FIGHTBACK TECHNOLOG IES
The reason that diesels fell out of favour was poor real-world emissions results (that infamously led to Dieselgate). It therefore makes sense that engineers target the main concern head-on: proving diesels can be environmentally friendly, but can also comply with the strict Euro 7 emission standards that regulators are planning for 2023. According to Siegfried Pint, with the introduction of Euro 7, there will be no difference between the emissions requirements for diesels and petrols, placing the two ICE types on an equal footing. 48 V MILD-HYBRID SYSTEMS This technology consists mainly of an integrated starter motor (ISG) and a small lithium-ion battery pack (round 0,5 kwh) that runs a 48 V system. The ISG is an electric motor connected to the engine via the auxiliary belt and can recuperate vehicle kinetic energy during braking or downhill situations by generating electricity when the vehicle’s brakes are applied. In the upcoming new Audi A8, the system generates up to 12 kw of electric power.
Using this stored electric energy, it can also perform a boosting function by adding to the engine output. This system lowers emissions in both diesel and petrol powertrains, but in diesels, known for high levels of noise, vibration and harshness, it offers a much smoother stop/start function than achieved with the conventional starter motor. ELECTRICALLY HEATED CATALYSTS With regard to catalytic converters, a downside of a diesel engine is that its exhaust gas is much cooler than the equivalent petrol version’s. This means long heat-up times for catalysts that function efficiently only at operating temperature. However, a new type of catalyst, showcased by Continental at the 2017 Techshow, has an electric heater element that improves heat-up times considerably and keeps the catalyst at optimum temperature. This helps further lower emissions during, for example, low loads or when the engine stops during stop-start system operation. This tech, together with a 48 V mild-hybrid system, was demonstrated on a Volkswagen Golf GTD, the result of which was 60% less CO emissions compared with the standard car. Selective catalyst-reduction systems and diesel-particulate filters (DPF) are mandatory after-treatment systems to meet strict emissions regulations.
DOUBLE-DECKER INTAKE MANIFOLDS
To achieve efficient and complete diesel combustion and minimise emissions, it is important that all the diesel that’s injected mixes with the air before combustion takes place. To achieve this, two techniques are employed: swirl, where the air circles the combustion chamber; or tumble, where the air tumbles like a wave into the combustion chamber during the intake (and compression) stroke.
For the first time, Audi is employing a double-decker intake manifold design in its new 3,0-litre TDI engine in which the air can either flow through the top or bottom sections, resulting in either swirl or tumble. This allows engineers to choose the most efficient method of mixing depending on the engine’s speed and load condition. High-pressure injection systems (2 500 bar) and multiple injections per cycle help further.
As we know, eliminating turbo lag improves driveability in turbocharged engines. Having an electric turbocharger in parallel with the conventional turbo achieves zero lag because the electric unit can reach peak boost in less than a quarter of a second. Thereafter, the conventional turbo takes over. The turbo is powered by the 48 V mild-hybrid system we mentioned earlier and this technology is used on diesel and petrol engines. The Audi SQ7 TDI is the first production model featuring this tech.
LOW-PRESSURE EGR SYSTEM
During part-load conditions in a diesel, some of the burnt exhaust gasses are recycled back into the intake to lower the oxygen content in the combustion chamber via the exhaust gas-recirculation (EGR) valve. The effect is reduced combustion temperatures during the part-load condition and fewer NOX emissions. The traditional, high-pressure EGR system routes hot exhaust gases before the turbo back to the intake manifold after the intercooler. The problem is that the pressure differential is not enough to allow adequate EGR flow rates. A new system is now used which takes colder exhaust gas after the DPF and pipes it to the intake system before it gets to the turbo’s compressor. Adding low pressure EGR flow to the high EGR flow further reduces emissions.
THE AUDI SQ7 IS THE FIRST PRODUCTION CAR WITH AN ELECTRIC TURBOCHARGER
Golf GTD fi ed with Continental emission test device.