The 16-valve, 150 bhp version is focused on delivering enhanced performance, while the 8-valve, 120 bhp configuration places a greater emphasis on low cost of ownership.
Compared to the 2.2 TiD unit it replaces, the 150 bhp 1.9TiD engine offers 20 per cent more power and 12.5 per cent more torque, as well as greater running refinement, reduced CO2 levels, and improved fuel consumption. Increased power translates to sparkling on-the-road performance. In-gear acceleration, the most important feature for everyday driving, is on a par with the top-of-the-line 9.3 Aero model while the zero to 60 mph dash, of rather less importance, is still accomplished in a brisk 9.3 seconds.
The 8-valve version returns fuel economy of 49.2 mpg (5.8 litres/100 km)* over the combined cycle, a useful 12 per cent improvement against the outgoing 2.2 TiD. CO2 emissions of 57 g/km* show an 11 per cent reduction.
Both new engines share the same four cylinder, cast-iron block and an alloy cylinder head. There are twin, chain-driven, overhead camshafts and hydraulic tappets for the 16-valve engine, and a single camshaft for the 8-valve format. Both have a steel crankshaft and connecting rods, a dual-mass flywheel, a weight-saving pressure cast aluminium intake manifold and electronically-controlled exhaust gas re-circulation (EGR) for quick warm-up and low emissions.
Common rail technology provides consistently high injection nozzle pressures of 1,600 bar, independent of the prevailing engine speed or load. This platform allows the use of small, multiple injections of fuel, between two and five, to release as much energy as possible from a given amount of fuel.
This extremely efficient combustion process pays dividends in a number of key areas. Apart from improving fuel consumption, emissions and power, it is crucial in helping to iron out the strong vibrations traditionally associated with compression ignition.
The Bosch ECM continually adjusts the number, frequency and size of the injections according to three main parameters: current engine speed, requested throttle setting and engine coolant temperature. Each injection pulse may be separated by as little as 150 microseconds, delivering a quantity of fuel as tiny as one cubic millimetre.