New Astra recall for engine emissions tweaking

Vauxhall Astra SRi CDTI

4.66 The testing results of the Astra raised concerns in terms of NOx.

4.67 Initial tests showed that the Astra failed the laboratory NEDC (cold and hot) tests. We arranged for a second vehicle to be tested to check that it wasn't an issue with that specific vehicle. Although the second vehicle passed the NEDC (cold) test, it did exhibit significantly increased NOx when running the NEDC (hot) test.

4.68 When we shared the results with Vauxhall they offered a number of possible explanations for the results, none of which were convincing.

4.69 We were surprised that NOx emissions had increased to more than twice the legislative limit when tested on the NEDC (hot) cycle in a condition where the vehicle would not know it was under test. This is a standard cycle in which the vehicle is not driven aggressively. WLTP (track) and RDE test results also showed high NOx. Vauxhall explained that they had not conducted a WLTP (track) cycle test for this vehicle so were unable to comment but they had carried out RDE tests and found similar results to MSU.

4.70 Vauxhall highlighted that the engines for these vehicles had been developed some time ago (2013/14) and were used in the previous generation Astra. Since that time, expectations have changed and all of their newer models contain an SCR system, rather than just LNT. Therefore, the high NOx on the RDE test could be expected from a vehicle which had no SCR system.

4.71 On the request of the manufacturer, the vehicle was retested. Vauxhall engineers inspected the vehicle and downloaded codes/data from the ECU. The preconditioning and DPF regeneration were both carried out the same day. The vehicle was tested the next day; NEDC (cold) followed by NEDC (hot).

4.72 Vauxhall shared with us that they are currently working with the German approval authority, KBA, to develop a recalibration of the emissions control system to improve emissions performance. Vauxhall expect the recalibrated software to reduce NOx emissions in the real world by about 50%.

4.73 Approval of the modification is still pending. Following approval, Vauxhall will apply the modification to all vehicles across Europe, including the 13,864 vehicles in the UK. Vauxhall will offer this upgrade to UK customers via direct mail. Vauxhall have informed us that the upgrade will be free of charge for customers and will take approximately 30 minutes.

4.74 It was agreed with Vauxhall that we will test a recalibrated vehicle to validate whether emissions in the real world are reduced. We expect to publish the results in the next report.

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Lean NOx Trap (LNT)

Unlike a petrol engine, a diesel engine's exhaust is 'lean' - a term meaning it has excess oxygen present. As a result, a standard catalyst cannot convert NOx emissions. A lean NOx trap is a device which looks similar to a standard catalyst, but which acts as a molecular sponge, chemically trapping NOx emissions (by adsorption) rather than converting them. The amount of NOxa trap can hold is dependent on its temperature. The optimum temperature window is typically around 250-450°C. However, once the trap is full, it can't adsorb any more NOx. The trap must therefore be periodically 'purged' by briefly creating 'rich' conditions (excess fuel) in the exhaust. When this happens the trap releases and simultaneously converts the NOx to nitrogen and water vapour. The frequency with which this happens will depend on the system and the driving conditions, but it is typically several times an hour.

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Selective Catalytic Reduction (SCR)

SCR is an alternative catalyst system that is able to convert NOx even under 'lean' exhaust gas conditions. The reaction takes place with ammonia (typically supplied as AdBlue) in the presence of a catalyst, either oxides of base metals (such as vanadium, molybdenum and tungsten), zeolites, or various precious metals. To be efficient, the SCR must be at its nominal operating temperature (350-450 °C) and it can reduce NOx emissions by up to 95%. Critically, unlike the other systems described here, SCR relies on a consumable reagent (to provide the ammonia) and only reduces emissions whilst the catalyst is being supplied or "dosed" with this reagent. As a result, regulations require a visible and audible driver warning when reagent levels are low and that vehicle performance is restricted or engine restart is prevented if the driver fails to refill the system

The temperature of the SCR is determined primarily by the exhaust gas. Therefore, the placement of the SCR in relation to the engine and the engine's duty cycle are critical with respect to the SCR's performance. The SCR canister is relatively large. In addition to the SCR, the following are also required:

• AdBlue tank - the AdBlue dosing rate will vary by engine and vehicle but this tank will be sized to avoid vehicle owners having to refill too frequently. The tank also contains heaters and sensors.
• A dosing pump - to pump the AdBlue from the tank into the exhaust pipe just before the SCR.
• A control module - to control the amount of AdBlue added.
• Pre and post SCR NOx sensors - to ensure that the SCR system is operating correctly.

Although readily available, the main design constraint is the amount of space needed for the installation.

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Pompeydave said:

Don't think it's just vx cars with these emission problems , VW caught out big time and splattered all over the TV / internet vauxhall could get away with this quietly if they play their cards right. Maybe mentioned in a few car mags but that's about it.
But they are all up to it with these emissions scams , my son-in-law is an mot tester and and some stories he tells are nothing short of amazing. A lot of "smaller" manufacturers have recalled vehicles that's gone under the radar of everyone and have got away with it........just.

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