ith the massive increase in the use of diesel engines in cars over the past 20 years, there was no way manufacturers could have kept producing the noisy, smoke-belching engines that typified the technology throughout the ‘80s, ‘90s and in to the new millennium. The biggest move forward in recent years has been the development and refinement of the common-rail diesels. This system has transformed how diesel vehicles are viewed in the eyes (and buying decisions) of the general public.
As late as the early 2000s, Ford was still fitting its cars and vans with the Endura-D and TDDi engines. In these systems, an electro-mechanical fuel pump pressurised the fuel, and as a secondary function delivered the fuel in timed ‘pulses’. The pressure of this fuel delivery controlled the opening of the injectors at the cylinder. While it was a basic, relatively trouble-free and economical design, a lack of precise control over the spray pattern at the injector and the need to keep the pump timing spot-on, meant that badly-tuned engines would often emit their own mini enviro-disasters out of the exhaust pipe.
Common-rail technology introduced electronically controlled injectors, mounted on one high-pressure accumulator (fuel rail), that were far more controllable in the way they delivered the fuel and the timing of that delivery. Here, the fuel pump only needs to pressurise the system (albeit to a massively increased level of up to 1600 bar/29,000 psi), while an ECU, fed with hundreds of sensor inputs from all over the car, controls when and how much fuel is injected. Indeed very modern systems fire the fuel into the cylinder in several stages to produce a perfect spray pattern and fuel burn throughout the power cycle of the engine. The latest piezo-electric injectors are so controllable they can have up to five separate injection stages.
The advance in diesel tech that comes with common-rail has, therefore, transformed power and torque outputs, fuel consumption plus noise and emission levels. All good things, but there are people who would, given the choice between a TDDi and TDCi (Duratorq common-rail) Ford, pick the old technology every time. Why? Reliability and repair expense are the main reasons. Common-rail technology is under scrutiny for its longevity. Some are questioning reports of premature injector failures (under such high pressures and with far more opening/closing cycles, more work is done by the modern injectors). And as the system is also ECU controlled, sensor failures can lead to erratic running in some cases.
Any problems will, without doubt, be sorted very soon and common rail diesel development will make diesels cleaner, cheaper, more powerful and reliable on an ever-increasing basis. None of which can be a bad thing.