Audi is targeting high-performance diesel engines with a specific output of 100kW per litre, challenging the power dominance of petrol engines relative to the same capacity.
That could mean a future Audi 2.0-litre turbo-diesel that produces 200kW of power, or roughly identical to the same-capacity petrol turbo engine currently used in the Audi S3. The highest power a 2.0-litre turbo diesel makes in an Audi model available today is 140kW.
Speaking at an Audi TDI technology workshop in Sweden, head of V6 TDI development Sven Beechle explained that new injector technology and increased boost pressures for turbo-diesel engines will deliver more power and reduced emissions.
“High-performance [diesel] concepts are being studied,” told Beechle, opening the door for future Audi S and RS diesel models.
Currently, he asserted, the pressure of the common rail direct injection system in Audi models is about 2000 bar, which has risen from 1600 bar on average a decade ago. In the future, Beechle confirmed that Audi is targeting injection pressure of between 2500 bar and 2700 bar, with 3000 bar currently used in racing cars not out of the question either.
“With most engines, Audi uses peak pressures of 2000 bar in the common rail injection system,” the German brand reiterated in a statement.
“The next target is 2500 bar, and the engineers are already thinking beyond this mark.
“The TDI engine in the Audi R18 e-tron quattro race car shows what is possible. The [4.0-litre] V6 uses an injection pressure of over 2800 bar to produce roughly 100kW per litre of displacement.”
Beechle admits that, generally, “the higher the rail pressure the higher the output [but] consumption and emissions are increased”. Yet more precise Piezo injectors are being developed in tandem that according to Audi can be “more precise” with a fuel mixture “that benefits not just power and torque, but also smoothness and quietness.”
Turbocharger boost pressure is also continuing to increase, but it being more intelligently utilised, claims Beechle. An Audi V6 diesel from a decade ago utilised 2.3 bar of boost pressure, compared with today’s bi-turbo V6 diesel accepting 3.2 bar.
According to Audi, new technology is being developed to allow even higher turbocharger boost pressures, naming as one such example: “Steel pistons [are] another option for production models [to] absorb the ignition pressure.”
Electrification of diesel powertrains such as that previewed in the Audi RS5 Concept (above) will in the near future also allow Audi to implement larger, high pressure turbochargers for more top-end power, with a small electrically powered compressor sending immediate boost to the engine to fill any torque hole that would usually be created by using a larger turbo.