Reduction of Diesel Emissions Andy, Nick and Elliott
Methods of reducing Emissions. Modern diesels engines are fitted with an array of emission reducing devices, these can consist of EGR valve, DPF and Catalytic Converter. EGR Valve: The EGR valve, or Exhaust Gas Recirculation valve, is a vacuum controlled valve which allows a specific amount of exhaust gas back into the intake manifold. This exhaust mixes with the intake air and actually cools the combustion process. Cooler is always better inside the engine. The exhaust gas the EGR valve recirculates also prevents the formation of Nitrogen related gases. These are referred to as NOX emissions, and are a common cause for failing emissions testing. Unfortunately, the EGR valve can get stuck, caused by a build up of carbon, causing NOX gases to build up. If the EGR valve is stuck or malfunctioning a vehicle will experience symptoms like rough idle and bucking on acceleration. MPG will also suffer, and you may see a Check Engine light.
DPF (Diesel Particulate Filter) Diesel Particulate filters (DPF) or 'traps' do just that, they catch bits of soot in the exhaust. As with any filter they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration' – the collected soot is burnt off at high temperature to leave only a tiny ash residue. Regeneration comes in two forms. Passive regeneration Passive regeneration takes place automatically on motorway or fast A-road runs when the exhaust temperature is high. Because many cars don't get this sort of use vehicle manufacturers have had to design-in 'active' regeneration where the engine management computer (ECU) takes control of the process. Active regeneration When the soot loading in the filter reaches a set limit (about 45%) the vehicle's ECU will initiate post combustion fuel injection to increase the exhaust temperature and trigger regeneration. If the journey is too short while the regeneration is in progress, it may not complete and the warning light will come on to show that the filter is partially
blocked. It should be possible to complete a regeneration cycle and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph. If a regeneration cannot be carried out, due to short stop/start journeys, then this can force the vehicle to go into limp mode, this can then only be rectified by the vehicle going to a specialist or main dealer to have forced regeneration carried out.
DPF Additives Use of an additive lowers the ignition temperature of the soot particles and the engine management ECU raises the temperature of the exhaust gas so the filter can be regenerated. The Additive The additive is stored in a separate tank. It is difficult to establish it’s precise chemical composition, but it is described as an iron-rich substance dissolved in a hydrocarbon mixture. It works by allowing the carbon particles trapped in the particulate filter to burn at a significantly lower temperature than would usually be required (500ºC rather than 600 - 650ºC). This means that the particulate filter can be regenerated at part throttle. The additive automatically mixes with the fuel at every fuel tank fill up. The fuel tank sender sends information to the engine ECU about how much fuel has been added. The engine ECU then actuates the particulate filter additive pump. Additive is supplied to the main fuel tank so that the concentration of iron molecules in the fuel is 10 parts per million. In practical terms this means you need 1 litre of additive to 2800 litres (about 620 gallons). Peugeot and Ford are just some of the manufactures that use additives in the operation of their DPF
Catalytic Converter. A catalytic converter is a vehicle emissions control device that converts toxic exhaust gas to less toxic pollutants by catalyzing a redox reaction (oxidation or reduction). Catalytic converters are used in internal combustion engines fuelled by either petrol (gasoline) or diesel including lean burn engines. It is used as a catalyst to convert three harmful compounds in car exhaust into harmless compounds. The three harmful compounds are: Hydrocarbons (in the form of unburned gasoline) Carbon monoxide (formed by the combustion of gasoline) Nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen For the catalytic converter to work efficiently it need to get up to a high working temperature. The normal operating temperature of the converter can range up to 1,200 to 1,600 degrees Fahrenheit. The converter needs to reach 400 to 600 degrees to begin functioning. There are two types of catalytic converter, they are two way and three way. Two way has two simultaneous tasks 1.Oxidation of carbon monoxide to carbon dioxide 2. Oxidation of hydrocarbons
Three way catalytic converters (TWC) have the additional advantage of controlling the emission of nitrogen oxides (NOx), in particular nitrous oxide, a greenhouse gas over three hundred times more potent than carbon dioxide. Reduction of nitrogen oxides to nitrogen and oxygen: Oxidation of carbon monoxide to carbon dioxide: Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water
Specialist Fuels Some fuel manufactures are now also offering fuels that can help with reducing emissions, they do this with additives that actively clean the engine from the inside. Shell is one company that has introduced this type of fuel, taken from their website they declare the following for their Nitro V+ fuel: • It’s specially formulated for increased cleanliness and protection of diesel fuel injection systems. • It contains anti-rust components designed to prevent corrosion of precision-engineered fuel injection systems. • Designed to act the moment it hits your engine to restore and maintain engine power through active protection. Esso is another company that is actively promoting its range of cleaner diesels, they say this of their Supreme range of fuels: Our Supreme Diesel contains twice the detergent additives of our standard diesel, which helps give a deeper clean of your fuel injectors to help give better engine performance.