80 (which was engine speed), making it very difficult to ensure that the correct amount of fuel was being delivered under all conditions. THE MYSTERY OF THE NAME These disadvantages led to the development of common rail. Such systems have been tried since before World War I, but the system was only really specifically adapted for vehicles by the mid-1990s. A modern common-rail system was put into production for the first time by the Japanese Denso Corporation and fitted to a 1995-model Hino truck, built by Toyota. The name is a mystery. It really is just a fuel reservoir supplied by a pump and kept at a constant pressure. It is attached to the engine near the cylinder head in such a position that each fuel line to its injector has the same length. This means all the injectors are kept Piezoelectric devices have become commonplace. They employ crystals that not only expand when a voltage is applied, but also generate a voltage when pressure is applied. The best known of such crystals is common in the house – sugar. PETROL ENGINES Diesel engines could not operate without fuel injection because they inhaled only air. Petrol engines inhale a mixture of fuel and air, and until 1990, most of them managed very well with the mixture being supplied by a carburettor. A carburettor utilises the suction created on the intake stroke by the engine’s downward-moving pistons to suck fuel out of a float-operated chamber. This set-up is too crude to deliver the correct mixture under all engine operating conditions, but it was good enough for the first 100 years of motoring. Several German aero-engine manufacturers utilised fuel injection on petrol engines during World War II, and one of the engineers involved had a hand in producing the first car to be fitted with fuel injection – the 1952 German Goliath. This nameplate did not last long, but fuel injection was used on racing cars in 1954 and production sports cars in 1955. By this time, various American tuners, as well as the major auto- mobile companies, were experimenting with mechanical fuel ABOVE: The brandnew series of Global Diesel (GD) engines used in the Hilux and Fortuner are at the cutting edge of modern injection technology that has ensured these powerplants are 25% more powerful and 15% more fuel efficient than their predecessors. The engines are the first in the world to benefit from Thermo Swing Wall Insulation Technology to make them some of the most thermally efficient, with a rating of 44%. Another engine feature is the use of a SiRPA (a silicareinforced porous, anodised aluminium) coating on the pistons that reduces cooling loss during combustion by about 30%. at the same constant pressure, so that the injector opening duration can be used as a measure of the amount of fuel being delivered. The engine control unit determines this duration based on inputs received from various sensors, with regard to engine speed, load demand, fuel, air and water temperature, as well as the quality of the previous combustion event. Initially, common-rail injectors were operated by solenoids, but the latest units are being operated by piezoelectric activators. These consist of stacks of very thin discs of piezoelectric material that expand when an electric voltage is applied. These units are up to four times faster than solenoids, with the result that when they’re combined with fuel rail pressures of 3 000 bar, the result is a level of combustion quality control that was only a dream a few years ago.
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