The engine uses a new common-rail direct injection system which builds up high injection pressure of up to 1,600 bar (previously: 1,350 bar) even at low revs, and injects the fuel into the combustion chambers with newly developed six-hole injectors, enabling an even more efficient combustion process.

The new fortwo cdi engine. Click to enlarge.

The three-cylinder engine has also adopted two-phase fuel injection from the CDI engines of its sister brand Mercedes-Benz. A few milliseconds before the main injection a small quantity of diesel is injected into the combustion chambers where it ignites and preheats the cylinders. This results in a noticeably quieter combustion noise level than an engine without this pilot injection. The engine control unit calculates how much fuel is needed and the interval at which pilot injection and main injection take place.

A compact turbocharger is housed in the exhaust manifold. The compressor wheel has a diameter of just 31 millimeters, yet it rotates at up to 290,000 rpm and builds up maximum charge pressure of approximately 1,150 millibars. This charge boost enables the engine to provide 85 Nm—more than three-quarters of the maximum torque—at 1,500 rpm. The smart fortwo cdi accelerates from 0-100 km/h in 19.8 seconds and reaches a top speed of 135 km/h (84 mpg).

As with the earlier models, the engine of the smart fortwo is fitted transversally in space-saving mode in front of the rear axle and inclined at an angle of 45 degrees towards the rear. The consistent use of lightweight materials means that the diesel engine weighs in at just 86 kilograms. The crankcase features a state-of-the-art diecast aluminium bedplate design and the cylinder head and cylinder head cover are likewise made of aluminium.

The three-cylinder diesel engine controls emissions in two stages. The high-tech common-rail injection and the efficient combustion process deliver a low level of engine-out emissions.  Depending on the driving situation and the engine load, up to 60% of the previously cooled exhaust gas is returned to the combustion chambers where it is combusted once again thus greatly reducing nitrogen oxide emissions. The exhaust gas recirculation works with an electropneumatic actuator which enables it to react quickly to changes. An oxidation catalytic converter and an open diesel particle filter are responsible for the aftertreatment of the exhaust gases. These are housed together with the exhaust silencer in a stainless steel case. The smart fortwo cdi is Euro-4 compliant.

The three-cylinder diesel engine works with a newly developed automated manual five-speed transmission which the driver operates by briefly tapping the shift lever on the center console. When briefly pushed forwards the transmission shifts to the next highest gear. Gently pulling the shift lever backwards is sufficient to shift down. Shift paddles on the steering wheel are optionally available and come as standard in the pulse model line. An automatic transmission mode is also available for all equipment variants.

The clutch is opened and closed by an electric motor—there is no clutch pedal in the new smart fortwo cdi. To enable quick intermediate spurts the smart engineers have developed a kick-down function that is activated with the accelerator pedal. This enables the driver to spontaneously change down by one or two gears and to make even better use of the engine’s low-speed torque.

The new smart fortwo cdi also features an extensive range of safety equipment making it, according to DaimlerChrysler, one of the safest cars in its class. The fortwo offers an anti-lock braking system (ABS) with electronic brake-force distribution, electronic stability programme (ESP), brake assist, full-size airbags for driver and passenger, seat belts with belt tensioners and belt-force limiters, safety seats with integral seat belts and the tridion safety cell.

The new smart fortwo cdi is available as a coupé and a cabrio.