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LONDON TAXIS: LIST OF PCO APPROVED EMISSIONS SYSTEM SUPPLIERSA number of system suppliers completed the trials of emissions abatement technology (EAT) for pre- Euro 3 taxis, and demonstrated a capability to meet Euro 3 emission limits. Suppliers listed in the table are eligible to fit approved EAT to pre-Euro 3 taxis to enable these vehicles to continue to operate with a Hackney Carriage plate in London. The Public Carriage Office will inspect taxis fitted with approved EAT prior to registration. | ||||||||||||||||||||||||||||||||||||||||
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1. SCR - Selective Catalytic Filter: a technique for reducing oxides of nitrogen (NOx) in the vehicle exhaust by catalysis 2. DPF - Diesel Particulate Filter: a device which filters exhaust gas emissions, removing solid carbonaceous particles (soot)
3. EGR - Exhaust Gas Recirculation: a technique for introducing a portion of the vehicle exhaust gases into the engine air intake manifold to reduce NOx emissions 4. DOC - Diesel Oxidation Catalyst: a device for reducing particulate and some gaseous pollutant emissions 5. STT - STT Emtec AB, Swedish company specializing in exhaust emissions after-treatment, and in particular, NOx reduction by EGR |
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We describe here briefly the three emissions control systems you are most likely to find fitted on your cab, if any: The STT Emtec CleanCab™ system, the Van Aaken system and the TaxiCat system. | ||||||||||||||||||||||||||||||||||||||||
1. STT EMTEC CLEAN CAB SYSTEMSTT Emtec´s Emission Reduction Technology, CleanCab™ The CleanCab™ system is based upon known technology as turbo charging, exhaust gas recirculation (EGR), intercooler and EGR cooling system, which will convert the existing engine to meet the latest Euro 3 emission standard. The main features of the CleanCab™ system is improved drivability, as the engine will maintain the power, no additional operational cost and no additive required. Just fit and forget, as no extra maintenance is required, only normal vehicle service in accordance with the manufacturer's specification. General description of the CleanCab™ system | ||||||||||||||||||||||||||||||||||||||||
A turbocharger is used to feed air into the engine in order to keep the air-fuel ratio at acceptable levels and optimize the combustion. The boost pressure is controlled by the main STT Emtec electronic control unit, ECU, operating a pulse width modulated valve. The ECU is also controlling the amount of exhaust gases to be recirculated by the EGR valve. The control system is depending on the engine load, speed and temperature. The exhaust gases are cooled by an EGR cooler to reduce the exhaust gas temperature before it is mixed with the inlet air. In addition an intercooler system is added to increase the density of the compressed inlet air. |
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Turbocharger system | ||||||||||||||||||||||||||||||||||||||||
Turbo Garrett |
Turbo Garrett |
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The purpose of turbo charging is not primary to increase engine power, but to increase Air Fuel Ratio, AFR, at intermediate to high load conditions to make it possible to use Exhaust Gas Recirculation, EGR, without significant increase in soot formation. Intercooler system | ||||||||||||||||||||||||||||||||||||||||
Intercooler |
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The purpose of an intercooler is to cool down the compressed air downstream of the turbocharger. The cooled air will reduce the combustion temperature as well as NOx formation, and at the same time also increase Air Fuel Ratio, AFR, due to higher density of the compressed inlet air. Cooled inlet air will also bring down the thermal stress on the combustion components. Exhaust Gas Recirculation, EGR, system The purpose of Exhaust Gas Recirculation, EGR, is to introduce exhaust gas, containing CO2 and water vapor, into the combustion chamber. EGR cooler The EGR-coolers purpose is to decrease the emissions of nitrogen oxides, carbon monoxide, hydrocarbons and particulates. The cooling has to be chosen carefully for optimum reduction of nitrogen oxide emissions. Diesel Oxidation Catalyst, DOC An oxidation catalyst is used to reduce emissions of CO and HC. It also affects the heavy hydrocarbons adsorbed on the particulates. | ||||||||||||||||||||||||||||||||||||||||
Stt Emtec clean cab system fitted to Fairway Driver |
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Stt Emtec intercooler |
Stt Emtec turbo Garrett |
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Stt Emtec system |
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2. VAN AAKEN SYSTEMThe Van Aaken system comprises an EGR valve (Exhaust Gas Recirculation valve) and a combined Diesel Particulate Filter and Diesel Oxidation Catalyst. It also includes a Van Aaken smartbox (Diesel ECU). | ||||||||||||||||||||||||||||||||||||||||
Van Aaken system fitted to a 1997 Fairway Driver (Picture courtesy of Chris) |
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Van Aaken EGR valve control (Picture courtesy of Chris) |
Connections into engine coolant system (Picture courtesy of Chris) |
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Van Aaken smartbox (Picture courtesy of Chris) |
Diesel ECU smartbox |
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3. TAXICAT SYSTEM - THE EURO3 SOLUTION FOR LONDON TAXISThe TaxiCat System has no electronic controls or moving parts. There are no complicated control modules, no drilling into engine components, and no connection into engine coolant system. The system is supplied with a complete stainless steel exhaust. |
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The TaxiCat System is the simplest solution to enable cabs to meet the Euro 3 emissions regulations for London. The benefits of that system are obvious in that there are no moving parts or electronics, and the exhaust purification is based on a "flow-though" catalyst rather than a filter or DPF. A complete stainless steel exhaust compliments the theme of durability and fit-and-forget. A leading catalyst supplier developed a flow-through specifically for the taxi. It was important to resist the temptation of using a particulate filter, or "partial filter" as these devices can easily become problematic after a short period on vehicles that have inconsistent duty-cycles. Differential pressures and flow rates within the exhaust pipe and the engine air intake are used to provide varying amounts of exhaust gas recirculation. This simple approach reduces harmful emissions without the need for electronic controls and moving valves; both of which could be prone to failure. The exhaust to be returned to the the air intake is taken after the catalyst so that it is cleaner and rich in CO2. A complete stainless exhaust was designed to give enhanced exhaust flow rates. This increases the efficiency of the engine by improving its ability to "breathe". Supplying a complete exhaust system also reduces the chances of miss-alignment and poor fitting of partial systems. The high quality stainless steel also eliminates future corrosion problems. The TaxiCat System does not interfere with the engine coolant system therefore there are no increased risks of overheating. There is no drilling of any part of the vehicle or engine, and no need for electronic connections. |
TaxiCat System layout |
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TaxiCat System - Exhaust gas recirculation to air filter |
TaxiCat System - flex-pipe from exhaust manifold to catalyst |
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