Air Pollution Due To Ic Engine Emissions

Air Pollution Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms Air pollution, or damages the natural environment, into the atmosphere. Pollutants  Sulfur oxides  Nitrogen oxides  Carbon monoxide  Carbon dioxide  Particulate matter Sources  Anthropogenic sources  Natural sources Health hazards  cardiopulmonary disease linked to breathing fine particle air pollution  pneumonia related deaths  heart attacks  asthma Types of engine emissions Exhaust emissions  Unburnt hydrocarbons (HC)  Oxides of carbon (CO,CO2)  Oxides of nitrogen(NO,NO2)  Oxides of sulphur(SO2,SO3)  Particulates  Soot and smoke Non-exhaust emissions  Emissions from fuel tank  Emissions from carburetor  Blow-by gases and fuel vapors from crankcase Hydrocarbons (HC)  Hydrocarbon emission consists of some unburnt part of fuel (nearly 40%) and partially reacted components (60%) not present in original fuel.  For SI engines, exhaust gases contain up to 6000 ppm or 1-1.15% of fuel.  Their emission is strong function of equivalence ratio. Higher its value (ie richer fuel) more unburnt fuel so more amount of emissions.  Emissions are high during starting and accelerating when mixture is richer  Too lean mixture also results in incomplete combustion so higher HC emissions Parameters affecting HC emissions  Type of fuel

 Equivalence ratio  Combustion chamber geometry  Valve timings  Speed and other operating parameters Effects  In air they act as irritants and odorants  Some of them are carcinogenic  They react with atmospheric gases to form photochemical smog Causes of HC emissions  Incomplete combustion  Crevice volumes and flow in crevices  Leakage past the exhaust valve  Valve overlap  Deposition on walls  Oil on combustion chamber walls Incomplete combustion  Improper mixing:• Due improper mixing or lack of swirl fuel particles do not find enough oxygen to react  Flame quenching:• As the flame goes close to the walls it gets quenched at the walls leaving unburnt fuel • Expansion of gases in power stroke retards combustion which causes HC emissions • High exhaust gas contamination also results in flame quenching at low loads and idle conditions  This problem can be solved by using multiple spark plugs at appropriate locations and restricting bore and stroke of combustion chamber Exhaust valve leakage  High pressure during compression and combustion, causes mixture to escape around exhaust valve and between the valve and valve seat  When the exhaust valve opens , fuel in crevice volumes gets carried into exhaust manifold  This does not contribute much towards pollution (nearly 2-3 %) Valve overlap  Valve overlap is generally kept to ensure complete combustion and proper scavenging  During valve overlap both intake and exhaust valve are simultaneously open, which can cause some fresh charge to directly escape with the exhaust  As valve overlap is in terms of crank angles, overlap time in milliseconds is high during low speed and idle

 Thus effect on pollution is most severe in these conditions  Properly located intake and exhaust valves can minimize this type of pollution Absorption due to deposits on wall  Fuel and other gas particles get absorbed by the deposits on walls of combustion chamber  This absorption is a function of gas pressure  As pressure is high during compression and combustion , rate of absorption is high  Later in the cycle as exhaust valve opens, pressure is reduced, so the gas particles (including HC) are desorbed back to the cylinder. These gases come out with exhaust and cause pollution  High compression ratios cause more pollution  Some additives when used with fuel reduce deposit build-up in engines  High swirl also helps in keeping deposits to a minimum OXIDES OF NITROGEN (NOX) • Exhaust gases of an engine has up to 2000 ppm of oxides of nitrogen (mostly NO with small amounts of NO2). • Oxides of nitrogen can be represented as NOX, where, X-some suitable no. • Sources for formation of NOX : 1) Mostly from N2 in air. 2) Fuel which contains N2 and trace amounts of NH3, NC, HCN. • Some reactions that occur during combustion and immediately after it are: O + N2 à NO + N N + O2 à NO + O N + OH à NO + H NO, in turn, forms NO2 : NO + H2O à NO2 + H2 NO + O2 à NO2 + O • In the temperature range of 2500-3000 K which prevails in the combustion chamber of an engine , some diatomic nitrogen (N2) (which is stable at low temperatures) breaks down to mono-atomic nitrogen (N): N2 à 2N • Other gases that contribute to formation of NOX at high temperatures are O2 and water vapor. O2 à 2O H2O à OH + ½ H2 • Chemical kinetics show that, higher the combustion reaction temperature, the more N2 will dissociate to N, and more NOX will be formed