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The peculiar geographical situation of Los Angeles, with its bowl configuration close to the sea, and its regular sunshine, together result in distressingly consistent smog formation. This has produced some very stringent legislation in the entire United States, which has been followed to a greater or lesser degree by the rest of the world. The intention of the legislation is to limit the amounts of certain, alleged, noxious emissions from car exhausts. The main emissions against which this campaign rages are carbon monoxide (CO), unburnt hydrocarbons (fuel), oxides of nitrogen (NOX) and lead compounds. The first three of these are dependent upon the air/fuel ratio of the mixture being burnt in the engine, the CO and hydrocarbons falling in percentage as the ratio weakens. The NOX, however, increases with the weaker mixtures, as it is largely produced at the higher temperatures reached by burning weak mixtures. The best ratio is just below fourteen to one though the emissions are still too high. Two systems are suggested to remove CO and hydrocarbons. One is to use a direct flame afterburner, which finally burns them in the exhaust systems. The other is to use a catalytic converter, as can be found on new Mercedes, new Porsche, new Rolls Royce and new Bentley models. This converter is a chamber containing an expensive coating, such as platinum, which changes the gases into acceptable compounds without itself changing. But the lead used in the fuel to improve its anti detonating properties tends to clog up the catalyst. Tests called for by the new laws are designed to simulate road driving conditions, and the primary means of meeting these tests is the use of weaker mixtures (hence the complicated design of modem carburettors) and the abolition of leaded fuels. The latter measure results in the use of lower compression ratios and, in consequence, the need for larger engines to produce the equivalent power. Obviously such engines use more fuel and so tend to cause greater pollution. Unburnt fuel emission results from fuel which has been cooled on the port or cylinder walls, or shielded from the flame in a nook or cranny in the cylinder head. It is also caused through fuel spilling or vaporizing out of tank vents and other parts of the fuel system. One source of hydrocarbon emission is a high suction, formed by a suddenly closed throttle, drawing off neat fuel, which is not burned. This can be minimized by a gulp-valve which, because it is sensitive to such sudden changes, adds extra air into the manifold. Another preventive is to feed the crankcase fumes, which include exhaust gases that have got past the piston rings, back through a one-way valve to the inlet manifold. Yet another emission antidote is to retard the ignition still further at the lowest idling speed by an extra vacuum servo system, fed from the choke near the point where the throttle closes. Even with the complex modem carburettors, which will provide correct mixture strength under all conditions, there still exist the two limitations of restriction of air flow by the choke design, and the great difficulty of getting the same strength mixture to all the cylinders through a tortuous inlet manifold. Separate carburettors for all cylinders have been tried but a more obvious solution is to squirt the correct amount of fuel either into the inlet ports or the manifold adjacent to the ports. This is known as fuel injection. While fuel injection has been tried for petrol engines by many inventors over the past 100 years, it is only within the last fifty years that techniques have been available to meter the very small quantities of fuel needed for injection and to adjust these quantities for variations of speed, load, temperature and driver’s demand. There have been a number of fuel injection systems based on different methods of injection and of fuel metering. Liquid fuel may be injected directly into the cylinders or into the manifold near the inlet valve. The quantity of fuel may be proportioned to the engine operating conditions by varying the effective stroke of a pump, by varying the opening time of an injection nozzle fed from a constant pressure main, or by varying the rate of flow through an injection nozzle.

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