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 2: Comparison between the verified and calculated consumption of the so called gasoline vehicles (gasoline + anhydrous alcohol) from the estimated fleet and from the 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 [1], 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)

	CO	HC	CH4	NOx	C02	Evapora.	C	Gasool(*)	Vol/Dist	Dist/Vol
	(g/km)	(g/km)	(g/km)	(g/km)	(g/km)	(g/km)	(g/km)	(g/km)	(ml/km)	(km/l)
pré-80	54	4,7	0,94	1,2	174,72	4,3	74,9	97,6	130,5	7,7
80-83	33	3	0,6	1,4	174,72	4,3	64,4	83,9	112,3	8,9
84-85	28	2,4	0,48	1,6	174,72	4,3	61,7	80,4	107,6	9,3
86-87	22	2	0,4	1,9	174,72	4,3	58,8	76,6	102,5	9,8
88	18,5	1,7	0,34	1,8	174,72	4,3	57,1	74,3	99,5	10,1
89	15,2	1,6	0,32	1,6	174,72	4,3	55,6	72,4	96,9	10,3
90	13,3	1,4	0,28	1,4	177,11	0,43	55,2	72,0	96,3	10,4
91	11,5	1,3	0,26	1,3	178,7	0,43	54,8	71,4	95,5	10,5
92	6,2	0,6	0,12	0,6	193,4	0,32	55,9	72,9	97,5	10,3
93	6,3	0,6	0,12	0,8	193,4	0,32	56,0	72,9	97,6	10,2
94	6	0,6	0,12	0,7	193,4	0,32	55,8	72,8	97,3	10,3
95	4,7	0,6	0,12	0,6	206,9	0,32	59,0	76,8	102,8	9,7

 (*) 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 3 – Emissions for New Vehicles– Hydrated Alcohol  

	CO	HC-met	CH4	NOx	C02	Evaporativas	C	Álcool Hidr.
	(g/km)	(g/km)	(g/km)	(g/km)	(g/km)