Diesel Particulate Filters. Separating Fact From Fiction
Diesel particulate filters, known as DPF systems, are currently being fitted from new to a vast variety of diesel-engine cars and commercial vehicles. On paper, they seem like an excellent idea, however, in actual operation they may not be. The filter is intended to remove minute particles of soot (carbon compounds) from vehicle exhausts and is being fitted by manufacturers in order to help cars vans and lorries meet various government standards worldwide for exhaust emissions. The system comprises a physical filter, fitted in the exhaust system and usually very close to the engine.
Many types of DPF units are made at present, but the majority use ceramics, metal mesh, cordierite, or silicon carbide for the internal filter. Experiments have been carried out on designs that use gas swirl to remove particles, but none are currently fitted to cars. Instead, the models currently available all work by forcing the gas through the unit. Whilst effective, this process creates back pressure in the exhaust and is inefficient, leading to a reduction in possible performance and, somewhat ironically, an increase in fuel consumption.
There is an on-going debate as to whether or not DPF is actually effective or not. To a large extent, carbon particles are the result of poor combustion and modern electronic engine management systems should be capable of enough fine tuning to ensure correct running in the first place. This is especially so in most European countries, where the quality of diesel fuel is relatively high. DPF systems are expensive and they add weight, so why do manufacturers continue to fit them? As with many things, the explanation is economies of scale and the manufacturing and distribution system. Cars and commercials need to be sold across arrange of countries, where operating conditions and fuel quality is variable at best. Because of the need to switch production for one market to another, it is simplest for makers to set a common, comparatively low standard for engine management and then add the filter.
Even ignoring the issues of performance and economy, diesel particulate filters suffer from a major issue with use, which is the fact that they relatively quickly become blocked. Manufacturers recognise this and use a process called regeneration. During this, the filter is heated until it reaches a temperature high enough for the carbon to be burned off. For large commercial vehicles, this is usually achieved by chemical or electrical heating, but for passenger cars this is impractical for various reasons. In normal cars therefore, the process of regeneration is achieved by driving the vehicle at a fairly high speed for some distance. As commentators rightly point out, this is not only a problem for people who drive mainly in towns, but is also somewhat counterproductive, as it means that more fuel is used and more emissions produced.
With this in mind, it is becoming debatable whether in most European countries, the use of DPF filters is beneficial at all. The units sometimes become completely blocked and are rendered useless. Replacement is complex and very costly and to many people, inside and outside the motor trade, DPF removal appears a sensible solution. This involves removing the unit entirely, together with the associated electronic sensors, and replacing the section of exhaust with a simple pipe. However, this alone is not sufficient. In order to meet relevant standards, and to ensure correct running, the engine management computer must be correctly and accurately re-programmed. This requires specialist equipment, expensive software, and correct training. However, many specialist garages now offer this service and when carried out correctly, DPF removal virtually guarantees better running, no increase in emissions, and improvements to both fuel consumption and performance. Not to mention removing the need for any regeneration.
If a warning light concerning the DPF system comes on in your vehicle, it is essential to get the system checked as quickly as possible. If you don't, then serious damage can occur. You may well decide that DPF removal is the best option. But then you might have already decided that even if there doesn't seem to be any problem!
Many types of DPF units are made at present, but the majority use ceramics, metal mesh, cordierite, or silicon carbide for the internal filter. Experiments have been carried out on designs that use gas swirl to remove particles, but none are currently fitted to cars. Instead, the models currently available all work by forcing the gas through the unit. Whilst effective, this process creates back pressure in the exhaust and is inefficient, leading to a reduction in possible performance and, somewhat ironically, an increase in fuel consumption.
There is an on-going debate as to whether or not DPF is actually effective or not. To a large extent, carbon particles are the result of poor combustion and modern electronic engine management systems should be capable of enough fine tuning to ensure correct running in the first place. This is especially so in most European countries, where the quality of diesel fuel is relatively high. DPF systems are expensive and they add weight, so why do manufacturers continue to fit them? As with many things, the explanation is economies of scale and the manufacturing and distribution system. Cars and commercials need to be sold across arrange of countries, where operating conditions and fuel quality is variable at best. Because of the need to switch production for one market to another, it is simplest for makers to set a common, comparatively low standard for engine management and then add the filter.
Even ignoring the issues of performance and economy, diesel particulate filters suffer from a major issue with use, which is the fact that they relatively quickly become blocked. Manufacturers recognise this and use a process called regeneration. During this, the filter is heated until it reaches a temperature high enough for the carbon to be burned off. For large commercial vehicles, this is usually achieved by chemical or electrical heating, but for passenger cars this is impractical for various reasons. In normal cars therefore, the process of regeneration is achieved by driving the vehicle at a fairly high speed for some distance. As commentators rightly point out, this is not only a problem for people who drive mainly in towns, but is also somewhat counterproductive, as it means that more fuel is used and more emissions produced.
With this in mind, it is becoming debatable whether in most European countries, the use of DPF filters is beneficial at all. The units sometimes become completely blocked and are rendered useless. Replacement is complex and very costly and to many people, inside and outside the motor trade, DPF removal appears a sensible solution. This involves removing the unit entirely, together with the associated electronic sensors, and replacing the section of exhaust with a simple pipe. However, this alone is not sufficient. In order to meet relevant standards, and to ensure correct running, the engine management computer must be correctly and accurately re-programmed. This requires specialist equipment, expensive software, and correct training. However, many specialist garages now offer this service and when carried out correctly, DPF removal virtually guarantees better running, no increase in emissions, and improvements to both fuel consumption and performance. Not to mention removing the need for any regeneration.
If a warning light concerning the DPF system comes on in your vehicle, it is essential to get the system checked as quickly as possible. If you don't, then serious damage can occur. You may well decide that DPF removal is the best option. But then you might have already decided that even if there doesn't seem to be any problem!
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