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Workshop: Soot Up


Words by Louis Redelinghuys. Pictures by Andrew Middleton.

The diesel-combustion engine has become one of the most competitively and exhaustively researched topics in the automotive industry. Gone are the days when diesel engines were regarded as filthy, underpowered, inefficient and unfit for passenger-car use. In fact, certain vehicle market sales are now dominated by dieselpowered models − sometimes by as much as 75%! To achieve these numbers, the evolution of diesel injection technologies in the past few decades has been nothing short of spectacular. Just take a moment to compare the ‘old’ systems of plunger pumps and simple four-hole injectors, to today’s high-pressure variants which use injector nozzles with up to twelve separate holes through which fuel is injected several times per engine stroke!

The typical working pressure of an older system would be around 180 to 220 kPa; today we see common-rail systems operating at up to 2 400 kPa. Previously, injectors were held open by fuel pressure, while the newer common-rail variants have electronically activated injectors, which are, in effect, a science in their own right. Twenty years ago, who would’ve imagined that we’d be applying a voltage to a piezo crystal (‘piezo’ means squeeze or press), thereby causing it to distort so that that microscopic distortion could vary the quantity of fuel being injected? The tolerances and accuracy associated with these systems have resulted in some of the most highly specialised engineering principles anywhere in the world, and it has all been done right here in front of us on a daily (driving) basis. It is, quite simply, spectacular!

Naturally, many of these technological marvels require some specialist care and maintenance. This is precisely why manufacturers specify certain types and grades of fuel for their vehicles. For example, certain engines must be operated on low-sulphur (less than 50 ppm) diesel; ultra-low 10 ppm is now freely available in parts of Europe and America, and even in some areas of South Africa.

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