Abstract : Nowadays, the growing trend of urban life and significant time spent on roads and highways is very evident, resulting in exposure to traffic-related pollutants . Research on air pollution caused by urban traffic has been one of the notable cases of researchers, which is due to this urban expansion and urbanization. In recent years, extensive research has been carried out on field measurements or empirical experimental models as well as software simulation by fluid computational dynamics [2,3,4]. One of the major sources of emissions and dispersion of polluting gases and particulate matter in urban spaces is the combustion caused by the motor vehicle engine. The presence of residential buildings and adjoining residential areas adjacent to highways and large streets exposed to polluting gases and particulate matter from urban traffic causes the accumulation of pollutants in these environments, which would endanger the health of humans. Considering that in Iran, the expansion of urbanization and the development of large cities and metropolitan areas has led to an increase in the number of highways and streets and, consequently, increased vehicle traffic and traffic, so it is essential that the accumulation and dispersion of various pollutants under the conditions Different motion can be investigated .
In this study, the effect of changes in vehicle conditions (different vehicle speeds), the type of fuel consumed in the combustion of the engine (gasoline, diesel and various mixtures of diesel and biodiesel) and the size of the vehicle (car and city trucks) on dispersion The exhaust gases emitted from the exhaust pipe at different intervals from the rear of the vehicle are models of a small comparison (about one-twentieth) and in the form of a replica and dispersion of exhaust gases emitted from the exhaust pipe at various intervals from the rear of the vehicle, experimentally sized Is done.
In this work, to create different driving conditions, the experiments are carried out in a wind tunnel, and the direction of wind blowing from the front to the back of the car is considered and the possibility of smoke out of the wind tunnel environment is also included. There is also a smoke generating equipment from various combustion fuels that ultimately leads to the gas outlet from the car's replica. However, the smoke output from each exhaust pipe exhaust pipe, according to the type of vehicle, should be calculated and calculated according to the following equation. Take :
U = (V_cly.n) / (π.D ^ 2) .Ƞ
Where the parameters are as follows:
U: The smoke outlet speed of the exhaust pipe
Vcly: Engine displacement volume
n: motor speed
D: Exhaust pipe diameter
η: motor volume yield
The figure shows a schematic diagram of the experimental set of research. In the research, the concentration and accumulation of pollutant emissions at different intervals (x, y and z) were measured from the exhaust pipe of the automotive replicas (Fig. 1) and using the five gaseous gas metering device in a steady state. The pollutants are carbon monoxide, carbon dioxide, sulfur dioxide and nitrogen oxides (as dependent variables). Independent research variables will be as follows:
1 Different vehicle speeds: The speeds considered will be in accordance with the speed of a car or truck in highways or highways (50 to 70 km / h)
2 Type of fuel used in engine ignition: In this research, emissions from gasoline combustion, pure gasoline and various mixtures of gasoline and biodiesel (B0, B20, B50, B80 and B100) are measured.
3 Vehicle size: In this research, the size of two types of passenger cars and urban trucks is considered in accordance with the usual cars in Iran and the models are used in a small comparison in the wind tunnel environment.
According to the previous research in this study, the assumptions of the problem are considered as follows:
1 The test is considered as a single car and in a direct transit path, and the vehicle does not re-rotate.
1 There is no overwhelming wind when driving.
2 The heat flux from combustion of side cars has no effect on the dispersion of pollutants.
General description of contaminants :
Carbon Monoxide (CO): A gaseous, pale, unhealthy gas that results from incomplete burning of carbon.
Carbon Dioxide (CO2): Carbon dioxide is one of the gases in the atmosphere. This gas is generated from the burning of organic matter in the presence of sufficient oxygen, and is a light and light gas. The carbon dioxide contained in the atmosphere acts as a thermal shield of the earth and prevents the surface from cooling down with the natural greenhouse effect. High concentrations of carbon dioxide in the atmosphere, derived from fossil fuels, are atmospheric greenhouse gases.
Sulfur dioxide (SO2): Sulfur dioxide (SO2) is a toxic and miscible gas used to produce sulfuric acid. Sulfur dioxide is used as a preservative in the food industry, solvent in the laboratory, cooling in cold stores, water purification, glass industry, mining and metallurgy.
Nitrogen oxides (NOx) are two important gases in the air pollution equations, nitric oxide (NO) and nitrogen dioxide (NO2). Nitrogen oxides occur in high-temperature combustion processes due to nitrogen and oxygen combinations.