RAC Cars News


Technological advancements to increase the appeal of diesel cars

By raccars Published

VW Golf

Technological advancements aim to enhance the appeal of diesel engines by reducing emissions.

Diesel cars haven’t received the best press in recent times as a result of the emissions they create but technology is charging forward to help secure the future appeal of this engine type.

New NOx diesel after-treatment systems, for example, allow the engines to match petrol when it comes to nitrogen oxide production.

Many automotive propulsion experts are now predicting that the new after-treatments will solve issues concerning air quality and emissions and should be in-play by the time Euro 6.2 begins to be enforced in driving emission tests in 2017.

The pros and cons of diesel cars

Diesel engines run on a fuel that is denser, meaning that they can produce around 15 per cent more energy in comparison to a petrol engine. Diesels are also known to be around 20 per cent more efficient.

The downside for diesel cars is that their engines typically create 2.65kg of C02 for every kilo consumed. Petrol, meanwhile, produces 2.3kg per kilo, although as a diesel engine uses a 25 per cent reduction in fuel compared to a petrol equivalent, it actually produces 15 per cent less CO2.

It is this fuel efficiency that is expected to be vital when car markers start having to avoid fines for each gram of CO2 that is produced in excess of 95g/km. With fines of €95 for every gram over - for each car sold - it is little wonder that manufacturers are also keen to embrace technology such as the exhaust after-treatment systems.

Diesel car after-treatments explained

Various EGT or exhaust gas treatment systems can be used depending on the size of the vehicle and its engine.

Bosch has created the Denoxtronic system in order to lower NOx emissions in diesel engines by as much as 95 per cent when combined with a Selective Catalytic Reduction or SCR catalytic converter. This allows nitrogen oxide emissions to be converted into nitrogen and water.

Variable compression ratio (CR)

Variable compression ratio technology is being used to boost fuel efficiency under different loads by adjusting an engine’s compression ratio as it works. Higher loads need lower ratios in order to operate to maximum efficiency and vice versa. Variable compression engines mean that the volume over the piston can be changed at what is known as Top dead centre.

Cylinder deactivation in diesel cars

The VW Golf is already making use of cylinder deactivation, although this is currently limited to its 1.4-litre petrol engine. Can it be employed for diesel?

Dynamic Skip Fire or DSF from Tula Technology uses digital signal processing derived from audio electronics to continuously change the number of cylinders which are firing at any given moment. This means that engine load does not have to have an impact on diesel exhaust temperature.

This sort of temperature control is important given that after-treatment devices - including those involving SCR catalysts and NOx traps - can be compromised by the wrong temperatures.

After-treatment systems have quite a narrow temperature window in which they can be effective, whilst the use of SCR and NOx traps at low loads can mean that after-treatment systems struggle when the exhaust is too cold.

DSF offers the opportunity to control exhaust temperature in order to promote the efficient working of after-treatment devices.

Electric charges

Pierburg’s electric AirCharger can improve the efficiency of engines when vehicles are travelling at low speeds. The eAC can bridge the turbo lag gap associated with low speed and engine load and more rapidly help to create the right temperature for efficient working of SCR.

This is said to have the potential to boost fuel economy by between three and five per cent and, therefore, reduce emissions. The eAC is expected to be seen in a small diesel engine during 2017 or 2018.

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