Volkswagen’s engineers say there are a number of improvements that come courtesy of the improved thermodynamic efficiency associated with Miller Cycle engines. An increase in the geometric compression ratio has, according to VW, allowed for improved efficiency in the load range most customers will actually use, while the final compression temperature has been lowered through early closing of the intake valve and the expansion cooling that brings.
As with Audi’s recently introduced turbocharged 2.0L 4-cyl., the new 1.5L adopts the Miller combustion cycle process and runs a comparatively high compression ratio of 12.5:1, up from 10.5:1 for the current 1.4L.
Further developments used by the new engine include a variable-vane turbocharger, newly developed fuel-injection system designed to operate at up to 5,075 psi (350 bar), a revised cylinder head with new hydraulic camshaft actuators and a cylinder-on-demand system that closes down the middle two cylinders on light throttle loads.
VW says reduced inertia and the lastest direct injection technology – which uses a smaller injector tip of 6mm that works at up to 350bar of pressure – also gives the new TSI engines faster response rates and cleaner exhaust emissions. This should help the range to conform to the next phase of European CO2 limits, which will require manufacturers to lower the average CO2 emissions of their line-up to 95g/km from 2020.