Paper # 1265 James A. Calcagno III, Wayne T. Davis and Terry L miller




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Evaluation of Heavy Duty Diesel Vehicle Emissions During Cold-Start and Steady-State Idling Conditions and Reduction of Emissions from a Truck-Stop Electrification Program

Paper # 1265




James A. Calcagno III, Wayne T. Davis and Terry L Miller


University of Tennessee, Department of Civil and Environmental Engineering,

223 Perkins Hall, Knoxville, TN 37996



ABSTRACT

Long-haul truck drivers idle their diesel engines while parked at travel centers located along the interstate highway system during federally mandated driver rest periods. Engine idling provides heat or air conditioning and maintains battery voltage so that electrical appliances can be used in the cab. Limited evidence suggests that idling trucks contribute significantly to microscale emissions. Truck-stop electrification (TSE) is a structure that is installed at the rest area to supply each parking space with a heating and air conditioning system, as well as external 120-volt outlets to power in-cab appliances. TSE is also believed to reduce idling emissions. In this study, the overall emission mass balance between truck idling and emissions produced from the electricity consumed in lieu of truck idling are investigated. Cold-start emissions are incorporated into the mass balance because the engine must be restated after using TSE technology. Cold-start and extended-idling emissions of carbon monoxide, oxides of nitrogen (NOx) and particulate matter (PM) were measured from 24 class-8b, heavy-duty diesel vehicles using portable emission monitoring equipment. The ratio of nitrogen dioxide to NOx and the ratio of PM2.5 to total PM are also reported. Truck model years ranged from 1992 to 2004. All vehicles were tested in the field during summer and fall months under ambient environmental conditions at low (600-800 rpm) and high (1000 rpm) engine idling speeds with the truck cab air-conditioner operating at “on” and “off” modes. Sampling data thus obtained were used to generate typical average cold-start and long-duration idling emission factors and were used to estimate potential emission reductions associated from using TSE. Electricity utilization and related emissions from TSE were calculated for a coal-fired power plant equipped with Selective Catalytic Reduction technology for NOx removal and that meets New Source Performance Standards for NOx and PM2.5 emissions.



INTRODUCTION

Currently, many local and state environmental planning agencies are evaluating and searching for new emission reduction strategies that can be applied in their areas. Long-haul truck drivers idle the diesel engines of the trucks while parked at travel centers located along the interstate highway system during federally mandated driver layover or rest periods. Engine idling provides heat or air conditioning and helps maintain adequate battery voltage so electrical appliances such as, microwave oven and refrigerator can be used in the cab. Limited evidence suggests that idling trucks contribute significantly to microscale emissions.


Truck-stop electrification (TSE) is a structure that is installed at the rest area to provide each parking space with heating, ventilation and air conditioning systems (HVAC), as well as external 120-volt outlets to power in-cab appliances. Previous emission reduction estimates that have been attributable to TSE have generally only included those idling emission savings that are associated with the driver simply shutting-off the engine and in using TSE during required rest periods. A more thorough and realistic emission mass balance between idling and TSE should include an estimation of the increased emissions associated with the consumption of electricity from the power grid. More importantly, since combustion inefficiency and the emissions generated during cold-start are known problems for all internal combustion engines, the cold-start emissions should also be counted in the mass balance equation because the engine must be restarted after using TSE technology.
Experimental results indicate that there may be sizable differences between short-term and long-term duration (or extended-idling) emission factors. Long-term idling typically occurs at truck-stop rest areas as distinguished from short-term idling, which occurs in congested traffic or at road signal stoplights. Long-duration idling is defined as the operation of the propulsion engine of the truck for a period greater than 15-minutes when it is not engaged in gear or motion.1 It is also possible that average emission factors may not provide the complete picture of idling emissions. Truck testing data seem to indicate that there is large variability between individual vehicles tested at different engine idling speeds, engine accessory load conditions and ambient environmental conditions. Running the in-cab heater and/or the air-conditioner (while the vehicle engine is idling) are examples of engine accessory-load conditions.
Limited historic field data exits concerning heavy-duty diesel vehicle idling emissions. Nonetheless between 2000 and 2003, several research groups (McCormick, et.al.2, Tang, et.al.3, Lambert, et.al.4, Brodrick, et.al.5, Lim6 and Storey, et.al.7) have quantified the effects of engine speed, accessory load and other background environmental conditions, such as ambient air temperature, on idling emissions and fuel consumption rates. Moreover, emissions from various idle-reduction devices have also been evaluated with respect to the potential benefits that these devices may provide toward a decrease in overall vehicle emissions and fuel usage. In the present study, cold-start and long-term duration idling emissions were measured in the field from class-8b, heavy-duty diesel vehicles (HDDV8b) using a portable emission monitoring system (PEMS). Trucks with a gross vehicle weight rating (GVWR) greater than 60,000 pounds are classified as HDDV8b.8 Real-time mass emissions of carbon monoxide (CO), nitrogen oxide (NO), nitrogen dioxide (NO2) and particulate matter (PM) were measured and used to generate typical average cold-start and long-duration idling emission factors on a grams per hour basis. The overall emission mass balance between truck idling and emissions produced from the electricity consumed in lieu of truck idling was also investigated. The electricity utilization and related emissions from TSE were calculated for a coal-fired power plant that meets the New Source Performance Standards (NSPS).9

Sampling MethologY and Equipment Layout

Experimental Protocol

Twenty-four (HDDV8b) trucks were tested during the summer and fall months between June and November 2004. The pertinent vehicle and engine information are shown in Table 1. Of the 24 (total) trucks tested, 50% were Freightliner; 16.7% were Mack; 12.5% each were International and Volvo; and 8.3% were Kenworth. Truck model years ranged from 1992 to 2004. Approximately, 20.8% of the trucks were between 1992 and 1997; 37.5% were between 1998 and 2000; 41.7% were between 2003 and 2004. The diesel engines were Detroit - 41.7%, Cummins - 25%, Mack - 16.7%, Volvo - 8.3% and Caterpillar - 8.3%. The odometer reading on about 50% of the trucks was roughly 500,000 miles or greater.


Table 1: General Description of Test Trucks

ID

Truck

VIN

Year

Engine

Model

HP

Disp (l)

Odom (mi)

1

Freightliner

2HSCEAPR25C003739

1996

Cummins N14

460

14

512,926

2

Freightliner

1FUYDSEB6XLB00220

1998

Detroit S60

430

12.7

591,476

3

Volvo

4V4NC9GHX5N381710

2004

Volvo Vectro

465

12.1

287

4

Volvo

4V4NC9GH65N381722

2004

Volvo Vectro

465

12.1

83

5

Mack

1M1AA18Y6XW112584

1999

Mack ASET

460

11.9

416,764

6

Kenworth

1XKADB9X45J087931

2004

Caterpillar ACERT

475

15.2

72

7

International

2HSFHAER5XC086741

1998

Cummins N14

500

14

655,380

8

Kenworth

1XKWDB9X05J081372

2004

Caterpillar ACERT

475

15.2

738

9

Volvo

4V4NC9JH1N259226

2000

Cummins N14

435

14

553,465

10

Freightliner

1FUPDCYB2XL904380

1998

Cummins N14

425

11

341,146

11

Freightliner

1FUJA3CG11LG36966

2000

Detroit S60

430

12.7

420,621

12

International

2HSFBAHR1SC056187

1995

Cummins M11

450

11

814,185

13

International

2HSCEAPR25C003739

2004

Cummins N14

475

15

58

14

Freightliner

1FUYDZYB1NP476082

1992

Detroit S60

450

12.7

279,922

15

Freightliner

1FUYJA6CK04LN3773

2004

Detroit S60

455

14

82,929

16

Freightliner

1FUYSSZB6YLG08382

1999

Detroit S60

500

12.7

568,539

17

Freightliner

1FUJA6CK44LM15160

2003

Detroit S60

435

14

147,334

18

Freightliner*

1FUYDZYB8WL903823

1997

Detroit S60

400

12.7

647,979

19

Mack*

IM1AEO6Y54N019364

2003

Mack ASET

430

11.9

78,960

20

Freightliner

1FUYDSEB1WL896080

1997

Detroit S60

430

12.7

834,028

21

Freightliner

1FUJA6CK54LM13479

2003

Detroit S60

455

14

154,156

22

Freightliner

1FUYSSEB7YLG51490

1999

Detroit S60

430

12.7

482,983

23

Mack*

1M1AE06Y54N019512

2003

Mack ASET

430

11.9

58,047

24

Mack

1M1AE06Y41W008703

2000

Mack ASET

355

11.6

484,108

ID = Identification number; VIN = Vehicle identification number (manufacturer); HP = Rated engine horsepower; Disp = Engine Displacement; l = Liters; Odom = Odometer; mi = miles; *Truck body has day cab only.
All vehicles were tested at ambient environmental conditions at low and high engine idling speeds. Low-idling speeds were between 600 and 800 revolutions per minute (rpm). The as-received condition or the factory idle setting established the low-idling speeds. The high-idling condition was chosen at 1000 rpm. The high-idling rpm was set via truck electronic onboard cruise control. Each truck was tested with the cab air-conditioner at the maximum output (i.e., AC-On condition) and with the air-conditioner system not operating (i.e., AC-Off condition). Trucks were not subjected to any special maintenance procedures; they were tested as received or as rented and used standard diesel fuel. Each truck was parked overnight in a staging area for at least 12-hours before cold-start testing was conducted. Before engaging the engine for cold-start testing, the air-conditioner switch was set to operate at maximum output.
Time-resolved emission measurements during engine cold-start and idling periods were collected. During testing, emissions were shown to reach steady-state condition within two to three hours after starting the engine. After the engine warm-up period, additional idling tests were conducted on each vehicle through the following typical progression: cold-start at low-idle with the AC-On (run time approximately 3-hrs), low-idle with the AC-Off (runtime approximately 2-hrs), high-idle with the AC-Off (run time approximately 1-hr) and finally high-idle with the AC-On (runtime approximately 1-hr). It should be noted that this sequence was chosen, as it typically resulted in a greater load on the engine with each consecutive test.

Instrumentation

Exhaust gases were measured with an ECOM Model AC-Plus portable analyzer. The instrument was obtained from ECOM America Ltd., 1895 Beaver Ridge Circle, Suite N, Norcross, Georgia. Separate electrochemical sensors measured CO, NO, and NO2 concentrations. The flow rate was 2.5 liters per minute (lpm). Pollutant concentrations were reported in parts per million (ppm). Ambient temperature, exhaust gas temperature and duct pressure were also measured by the analyzer. The ECOM-AC was calibrated on a weekly basis using Environmental Protection Agency (EPA) protocol calibration gases.


Particulate matter (PM) was measured with a DataRAM Model DR-4000 portable aerosol analyzer. The instrument was obtained from Thermo Mie Corp., 7 Oak Park, Bedford, Massachusetts. The unit was operated as a single wavelength light scattering photometer at a wavelength of 880 nm. An in-line jet-to-plate type impactor head was used to measure PM2.5 (i.e., PM with an aerodynamic equivalent particle diameter of 2.5 m or less). The sampling flow rate was 2-lpm. An internal Millipore membrane filter was used to collect an integrated sample over the entire test period for any given vehicle that was tested. The gravimetric data from each test was used to calibrate the response of the instrument for each test. The impactor has a cassette filter, which collects the PM that does not pass the 2.5 m cut diameter. This filter was also weighed, and the data were used to provide an estimation of the PM greater than 2.5 m. The sum of the weight collected on the impactor cassette filter and the inline membrane filter provided the total mass collected. All filters were pre- and post-conditioned in a desiccator before being weighed with a microbalance scale.
The diesel exhaust flow rate was measured with a Kurz Model 454FT-12-MT insertion meter. The instrument was obtained from Kurz Instruments Inc., 2411 Garden Road, Monterey, California. The Kurz flow meter is a point velocity-sensing thermal anemometer that requires an in-situ calibration using a velocity traverse of the flow profile. Flow rate from the Kurz meter is reported in units of standard cubic feet per minute (scfm). The flow meter was field calibrated by conducting velocity traverses inside the primary test chamber using a type-S pitot tube.

Sampling System

A two-stage sampling system was used to measure exhaust emissions as shown in Figure 1. Gaseous emissions were measured in the primary sampling chamber. The PM emissions were measured in the secondary sampling chamber or dilution tunnel, due to the need to cool the flow by dilution to avoid exceeding the maximum operating temperature of the PM monitor. The vertical muffler of each truck was disconnected from the engine exhaust manifold, and the sampling system attached directly to the engine turbocharger exhaust duct via a flexible stainless steel hose. The dilution tunnel was attached through the downstream 90o elbow of the primary sampling chamber via thin wall stainless-steel tubing. Figure 1 (not drawn to scale) illustrates the location of the key components of the sampling system. Field photographs of the entire sampling equipment are shown Figure 2.



Figure 1: Diagram of sampling system and equipment layout (not drawn to scale).




The primary sampling chamber contained sampling ports for instrumentation and permits bypassing the vertical exhaust muffler of the truck. The dimensions of the sampling chamber are 8-ft in length and 8.25-ins in diameter. It was constructed of 316 stainless steel pipe and fittings. A flexible stainless steel hose is used to join the sampling chamber to the turbine outlet of the truck. Combustion exhaust gas is directed away from the area through a high temperature resistant, polymer flexible pipe, which is attached to the downstream side of the sampling chamber and stretched along the ground. The ECOM gas analyzer probe, the Kurz flow meter sensor and a humidity sensor are inserted through sampling ports situated along the side of the primary sampling chamber. The exhaust gas-phase species concentrations, flow rate, temperature and humidity were measured inside the primary sampling chamber. The dilution tunnel and other essential monitoring and recording equipment are also attached to the primary sampling chamber. All the instruments are mounted to a 10-ft long by 3-ft high tube steel, mobile cart to make it easy to position the entire apparatus next to a test truck.



Figure 2: Field photographs of sampling system and equipment layout.





Diesel exhaust gas temperature in the sampling chamber generally ranged between 200 and 300oF. Maximum allowable temperature for the PM analyzer was 140oF. Thus, a dilution tunnel was required to extract a representative sample from the primary chamber and then cool it, too well below the safe temperature of 120oF, by mixing it with cleaned and dry ambient air. Dimensions of the dilution tunnel are 3-ft in length and 1-in in diameter. It was constructed of 316 stainless steel pipe and fittings. Thin wall tubing connected the dilution tunnel to the primary chamber and to the PM analyzer, without any bends or changes in direction. The tubes were sized to achieve near isokinetic conditions at the inlet to the dilution tunnel and at the inlet to the DataRAM. Two regenerative blowers (or pumps) are used to mix ambient air and exhaust gas. Rotameters are attached to the dilution tunnel to control and measure the flow rate of the dilution air. Bypass values are used for coarse flow control. A high-efficiency particulate (HEPA) filter and the desiccant Drierite were used to remove particles and moisture, respectively from the ambient air. Temperature and pressure gauges located adjacent to the rotameters were used to change the gas flow rates from nonstandard operating conditions to standard gas conditions (i.e., temperature at 68oF and pressure at 1-atmosphere). Throughout the entire experiment, the dilution ratio was approximately 3:1 (i.e., 3-parts fresh air to 1-part exhaust gas). The DataRAM unit, which is attached directly to the opposite end of the dilution tunnel, was used for measuring total PM and PM2.5 concentration in the exhaust gas.



Collection and Treatment of Data

The internal data logging capacity of the analytical equipment was utilized to collect all data during actual testing, after which the data were transferred to a personal computer. It should be noted that during the early stage of the idling tests, the DataRAM analyzer had to be sent to the manufacturer for repairs. Therefore, seven trucks (ID-2 through ID-8) were not tested for PM.


The truck engine operation during the warm-up period (between starting the engine and until steady-state emissions were reached) constitutes the cold-start period. These emissions were averaged over the time period it took to reach steady-state; cold-start steady-state (CS-SS) emission factors were calculated from the data set. Emissions were also averaged over the first 5-minutes after the engine had been started to generate cold-start 5-min (CS-5) emission factors. Data collected after emissions reached steady-state constituted the long-duration or extended idling period. Ten-minute averaging periods were selected from the long-duration data at locations in the data where the emission rate was relatively constant on the emission curves. All cold-start and idling emission factors were reported in units of grams (pollutant) per hour.
Gaseous emission factors were calculated by multiplying the measured concentration by the flow rate as measured in the sampling chamber. Standard units of concentration and flow rate (e.g., mg/dry m3 @ 7% O2) are not necessary as long as conditions of temperature, pressure, moisture and percent O2 are consistent for both parameters in the calculation. The NOx emissions are the sum of NO and NO2 but the emission rates are reported as NO2. The dilution ratio must also be incorporated into PM emission factor computations. (See sample calculations in the appendix.)

results/discussion

A graph of CO, NOx and PM2.5 emission rates for an entire testing period is shown in Figure 3 for the 1996 Freightliner truck (ID-1) to illustrate the typical response of emissions that occurred during the idling cycles. Initially, during the cold-start period of the engine, NOx emissions peaked between 350 and 400 g/hr, and CO emissions peaked around 100 g/hr. These emission rates gradually declined, over time as the engine warmed, until steady-state was achieved. For NOx, steady-state was reached about three hours after cold-starting the engine, whereas it took only about one hour for the CO emission to reach steady-state. When the engine idling speed was increased from 750 to 1000 rpm and/or the setting of the air-conditioner was switched from “off” to “on” mode, the gaseous emissions also increased in magnitude and remained relatively stable throughout the testing period. As shown in Figure 3, average gaseous emission rates for the engine idling at 750 rpm with the AC-Off were approximately 140 g/hr NOx and 40 g/hr CO. With the AC-On, they were approximately 250 g/hr NOx and 50 g/hr CO. Average gaseous emission rates for the engine idling at 1000 rpm were approximately 155 g/hr NOx and 53 g/hr CO with the AC-Off; they were approximately 255 g/hr NOx and 63 g/hr CO with the AC-On.


For PM emissions during the cold-start period, the high peak and gradual drop-off in emissions, which were characteristic for gaseous emissions, did not occur for the truck that was illustrated in Figure 3. In addition, PM emissions did not completely achieve steady-state during the idling engine speed and air-conditioner tests. It should be noted that these characteristics of the PM curve were seen in about 40% of the trucks that were tested. However for the other cases, a series of emission spikes that varied in magnitude occurred throughout the cold-start period and the idling engine speed/air-conditioner tests. As shown in Figure 3, average PM2.5 emission rates for the engine idling at 750 rpm were approximately 4.6 g/hr at the AC-Off setting and approximately 5.0 g/hr for the AC-On setting. Average PM2.5 emission rates for the engine idling at 1000 rpm were noticeably higher at approximately 7.8 g/hr with the AC-Off and approximately 7.2 g/hr with the AC-On.

F
igure 3: Emission rate behavior for the 1996 Freightliner truck.




At present, there is no solid data to explain the cause of the variations in the pattern between the emission curves. It is possible however that for PM emissions, the engine performs more and more poorly during extended idling. Some evidence seems to suggest that incompletely burned fuel in the form of PM can accumulate in the exhaust system by a phenomenon called wet-stacking.10 When the engine is operated at low idling speed the exhaust temperature is cooler, which is conducive for the condensation of liquid droplets. Soot particles mix with the liquid droplets and collect on the walls of the exhaust system, which is called wet-stacking. Eventually the material on the wall dehydrates, forming tiny loose projections that can dislodge and reenter the exhaust gas stream. Nevertheless, it is unlikely that the agglomerated materials would be re-entrained as PM2.5, rather more likely, it would be re-entrained as larger particulate matter.


It is speculated that the prior road history of the truck and wet-stacking can influence the amount of PM that is emitted during an engine cold-start episode and/or during extended idling periods. For example, if a truck is driven on the road at high engine speed, and after that, is immediately parked and the engine shut down, then condensate would not have had time to accumulate in the exhaust system. Under this scenario when the engine is started again, the ensuing PM emissions in the exhaust gas could only have derived from the combustion inefficiency of the engine during the cold-start period. However, if the truck was driven at lower speeds or if the truck was idled for a period of time before the engine was shutdown, and then if wet-stacking occurred, a cold-start condition is created that has the potential for the re-entrainment of PM.
Figure 4 is a graph of CO, NOx and PM2.5 emission rates for the 1995 International truck (ID-12) during a segment of the testing period to illustrate the complex nature of the emission curves. The detail shown in the curves illustrate the high and low cyclic nature of emissions that are occurring during extended idling for the AC-On and AC-Off conditions. The overall effect of running the air-condition system is to increase emissions. The action of the air-conditioning compressor also creates cyclic power demands on the engine. Operational and environmental factors inside and outside the cab influence the cyclic nature of the air-conditioning compressor. The pattern of spikes appearing in these curves is primarily the result of cyclic power demands that are made on the engine from the radiator coolant fan. It should be noted that the radiator fan of a heavy-duty diesel engine does not normally operate continuously, like the radiator fan on a gasoline engine. The radiator fan clutch of a heavy-duty diesel engine is dependent instead on the coolant temperature of the engine. It is electronically activated when the set-point temperature of the coolant is reached and deactivated when the coolant temperature drops below the set-point temperature.

F
igure 4: Emission rate behavior for the 1995 International truck.




Average emission values from the cold-starting and extended idling conditions were determined for each truck tested in the study with the response of each truck being similar to that shown in Figure 3. Overall average emission factors were calculated for CO, NOx and PM2.5 emissions and for the ratio of NO2/NOx emissions. These typical (average) emission factors are summarized in Table 2. The values from column 8 in the table are the average valued from AC-Off and AC-On, at low- and high-rpm idling conditions (i.e., the average value of columns 4, 5, 6 and 7). As expected, the CS-5 rates were higher than CS-SS rates. For example, average NOx emissions were 188 g/hr at CS-SS and 246 g/hr at CS-5. In general for long-duration idling emissions, the average CO, NOx and PM2.5 emission rates were greater for the both AC-On conditions at low and high idling, with the high-idling emission rates greater than the low-idling emission rates. For example, average NOx emissions at low-idling speeds were 120 g/h at AC-Off and 159 g/hr at AC-On. At high-idling speed, they were 164 g/hr at AC-Off and 223 g/hr at AC-On. It should be noted that the ratio of NO2 to NOx emissions remained fairly constant throughout cold-start and long-term duration idling conditions between the values of 0.16 and 0.19. This indicates that the effect of idling speed and the in-cab accessory load AC conditions had little noticeable effect on the ratio of NO and NO2 in the exhaust gas.


Table 2: Overall Typical (Average) Emission Factors


Pollutant

Low-Idling

Low-Idling

High-Idling

Average Low & High rpm Idling only

CS-SS

CS-5

(600-800 rpm)

(1000 rpm)

AC-On

AC-Off

AC-On

AC-Off

AC-On

CO

87.3

146

36.8

47.5

74.5

98.6

64.4

NOx

188

246

120

159

164

223

167

Ratio: NO2/NOx

0.16

0.17

0.18

0.16

0.19

0.18

0.18

PM2.5

3.45

4.79

2.51

2.90

3.31

4.02

3.18

Emission factor units = (g/hr) except Ratio: NO2/NOx; CS-SS = Engine cold-start to reach steady-state condition; CS-5 = Engine cold-start during the first 5 minutes; AC = Air-conditioner at Off and On settings.
Raw data that were used to generate the summary in Table 2 were plotted as a function of the engine idling speed and the in-use status of the air-conditioning system. These plots are shown in Figures 5 through 7 for the three pollutants. Best-fit lines are drawn through the data points for the AC-Off and AC-On modes. Inspections of these graphs reveal that the highest engine idling speed (i.e., 1000 rpm) and the AC-On setting produced higher emissions. On the other hand, there was also wide dispersion in the data especially at the 1000 rpm engine idling speed. Preliminary statistical analysis of the data for both air-conditioner settings revealed statistical significance (at greater than the 0.05 probability level) between low (600-800 rpm) and high (1000 rpm) engine idling speeds for CO and NOx emissions but not for PM2.5 emissions. That is at 1000 rpm, higher CO emissions were produced at both the AC-Off setting (p < 0.0001) and the AC-On setting (p = 0.0004), and higher NOx emissions were produced at both the AC-Off setting (p = 0.0006) and at the AC-On setting (p = 0.009). Comparisons of just the air-conditioner effect across all engine idling speeds again revealed fairly significant results for the gaseous pollutants but no effect for PM2.5 emissions. That is at the AC-On setting, higher CO and NOx emissions were produced, (p = 0.07) and (p = 0.001), respectively.
Table 3 shows an overall comparison between the long-term idling emission factors that were determined in the field by the present study and the U.S. EPA suggested emission factors for State Implementation Plans (SIP)1 and the average values that were calculated from a review of current literature (McCormick, et.al.2, Lambert, et.al.4, Brodrick, et.al.5, Lim6 and Storey, et.al.7). In summary, the NOx emission rates observed in this study and summarized in Table 3 were greater than those reported for EPA-SIP purposes and from the literature review by 23.7% and 17.6%, respectively. The PM2.5 emission rates observed in this study were less than those reported for EPA-SIP purposes and from the literature review by 13.6% and 4.5%, respectively. It should be noted that the emission rates for CO are not published for EPA-SIP purposes. Nevertheless, the average CO emission rates observed in this study were less than that reported as the average literature review value by 14.3%.

F
igure 5: CO emission rate versus idling speed for air-conditioner settings.







F
igure 6: NOx emission rate versus idling speed for air-conditioner settings.






F
igure 7: PM2.5 emission rate versus idling speed for air-conditioner settings.






Table 3: Comparison of Overall Emission Factors


Pollutant

Average Low & High rpm Idling only

EPA (SIP)

Literature Review Average

CO

64.4

NA

75.1

NOx

167

135

142

PM2.5

3.18

3.68

3.33

Ratio: PM2.5/PMTotal

0.729

NA

NA

Emission factor units = (g/hr) except Ratio: PM2.5/PMTotal
The results from the PM gravimetric analysis are also show in Table 3. Total PM is the sum of PM2.5 and PM > 2.5 m; both were collected on filters during real time emission testing with the DataRAM monitor. The ratio of PM2.5 and total PM ranged between 0.40 and 0.98. The average ratio between PM2.5 and total PM showed that about 72.9% of the PM emissions were PM2.5.

Truck-Stop Electrification

Large emission reduction benefits are associated with TSE technology. However, reduction benefits from TSE will be slightly smaller when the cold-start emissions and the emissions that are associated with the consumption of electricity have been subtracted from the initial emission benefits. To quantify the actual reduction in emissions that are associated with TSE on a per truck basis, the following equation was used:



where, for any pollutant, i,

AERR = Actual emission reduction rate (g/hr),

EIER = Extended-idling emission rate (g/hr),

CSER = Cold-starting emission rate (g/hr) and

EUER = Electricity-use emission rate, (g/hr).
The EIER term is the extended-idling emission factor for the pollutants (i.e., CO, NOx or PM2.5). These emission factors have been determined by experimentation and/or listed by federal regulation (e.g., EPA-SIP). These emission factors are ordinarily used to determine the emission reduction benefits that are associated with TSE technology.
The CSER term describes the cold-start emission rate assuming that it has been spread over the entire period of idling, tA, and is defined by the following equation:

where, for any pollutant, i,

CSEF = Cold-start emission factor (g/hr),

tA = Extended-idling rest period or TSE time (hr) and

tB = Idling time during cold-start period, (min).


The CSEF term is the cold-start emission factor for the pollutants (i.e., CO, NOx or PM2.5) that occurs during the actual time of cold-start, tB. This emission factor is determined by experimentation. Cold-start emissions will occur for only a short period of idling time (tB) between moments that the engine is started and until the driver places the engine in gear causing truck movement or until the engine has warmed, whichever comes first. For illustration purpose, the cold-start idling time period (tB) is 5-mins in duration, and the driver rest period (tA) is 8-hrs.
To approximate the electricity-use emission rate, the following equation was used:

where, for any pollutant, i,

ECES = Electric consumption emission standard (lb/106 Btu),

e = Power-plant thermal efficiency (unit less),

WP = Power utilization by HVAC (watt) and



L = Load applied to the HVAC (percent).
The ECES term is expressed on a mass of pollutant emitted per heat-input basis. For NOx and PM2.5, the ECES values are the New Source Performance Standards (NSPS) for the Fossil-fuel Electric Utility Steam Generating Facilities (i.e., 0.6 lb NOx/106 Btu and 0.03 lb PM2.5/106 Btu). It should be noted that the NOx standard is based on the more prudent heat-input value from anthracite or bituminous coal. Since there is no NSPS for CO, the emission factor for CO was taken from AP-42. Using the configuration from external combustion sources for pulverized (bituminous) coal, dry bottom, tangentially fired-furnaces, the AP-42 emission factor for CO is 10 lb/ton. Based on an assumed coal Btu value of 26x106 Btu/ton coal, the ECES for CO is approximately 0.4 lb CO/106 Btu.
The power demand (WP) of the HVAC unit depends on environmental factors, such as solar load, ambient temperature and cloudiness, etc. When the HVAC unit is initially engaged, the duty cycle will be continuous, until the inside cab temperature attains the thermostat set-point temperature, then the HVAC system starts cycling and load is reduced. The HVAC power consumption for a single TSE unit during a 1-hr period was estimated to be 2.2 kilowatt-hours or 2,200 watts. This figure is based on actual field –tests that were conducted during a typical summer day at the fully loaded condition (i.e., L = 100%).
The emission rates for extended-idling, cold-start, electricity-use and the actual reductions from TSE are shown in Table 4 for CO, NOx and PM2.5. The actual emission reductions that can be expected with TSE are shown in the last column of Table 4. This was obtained by subtracting the cold-start emission rate (column 3) and the electricity-use emission rate (column 4) from the extended-idling emission rate (column 2). Comparison of the emission rates in the table show that the actual or corrected emission savings are slightly less than if one used the extended-idling emission rates to estimate the TSE savings. The corrected or actual emission reductions for CO, NOx and PM2.5 are 8.2%, 5.4% and 10.7% less than the extended-idling emission rate, respectively. (See sample calculations in the appendix.)
Table 4: Summary for Emission Rates (g/hr) for TSE


Pollutant

Extended-Idling (EIER)

Cold-Start (CSER)

Electric-Use (EUER)

Actual Emission Reduction (AERR)

CO

64.4

1.52

3.74

59.1

NOx

167

2.56

5.84

158

PM2.5

3.18

0.05

0.29

2.84



CONCLUSIONS

This study measured cold-start and extended-idling emissions of CO, NOx and PM2.5 from diesel trucks in the field and determined the equivalent emissions that are associated with producing electricity in the TSE process. Average typical cold-start and extended-idling emission factors were then developed for the pollutants. For all three pollutants, the cold-start emission factors were higher than the extended-idling emission factors. Overall, the extended-idling emission factors of the present study compared favorable (but were slightly higher) than both the EPA suggested values and the average values that were determined from a summary of the current literature. The average extended idling emission factors from the present study were 64.4 g/hr for CO, 167 g/hr for NOx and 3.18 g/hr for PM2.5. The average ratio of NO2 to NOx was 0.18. The average ration of PM2.5 to total PM was 0.729.


Real or actual emission reductions that can be expected with TSE are needed to support future administrative decisions from standpoints of environmental planning, human health and economic cost. To aid in this end, cold-start emissions and emissions that are associated with production of electricity, which is necessary to provide TSE in lieu of engine idling were used to correct or adjust the emission reduction estimates for TSE. The cold-start emissions are counted because the engine must be restarted after using TSE technology. In general, it was found that the cold-start emissions and the emissions from electricity were small in comparison with the extended-idling emissions. On the other hand, it was found that the actual emission reductions were (8.2% for CO, 5.0% for NOx and 10.7% for PM2.5) less than those emission reductions, which were estimated from applying the extended-idling only circumstance to TSE technology.

REFERENCES





  1. U.S. Environmental Protection Agency. Guidance for Quantifying and Using Long Duration Truck Idling Emission Reductions in State Implementation Plans and Transportation. EPA420-B-04-001. Office of Transportation and Air Quality; Research Triangle Park, NC. January 2004.




  1. McCormick, Robert L., Michael S. Grabosku, Teresa L. Alleman and Janet Yanowitz. Idle Emissions from Heavy-Duty Diesel and Natural Gas Vehicles at High Altitude. Journal of Air & Waste Management Association; 50:1992-1998. November 2000.




  1. Tang, Shida and John Munn. Internal Report: Idle Emissions from heavy Duty Diesel Trucks in the New York Metropolitan Area. New York State Department of Environmental Conservation; Division of Air Resources, Bureau of Mobile Sources. New York, NY. November 2001.




  1. Lambert, Douglas C., Michal Vojtisek-Lom and P. Joshua Wilson. Roadside Emissions Study: Preliminary Results for Stationary and On-Road Testing of Diesel Trucks in Tulaire, CA. Clean Air Technologies International, Inc. Buffalo, NY. May 2002.




  1. Brodrick, Christie-Joy, Harry A. Dwyer, Mohammad Farshchi, D. Bruce Harris and Foy G. King, Jr. Effects of Engine Speed and Accessory Load on Idling Emissions from Heavy-Duty Diesel Truck Engines. Journal of Air & Waste Management Association; 52:1026-1031. September 2002.




  1. Lim, Han. U.S. Environmental Protection Agency. Study of Exhaust Emissions from Idling Heavy-Duty Diesel Trucks and Commercially Available Idle-Reducing Devices. EPA420-R-02-025. Office of Transportation and Air Quality; Certification and Compliance Division; Ann Arbor, MI. October 2002.




  1. Storey, John M., Samuel A. Lewis, Sr., Thang Q. Dam, John F. Thomas, K. Dean Edwards, Gerald L. DeVault and Dominic J. Retrossa. Particulate Matter and Aldehyde Emissions from Idling Heavy-Duty Diesel Trucks. SAE 2003-01-0289. Society of Automotive Engineering International. Warrendale, PA. March 2003.




  1. U.S. Environmental Protection Agency. User’s Guide to MOBILE6.1 and MOBILE6.2: Mobile Source Emission Factor Model. EPA420-R-02-028. Office of Transportation and Air Quality; Ann Arbor, MI. October 2002.




  1. U.S. Environmental Protection Agency. Code of Federal Regulations No. 40, Part 60, Subpart Da-Standards of Performance for Electric Utility Steam Generating Units for Which Construction is Commenced After September 18, 1978. Washingtion DC. October 12, 2004.




  1. Irick, David. I and Bob Wilson. NOx Emissions and Fuel Consumption of HDDVs During Extended Idle. Coordinated Research Council, Twelfth Annual On-Road Vehicle Emissions Workshop; San Diego, CA. April 15-17, 2002.



Appendix

A1a: Sample Calculations NOx Emission Factor


ECOM analyzer measured NO and NO2 concentrations, and Kurz meter measured flow rate (both from inside the primary sampling chamber).
Flow rate in units of standard cubic feet per minute (scfm) multiplied by the gaseous pollutant concentration in units part per million (ppm) gives mass of pollutant per time (g/hr).
For example, if NO = 276 ppm & NO2 = 24 ppm and average flow rate 272 scfm, then the emission factor for NOx reported as NO2 is approximately 256 g/hr.

Where: 46 g/mole is the gram molecular weight of NO2; 24.1 L is the volume of gas at the standard conditions measured by the flow meter [i.e., temperature 68o F (20o C) & 1-atmosphere]; [(L/0.0353 ft3) & (60 min/hr)] are conversion factors.



A1b: Sample Calculations PM2.5 Emission Factor


Particulate matter pollutant: DataRAM analyzer measures PM concentration from the dilution tunnel; Kurz meter measured flow rate from the primary sampling chamber; rotometers, etc. measured dilution air from the dilution tunnel.
Data from rotometers and temperature/pressure gauges are used to determine the dilution air. Applying the conservation law for mass at the locations shown in Figure 1 for the dilution tunnel. The symbols Q1, Q2, Q3 and Q4 represent flow rates. The flow rate of the extracted sample (Q1) plus the dilution airflow rate (Q2) is equal to the flow rate of the discharged air (Q3) plus the sampling flow rate of the DataRAM (Q4). That is, (Q1 + Q2) = (Q3 + Q4).
The flow rate of the extracted sample Q1 is unknown; the other three flow rates Q2, Q3, and Q4 are known values. Thus, solving for the unknown, Q1 = (Q3 + Q4) – Q2. The dilution ratio is Q2/Q1. The recommend equation to correct nonstandard operating conditions for the rotometer is as follows:

where: Q = Actual or observed flow meter reading

Q’ = Standard flow corrected for pressure and temperature

P = Actual pressure (14.7 psi + gauge pressure)

P’ = Standard pressure (14.7 psi, which is 0 psi gauge)

T = Actual temperature (460 R + temp oF)

T’ = Standard temperature (528 R, which is 68 oF)


Pressure will not be included in the calculations because static pressure differences between the points 2 and 3 were between 0.05 and 0.1 inches of water gauge, which equated to less than 0.01 psi. Similarly, the equation to convert nonstandard operating conditions for the flow rate of the DataRAM is a follows:

Combining the above equation and ignoring pressure:

Approximate typical (actual) values are Q2 = 30 cfh & T2 = 72o F, Q3 = 35 cfh & T3 = 76o F and Q4 = 2 Lpm (4.24 cfh) & T4 = 86.

The dilution ratio is

Finally, the emission factor for PM can be determined by mass balance.

where, concentrations (C) are C2 = 0 because the diluted air is clean via HEPA filter, C4 = C3 from complete mixing inside the dilution chamber and C4 is the PM concentration as measured by DataRAM. Thus, solving for the unknown concentration or PM in the primary chamber, C1:

Again converting to standard conditions,

Concentration from DataRAM is C4 = 7500 g/m3

Finally, multiplying the adjusted PM concentration by the flow rate from the primary sampling chamber gives the PM emission factor 3.5 g/hr:

where, the ratio [(460 + 86)/528] converts temperature into standard conditions that are equivalent to the Kurz flow meter (i.e., 272 scfm) and [(35.3 ft3/m3) & (g/106 g)] are conversion factors.

A2: Sample Calculations (TSE)

PM2.5 Cold-start, Electric-use and Actual Emission Reduction Rates



Cold-Start Emission Rate



Electricity-Use Emission Rate



Actual Emission Reduction Rate


KEYWORDS: Heavy-duty diesel vehicles; HDDV8; long-duration idling emissions; extended idling emissions; diesel emission monitoring; truck stop electrification.







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