The new smart fortwo cdi: The CO2 champion - a masterpiece of engine development

Jul 6, 2007
With the development of the world's smallest direct-injection diesel engine, smart has produced a masterpiece of engine development that earns the new smart fortwo cdi the distinction of the world's most economical production car with combustion drive. The 33 kW/45 bhp two-door car consumes just 3.3 litres of fuel per 100 kilometres (NEDC), which means that it can travel approximately 1000 kilometres without refuelling. Emitting just 88 grams of CO2 per kilometre, the smart fortwo diesel is the world champion in low CO2 emissions.
State-of-the-art common-rail direct injection enables a combustion process that is even more efficient than that of the well-proven cdi engine from the pre-decessor model . High injection pressure of up to 1600 bar (previously 1350 bar) is built up, even at low revs, and the fuel is injected into the combustion chambers with newly developed seven-hole injectors. The power and torque have each improved by 10 percent. At the same time, fuel consumption is reduced by 13 percent. Depending on the driving situation and engine load, up to 60 percent of the previously cooled exhaust gases are returned to the combustion chambers.
High-tech fuel injection
Like the CDI engines of its sister brand Mercedes-Benz, fuel injection in the smart fortwo cdi is carried out in two phases: 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 electronic "brain" of the cdi engine – a high-performance micro-computer that controls the whole engine system – calculates how much fuel is needed and the interval at which pilot injection and main injection take place.
The quick response of the cdi engine is first and foremost thanks to the compact yet extremely effective turbocharger that is housed in the exhaust manifold. Its compressor wheel has a diameter of just 33 millimetres, yet it rotates at up to 280,000 rpm and thus builds up maximum charge pressure of approximately 1200 millibars. This gives the three-cylinder engine more air to "breathe" and enables it to develop impressive torque, even at low revs: 85 metres are available even from 1500 rpm – more than three quarters of the maximum torque.
This torque curve plays an important part in the fun behind the wheel that drivers experience with every kilometre driven in a smart fortwo cdi. The new smart fortwo cdi accelerates from zero to 100 km/h in 19.8 seconds and reaches a top speed of 135 km/h. It therefore offers a combination of agility, economy and environmental compatibility that is unique in this class.
The most important technical data on the new smart fortwo cdi at a glance:
R3/2 valves per cylinder
Engine capacity
799 cc
65.5 x 79 mm
Rated output
33 kW/45 bhp at 3,800 rpm
Max. torque
110 Nm at 2,000–2,500 rpm
0-100 km/h
19.8 s
Maximum speed
135 km/h
Fuel consumption*
3.3 l/100 km
CO2 emissions*
88 g/km
smart fortwo CDI
smart fortwo CDI
smart fortwo CDI
smart fortwo CDI