e&e No 25
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
2 – Average Specific Consumption of the FleetThe 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 FleetO 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
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).
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 .
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 .
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)
* total for control
Table 7 - HC emission by category (thousand tones)
Table 8 - NOx Emission by vehicle category (thousand tones)
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 :
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:
= 24,3 Mm3 x 0,852 t/m3 = 20,7 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
Veja Também: Emissões em Veículos Leves