According to WHO, ambient air pollution, in both cities and rural areas, was estimated to cause 4.2 million premature deaths worldwide in 2016; this mortality, it says, comes from exposure to PM2.5, which can cause cardiovascular and respiratory diseases, and cancers. The new BS-VI regulations cut PM by more than 80% from current limits. In addition, BS-VI introduces a limit for particulate number (PN) as a new parameter, with a limit of 6 x 10 #/Km.

India particulate matter limits

maintained at ~350°C for a significant time period during vehicle operation. However, the low average speeds, frequent start/stop events, lengthy idling periods and short distances typical of city driving can make passive regeneration conditions difficult to achieve, which hinders regeneration efficiency.

It is therefore likely that high frequencies of active regeneration events will be required in India’s predominantly city-based diesel vehicles. Active regeneration is the combustion of soot in oxygen, which occurs at temperatures exceeding 550°C. To achieve these high exhaust gas temperatures, post or late fuel injection strategies are required, which means active regeneration often incurs a significant fuel economy penalty. The combination of these factors means the European aftertreatment layout may not, in all cases, be the most suitable for Indian OEMs.

Diesel particulate filters Diesel particulate filters are one of the exhaust gas aftertreatment options that have been adopted as an effective means of reducing both PM and PN. To comply with the strict limits in BS-VI the introduction of DPFs in Indian diesel vehicles seems inevitable.

These devices are very efficient at trapping the soot and fine particles contained in the exhaust gas; preventing their release out of the tailpipe. However, over time the trapped soot accumulates in the filter, which if not removed increases backpressure. High backpressure, caused by an overloaded DPF can compromise engine performance, increase fuel consumption and eventually lead to DPF failure or vehicle breakdown. To prevent this, the DPF must be periodically regenerated to remove the soot. However, the efficiency of regeneration is dependent on the exhaust gas temperature and thus on driving conditions.

Catalysed DPF (cDPF) is the most common particulate trap technology currently used in European vehicles. Here, the cDPF’s platinum catalytic coating is used to convert nitrogen oxide (NO) in the exhaust to nitrogen dioxide (NO2

). The NO then reacts with soot at low

temperatures and provides continuous soot burning, which is known as passive regeneration. For effective passive regeneration, exhaust temperatures must be

Unlike cDPF technology, the FBC system relies on oxygen to achieve soot combustion in the filter. Because the FBC enables faster regeneration at lower temperatures it is highly suited to city driving conditions and is completely independent of NOx concentrations.

The FBC additive, which has been VERT (Verification of Emission Reduction Technologies) certified, has been successfully used in the field for over 250 billion vehicle kilometres. With the growing worldwide adoption of DPFs, Infineum commissioned a study to compare different regeneration strategies in Euro 5 engines fitted with either a cDPF or an uncatalysed (bare) DPF with FBC.

Results of DPF regeneration study The results of the study show that the FBC can achieve faster active regeneration at lower temperatures than the cDPF. This is highly beneficial in city driving, allowing a greater opportunity for complete regeneration to take place, whilst the lower temperatures keep the DPF, and any other aftertreatment technology in use, in better condition.

OEM costs can be reduced by removing platinum group metal (PGM) content from the DPF. And, building on this, as the FBC lowers the temperature required to achieve active regeneration and is independent of NOx concentration, the option to reduce the PGM content of the diesel oxidation catalyst is also provided.

Continued on page 16 LUBE MAGAZINE NO.148 DECEMBER 2018 15

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