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Economy & Energy
No 25:  April-May 2001   ISSN 1518-2932

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Emission Parameters of Heavy Vehicles

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EVALUATION OF HEAVY VEHICLES EMISSIONS  

1 Consumption Division Factors

In Table 1 are indicated the participation in consumption of the vehicle categories in the different years

Table 1

Category

Consumption
(g/kWh) 

Power
(kW)

1990

1991

1992

1993

1994

1995

1996

1997

Light Commercial

201

90

0,123

0,129

0,135

0,139

0,146

0,147

0,145

0,144

Light trucks

194

150

0,216

0,22

0,217

0,212

0,208

0,21

0,207

0,207

Heavy trucks

190

280

0,56

0,547

0,54

0,544

0,534

0,53

0,531

0,53

Buses

197

155

0,104

0,106

0,11

0,111

0,111

0,113

0,116

0,118

2 – Average Specific Consumption of the Fleet

The average consumption of the fleet will be used to convert the emission coefficients from g/kWh to g/l of fuel and it is calculated as the weighted average of the specific consumption of the categories (supplied by Mercedes Benz) where the weighting factor is the product of the participation of each category and the nominal power of the category. The result of the calculation for the considered period is 195 g/kWh  average specific consumption with an average relative deviation of 0.3%.

3 – Emission indexes 

The indexes are presented in the tables of Annex 3, including for 1993 the indexes of ECE-R 49, in the unit adopted by PROCONVE (gram of pollutant by kWh). In order to facilitate the emission calculation, the PROCONVE indexes are converted to indexes for the fleet of each year, using the fleet’s average specific consumption  (195 g/kWh).

4 Diffusion of Technological Improvements into the Fleet  

O PROCONVE requires that the manufacture and sale of 80% of engines should satisfy the indexes of each phase in the same year of validity of the phase, allowing the following phase to differ 20%. With this measure, the decrease of emission indexes for new vehicles propagates gradually into the fleet, as shown in the graphic below

Figure 1: Evolution of Emission Indexes

In the present case, due to the small amplitude of the studied interval, the calculation of the technology diffusion into the emission indexes was simplified considering that the fraction of new vehicles sold in 1997, year of larger incidence of differences, represents 6% of the fleet of the year and that the scraping probability of a 3-year-old vehicle is smaller than 3% (according to the logistic curve used). Therefore, in 1997 the difference would reach less than 0.3% of the fleet, which , from our point of view, does not compensates the efforts involving detailed calculation. Once the approximation is accepted, one can make the technology diffusion table (Table 2).

Table 2 – 

Tabela 2 - Technology Diffusion                                                    Thousand of Vehicle       

 

Year

 

Fleet

 

Sales

 

Scrapping

Distribution

Indexes 93

Indexes 94

Indexes 96

 1993

1.454

92,3

65,8

1.454

-

-

 1994

1.497

  106,3

62,9

1.391

106,3

-

 1995

1.538

91,7

51,3

1.340

198,0

-

 1996

1.559

73,9

52,6

1.287

198,0

-

1997

1.580

95,9

75,0

1.212

198,0

169,8

Obs. 1 – The thousand of vehicles unit is justified by the number of significant figures of the emission indexes. (maximum 3) 2 – Before 1994 the CO, HC and NOx indexes were not specified.

5 Effect of New Technologies on the Emission Indexes 

The distribution of vehicles by  PROCONVE implantation phase is reflected on the emission indexes as shown in Table 3 that follows :

Table 3 -  Emission indexes for the fleet (cf. IBAMA’s Administrative Rule).

 

Year

Indexes (g/kWh)

CO

HC

NOx

1993 e anter.

14,0

3,5

18,0 (ECE-R 49)

1994

13,8

3,4

17,7

1995

13,7

3,2

17,5

1996

13,2

3,1

17,1

1997

12,7

3,1

16,6

As a convenience for calculation, the above indexes are converted to g/l using the average specific consumption (195 g/kWh) and the oil density (852 g/l) as shown in Table 4.

Table 4 – Emission indexes for the fleet in g/liter of fuel .

         Year

            CO

             HC

            NOx

 1993 e anteriores

            61,4

            15,4

           78,9

         1994

            60,5

            14,9

           77,6 

         1995

            60,1

            14,0

           76,8

         1996

            57,9

            13,6

           75,0

         1997

            55,7

            13,6

           72,8

6 Emission calculation using the fleet in each year 

Using the BEN’s data the consumption of diesel oil in the Road Sector is introduced and the indexes of each year is used to obtain the fleet’s emission (Table 5).

Table 5 – Emissions of the Diesel fleet .

 

Year

Consumption

109 litro

 Emissions - thousand tones

CO

HC

NOx

1990

18,3

1.124

282

1.444

1991

19,1

1.173

294

1.507

1992

19,4

1.191

299

1.531

1993

19,9

1.222

307

1.570

1994

20,8

1.258

310

1.618

1995

22,1

1.328

309

1.697

1996

23,2

1.343

316

1.740

1997

24,3

1.354

331

1.769

7 - Emissions by Vehicle Categories 

Once the fleet emissions are calculated, the emissions by category are calculated by dividing the consumption  (Tables 6, 7 and 8).

Table 6  - CO emission by category  (thousand tones)

Year

 Cars and Light  Com.

Light Com.

 Heavy Com.

Bus

Total *

   1990

139

244

633

118

1.134

   1991

152

259

646

128

1.185

   1992

162

260

648

132

1.202

   1993

171

260

667

136

1.234

   1994

185

263

677

140

1.265

   1995

197

281

708

151

1.337

   1996

196

280

718

157

1.351

   1997

197

282

731

155

1.365

* total for control

Table 7 - HC emission by category (thousand tones)

Year

Cars and Light  Com.

Light Cam.

Heavy Cam.

Bus

Total

  1990

34,9

61,4

159

28,6

284

  1991

38,2

65,2

164

30,3

298

  1992

40,6

65,3

164

32,0

302

  1993

42,9

65,4

169

33,1

309

  1994

45,5

64,9

168

33,6

312

  1995

45,8

65,4

167

34,0

312

  1996

46,1

65,8

170

35,6

318

  1997

48,3

69,4

180

38,2

335

Table 8 - NOx Emission by vehicle category (thousand tones)

Year

Cars and Light. Com. 

Light Com.

Heavy Com.

Bus

Total

  1990

179

315

818

146

1.458

  1991

196

335

832

155

1.518

  1992

208

334

831

164

1537

  1993

220

336

861

169

1.586

  1994

237

338

868

174

1.617

  1995

251

359

906

187

1.703

  1996

254

363

930

197

1.744

  1997

257

369

955

203

1.78

7 - CO2 Emission

The CO2 emission from the whole fleet assumes that the Cetane Number is known. This characteristics varies from one refinery to the other, therefore it is necessary to admit an average value for all the diesel oil consumed. Considering the specification values in force for the metropolitan, road and other uses of  diesel oil, the consumption distribution among these uses and the variation of characteristics among refineries, a representative value would be CN= 42. Using this figure, one can represent the diesel oil composition , for carbon balance purposes, by the mixture of 42% of n-hexadecane – C16H34 – that has the same ignition characteristics of the diesel oil considered, and 58% of alfa-naphthene – C11H10 – whose addition to hexadecane permits to gauge the cetane number of the sample.

Another data necessary for the balance is the vehicle’s average consumption in the real conditions of use. This information is hard to be obtained since in Brazil it is not usual to carry out this type of tests. An approximate value can be obtained from recent tests carried out at IPT in order to determine the effect of adding alcohol to diesel oil on emissions (Diesel-Alcohol Program, coordinated by the MCT). This test was made with Mercedes Benz bus engines (OM 366 LA II/21, that equips an important part of Brazilian buses) and it followed the method adopted by ABNT for emissions (European method of 13 points). The relevant information is that the average specific consumption observed in the test was 215 g/kWh, about 9% higher than the corresponding minimum consumption, supplied by Mercedes Benz for this engine. Therefore, the consumption to be considered in the carbon balance must be corrected by the 1.09 multiplier. Since the minimum specific consumption calculated for the fleet was 193 g/kWh, the balance for the whole fleet  would be based on the corrected value, namely 211 g/kWh.

The balance can be expressed by the equation :

Number of carbon atoms in the fuel = number of atoms in the emitted substances.

Besides the greenhouse effect gases, the Diesel engine emits  particulate material that  consists of carbon particulate and hydrocarbons adsorbed by carbon. The mass of particulate emitted in the typical engine is about 0,1% of CO2 mass . Therefore, since the legislation does not require analysis of the particulate material and since the proportion is small, this material is considered as incorporated in CO2 for balance purposes .

In the concrete case, the fuel consumed (211 g/kWh), containing 42% of hexa-decane, has 89,6% of its mass corresponding to carbon. As already mentioned, the HC composition is not known and, since its contribution  is small, one can consider it as having the same composition as that of the fuel.

As a calculation example, we take the 1997 emission (table 2) and the diesel oil consumption diesel in road transport in the same year (24,3 Mm3 - BEN/98).

In terms of  balance they will be:

Fuel consumption                     = 24,3 Mm3 x 0,852 t/m3      = 20,7 Mt
Mass of carbon  in fuel             = 20,7 Mt x 0,896                  = 18,6 Mt

Mass of emitted CO                 = 1,363 Mt

Mass of C in the emitted CO    = 1,363 Mt x 12/28                = 0,584 Mt

Mass of emitted HC                 = 0,335 Mt.

Mass of C in the emitted HC    = 0,331Mt x 0,896                 =0,297 Mt

Mass of C in the emitted CO2  = 18,6 Mt - 0,584 Mt - 0,297 Mt @ 17,7 Mt

Mass of emitted CO2             = 17,7Mt x 44/12                     = 65,0 Mt

CO2 / CO ration (in mass)       = 65,0 Mt / 1,36 t                   = 48

The calculation results for the other years are in Table 7.

7  Methane Emissions

Methane is not considered in the legislation, and there is no way to calculate its emission . We have used IPPC’s Guidelines (5 kg/ Tj ) to complete table 9. Using  BEN’s data, this value is converted to 192 t  methane by Mm3   diesel oil. Methane emission is presented in  table 9-

Table 9 - Consolidation of emissions by the Diesel fleet- thousand tones

Year

Consumption Mm3  M t

CO

HC

NOx

CO2 / part.

CH4

1990

18,3   15,6

1.124

282

1.444

49.840

3,5

1991

19,1   16,3

1.173

294

1.507

51.650

3,7

1992

19,4   16,5

1.191

299

1.531

52.450

3,8

1993

19,9   17,0

1.222

307

1.570

52.800

3,8

1994

20,8   17,7

1.258

310

1.618

56.250

4,0

1995

22,1   18,8

1.328

309

1.7697

59.760

4,3

1996

23,2   19,8

1.343

316

1.740

62.740

4,5

1997

24,3   20,7

1.354

331

1.769

65.000

4,7

1997

24,3   20,7

1.354

331

1.769

65.000

4,7

Veja Também: Emissões em Veículos Leves