piston-top shapes. The mixture in the rest of the combustion chamber is kept leaner than normal, with the result that fuel consumption is improved. Petrol engines also experienced the switch from electromagnetic to piezoelectric injectors. Engines in the Toyota and Lexus ranges have been at the forefront in the development of fuel injection and direct injection for production cars, and today lay claim to being some of the most powerful versus fuelefficient models on the market. 81 injection, but the big push came when fitting catalytic converters became mandatory. Such a converter, which drastically reduces the amount of harmful carbon monoxide, nitrogen oxides and unburnt hydrocarbons in a car’s exhaust gases, is only efficient if the fuel/air mixture is close to chemically correct. A carburettor could be made to deliver such a mixture at one particular engine speed, but it could never do this under all motoring conditions. Fuel injection had to come to the rescue. The first injectors were modified mechanical diesel units, but electronic fuel-injection systems appeared in production cars by the late 1960s. The first units employed engine speed and air density sensors to calculate the mass of air being inhaled so that the correct amount of fuel could be calculated. The fuel was injected either by a single injector at the entrance to the intake manifold, or by an injector for each cylinder that squirted fuel into the intake manifold. Over the next 20 years, many additions and improvements followed. Air mass sensors became more accurate and sensors inside the exhaust manifold measured the amount of oxygen left after combustion. These socalled lambda-sensors enabled the central engine computer to base its next fuel delivery on the accuracy of the previous fuel delivery. Later, a sensor was added near the outlet of the catalytic converter to monitor the quality of the car’s purification process. The last few years have seen the development of direct fuel injection. This has the advantage that the fuel evaporation process helps to cool the engine interior. Direct injection also makes it possible to use multiple fuel squirts to achieve a measure of lean-burn combustion. In such an engine, the spark plugs have to be surrounded by a richer mixture in order for the flame to start. This is achieved by using special port and HOWSTUFFWORKS BELOW: Before fuel injection was adopted as a mainstream technology, carburettors regulated the fuel flow for combustion. An engine’s downwardmoving pistons sucked fuel out of a float-operated chamber on top of which was placed an air filter, which looked like a giant frying pan. Inset: The carburettor is actually a small device and is round in appearance.
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