Module 8 : Specialized Traffic Studies

Lecture 43 : Fuel Consumption and Emission Studies

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	Automobile Pollution The pollution caused due to the emissions from vehicles is generally referred to as automobile pollution. The transportation sector is the major contributor to air pollution. Vehicular emissions are of particular concerns, since these are ground level sources and hence have the maximum impact on the general population. The rapid increase in urban population have resulted in unplanned urban development, increase in consumption patterns and higher demands for transport and energy sources, which all lead to automobile pollution. The automobile pollution will be higher in congested urban areas. The vehicle obtains its power by burning the fuel. The automobile pollution is majorly caused due to this combustion, which form the exhaust emissions, as well as, due to the evaporation of the fuel itself. The chemical reactions occurring during ideal combustion stages may be represented as follows: $$Fuel~(HC) + Air~(O_2, N_2) \longrightarrow CO_2 + H_20 + {\mathrm{unaffected~Nitrogen}}$$ (1) Similarly, the typical engine combustion which occurs in vehicles can be represented by the below chemical equation. $$Fuel~(HC) + Air~(O_2, N_2) \longrightarrow {\mathrm{Unburned}}~HC+NO_x+CO+CO_2+H_2O$$ (2) Types of Vehicular Emissions The fuel loss of vehicles may be due to emissions or refuelling. The emissions maybe evaporative or exhaust emissions. The fuel losses in a vehicle are shown in Fig. 1. Figure 1: Losses of fuel in vehicles Exhaust emissions: Exhaust emissions are those which are emitted through the exhaust pipe when the vehicle is running or is started. Hence, the exhaust emissions maybe of 2 types - start up emissions and running emissions. Startup emissions: Emissions when the vehicle is started initially. Based on how long the vehicle had been turned off after use, they may be cold start and hot start. Cold start refers to when the vehicle is started suddenly after a long gap of use, whereas, hot start refers to when the vehicle is started without the vehicle getting enough time to cool off after its previous use. Running emissions: Emissions during normal running of the vehicle, i.e., when the vehicle is in a hot stabilized mode. Evaporative emissions: These include running losses and hot soak emissions produced from fuel evaporation when an engine is still hot at the end of a trip, and diurnal emissions (daily temperature variations). Exhaust Pollutants The pollutants which are emitted from the exhaust pipe of the automobiles are known as exhaust pollutants. They are formed as a result of combustion of the fuel in the engine. These pollutants are harmful to the atmosphere and living things in particular. The major types of exhaust pollutants are discussed in the following sections. Sulphur Oxides $(SO_x)$ Combustion of petroleum generates Sulfur Dioxide. It is a colorless, pungent and non – flammable gas. It causes respiratory illness, but occurs only in very low concentrations in exhaust gases. Further oxidation of $SO_x$ forms $H_2SO_4$ and thus acid rains. Nitrogen Oxides $(NO_x)$ Combustion under high temperature and pressure emits Nitrogen dioxide. It is reddish brown gas. Nitrogen oxides contribute to the formation of ground level Ozone and acid rain. Hydrocarbons and Volatile Organic Compounds ($HC$ and $VOC$) Hydrocarbons result from the incomplete combustion of fuels. Their subsequent reaction with the sunlight causes smog and ground level Ozone formation. $VOC$s are a special group of Hydrocarbons. They are divided into 2 types – methane and non – methane. Prolonged exposure to some of these compounds (like Benzene, Toluene and Xylene) may also cause Leukemia. Carbon Dioxide $(CO_2)$ It is an indicator of complete combustion of the fuel. Although it does not directly affect our health, it is a greenhouse gas which causes global warming. Carbon Monoxide $(CO)$ It is a product of the incomplete burning of fuel and is formed when Carbon is partially oxidized. $CO$ is an odorless, colorless gas, but is toxic in nature. It reaches the blood stream to form Carboxyhemoglobin, which reduces the flow of Oxygen in blood. Lead $(Pb)$ It is a malleable heavy metal. Lead present in the fuel helps in preventing engine knock. Lead causes harm to the nervous and reproductive systems. It is a neurotoxin which accumulates in the soft tissues and bones. Particulate Matter $(PM)$ These are tiny solid or liquid particles suspended in gas (soot or smoke). Particulate Matter in higher concentrations may lead to heart diseases and lung cancer.