e&e No 25
See Also: Emission Parameters of Heavy Vehicles
Evaluation of Light Vehicles Emissions
1 – Results of the Historical Study
A historical study made for the period from 1970 to 1998 has permitted to evaluate some parameters concerning the behavior of the fleet and the influence of age on vehicle’s consumption. It was also possible to infer the share of gasoline whose consumption can be assigned to the heavy fleet. Since this consumption is of relatively little importance, we have opted to treat the emissions of the heavy fleet (trucks and buses) using gasoline together with Otto cycle vehicles. For the purpose of analyzing emission by vehicle range, we will also consider emissions of diesel light vehicles and gasoline heavy vehicles.
The evaluation of the circulating and total fleet by age was object of the work presented in the previous issue of e&e. It was possible to obtain the evolution of the light and heavy fleet along the last decades. In the emission evaluation we will use values from 1970 on. The physical module that describes the fleet supplies data: by type of fuel (diesel, gasoline and alcohol), by type of vehicle (cars, light commercials, heavy commercials and buses) and by age range (1 year, 2 years, 3 to 5 years, 6 to 10 years and V Fleet that designates the old fleet that is more than 15 years old). In the case of the light fleet we are mainly interested in alcohol and gasoline vehicles. The values referring to diesel consumption in cars and light commercials were treated in chapters 4 and 5. The natural gas consumption in light vehicles and that of gasoline (and anhydrous alcohol in the mixture) in heavy vehicles were treated with the help of general emission coefficients at the end of the present chapter.
2 Consumption Parameters
The consumption of vehicles within the same range varies according to the manufacturing year and age. The first factor refers to innovation and model profiles sold in each year. The use of the vehicles, in terms of kilometers annually traveled, varies according to the vehicle’s age since older vehicles are generally in the hands of people with smaller purchase power who use them less. In a country like Brazil, where the number of vehicles is not known, one cannot expect to have precise data about specific consumption and emission by manufacturing year and fleet’s age.
As it is clear in our historical and prospective study (MCT/PNUD report), previously mentioned, these data were tentatively extracted from global data and took advantage of the strong variation in the fleet’s composition. In the present study we have tried to introduce consumption values as a function of the vehicles’ age range. In the above mentioned report, the historical data permit to evaluate consumption as a function of the average age because of the variation of age in the alcohol car fleet, introduced in the market from 1979 on, and that of gasoline cars that aged during the period when sales of alcohol cars were predominant, followed by their rejuvenation with the return to the predominance of light gasoline vehicles.
When reliable parameters are available, the problem can be treated using for each manufacturing year a specific consumption by traveled kilometer, as a function of the vehicle’s age, multiplied by the distance annually traveled, as a function of the vehicle’s age.
We consider that this treatment introduces a refining that would be incoherent vis-à-vis the uncertainty of the existing data. This fact led us to suggest a treatment that is slightest different from the usual one but that can be a posteriori inferred.
The light fleet – cars and light commercial vehicles – was treated in an homogeneous way. It is known that the permitted tonnage for the so called light commercial vehicles of the Otto cycle has limited its real commercial use. Since it has not a very high specific consumption and its participation in the light fleet is about 10% (1994 values), it seemed that it would be not useful to treat it separately. However, it was considered that its consumption is equivalent to that of two cars manufactured in the same.
The consumption variation with age was considered as a function of the average age when treating historical data. The consumption was assumed to decrease in a linear way from the moment of purchase on until reaching the minimum value of 0.5 tep in equivalent energy gasoline (or NG). This value is coherent with what was observed for the gasoline fleet in the 13-year-old range (average), as the historical study has shown.
The consumption was supposed to vary according to a straight line [c = a.t + b] where a is negative (function decreasing with time) and b is the initial consumption level. The inferior value of c was limited to 0.5. We have varied these parameters in order to better reproduce the consumption curve along the years. The value of a=- 0.1, corresponding to fitting for alcohol, was considered the same for gasoline and alcohol vehicles and the value of b was adjusted for each fuel.
Figures 1 and 2 show the adjustment obtained for the consumption, when the fleet was considered by age for gasoline and alcohol vehicles.
Figure 1: Alcohol consumption of the lasting fleet and consumption curve by age shown in 3
Figure 3: Consumption curve by age and values used by age range.
The reproduction of alcohol consumption verified and even that of gasoline, from adjustment of parameters, is really acceptable, considering that in the adjustment there isn’t any hypothesis concerning consumption variation as a function of fuel prices and vehicles’ technical evolution. Only the larger alcohol fleet consumption is explained by the policy maintained along the years, namely favoring the price of the traveled kilometer using this fuel.
As in the last years this difference had been reduced, the gasoline cars were destined to more intensive use such as taxi and service fleets, what would explain a consumption larger than the calculated one for the last years.
The adjustment is useful for defining the consumption by different age ranges since with aging of the vehicle the emission conditions are also modified. This profile consumption as a function of age is used as the real consumption of each year for emission evaluation.
3 – Emissions Generating the Greenhouse Effect
For new vehicles, the emission factors applied for gasoline (fuel mixture with 22% anhydrous alcohol in volume) were based on CETESB’s data presented in Table 1. For evaporation, the adopted data were based on American cars of the previous generation. These data were adopted in the Brazilian Inventory of Greenhouse Effect Gases in its present edition , available at http://www.mct.gov.br.
In what follows, some comparisons will be made between the results of the present work – elaborated together with that for prospective ends – and those of the previous work (COLOCAR O NOME DO TRABALHO) that aimed at evaluating the inventory of emissions between 1990 and 1994.
In Table 1 are presented emission data for new vehicles in g/km. In order to be used in the present work they were converted to carbon values. Table 1 contains implicitly the consumption by the assumed km for each manufacturing year.
Table 1 – Emissions for New Vehicles – Gasohol (22% anhydrous alcohol in volume)
(*) 22% anhydrous alcohol 76,75% of mass is C and specific mass of 0,7474 kg/liter
In the following Table 2 data is presented as a function of emitted carbon, what will ease our calculations.
Table 2 – Mass of gases emitted by one unit of carbon mass contained (gasohol)
In tables 3 and 4 the corresponding values for hydrated alcohol are shown
Table 4 - Mass of emitted gases as a function of carbon mass contained (hydrated alcohol)
5 – Emissions in the 1990-1997 Period
The general treatment applied to the data permits to obtain results for the whole 1990-1997 period and they will be presented in the annexed tables 6A 1 to 3. The values of annual fuel consumption were distributed among the vehicles so that there would be the same consumption proportion by age range as those calculated. In Table 5 we compare the fleet of the present work with that considered in the Inventory. The fleet of the present work is 20% higher than that of the Inventory. As we have already commented, Brazilian statistics concerning the fleet are precarious. Our fleet was adjusted so that it would reproduce the amount and average age of DENATRAN’s statistics quoted by ANFAVEA in (R8). They practically coincide with the total fleet for the last years used by ANFAVEA. The mentioned discrepancies found when calculating emissions are adjusted in order to reproduce the consumption values.
Table 5 – Light Vehicle Fleet (thousand vehicles Inventory (R11)
Comparison between the two works (our values=100)
The emission values are shown in Table 6
In the emissions it was considered :
· Estimated fleet in the age ranges,
· Consumption corresponding to this fleet, considering the consumption of the new vehicle in the year of origin and the age of the vehicle,
· Re-normalized consumption so that it reproduces the Otto cycle demand for light vehicles,
· Evaluation of emission levels degradation for hydrocarbons (including methane) and carbon monoxide;.
· Determination of emission in carbon from the carbon mass by kg of fuel,·
· Determination of emission in the initial year according to Tables 2 and 4,·
Propagation of emissions in the year of sale of the vehicle for each age range (weighted average of values, according to the case)
· Evaluation of the aging effect by age range for CO and HC, and
· Determination of emissions by fuel and by polluting gas
· Table 6 – Emissions by Light Vehicles (thousand t/year)
Anhydrous Alcohol (in mixture)
Fuel Mixture (gasohol)
(*) The CO2 emitted by biomass is annulled in the production from the point of view of the greenhouse effect . From the cumulative point of view, the same procedure should be adopted for CO.
The results of the present work concerning emissions are not far from the expected one for hydrated alcohol. Actually the specific consumption adjustment compensates the superior value of the fleet. There are significant differences referring to fuel mixture or gasohol. Apparently these differences are due to the criterion adopted, namely considering the CO2 emissions as the total conversion of the carbon contained in the fuel. Analysis of these differences are made in the annex.
6 – Variation in the Mixture
Emissions from fuel mixtures vary according to their composition. The correct consideration of this variation would nevertheless demand analysis of the effect on these emissions.. It has been reported that the worse the emission conditions are, the effects on CO emission would be more positive in percent terms. This fact does not seem to be reflected in the table used as reference.The variation in the fuel mixtures are shown in Figure 4.
In the period examined by the present work, 1990/1997, there was considerable change in the mixture, mainly in the two last years. In our calculation process, the division between anhydrous alcohol and gasoline is carried out automatically.
7- Emissions by Age of Fleet
The adopted procedure permits to identify the age range from where the emission comes, by type of emission. The process allows to easily change this range. The evaluation was made year by year between 1990 and 1998. The corresponding tables are Tables 6 A 4, 5 and 6.
In Figure 5 the evolution of CO2 emissions from gasoline by age range is shown (not including those due to anhydrous alcohol which should not be accounted for because they originate from biomass).
Figure 5: Emissions from the gasoline light fleet by age range
Figure 6 shows the dramatic changes in emissions resulting from modifications in the fleet.
Figure 7: Emissions from vehicles that were more than 5 years old were responsible for almost 90% of emissions in 1988.
8 - Avoided Emissions
Emissions that were prevented due to substitution and displacement that occurred in the country’s fleet in the past but whose effects last until now should consider at least three factors:
· The presence of anhydrous and hydrated alcohol,
· Displacement of gasoline by diesel (of larger efficiency) and
· Improvement in efficiency of engines.
We will try to evaluate the first two factors.
The use of useful energy permits to treat in a clear and simple way the substitution process without confounding it with a general improvement in efficiency which would be the third factor that affects the group of fuels.
Table 7:Avoided Emissions
Emissions Using Gasoline
Avoided Emissions (percent relative to gasoline)
The avoided emissions (average in the period) are summarized in the substitution table. The substitution of one tep of gasoline (equivalent) by anhydrous alcohol in the mixture produced a reduction of 2.26 t of CO2 in the emission. The effects of adding anhydrous alcohol for reduction of emissions were not calculated for other gases since emission from gasoline was considered as being the same as that of fuel mixture. Tests carried out in Brazil, the United States and Japan verified a reduction of CO and HC emission and increase of NOx and CH4. Normally, the beneficial effects are larger than the negative ones. In a general way, mixture reduction for cars adjusted to use it has negative effects on the performance and emissions.
The substitution of one tep of gasoline by hydrated alcohol produced on the average a reduction of 2.13 t of CO2, 0.24 t of CO and practically negligible results for the other gases.
In the 1997 conditions , the effects of better yields in gasoline vehicles, reduction of improvements in alcohol vehicles and mainly the aging of the fleet made the effects of substitution less significant.
In Table 8 we have also marked the carbon emissions in the form of CO* that represent material of organic nature that once completely oxidized interrupt their effects on the environment. The alternative is to consider the CO2 credit in biomass production and the debit in CO.
(1) Um Modelo econométrico para Demanda de Gasolina pelos Automóveis de Passeio Ricardo Paes de Barros e Silvério Soares Ferreira IPEA - May 1992 - 135 pag
(2) Estatísticas Históricas do Brasil IBGE 1987 - Volume 3
(3) Últimos anos GEIPOT e ANFAVEA - Anuário Estatístico / Statistical Yearbook 1998 (Internet)