Combined solution reduces particulate emissions

Keith Howard and Bob Cawdell, of Lubrizol ECS, describe how a combination of oxidation catalysts and filters can have a significant impact on the reduction of particulate emissions, resulting in tangible health benefits

Particle emissions from diesel powered vehicles are causing deaths across Europe. Studies indicate that air pollution related deaths in Europe, outnumber deaths from road traffic accidents by a factor of around two to one. Compared to other European countries, UK roads have fewer accident related deaths, and are far more congested, so we should be especially concerned. Apart from the immediate problems related to asthma and bronchitis, more and more evidence links diesel particulate emissions with serious long-term illnesses including lung cancer and heart disease.

So what are these particles? The core of a diesel particle is created during the incomplete combustion of the injected fuel. Particles grow as they cool on their way through the exhaust system. Individual particles agglomerate, and other materials then condense onto the surfaces these provide. The resulting particles range in size from a few nanometres (millionths of a millimetre) to a few microns (thousandths of a millimetre). In recent years more emphasis has been placed on finer particles due to their ability to penetrate deeply into the lungs, and even into the bloodstream.

Tackling particulate

There is good news, however. There are straightforward ways to reduce or virtually eliminate particulate matter on existing vehicle fleets, and there are grants from the government's Energy Savings Trust "clean-up" fund to help operators do it. Lubrizol Engine Control Systems (ECS) oxidation catalysts and particulate filters are easily installed into the exhaust lines of existing vehicles, they are often a direct replacement for the existing silencer. From the moment you start the engine after installing a catalyst or filter you are reducing the output of particulates from your vehicle, and ultimately helping to reduce particulate related health problems.

Oxidation catalysts work by "burning off" much of the material which has condensed onto particle surfaces, mainly turning it into water and carbon dioxide. Overall particulate output can be reduced by 25 to 50%. Lubrizol ECS produce a range of oxidation catalysts covering almost any diesel application.

Filters trap particulates in the fine pores of their ceramic walls. They are extremely efficient, often reducing the particle count by over 99%. The collected particulate matter must then be burned off fairly regularly (known as "regeneration") in order to prevent filter blockage. The collected matter would normally need temperatures of over 500 Celsius to burn (this is well above the normal operating range of a typical diesel engine exhausts). One way around this need for high temperatures is to give the filter a "helping hand" in the form of a coating of catalyst material, which significantly reduces the regeneration temperature.

The Lubrizol ECS Purifilter™ combines a high durability silicon carbide ceramic core with a precious metal catalytic coating to reduce regeneration temperatures. The Silicon Carbide ceramic core is capable of withstanding much higher physical and thermal stresses than Cordierite materials common in most particulate filters. Silicon Carbide allows the temperature (and therefore regeneration and burning of the collected particulate matter) to propagate rapidly thorough the filter, which reduces the potential for incomplete regeneration and exhaust back-pressure increases. ECS refers to the combination of Silicon Carbide and the Catalytic coating as "Heat Sense" technology.

A vehicle with exhaust temperatures in the range of 280 to 320 Celsius, or higher, for 25% of the duty cycle will satisfy the requirements for Purifilter regeneration. Lubrizol ECS engineers work closely with customers at their site to monitor vehicles and verify that conditions for reliable operation are met before any filters are sold.

Stop-go vehicles

Though many vehicles have exhaust temperature sufficient for the regeneration of catalysed particulate filters, most trucks operating within urban areas are used in stop-go situations (for example, refuse collection vehicles, local delivery vehicles and maintenance vehicles) and therefore the exhaust temperatures can be too low for complete "passive" regeneration during normal uses.

Lubrizol ECS has recognised that these are the very vehicles that operate in highly populated areas, and that the need to purify the exhaust from these types of vehicles is essential to reduce the health effects of diesel emissions and improve air quality.

The combination of a well proven electrically assisted regeneration process with the catalysed Purifilter™ allows these low temperature operation vehicles to operate cleanly.

The electrically regenerated system, which was developed by ECS Europe (formally Unikat) has been used for almost twenty years on off-road vehicles. Called the CombiFilter™, this system has an impressive pedigree, and has significantly improved the working environments in mines, tunnels, constructions sites, and warehouses.

The combination of Purifilter™ and CombiFilter™ enables users to benefit from VED rebate. It is also approved by the Energy Saving Trust and therefore will receive a cost saving grant towards purchase.

For fleet and local authority operators, Lubrizol ECS is able to provide a profile of fleet emissions. This service will estimate the current emissions of the fleet, and provide model based guidance on the most cost effective approaches in reducing emissions. As Lubrizol ECS has a wide range of emissions solutions they are able to use the model to identify a "best practice" approach to emission control and vehicle exhaust purification.



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