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Intake Fuel-mixture Heating



Assignment

The multipoint injection requires no intake mixture pre-heating because this is formed only at the end of the inlet manifold or in the combustion chamber. It is only meaningful, in engines whose mixture is formed at the beginning of the inlet manifold, as in the case of the central injection, the single carburetor and the register carburettor. Here the fuel can condense on the cold walls of the inlet manifold thus, causing a certain amount of the ignitable mixture to be lost. This means that, during, and after cold starting, the mixture has to be made richer, which is reflected particularly, in a higher hydrocarbon content in the exhaust gas, and of course, in higher engine wear-and-tear and fuel consumption.

Function

Mostly, directly below the throttle-valve(s), before the inlet manifold fans out to the individual cylinders, a "hedgehog" type element is mounted below. It's "quills" reach deep into the inlet manifold cross section. It is, first of all, electrically heated with a high amont of current (approx. 30 A), thus quickly warming the fuel-air mixture. Thereby, the condensation on the cylinder-walls is reduced.
Through the PTC-character of the electric mixture-pre-heating, the current requirement drops with the warming up. The component can be switched off when, either the coolant takes over the heating, or if the heating is no longer necessary. This is because a heated inlet manifold in an engine that is already warm, causes a loss in performance and efficiency. By the way, care should be taken, not to leave the ignition switched on for longer periods without starting the engine. If the control device is not fitted with a suitable cut-off circuit, the battery will discharge in a relatively short time. 05/10

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