 [(N0 2 ) /TLV for N0 2 
 
 + (RCD)/TLV for RCD], 
 
where the gaseous components are ex- 
 pressed in parts per million and respi- 
 rable combustible dust (RCD) is expressed 
 in milligrams per cubic meter. In prac- 
 tice AQI is determined at different loca- 
 tions in the mine, and AQI decreases as 
 the exhaust is diluted. 
 
 The denominator values for 
 
 N0 2 , and S0 2 were originally 
 
 CO, NO, 
 the 1978 
 of Gov- 
 (ACGIH) 
 The cur- 
 
 recommended American Conference 
 ernmental Industrial Hygienists 
 threshold limit values (TLV). 
 rent TLV's should be used; 50 ppm for CO, 
 25 ppm for NO, 3 ppm for N0 2 , and 2 ppm 
 for S0 2 (20). There is no TLV for RCD 
 so the respirable coal mine dust standard 
 of 2.0 mg/m 3 was proposed for RCD. The 
 index applies the ACGIH additive princi- 
 ple for the presence of multiple pollut- 
 ants (20) and incorporates two factors, 
 1.5 and 1.2, to account for possible syn- 
 ergistic effects. 
 
 It was suggested that ( 19 ) an AQI value 
 between 3 and 4 be interpreted as pos- 
 ing a moderate health risk, and a value 
 greater than 4 poses a serious health 
 threat, which required either reductions 
 in pollutant concentrations or increased 
 ventilation. In any case no individual 
 pollutant should exceed its TLV. For 
 more detailed information on the AQI 
 refer to references 19 and 21 through 23. 
 
 Mogan (24) extended the use of the AQI 
 by applying the definition to raw and 
 treated diesel exhaust and refers to this 
 measure as the EQI. Since the goal for 
 the AQI value in underground mines was 3, 
 measuring the concentrations of the con- 
 taminants at the exhaust pipe with and 
 without emission controls, calculating 
 the EQI, and dividing by 3 provides an 
 estimate of the number of equivalent vol- 
 umes of fresh air needed to dilute the 
 exhaust to achieve an acceptable AQI. 
 This application of the EQI assumes that 
 the chemical composition and quantity of 
 exhaust products does not change with 
 dilution. 
 
 Mogan (17) reported that the EQI for 
 a bare engine was 215; for a converter 
 equipped engine it was 397. The higher 
 EQI was mainly due to the increase in RCD 
 caused by the increase in sulfate. Sul- 
 fate emissions are directly related to 
 the fuel sulfur content, and the increase 
 
 in RCD owing to an increase in sulfates 
 can be minimized by using a low-sulfur 
 fuel. The fuel used in these tests con- 
 tained 0.25 pet sulfur. Diesel fuel with 
 less than 0. 1 pet sulfur content should 
 be used to minimize sulfate emissions (6, 
 25). 
 
 Similar tests were performed (_5) on a 
 Deutz F6L 714 and a Detroit 8V71N diesel 
 engines equipped with monolithic conver- 
 ters. The emissions were measured for 
 each mode and averaged to yield inte- 
 grated values that were substituted into 
 the EQI expression. For the Deutz en- 
 gine, the EQI increased from 140 to 417 
 when the converter was used, and it 
 increased by a factor of 2.5 for the 
 Detroit engine. The increase in the AQI 
 was due to increases in the emissions of 
 N0 2 and sulfates. 
 
 Mogan (26) summarized estimates derived 
 from data from a number of investigations 
 by using the EQI to compare catalytic 
 converter performance on engines tested 
 with No. 2 diesel fuel. The results are 
 shown in table 3. The percent of base- 
 line columns in the table are determined 
 by dividing the EQI for the exhaust con- 
 trol by the EQI for the bare engine and 
 multiplying by the percent of baseline 
 for the bare engine. This amounts to 
 defining the performance of the untreated 
 indirect-injection engine as a unit of 
 EQI. Catalytic converters increased the 
 EQI in some cases by more than a factor 
 of 2. The table shows the benefits are 
 derived when converters are used with 
 low-sulfur fuel and water scrubbers. 
 
 Hunter (27) conducted tests to deter- 
 mine the effect that a monolithic oxida- 
 tive catalytic converter had on emissions 
 from a Caterpillar 3208 diesel engine 
 using No. 2 fuel. Test results from four 
 steady-state engine modes, showed that 
 large increases in the amounts of DPM and 
 sulfates and reduction of the soluble 
 organic fraction (SOF) occurs when con- 
 verters are used. In the mode exhibit- 
 ing the most extreme case, S0 4 emission 
 increased from a fraction of gram per 
 kilowatt hour to more than 2.5 g/kW'h as 
 the exhaust passed through the catalyst. 
 Similar results were obtained for the 
 other three modes. 
 
TABLE 3. - Effect of catalytic converters on EQI 
 
 Exhaust treatment 
 
 DI engine 
 
 IDI engine 
 
 
 EQI 
 
 Pet of baseline 
 
 EQI 
 
 Pet of baseline 
 
 
 224 
 314 
 314 
 
 102 
 
 102 
 
 103 
 
 103 
 
 74 
 
 74 
 
 113 
 158 
 158 
 
 51 
 
 51 
 
 52 
 
 52 
 
 37 
 
 37 
 
 199 
 484 
 292 
 
 197 
 84 
 
 197 
 84 
 
 133 
 
 55 
 
 100 
 
 
 243 
 147 
 
 Monolithic converter plus 
 
 99 
 
 Pellet converter plus 
 
 Monolithic converter plus 
 
 water scrubber 1 
 
 Pellet converter plus 
 
 42 
 99 
 42 
 
 Monolithic converter plus 
 water scrubber and low- 
 
 67 
 
 Pellet converter plus 
 water scrubber and low- 
 
 28 
 
 DI Direct-injection. 
 'For coal operations, 
 exhaust. 
 
 IDI Indirect-injection. 
 
 a water scrubber is required to cool the 
 
 An explanation offered for the increase 
 in DPM is that it is caused by the de- 
 hydrogenation of the organic compounds 
 present in the exhaust (27). This reac- 
 tion results in the formation of solid 
 carbon and low hydrogen-to-carbon ratio 
 hydrocarbons. The fact that the S0F was 
 decreased in all test modes is consistent 
 with this explanation. 
 
 A similar catalyst was tested (28) on a 
 single-cylinder diesel engine operated 
 under different conditions and a 70-pct 
 reduction of both DPM and SOF was ob- 
 tained when catalytic temperatures ex- 
 ceeded 250° C. For polyaromatic HC and 
 other high-molecular-weight compounds in 
 the SOF, a 70-pct reduction was achieved 
 at temperatures above 170° C. This re- 
 sult was attributed to the high-molec- 
 ular-weight compounds 
 carbon particulate 
 brought into direct 
 catalyst surface. 
 
 The effect of monolithic and pelletized 
 catalytic converters on mutagen levels 
 in a salt mine was assessed (29), and a 
 fivefold increase in mutagen level was 
 observed when the monolithic converter 
 was used. This finding is similar to 
 
 adsorbed onto the 
 
 and thereby being 
 
 contact with the 
 
 laboratory data reported by Hunter (27). 
 In Hunter's study the Ames bioassay 
 showed that mutagenicity per gram of sol- 
 uble organic material increased when the 
 catalyst was used, but was partially off- 
 set by a reduction in the mass of SOF 
 emitted. 
 
 The pelletized catalytic converter re- 
 sulted in a thirtyfold increase in muta- 
 gen levels over the untreated engine 
 despite a substantial decrease in poly- 
 nuclear aromatic HC. This decrease in 
 polynuclear aromatic HC accompanied by an 
 increase in mutagenic activity results 
 from nitration of the polynuclear aro- 
 matic HC, which are trapped and later 
 released by the pelletized converter. 
 Evidence suggests that very strong muta- 
 gens such as the dinitropyrenes are 
 formed (30-31 ). Even though there is no 
 direct relationship between Ames activity 
 and adverse health effects it has been 
 recommended (32) that the Ames test and 
 other in vitro tests be used to screen 
 engineering alternatives and that the 
 information obtained be combined with 
 data from animal and epidemiological 
 studies to aid in the decision making 
 process. 
 
10 
 
 CONCLUSIONS AND RECOMMENDATIONS 
 
 1. Catalytic converters are effective 
 in reducing CO, HC, and odors when the 
 exhaust temperature remains above 250° C. 
 Converter temperature is dependent upon 
 engine duty cycle, and engines operating 
 under moderate to heavy loads generally 
 have high enough temperatures to allow 
 efficient converter operation. 
 
 2. Catalytic converters slightly in- 
 crease N0 X emissions. 
 
 3. Sulfate emissions are increased by 
 the use of catalytic converters, but this 
 increase can be offset by using fuel con- 
 taining 0.1- pet sulfur or less. If low- 
 sulfur fuels are not used, the increase 
 in sulfate and N0 2 emissions can offset 
 any advantages of the catalytic converter 
 as measured by the EQI. 
 
 4. Mutagenic activity of the SOF is 
 increased when catalytic converters are 
 used. 
 
 Based upon criteria recommended by 
 a joint Canadian-United States research 
 panel (18) , catalytic converters should 
 have very limited use in underground 
 mines. Converters can reduce CO, HC, and 
 odor emissions, but these reductions 
 are frequently offset by increased lev- 
 els of the more toxic pollutants, N0 2 
 and sulfates, thus causing an increase 
 in the EQI. In addition, studies have 
 shown that catalytic converters produce 
 soluble organic compounds with high muta- 
 genic activity. Although mutagenic ac- 
 tivity is not directly linked to adverse 
 health effects, these assays have been 
 recommended for screening engineering 
 alternatives and mine operators should be 
 aware of the results. Vehicles equipped 
 with converters should operate under 
 moderate- to heavy-load conditions and 
 use fuel with a sulfur content less than 
 0.1 pet. 
 
 REFERENCES 
 
 1. Daniel, J. H. , Jr. Diesels in Un- 
 derground Mining: A Review and an Evalu- 
 ation of an Air Quality Monitoring Meth- 
 odology. BuMines RI 8884, 1984, 36 pp. 
 
 2. Ogden, S. 0. Economics, Safety and 
 Operating Advantages of Diesels in Under- 
 ground Coal Mines. Min. Cong. J. , v. 64, 
 No. 9, 1978, pp. 237-242. 
 
 3. Richards, W. M. Switch to Cata- 
 lytic Exhaust Purifiers Cuts Maintenance 
 Costs at Copper Mine. Eng. Min. J. , v. 
 176, No. 10, 1975, pp. 102-103. 
 
 4. Partridge, P. A., F. J. Shala, 
 N. P. Cernansky, and I. H. Suffet. Char- 
 acterization and Analysis of Diesel Ex- 
 haust Odor. Environ. Sci. Technol. , v. 
 21, No. 4, 1987, pp. 403-408. 
 
 5. Dainty, E. D. , A. Lawson, and J. P. 
 Mogan. Synopsis of Contract Findings: 
 The Ventilation Implications of the Re- 
 duction of Diesel Emissions Toxicity by 
 Water - in Oil Fuel Emulsif ication. CAN- 
 MET, Energy, Mines and Resour. , Ontario, 
 
 Canada, Report MRP/MRL 80-15(TR), Feb. 
 
 1980, 32 pp. 
 
 6. Johnson, J. H. , E. 0. Reinbold, 
 and D. H. Carlson. The Engineering Con- 
 trol of Diesel Pollutants in Underground 
 Mining. SAE Tech. Pap. Series 810684, 
 
 1981, 46 pp. 
 
 7. Engelhard Corporation. Control 
 of Diesel Exhaust Emissions in Under- 
 ground Mines. Ongoing BuMines contract 
 H0199029; for inf., contact E. D. Thim- 
 ons, TP0, Dust Control and Ventilation 
 Div. , BuMines, Pittsburgh, PA. 
 
 8. Eccleston, B. H. , D. E. Seizinger, 
 and J. M. Clingenpeel. Diesel Exhaust 
 Emissions from Engines for Use in Under- 
 ground Mines. Bartlesville Energy Tech- 
 nology Center, Bartlesville, OK, DOE/ 
 BETC/RI-80/6, Apr. 1981, 42 pp. 
 
 9. Acres, J. K. Platinum Catalyst 
 for Diesel Engine Exhaust Purification. 
 Platinum Met. Rev., v. 14, No. 3, 1970, 
 pp. 78-85. 
 
11 
 
 10. Sercombe, E. J. Exhaust Purifiers 
 for Compression Ignition Engines. Plati- 
 num Met. Rev., v. 19-20, No. 1, 1975, 
 pp. 2-11. 
 
 11. Bykowski, B. B. Preliminary In- 
 vestigation of Light-Duty Diesel Cata- 
 lysts. Emission Control Technology Divi- 
 sion, Ann Arbor, MI, EPA-460/3-80-002, 
 
 1980, 45 pp. 
 
 12. Fleming, R. D. , and T. R. French. 
 Durability of Advanced Emission Controls 
 for Heavy Duty Diesel and Gasoline Fueled 
 Engines. Bartlesville, OK, EPA-460/3-73- 
 010, 1973, 120 pp. 
 
 13. Marshall, W. F., D. E. Seizinger, 
 and R. W. Freedman. Effects of Catalytic 
 Reactors on Diesel Exhaust Composition. 
 BuMines TPR 105, 1978, 9 pp. 
 
 14. Marshall, W. F. Emission Control 
 for Diesels Operated Underground: Cata- 
 lytic Converters. Bartlesville Energy 
 Res. Centr. , Bartlesville, OK, BERC/RI- 
 75/8, 1979, 10 pp. 
 
 15. Lilly, L. C. R. (ed.). Part 2 - 
 Engine Design Practice, Section 10 - Fuel 
 Injection Systems in Diesel Engine Refer- 
 ence Book. Butterworth, 1984, pp. 10-1 
 to 10-29. 
 
 16. Institute of Machinery and Insti- 
 tute of Chemical of Westgalische Berg- 
 gewerkschaf tskasses. Verminderung des 
 Gehaltes and schadlichen Bestandteilen in 
 den Abgasen von Diselmotoren bei methan- 
 haltiger Ansaugluft (Reduction in the 
 Content of Noxious Constituents in the 
 Exhausts of Diesel Engines with Methane- 
 Containing Intake Air). Final Report, 
 
 1981, 52 pp.; available for consultation 
 at the Twin Cities Res. Cent. , Minne- 
 apolis, MN. 
 
 17. Mogan, J. P., and E. D. Dainty. 
 Emission Control Performance of Diesel 
 Exhaust Treatment Devices. CIM Spec. 
 Vol. 36, 1986, pp. 135-142. 
 
 18. Schnakenberg, G. H. , Jr., J. P. 
 Mogan, and E. W. Mitchell. Diesel Emis- 
 sion Control — A Joint United States and 
 Canadian Program. Pres. at 1986 Am. Min- 
 ing Cong. Int. Mining Show, 20 pp.; 
 available from G. H. Schnakenberg, Jr. , 
 BuMines, Pittsburgh, PA. 
 
 19. Ian W. French and Associates, Ltd. 
 (Claremont, Ontario). Health Implica- 
 tions of Exposure of Underground Mine 
 Workers to Diesel Exhaust Emissions - An 
 Update. (Contract 0SQ82-00121). Rep. to 
 the Dep. of Energy, Mines and Resources, 
 Ottawa, Canada, Apr. 20, 1984, 607 pp. 
 
 20. American Conference of Governmen- 
 tal Industrial Hygienists (Cincinnati, 
 OH). TLV's-Threshold Limit Values for 
 Chemical Substances in the Work Envi- 
 ronment Adopted by ACGIH With Intended 
 Changes for 1986-87. 1986, 111 pp. 
 
 21. Schnakenberg, G. H. , Jr. Current 
 State-of-the-Art of Diesel Emission Con- 
 trol - An Overview. Ann. ACGIH, v. 4, 
 
 1986, pp. 233-243. 
 
 22. Watts, W. F., Jr. Industrial Hy- 
 giene Issues Arising From the Use of 
 Diesel Equipment in Underground Mines. 
 Paper in Diesels in Underground Mines. 
 Proceedings: Bureau of Mines Technol- 
 ogy Transfer Seminar, Louisville, KY, 
 April 21, 1987, and Denver, CO, April 23, 
 
 1987, comp. by Staff, BuMines. BuMines 
 IC 9141, 1987, pp. 4-8. 
 
 23. Daniel, J. H. , Jr. Carbon Diox- 
 ide and an Index of Diesel Pollutants. 
 Paper in Diesels in Underground Mines. 
 Proceedings: Bureau of Mines Technol- 
 ogy Transfer Seminar, Louisville, KY, 
 April 21, 1987, and Denver, CO, April 23, 
 1987, comp. by Staff, BuMines. BuMines 
 IC 9141, 1987, pp. 52-57. 
 
 24. Mogan, J. P. , and E. D. Dainty. 
 Development of the AQI/EQI Concept — A 
 Ventilation Performance Standard for Die- 
 selized Underground Mines. Ann. ACGIH, 
 v. 14, 1987, pp. 245-247. 
 
 25. Rehnberg, 0. Effects of Diesel 
 Exhaust Catalytic Converters for Under- 
 ground Use, Soc. Min. Eng. AIME, Trans., 
 v. 1, 1981, pp. 1990-1994. 
 
 26. Mogan, J. P. , and E. D. Dainty. 
 Assessment of Diesel Exhaust Treatment 
 Options by a New Diesel Ventilation Cri- 
 terion. Paper in Proceedings of the Sec- 
 ond International Mine Ventilation Con- 
 gress, ed. by P. Mousset-Jones , 1980, 
 pp. 191-194. 
 
12 
 
 27. Hunter, G. , J. 
 bier, S. Bagley, D. Leddy 
 J. Johnson. The Effect 
 Catalyst on the Physical 
 Biological Character of 
 late Emissions. SAE Tec 
 810263, 1981, 32 pp. 
 
 28. Andrews, G. E. , 
 Ejiofor, and S. W. Pang, 
 late SOF Emissions Redu 
 Exhaust Catalyst. SAE Te 
 870251, 1987, pp. 103-112 
 
 29. Mogan, J. P., E. 
 Westaway, and A. J. Hort 
 Aromatic Hydrocarbons and 
 Air of Underground Diesel 
 Spec. vol. 36, 1986, pp. 
 
 Scholl, F. Hib- 
 , D. Abata, and 
 of an Oxidation 
 , Chemical, and 
 Diesel Particu- 
 h. Pap. Series 
 
 I. E. Iheozor- 
 
 Diesel Particu- 
 
 ction Using an 
 
 ch. Pap. Series 
 
 • 
 
 D. Dainty, K. C. 
 on. Polynuclear 
 Mutagens in the 
 ized Mines. CIM 
 188-197. 
 
 30. Mogan, 
 Diesel Emis 
 Friend or Foe 
 pp. 254-260. 
 
 31. Mogan, 
 Vergeer, and 
 son of Labora 
 Levels for Tr 
 CIM Spec, vol 
 
 32. Holmbe 
 (eds. ). Cons 
 and Carcinoge 
 Coal Combust 
 Health Perspe 
 
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 sion Control Catalysts: 
 ? CIM Spec. vol. 36, 1986, 
 
 J. P. , A. J. Horton, H. C. 
 
 K. C. Westaway. A Compari- 
 tory and Underground Mutagen 
 eated and Untreated Exhaust. 
 . 36, 1986, pp. 78-91. 
 rg, B., and U. Ahlborg, 
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 ct. , v. 47, pp. 1-30, 1983. 
 
13 
 
 APPENDIX. —ABBREVIATIONS AND 
 
 This listing does not include unit of 
 measure abbreviations, which are listed 
 after the table of contents, or abbrevi- 
 ations that are used and identified in 
 the tables. 
 
 ACGIH - American Conference of Govern- 
 mental Industrial Hygienists. 
 
 AQI - Air quality index. 
 
 DPM - Diesel particulate matter. 
 
 EQI - Emissions quality index. 
 
 LHD - Load-haul-dump. 
 
 RCD - Respirable combustible dust. 
 
 SOF - Soluble organic fraction. 
 
 TLV - Threshold limit value. 
 
 SYMBOLS USED IN THIS REPORT 
 
 CO - Carbon monoxide. 
 C0 2 - Carbon dioxide. 
 HC - Hydrocarbon. 
 H 2 S0 4 - Sulfuric acid. 
 NO - Nitric oxide. 
 N0 X - Oxides of nitrogen. 
 N0 2 - Nitrogen dioxide. 
 
 S0 X - Oxides of sulfur. 
 
 50 2 - Sulfur dioxide. 
 
 503 - Sulfur trioxide. 
 
 50 4 - Sulfate. 
 
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